Resonant scattering on impurities in the quantum Hall effect
International Nuclear Information System (INIS)
Gurvitz, A.
1994-06-01
We developed a new approach to carrier transport between the edge states via resonant scattering on impurities, which is applicable both for short and long range impurities. A detailed analysis of resonant scattering on a single impurity is performed. The results used for study of the inter-edge transport by multiple resonant hopping via different impurities' site. We found the total conductance can be obtained from an effective Schroedinger equation with constant diagonal matrix elements in the Hamiltonian, where the complex non-diagonal matrix elements are the amplitudes of a carrier hopping between different impurities. It is explicitly shown how the complex phase leads to Aharonov-Bohm oscillations in the total conductance. Neglecting the contribution of self-crossing resonant-percolation trajectories, we found that the inter-edge carrier transport is similar to propagation in one-dimensional system with off-diagonal disorder. Then we demonstrated that each Landau band has an extended state Ε Ν , while all other states are localized, and the localization length behaves as L - 1 Ν (Ε) ∼ (Ε - Ε Ν ) 2 . (author)
Effects of magnetic impurity scattering on superfluid 3He in aerogel
Aoyama, Kazushi; Ikeda, Ryusuke
2009-02-01
We investigate impurity effects on superfluid 3He in aerogel whose surface is not coated with 4He, different from most experimental situations. In systems with no 4He coating, spins of solid 3He absorbed on the aerogel surface are active and interact with spins of quasiparticles relevant to superfluidity and, for this reason, such an aerogel is treated as magnetic scatterers. It is found that, in the ABM pairing state affected by magnetic scatterings, not only the l-vector but also the d-vector has no long-ranged orientational order, and that the strong-coupling correction due to impurity scatterings is less suppressed than that in the nonmagnetic case, implying an expansion of the A-like phase region.
Phonon scattering by isotopic impurities
International Nuclear Information System (INIS)
Dacol, D.K.
1974-06-01
The effects upon vibrations of a perfect crystal lattice due to the replacement of some of its atoms by isotopes of these atoms are studied. The approach consists in considering the isotopic impurities as scattering centres for the quanta of the elastic waves the objective is to obtain the scattering amplitudes. These amplitudes are obtained through a canonical transformation method which was introduced by Chevalier and Rideau in the study of the Wentzel's model in quantum field theory
Scattering of waves by impurities in precompressed granular chains.
Martínez, Alejandro J; Yasuda, Hiromi; Kim, Eunho; Kevrekidis, P G; Porter, Mason A; Yang, Jinkyu
2016-05-01
We study scattering of waves by impurities in strongly precompressed granular chains. We explore the linear scattering of plane waves and identify a closed-form expression for the reflection and transmission coefficients for the scattering of the waves from both a single impurity and a double impurity. For single-impurity chains, we show that, within the transmission band of the host granular chain, high-frequency waves are strongly attenuated (such that the transmission coefficient vanishes as the wavenumber k→±π), whereas low-frequency waves are well-transmitted through the impurity. For double-impurity chains, we identify a resonance-enabling full transmission at a particular frequency-in a manner that is analogous to the Ramsauer-Townsend (RT) resonance from quantum physics. We also demonstrate that one can tune the frequency of the RT resonance to any value in the pass band of the host chain. We corroborate our theoretical predictions both numerically and experimentally, and we directly observe almost complete transmission for frequencies close to the RT resonance frequency. Finally, we show how this RT resonance can lead to the existence of reflectionless modes in granular chains (including disordered ones) with multiple double impurities.
Enhanced ionized impurity scattering in nanowires
Oh, Jung Hyun; Lee, Seok-Hee; Shin, Mincheol
2013-06-01
The electronic resistivity in silicon nanowires is investigated by taking into account scattering as well as the donor deactivation from the dielectric mismatch. The effects of poorly screened dopant atoms from the dielectric mismatch and variable carrier density in nanowires are found to play a crucial role in determining the nanowire resistivity. Using Green's function method within the self-consistent Born approximation, it is shown that donor deactivation and ionized impurity scattering combined with the charged interface traps successfully to explain the increase in the resistivity of Si nanowires while reducing the radius, measured by Björk et al. [Nature Nanotech. 4, 103 (2009)].
Influence of argon impurities on the elastic scattering of x-rays from imploding beryllium capsules
Saunders, A. M.; Chapman, D. A.; Kritcher, A. L.; Schoff, M.; Shuldberg, C.; Landen, O. L.; Glenzer, S. H.; Falcone, R. W.; Gericke, D. O.; Döppner, T.
2018-03-01
We investigate the effect of argon impurities on the elastic component of x-ray scattering spectra taken from directly driven beryllium capsule implosions at the OMEGA laser. The plasma conditions were obtained in a previous analysis [18] by fitting the inelastic scattering component. We show that the known argon impurity in the beryllium modifies the elastic scattering due to the larger number of bound electrons. We indeed find significant deviations in the elastic scattering from roughly 1 at.% argon contained in the beryllium. With knowledge of the argon impurity fraction, we use the elastic scattering component to determine the charge state of the compressed beryllium, as the fits are rather insensitive to the argon charge state. Finally, we discuss how doping small fractions of mid- or high-Z elements into low-Z materials could allow ionization balance studies in dense plasmas.
Impurity scattering effect on charge transport in high-Tc cuprate junctions
International Nuclear Information System (INIS)
Tanaka, Y.; Asano, Y.; Kashiwaya, S.
2004-01-01
It is known that the zero-bias conductance peak (ZBCP) is expected in tunneling spectra of normal-metal/high-Tc cuprate junctions because of the formation of the midgap Andreev resonant states (MARS) at junction interfaces. In the present review, we report the recent theoretical study of impurity scattering effects on the tunneling spectroscopy. In the former part of the present paper, we discuss impurity effects in normal metal. We calculate tunneling conductance for diffusive normal metal (DN)/high Tc cuprate junctions based on the Keldysh Green's function technique. Besides the ZBCP due to the MARS, we can expect ZBCP caused by the different origin, i.e., the coherent Andreev reflection (CAR) assisted by the proximity effect in DN. Their relative importance depends on the angle a between the interface normal and the crystal axis of high-Tc superconductors. At α = 0, we find the ZBCP by the CAR for low transparent junctions with small Thouless energies in DN; this is similar to the case of diffusive normal metal/insulator/s-wave superconductor junctions. Under increase of α from zero to π/4, the contribution of MARS to ZBCP becomes more prominent and the effect of the CAR is gradually suppressed. Such complex spectral features would be observable in conductance spectra of high-Tc junctions at very low temperatures. In the latter part of our paper, we study impurity effects in superconductors. We consider impurities near the junction interface on the superconductor side. The conductance is calculated from the Andreev and the normal reflection coefficients which are estimated by using the single-site approximation in an analytic calculation and by the recursive Green function method in a numerical simulation. We find splitting of the ZBCP in the presence of the time reversal symmetry. Thus the zero-field splitting of ZBCP in the experiment does not perfectly prove an existence of broken time reversal symmetry state
Quasibound states at thresholds in multichannel impurity scattering
International Nuclear Information System (INIS)
Kim, Sang Wook; Park, Hwa-Kyun; Sim, H-S; Schomerus, Henning
2003-01-01
We investigate the threshold behaviour of transmission resonances and quasibound states in the multichannel scattering problems of a one-dimensional (1D) time-dependent impurity potential, and the related problem of a single impurity in a quasi-1D wire. It was claimed before in the literature that a quasibound state disappears when a transmission zero collides with the subband boundary. However, the transmission line shape, the Friedel sum rule, and the delay time show that the quasibound states still survive and affect the physical quantities. We discuss the relation between threshold behaviour of transmission resonances, and quasibound states and their boundary conditions in the general context of multichannel scatterings
International Nuclear Information System (INIS)
Fortier, Dominique.
1976-07-01
Besides the three phonon scattering mechanisms generally considered in insulators, i.e. boundary effect, isotopic scattering and phonon-phonon interaction, the electron-phonon scattering mechanism was studied with special reference to the scattering of thermal phonons by donor impurities in silicon. In order to demonstrate clearly the effect of the electronic structure of the impurity on this scattering, three donor centres were investigated: Li, Li-O and P. On the basis of the calculated relaxation times it was possible from theoretical analysis to account for the main results and to explain why the Li centre scatters thermal phonons more efficiently than Li-O and P centres in the isolated impurity range [fr
Plasmon-enhanced phonon and ionized impurity scattering in doped silicon
International Nuclear Information System (INIS)
Chen, Ming-Jer; Hsieh, Shang-Hsun; Chen, Chuan-Li
2015-01-01
Historically, two microscopic electron scattering calculation methods have been used to fit macroscopic electron mobility data in n-type silicon. The first method was performed using a static system that included long-range electron-plasmon scattering; however, the well-known Born approximation fails in this case when dealing with electron-impurity scattering. In the second method, sophisticated numerical simulations were developed around plasmon-excited potential fluctuations and successfully reproduced the mobility data at room temperature. In this paper, we propose a third method as an alternative to the first method. First, using a fluctuating system, which was characterized on the basis of our recently experimentally extracted plasmon-excited potential fluctuations, the microscopic calculations reveal enhanced short-range scattering of electrons by phonons and ionized impurities due to increased electron temperature and increased screening length, respectively. The increased hot electron population makes the Born approximation hold, which eases the overall calculation task substantially. Then, we return to the static system while incorporating plasmon-enhanced impurity scattering. The resulting macroscopic electron mobility shows fairly good agreement with data over wide ranges of temperatures (200–400 K) and doping concentrations (10 15 –10 20 cm −3 ). Application of the proposed method to strained silicon is also demonstrated
Impurity and quaternions in nonrelativistic scattering from a quantum memory
International Nuclear Information System (INIS)
Margetis, Dionisios; Grillakis, Manoussos G
2008-01-01
Models of quantum computing rely on transformations of the states of a quantum memory. We study mathematical aspects of a model proposed by Wu in which the memory state is changed via the scattering of incoming particles. This operation causes the memory content to deviate from a pure state, i.e. induces impurity. For nonrelativistic particles scattered from a two-state memory and sufficiently general interaction potentials in (1+1) dimensions, we express impurity in terms of quaternionic commutators. In this context, pure memory states correspond to null hyperbolic quaternions. In the case with point interactions, the scattering process amounts to appropriate rotations of quaternions in the frequency domain. Our work complements previous analyses by Margetis and Myers (2006 J. Phys. A 39 11567)
Soliton scatterings by impurities in a short-length sine-Gordon chain
International Nuclear Information System (INIS)
Dikande, A.M.; Kofane, T.C.
1995-07-01
The scattering of soliton by impurities at the frontiers of a finite-length region of an infinite sine-Gordon chain is analyzed. The impurities consist of two isotopic inhomogeneities installed at the boundaries of the finite-length region. The soliton solution in the region is found in term of snoidal sine-Gordon soliton which properly takes into account the effects of the boundaries. By contrast, the soliton solutions in the neighboring sides of the region are obtained in terms of the so-called large-amplitude, localized kinks with limiting spatial extensions at x → ± ∞, which is equal ±π. Using the continuity of these soliton solutions at the frontiers as well as appropriate boundary conditions, it is shown that the soliton may be either i) reflected by the incident impurity; ii) trapped (with oscillating motions) between the two impurities (i.e. inside the infinite region); or iii) transmitted by the second impurity into the third, infinitely extended region. The threshold velocities for the reflection and transmission into different regions are found and shown to vary exponentially as a function of the length of the bounded region. The frequency of soliton oscillations between the impurities has also been calculated in some acceptable limit. (author). 28 refs, 1 fig
International Nuclear Information System (INIS)
Vanyolos, Andras; Dora, Balazs; Maki, Kazumi; Virosztek, Attila
2007-01-01
We present a detailed theoretical study on the thermodynamic properties of impure quasi-one-dimensional unconventional charge and spin density waves in the framework of mean-field theory. The impurities are of the ordinary non-magnetic type. Making use of the full self-energy that takes into account all ladder- and rainbow-type diagrams, we are able to calculate the relevant low temperature quantities for arbitrary scattering rates. These are the density of states, specific heat and the shift in the chemical potential. Our results therefore cover the whole parameter space: they include both the self-consistent Born and the resonant unitary limits, and most importantly give exact results in between
International Nuclear Information System (INIS)
Nielsen, J.B.; Smith, H.; Ono, Y.A.; Pethick, C.J.
1980-01-01
The charge imbalance generated in a current-carrying clean superconductor by a temperature gradient is calculated, assuming that non-magnetic or magnetic impurities are the only source of scattering. The charge imbalance is obtained from exact solutions of the quasiparticle Boltzmann equation, valid at any temperature and superfluid velocity. (author)
The screening of charged impurities in bilayer graphene
International Nuclear Information System (INIS)
Zhang Wenjing; Li, Lain-Jong
2010-01-01
Positively charged impurities were introduced into a bilayer graphene (BLG) transistor by n-doping with dimethylformamide. Subsequent exposure of the BLG device to moisture resulted in a positive shift of the Dirac point and an increase of hole mobility, suggesting that moisture could reduce the scattering strength of the existing charged impurities. In other words, moisture screened off the 'effective density' of charged impurities. At the early stage of moisture screening the scattering of hole carriers is dominated by long-range Coulomb scatter, but an alternative scattering mechanism should also be taken into consideration when the effective density of impurities is further lowered on moisture exposure.
Impurity effect in the quantum Nernst effect
International Nuclear Information System (INIS)
Shirasaki, Ryoen; Nakamura, Hiroaki; Hatano, Naomichi
2005-11-01
We theoretically study the Nernst effect and the Seebeck effect in a two-dimensional electron ga in a strong magnetic field and a temperature gradient under adiabatic condition. We recently predicted for a pure system in the quantum Hall regime that the Nernst coefficients strongly suppressed and the thermal conductance is quantized due to quantum ballistic transport. Taking account of impurities, we here compute the Nernst coefficient and the Seebeck coefficient when the chemical potential coincides with a Landau level. We adopt the self-consistent Born approximation and consider the linear transport equations of the thermal electric transport induced by the temperature gradient. The thermal conductance and the Nernst coefficient are slightly modified from the pure case and the Seebeck coefficient newly appears because of the impurity scattering of electrons in the bulk states. (author)
Magnetothermoelectric properties of layered structures for ion impurity scattering
Figarova, S. R.; Huseynov, H. I.; Figarov, V. R.
2018-05-01
In the paper, longitudinal and transverse thermoelectric powers are considered in a magnetic field parallel to the layer plane for scattering of charge carriers by weakly screened impurity ions. Based on the semiclassical approximation, it is obtained that, depending on the position of the Fermi level relative to the miniband top and superlattice period, the thermoelectric power can change sign and amplify.
International Nuclear Information System (INIS)
Okabe, Y.; Nagi, A.D.S.
1983-01-01
The Shiba-Rusinov theory of magnetic impurities in a superconductor is investigated, with special attention paid to the role of the potential scattering term in the electron-impurity interaction. The meaning of Anderson's theorem in the Shiba-Rusinov theory is discussed
Donor-impurity-related optical response and electron Raman scattering in GaAs cone-like quantum dots
Gil-Corrales, A.; Morales, A. L.; Restrepo, R. L.; Mora-Ramos, M. E.; Duque, C. A.
2017-02-01
The donor-impurity-related optical absorption, relative refractive index changes, and Raman scattering in GaAs cone-like quantum dots are theoretically investigated. Calculations are performed within the effective mass and parabolic band approximations, using the variational procedure to include the electron-impurity correlation effects. The study involves 1 s -like, 2px-like, and 2pz-like states. The conical structure is chosen in such a way that the cone height is large enough in comparison with the base radius thus allowing the use a quasi-analytic solution of the uncorrelated Schrödinger-like electron states.
International Nuclear Information System (INIS)
Lotfi, E; Rezania, H; Arghavaninia, B; Yarmohammadi, M
2016-01-01
We address the electrical conductivity of bilayer graphene as a function of temperature, impurity concentration, and scattering strength in the presence of a finite bias voltage at finite doping, beginning with a description of the tight-binding model using the linear response theory and Green’s function approach. Our results show a linear behavior at high doping for the case of high bias voltage. The effects of electron doping on the electrical conductivity have been studied via changing the electronic chemical potential. We also discuss and analyze how the bias voltage affects the temperature behavior of the electrical conductivity. Finally, we study the behavior of the electrical conductivity as a function of the impurity concentration and scattering strength for different bias voltages and chemical potentials respectively. The electrical conductivity is found to be monotonically decreasing with impurity scattering strength due to the increased scattering among electrons at higher impurity scattering strength. (paper)
An unusually strong resonant phonon scattering by 3-d impurities in II-VI semiconductors
Energy Technology Data Exchange (ETDEWEB)
Lonchakov, A.T.; Sokolov, V.I.; Gruzdev, N.B. [Institute of Metal Physics, Russian Academy of Sciences, Ural Branch, S. Kovalevskaya Str. 18, 620219 Ekaterinburg (Russian Federation)
2004-11-01
Low temperature phonon heat conductivity was measured for ZnSe and ZnS crystals, doped with 3-d impurities. A strong resonance-like phonon scattering by 3-d ions with orbitally degenerate ground state was observed. The Jahn-Teller effect is proposed as the reason of the strong resonance-like behaviour of heat conductivity. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Yoshida, N; Itoh, H; Tanaka, Y; Inoue, J I; Kashiwaya, S
2003-01-01
Effects of impurity-scattering on a zero-bias conductance peak in ferromagnet/insulator/d-wave superconductor junctions are theoretically studied. The impurities are introduced through the random potential in ferromagnets near the junction interface. As in the case of normal-metal/insulator/d-wave superconductor junctions, the magnitude of zero-bias conductance peak decreases with increasing the degree of disorder. However, when the magnitude of the exchange potential in ferromagnet is sufficiently large, the random potential can enhance the zero-bias conductance peak in ferromagnetic junctions. (author)
Quasiparticle Properties of a Mobile Impurity in a Bose-Einstein Condensate.
Christensen, Rasmus Søgaard; Levinsen, Jesper; Bruun, Georg M
2015-10-16
We develop a systematic perturbation theory for the quasiparticle properties of a single impurity immersed in a Bose-Einstein condensate. Analytical results are derived for the impurity energy, effective mass, and residue to third order in the impurity-boson scattering length. The energy is shown to depend logarithmically on the scattering length to third order, whereas the residue and the effective mass are given by analytical power series. When the boson-boson scattering length equals the boson-impurity scattering length, the energy has the same structure as that of a weakly interacting Bose gas, including terms of the Lee-Huang-Yang and fourth order logarithmic form. Our results, which cannot be obtained within the canonical Fröhlich model of an impurity interacting with phonons, provide valuable benchmarks for many-body theories and for experiments.
Size, Shape and Impurity Effects on Superconducting critical temperature.
Umeda, Masaki; Kato, Masaru; Sato, Osamu
Bulk superconductors have their own critical temperatures Tc. However, for a nano-structured superconductor, Tc depends on size and shape of the superconductor. Nishizaki showed that the high pressure torsion on bulks of Nb makes Tc higher, because the torsion makes many nano-sized fine grains in the bulks. However the high pressure torsion on bulks of V makes Tc lower, and Nishizaki discussed that the decrease of Tc is caused by impurities in the bulks of V. We studied size, shape, and impurity effects on Tc, by solving the Gor'kov equations, using the finite element method. We found that smaller and narrower superconductors show higher Tc. We found how size and shape affects Tc by studying spacial order parameter distributions and quasi-particle eigen-energies. Also we studied the impurity effects on Tc, and found that Tc decreases with increase of scattering rate by impurities. This work was supported in part of KAKENHI Grant Number JP26400367 and JP16K05460, and program for leading graduate schools of ministry of education, culture, sports, science and technology-Japan.
Energy Technology Data Exchange (ETDEWEB)
Yu, Xiang-Long, E-mail: xlyu@theory.issp.ac.cn [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, P. O. Box 1129, Hefei 230031 (China); Liu, Da-Yong; Quan, Ya-Min; Zheng, Xiao-Jun [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, P. O. Box 1129, Hefei 230031 (China); Zou, Liang-Jian, E-mail: zou@theory.issp.ac.cn [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, P. O. Box 1129, Hefei 230031 (China); Department of Physics, University of Science and Technology of China, Hefei 230026 (China)
2015-12-15
Highlights: • Effects of single interstitial impurity are studied in iron-based superconductors. • Bound states within the superconducting gap can be induced. • The interstitial impurity can induce a π phase shift of pairing order parameter. • For strong magnetic scattering the bound-state peak can appear at the Fermi level. - Abstract: We employ the self-consistent Bogoliubov-de Gennes (BdG) formulation to investigate the effect of single interstitial nonmagnetic/magnetic impurity in iron-based superconductors with s ± -wave pairing symmetry. We find that both the nonmagnetic and magnetic impurities can induce bound states within the superconducting (SC) gap and a π phase shift of SC order parameter at the impurity site. However, different from the interstitial-nonmagnetic-impurity case characterized by two symmetric peaks with respect to zero energy, the interstitial magnetic one only induces single bound-state peak. In the strong scattering regime this peak can appear at the Fermi level, which has been observed in the recent scanning tunneling microscope (STM) experiment of Fe(Te,Se) superconductor with interstitial Fe impurities (Yin et al. 2015 [44]). This novel single in-gap peak feature also distinguishes the interstitial case from the substitutional one with two peaks. These results provide important information for comparing the different impurity effects in the iron-based superconductors.
Yarmohammadi, Mohsen
2016-12-01
Using the Harrison model and Green's function technique, impurity doping effects on the orbital density of states (DOS), electronic heat capacity (EHC) and magnetic susceptibility (MS) of a monolayer hydrogenated graphene, chair-like graphane, are investigated. The effect of scattering between electrons and dilute charged impurities is discussed in terms of the self-consistent Born approximation. Our results show that the graphane is a semiconductor and its band gap decreases with impurity. As a remarkable point, comparatively EHC reaches almost linearly to Schottky anomaly and does not change at low temperatures in the presence of impurity. Generally, EHC and MS increases with impurity doping. Surprisingly, impurity doping only affects the salient behavior of py orbital contribution of carbon atoms due to the symmetry breaking.
Oscillations of quantum transport through double-AB rings with magnetic impurity
International Nuclear Information System (INIS)
Gao Yingfang; Liang, J-Q
2006-01-01
We have studied the effect of impurity scattering on the quantum transport through double AB rings in the presence of spin-flipper in the middle lead in terms of one-dimensional quantum waveguide theory. The electron interacts with the impurity through the exchange interaction leading to spin-flip scattering. Transmissions in the spin-flipped and non-spin-flipped channels are calculated explicitly. It is found that the overall transmission and the conductance are distorted due to the impurity scattering. The extent of distortion not only depends on the strength of the impurity potential but also on the impurity position. Moreover, the transmission probability and the conductance are modulated by the magnetic flux, the size of the ring and the impurity potential strength as well
Impurity induced resistivity upturns in underdoped cuprates
Energy Technology Data Exchange (ETDEWEB)
Das, Nabyendu, E-mail: nabyendudas@gmail.com; Singh, Navinder
2016-01-28
Impurity induced low temperature upturns in both the ab-plane and the c-axis dc-resistivities of cuprates in the pseudogap state have been observed in experiments. We provide an explanation of this phenomenon by incorporating impurity scattering of the charge carriers within a phenomenological model proposed by Yang, Rice and Zhang. The scattering between charge carriers and the impurity atom is considered within the lowest order Born approximation. Resistivity is calculated within Kubo formula using the impurity renormalized spectral functions. Using physical parameters for cuprates, we describe qualitative features of the upturn phenomena and its doping evolution that coincides with the experimental findings. We stress that this effect is largely due to the strong electronic correlations.
Impurity induced resistivity upturns in underdoped cuprates
International Nuclear Information System (INIS)
Das, Nabyendu; Singh, Navinder
2016-01-01
Impurity induced low temperature upturns in both the ab-plane and the c-axis dc-resistivities of cuprates in the pseudogap state have been observed in experiments. We provide an explanation of this phenomenon by incorporating impurity scattering of the charge carriers within a phenomenological model proposed by Yang, Rice and Zhang. The scattering between charge carriers and the impurity atom is considered within the lowest order Born approximation. Resistivity is calculated within Kubo formula using the impurity renormalized spectral functions. Using physical parameters for cuprates, we describe qualitative features of the upturn phenomena and its doping evolution that coincides with the experimental findings. We stress that this effect is largely due to the strong electronic correlations.
Scattering Theory on Surface Majorana Fermions by an Impurity in ^{3}He-B.
Tsutsumi, Yasumasa
2017-04-07
We have formulated the scattering theory on Majorana fermions emerging in the surface bound state of the superfluid ^{3}He B phase (^{3}He-B) by an impurity. By applying the theory to the electron bubble, which is regarded as the impurity, trapped below a free surface of ^{3}He-B, the observed mobility of the electron bubble [J. Phys. Soc. Jpn. 82, 124607 (2013)JUPSAU0031-901510.7566/JPSJ.82.124607] is quantitatively reproduced. The mobility is suppressed in low temperatures from the expected value in the bulk ^{3}He-B by the contribution from the surface Majorana fermions. By contrast, the mobility does not depend on the trapped depth of the electron bubble in spite of the spatial variation of the wave function of the surface Majorana fermions. Our formulated theory demonstrates the depth-independent mobility by considering intermediate states in the scattering process. Therefore, we conclude that the experiment has succeeded in observing Majorana fermions in the surface bound state.
Multiple x-ray diffraction applied to the study of crystal impurities
International Nuclear Information System (INIS)
Cardoso, L.P.
1983-06-01
The x-ray multiple diffraction technique is used in the study of impurities concentration and localization in the crystal lattice, implemented with the fundamental observation that the impurities cannot be distributed with the same spatial group symmetry of the crystal. This fact could introduce scattered intensity in the crystal reciprocal lattice forbidden nodes. This effect was effectively observed in multiple diffraction diagrams, where a reinforcement of the scattered intensity in the pure crystal is produced, when choosing conveniently the involved reflections. The reflectivity theory was developed in the kinematic case, which take into account the scattering by the impurities atoms, and the analysis showed that, in the first approximation, the impurities can influence both in the allowed and forbidden positions for the pure crystal. (L.C.J.A.)
International Nuclear Information System (INIS)
Yavary, H.
2006-01-01
The magnetic penetration depth of a quasi-two dimensional d-wave superconductor in the presence of nonlineary, nonlocality, and impurity effects is investigated by using Green's function method. It is shown that a d-wave superconductor would inevitably avoid the violation of the Nernst theorem by creating a T 2 term in its penetration depth through a competition of nonlinear, nonlocal, and impurity effects and this system may be stable at low temperatures. I also show that in the impure sample at low temperatures, T < T * ∝ γ the impurity effect determines the temperature dependence of the penetration depth, i.e., nonlocal and nonlinear effects are completely masked by impurities
Effect of spin-orbit scattering on transport properties of low-dimensional dilute alloys
Energy Technology Data Exchange (ETDEWEB)
Heers, Swantje
2011-09-21
The scope of this thesis is to gain insight, by means of ab initio-calculations, into the physics of momentum and spin relaxation phenomena induced by electron scattering at impurities and defects in the noble metals copper, silver and gold. The main results are subdivided in three parts. In the first part, momentum- and spinrelaxation times due to scattering at 3d, 4sp, 4d, 5sp, 5d and 6sp impurities in copper and gold fcc bulk are investigated. The inversion symmetry of the crystals leads to a two-fold degeneracy of all states on the Fermi surface, and therefore spin relaxation is dominated by the Elliott-Yafet mechanism as well as the spin-orbit coupling of the impurity. For impurities in gold, we calculate much shorter spin-relaxation times than in copper because of the stronger spin-orbit coupling of the gold host. Furthermore, we have found important qualitative differences between the relaxation times obtained for the d- and the sp- impurities. As scattering at d-impurities is resonant, the electrons spend much more time at the impurity sites than in the case of the sp-impurities; therefore, they are much longer exhibited to the spin-orbit coupling of the impurity. This results in considerably shorter spin-relaxation times, even if the momentum scattering rates are in the same order of magnitude. Finally, the investigation of interference of scattering processes at impurity dimers reveals that relevant differences to the independent-impurity approximation appear only for strong d-scatterer, placed at nearest neighboring sites. In the second part we investigate the reduction of spin-conserving surface-state lifetimes induced by adatom- and impurity-scattering on the (111) surfaces of copper, silver and gold films with different thicknesses. We have found strong qualitative differences in the lifetimes when comparing the results for adatoms to those of impurities in the first and second layer. The trends for the latter ones are similar to those calculated in
Impurity bound states in mesoscopic topological superconducting loops
Jin, Yan-Yan; Zha, Guo-Qiao; Zhou, Shi-Ping
2018-06-01
We study numerically the effect induced by magnetic impurities in topological s-wave superconducting loops with spin-orbit interaction based on spin-generalized Bogoliubov-de Gennes equations. In the case of a single magnetic impurity, it is found that the midgap bound states can cross the Fermi level at an appropriate impurity strength and the circulating spin current jumps at the crossing point. The evolution of the zero-energy mode can be effectively tuned by the located site of a single magnetic impurity. For the effect of many magnetic impurities, two independent midway or edge impurities cannot lead to the overlap of zero modes. The multiple zero-energy modes can be effectively realized by embedding a single Josephson junction with impurity scattering into the system, and the spin current displays oscillatory feature with increasing the layer thickness.
Theory of s-wave superconductor containing impurities with retarded interaction with quasiparticles
International Nuclear Information System (INIS)
K V Grigorishin
2014-01-01
We propose a perturbation theory and diagram technique for a disordered metal when scattering of quasiparticles by nonmagnetic impurities is caused with a retarded interaction. The perturbation theory generalizes a case of elastic scattering in a disordered metal. Eliashberg equations for s-wave superconductivity are generalized for such a disordered superconductor. Anderson's theorem is found to be violated in the sense that embedding of the impurities into an s-wave superconductor increases its critical temperature. We show that the amplification of superconducting properties is a result of nonelastic effects in a scattering by the impurities. (paper)
Impurity effects on the magnetic ordering in chromium
International Nuclear Information System (INIS)
Fishman, R.S.
1992-05-01
It is well-known that impurities profoundly alter the magnetic properties of chromium. While vanadium impurities suppress the Neel temperature T N , manganese impurities enhanced T N substantially. As evidenced by neutron scattering experiments, doping with as little as 0.2% vanadium changes the transition from weakly first order to second order. Young and Sokoloff explained that the first-order transition in pure chromium is caused by a charge-density wave which is the second harmonic of the spin-density wave. By examining the subtle balance between the spin-density and charge- density wave terms in the mean-field free energy, we find that the first-order transition is destroyed when the vanadium concentration exceeds about 0.15%, in agreement with experiments
Impurities and conductivity in a D-wave superconductor
International Nuclear Information System (INIS)
Balatsky, A.V.
1994-01-01
Impurity scattering in the unitary limit produces low energy quasiparticles with anisotropic spectrum in a two-dimensional d-wave superconductor. The authors describe a new quasi-one-dimensional limit of the quasiparticle scattering, which might occur in a superconductor with short coherence length and with finite impurity potential range. The dc conductivity in a d-wave superconductor is predicted to be proportional to the normal state scattering rate and is impurity-dependent. They show that quasi-one-dimensional regime might occur in high-T c superconductors with Zn impurities at low temperatures T approx-lt 10 K
International Nuclear Information System (INIS)
Askerov, B. M.; Figarova, R.; Guseynov, G.I.
2012-01-01
Full Text : The transverse magnetoresistance in superlattices with the cosine dispersion law of conduction electrons in a case, when a weak magnetic field in plane of layer at scattering of the charge carriers of impurity ions has been studied. It has been shown that in a quasi-two-dimensional case the magnetoresistance was positive, while in a quasi-three-dimensional case can become negative depending of a degree of mini-band filling. Such behavior of magnetoresistance, apparently, has been related to presence in a mini-band of region with the negative effective mass
Effect of normal impurities on anisotropic superconductors with variable density of states
Whitmore, M. D.; Carbotte, J. P.
1982-06-01
We develop a generalized BCS theory of impure superconductors with an anisotropic electron-electron interaction represented by the factorizable model introduced by Markowitz and Kadanoff, and a variable electronic density of states N(ɛ), assumed to peak at the Fermi energy, which is modeled by a Lorentzian superimposed on a uniform background. As the impurity scattering is increased, the enhancement of T c by both the anisotropy and the peak in N(ɛ) is washed out. The reduction is investigated for different values of the anisotropy and different peak heights and widths. It is concluded that the effects of anisotropy and the peak are reduced together in such a way that any effect due to anisotropy is not easily distinguishable from that due to the peak.
International Nuclear Information System (INIS)
Satter, M.A.
1990-08-01
In this paper, a formalism for studying the anisotropic interaction between two substitutional magnetic impurities and the magnetic anisotropic effect in a dilute noble metal- transition metal magnetic alloy has been developed from relativistic scattering theory. The theoretical development and the computational techniques of this formalism are based on relativistic spin-polarized scattering theory and relativistic band structure frameworks. For studying the magnetic anisotropic effect a convenient ''working'' frame of reference with its axes oriented along the fcc crystal axes is set up. This formalism is applied to study the situation for two Fe impurities in paramagnetic Au hosts. For AuFe dilute alloy, the two impurity site interaction as a function of separation is not oscillatory and the anisotropic effect is found to be less than the two site interaction itself only by an order of magnitude. Apart from the anisotropic coupling of the two impurity spins to the separation vector, for the first time, another weak anisotropic coupling to the crystal axes is also contained in the two site interaction. These anisotropic effects are the results of the relativistic spin-orbit interaction which are incorporated into the formalism. (author). 22 refs, 5 figs
Magnetic states of single impurity in disordered environment
Directory of Open Access Journals (Sweden)
G.W. Ponedilok
2013-01-01
Full Text Available The charged and magnetic states of isolated impurities dissolved in amorphous metallic alloy are investigated. The Hamiltonian of the system under study is the generalization of Anderson impurity model. Namely, the processes of elastic and non-elastic scattering of conductive electrons on the ions of a metal and on a charged impurity are included. The configuration averaged one-particle Green's functions are obtained within Hartree-Fock approximation. A system of self-consistent equations is given for calculation of an electronic spectrum, the charged and the spin-polarized impurity states. Qualitative analysis of the effect of the metallic host structural disorder on the observed values is performed. Additional shift and broadening of virtual impurity level is caused by a structural disorder of impurity environment.
Lausch, Tobias; Widera, Artur; Fleischhauer, Michael
2018-03-01
We numerically study the relaxation dynamics of a single, heavy impurity atom interacting with a finite one- or two-dimensional, ultracold Bose gas. While there is a clear separation of time scales between processes resulting from single- and two-phonon scattering in three spatial dimensions, the thermalization in lower dimensions is dominated by two-phonon processes. This is due to infrared divergences in the corresponding scattering rates in the thermodynamic limit, which are a manifestation of the Mermin-Wagner-Hohenberg theorem. This makes it necessary to include second-order phonon scattering above a crossover temperature T2ph . T2ph scales inversely with the system size and is much smaller than currently experimentally accessible.
Effect of normal impurities on anisotropic superconductors with variable density of states
International Nuclear Information System (INIS)
Whitmore, M.D.; Carbotte, J.P.
1982-01-01
We develop a generalized BCS theory of impure superconductors with an anisotropic electron--electron interaction represented by the factorizable model introduced by Markowitz and Kadanoff, and a variable electronic density of states N(epsilon-c), assumed to peak at the Fermi energy, which is modeled by a Lorentzian superimposed on a uniform background. As the impurity scattering is increased, the enhancement of T/sub c/ by both the anisotropy and the peak in N(epsilon-c) is washed out. The reduction is investigated for different values of the anisotropy and different peak heights and widths. It is concluded that the effects of anisotropy and the peak are reduced together in such a way that any effect due to anisotropy is not easily distinguishable from that due to the peak
Decoupling single nanowire mobilities limited by surface scattering and bulk impurity scattering
International Nuclear Information System (INIS)
Khanal, D. R.; Levander, A. X.; Wu, J.; Yu, K. M.; Liliental-Weber, Z.; Walukiewicz, W.; Grandal, J.; Sanchez-Garcia, M. A.; Calleja, E.
2011-01-01
We demonstrate the isolation of two free carrier scattering mechanisms as a function of radial band bending in InN nanowires via universal mobility analysis, where effective carrier mobility is measured as a function of effective electric field in a nanowire field-effect transistor. Our results show that Coulomb scattering limits effective mobility at most effective fields, while surface roughness scattering only limits mobility under very high internal electric fields. High-energy α particle irradiation is used to vary the ionized donor concentration, and the observed decrease in mobility and increase in donor concentration are compared to Hall effect results of high-quality InN thin films. Our results show that for nanowires with relatively high doping and large diameters, controlling Coulomb scattering from ionized dopants should be given precedence over surface engineering when seeking to maximize nanowire mobility.
Theoretical study of impurity effects in iron-based superconductors
Navarro Gastiasoro, Maria; Hirschfeld, Peter; Andersen, Brian
2013-03-01
Several open questions remain unanswered for the iron-based superconductors (FeSC), including the importance of electronic correlations and the symmetry of the superconducting order parameter. Motivated by recent STM experiments which show a fascinating variety of resonant defect states in FeSC, we adopt a realistic five-band model including electronic Coulomb correlations to study local effects of disorder in the FeSC. In order to minimize the number of free parameters, we use the pairing interactions obtained from spin-fluctuation exchange to determine the homogeneous superconducting state. The ability of local impurity potentials to induce resonant states depends on their scattering strength Vimp; in addition, for appropriate Vimp, such states are associated with local orbital- and magnetic order. We investigate the density of states near such impurities and show how tunneling experiments may be used to probe local induced order. In the SDW phase, we show how C2 symmetry-breaking dimers are naturally formed around impurities which also form cigar-like (pi,pi) structures embedded in the (pi,0) magnetic bulk phase. Such electronic dimers have been shown to be candidates for explaining the so-called nematogens observed previously by QPI in Co-doped CaFe2As2.
Graphene plasmons: Impurities and nonlocal effects
Viola, Giovanni; Wenger, Tobias; Kinaret, Jari; Fogelström, Mikael
2018-02-01
This work analyzes how impurities and vacancies on the surface of a graphene sample affect its optical conductivity and plasmon excitations. The disorder is analyzed in the self-consistent Green's function formulation and nonlocal effects are fully taken into account. It is shown that impurities modify the linear spectrum and give rise to an impurity band whose position and width depend on the two parameters of our model, the density and the strength of impurities. The presence of the impurity band strongly influences the electromagnetic response and the plasmon losses. Furthermore, we discuss how the impurity-band position can be obtained experimentally from the plasmon dispersion relation and discuss this in the context of sensing.
Hopkins, R. H.; Davis, J. R.; Rohatgi, A.; Campbell, R. B.; Blais, P. D.; Rai-Choudhury, P.; Stapleton, R. E.; Mollenkopf, H. C.; Mccormick, J. R.
1980-01-01
Two major topics are treated: methods to measure and evaluate impurity effects in silicon and comprehensive tabulations of data derived during the study. Discussions of deep level spectroscopy, detailed dark I-V measurements, recombination lifetime determination, scanned laser photo-response, conventional solar cell I-V techniques, and descriptions of silicon chemical analysis are presented and discussed. The tabulated data include lists of impurity segregation coefficients, ingot impurity analyses and estimated concentrations, typical deep level impurity spectra, photoconductive and open circuit decay lifetimes for individual metal-doped ingots, and a complete tabulation of the cell I-V characteristics of nearly 200 ingots.
Models for impurity effects in tokamaks
International Nuclear Information System (INIS)
Hogan, J.T.
1980-03-01
Models for impurity effects in tokamaks are described with an emphasis on the relationship between attainment of high β and impurity problems. We briefly describe the status of attempts to employ neutral beam heating to achieve high β in tokamaks and propose a qualitative model for the mechanism by which heavy metal impurities may be produced in the startup phase of the discharge. We then describe paradoxes in impurity diffusion theory and discuss possible resolutions in terms of the effects of large-scale islands and sawtooth oscillations. Finally, we examine the prospects for the Zakharov-Shafranov catastrophe (long time scale disintegration of FCT equilibria) in the context of present and near-term experimental capability
Impurity effects on ionic-liquid-based supercapacitors
International Nuclear Information System (INIS)
Liu, Kun; Lian, Cheng; Henderson, Douglas; Wu, Jianzhong
2016-01-01
Small amounts of an impurity may affect the key properties of an ionic liquid and such effects can be dramatically amplified when the electrolyte is under confinement. Here the classical density functional theory is employed to investigate the impurity effects on the microscopic structure and the performance of ionic-liquid-based electrical double-layer capacitors, also known as supercapacitors. Using a primitive model for ionic species, we study the effects of an impurity on the double layer structure and the integral capacitance of a room temperature ionic liquid in model electrode pores and find that an impurity strongly binding to the surface of a porous electrode can significantly alter the electric double layer structure and dampen the oscillatory dependence of the capacitance with the pore size of the electrode. Meanwhile, a strong affinity of the impurity with the ionic species affects the dependence of the integral capacitance on the pore size. Up to 30% increase in the integral capacitance can be achieved even at a very low impurity bulk concentration. As a result, by comparing with an ionic liquid mixture containing modified ionic species, we find that the cooperative effect of the bounded impurities is mainly responsible for the significant enhancement of the supercapacitor performance.
Impurity effects on ionic-liquid-based supercapacitors
Liu, Kun; Lian, Cheng; Henderson, Douglas; Wu, Jianzhong
2017-02-01
Small amounts of an impurity may affect the key properties of an ionic liquid and such effects can be dramatically amplified when the electrolyte is under confinement. Here the classical density functional theory is employed to investigate the impurity effects on the microscopic structure and the performance of ionic-liquid-based electrical double-layer capacitors, also known as supercapacitors. Using a primitive model for ionic species, we study the effects of an impurity on the double layer structure and the integral capacitance of a room temperature ionic liquid in model electrode pores and find that an impurity strongly binding to the surface of a porous electrode can significantly alter the electric double layer structure and dampen the oscillatory dependence of the capacitance with the pore size of the electrode. Meanwhile, a strong affinity of the impurity with the ionic species affects the dependence of the integral capacitance on the pore size. Up to 30% increase in the integral capacitance can be achieved even at a very low impurity bulk concentration. By comparing with an ionic liquid mixture containing modified ionic species, we find that the cooperative effect of the bounded impurities is mainly responsible for the significant enhancement of the supercapacitor performance.
Valley Hall Conductivity in Graphene: Effects of Higher-Order Scattering
Ando, Tsuneya
2018-04-01
The valley Hall conductivity, having opposite signs between the K and K' valleys, is calculated in monolayer and bilayer graphenes with nonzero gap in the presence of short-range scatterers within a single-site approximation. In the case of small disorder, the Hall conductivity is quantized into ±e2/2h and ±e2/h in the monolayer and bilayer graphene, respectively, in the gap region, while it is enhanced over the results in the absence of scatterers in the band region. With the increase in the strength of each impurity potential, large asymmetry between the conduction and valence band appears. For scatterers with attractive potential, the disorder parameter is effectively enhanced and reduced in the conduction and valence band, respectively. The behavior is opposite for repulsive scatterers. Effects of skew scattering causing asymmetry in the scattering direction remain small and do not play significant role.
Effect of impurities on the two-dimensional electron gas polarizability
International Nuclear Information System (INIS)
Nkoma, J.S.
1980-06-01
The polarizability for a two-dimensional electron gas is calculated in the presence of impurities by a Green function formalism. This leads to a system with finite mean free path due to electrons scattering off impurities. The calculated polarizability is found to be strongly dependent on the mean free path. The main feature is the suppression of the sharp corner at wave vector 2ksub(F) for finite mean free paths, and the pure metal result is recovered for the infinite mean free path. A possible application of the results to the transport properties of semiconductor inversion layers is discussed. (author)
Magnetic impurity effect on charge and magnetic order in doped La1.5Ca0.5CoO4
Horigane, K.; Hiraka, H.; Tomiyasu, K.; Ohoyama, K.; Louca, D.; Yamada, K.
2012-02-01
Neutron scattering experiments were performed on single crystals of magnetic impurity doped cobalt oxides La1.5Ca0.5CoO4 to characterize the charge and spin orders. We newly found contrasting impurity effects. Two types of magnetic peaks are observed at q = (0.5,0,L) with L = half-integer and integer in La1.5Ca0.5CoO4, while magnetic peak at L = half-integer (integer) was only observed in Mn (Fe)-substituted sample. Although Mn and Fe impurities degrade charge and magnetic order, Cr impurity stabilizes the ordering at x = 0.5. Based on the crystal structural analysis of Cr doped sample, we found that the excess oxygen and change of octahedron around Co3+ were realized in Cr doped sample.
Anisotropy effects in superconductors with magnetic impurities. Pt. 2
International Nuclear Information System (INIS)
Entel, P.
1976-01-01
The influence of Fermi surface anisotropy on the specific heat jumps, ΔC, at the phase transition for superconductors containing magnetic and nonmagnetic impurities is discussed. In the framework of a simple two-band or two-zone model we find for small interband electron-phonon coupling constants characteristic maxima in the ΔC(Tsub(c))-curve. These departures from the corresponding ΔC-curve of a single-band isotropic superconductor are mostly pronounced for weak and strong interband Coulomb scattering of conduction electrons on nonmagnetic ions. There is only a small range of intermediate scattering rates for which the maxima are smeared out. (orig.) [de
Directory of Open Access Journals (Sweden)
Lidong Cao
2018-02-01
Full Text Available The discovery of brassinolide in 1979, a milestone in brassinosteroids research, has sparked great interest of brassinolide analogs (BLs in agricultural applications. Among these BLs, propionylbrassinolide has captured considerable attention because it shows plant growth regulating activity with an excellent durability. Two impurities of propionylbrassinolide were isolated and purified by semi-preparative high-performance liquid chromatography (HPLC, and the chemical structures were confirmed. For simultaneous separation and determination of propionylbrassinolide and impurities, an efficient analytical method based on HPLC with evaporative light scattering detector (HPLC-ELSD was developed. The optimized analysis was performed on a C18 reversed phase column (250 mm × 4.60 mm, 5 μm with isocratic elution of acetonitrile and water (90:10, v/v as the mobile phase. The drift tube temperature of the ELSD system was set to 50 °C and the auxiliary gas pressure was 150 kPa. The regression equations demonstrated a good linear relationship (R2 = 0.9989–0.9999 within the test ranges. The limits of detection (LODs and quantification (LOQs for propionylbrassinolide, impurity 1 and 2 were 1.3, 1.2, 1,3 and 4.3, 4.0, 4.2 mg/L, respectively. The fully validated HPLC-ELSD method was readily applied to quantify the active ingredient and impurities in propionylbrassinolide technical concentrate. Moreover, the optimized separation conditions with ELSD have been successfully transferred to mass spectrometry (MS detector for LC-MS determination.
Transport properties and Raman spectra of impurity substituted MgB2
International Nuclear Information System (INIS)
Masui, T.
2007-01-01
Recent advances in the study of MgB 2 are reviewed, with focus on the transport properties and Raman scattering measurements for impurity substituted crystals. Carbon and Aluminium substitution change band filling, introduce intraband and interband scattering. These effects are seen in the temperature dependence of resistivity, Hall coefficients, and phonon peak of Raman spectra. Manganese substitution introduces magnetic scattering, that increases resistivity but gives little change in Raman spectra. The effect of disorder in neutron irradiated samples is also discussed
Modification of the electronic transport in Au by prototypical impurities and interlayers
Fadlallah, Majida M.
2010-02-01
Electronic transport calculations for metallic interfaces based on density functional theory and a scattering theory on the Landauer-Büttiker level are presented. We study the modifications of the transport through Au due to prototypical impurities and interlayers. Our results show that the influence of S and Si impurities is well described in terms of simple vacancies. Metallic impurities and interlayers, on the other hand, have even more drastic effects, in particular when the Au s-d hybrid states at the Fermi energy are perturbed. The effects of a possible interface alloy formation are discussed in detail. © 2010 EPLA.
Modification of the electronic transport in Au by prototypical impurities and interlayers
Fadlallah, Majida M.; Schuster, Cosima B.; Eckern, Ulrich; Schwingenschlö gl, Udo
2010-01-01
Electronic transport calculations for metallic interfaces based on density functional theory and a scattering theory on the Landauer-Büttiker level are presented. We study the modifications of the transport through Au due to prototypical impurities and interlayers. Our results show that the influence of S and Si impurities is well described in terms of simple vacancies. Metallic impurities and interlayers, on the other hand, have even more drastic effects, in particular when the Au s-d hybrid states at the Fermi energy are perturbed. The effects of a possible interface alloy formation are discussed in detail. © 2010 EPLA.
Effects of helium impurities on superalloys
International Nuclear Information System (INIS)
Selle, J.E.
1977-07-01
A review of the literature on the effects of helium impurities on superalloys at elevated temperatures was undertaken. The actual effects of these impurities vary depending on the alloy, composition of the gas atmosphere, and temperature. In general, exposure in helium produces significant but not catastrophic changes in the structure and properties of the alloys. The effects of these treatments on the structure, creep, fatigue, and mechanical properties of the various alloys are reviewed and discussed. Suggestions for future work are presented
Scattering Effect on Anomalous Hall Effect in Ferromagnetic Transition Metals
Zhang, Qiang
2017-11-30
contributed side jump. The interfacial scattering effect on the AHE is much more complicated than surface scattering in thin films or scattering by delta-impurities in bulk-like samples.
Effect of thallium impurity on hole scattering in lead telluride
International Nuclear Information System (INIS)
Kajdanov, V.I.; Nemov, S.A.
1981-01-01
Hole mobility in PbTe monocrystalline specimens in the temperature range from 4.2 to 300 K has been investigated. Detected is a sharp increase in scattering cross section of light and heavy holes in the specimens having the Hall hole concentration p approximately (5+-9)x10 19 cm -3 explained by resonant scattering into a band of quasilocal states of thallium located lower than the ceiling of heavy carrier zone by 0.01+-0.01 eV. Very large differences in resonant scattering of current carriers into the quasilocal states of In and Tl in PbTe result from the inertial polarizability of a crystal. The same mechanism is used to explain long-lived relaxation of zone electron concentration in lead telluride and Pbsub(1-x)Snsub(x)Te doped with indium [ru
Effects of the ohmic current on collective scattering spectra
International Nuclear Information System (INIS)
Castiglioni, S.; Lontano, M.; Tartari, U.
1993-01-01
A numerical and analytical study of the modifications induced in the collective scattering spectra by the ohmic current governing the equilibrium magnetic configuration in toroidal plasmas is presented. The spectral density function is calculated assuming equilibrium distributions for the (bulk and impurity) ion species and a Spitzer-like distribution to describe the response of the electrons to the applied DC electric field. As expected, the spectral asymmetries can be non-negligibly enhanced in the region of the ion-acoustic frequency. They reach their maxima for tangential scattering geometries, where the magnetic effects on the spectra are negligible. This justifies the assumption of the non-magnetized spectra. A theoretically motivated potential is shown to exist for a more detailed experimental investigation of the feasibility of current-density measurements in ohmic plasmas, based on collective scattering. (author)
Impurity effects in the electrothermal instability
International Nuclear Information System (INIS)
Tomimura, A.; Azevedo, M.T. de
1982-01-01
A 'impure' plasma model is proposed based on the homogeneous hydrogen plasma used in the theory formulated by Tomimura and Haines to explain the electrothermal instable mode growth with the wave vector perpendicular to the applied magnetic field. The impurities are introduced implicitly in the transport coefficients of the two-fluid model through a effective charge number Z sub(eff). (Author) [pt
Electron-electron scattering and mobilities in semiconductors and quantum wells
International Nuclear Information System (INIS)
Lyo, S.K.
1986-01-01
The effect of electron-electron scattering on the mobility in semiconductors and semiconductor quantum wells is examined. A general exact formula is derived for the mobility, when the electron-electron collision rate is much faster than other scattering rates such as those by ionized impurities and phonons. In this limit, the transport relaxation rate is independent of the carrier's energy and contributions to the inverse mobility from individual scattering mechanism add up. The mobility becomes significantly reduced from its value in the absence of electron-electron scattering. When the collision rates are not necessarily dominated by electron-electron scattering, the mobility is calculated by the Kohler-Sondheimer variational method in the presence of ionized-impurity scattering and acoustic-phonon scattering in a nondegenerate two-dimensional quantum well
Institute of Scientific and Technical Information of China (English)
YANGYong－Hong; WANGYong－Gang; 等
2002-01-01
Two kinds of spin-dependent scattering effects (magnetic-impurity and spin-orbit scatterings) are investigated theoretically in a quasi-tow-dimensional (quasi-2D) disordered electron system.By making use of the diagrammatic techniques in perturbation theory,we have calculated the dc conductivity and magnetoresistance due to weak-localization effects,the analytical expressions of them are obtained as functions of the interlayer hopping energy and the characteristic times:elastic,inelastic,magnetic and spin-orbit scattering times.The relevant dimensional crossover behavior from 3D to 2D with decreasing the interlayer coupling is discussed,and the condition for the crossover is shown to be dependent on the aforementioned scattering times.At low temperature there exists a spin-dependent-scattering-induced dimensional crossover in this system.
Anisotropic charged impurity-limited carrier mobility in monolayer phosphorene
International Nuclear Information System (INIS)
Ong, Zhun-Yong; Zhang, Gang; Zhang, Yong Wei
2014-01-01
The room temperature carrier mobility in atomically thin 2D materials is usually far below the intrinsic limit imposed by phonon scattering as a result of scattering by remote charged impurities in its environment. We simulate the charged impurity-limited carrier mobility μ in bare and encapsulated monolayer phosphorene. We find a significant temperature dependence in the carrier mobilities (μ ∝ T −γ ) that results from the temperature variability of the charge screening and varies with the crystal orientation. The anisotropy in the effective mass leads to an anisotropic carrier mobility, with the mobility in the armchair direction about one order of magnitude larger than in the zigzag direction. In particular, this mobility anisotropy is enhanced at low temperatures and high carrier densities. Under encapsulation with a high-κ overlayer, the mobility increases by up to an order of magnitude although its temperature dependence and its anisotropy are reduced
Anisotropic charged impurity-limited carrier mobility in monolayer phosphorene
Energy Technology Data Exchange (ETDEWEB)
Ong, Zhun-Yong; Zhang, Gang; Zhang, Yong Wei [Institute of High Performance Computing, A*STAR, Singapore 138632 (Singapore)
2014-12-07
The room temperature carrier mobility in atomically thin 2D materials is usually far below the intrinsic limit imposed by phonon scattering as a result of scattering by remote charged impurities in its environment. We simulate the charged impurity-limited carrier mobility μ in bare and encapsulated monolayer phosphorene. We find a significant temperature dependence in the carrier mobilities (μ ∝ T{sup −γ}) that results from the temperature variability of the charge screening and varies with the crystal orientation. The anisotropy in the effective mass leads to an anisotropic carrier mobility, with the mobility in the armchair direction about one order of magnitude larger than in the zigzag direction. In particular, this mobility anisotropy is enhanced at low temperatures and high carrier densities. Under encapsulation with a high-κ overlayer, the mobility increases by up to an order of magnitude although its temperature dependence and its anisotropy are reduced.
Collective impurity effects in the Heisenberg triangular antiferromagnet
International Nuclear Information System (INIS)
Maryasin, V S; Zhitomirsky, M E
2015-01-01
We theoretically investigate the Heisenberg antiferromagnet on a triangular lattice doped with nonmagnetic impurities. Two nontrivial effects resulting from collective impurity behavior are predicted. The first one is related to presence of uncompensated magnetic moments localized near vacancies as revealed by the low-temperature Curie tail in the magnetic susceptibility. These moments exhibit an anomalous growth with the impurity concentration, which we attribute to the clustering mechanism. In an external magnetic field, impurities lead to an even more peculiar phenomenon lifting the classical ground-state degeneracy in favor of the conical state. We analytically demonstrate that vacancies spontaneously generate a positive biquadratic exchange, which is responsible for the above degeneracy lifting
Theory of Raman scattering in coupled electron-phonon systems
Itai, K.
1992-01-01
The Raman spectrum is calculated for a coupled conduction-electron-phonon system in the zero-momentum-transfer limit. The Raman scattering is due to electron-hole excitations and phonons as well. The phonons of those branches that contribute to the electron self-energy and the correction of the electron-phonon vertex are assumed to have flat energy dispersion (the Einstein phonons). The effect of electron-impurity scattering is also incorporated. Both the electron-phonon interaction and the electron-impurity interaction cause the fluctuation of the electron distribution between different parts of the Fermi surface, which results in overdamped zero-sound modes of various symmetries. The scattering cross section is obtained by solving the Bethe-Salpeter equation. The spectrum shows a lower threshold at the smallest Einstein phonon energy when only the electron-phonon interaction is taken into consideration. When impurities are also taken into consideration, the threshold disappears.
International Nuclear Information System (INIS)
Wampler, W.
1976-05-01
The physics of the dHvA effect is discussed and it is shown how it can be used to determine the Fermi surface geometry, the Fermi velocities and the local scattering rates. Dingle temperature measurements are discribed and discussed. Furthermore the way in which the samples were prepared is described. Also discussed are some aspects of the metallurgical behavior of hydrogen in copper which are relevant to the sample preparation such as solubility, diffusion, precipitation, and trapping at impurities. The experimental results are presented, and the local scattering rates are determined from the results. These are then compared with lifetimes from previously reported measurements on substitutional impurities in noble metals. The experimental results are found to be in excellent agreement with a recent calculation of the scattering rates for hydrogen in copper by Huisman and Weiss. The data is also analysed in terms of phase shifts using the Greens function theory of Holtzworth and Lee for scattering from interstitials. (HPOE) [de
The effects of naturally occurring impurities in rock salt
Indian Academy of Sciences (India)
In this paper we investigate the effect that naturally occurring impurities in salt mines have both on effective permittivity of the medium and on radio wave propagation at ∼200 MHz. The effective permittivity is determined based on the dielectric properties of salt and the characteristics of the main impurities. We conclude that ...
Impurity levels: corrections to the effective mass approximation
International Nuclear Information System (INIS)
Bentosela, F.
1977-07-01
Some rigorous results concerning the effective mass approximation used for the calculation of the impurity levels in semiconductors are presented. Each energy level is expressed as an asymptotic series in the inverse of the dielectric constant K, in the case where the impurity potential is 1/μ
Effects of impurities on radiation damage in InP
International Nuclear Information System (INIS)
Yamaguchi, M.; Ando, K.
1986-01-01
Strong impurity effects upon introduction and annealing behavior of radiation-induced defects in InP irradiated with 1-MeV electrons have been found. The main defect center of 0.37-eV hole trap H4 in p-InP, which must be due to a point defect, is annealed even at room temperature. Its annealing rate is found to be proportional to the 2/3 power of the preirradiation carrier concentration in InP. Moreover, the density of the hole trap H5 (E/sub v/+0.52 eV) in p-InP, which must be due to a point defect--impurity complex, increases with increase in the InP carrier concentration. These results suggest that the radiation-induced defects in InP must recover through long-range diffusion mediated by impurity atoms. A model is proposed in which point defects diffuse to sinks through impurities so as to disappear or bind impurities so as to form point defect--impurity complexes. In addition to the long-range diffusion mechanism, the possibility of charge-state effects responsible for the thermal annealing of radiation-induced defects in InP is also discussed
Variational method for magnetic impurities in metals: impurity pairs
Energy Technology Data Exchange (ETDEWEB)
Oles, A M [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany, F.R.); Chao, K A [Linkoeping Univ. (Sweden). Dept. of Physics and Measurement Technology
1980-01-01
Applying a variational method to the generalized Wolff model, we have investigated the effect of impurity-impurity interaction on the formation of local moments in the ground state. The direct coupling between the impurities is found to be more important than the interaction between the impurities and the host conduction electrons, as far as the formation of local moments is concerned. Under certain conditions we also observe different valences on different impurities.
On the radiative effects of light-absorbing impurities on snowpack evolution
Dumont, M.; Tuzet, F.; Lafaysse, M.; Arnaud, L.; Picard, G.; Lejeune, Y.; Lamare, M.; Morin, S.; Voisin, D.; Di Mauro, B.
2017-12-01
The presence of light absorbing impurities in snow strongly decreases snow reflectance leading to an increase in the amount of solar energy absorbed by the snowpack. This effect is also known as impurities direct radiative effect. The change in the amount of energy absorbed by the snowpack modifies the temperature profile inside the snowpack and in turn snow metamorphism (impurities indirect radiative effects). In this work, we used the detailed snowpack model SURFEX/ISBA-Crocus with an explicit representation of snow light-absorbing impurities content (Tuzet et al., 2017) fed by medium-resolution ALADIN-Climate atmospheric model to represent dust and black carbon atmospheric deposition fluxes. The model is used at two sites: Col de Porte (medium elevation site in the French Alps) and Torgnon (high elevation site in the Italian Alps). The simulations are compared to in-situ observations and used to quantify the effects of light-absorbing impurities on snow melt rate and timing. The respective parts of the direct and indirect radiative effects of light-absorbing impurities in snow are also computed for the two sites, emphasizing the need to account for the interactions between snow metamorphism and LAI radiative properties, to accurately predict the effects of light-absorbing impurities in snow. Moreover, we describe how automated hyperspectral reflectance can be used to estimate effective impurities surface content in snow. Finally we demonstrate how these reflectances measurements either from in situ or satellite data can be used via an assimilation scheme to constrain snowpack ensemble simulations and better predict the snowpack state and evolution.
International Nuclear Information System (INIS)
Wagner, P.
1976-04-01
Effects on graphite thermal conductivities due to controlled alterations of the graphite structure by impurity addition, porosity, and neutron irradiation are shown to be consistent with the phonon-scattering formulation 1/l = Σ/sub i equals 1/sup/n/ 1/l/sub i/. Observed temperature effects on these doped and irradiated graphites are also explained by this mechanism
Characteristics of post-disruption runaway electrons with impurity pellet injection
International Nuclear Information System (INIS)
Kawano, Yasunori; Nakano, Tomohide; Isayama, Akihiko; Asakura, Nobuyuki; Tamai, Hiroshi; Kubo, Hirotaka; Takenaga, Hidenobu; Bakhtiari, Mohammad; Ide, Shunsuke; Kondoh, Takashi; Hatae, Takaki
2005-01-01
Characteristics of post-disruption runaway electrons with impurity pellet injection were investigated for the first time using the JT-60U tokamak device. A clear deposition of impurity neon ice pellets was observed in a post-disruption runaway plasma. The pellet ablation was attributed to the energy deposition of relativistic runaway electrons in the pellet. A high normalized electron density was stably obtained with n e bar /n GW ∼2.2. Effects of prompt exhaust of runaway electrons and reduction of runaway plasma current without large amplitude MHD activities were found. One possible explanation for the basic behavior of runaway plasma current is that it follows the balance of avalanche generation of runaway electrons and slowing down predicted by the Andersson-Helander model, including the combined effect of collisional pitch angle scattering and synchrotron radiation. Our results suggested that the impurity pellet injection reduced the energy of runaway electrons in a stepwise manner. (author)
Yarmohammadi, Mohsen; Mirabbaszadeh, Kavoos
2017-05-01
Using the Kane-Mele Hamiltonian, Dirac theory and self-consistent Born approximation, we investigate the effect of dilute charged impurity on the electronic heat capacity and magnetic susceptibility of two-dimensional ferromagnetic honeycomb structure of group-IV elements including silicene, germanene and stanene within the Green’s function approach. We also find these quantities in the presence of applied external electric field. Our results show that the silicene (stanene) has the maximum (minimum) heat capacity and magnetic susceptibility at uniform electric fields. From the behavior of theses quantities, the band gap has been changed with impurity concentration, impurity scattering strength and electric field. The analysis on the impurity-dependent magnetic susceptibility curves shows a phase transition from ferromagnetic to paramagnetic and antiferromagnetic phases. Interestingly, electronic heat capacity increases (decreases) with impurity concentration in silicene (germanene and stanene) structure.
Magnetic diffuse scattering: a theorist's perspective
International Nuclear Information System (INIS)
Long, M.W.
1996-01-01
We attempt to show that magnetic diffuse scattering is the natural probe for frustrated antiferromagnetism. Comparison between nuclear and magnetic diffuse scattering compares the range of atomic clustering with the range of the magnetic impurity. At low temperature frustration is expected to lead to large differences which are a natural signature for the relevance of such frustration effects. We provide some elementary examples in first-row transition metals which display fairly dramatic effects. (author) 11 figs., tabs., 8 refs
Energy Technology Data Exchange (ETDEWEB)
Hu, Bo, E-mail: hubo2011@semi.ac.cn
2015-03-15
The effect of surface polar optical phonons (SOs) from the dielectric layers on electron mobility in dual-gated graphene field effect transistors (GFETs) is studied theoretically. By taking into account SO scattering of electron as a main scattering mechanism, the electron mobility is calculated by the iterative solution of Boltzmann transport equation. In treating scattering with the SO modes, the dynamic dielectric screening is included and compared to the static dielectric screening and the dielectric screening in the static limit. It is found that the dynamic dielectric screening effect plays an important role in the range of low net carrier density. More importantly, in-plane acoustic phonon scattering and charged impurity scattering are also included in the total mobility for SiO{sub 2}-supported GFETs with various high-κ top-gate dielectric layers considered. The calculated total mobility results suggest both Al{sub 2}O{sub 3} and AlN are the promising candidate dielectric layers for the enhancement in room temperature mobility of graphene in the future.
Effect of suprathermal electrons on the impurity ionization state
International Nuclear Information System (INIS)
Ochando, M A; Medina, F; Zurro, B; McCarthy, K J; Pedrosa, M A; Baciero, A; Rapisarda, D; Carmona, J M; Jimenez, D
2006-01-01
The effect of electron cyclotron resonance heating induced suprathermal electron tails on the ionization of iron impurities in magnetically confined plasmas is investigated. The behaviour of plasma emissivity immediately after injection provides evidence of a spatially localized 'shift' towards higher charge states of the impurity. Bearing in mind that the non-inductive plasma heating methods generate long lasting non-Maxwellian distribution functions, possible implications on the deduced impurity transport coefficients, when fast electrons are present, are discussed
Microscopic models of impurities in silicon
International Nuclear Information System (INIS)
Assali, L.V.C.
1985-01-01
The study of electronic structure of insulated and complex puntual impurities in silicon responsible by the appearing of deep energy levels in the forbiden band of semiconductor, is presented. The molecular cluster model with the treatment of surface orbitals by Watson sphere within the formalism of Xα multiple scattering method, was used. The electronic structures of three clusters representative of perfect silicon crystal, which were used for the impurity studies, are presented. The method was applied to analyse insulated impurities of substitutional and interstitial hydrogen (Si:H and Si:H i ), subtitutional and interstitial iron in neutral and positive charge states (Si:Fe 0 , + , Si:Fe 0 , + ) and substitutional gold in three charge states(Si,Au - , 0 , + ). The thetraedic interstitial defect of silicon (Si:Si i ) was also studied. The complex impurities: neighbour iron pair in the lattice (Si:Fe 2 ), substitutional gold-interstitial iron pair (Si:Au s Fe) and substitutional boron-interstitial hydrogen pair (Si:B s H i ), were analysed. (M.C.K.) [pt
Energy Technology Data Exchange (ETDEWEB)
Cai, Qi; Liu, Yongchang; Guo, Qianying; Ma, Zongqing [Tianjin University, State Key Lab of Hydraulic Engineering Simulation and Safety, School of Materials Science and Engineering, Tianjin (China)
2017-04-15
Glycine-doped MgB{sub 2} bulk was prepared by two-step sintering in this study, first at 750 C and then 900 C. The MgB{sub 4} particles are induced to precipitate where the dislocations concentrated after C substitution or along the steps of screw dislocation during crystal growth, forming ordered MgB{sub 4} arrays throughout the MgB{sub 2} grain. By means of atomic force microscope, the detected magnetic domains are arranged in agreement with the ordered MgB{sub 4} particles after the measurement of magnetic hysteresis loop, which supported that the nano-scale MgB{sub 4} domain structure brought strong scattering effects and indicated that atomic force microscopy could test the role of the impurities. As a result, the extrapolating upper critical field H{sub c2}(0 K) is enhanced to 22.8 T for the sample with ordered MgB{sub 4}, while only 18.1 T for the un-doped sample underwent the same sintering program. Besides, carbon substitution contributed to the enhancement of H{sub c2} as well. (orig.)
Calculation of forces acting on an impurity in a metal subjected to a temperature gradient
International Nuclear Information System (INIS)
Gerl, M.
1966-01-01
In a metal subject to a temperature gradient, an impurity is submitted to both an electrostatic force due to the thermoelectric field and a force due to the scattering of electrons and phonons by this point defect. The scattering of the electrons is treated using a semi-classical approach and a quantum mechanical method. The numerical computation for several impurities in Cu, Ag, and Au requires the knowledge of the resistivity cross-section. and of the thermoelectric power of the impurity in the metal. A tentative estimation of the force due to the phonon-scattering is given for the self-diffusion in Cu. However, the approximations of this calculation do not allow a good comparison with the force due to the electrons. (author) [fr
Li, Shuai; Wang, Chen; Zheng, Shi-Han; Wang, Rui-Qiang; Li, Jun; Yang, Mou
2018-04-01
The impurity effect is studied in three-dimensional Dirac semimetals in the framework of a T-matrix method to consider the multiple scattering events of Dirac electrons off impurities. It has been found that a strong impurity potential can significantly restructure the energy dispersion and the density of states of Dirac electrons. An impurity-induced resonant state emerges and significantly modifies the pristine optical response. It is shown that the impurity state disturbs the common longitudinal optical conductivity by creating either an optical conductivity peak or double absorption jumps, depending on the relative position of the impurity band and the Fermi level. More importantly, these conductivity features appear in the forbidden region between the Drude and interband transition, completely or partially filling the Pauli block region of optical response. The underlying physics is that the appearance of resonance states as well as the broadening of the bands leads to a more complicated selection rule for the optical transitions, making it possible to excite new electron-hole pairs in the forbidden region. These features in optical conductivity provide valuable information to understand the impurity behaviors in 3D Dirac materials.
Magnetic diffuse scattering: a theorist`s perspective
Energy Technology Data Exchange (ETDEWEB)
Long, M W [Birmingham Univ., School of Physics, Birmingham (United Kingdom)
1996-11-01
We attempt to show that magnetic diffuse scattering is the natural probe for frustrated antiferromagnetism. Comparison between nuclear and magnetic diffuse scattering compares the range of atomic clustering with the range of the magnetic impurity. At low temperature frustration is expected to lead to large differences which are a natural signature for the relevance of such frustration effects. We provide some elementary examples in first-row transition metals which display fairly dramatic effects. (author) 11 figs., tabs., 8 refs.
Strong quantum scarring by local impurities
Luukko, Perttu J. J.; Drury, Byron; Klales, Anna; Kaplan, Lev; Heller, Eric J.; Räsänen, Esa
2016-11-01
We discover and characterise strong quantum scars, or quantum eigenstates resembling classical periodic orbits, in two-dimensional quantum wells perturbed by local impurities. These scars are not explained by ordinary scar theory, which would require the existence of short, moderately unstable periodic orbits in the perturbed system. Instead, they are supported by classical resonances in the unperturbed system and the resulting quantum near-degeneracy. Even in the case of a large number of randomly scattered impurities, the scars prefer distinct orientations that extremise the overlap with the impurities. We demonstrate that these preferred orientations can be used for highly efficient transport of quantum wave packets across the perturbed potential landscape. Assisted by the scars, wave-packet recurrences are significantly stronger than in the unperturbed system. Together with the controllability of the preferred orientations, this property may be very useful for quantum transport applications.
Effects of Sample Impurities on the Analysis of MS2 Bacteriophage by Small-Angle Neutron Scattering
National Research Council Canada - National Science Library
Elashvili, Ilya; Wick, Charles H; Kuzmanovic, Deborah A; Krueger, Susan; O'Connell, Catherine
2005-01-01
.... The impact of small molecular weight impurities of the resolution of structural data obtained by SANS of the bacteriophage MS2 distorts the resolution and sharpness of contrast variation peaks...
Electromagnetic effects on trace impurity transport in tokamak plasmas
Hein, T.; Angioni, C.
2010-01-01
The impact of electromagnetic effects on the transport of light and heavy impurities in tokamak plasmas is investigated by means of an extensive set of linear gyrokinetic numerical calculations with the code GYRO [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] and of analytical derivations with a fluid model. The impurity transport is studied by appropriately separating diffusive and convective contributions, and conditions of background microturbulence dominated by both ion temperature gradient (ITG) and trapped electron modes (TEMs) are analyzed. The dominant contribution from magnetic flutter transport turns out to be of pure convective type. However it remains small, below 10% with respect to the E ×B transport. A significant impact on the impurity transport due to an increase in the plasma normalized pressure parameter β is observed in the case of ITG modes, while for TEM the overall effect remains weak. In realistic conditions of high β plasmas in the high confinement (H-) mode with dominant ITG turbulence, the impurity diffusivity is found to decrease with increasing β in qualitative agreement with recent observations in tokamaks. In contrast, in these conditions, the ratio of the total off-diagonal convective velocity to the diagonal diffusivity is not strongly affected by an increase in β, particularly at low impurity charge, due to a compensation between the different off-diagonal contributions.
Spatial variations of order parameter around Kondo impurity for T<=Tsub(c)
International Nuclear Information System (INIS)
Yoksan, S.
1980-04-01
Analytic expressions for the spatial variations of the order parameter around a Kondo impurity are obtained. The oscillatory contribution due to the impurity scattering is calculated using the t matrix of Matsuura which conveniently yields the general results below Tsub(c). Differences between our values and those of Schlottmann are reported. (author)
Patterns induced by magnetic impurities in d-wave superconductors
International Nuclear Information System (INIS)
Zuo Xianjun; Gong Changde; Zhou Yuan
2010-01-01
We investigate the modulated patterns induced by magnetic impurities in d-wave superconductors (DSCs) near optimal doping based on the t-t ' -U-V model. Modulated checkerboard patterns with periodicity of eight or four lattice constants (8a or 4a) in the spin-, charge- and DSC orders are observed. Moreover, the checkerboard modulation in the spin order appear to be robust against parameter changes, which is consistent with neutron-scattering experiments. For the two-impurity case, a modulated stripe-like spin order with periodicity 8a is induced, which coexists with the DSC order. Further experiments of magnetic impurity substitution in DSCs are expected to check these results.
Patterns induced by magnetic impurities in d-wave superconductors
Zuo, Xian-Jun; Gong, Chang-De; Zhou, Yuan
2010-07-01
We investigate the modulated patterns induced by magnetic impurities in d-wave superconductors (DSCs) near optimal doping based on the t-t-U-V model. Modulated checkerboard patterns with periodicity of eight or four lattice constants (8 a or 4 a) in the spin-, charge- and DSC orders are observed. Moreover, the checkerboard modulation in the spin order appear to be robust against parameter changes, which is consistent with neutron-scattering experiments. For the two-impurity case, a modulated stripe-like spin order with periodicity 8 a is induced, which coexists with the DSC order. Further experiments of magnetic impurity substitution in DSCs are expected to check these results.
The effect of impurities on the electronic properties of MgO
Energy Technology Data Exchange (ETDEWEB)
Jalili, Seifollah [Department of Chemistry, K.N. Toosi University of Technology, P.O. Box 16315-1618, Tehran (Iran, Islamic Republic of); Computational Physical Sciences Research Laboratory, Department of Nano-Science, Institute for Studies in Theoretical Physics and Mathematics (IPM), P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of)], E-mail: sjalili@nano.ipm.ac.ir; Majidi, Roya [Department of Physics, Shahid Beheshti University, Tehran (Iran, Islamic Republic of)
2008-10-01
The effect of impurities on the electronic properties of MgO is investigated using the full potential linearized augmented plane-wave plus local-orbitals method based on density functional theory. The electronic band structures and density of states of MgO in the presence of Ca, Li, and Na impurities were calculated. It is found that increasing the amount of Ca impurity decreases the energy band gap and increases the width of the upper part of the valence band. Some of the considered impurities (Li and Na) change the electronic properties of MgO extensively.
The effect of impurities on the electronic properties of MgO
International Nuclear Information System (INIS)
Jalili, Seifollah; Majidi, Roya
2008-01-01
The effect of impurities on the electronic properties of MgO is investigated using the full potential linearized augmented plane-wave plus local-orbitals method based on density functional theory. The electronic band structures and density of states of MgO in the presence of Ca, Li, and Na impurities were calculated. It is found that increasing the amount of Ca impurity decreases the energy band gap and increases the width of the upper part of the valence band. Some of the considered impurities (Li and Na) change the electronic properties of MgO extensively
Lattice dynamics of a crystal with a molecular impurity
International Nuclear Information System (INIS)
Sahoo, D.; Venkataraman, G.
1975-01-01
The dynamics of a crystal containing a molecular impurity is discussed with allowance for the effects of internal vibrations of the molecule. Cartesian coordinates are used to describe internal vibrations, angular oscillations and centre of mass translations of the impurity, and the displacement of atoms of the host lattice. Next the Hamiltonian is set up and the equations of motion derived. In this process, use is made of Dirac brackets when dealing with vibrational coordinates (of the molecule) which have redundancy and constraints. A method of solution of the normal modes of the system is indicated by using the defect space matrixpartitioning technique. The special case of a rigid molecular impurity is then discussed along with the relevance of the present formalism in the interpretation of a recent neutron scattering experiment. It is also shown how the results of crystal-field approximation model and those of the molecular model approximation are obtained as further special cases of the present formalism. A comparison of the present work with those of others has been made. (author)
Conductance of a quantum ring with spin-orbit interaction in the presence of an impurity
International Nuclear Information System (INIS)
Kovalev, V. M.; Chaplik, A. V.
2006-01-01
The conductance of a quantum ring has been calculated on the basis of the tunneling Hamiltonian in the quasiballistic regime of the motion of electrons with allowance for the spin-orbit interaction. The effect of the scattering of electrons by a single short-range interacting impurity in the quantum ring on the tunneling electron current is analyzed. Two types of impurities, spinless and paramagnetic, are considered. The conductance symmetry is discussed for various electron-spin orientations with respect to change in the sign of the magnetic flux through the quantum ring
Impurity Effects in Electroplated-Copper Solder Joints
Directory of Open Access Journals (Sweden)
Hsuan Lee
2018-05-01
Full Text Available Copper (Cu electroplating is a mature technology, and has been extensively applied in microelectronic industry. With the development of advanced microelectronic packaging, Cu electroplating encounters new challenges for atomic deposition on a non-planar substrate and to deliver good throwing power and uniform deposit properties in a high-aspect-ratio trench. The use of organic additives plays an important role in modulating the atomic deposition to achieve successful metallic coverage and filling, which strongly relies on the adsorptive and chemical interactions among additives on the surface of growing film. However, the adsorptive characteristic of organic additives inevitably results in an incorporation of additive-derived impurities in the electroplated Cu film. The incorporation of high-level impurities originating from the use of polyethylene glycol (PEG and chlorine ions significantly affects the microstructural evolution of the electroplated Cu film, and the electroplated-Cu solder joints, leading to the formation of undesired voids at the joint interface. However, the addition of bis(3-sulfopropyl disulfide (SPS with a critical concentration suppresses the impurity incorporation and the void formation. In this article, relevant studies were reviewed, and the focus was placed on the effects of additive formula and plating parameters on the impurity incorporation in the electroplated Cu film, and the void formation in the solder joints.
Impurity effects of hydrogen isotope retention on boronized wall in LHD
International Nuclear Information System (INIS)
Oya, Yasuhisa; Okuno, Kenji; Ashikawa, Naoko; Nishimura, Kiyohiko; Sagara, Akio
2010-11-01
The impurity effect on hydrogen isotopes retention in the boron film deposited in LHD was evaluated by means of XPS and TDS. It was found that the impurity concentrations in boron film were increased after H-H main plasma exposure in LHD. The ratio of hydrogen retention trapped by impurity to total hydrogen retention during H-H main plasma exposure was reached to 70%, although that of deuterium retention by impurity in D 2 + implanted LHD-boron film was about 35%. In addition, the dynamic chemical sputtering of hydrogen isotopes with impurity as the form of water and / or hydrocarbons was occurred by energetic hydrogen isotopes irradiation. It was expected that the enhancement of impurity concentration during plasma exposure in LHD would induce the dynamic formation of volatile molecules and their re-emission to plasma. These facts would prevent stable plasma operation in LHD, concluding that the dynamic impurity behavior in boron film during plasma exposure is one of key issues for the steady-state plasma operation in LHD. (author)
Effects of impurities on crystal growth in fructose crystallization
Chu, Y. D.; Shiau, L. D.; Berglund, K. A.
1989-10-01
The influence of impurities on the crystallization of anhydrous fructose from aqueous solution was studied. The growth kinetics of fructose crystals in the fructose-water-glucose and fructose-water-difructose dianhydrides systems were investigated using photomicroscopic contact nucleation techniques. Glucose is the major impurity likely to be present in fructose syrup formed during corn wet milling, while several difructose dianhydrides are formed in situ under crystallization conditions and have been proposed as a cause in the decrease of overall yields. Both sets of impurities were found to cause inhibition of crystal growth, but the mechanisms responsible in each case are different. It was found that the presence of glucose increases the solubility of fructose in water and thus lowers the supersaturation of the solution. This is probably the main effect responsible for the decrease of crystal growth. Since the molecular structures of difructose dianhydrides are similar to that of fructose, they are probably "tailor-made" impurities. The decrease of crystal growth is probably caused by the incorporation of these impurities into or adsorption to the crystal surface which would accept fructose molecules in the orientation that existed in the difructose dianhydride.
International Nuclear Information System (INIS)
Dzyub, I.P.; Kochmarskij, V.Z.
1978-01-01
The specific features of coherent slow-neutron scattering in the neighbourhood of the quasilocal oscillation (QLO) frequency are investigated. By means of the calculation for a simple cubic crystal containing substitutional impurities it is demonstrated that the dispersion curves are discontinuous in the QLO frequency range. This dispersion curve discontinuity is associated with one-phonon peak in the neighbourhood of the QLO frequency. The results of neutron scattering experiments on Crsub(1-x)Wsub(x) and Cusub(1-x)Ausub(x) solutions are then considered from this standpoint. Selection rules for the phonon mass operator are established which allow to determine the symmetry of QLO which contribute to the broadening and shift of one-phonon peaks in the directions of high symmetry, depending on the transfer neutron-momentum orientation with respect to the principal axes of a crystal
Effect of impurities on vacancy migration energy in Fe-based alloys
International Nuclear Information System (INIS)
Hashimoto, N.; Sakuraya, S.; Tanimoto, J.; Ohnuki, S.
2014-01-01
Effects of impurities, such as carbon, nitrogen, helium and hydrogen, on microstructural evolution in pure iron were investigated by means of a multi-beam electron microscope. Growth rate of dislocation loops were measured to calculate vacancy migration energies. In all irradiation temperature conditions, both the size and the number density of dislocation loops were increased as a function of dose. Irradiation with more impurities showed an increase in the temperature dependence of the dislocation loop growth rate compared to irradiation with little impurities. The in situ experiment indicated that the net migration energy of vacancies could be increased due to trapping by impurities, and the effect of C and N on the migration energy of vacancy would be larger than that of W, V, Ta. Furthermore, H and He would increase vacancy migration energy greater than C and N, as well as W, V, Ta. The density functional theory (DFT), applied to the atomic models of BCC iron, indicated an increase in vacancy migration energy by the trapping of impurity atoms, that is a good agreement with this in situ experiment
Effect of impurities on kinetic transport processes in fusion plasmas
Energy Technology Data Exchange (ETDEWEB)
Braun, Stefanie
2010-12-10
Within the framework of this thesis, different problems arising in connection with impurities have been investigated. Collisional damping of zonal flows in tokamaks: Since the Coulomb collision frequency increases with increasing ion charge, heavy, highly charged impurities play an important role in this process. The effect of such impurities on the linear response of the plasma to an external potential perturbation, as caused by zonal flows, is calculated with analytical methods. In comparison with a pure plasma, the damping of the flows occurs, as expected, considerably faster; for experimentally relevant parameters, the enhancement exceeds the effective charge Z{sub eff} of the plasma. Impurity transport driven by microturbulence in tokamaks: With regard to impurities, it is especially important whether the resulting flows are directed inwards or outwards, since they are deleterious for core energy confinement on the one hand, but on the other hand help protecting plasma-facing components from too high energy fluxes in the edge region. A semi-analytical model is presented describing the resulting impurity fluxes and the stability boundary of the underlying mode. The main goal is to bridge the gap between, on the one hand, costly numerical simulations, which are applicable to a broad range of problems but yield scarcely traceable results, and, on the other hand, analytical theory, which might ease the interpretation of the results but is so far rather rudimentary. The model is based on analytical formulae whenever possible but resorts to a numerical treatment when the approximations necessary for an analytical solution would lead to a substantial distortion of the results. Both the direction of the impurity flux and the stability boundary are found to depend sensitively on the plasma parameters such as the impurity density and the temperature gradient. Pfirsch-Schlueter transport in stellarators: Due to geometry effects, collisional transport plays a much more
International Nuclear Information System (INIS)
Tsang, J.K.
1980-01-01
Tunneling measurements of quench-condensed In-Mn and Pb-Mn alloy films were made. The results were compared with Shiba's theory of superconductors containing magnetic impurities. The localized excited impurity states predicted by Shiba's theory were observed in both alloys. In addition to s-wave scattering, it was necessary to include p- and d-wave scattering of the conduction electrons in the theory in order to explain the experimental data. Partial agreement between the theory and the experimental data was obtained using phase shifts from band calculations by A.B. Kunz. The results on In-Mn also agree with thermal conductivity data
Analysis of impurity effect on Silicide fuels of the RSG-GAS core
International Nuclear Information System (INIS)
Tukiran-Surbakti
2003-01-01
Simulation of impurity effect on silicide fuel of the RSG-GAS core has been done. The aim of this research is to know impurity effect of the U-234 and U-236 isotopes in the silicide fuels on the core criticality. The silicide fuels of 250 g U loading and 19.75 of enrichment is used in this simulation. Cross section constant of fuels and non-structure material of core are generated by WIMSD/4 computer code, meanwhile impurity concentration was arranged from 0.01% to 2%. From the result of analysis can be concluded that the isotopes impurity in the fuels could make trouble in the core and the core can not be operated at critical after a half of its cycle length (350 MW D)
Directory of Open Access Journals (Sweden)
Useong Kim
2014-05-01
Full Text Available We studied the conduction mechanism in Sb-doped BaSnO3 epitaxial films, and compared its behavior with that of the mechanism of its counterpart, La-doped BaSnO3. We found that the electron mobility in BaSnO3 films was reduced by almost 7 times when the dopant was changed from La to Sb, despite little change in the effective mass of the carriers. This indicates that the scattering rate of conduction electrons in the BaSnO3 system is strongly affected by the site at which the dopants are located. More importantly, we found that electron scattering by threading dislocations also depends critically on the dopant site. We propose that the large enhancement of scattering by the threading dislocations in Sb-doped BaSnO3 films is caused by the combination effect of the change in the distribution of Sb impurities in the films, the formation of the Sb impurity clusters near the threading dislocations, and the conduction electron clustering near the Sb impurities.
Active beam scattering apparatus and its application to JFT-2 tokamak
International Nuclear Information System (INIS)
Takeuchi, Hiroshi; Matsuda, Toshiaki; Nishitani, Takeo; Shiho, Makoto; Maeda, Hikosuke; Konagai, Chikara; Kimura, Hironobu.
1983-09-01
The capability to assess the ion temperatures using a neutral beam scattering system is investigated on the JFT-2 tokamak. The neutral beam scattering system consists of a 15 KeV neutral hydrogen atom beam and a momentum analyser with silicon surface barrier detectors. The energy analysis of scattered particles on the scattering angle of 4 0 gives the estimation of ion temperatures, which agree well with the one deduced from passive charge-exchange neutral measurements. The influence of impurity ions to the scattering spectrum is not observed and the results of gas scattering experiments suggests that this phenomenon occurs because of the ionization of neutral beam due to the collisions with impurity ions. (author)
Sengupta, D.; Gao, L.; Wilcox, E. M.; Beres, N. D.; Moosmüller, H.; Khlystov, A.
2017-12-01
Radiative forcing and climate change greatly depends on earth's surface albedo and its temporal and spatial variation. The surface albedo varies greatly depending on the surface characteristics ranging from 5-10% for calm ocean waters to 80% for some snow-covered areas. Clean and fresh snow surfaces have the highest albedo and are most sensitive to contamination with light absorbing impurities that can greatly reduce surface albedo and change overall radiative forcing estimates. Accurate estimation of snow albedo as well as understanding of feedbacks on climate from changes in snow-covered areas is important for radiative forcing, snow energy balance, predicting seasonal snowmelt, and run off rates. Such information is essential to inform timely decision making of stakeholders and policy makers. Light absorbing particles deposited onto the snow surface can greatly alter snow albedo and have been identified as a major contributor to regional climate forcing if seasonal snow cover is involved. However, uncertainty associated with quantification of albedo reduction by these light absorbing particles is high. Here, we use Mie theory (under the assumption of spherical snow grains) to reconstruct the single scattering parameters of snow (i.e., single scattering albedo ῶ and asymmetry parameter g) from observation-based size distribution information and retrieved refractive index values. The single scattering parameters of impurities are extracted with the same approach from datasets obtained during laboratory combustion of biomass samples. Instead of using plane-parallel approximation methods to account for multiple scattering, we have used the simple "Monte Carlo ray/photon tracing approach" to calculate the snow albedo. This simple approach considers multiple scattering to be the "collection" of single scattering events. Using this approach, we vary the effective snow grain size and impurity concentrations to explore the evolution of snow albedo over a wide
Isotope effects of trapped electron modes in the presence of impurities in tokamak plasmas
Shen, Yong; Dong, J. Q.; Sun, A. P.; Qu, H. P.; Lu, G. M.; He, Z. X.; He, H. D.; Wang, L. F.
2016-04-01
The trapped electron modes (TEMs) are numerically investigated in toroidal magnetized hydrogen, deuterium and tritium plasmas, taking into account the effects of impurity ions such as carbon, oxygen, helium, tungsten and others with positive and negative density gradients with the rigorous integral eigenmode equation. The effects of impurity ions on TEMs are investigated in detail. It is shown that impurity ions have substantially-destabilizing (stabilizing) effects on TEMs in isotope plasmas for {{L}ez}\\equiv {{L}ne}/{{L}nz}>0 (TEM turbulences in hydrogenic isotope plasmas with and without impurities are performed. The relations between the maximum growth rate of the TEMs with respect to the poloidal wave number and the ion mass number are given in the presence of the impurity ions. The results demonstrate that the maximum growth rates scale as {γ\\max}\\propto Mi-0.5 in pure hydrogenic plasmas. The scale depends on the sign of its density gradient and charge number when there is a second species of (impurity) ions. When impurity ions have density profiles peaking inwardly (i.e. {{L}ez}\\equiv {{L}ne}/{{L}nz}>0 ), the scaling also depends on ITG parameter {ηi} . The maximum growth rates scale as {γ\\max}\\propto M\\text{eff}-0.5 for the case without ITG ({ηi}=0 ) or the ITG parameter is positive ({ηi}>0 ) but the impurity ion charge number is low (Z≤slant 5.0 ). However, when {ηi}>0 and the impurity ion charge number is moderate (Z=6.0-8.0 ), the scaling law is found as {γ\\max}\\propto M\\text{eff}-1.0 . Here, Z is impurity ion charge number, and the effective mass number, {{M}\\text{eff}}=≤ft(1-{{f}z}\\right){{M}i}+{{f}z}{{M}z} , with {{M}i} and {{M}Z} being the mass numbers of the hydrogenic and impurity ions, respectively, and {{f}z}=Z{{n}0z}/{{n}0e} being the charge concentration of impurity ions. In addition, with regard to the case of {{L}ez}<0 , the maximum growth rate scaling is {γ\\max}\\propto Mi-0.5 . The possible relations of the results
Isotope effect of impurity diffusion of cadmium in silver
International Nuclear Information System (INIS)
Rockosch, H.J.; Herzig, C.
1984-01-01
The isotope effect of impurity diffusion of cadmium in silver single crystals was measured with the radioisotopes 115 Cd/ 109 Cd by gamma spectrometry. As a mean value E = 0.37 at T = 1060 K was obtained. The correlation factor f /SUB Cd/ = 0.41 is in disagreement with previous results of other investigators due to their unfavourable experimental approach. The present value of f /SUB Cd/ , however, is consistent with those of In and Sn in Ag. A comparison with the corresponding correlation factors in the copper solvent reveals a distinct influence of lattice perturbations because of the different atomic volumes of the solvents. Since the size effect is neglected in the electrostatic diffusion model, the agreement with this model is only qualitative. The frequency ratios for vacancy jumps were calculated. The free binding enthalpy of the vacancy-impurity complex was estimated to be Δg /SUB Cd/ = -0.064 eV. This value is smaller than those for In and Sn in Ag and complies with the relative diffusivities of these impurities in Ag
Effect of light impurities on the early stage of swelling in austenitic stainless steel
International Nuclear Information System (INIS)
Igata, N.
1998-01-01
The objective of this study is to analyse the early stage of swelling and clarify the role of light impurities (nitrogen) in swelling of austenitic stainless steel. Recent results show that light impurities affect the swelling of 316 stainless steel under HVEM irradiation up to 10 dpa. At low concentration of light impurities the radiation swelling increases then decreases through the maximum as the concentration of light impurities increases. In the present paper the theoretical model is presented for the explanation of this effect. The model is based on the two factors: the influence of absorbed impurities on the voids caused by the production of an additional gas pressure in voids for their stabilization and the effect of impurities segregated around the surface of voids by the lowering of surface tension. These two affects are taken into account in the calculations of the critical size and the growth rate of cavities. The theoretical predictions on the radiation swelling rate dependent on the impurity concentration and temperature coincided with the experimental results on 316 stainless steel irradiated by HVEM. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Kim, Useong; Park, Chulkwon; Kim, Rokyeon; Mun, Hyo Sik; Kim, Hoon Min; Kim, Namwook; Yu, Jaejun; Char, Kookrin, E-mail: kchar@phya.snu.ac.kr [Center for Strongly Correlated Materials Research, Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of); Ha, Taewoo; Kim, Jae Hoon [Department of Physics, Yonsei University, Seoul 120-749 (Korea, Republic of); Kim, Hyung Joon; Kim, Tai Hoon; Kim, Kee Hoon [Center for Novel States of Complex Materials Research, Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of)
2014-05-01
We studied the conduction mechanism in Sb-doped BaSnO{sub 3} epitaxial films, and compared its behavior with that of the mechanism of its counterpart, La-doped BaSnO{sub 3}. We found that the electron mobility in BaSnO{sub 3} films was reduced by almost 7 times when the dopant was changed from La to Sb, despite little change in the effective mass of the carriers. This indicates that the scattering rate of conduction electrons in the BaSnO{sub 3} system is strongly affected by the site at which the dopants are located. More importantly, we found that electron scattering by threading dislocations also depends critically on the dopant site. We propose that the large enhancement of scattering by the threading dislocations in Sb-doped BaSnO{sub 3} films is caused by the combination effect of the change in the distribution of Sb impurities in the films, the formation of the Sb impurity clusters near the threading dislocations, and the conduction electron clustering near the Sb impurities.
International Nuclear Information System (INIS)
Lanfredi, A.J.C.; Sergeenkov, S.; Araujo-Moreira, F.M.
2006-01-01
Using a highly-sensitive home-made mutual-inductance technique, temperature profiles of the magnetic penetration depth λ(T) in the optimally-doped Sm 1.85 Ce 0.15 CuO 4 thin films have been extracted. The low-temperature behavior of λ(T) is found to be best-fitted by linear Δλ(T)/λ(0)=ln(2)k B T/Δ 0 and quadratic Δλ(T)/λ(0)=Γ -1/2 Δ 0 -3/2 T 2 laws above and below T=0.22T C , respectively, which clearly indicates the presence of d-wave pairing mechanism dominated by strong paramagnetic scattering at the lowest temperatures. The best fits produce Δ 0 /k B T C =2.07 and Γ/T C =0.25(T C /Δ 0 ) 3 for the estimates of the nodal gap parameter and impurity scattering rate
Energy Technology Data Exchange (ETDEWEB)
Liu, K M; Juang, C H; Hsu, S Y [Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan (China); Umansky, V, E-mail: syhsu@mail.nctu.edu.t [Braun Center for Submicron Research, Weizmann Institute of Science, Rehovot 76100 (Israel)
2010-10-06
We have studied the linear conductance and source-drain bias spectroscopies of clean and disordered quantum wires (QWs) against thermal cycling and lateral shifting, which change the impurity configuration. Conductance quantization and the zero bias anomaly (ZBA) are robust in clean QWs. In contrast, disordered QWs show complexities in the ways of conductance resonance, peak splitting and trace crossing in source-drain bias spectroscopies. The experimental results and theoretical predictions are in congruence. Moreover, the resonant state arising from the impurities results in either a single peak or double-splitting peaks in the spectroscopies from the detailed impurity configurations. The resonant splitting peaks are found to influence the ZBA, indicating that a clean QW is crucial for investigating the intrinsic characteristics of the ZBA of QWs.
International Nuclear Information System (INIS)
Liu, K M; Juang, C H; Hsu, S Y; Umansky, V
2010-01-01
We have studied the linear conductance and source-drain bias spectroscopies of clean and disordered quantum wires (QWs) against thermal cycling and lateral shifting, which change the impurity configuration. Conductance quantization and the zero bias anomaly (ZBA) are robust in clean QWs. In contrast, disordered QWs show complexities in the ways of conductance resonance, peak splitting and trace crossing in source-drain bias spectroscopies. The experimental results and theoretical predictions are in congruence. Moreover, the resonant state arising from the impurities results in either a single peak or double-splitting peaks in the spectroscopies from the detailed impurity configurations. The resonant splitting peaks are found to influence the ZBA, indicating that a clean QW is crucial for investigating the intrinsic characteristics of the ZBA of QWs.
Hydrostatic pressure effects on impurity states in InAs/GaAs quantum dot
International Nuclear Information System (INIS)
Xia Congxin; Liu Yaming; Wei Shuyi
2008-01-01
Within the framework of effective-mass approximation, the hydrostatic pressure effects on the donor binding energy of a hydrogenic impurity in InAs/GaAs self-assembled quantum dot(QD) are investigated by means of a variational method. Numerical results show that the donor binding energy increases when the hydrostatic pressure increases for any impurity position and QD size. Moreover, the hydrostatic pressure has a remarkable influence on the donor binding energy for small QD. Realistic cases, including the impurity in the QD and the surrounding barrier, are considered
Impurity photovoltaic effect in silicon solar cell doped with sulphur: A numerical simulation
International Nuclear Information System (INIS)
Azzouzi, Ghania; Chegaar, Mohamed
2011-01-01
The impurity photovoltaic effect (IPV) has mostly been studied in various semiconductors such as silicon, silicon carbide and GaAs in order to increase infrared absorption and hence cell efficiency. In this work, sulphur is used as the IPV effect impurity incorporated in silicon solar cells. For our simulation we use the numerical device simulator (SCAPS). We calculate the solar cell performances (short circuit current density J sc , open circuit voltage V oc , conversion efficiency η and quantum efficiency QE). We study the influence of light trapping and certain impurity parameters like impurity concentration and position in the gap on the solar cell performances. Simulation results for IPV effect on silicon doped with sulphur show an improvement of the short circuit current and the efficiency for sulphur energy levels located far from the middle of the band gap especially at E c -E t =0.18 eV.
Key scattering mechanisms limiting the lateral transport in a modulation-doped polar heterojunction
Energy Technology Data Exchange (ETDEWEB)
Tien, Nguyen Thanh, E-mail: nttien@ctu.edu.vn; Thao, Pham Thi Bich [College of Natural Sciences, Can Tho University, 3-2 Road, Can Tho City (Viet Nam); Thao, Dinh Nhu [Center for Theoretical and Computational Physics, College of Education, Hue University, 34 Le Loi Street, Hue City (Viet Nam); Quang, Doan Nhat [Institute of Physics, Vietnamese Academy of Science and Technology, 10 Dao Tan Street, Hanoi (Viet Nam)
2016-06-07
We present a study of the lateral transport of a two-dimensional electron gas (2DEG) in a modulation-doped polar heterojunction (HJ). In contrast to previous studies, we assume that the Coulomb correlation among ionized impurities and among charged dislocations in the HJ is so strong that the 2DEG low-temperature mobility is not limited by impurity and dislocation scattering. The mobility, however, is specified by alloy disorder scattering and combined roughness scattering, which is the total effect induced by both the potential barrier and polarization roughness. The obtained results show that the alloy disorder and combined roughness scattering strongly depend on the alloy content and on the near-interface electron distribution. Our theory is capable of explaining the bell-shaped dependence of the lateral mobility on alloy content observed in AlGaN/GaN and on 2DEG density observed in AlN/GaN, which have not previously been explained.
Impurity effects in two-electron coupled quantum dots: entanglement modulation
International Nuclear Information System (INIS)
Acosta Coden, Diego S; Romero, Rodolfo H; Ferrón, Alejandro; Gomez, Sergio S
2013-01-01
We present a detailed analysis of the electronic and optical properties of two-electron quantum dots with a two-dimensional Gaussian confinement potential. We study the effects of Coulomb impurities and the possibility of manipulating the entanglement of the electrons by controlling the confinement potential parameters. The degree of entanglement becomes highly modulated by both the location and charge screening of the impurity atom, resulting in two regimes: one of low entanglement and the other of high entanglement, with both of them mainly determined by the magnitude of the charge. It is shown that the magnitude of the oscillator strength of the system could provide an indication of the presence and characteristics of impurities and, therefore, the degree of entanglement. (paper)
Thomson scattering if FIR radiation
International Nuclear Information System (INIS)
Evans, D.E.
1976-12-01
The frequency spectrum of radiation scattered by collective density fluctuations of electrons in a hot plasma is influenced by ion and electron temperatures, impurity concentration and plasma effective charge, magnetic field, and the level of microturbulence. A pulsed laser suitable for measuring collective scattering in a tokamak will have infrared wavelength, power of the order of MWs and bandwidth of a few 10s of MHz. The extent to which these conditions can be met by optically pumped submillimetre lasers, including narrow band oscillators, amplifiers and superradiance - injection assemblies operated in CH 3 F and D 2 O, under development at the Culham Laboratory, is discussed. (author)
Very high upper critical fields in MgB2 produced by selective tuning of impurity scattering
International Nuclear Information System (INIS)
Gurevich, A; Patnaik, S; Braccini, V; Kim, K H; Mielke, C; Song, X; Cooley, L D; Bu, S D; Kim, D M; Choi, J H; Belenky, L J; Giencke, J; Lee, M K; Tian, W; Pan, X Q; Siri, A; Hellstrom, E E; Eom, C B; Larbalestier, D C
2004-01-01
We report a significant enhancement of the upper critical field H c2 of different MgB 2 samples alloyed with nonmagnetic impurities. By studying films and bulk polycrystals with different resistivities ρ, we show a clear trend of an increase in H c2 as ρ increases. One particular high resistivity film had a zero-temperature H c2 (0) well above the H c2 values of competing non-cuprate superconductors such as Nb 3 Sn and Nb-Ti. Our high-field transport measurements give record values H c2 perp (0) ∼ 34 T and H c2 par (0) ∼ 49 T for high resistivity films and H c2 (0) ∼ 29 T for untextured bulk polycrystals. The highest H c2 film also exhibits a significant upward curvature of H c2 (T) and a temperature dependence of the anisotropy parameter γ(T)=H c2 par / H c2 opposite to that of single crystals: γ(T) decreases as the temperature decreases, from γ(T c ) ∼ 2 γ(0) ∼ 1.5. This remarkable H c2 enhancement and its anomalous temperature dependence are a consequence of the two-gap superconductivity in MgB 2 , which offers special opportunities for further H c2 increases by tuning of the impurity scattering by selective alloying on Mg and B sites. Our experimental results can be explained by a theory of two-gap superconductivity in the dirty limit. The very high values of H c2 (T) observed suggest that MgB 2 can be made into a versatile, competitive high-field superconductor
Final Report - Effects of Impurities on Fuel Cell Performance and Durability
Energy Technology Data Exchange (ETDEWEB)
Trent Molter
2012-08-18
This program is focused on the experimental determination of the effects of key hydrogen side impurities on the performance of PEM fuel cells. Experimental data has been leveraged to create mathematical models that predict the performance of PEM fuel cells that are exposed to specific impurity streams. These models are validated through laboratory experimentation and utilized to develop novel technologies for mitigating the effects of contamination on fuel cell performance. Results are publicly disseminated through papers, conference presentations, and other means.
Impurity effects on the grain boundary cohesion in copper
Li, Yunguo; Korzhavyi, Pavel A.; Sandström, Rolf; Lilja, Christina
2017-12-01
Segregated impurities at grain boundaries can dramatically change the mechanical behavior of metals, while the mechanism is still obscure in some cases. Here, we suggest a unified approach to investigate segregation and its effects on the mechanical properties of polycrystalline alloys using the example of 3 s p impurities (Mg, Al, Si, P, or S) at a special type Σ 5 (310 )[001 ] tilt grain boundary in Cu. We show that for these impurities segregating to the grain boundary, the strain contribution to the work of grain boundary decohesion is small and that the chemical contribution correlates with the electronegativity difference between Cu and the impurity. The strain contribution to the work of dislocation emission is calculated to be negative, while the chemical contribution is calculated to be always positive. Both the strain and chemical contributions to the work of dislocation emission generally become weaker with the increasing electronegativity from Mg to S. By combining these contributions together, we find, in agreement with experimental observations, that a strong segregation of S can reduce the work of grain boundary separation below the work of dislocation emission, thus embrittling Cu, while such an embrittlement cannot be produced by a P segregation because it lowers the energy barrier for dislocation emission relatively more than for work separation.
Effects of Density and Impurity on Edge Localized Modes in Tokamaks
Zhu, Ping
2017-10-01
Plasma density and impurity concentration are believed to be two of the key elements governing the edge tokamak plasma conditions. Optimal levels of plasma density and impurity concentration in the edge region have been searched for in order to achieve the desired fusion gain and divertor heat/particle load mitigation. However, how plasma density or impurity would affect the edge pedestal stability may have not been well known. Our recent MHD theory modeling and simulations using the NIMROD code have found novel effects of density and impurity on the dynamics of edge-localized modes (ELMs) in tokamaks. First, previous MHD analyses often predict merely a weak stabilizing effect of toroidal flow on ELMs in experimentally relevant regimes. We find that the stabilizing effects on the high- n ELMs from toroidal flow can be significantly enhanced with the increased edge plasma density. Here n denotes the toroidal mode number. Second, the stabilizing effects of the enhanced edge resistivity due to lithium-conditioning on the low- n ELMs in the high confinement (H-mode) discharges in NSTX have been identified. Linear stability analysis of the experimentally constrained equilibrium suggests that the change in the equilibrium plasma density and pressure profiles alone due to lithium-conditioning may not be sufficient for a complete suppression of the low- n ELMs. The enhanced resistivity due to the increased effective electric charge number Zeff after lithium-conditioning provides additional stabilization of the low- n ELMs. These new effects revealed in our theory analyses may help further understand recent ELM experiments and suggest new control schemes for ELM suppression and mitigation in future experiments. They may also pose additional constraints on the optimal levels of plasma density and impurity concentration in the edge region for H-mode tokamak operation. Supported by National Magnetic Confinement Fusion Science Program of China Grants 2014GB124002 and 2015GB
Effect of a Nitrogen Impurity on the Fundamental Raman Band of Diamond Single Crystals
Gusakov, G. A.; Samtsov, M. P.; Voropay, E. S.
2018-05-01
The effect of nitrogen defects in natural and synthetic diamond single crystals on the position and half-width of the fundamental Raman band was investigated. Samples containing the main types of nitrogen lattice defects at impurity contents of 1-1500 ppm were studied. The parameters of the Stokes and anti-Stokes components in Raman spectra of crystals situated in a cell with distilled water to minimize the influence of heating by the exciting laser radiation were analyzed to determine the effect of a nitrogen impurity in the diamond crystal lattice. It was shown that an increase of impurity atoms in the crystals in the studied concentration range resulted in broadening of the Raman band from 1.61 to 2.85 cm-1 and shifting of the maximum to lower frequency from 1332.65 to 1332.3 cm-1. The observed effect was directly proportional to the impurity concentration and depended on the form of the impurity incorporated into the diamond lattice. It was found that the changes in the position and half-width of the fundamental Raman band for diamond were consistent with the magnitude of crystal lattice distortions due to the presence of impurity defects and obeyed the Gruneisen law.
Numerical simulation of the impurity photovoltaic effect in silicon solar cells doped with thallium
International Nuclear Information System (INIS)
Zhao Baoxing; Zhou Jicheng; Chen Yongmin
2010-01-01
Many attempts have been made to increase the efficiency of solar cells by introducing a deep impurity level in the semiconductor band gap. Since Tl may be the most suitable impurity for crystalline Si solar cells, the impurity photovoltaic (IPV) effect in silicon solar cell doped with thallium as impurity was investigated by the numerical solar cell simulator SCAPS. Results show that the IPV effect of thallium extends the spectral sensitivity in the sub-band gap range from 1000 to about 1400 nm. When the Tl concentration (N t ) is lower than the base doping density (N D ), the short-circuit current density and efficiency increase with increasing N t . But they decrease rapidly as the impurity density exceeds the shallow base doping density (N t >N D ). The optimum Tl concentration is about equal to the base doping density. For the Si solar cells with high internal reflection coefficients, the IPV effect becomes appreciable (ΔJ sc ∼9 mA/cm 2 and Δη∼2%).
Dinh Hoi, Bui; Yarmohammadi, Mohsen
2018-04-01
We address control of electronic phase transition in charged impurity-infected armchair-edged boron-nitride nanoribbons (ABNNRs) with the local variation of Fermi energy. In particular, the density of states of disordered ribbons produces the main features in the context of pretty simple tight-binding model and Green's functions approach. To this end, the Born approximation has been implemented to find the effect of π-band electron-impurity interactions. A modulation of the π-band depending on the impurity concentrations and scattering potentials leads to the phase transition from insulator to semimetallic. We present here a detailed physical meaning of this transition by studying the treatment of massive Dirac fermions. From our findings, it is found that the ribbon width plays a crucial role in determining the electronic phase of disordered ABNNRs. The obtained results in controllable gap engineering are useful for future experiments. Also, the observations in this study have also fueled interest in the electronic properties of other 2D materials.
Regularization of the Coulomb scattering problem
International Nuclear Information System (INIS)
Baryshevskii, V.G.; Feranchuk, I.D.; Kats, P.B.
2004-01-01
The exact solution of the Schroedinger equation for the Coulomb potential is used within the scope of both stationary and time-dependent scattering theories in order to find the parameters which determine the regularization of the Rutherford cross section when the scattering angle tends to zero but the distance r from the center remains finite. The angular distribution of the particles scattered in the Coulomb field is studied on rather a large but finite distance r from the center. It is shown that the standard asymptotic representation of the wave functions is inapplicable in the case when small scattering angles are considered. The unitary property of the scattering matrix is analyzed and the 'optical' theorem for this case is discussed. The total and transport cross sections for scattering the particle by the Coulomb center proved to be finite values and are calculated in the analytical form. It is shown that the effects under consideration can be important for the observed characteristics of the transport processes in semiconductors which are determined by the electron and hole scattering by the field of charged impurity centers
Impurity diffusion in transition-metal oxides
International Nuclear Information System (INIS)
Peterson, N.L.
1982-06-01
Intrinsic tracer impurity diffusion measurements in ceramic oxides have been primarily confined to CoO, NiO, and Fe 3 O 4 . Tracer impurity diffusion in these materials and TiO 2 , together with measurements of the effect of impurities on tracer diffusion (Co in NiO and Cr in CoO), are reviewed and discussed in terms of impurity-defect interactions and mechanisms of diffusion. Divalent impurities in divalent solvents seem to have a weak interaction with vacancies whereas trivalent impurities in divalent solvents strongly influence the vacancy concentrations and significantly reduce solvent jump frequencies near a trivalent impurity. Impurities with small ionic radii diffuse more slowly with a larger activation energy than impurities with larger ionic radii for all systems considered in this review. Cobalt ions (a moderate size impurity) diffuse rapidly along the open channels parallel to the c-axis in TiO 2 whereas chromium ions (a smaller-sized impurity) do not. 60 references, 11 figures
Effect of impurities in description of surface nanobubbles
Das, S.; Snoeijer, Jacobus Hendrikus; Lohse, Detlef
2010-01-01
Surface nanobubbles emerging at solid-liquid interfaces of submerged hydrophobic surfaces show extreme stability and very small (gas-side) contact angles. In a recent paper Ducker [ W. A. Ducker Langmuir 25 8907 (2009)]. conjectured that these effects may arise from the presence of impurities at the
Impurity effect of iron(III) on the growth of potassium sulfate crystal in aqueous solution
Kubota, Noriaki; Katagiri, Ken-ichi; Yokota, Masaaki; Sato, Akira; Yashiro, Hitoshi; Itai, Kazuyoshi
1999-01-01
Growth rates of the {1 1 0} faces of a potassium sulfate crystal were measured in a flow cell in the presence of traces of impurity Fe(III) (up to 2 ppm) over the range of pH=2.5-6.0. The growth rate was significantly suppressed by the impurity. The effect became stronger as the impurity concentration was increased and at pH5 it finally disappeared completely. The concentration and supersaturation effects on the impurity action were reasonably explained with a model proposed by Kubota and Mullin [J. Crystal Growth, 152 (1995) 203]. The surface coverage of the active sites by Fe(III) is estimated to increase linearly on increasing its concentration in solution in the range examined by growth experiments. The impurity effectiveness factor is confirmed to increase inversely proportional to the supersaturation as predicted by the model. Apart from the discussion based on the model, the pH effect on the impurity action is qualitatively explained by assuming that the first hydrolysis product of aqua Fe(III) complex compound, [Fe(H 2O) 5(OH)] 2+, is both growth suppression and adsorption active, but the second hydrolysis product, [Fe(H 2O) 4(OH) 2] +, is only adsorption active.
Hamada, Yoshito; Ono, Makoto; Ohara, Motomu; Yonemochi, Etsuo
2016-12-30
In this study, the effect of structurally related impurities on crystallinity reduction of sulfamethazine by grinding was evaluated. The crystallinity of sulfamethazine was not decreased when it was ground alone. However, when structurally related impurities with sulfonamide derivatives were blended, the crystallinity of sulfamethazine was decreased by grinding. Other materials without a sulfonamide moiety showed no such effect. The Raman spectra of sulfamethazine demonstrated that there was a difference between its crystalline and amorphous states within its sulfonamide structure. It was suggested that the sulfonamide structure of the impurities was important in causing the inhibition of recrystallization of sulfamethazine during grinding. Copyright Â© 2016 Elsevier B.V. All rights reserved.
Impurity effects in superconducting UPt3
International Nuclear Information System (INIS)
Aronson, M.C.; Vorenkamp, T.; Koziol, Z.; de Visser, A.; Bakker, K.; Franse, J.J.M.; Smith, J.L.
1991-01-01
Superconducting UPt 3 is characterized by a novel and complex magnetic field-temperature phase diagram, with two superconducting transitions at T c1 and T c2 in zero field. We have studied the effects of Pd and Y impurities on the zero field superconducting properties of UPt 3 . Resistance measurements show that both dopants increase the residual resistivity and decrease the spin fluctuation temperature in the normal state. T c1 is depressed by both dopants, but more effectively by Pd. |T c1 - T c2 | is essentially unaffected by Y doping, but increases dramatically with Pd doping
Coulomb singularity effects in tunnelling spectroscopy of individual impurities
Arseyev, P. I.; Maslova, N. S.; Panov, V. I.; Savinov, S. V.
2002-01-01
Non-equilibrium Coulomb effects in resonant tunnelling processes through deep impurity states are analyzed. It is shown that Coulomb vertex corrections to the tunnelling transfer amplitude lead to a power-law singularity in current- voltage characteristics
Magnetoconductivity of quantum wires with elastic and inelastic scattering
DEFF Research Database (Denmark)
Bruus, Henrik; Flensberg, Karsten; Smith
1993-01-01
We use a Boltzmann equation to determine the magnetoconductivity of quantum wires. The presence of a confining potential in addtion to the magnetic field removes the degeneracy of the Landau levels and allows one to associate a group velocity with each single-particle state. The distribution...... function describing the occupation of these single-particle states satisfies a Boltzmann equation, which may be solved exactly in the case of impurity scattering. In the case where the electrons scatter against both phonons and impurities we solve numerically—and in certain limits analytically—the integral...
International Nuclear Information System (INIS)
Correa, J.D.; Duque, C.A.; Porras-Montenegro, N.
2004-01-01
Full text: Using a variational procedure for a hydrogenic donor-impurity we have calculated the photoionization cross-section in spherical GaAs quantum dots. We discuss the dependence on the photoionization cross-section for hydrogenic donor impurity in in nite and nite barrier quantum dots as a function of the size of the dot, impurity position, polarization of the photon, applied hydrostatic pressure, and normalized photon energy. For the nite case, calculations for the pressure effects are both in direct and indirect GaAsAl gap regime. We have considered the different transition rules that depend of the impurity position and photon polarization. Calculations are presented for impurity on-center, and o -center in the spherical quantum dots. We found that the photoionization cross-section increases with the applied hydrostatic pressure both for on-center and o - center impurities. The photoionization cross-section increases or decreases depending of the impurity position, photon polarization, and radius of dots. Also we have showed that the photoionization cross-section decreases as the normalized photon energy increases. The results we have obtained show that the photoionization cross- section is strongly a effected by the quantum dot size, and the position of the impurity. The measurement of photoionization in such systems would be of great interest in understanding the optical properties of carriers in quantum dots. (author)
The impurity transport in HT-6M tokamak
International Nuclear Information System (INIS)
Xu Wei; Wan Baonian; Xie Jikang
2003-01-01
The space-time profile of impurities has been measured with a multichannel visible spectroscopic detect system and UV rotation-mirror system in the HT-6M tokamak. An ideal impurity transport code has been used to simulate impurities (carbon and oxygen) behaviour during the OHM discharge. The profiles of impurities diffusion and convection coefficient, impurities ion densities in different ionized state, loss power density and effective charge number have been derived. The impurity behaviour during low-hybrid current drive has also been analyzed, the results show that the confinement of particles, impurities and energy has been improved, and emission power and effective charge number have been reduced
Introduction to Schroedinger inverse scattering
International Nuclear Information System (INIS)
Roberts, T.M.
1991-01-01
Schroedinger inverse scattering uses scattering coefficients and bound state data to compute underlying potentials. Inverse scattering has been studied extensively for isolated potentials q(x), which tend to zero as vertical strokexvertical stroke→∞. Inverse scattering for isolated impurities in backgrounds p(x) that are periodic, are Heaviside steps, are constant for x>0 and periodic for x<0, or that tend to zero as x→∞ and tend to ∞ as x→-∞, have also been studied. This paper identifies literature for the five inverse problems just mentioned, and for four other inverse problems. Heaviside-step backgrounds are discussed at length. (orig.)
Effect of impurity radiation on tokamak equilibrium
International Nuclear Information System (INIS)
Rebut, P.H.; Green, B.J.
1977-01-01
The energy loss from a tokamak plasma due to the radiation from impurities is of great importance in the overall energy balance. Taking the temperature dependence of this loss for two impurities characteristic of those present in existing tokamak plasmas, the condition for radial power balance is derived. For the impurities considered (oxygen and iron) it is found that the radiation losses are concentrated in a thin outer layer of the plasma and the equilibrium condition places an upper limit on the plasma paraticle number density in this region. This limiting density scales with mean current density in the same manner as is experimentally observed for the peak number density of tokamak plasmas. The stability of such equilibria is also discussed. (author)
Fractals: Giant impurity nonlinearities in optics of fractal clusters
International Nuclear Information System (INIS)
Butenko, A.V.; Shalaev, V.M.; Stockman, M.I.
1988-01-01
A theory of nonlinear optical properties of fractals is developed. Giant enhancement of optical susceptibilities is predicted for impurities bound to a fractal. This enhancement occurs if the exciting radiation frequency lies within the absorption band of the fractal. The giant optical nonlinearities are due to existence of high local electric fields in the sites of impurity locations. Such fields are due to the inhomogeneously broadened character of a fractal spectrum, i.e. partial conservation of individuality of fractal-forming particles (monomers). The field enhancement is proportional to the Q-factor of the resonance of a monomer. The effects of coherent anti-Stokes Raman scattering (CARS) and phase conjugation (PC) of light waves are enhanced to a much greater degree than generation of higher harmonics. In a general case the susceptibility of a higher-order is enhanced in the maximum way if the process includes ''subtraction'' of photons (at least one of the strong field frequencies enters the susceptibility with the minus sign). Alternatively, enhancement for the highest-order harmonic generation (when all the photons are ''accumulated'') is minimal. The predicted phenomena bear information on spectral properties of both impurity molecules and a fractal. In particular, in the CARS spectra a narrow (with the natural width) resonant structure, which is proper to an isolated monomer of a fractal, is predicted to be observed. (orig.)
Impurities in uranium process solutions
International Nuclear Information System (INIS)
Boydell, D.W.
1980-01-01
Several uranium purification circuits are presented in tabular form together with the average major impurity levels associated with each. The more common unit operations in these circuits, namely strong- and weak-base ion-exchange, solvent extraction and the precipitation of impurities are then discussed individually. Particular attention is paid to the effect and removal of impurities in each of these four unit operations. (author)
Nonmagnetic impurity in the spin-gap state
International Nuclear Information System (INIS)
Nagaosa, N.; Ng, T.
1995-01-01
The effects of nonmagnetic strong scatterers (unitary limit) on magnetic and transport properties are studied for resonating-valence-bond states in both the slave-boson and slave-fermion mean-field theories with the gap for the triplet excitations. In the d-wave pairing state of the slave-boson mean-field theory in two dimensions, there is no true gap for spinons, but the Anderson localization occurs, which leads to the local moment when the repulsive interaction is taken into account. In the slave-fermion mean-field theory, local moments are found bound to nonmagnetic impurities as a result of (staggered) gauge interaction. However, in both theories, localization of spinon does not appear in the resistivity, which shows the classical value for the holon
Time-Dependent Impurity in Ultracold Fermions: Orthogonality Catastrophe and Beyond
Directory of Open Access Journals (Sweden)
Michael Knap
2012-12-01
Full Text Available The recent experimental realization of strongly imbalanced mixtures of ultracold atoms opens new possibilities for studying impurity dynamics in a controlled setting. In this paper, we discuss how the techniques of atomic physics can be used to explore new regimes and manifestations of Anderson’s orthogonality catastrophe (OC, which could not be accessed in solid-state systems. Specifically, we consider a system of impurity atoms, localized by a strong optical-lattice potential, immersed in a sea of itinerant Fermi atoms. We point out that the Ramsey-interference-type experiments with the impurity atoms allow one to study the OC in the time domain, while radio-frequency (RF spectroscopy probes the OC in the frequency domain. The OC in such systems is universal, not only in the long-time limit, but also for all times and is determined fully by the impurity-scattering length and the Fermi wave vector of the itinerant fermions. We calculate the universal Ramsey response and RF-absorption spectra. In addition to the standard power-law contributions, which correspond to the excitation of multiple particle-hole pairs near the Fermi surface, we identify a novel, important contribution to the OC that comes from exciting one extra particle from the bottom of the itinerant band. This contribution gives rise to a nonanalytic feature in the RF-absorption spectra, which shows a nontrivial dependence on the scattering length, and evolves into a true power-law singularity with the universal exponent 1/4 at the unitarity. We extend our discussion to spin-echo-type experiments, and show that they probe more complicated nonequilibirum dynamics of the Fermi gas in processes in which an impurity switches between states with different interaction strength several times; such processes play an important role in the Kondo problem, but remained out of reach in the solid-state systems. We show that, alternatively, the OC can be seen in the energy-counting statistics
Amount of impurity and its behavior in the STP-2 screw pinch tokamak
International Nuclear Information System (INIS)
Yamaguchi, S.
1981-05-01
Temporal and spatial evolution of oxygen spectral line intensities have been measured in the STP-2 screw pinch tokamak. The electron density and temperature as measured by Thomson scattering are of the order of 10 14 cm -3 and 10 eV, respectively. On the basis of these measurements, quasi-steady-state rate equations have been solved to give the OII and OIII ion densities. It is found that the density of oxygen impurity is about several percent of the electron density, and the impurity moves with the bulk plasma. It is confirmed that the impurity originates from the wall of the discharge tube during the initial phase of the discharge. (author)
International Nuclear Information System (INIS)
Yamakami, Tomoyuki; Fujita, Takaaki; Arimoto, Hideki; Yamazaki, Kozo
2014-01-01
In future fusion reactors, density control, such as fueling by pellet injection, is an effective method to control the formation of the internal transport barrier (ITB) in reversed magnetic shear plasma, which can improve plasma performance. On the other hand, an operation with ITB can cause accumulation of impurities inside the core ITB region. We studied the relation between pellet injection and ITB formation and the effect of impurity transport on the core of ITB for tokamak plasmas by using the toroidal transport analysis linkage. For ITB formation, we showed that the pellet has to be injected beyond the position where the safety factor q takes the minimum value. We confirmed that the accumulation of impurities causes the attenuation of ITB owing to radiation loss inside the ITB region. Moreover, in terms of the divertor heat flux reduction by impurity gas, the line radiation loss is high for high-Z noble gas impurities, such as Kr, whereas factor Q decreases slightly. (author)
International Nuclear Information System (INIS)
Arenas, Claudio; Henriquez, Ricardo; Moraga, Luis; Muñoz, Enrique; Munoz, Raul C.
2015-01-01
Highlights: • Quantum theory of the resistivity arising from electron-grain boundary scattering in nanometric metallic structures. • The resistivity is controlled by the collective properties of the grain assembly, by the allowed Kronig-Penney (KP) bands and by the electron transmission probability across successive grains. • When the grain diameter d is larger than the electron mean free path l, the increase in resistivity arises mainly from a decrease of the number of states at the Fermi surface that are allowed KP bands. • When the grain diameter d is smaller than the electron mean free path l, the increase in resistivity arises primarily from Anderson localization caused by electron transmission across successive grains. - Abstract: We calculate the electrical resistivity of a metallic specimen, under the combined effects of electron scattering by impurities, grain boundaries, and rough surfaces limiting the film, using a quantum theory based upon the Kubo formalism. Grain boundaries are represented by a one-dimensional periodic array of Dirac delta functions separated by a distance “d” giving rise to a Kronig–Penney (KP) potential. We use the Green's function built from the wave functions that are solutions of this KP potential; disorder is included by incorporating into the theory the probability that an electron is transmitted through several successive grain boundaries. We apply this new theory to analyze the resistivity of samples S1, S2, S7 and S8 measured between 4 and 300 K reported in Appl. Surf. Science273, 315 (2013). Although both the classical and the quantum theories predict a resistivity that agrees with experimental data to within a few percent or better, the phenomena giving rise to the increase of resistivity over the bulk are remarkably different. Classically, each grain boundary contributes to the electrical resistance by reflecting a certain fraction of the incoming electrons. In the quantum description, there are states
Energy Technology Data Exchange (ETDEWEB)
Arenas, Claudio [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Blanco Encalada 2008, Casilla 487-3, Santiago 8370449 (Chile); Synopsys Inc., Avenida Vitacura 5250, Oficina 708, Vitacura, Santiago (Chile); Henriquez, Ricardo [Departamento de Física, Universidad Técnica Federico Santa María, Av. España 1680, Casilla 110-V, Valparaíso (Chile); Moraga, Luis [Universidad Central de Chile, Toesca 1783, Santiago (Chile); Muñoz, Enrique [Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 7820436 (Chile); Munoz, Raul C., E-mail: ramunoz@ing.uchile.cl [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Blanco Encalada 2008, Casilla 487-3, Santiago 8370449 (Chile)
2015-02-28
Highlights: • Quantum theory of the resistivity arising from electron-grain boundary scattering in nanometric metallic structures. • The resistivity is controlled by the collective properties of the grain assembly, by the allowed Kronig-Penney (KP) bands and by the electron transmission probability across successive grains. • When the grain diameter d is larger than the electron mean free path l, the increase in resistivity arises mainly from a decrease of the number of states at the Fermi surface that are allowed KP bands. • When the grain diameter d is smaller than the electron mean free path l, the increase in resistivity arises primarily from Anderson localization caused by electron transmission across successive grains. - Abstract: We calculate the electrical resistivity of a metallic specimen, under the combined effects of electron scattering by impurities, grain boundaries, and rough surfaces limiting the film, using a quantum theory based upon the Kubo formalism. Grain boundaries are represented by a one-dimensional periodic array of Dirac delta functions separated by a distance “d” giving rise to a Kronig–Penney (KP) potential. We use the Green's function built from the wave functions that are solutions of this KP potential; disorder is included by incorporating into the theory the probability that an electron is transmitted through several successive grain boundaries. We apply this new theory to analyze the resistivity of samples S1, S2, S7 and S8 measured between 4 and 300 K reported in Appl. Surf. Science273, 315 (2013). Although both the classical and the quantum theories predict a resistivity that agrees with experimental data to within a few percent or better, the phenomena giving rise to the increase of resistivity over the bulk are remarkably different. Classically, each grain boundary contributes to the electrical resistance by reflecting a certain fraction of the incoming electrons. In the quantum description, there are states
Void growth suppression by dislocation impurity atmospheres
International Nuclear Information System (INIS)
Weertman, J.; Green, W.V.
1976-01-01
A detailed calculation is given of the effect of an impurity atmosphere on void growth under irradiation damage conditions. Norris has proposed that such an atmosphere can suppress void growth. The hydrostatic stress field of a dislocation that is surrounded by an impurity atmosphere was found and used to calculate the change in the effective radius of a dislocation line as a sink for interstitials and vacancies. The calculation of the impurity concentration in a Cottrell cloud takes into account the change in hydrostatic pressure produced by the presence of the cloud itself. It is found that void growth is eliminated whenever dislocations are surrounded by a condensed atmosphere of either oversized substitutional impurity atoms or interstitial impurity atoms. A condensed atmosphere will form whenever the average impurity concentration is larger than a critical concentration
International Nuclear Information System (INIS)
Zhernov, A.P.; Malov, Yu.A.; Panova, G.Kh.
1975-01-01
An anisotropic irregular semiconductor is under consideration. It is believed that the effective parameter of the interaction-lambda-which determines electron coupling is less or about 0.5. The Eliashberg integral equation system is solved for T→Tsub(c). A simple analytic expression is obtained for Tsub(c). The character of a varying critical temperature in superconductors with impurity atoms is analyzed in detail. The dependence of the critical temperature on parameters describing the phonon spectrum of an impurity system is investigated. The existence of impurity modes with quasilocal and local frequencies in the phonon spectra can lead both to relatively small and to rather noticeable variations in Tsub(c). The first case is typical of the situation when an impurity atom is practically an isotopic defect. If an impurity atom is very heavy (Msub(I) 1 0 ) or strongly (γ 1 >>γ 0 ) coupled with matrix atoms. A sharp decrease in the effective force constant γ 1 for an impurity atom results in the growth of delta Tsub(c): delta Tsub(c) approximately cγ0/γ 1 (lambda - μsup((0)). On the contrary a rise in the γ 1 value requires a negative correction to Tsub(c), and delta Tsub(c) approximately c/(lambda - μsup((0)), where c - an impurity concentration, μ - matrix element of the Coulomb screened interaction averaged over the Fermi surface and multiplied for the density of normal electron states on the Fermi level. Comparison with experimental data is made. A qualitative description of the Tsub(c) change due to the impurity presence is given for a set of solutions. There is a satisfactory quantitative agreement between calculated and experimental values of delta Tsub(c)
Superconducting Gap Symmetry of LaFeP(O,F Observed by Impurity Doping Effect
Directory of Open Access Journals (Sweden)
Shigeki Miyasaka
2016-08-01
Full Text Available We have investigated Mn, Co and Ni substitution effects on polycrystalline samples of LaFePO0.95F0.05 by resistivity and magnetoresistance measurements. In LaFe1-xMxPO0.95F0.05 (M = Mn, Co and Ni, the superconducting transition temperature (Tc monotonously decreases with increasing the impurity doping level of x. There is a clear difference of Tc suppression rates among Mn, Co and Ni doping cases, and the decreasing rate of Tc by Mn doping as a magnetic impurity is larger than those by the nonmagnetic doping impurities (Co/Ni. This result indicates that in LaFePO0.95F0.05, Tc is rapidly suppressed by the pair-breaking effect of magnetic impurities, and the pairing symmetry is a full-gapped s-wave. In the nonmagnetic impurity-doped systems, the residual resistivity in the normal state has nearly the same value when Tc becomes zero. The residual resistivity value is almost consistent with the universal value of sheet resistance for two-dimensional superconductors, suggesting that Tc is suppressed by electron localization in Co/Ni-doped LaFePO0.95F0.05.
International Nuclear Information System (INIS)
Galluzzi, F.; Scafe, E.; Beghi, M.; Fossati, S.; Tincani, M.; Pizzini, S.
1985-01-01
An extensive experimental study of minority carrier recombination in CZ grown polycrystalline silicon intentionally doped with metallic impurities (Ti, V, Fe, Cr, Zr) is reported. Experimental values of average diffusion lengths have been compared with values calculated by a simple model of carrier recombination, taking into account the effects of impurities, grain boundaries and intragrain crystal defects. The results are fairly consistent and allow the determination of threshold densities for structural defects and deep impurities. The author's analysis gives a simple quantitative description of recombination processes in solar-grade silicon, as far as the average behaviour is concerned
Effect of homologous impurities on primary radiation defect accumulation in alkali halides
International Nuclear Information System (INIS)
Chernov, S.A.; Gavrilov, V.V.
1981-01-01
To clarify the mechanism of the effect of anion and cation homologous impurities on the primary radiation-induced defect accumulation, the transient absorption of H and F centers was studied in KCl and KBr crystals. Pulse electron accelerator technique was used. Pure and doped crystals were investigated. It was obtained that the cation homologue Na in the concentration range from 0 to 0.5 m. % in 10 -8 -10 -6 s post-irradiation time has no effect on the defect accumulation efficiency at low temperature and increases the latter at high temperature. At large post-irradiation time and at high temperatures the rise of efficiency at low Na concentration and decrease of it at high Na concentrations were observed. The conclusion was made that Na does not affect the generation process. The anion homologous impurities (I and Br) lead to a significant increase of the accumulation efficiency due to the formation of more stable F-H pair at self-trapped exciton decay on anion impurities compared with that formed in perfect lattice. Some assumptions are advanced to explain the effect [ru
International Nuclear Information System (INIS)
Gondhalekar, A.; Stangeby, P.C.; Elder, J.D.
1994-01-01
Inhibition of contamination of the plasma core in JET by edge impurities during high power heating of deuterium plasmas in limiter configuration using fuelling is demonstrated. By injecting deuterium gas during heating, in the presence of a much larger recycling deuterium flux, a reduction of more than a factor of 2 was effected in n z (0)/Φ z , the ratio of central impurity density to impurity influx at the plasma edge. The reduction in n z (0) was obtained without much effect on peak electron temperature and density. Reduction of plasma contamination by gas fuelling was observed also when hot spots formed on the limiter, a condition that without simultaneous gas fuelling culminated in runaway plasma contamination. Detailed analysis of the experiments is undertaken with the purpose of identifying the processes by which plasma contamination was inhibited, employing standard limiter plasma contamination modelling. Processes which might produce the observed impurity inhibiting effects of gas injection include: (a) reduction in impurity production at the limiter; (b) increase in impurity screening in the scrape-off layer; (c) increase in radial impurity transport at the plasma edge; (d) increase in average deuteron flow velocity to the limiter along the scrape-off layer. These are examined in detail using the Monte Carlo limiter impurity transport code LIM. Bearing in mind that uncertainties exist both in the choice of appropriate modelling assumptions to be used and in the measurement of required edge plasma parameters, changes in n z (0)/Φ z by a factor of 2 are at the limit of the present modelling capability. However, comparison between LIM code simulations and measurements of plasma impurity content indicate that the standard limiter plasma contamination model may not be adequate and that other processes need to be added in order to be able to describe the experiments in JET. (author). 24 refs, 2 figs, 8 tabs
Impurity-induced anisotropic semiconductor-semimetal transition in monolayer biased black phosphorus
Bui, D. H.; Yarmohammadi, Mohsen
2018-07-01
Taking into account the electron-impurity interaction within the continuum approximation of tight-binding model, the Born approximation, and the Green's function method, the main features of anisotropic electronic phase transition are investigated in monolayer biased black phosphorus (BP). To this end, we concentrated on the disordered electronic density of states (DOS), which gives useful information for electro-optical devices. Increasing the impurity concentration in both unbiased and biased impurity-infected single-layer BP, in addition to the decrease of the band gap, independent of the direction, leads to the midgap states and an extra Van Hove singularity inside and outside of the band gap, respectively. Furthermore, strong impurity scattering potentials lead to a semiconductor-semimetal transition and one more Van Hove singularity in x-direction of unbiased BP and surprisingly, this transition does not occur in biased BP. We found that there is no phase transition in y-direction. Since real applications require structures with modulated band gaps, we have studied the influence of different bias voltages on the disordered DOS in both directions, resulting in the increase of the band gap.
Superpermeable membrane for particle control in divertor: the effect of impurity deposition
International Nuclear Information System (INIS)
Nakahara, Y.; Nakamura, Y.; Ohyabu, N.; Suzuki, H.; Busnyuk, A.; Alimov, V.
2000-01-01
The effect of impurity (stainless steel (SS) components, carbon) deposition onto niobium membrane surface on the membrane permeability to hydrogen particles is investigated with a plasma device. The deposition of SS components onto the upstream surface of the membrane at the membrane temperature (T M ) M M ≥800 deg. C. It appears to be due to the dissolution of the impurities deposited onto the upstream surface into the membrane bulk within the measurements
Impurity Induced Phase Competition and Supersolidity
Karmakar, Madhuparna; Ganesh, R.
2017-12-01
Several material families show competition between superconductivity and other orders. When such competition is driven by doping, it invariably involves spatial inhomogeneities which can seed competing orders. We study impurity-induced charge order in the attractive Hubbard model, a prototypical model for competition between superconductivity and charge density wave order. We show that a single impurity induces a charge-ordered texture over a length scale set by the energy cost of the competing phase. Our results are consistent with a strong-coupling field theory proposed earlier in which superconducting and charge order parameters form components of an SO(3) vector field. To discuss the effects of multiple impurities, we focus on two cases: correlated and random distributions. In the correlated case, the CDW puddles around each impurity overlap coherently leading to a "supersolid" phase with coexisting pairing and charge order. In contrast, a random distribution of impurities does not lead to coherent CDW formation. We argue that the energy lowering from coherent ordering can have a feedback effect, driving correlations between impurities. This can be understood as arising from an RKKY-like interaction, mediated by impurity textures. We discuss implications for charge order in the cuprates and doped CDW materials such as NbSe2.
Orbit effects on impurity transport in a rotating plasma
International Nuclear Information System (INIS)
Wong, K.L.; Cheng, C.Z.
1988-01-01
In 1985, very high ion temperature plasmas were first produced in TFTR with co-injecting neutral beams in low current, low density plasmas. This mode of operation is called the energetic ion mode in which the plasma rotates at very high speed. It was found that heavy impurities injected into these plasmas diffused out very quickly. In this paper, the authors calculate the impurity ion orbits in a rotating tokamak plasma based on the equation of motion in the frame that rotates with the plasma. It is shown that heavy particles in a rotating plasma can drift away from magnetic surfaces significantly faster. Particle orbits near the surface of a rotating tokamak are also analyzed. During impurity injection experiments, freshly ionized impurities near the plasma surface are essentially stationary in the laboratory frame and they are counter-rotating in the plasma frame with co-beam injection. The results are substantiated by numeral particle simulation. The computer code follows the impurity guiding center positions by integrating the equation of motion with the second order predictor-corrector method
Impurities in a non-axisymmetric plasma: Transport and effect on bootstrap current
Energy Technology Data Exchange (ETDEWEB)
Mollén, A., E-mail: albertm@chalmers.se [Department of Applied Physics, Chalmers University of Technology, Göteborg (Sweden); Max-Planck-Institut für Plasmaphysik, 17491 Greifswald (Germany); Landreman, M. [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States); Smith, H. M.; Helander, P. [Max-Planck-Institut für Plasmaphysik, 17491 Greifswald (Germany); Braun, S. [Max-Planck-Institut für Plasmaphysik, 17491 Greifswald (Germany); German Aerospace Center, Institute of Engineering Thermodynamics, Pfaffenwaldring 38-40, D-70569 Stuttgart (Germany)
2015-11-15
Impurities cause radiation losses and plasma dilution, and in stellarator plasmas the neoclassical ambipolar radial electric field is often unfavorable for avoiding strong impurity peaking. In this work we use a new continuum drift-kinetic solver, the SFINCS code (the Stellarator Fokker-Planck Iterative Neoclassical Conservative Solver) [M. Landreman et al., Phys. Plasmas 21, 042503 (2014)] which employs the full linearized Fokker-Planck-Landau operator, to calculate neoclassical impurity transport coefficients for a Wendelstein 7-X (W7-X) magnetic configuration. We compare SFINCS calculations with theoretical asymptotes in the high collisionality limit. We observe and explain a 1/ν-scaling of the inter-species radial transport coefficient at low collisionality, arising due to the field term in the inter-species collision operator, and which is not found with simplified collision models even when momentum correction is applied. However, this type of scaling disappears if a radial electric field is present. We also use SFINCS to analyze how the impurity content affects the neoclassical impurity dynamics and the bootstrap current. We show that a change in plasma effective charge Z{sub eff} of order unity can affect the bootstrap current enough to cause a deviation in the divertor strike point locations.
Impurity-induced moments in underdoped cuprates
International Nuclear Information System (INIS)
Khaliullin, G.; Kilian, R.; Krivenko, S.; Fulde, P.
1997-01-01
We examine the effect of a nonmagnetic impurity in a two-dimensional spin liquid in the spin-gap phase, employing a drone-fermion representation of spin-1/2 operators. The properties of the local moment induced in the vicinity of the impurity are investigated and an expression for the nuclear-magnetic-resonance Knight shift is derived, which we compare with experimental results. Introducing a second impurity into the spin liquid an antiferromagnetic interaction between the moments is found when the two impurities are located on different sublattices. The presence of many impurities leads to a screening of this interaction as is shown by means of a coherent-potential approximation. Further, the Kondo screening of an impurity-induced local spin by charge carriers is discussed. copyright 1997 The American Physical Society
International Nuclear Information System (INIS)
Wasserbaech, W.; Thompson, E.
2001-01-01
The internal friction Q -1 of plastically deformed, high-purity monocrystalline and impure polycrystalline niobium specimens was measured in the temperature range between 65 mK and about 2 K. Plastic deformation has a pronounced effect on the internal friction Q -1 of the high-purity monocrystalline specimens, and the effect has been found to be almost temperature independent. By contrast, surprisingly, the internal friction Q -1 of the impure polycrystalline specimens was found to be almost independent of the extent of plastic deformation. Comparison of the experimental results with different models of a dynamic scattering of acoustic phonons by dislocations leads to the conclusion that the results cannot be explained with the two-level tunneling model. Instead it is suggested that a strong interaction between acoustic phonons and geometrical kinks in non-screw dislocations is responsible for the observed internal friction Q -1 . (orig.)
International Nuclear Information System (INIS)
Restrepo, R.L.; Giraldo, E.; Miranda, G.L.; Ospina, W.; Duque, C.A.
2009-01-01
The combined effects of the hydrostatic pressure and in-growth direction applied electric field on the binding energy of hydrogenic shallow-donor impurity states in parallel-coupled-GaAs-Ga 1-x Al x As-quantum-well wires are calculated using a variational procedure within the effective-mass and parabolic-band approximations. Results are obtained for several dimensions of the structure, shallow-donor impurity positions, hydrostatic pressure, and applied electric field. Our results suggest that external inputs such us hydrostatic pressure and in-growth direction electric field are two useful tools in order to modify the binding energy of a donor impurity in parallel-coupled-quantum-well wires.
Superconducting quasiparticle lifetimes due to spin-fluctuation scattering
International Nuclear Information System (INIS)
Quinlan, S.M.; Scalapino, D.J.; Bulut, N.
1994-01-01
Superconducting quasiparticle lifetimes associated with spin-fluctuation scattering are calculated. A Berk-Schrieffer interaction with an irreducible susceptibility given by a BCS form is used to model the quasiparticle damping due to spin fluctuations. Results are presented for both s-wave and d-wave gaps. Also, quasiparticle lifetimes due to impurity scattering are calculated for a d-wave superconductor
Effect of magnetic islands on the impurity transport in a tokamak
International Nuclear Information System (INIS)
Ivanov, N.V.; Khvostenko, P.P.; Chudnovskij, A.N.
1986-01-01
Effect of magnetic islands m=2, created in plasma with the help of special quadrupole winding, on the behaviour of impurity in the T-7 tokamak is studied. The use of quadrupole winding permitted to exlude the magnetic island nonstationarity typical to spontaneous development of the Tiaring instability. The results obtained confirm the point of view that splitting of rational magnetic surface results in the change of impurity ion density gradient in its vicinity. This change occurs under the action of ambipolar electric field, that is excited due to the increase of radial electron transport in magnetic islands
Energy Technology Data Exchange (ETDEWEB)
Pusztai, I. [Applied Physics, Chalmers University of Technology and Euratom-VR Association, SE-41296 Goeteborg (Sweden); Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Landreman, M. [University of Maryland, College Park, MD 20742 (United States); Mollen, A.; Fueloep, T. [Applied Physics, Chalmers University of Technology and Euratom-VR Association, SE-41296 Goeteborg (Sweden); Kazakov, Ye.O. [Laboratory for Plasma Physics, ERM/KMS, Association ' EURATOM-Belgian State' , TEC Partner, BE-1000 Brussels (Belgium)
2014-06-15
Poloidal asymmetries in the impurity density can be generated by radio frequency heating in the core and by neoclassical effects in the edge of tokamak plasmas. In a pedestal case study, using global neoclassical simulations we find that finite orbit width effects can generate significant poloidal variation in the electrostatic potential, which varies on a small radial scale. Gyrokinetic modeling shows that these poloidal asymmetries can be strong enough to significantly modify turbulent impurity peaking. In the pedestal the E x B drift in the radial electric field can give a larger contribution to the poloidal motion of impurities than that of their parallel streaming. Under such circumstances we find that up-down asymmetries can also affect impurity peaking. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Effects of calcium impurity on phase relationship, ionic conductivity ...
Indian Academy of Sciences (India)
Home; Journals; Bulletin of Materials Science; Volume 39; Issue 3. Effects of calcium impurity on phase relationship, ionic conductivity and microstructure of Na + - β / b e t a " -alumina solid electrolyte. SUNG-TAE LEE DAE-HAN LEE SANG-MIN LEE SANG-SOO HAN SANG-HYUNG LEE SUNG-KI LIM. Volume 39 Issue 3 ...
Spin-1 two-impurity Kondo problem on a lattice
Allerdt, A.; Žitko, R.; Feiguin, A. E.
2018-01-01
We present an extensive study of the two-impurity Kondo problem for spin-1 adatoms on a square lattice using an exact canonical transformation to map the problem onto an effective one-dimensional system that can be numerically solved using the density matrix renormalization group method. We provide a simple intuitive picture and identify the different regimes, depending on the distance between the two impurities, Kondo coupling JK, longitudinal anisotropy D , and transverse anisotropy E . In the isotropic case, two impurities on opposite (the same) sublattices have a singlet (triplet) ground state. However, the energy difference between the triplet ground state and the singlet excited state is very small and we expect an effectively fourfold-degenerate ground state, i.e., two decoupled impurities. For large enough JK the impurities are practically uncorrelated forming two independent underscreened states with the conduction electrons, a clear nonperturbative effect. When the impurities are entangled in an RKKY-like state, Kondo correlations persist and the two effects coexist: the impurities are underscreened, and the dangling spin-1 /2 degrees of freedom are responsible for the interimpurity entanglement. We analyze the effects of magnetic anisotropy in the development of quasiclassical correlations.
Impurity screening of scrape-off plasma in a tokamak
International Nuclear Information System (INIS)
Kishimoto, Hiroshi; Tani, Keiji; Nakamura, Hiroo
1981-11-01
Impurity screening effect of a scrape-off layer has been studied in a tokamak, based on a simple model of wall-released impurity behavior. Wall-sputtered impurities are stopped effectively by the scrape-off plasma for a medium-Z or high-Z wall system while major part of impurities enters the main plasma in a low-Z wall system. The screening becomes inefficient with increase of scrape-off plasma temperature. Successive multiplication of recycling impurities in the scrape-off layer is large for a high-Z wall and is enhanced by a rise of scrape-off plasma temperature. The stability of plasma-wall interaction is determined by a multiplication factor of recycling impurities. (author)
Effects of electronically neutral impurities on muonium in germanium
International Nuclear Information System (INIS)
Clawson, C.W.; Crowe, K.M.; Haller, E.E.; Rosenblum, S.S.; Brewer, J.H.
1983-04-01
Low-temperature measurements of muonium parameters in various germanium crystals have been performed. We have measured crystals with different levels of neutral impurities, with and without dislocations, and with different annealing histories. The most striking result is the apparent trapping of Mu by silicon impurities in germanium
The effect of iron and copper impurities on the wettability of sphalerite (110) surface.
Simpson, Darren J; Bredow, Thomas; Chandra, Anand P; Cavallaro, Giuseppe P; Gerson, Andrea R
2011-07-15
The effect of impurities in the zinc sulfide mineral sphalerite on surface wettability has been investigated theoretically to shed light on previously reported conflicting results on sphalerite flotation. The effect of iron and copper impurities on the sphalerite (110) surface energy and on the water adsorption energy was calculated with the semi-empirical method modified symmetrically orthogonalized intermediate neglect of differential overlap (MSINDO) using the cyclic cluster model. The effect of impurities or dopants on surface energies is small but significant. The surface energy increases with increasing surface iron concentration while the opposite effect is reported for increasing copper concentration. The effect on adsorption energies is much more pronounced with water clearly preferring to adsorb on an iron site followed by a zinc site, and copper site least favorable. The theoretical results indicate that a sphalerite (110) surface containing iron is more hydrophilic than the undoped zinc sulfide surface. In agreement with the literature, the surface containing copper (either naturally or by activation) is more hydrophobic than the undoped surface. Copyright © 2011 Wiley Periodicals, Inc.
Effect of HEH[EHP] impurities on the ALSEP solvent extraction process
Energy Technology Data Exchange (ETDEWEB)
Holfeltz, Vanessa E. [Nuclear Chemistry and Engineering Group, Pacific Northwest National Laboratory, Richland, WA, USA; School of Nuclear Science and Engineering, Oregon State University, Corvallis, OR, USA; Campbell, Emily L. [Nuclear Chemistry and Engineering Group, Pacific Northwest National Laboratory, Richland, WA, USA; Peterman, Dean R. [Aqueous Separations and Radiochemistry Department, Idaho National Laboratory, Idaho Falls, ID, USA; Standaert, Robert F. [Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA; Department of Biochemistry & amp, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN, USA; Biology & amp, Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA; Shull Wollan Center — a Joint Institute for Neutron Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, USA; Paulenova, Alena [School of Nuclear Science and Engineering, Oregon State University, Corvallis, OR, USA; Lumetta, Gregg J. [Nuclear Chemistry and Engineering Group, Pacific Northwest National Laboratory, Richland, WA, USA; Levitskaia, Tatiana G. [Nuclear Chemistry and Engineering Group, Pacific Northwest National Laboratory, Richland, WA, USA
2017-12-20
In solvent extraction processes, organic phase impurities can negatively impact separation factors, hydrolytic performance, and overall system robustness. This affects the process-level viability of a separation concept and necessitates knowledge of the behavior and mechanisms to control impurities in the solvent. The most widespread way through which impurities are introduced into a system is through impure extractants and/or diluents used to prepare the solvent, and often development of new purification schemes to achieve the desired level of purity is needed. In this work, the acidic extractant, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP])—proposed for application in extractive processes aimed at separating trivalent minor actinides from lanthanides and other fission products—is characterized with respect to its common impurities and their impact on Am(III) stripping in the Actinide Lanthanide SEParation (ALSEP) system. To control impurities in HEH[EHP], existing purification technologies commonly applied for the acidic organophosphorus reagents are reviewed, and a new method specific to HEH[EHP] purification is presented.
International Nuclear Information System (INIS)
Sánchez, Vicenta; Ramírez, Carlos; Sánchez, Fernando; Wang, Chumin
2014-01-01
In this paper, we analyze the effects of site and bond impurities on the electrical conductance of periodic and quasiperiodic systems with macroscopic length by means of a real-space renormalization plus a convolution method developed for the Kubo–Greenwood formula. All analyzed systems are connected to semi-infinite periodic leads. Analytical and numerical conductivity spectra are obtained for one and two site impurities in a periodic chain, where the separation between impurities determines the number of maximums in the spectra. We also found transparent states at the zero chemical potential in Fibonacci chains of every three generations with bond impurities, whose existence was confirmed by an analytical analysis within the Landauer formalism. For many impurities, the spectral average of the conductivity versus the system length reveals a power-law behavior, when the distance between impurities follows the Fibonacci sequence. Finally, we present an analysis of the conductance spectra of segmented periodic and Fibonacci chains and nanowires
Energy Technology Data Exchange (ETDEWEB)
Sánchez, Vicenta; Ramírez, Carlos; Sánchez, Fernando [Departamento de Física, Facultad de Ciencias, Universidad Nacional Autónoma de México, Apartado Postal 70-542, 04510 México D.F., México (Mexico); Wang, Chumin, E-mail: chumin@unam.mx [Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, 04510 México D.F. (Mexico)
2014-09-15
In this paper, we analyze the effects of site and bond impurities on the electrical conductance of periodic and quasiperiodic systems with macroscopic length by means of a real-space renormalization plus a convolution method developed for the Kubo–Greenwood formula. All analyzed systems are connected to semi-infinite periodic leads. Analytical and numerical conductivity spectra are obtained for one and two site impurities in a periodic chain, where the separation between impurities determines the number of maximums in the spectra. We also found transparent states at the zero chemical potential in Fibonacci chains of every three generations with bond impurities, whose existence was confirmed by an analytical analysis within the Landauer formalism. For many impurities, the spectral average of the conductivity versus the system length reveals a power-law behavior, when the distance between impurities follows the Fibonacci sequence. Finally, we present an analysis of the conductance spectra of segmented periodic and Fibonacci chains and nanowires.
Hopkins, R. H.; Davis, J. R.; Rohatgi, A.; Hanes, M. H.; Rai-Choudhury, P.; Mollenkopf, H. C.
1982-01-01
The effects of impurities and processing on the characteristics of silicon and terrestrial silicon solar cells were defined in order to develop cost benefit relationships for the use of cheaper, less pure solar grades of silicon. The amount of concentrations of commonly encountered impurities that can be tolerated in typical p or n base solar cells was established, then a preliminary analytical model from which the cell performance could be projected depending on the kinds and amounts of contaminants in the silicon base material was developed. The impurity data base was expanded to include construction materials, and the impurity performace model was refined to account for additional effects such as base resistivity, grain boundary interactions, thermal processing, synergic behavior, and nonuniform impurity distributions. A preliminary assessment of long term (aging) behavior of impurities was also undertaken.
Impurity and trace tritium transport in tokamak edge turbulence
DEFF Research Database (Denmark)
Naulin, V.
2005-01-01
The turbulent transport of impurity or minority species, as for example tritium, is investigated in drift-Alfven edge turbulence. The full effects of perpendicular and parallel convection are kept for the impurity species. The impurity density develops a granular structure with steep gradients...... and locally exceeds its initial values due to the compressibility of the flow. An approximate decomposition of the impurity flux into a diffusive part and an effective convective part (characterized by a pinch velocity) is performed and a net inward pinch effect is recovered. The pinch velocity is explained...
Fermionic phase transition induced by the effective impurity in holography
Energy Technology Data Exchange (ETDEWEB)
Fang, Li-Qing [IFSA Collaborative Innovation Center, Department of Physics and Astronomy,Shanghai Jiao Tong University, Shanghai 200240 (China); School of Physics and Electronic Information, Shangrao Normal University,Shangrao 334000 (China); Kuang, Xiao-Mei [Department of Physics, National Technical University of Athens,GR-15780 Athens (Greece); Instituto de Física, Pontificia Universidad Católica de Valparaíso,Casilla 4059, Valparaíso (Chile); Wang, Bin [IFSA Collaborative Innovation Center, Department of Physics and Astronomy,Shanghai Jiao Tong University, Shanghai 200240 (China); Wu, Jian-Pin [Institute of Gravitation and Cosmology, Department of Physics,School of Mathematics and Physics, Bohai University, Jinzhou 121013 (China); State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics,Chinese Academy of Sciences, Beijing 100190 (China)
2015-11-20
We investigate the holographic fermionic phase transition induced by the effective impurity in holography, which is introduced by massless scalar fields in Einstein-Maxwell-massless scalar gravity. We obtain a phase diagram in (α,T) plane separating the Fermi liquid phase and the non-Fermi liquid phase.
Divertor experiment for impurity control in DIVA
International Nuclear Information System (INIS)
Nagami, Masayuki
1979-04-01
Divertor actions of controlling the impurities and the transport of impurity ions in the plasma have been investigated in the DIVA device. Following are the results: (1) The radial transport of impurity ions is not described only by neoclassical theory, but it is strongly influenced by anomalous process. Radial diffusion of impurity ions across the whole minor radius is well described by a neoclassical diffusion superposed by the anomalous diffusion for protons. Due to this anomalous process, which spreads the radial density profile of impurity ions, 80 to 90% of the impurity flux in the plasma outer edge is shielded even in a nondiverted discharge. (2) The divertor reduces the impurity flux entering the main plasma by a factor of 2 to 4. The impurity ions shielded by the scrape-off plasma are rapidly guided into the burial chamber with a poloidal excursion time roughly equal to that of the scrape-off plasma. (3) The divertor reduces the impurity ion flux onto the main vacuum chamber by guiding the impurity ions diffusing from the main plasma into the burial chamber, thereby reducing the plasma-wall interaction caused by diffusing impurity ions at the main vacuum chamber. The impurity ions produced in the burial chamber may flow back to the main plasma through the scrape-off layer. However, roughly only 0.3% of the impurity flux into the scrape-off plasma in the burial chamber penetrates into the main plasma due to the impurity backflow. (4) A slight cooling of the scrape-off plasma with light-impurity injection effectively reduces the metal impurity production at the first wall by reducing the potential difference between the plasma and the wall, thereby reducing the accumulation of the metal impurity in the discharge. Radiation cooling by low-Z impurities in the plasma outer edge, which may become an important feature in future large tokamaks both with and without divertor, is numerically evaluated for carbon, oxygen and neon. (author)
Moessbauer Studies of Implanted Impurities in Solids
2002-01-01
Moessbauer studies were performed on implanted radioactive impurities in semiconductors and metals. Radioactive isotopes (from the ISOLDE facility) decaying to a Moessbauer isotope were utilized to investigate electronic and vibrational properties of impurities and impurity-defect structures. This information is inferred from the measured impurity hyperfine interactions and Debye-Waller factor. In semiconductors isoelectronic, shallow and deep level impurities have been implanted. Complex impurity defects have been produced by the implantation process (correlated damage) or by recoil effects from the nuclear decay in both semiconductors and metals. Annealing mechanisms of the defects have been studied. \\\\ \\\\ In silicon amorphised implanted layers have been recrystallized epitaxially by rapid-thermal-annealing techniques yielding highly supersaturated, electrically-active donor concentrations. Their dissolution and migration mechanisms have been investigated in detail. The electronic configuration of Sb donors...
Holovatsky, V. A.; Voitsekhivska, O. M.; Yakhnevych, M. Ya
2018-04-01
The effect of homogeneous magnetic field and location of donor impurity on the electron energy spectrum and distribution of its probability density in spherical core-shell quantum dot is investigated. In the framework of the effective mass approximation and rectangular infinitely deep potential well, the solutions of the Schrodinger equation are found using the matrix method. The wave functions are expanded over the complete set of exact functions obtained without the magnetic field and impurity. It is shown that when the induction of magnetic field increases, the ground state of electron in the nanostructure without impurity or on-center impurity is successively formed by the states with m = 0, -1, -2, … (Aharonov-Bohm effect). When donor impurity is located in the shell of the nanostructure the Aharonov-Bohm effect vanishes. The dependences of electron energy spectrum and its wave functions on the location of impurity, placed along the direction of magnetic field or perpendicularly to it, are studied. It is shown, that in the first case, the quantum states are characterized by the certain value of magnetic quantum number m and the expansion contains the wave functions of the states with it only. In the second case, the cylindrical symmetry of the problem is broken and the new quantum states are formed from the states with different values of all three quantum numbers n, l, m and electron energy spectrum weakly depends on the magnetic field induction.
Impurity-generated non-Abelions
Simion, G.; Kazakov, A.; Rokhinson, L. P.; Wojtowicz, T.; Lyanda-Geller, Y. B.
2018-06-01
Two classes of topological superconductors and Majorana modes in condensed matter systems are known to date: one in which disorder induced by impurities strongly suppresses topological superconducting gap and is detrimental to Majorana modes, and another where Majorana fermions are protected by a disorder-robust topological superconductor gap. Observation and control of Majorana fermions and other non-Abelions often requires a symmetry of an underlying system leading to a gap in the single-particle or quasiparticle spectra. In semiconductor structures, impurities that provide charge carriers introduce states into the gap and enable conductance and proximity-induced superconductivity via the in-gap states. Thus a third class of topological superconductivity and Majorana modes emerges, in which topological superconductivity and Majorana fermions appear exclusively when impurities generate in-gap states. We show that impurity-enabled topological superconductivity is realized in a quantum Hall ferromagnet, when a helical domain wall is coupled to an s -wave superconductor. As an example of emergence of topological superconductivity in quantum Hall ferromagnets, we consider the integer quantum Hall effect in Mn-doped CdTe quantum wells. Recent experiments on transport through the quantum Hall ferromagnet domain wall in this system indicated a vital role of impurities in the conductance, but left unresolved the question whether impurities preclude generation of Majorana fermions and other non-Abelions in such systems in general. Here, solving a general quantum-mechanical problem of impurity bound states in a system of spin-orbit coupled Landau levels, we demonstrate that impurity-induced Majorana modes emerge at boundaries between topological and conventional superconducting states generated in a domain wall due to proximity to an s superconductor. We consider both short-range disorder and a smooth random potential. The phase diagram of the system is defined by
Directory of Open Access Journals (Sweden)
Thai T. H. Nguyen
2017-09-01
Full Text Available Sono-crystallisation has been used to enhance crystalline product quality particularly in terms of purity, particle size and size distribution. In this work, the effect of impurities and ultrasound on crystallisation processes (nucleation temperature, yield and crystal properties (crystal size distribution determined by Focused Beam Reflectance Measurement (FBRM, crystal habit, filtration rate and impurity content in the crystal product by Liquid Chromatography-Mass Spectroscopy (LC-MS were investigated in bulk suspension crystallisation experiments with and without the use of ultrasound. The results demonstrate that ultrasonic intervention has a significant effect on both crystallisation and product crystal properties. It increases the nucleation rate resulting in smaller particles and a narrower Particle Size Distribution (PSD, the yield has been shown to be increase as has the product purity. The effect of ultrasound is to reduce the level acetanilide impurity incorporated during growth from a 2 mol% solution of the selected impurity from 0.85 mol% to 0.35 mol% and likewise ultrasound reduces the uptake of metacetamol from 1.88 mol% to 1.52 mol%.
Effect of abnormal high solubility of impurity in nanocrystalls and its metrological aspects
International Nuclear Information System (INIS)
Oksengendler, B L; Turaeva, N N; Nikiforov, V N; Sredin, V G; Maksimov, S E
2011-01-01
The problem of doping impurity intrusion into nanoparticles is analyzed. Thermodynamical model of the effect is developed, taking into account specific properties of nanoparticles: quantum confinement of elementary excitations and the impact of nanoparticle surface states compared with bulk ones. We obtained the size dependence of impact equilibrium solubility in nanoparticles. Magnetometric experiments, carried out on nanoparticle ensemble of iron oxide doped with gadolinium and other impurities, show lack of contradictions and good qualitative accordance between the model and the experiment.
International Nuclear Information System (INIS)
Nakajima, Y.; Hidaka, H.; Tamegai, T.
2013-01-01
Highlights: ► Non-magnetic impurities suppress T c and the amplitude of gaps in Lu 2 Fe 3 Si 5 . ► Critical scattering rate is higher than that expected in s ± -pairing scenario. ► The evolution of two distinct gaps dose not show merging the amplitude of gaps. -- Abstract: We report the suppression of T c and the evolution of amplitudes of the two gaps with the introduction of non-magnetic impurities in a two-gap superconductor Lu 2 Fe 3 Si 5 . While T c rapidly decreases by a small amount of substitution of Sc for Lu, the suppression of T c is more than ten times slower than that expected from the Abrikosov–Gor’kov equation describing the reduction of T c in a superconductor with sign reversal in the gap function. The evolution of two distinct gaps by the introduction of non-magnetic impurities does not show merging the amplitude of two gaps, which is strikingly different from the typical two-gap superconductor MgB 2
Optical coefficients in a semiconductor quantum ring: Electric field and donor impurity effects
Duque, C. M.; Acosta, Ruben E.; Morales, A. L.; Mora-Ramos, M. E.; Restrepo, R. L.; Ojeda, J. H.; Kasapoglu, E.; Duque, C. A.
2016-10-01
The electron states in a two-dimensional quantum dot ring are calculated in the presence of a donor impurity atom under the effective mass and parabolic band approximations. The effect of an externally applied electric field is also taken into account. The wavefunctions are obtained via the exact diagonalization of the problem Hamiltonian using a 2D expansion within the adiabatic approximation. The impurity-related optical response is analyzed via the optical absorption, relative refractive index change and the second harmonics generation. The dependencies of the electron states and these optical coefficients with the changes in the configuration of the quantum ring system are discussed in detail.
Effects of radiation and impurities on gaseous iodine behavior in a containment vessel
International Nuclear Information System (INIS)
Takahashi, Masato; Watanabe, Atsushi; Hashimoto, Takashi
2000-01-01
In order to estimate the effect of impurities and radiation on gaseous iodine behavior in containment vessel, NUPEC has improved IMPAIR-3 code developed by PSI. Several modifications on the iodine oxidation by radiolysis and the production of nitric acid, the existence of boric acid, and the reaction of silver particle with iodine were newly added in evaluating the effect of radiolysis and impurities. pH change resulting from presence of boric acid, nitric acid production by radiolysis of air, and sodium hydroxide addition by AM operation, was also considered. The code verification for pH change was performed using the RTF experimental results. Additionally, the effects of boric acid and silver impurities on gaseous iodine behavior were evaluated by the sensitivity analysis. As a result, the experimental results of iodine concentration transient under pH change were well simulated. The following results were also obtained from the sensitive analysis. The gaseous iodine behavior was not affected by the existence of boric acid. In the case of silver existence in liquid phase, the gaseous iodine concentration rapidly decreased because a large amount of iodine changed into AgI species in liquid phase. The restraint effect of silver on gaseous iodine, production was larger than that of pH change. (author)
Lowest excited-state impurity binding energy in InGaN/GaN parabolic QWW: magnetic field effect
International Nuclear Information System (INIS)
Haddou El Ghazi; Anouar Jorio; Izeddine Zorkani
2013-01-01
In this paper, we have investigated the magnetic field effect on the lowest excited-state binding energy of hydrogenic shallow-donor impurity in wurtzite (In,Ga)N/GaN parabolic transversal-section quantum-well wire (PQWW) using the finite-difference method within the quasi-one-dimensional effective potential model. The calculations are performed within the framework of the effective mass approximation. A cylindrical QWW effective radius is taken into account to describe the lateral confinement strength. The numerical results show that: (i) the probability density is the largest on a circularity whose radius is the effective radius and (ii) the lowest excited-state binding energy is the largest when an impurity is located on this circularity while it starts to decrease as the impurity is away from the circularity. (author)
Alloy scattering dependence of electron transport in AlGaN
International Nuclear Information System (INIS)
Yarar, Z.; Ozdemir, M.
2010-01-01
The electron transport and velocity characteristics in AlGaN are examined using an ensemble Monte Carlo simulation method. A three valley band structure model where nonparabolicity effects are considered in all valleys is used for Monte Carlo calculations. All of the major electron scattering interactions like acoustic and optical phonon, intervaley, ionized impurity and alloy disorder scatterings are included in the calculations. The velocity-applied electric field characteristics are analyzed as a function of Al molar fraction and temperature in the ranges of x=0.1 to x=0.5 and 77 K to 500 K, respectively. The velocity overshoot is clearly observed and the population of valleys seems well-matched with the occupancy of valleys in AlGaN. The results of electron steady state velocity-field curves are found that the alloy disorder scattering has important effects on the electron transport characteristics of AlGaN.
Energy Technology Data Exchange (ETDEWEB)
Sekizawa, T
1974-01-01
In order to examine the possibility of reducing the heat treatment temperature in the manufacturing process of the superconducting intermetallic compounds wire or ribbon by the metallurgical bond method, tin cored specimens of niobium including a small amount of impurity (Al, Cu, Ge, Si, Sn and Zr) have been prepared, and the critical currents measured as a function of the heat treatment temperature and time. Experimental results are summarized as follows. (1) The effect of the impurity added into niobium is to stabilize the dislocation network cell structure in niobium, caused by the cold working, up to the forming temperature of Nb/sub 3/Sn. The stabilized dislocation network structure is considered to serve as diffusion pipes of the tin atom. As this diffusion (microscopic) is predominant over bulk diffusion (macroscopic), the cored specimen made of niobium including impurities has lower forming temperature of Nb/sub 3/Sn compared with the specimen made of pure niobium. (2) The critical current vs. heat treatment temperature characteristics show that the critical current peaks at 900/sup 0/C in the case of niobium including Si, while at 950/sup 0/C in the case of pure niobium. 6 references.
Extrinsic spin Hall effect in graphene
Rappoport, Tatiana
The intrinsic spin-orbit coupling in graphene is extremely weak, making it a promising spin conductor for spintronic devices. In addition, many applications also require the generation of spin currents in graphene. Theoretical predictions and recent experimental results suggest one can engineer the spin Hall effect in graphene by greatly enhancing the spin-orbit coupling in the vicinity of an impurity. The extrinsic spin Hall effect then results from the spin-dependent skew scattering of electrons by impurities in the presence of spin-orbit interaction. This effect can be used to efficiently convert charge currents into spin-polarized currents. I will discuss recent experimental results on spin Hall effect in graphene decorated with adatoms and metallic cluster and show that a large spin Hall effect can appear due to skew scattering. While this spin-orbit coupling is small if compared with what it is found in metals, the effect is strongly enhanced in the presence of resonant scattering, giving rise to robust spin Hall angles. I will present our single impurity scattering calculations done with exact partial-wave expansions and complement the analysis with numerical results from a novel real-space implementation of the Kubo formalism for tight-binding Hamiltonians. The author acknowledges the Brazilian agencies CNPq, CAPES, FAPERJ and INCT de Nanoestruturas de Carbono for financial support.
Impurity-related nonlinear optical properties in delta-doped quantum rings: Electric field effects
Energy Technology Data Exchange (ETDEWEB)
Restrepo, R.L., E-mail: rrestre@gmail.com [Escuela de Ingeniería de Antioquia-EIA, Medellín (Colombia); Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Morales, A.L. [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Martínez-Orozco, J.C. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, CP 98060, Zacatecas (Mexico); Baghramyan, H.M.; Barseghyan, M.G. [Department of Solid State Physics, Yerevan State University, Al. Manookian 1, 0025 Yerevan (Armenia); Mora-Ramos, M.E. [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Ave. Universidad 1001, CP 62209, Cuernavaca, Morelos (Mexico); Duque, C.A. [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia)
2014-11-15
Using a variational procedure within the effective mass approximation, we have calculated the donor impurity binding energy for the ground (1s-like) and the excited (2p{sub z}-like) states as well as the impurity-related nonlinear optical absorption and relative changes in the refraction index in a GaAs single quantum ring with axial n-type delta-doping. The delta-like potential along the z-direction is an approximate model analytically described using a Lorentzian function with two parameters. Additionally we consider the application of an electric field along the z-direction. It is found that the changes in the geometry of the quantum ring, the change in the 2D impurity density of the delta-like doping, and different values of the electric field lead to a shifting of the resonant peaks of the optical responses spectrum.
Impurity-related nonlinear optical properties in delta-doped quantum rings: Electric field effects
International Nuclear Information System (INIS)
Restrepo, R.L.; Morales, A.L.; Martínez-Orozco, J.C.; Baghramyan, H.M.; Barseghyan, M.G.; Mora-Ramos, M.E.; Duque, C.A.
2014-01-01
Using a variational procedure within the effective mass approximation, we have calculated the donor impurity binding energy for the ground (1s-like) and the excited (2p z -like) states as well as the impurity-related nonlinear optical absorption and relative changes in the refraction index in a GaAs single quantum ring with axial n-type delta-doping. The delta-like potential along the z-direction is an approximate model analytically described using a Lorentzian function with two parameters. Additionally we consider the application of an electric field along the z-direction. It is found that the changes in the geometry of the quantum ring, the change in the 2D impurity density of the delta-like doping, and different values of the electric field lead to a shifting of the resonant peaks of the optical responses spectrum
Effect of impurities in the electrothermic instability
International Nuclear Information System (INIS)
Azevedo, M.T. de.
1982-04-01
It is proposed a model for a ''impure'' plasma based on the homogenous hydrogen plasma used in the theory formulated by Tomimura and Haines to explain the increasing of instable electrothermal modes with wave vector perpendicular to the applyed magnetic field. The impurities are implicity introduced in the transport coeficients of the model of two fluids through the effective charge number Z eff as suggested by Duechs et al., Furth etc... The results obtained are: (i) the greatest increasing ratio for the absolute mode (non-convective) decreases with the increasing of Z eff going to zero for a given value of these parameter which is denominated Z crit ; (ii) the wavelenght associated with that greatest ratio of increasing decreases with the increasing of Z eff ; (iii) Z crit x T eo /T io curves, where T eo and T io are the electronic and ionic temperatures of equilibri um show that, for each value of T eo (used as a parameter) there is a limiting value Z crit from which the plasma is stable, independently of the temperature ratio. The correlation of these results with that of a difuse pinch model, which shows the tendency in assume in the stationary state a filamental current structure is inconclusive with respect to the Z eff dependence. (M.W.O.) [pt
International Nuclear Information System (INIS)
Cygorek, M; Axt, V M
2015-01-01
Starting from a quantum kinetic theory for the spin dynamics in diluted magnetic semiconductors, we derive simplified equations that effectively describe the spin transfer between carriers and magnetic impurities for an arbitrary initial impurity magnetization. Taking the Markov limit of these effective equations, we obtain good quantitative agreement with the full quantum kinetic theory for the spin dynamics in bulk systems at high magnetic doping. In contrast, the standard rate description where the carrier–dopant interaction is treated according to Fermi’s golden rule, which involves the assumption of a short memory as well as a perturbative argument, has been shown previously to fail if the impurity magnetization is non-zero. The Markov limit of the effective equations is derived, assuming only a short memory, while higher order terms are still accounted for. These higher order terms represent the precession of the carrier–dopant correlations in the effective magnetic field due to the impurity spins. Numerical calculations show that the Markov limit of our effective equations reproduces the results of the full quantum kinetic theory very well. Furthermore, this limit allows for analytical solutions and for a physically transparent interpretation. (paper)
Influence of impurities on the crystallization of dextrose monohydrate
Markande, Abhay; Nezzal, Amale; Fitzpatrick, John; Aerts, Luc; Redl, Andreas
2012-08-01
The effects of impurities on dextrose monohydrate crystallization were investigated. Crystal nucleation and growth kinetics in the presence of impurities were studied using an in-line focused beam reflectance monitoring (FBRM) technique and an in-line process refractometer. Experimental data were obtained from runs carried out at different impurity levels between 4 and 11 wt% in the high dextrose equivalent (DE) syrup. It was found that impurities have no significant influence on the solubility of dextrose in water. However, impurities have a clear influence on the nucleation and growth kinetics of dextrose monohydrate crystallization. Nucleation and growth rate were favored by low levels of impurities in the syrup.
Impurity Correction Techniques Applied to Existing Doping Measurements of Impurities in Zinc
Pearce, J. V.; Sun, J. P.; Zhang, J. T.; Deng, X. L.
2017-01-01
Impurities represent the most significant source of uncertainty in most metal fixed points used for the realization of the International Temperature Scale of 1990 (ITS-90). There are a number of different methods for quantifying the effect of impurities on the freezing temperature of ITS-90 fixed points, many of which rely on an accurate knowledge of the liquidus slope in the limit of low concentration. A key method of determining the liquidus slope is to measure the freezing temperature of a fixed-point material as it is progressively doped with a known amount of impurity. Recently, a series of measurements of the freezing and melting temperature of `slim' Zn fixed-point cells doped with Ag, Fe, Ni, and Pb were presented. Here, additional measurements of the Zn-X system are presented using Ga as a dopant, and the data (Zn-Ag, Zn-Fe, Zn-Ni, Zn-Pb, and Zn-Ga) have been re-analyzed to demonstrate the use of a fitting method based on Scheil solidification which is applied to both melting and freezing curves. In addition, the utility of the Sum of Individual Estimates method is explored with these systems in the context of a recently enhanced database of liquidus slopes of impurities in Zn in the limit of low concentration.
Energy Technology Data Exchange (ETDEWEB)
Barseghyan, M.G., E-mail: mbarsegh@ysu.am
2016-11-10
Highlights: • The electron-impurity interaction on energy levels in nanoring have been investigated. • The electron-impurity interaction on far-infrared absorption have been investigated. • The energy levels are more stable for higher values of electric field. - Abstract: The effects of electron-impurity interaction on energy levels and far-infrared absorption in semiconductor nanoring under the action of intense laser and lateral electric fields have been investigated. Numerical calculations are performed using exact diagonalization technique. It is found that the electron-impurity interaction and external fields change the energy spectrum dramatically, and also have significant influence on the absorption spectrum. Strong dependence on laser field intensity and electric field of lowest energy levels, also supported by the Coulomb interaction with impurity, is clearly revealed.
Corrosion behavior of pyroclore-rich titanate ceramics for plutonium disposition; impurity effects
International Nuclear Information System (INIS)
Bakel, A. J.
1999-01-01
The baseline ceramic contains Ti, U, Ca, Hf, Gd, and Ce, and is made up of only four phases, pyrochlore, zirconolite, rutile, and brannerite. The impurities present in the three other ceramics represent impurities expected in the feed, and result in different phase distributions. The results from 3 day, 90 C MCC-1 tests with impurity ceramics were significantly different than the results from tests with the baseline ceramic. Overall, the addition of impurities to these titanate ceramics alters the phase distributions, which in turn, affects the corrosion behavior
Isospin impurity and super-allowed β transitions
International Nuclear Information System (INIS)
Sagawa, H.; Van Giai Nguyen; Suzuki, T.
1999-01-01
We study the effect of isospin impurity on the super-allowed Fermi β decay using microscopic HF and RPA (or TDA) model taking into account CSB and CIB interactions. It is found that the isospin impurity of N = Z nuclei gives enhancement of the sum rule of Fermi transition probabilities. On the other hand, the super-allowed transitions between odd-odd J = 0 nuclei and even-even J = 0 nuclei are quenched because on the cancellation of the isospin impurity effects of mother and daughter nuclei. An implication of the calculated Fermi transition rate on the unitarity of Cabbibo-Kobayashi-Maskawa mixing matrix is also discussed. (authors)
Effect of magnetic field on the impurity binding energy of the excited ...
Indian Academy of Sciences (India)
The effect of external magnetic field on the excited state energies in a spherical quantum dot was studied. The impurity energy and binding energy were calculated using the variational method within the effective mass approximation and finite barrier potential. The results showed that by increasing the magnetic field, the ...
Effect of magnetic field on the impurity binding energy of the excited ...
Indian Academy of Sciences (India)
Abstract. The effect of external magnetic field on the excited state energies in a spher- ical quantum dot was studied. The impurity energy and binding energy were calculated using the variational method within the effective mass approximation and finite barrier potential. The results showed that by increasing the magnetic ...
International Nuclear Information System (INIS)
Schneider, W.J.; Edwards, D. Jr.
1979-01-01
The desirability for long-term reliability of large scale helium refrigerator systems used on superconducting accelerator magnets has necessitated detection of impurities to levels of a few ppM. An analyzer that measures trace impurity levels of condensable contaminants in concentrations of less than a ppM in 15 atm of He is described. The instrument makes use of the desorption temperature at an indicated pressure of the various impurities to determine the type of contaminant. The pressure rise at that temperature yields a measure of the contaminant level of the impurity. A LN 2 cryogenic charcoal trap is also employed to measure air impurities (nitrogen and oxygen) to obtain the full range of contaminant possibilities. The results of this detector which will be in use on the research and development helium refrigerator of the ISABELLE First-Cell is described
Impurities effect on the swelling of neutron irradiated beryllium
International Nuclear Information System (INIS)
Donne, M.D.; Scaffidi-Argentina, F.
1995-01-01
An important factor controlling the swelling behaviour of fast neutron irradiated beryllium is the impurity content which can strongly affect both the surface tension and the creep strength of this material. Being the volume swelling of the old beryllium (early sixties) systematically higher than that of the more modem one (end of the seventies), a sensitivity analysis with the aid of the computer code ANFIBE (ANalysis of Fusion Irradiated BEryllium) to investigate the effect of these material properties on the swelling behaviour of neutron irradiated beryllium has been performed. Two sets of experimental data have been selected: the first one named Western refers to quite recently produced Western beryllium, whilst the second one, named Russian refers to relatively old (early sixties) Russian beryllium containing a higher impurity rate than the Western one. The results obtained with the ANFIBE Code were assessed by comparison with experimental data and the used material properties were compared with the data available in the literature. Good agreement between calculated and measured values has been found
Impurity Trapping of Positive Muons in Metals
2002-01-01
Polarized positive muons are implanted into metal samples. In an applied magnetic field the muon spin precession is studied. The line width in the precession frequency spectrum gives information about the static and dynamic properties of muons in a metal lattice. At temperatures where the muon is immobile within its lifetime the line width gives information about the site of location. At temperatures where the muon is mobile, the line width gives information on the diffusion process. It is known from experiments on quasi-elastic neutron scattering on hydrogen in niobium that interstitial impurities like nitrogen tend to act as traps for hydrogen. These trapping effects have now been studied systematically for muons in both f.c.c. metals (aluminium and copper) and b.c.c. metals (mainly niobium). Direct information on the trapping rates and the nature of the diffusion processes can be obtained since the muonic lifetime covers a time range where many of these processes occur.\\\\ \\\\ Mathematical models are set up ...
International Nuclear Information System (INIS)
Hegedus, Zoltan; Gubicza, Jeno; Kawasaki, Megumi; Chinh, Nguyen Q.; Fogarassy, Zsolt; Langdon, Terence G.
2011-01-01
Highlights: → Effect of impurity content on microstructure in ECAP-processed silver was studied. → There is a lower degree of twinning in the less pure material for high strains. → The samples processed for 4-16 passes showed self-annealing during storage at RT. → Small increase of impurity level resulted in a much better stability at RT. - Abstract: The effect of impurity content on the evolution of microstructure in low stacking fault energy silver processed by severe plastic deformation (SPD) was studied. The SPD-processing was carried out on 4N5 and 4N purity Ag samples by equal-channel angular pressing (ECAP) up to 16 passes. It was found that, although the minimum grain size and the maximum dislocation density were not affected by the different impurity atom content, there is a lower degree of twinning in the less pure material for high number of passes. The small increase of impurity level from 4N5 to 4N in Ag resulted in a significantly better thermal stability at room temperature for the ultrafine-grained microstructures obtained by ECAP.
Anomalous temperature behavior of Sn impurities
International Nuclear Information System (INIS)
Haskel, D.; Shechter, H.; Stern, E.A.; Newville, M.; Yacoby, Y.
1993-01-01
Sn impurities in Pb and Ag hosts have been investigated by Moessbauer effect and in Pb by x-ray-absorption fine-structure (XAFS) studies. The Sn atoms are dissolved up to at least 2 at. % in Pb and up to at least 8 at. % in Ag for the temperature ranges investigated. The concentration limit for Sn-Sn interactions is 1 at. % for Pb and 2 at. % for Ag as determined experimentally by lowering the Sn concentration until no appreciable change occurs in the Moessbauer effect. XAFS measurements verify that the Sn impurities in Pb are dissolved and predominantly at substitutional sites. For both hosts the temperature dependence of the spectral intensities of isolated Sn impurities below a temperature T 0 is as expected for vibrating about a lattice site. Above T 0 the Moessbauer spectral intensity exhibits a greatly increased rate of drop-off with temperature without appreciable broadening. This drop-off is too steep to be explained by ordinary anharmonic effects and can be explained by a liquidlike rapid hopping of the Sn, localized about a lattice site. Higher-entropy-density regions of radii somewhat more than an atomic spacing surround such impurities, and can act as nucleation sites for three-dimensional melting
Multiscaling Dynamics of Impurity Transport in Drift-Wave Turbulence
International Nuclear Information System (INIS)
Futatani, S.; Benkadda, S.; Nakamura, Y.; Kondo, K.
2008-01-01
Intermittency effects and the associated multiscaling spectrum of exponents are investigated for impurities advection in tokamak edge plasmas. The two-dimensional Hasagawa-Wakatani model of resistive drift-wave turbulence is used as a paradigm to describe edge tokamak turbulence. Impurities are considered as a passive scalar advected by the plasma turbulent flow. The use of the extended self-similarity technique shows that the structure function relative scaling exponent of impurity density and vorticity follows the She-Leveque model. This confirms the intermittent character of the impurities advection in the turbulent plasma flow and suggests that impurities are advected by vorticity filaments
International Nuclear Information System (INIS)
Romanelli, M.
1999-09-01
The poloidal variation of impurity densities over magnetic surfaces brings about an enhancement of neoclassical transport coefficients, as shown by Romanelli and Ottaviani for impurities in the Pfirsch Schlueter regime and by Helander for particles in the banana-plateau regime, both in a large aspect ratio tokamak. The same effect will occur in a finite aspect ratio tokamak and therefore it is considered to be relevant for inclusion in transport codes for comparison with the experimental measurements of impurity transport. Here an expression for the impurity-density poloidal-variation generated by the fast toroidal rotation of the plasma column is presented in general coordinates. (author)
International Nuclear Information System (INIS)
Duque, C.A.; Kasapoglu, E.; Sakiroglu, S.; Sari, H.; Soekmen, I.
2010-01-01
Using the effective mass and parabolic band approximations and a variational procedure we have calculated the combined effects of intense laser radiation, hydrostatic pressure, and applied electric field on shallow-donor impurity confined in cylindrical-shaped single and double GaAs-Ga 1-x Al x As QD. Several impurity positions and inputs of the heterostructure dimensions, hydrostatic pressure, and applied electric field have been considered. The laser effects have been introduced by a perturbative scheme in which the Coulomb and the barrier potentials are modified to obtain dressed potentials. Our findings suggest that (1) for on-center impurities in single QD the binding energy is a decreasing function of the dressing parameter and for small dot dimensions of the structures (lengths and radius) the binding energy is more sensitive to the dressing parameter, (2) the binding energy is an increasing/decreasing function of the hydrostatic pressure/applied electric field, (3) the effects of the intense laser field and applied electric field on the binding energy are dominant over the hydrostatic pressure effects, (4) in vertically coupled QD the binding energy for donor impurity located in the barrier region is smaller than for impurities in the well regions and can be strongly modified by the laser radiation, and finally (5) in asymmetrical double QD heterostructures the binding energy as a function of the impurity positions follows a similar behavior to the observed for the amplitude of probability of the noncorrelated electron wave function.
International Nuclear Information System (INIS)
Charit, I.; Seok, C.S.; Murty, K.L.
2007-01-01
Ferritic steels are generally used in pressure vessels and various reactor support structures in light water reactors. They are known to exhibit radiation embrittlement in terms of decreased toughness and increased ductile-brittle transition temperature as a result of exposure to neutron radiation. The superimposed effects of strain aging due to interstitial impurity atoms on radiation embrittlement were considered first by Wechsler, Hall and others. Here we summarize some of our efforts on the investigation of synergistic effects between interstitial impurity atoms (IIAs) and radiation-induced point defects, which result in interesting effects at appropriate temperature and strain rate conditions. Two materials, a mild steel and a pressure vessel steel (A516 Gr.70), are evaluated using tensile and three-point bend tests
Surface effects and impurity production in tokamak machines
International Nuclear Information System (INIS)
Staib, P.; Staudenmaier, G.
1978-01-01
Plasma-wall interactions are presently investigated in two ways: a) The a priori assumption of a mechanism responsible for impurity release. Relevant experimental data can be used in a model and calculations made in order to understand the observed impurity behaviour in plasma. b) The comprehensive investigation of samples exposed to a plasma. Recent investigations have confirmed the earlier assumption that the interactions occur only in the topmost atomic layers of the wall, and so emphasize the major role of surface physics on this field. These investigations have further shown that besides atomic processes, such a desorption or sputtering, other processes occur, extending on a microscopic rather than an atomic scale. These are for example evaporation, arcing, and mechanical stress. Both aspects are discussed as far as possible in a quantitative way. The contribution of most probable processes is estimated using data available on flux and energy of particles and yields of single processes. The conclusion is reached that no process can be disregarded. Several processes seem to contribute to the impurity release and are different at different phases of the discharge. An interdependence between these processes is likely. (Auth.)
Energy Technology Data Exchange (ETDEWEB)
Mohapatra, Rasmita, E-mail: rmrmmohapatra@gmail.com [P.G. Department of Applied Physics and Ballistics, F.M. University, Balasore, Odisha 756019 (India); Rout, G.C., E-mail: gcr@iopb.res.in [Physics Enclave, Plot no-664/4825, Lane-4A, Shree Vihar, Patia, Bhubaneswar, Odisha 751024 (India)
2015-05-15
Highlights: • We considered here the interplay of antiferromagnetism (AFM) and Superconductivity (SC) with d-wave pairing symmetry in presence of impurity effect. • The tunneling conductance explains the multiple peaks and dip-hump structure. • It is observed that AFM coupling enhances the superconducting transition temperature. • The low temperature specific heat anomaly due to impurity atoms. - Abstract: We present here a model Hamiltonian to study the interplay between staggered magnetic field and the superconductivity with d-wave pairing symmetry in presence of hybridization between impurity f-electrons of rare-earth ions and 3d-electrons of copper ions. The staggered field and superconducting (SC) gaps are calculated by Green’s function technique and solved self-consistently. The coupling constants are compared using s-wave and d-wave pairings. The strength of hybridization suppresses the magnitude of the gaps; while antiferromagnetic coupling enhances the superconducting transition temperature, but suppresses the Neel temperature. The density of states (DOS) representing tunneling conductance shows complex character with impurity level lying at the Fermi level. The electronic specific heat explains prototype heavy fermion behavior in cuprate systems at low temperatures.
International Nuclear Information System (INIS)
Mohapatra, Rasmita; Rout, G.C.
2015-01-01
Highlights: • We considered here the interplay of antiferromagnetism (AFM) and Superconductivity (SC) with d-wave pairing symmetry in presence of impurity effect. • The tunneling conductance explains the multiple peaks and dip-hump structure. • It is observed that AFM coupling enhances the superconducting transition temperature. • The low temperature specific heat anomaly due to impurity atoms. - Abstract: We present here a model Hamiltonian to study the interplay between staggered magnetic field and the superconductivity with d-wave pairing symmetry in presence of hybridization between impurity f-electrons of rare-earth ions and 3d-electrons of copper ions. The staggered field and superconducting (SC) gaps are calculated by Green’s function technique and solved self-consistently. The coupling constants are compared using s-wave and d-wave pairings. The strength of hybridization suppresses the magnitude of the gaps; while antiferromagnetic coupling enhances the superconducting transition temperature, but suppresses the Neel temperature. The density of states (DOS) representing tunneling conductance shows complex character with impurity level lying at the Fermi level. The electronic specific heat explains prototype heavy fermion behavior in cuprate systems at low temperatures
Visualizing One-Dimensional Electronic States and their Scattering in Semi-conducting Nanowires
Beidenkopf, Haim; Reiner, Jonathan; Norris, Andrew; Nayak, Abhay Kumar; Avraham, Nurit; Shtrikman, Hadas
One-dimensional electronic systems constitute a fascinating playground for the emergence of exotic electronic effects and phases, within and beyond the Tomonaga-Luttinger liquid paradigm. More recently topological superconductivity and Majorana modes were added to that long list of phenomena. We report scanning tunneling microscopy and spectroscopy measurements conducted on pristine, epitaxialy grown InAs nanowires. We resolve the 1D electronic band structure manifested both via Van-Hove singularities in the local density-of-states, as well as by the quasi-particle interference patterns, induced by scattering from surface impurities. By studying the scattering of the one-dimensional electronic states off various scatterers, including crystallographic defects and the nanowire end, we identify new one-dimensional relaxation regimes and yet unexplored effects of interactions. Some of these may bear implications on the topological superconducting state and Majorana modes therein. The authors acknowledge support from the Israeli Science Foundation (ISF).
Energy Technology Data Exchange (ETDEWEB)
Dubois, S
2007-05-15
This study aims at understanding the influence of the impurity - defect interaction on the silicon solar cell performances. We studied first the case of single-crystalline silicon. We combined numerical simulations and experimental data providing new knowledge concerning metal impurities in silicon, to quantify the evolution of the conversion efficiency with the impurity concentration. Mainly due to the gettering effects, iron appears to be quite well tolerated. It is not the case for gold, diffusing too slowly. Hydrogenation effects were limited. We transposed then this study toward multi-crystalline silicon. Iron seems rather well tolerated, due to the gettering effects but also due to the efficiency of the hydrogenation. When slow diffusers are present, multi crystalline silicon is sensitive to thermal degradation. n-type silicon could solve this problem, this material being less sensitive to metal impurities. (author)
Intrinsic and extrinsic spin Hall effects of Dirac electrons
International Nuclear Information System (INIS)
Fukazawa, Takaaki; Kohno, Hiroshi; Fujimoto, Junji
2017-01-01
We investigate the spin Hall effect (SHE) of electrons described by the Dirac equation, which is used as an effective model near the L-points in bismuth. By considering short-range nonmagnetic impurities, we calculate the extrinsic as well as intrinsic contributions on an equal footing. The vertex corrections are taken into account within the ladder type and the so-called skew-scattering type. The intrinsic SHE which we obtain is consistent with that of Fuseya et al. It is found that the extrinsic contribution dominates the intrinsic one when the system is metallic. The extrinsic SHE due to the skew scattering is proportional to Δ/n i u, where 2Δ is the band gap, n i is the impurity concentration, and u is the strength of the impurity potential. (author)
Achieving improved ohmic confinement via impurity injection
International Nuclear Information System (INIS)
Bessenrodt-Weberpals, M.; Soeldner, F.X.
1991-01-01
Improved Ohmic Confinement (IOC) was obtained in ASDEX after a modification of the divertors that allowed a larger (deuterium and impurity) backflow from the divertor chamber. The quality of IOC depended crucially on the wall conditions, i.e. IOC was best for uncovered stainless steels walls and vanished with boronization. Furthermore, IOC was found only in deuterium discharges. These circumstances led to the idea that IOC correlates with the content of light impurities in the plasma. To substantiate this working hypothesis, we present observations in deuterium discharges with boronized wall conditions into which various impurities have been injected with the aim to induce IOC conditions. Firstly, the plasma behaviour in typical IOC discharges is characterized. Secondly, injection experiments with the low-Z impurities nitrogen and neon as well as with the high-Z impurities argon and krypton are discussed. Then, we concentrate on optimized neon puffing that yields the best confinement results which are similar to IOC conditions. Finally, these results are compared with eperiments in other tokamaks and some conclusions are drawn about the effects of the impurity puffing on both, the central and the edge plasma behaviour. (orig.)
Effects of low-Z and high-Z impurities on divertor detachment and plasma confinement
Directory of Open Access Journals (Sweden)
H.Q. Wang
2017-08-01
Full Text Available The impurity-seeded detached divertor is essential for heat exhaust in ITER and other reactor-relevant devices. Dedicated experiments with injection of N2, Ne and Ar have been performed in DIII-D to assess the impact of the different impurities on divertor detachment and confinement. Seeding with N2, Ne and Ar all promote divertor detachment, greatly reducing heat flux near the strike point. The upstream plasma density at the onset of detachment decreases with increasing impurity-puffing flow rates. For all injected impurity species, the confinement and pedestal pressure are correlated with the impurity content and the ratio of separatrix loss power to the l-H transition threshold power. As the divertor plasma approaches detachment, the high-Z impurity seeding tends to degrade the core confinement owing to the increased core radiation. In particular, Ar injection with up to 50% of the injected power radiating in the core cools the pedestal and core plasmas, thus significantly degrading the confinement. As for Ne seeding, medium confinement with H98∼0.8 can be maintained during the detachment phase with the pedestal temperature being reduced by about 50%. In contrast, in the N2 seeded plasmas, radiation is predominately confined in the boundary plasma, which leads to less effect on the confinement and pedestal. In the case of strong N2 gas puffing, the confinement recovers during the detachment, from ∼20% reduction at the onset of the detachment to greater than unity comparable to that before the seeding. The core and pedestal temperatures feature a reduction of 30% from the initial attached phase and remain nearly constant during the detachment phase. The improvement in confinement appears to arise from the increase in pedestal and core density despite the temperature reduction.
Effect of impurities and ripple upon power regulation in self-sustained tokamaks
International Nuclear Information System (INIS)
Bromberg, L.; Cohn, D.R.
1981-01-01
Tokamak power reactors will likely operate in a self sustained heating mode where additional power losses are introduced to permit higher levels of alpha particle heating (and thus higher levels of total fusion power) at thermal equilibrium. Illustrative 0-dimensional calculations are made to assess requirements for power regulation of self sustained tokamak plasmas by the use of impurity radiation. Effects of impurities upon allowable fuel density and thermal stability are determined. Requirements are calculated for passive thermal stability control by temperature driven radial motion in the presence of ripple transport losses; it appears that stability might be attained over a relatively wide temperature range with a small amount of ripple transport loss. Requirements for power regulation by the use of ripple transport are also determined
Impurity-induced states in superconducting heterostructures
Liu, Dong E.; Rossi, Enrico; Lutchyn, Roman M.
2018-04-01
Heterostructures allow the realization of electronic states that are difficult to obtain in isolated uniform systems. Exemplary is the case of quasi-one-dimensional heterostructures formed by a superconductor and a semiconductor with spin-orbit coupling in which Majorana zero-energy modes can be realized. We study the effect of a single impurity on the energy spectrum of superconducting heterostructures. We find that the coupling between the superconductor and the semiconductor can strongly affect the impurity-induced states and may induce additional subgap bound states that are not present in isolated uniform superconductors. For the case of quasi-one-dimensional superconductor/semiconductor heterostructures we obtain the conditions for which the low-energy impurity-induced bound states appear.
Energy Technology Data Exchange (ETDEWEB)
El Ghazi, Haddou, E-mail: hadghazi@gmail.com [LPS, Faculty of Science, Dhar El Mehrez, BP 1796 Fes-Atlas (Morocco); Special Mathematics, CPGE My Youssef, Rabat (Morocco); Jorio, Anouar [LPS, Faculty of Science, Dhar El Mehrez, BP 1796 Fes-Atlas (Morocco)
2014-10-01
By means of a combination of Quantum Genetic Algorithm and Hartree–Fock–Roothaan method, the changes in linear, third-order nonlinear and total refractive index associated with intra-conduction band transition are investigated with and without shallow-donor impurity in wurtzite (In,Ga)N–GaN spherical quantum dot. For both cases with and without impurity, the calculation is performed within the framework of single band effective-mass and parabolic band approximations. Impurity's position and relaxation time effects are investigated. It is found that the modulation of the refractive index changes, suitable for good performance optical modulators and various infra-red optical device applications can be easily obtained by tailoring the relaxation time and the position of the impurity.
International Nuclear Information System (INIS)
El Ghazi, Haddou; Jorio, Anouar
2014-01-01
By means of a combination of Quantum Genetic Algorithm and Hartree–Fock–Roothaan method, the changes in linear, third-order nonlinear and total refractive index associated with intra-conduction band transition are investigated with and without shallow-donor impurity in wurtzite (In,Ga)N–GaN spherical quantum dot. For both cases with and without impurity, the calculation is performed within the framework of single band effective-mass and parabolic band approximations. Impurity's position and relaxation time effects are investigated. It is found that the modulation of the refractive index changes, suitable for good performance optical modulators and various infra-red optical device applications can be easily obtained by tailoring the relaxation time and the position of the impurity
[Impurity removal technology of Tongan injection in liquid preparation process].
Yang, Xu-fang; Wang, Xiu-hai; Bai, Wei-rong; Kang, Xiao-dong; Liu, Jun-chao; Wu, Yun; Xiao, Wei
2015-08-01
In order to effectively remove the invalid impurities in Tongan injection, optimize the optimal parameters of the impurity removal technology of liquid mixing process, in this paper, taking Tongan injection as the research object, with the contents of celandine alkali, and sinomenine, solids reduction efficiency, and related substances inspection as the evaluation indexes, the removal of impurities and related substances by the combined process of refrigeration, coction and activated carbon adsorption were investigated, the feasibility of the impurity removal method was definited and the process parameters were optimized. The optimized process parameters were as follows: refrigerated for 36 h, boiled for 15 min, activated carbon dosage of 0.3%, temperature 100 degrees C, adsorption time 10 min. It can effectively remove the tannin, and other impurities, thus ensure the quality and safety of products.
Nucleation of voids - the impurity effect
International Nuclear Information System (INIS)
Chen, I-W; Taiwo, A.
1984-01-01
Nucleation of voids under irradiation in multicomponent alloys remains an unsolved theoretical problem. Of particular interest are the effects of nonequilibrium solute segregation phenomena on the critical nucleus and the nucleation rate. The resolution of the multicomponent nucleation in a dissipative system also has broader implication to the field of irreversible thermodynamics. The present paper describes a recent study of solute segregation effects in void nucleation. We begin with a thermodynamic model for a nonequilibrium void with interfacial segregation. The thermodynamic model is coupled with kinetic considerations of solute/solvent diffusion under a bias, which is itself related to segregation by the coating effect, to assess the stability of void embryos. To determine nucleation rate, we develop a novel technique by extending the most probable path method in statistical mechanics for nonequilibrium steady state to simulate large fluctuation with nonlinear dissipation. The path of nucleation is determined by solving an analogous problem on particle trajectory in classical dynamics. The results of both the stability analysis and the fluctuation analysis establish the paramount significance of the impurity effect via the mechanism of nonequilibrium segregation. We conclude that over-segregation is probably the most general cause for the apparently low nucleation barriers that are responsible for nearly ubiquitous occurrence of void swelling in common metals
Impurity transport in the Wendelstein VII-A stellarator
International Nuclear Information System (INIS)
1985-01-01
Impurity radiation losses in net-current-free neutral-beam-heated plasmas in the Wendelstein W VII-A stellarator are the combined effect of particularly strong impurity sources and improved particle confinement as compared with ohmically heated tokamak-like plasma discharges. Experiments are described and conclusions are drawn about the impurity species, their origin and their transport behaviour. The impurity transport is modelled by a 1-D impurity transport and radiation code. The evolution of the total radiation in time and space deduced from soft-X-ray and bolometer measurements can be fairly well simulated by the code. Experimentally, oxygen was found to make the main contribution to the radiation losses. In the calculations, an influx of cold oxygen desorbed from the walls of the order of 10 13 -10 14 cm -2 .s -1 and a rate of fast injected oxygen corresponding to a 1% impurity content of the neutral beams in combination with neoclassical impurity transport leads to quantitative agreement between the simulation and the observed radiation. The transport of A1 trace impurities injected by the laser blow-off technique was experimentally studied by soft-X-ray measurements using a differential method allowing extraction of the time evolution of A1 XII, XIII radial profiles. These are compared with code predictions, together with additional spectroscopic measurements. The main features of the impurity transport are consistent with neoclassical predictions, which explain particularly the central impurity accumulation. Some details, however, seem to require additional 'anomalous' transport. Such an enhancement is correlated with distortions of the magnetic configuration around resonant magnetic surfaces. (author)
International Nuclear Information System (INIS)
Karimi, M.J.; Rezaei, G.; Nazari, M.
2014-01-01
Based on the effective mass and parabolic one band approximations, simultaneous effects of the geometrical size, hydrogenic impurity, hydrostatic pressure, and temperature on the intersubband optical absorption coefficients and refractive index changes in multilayered spherical quantum dots are studied. Energy eigenvalues and eigenvectors are calculated using the fourth-order Runge–Kutta method and optical properties are obtained using the compact density matrix approach. The results indicate that the hydrogenic impurity, hydrostatic pressure, temperature and geometrical parameters such as the well and barrier widths have a great influence on the linear, the third-order nonlinear and the total optical absorption coefficients and refractive index changes. -- Highlights: • Hydrogenic impurity effects on the optical properties of a MSQD are investigated. • Hydrostatic pressure and temperature effects are also studied. • Hydrogenic impurity has a great influence on the linear and nonlinear ACs and RICs. • Hydrostatic pressure and temperature change the linear and nonlinear ACs and RICs
Striped morphologies induced by magnetic impurities in d-wave superconductors
International Nuclear Information System (INIS)
Zuo Xianjun
2011-01-01
Research Highlights: → We investigate striped morphologies induced by magnetic impurities in d-wave superconductors (DSCs). → For the single-impurity and two-impurity cases, modulated checkerboard pattern and stripe-like structures are induced. → When more magnetic impurities are inserted, more complex modulated structures could be induced, including rectilinear and right-angled stripes and quantum-corral-like structures. → Impurities could induce complex striped morphologies in DSCs. - Abstract: We study striped morphologies induced by magnetic impurities in d-wave superconductors (DSCs) near optimal doping by self-consistently solving the Bogoliubov-de Gennes equations based on the t - t' - U - V model. For the single-impurity case, it is found that the stable ground state is a modulated checkerboard pattern. For the two-impurity case, the stripe-like structures in order parameters are induced due to the impurity-pinning effect. The modulations of DSC and charge orders share the same period of four lattice constants (4a), which is half the period of modulations in the coexisting spin order. Interestingly, when three or more impurities are inserted, the impurities could induce more complex striped morphologies due to quantum interference. Further experiments of magnetic impurity substitution in DSCs are expected to check these results.
Hankiewicz, Ewelina M.; Culcer, Dimitrie
2017-01-01
Topological materials have attracted considerable experimental and theoretical attention. They exhibit strong spin-orbit coupling both in the band structure (intrinsic) and in the impurity potentials (extrinsic), although the latter is often neglected. In this work, we discuss weak localization and antilocalization of massless Dirac fermions in topological insulators and massive Dirac fermions in Weyl semimetal thin films, taking into account both intrinsic and extrinsic spin-orbit interactions. The physics is governed by the complex interplay of the chiral spin texture, quasiparticle mass, and scalar and spin-orbit scattering. We demonstrate that terms linear in the extrinsic spin-orbit scattering are generally present in the Bloch and momentum relaxation times in all topological materials, and the correction to the diffusion constant is linear in the strength of the extrinsic spin-orbit. In topological insulators, which have zero quasiparticle mass, the terms linear in the impurity spin-orbit coupling lead to an observable density dependence in the weak antilocalization correction. They produce substantial qualitative modifications to the magnetoconductivity, differing greatly from the conventional Hikami-Larkin-Nagaoka formula traditionally used in experimental fits, which predicts a crossover from weak localization to antilocalization as a function of the extrinsic spin-orbit strength. In contrast, our analysis reveals that topological insulators always exhibit weak antilocalization. In Weyl semimetal thin films having intermediate to large values of the quasiparticle mass, we show that extrinsic spin-orbit scattering strongly affects the boundary of the weak localization to antilocalization transition. We produce a complete phase diagram for this transition as a function of the mass and spin-orbit scattering strength. Throughout the paper, we discuss implications for experimental work, and, at the end, we provide a brief comparison with transition metal
Striped morphologies induced by magnetic impurities in d-wave superconductors
Zuo, Xian-Jun
2011-05-01
We study striped morphologies induced by magnetic impurities in d-wave superconductors (DSCs) near optimal doping by self-consistently solving the Bogoliubov-de Gennes equations based on the t - t‧ - U - V model. For the single-impurity case, it is found that the stable ground state is a modulated checkerboard pattern. For the two-impurity case, the stripe-like structures in order parameters are induced due to the impurity-pinning effect. The modulations of DSC and charge orders share the same period of four lattice constants (4 a), which is half the period of modulations in the coexisting spin order. Interestingly, when three or more impurities are inserted, the impurities could induce more complex striped morphologies due to quantum interference. Further experiments of magnetic impurity substitution in DSCs are expected to check these results.
Directory of Open Access Journals (Sweden)
Stanislaw Han
2013-01-01
Full Text Available In the course of research and development of a new pharmaceutical formulation of azelaic acid in the liposomal form, we developed a rapid and accurate method for the detection of impurities using high-performance liquid chromatography. A chromatographic column from Merck (Purospher Star RP C18, 250–4 mm (5 μm was used in the assay, and the mobile phase gradient consisted of three phases: A—methanol : water (5 : 95 + 1.5% (v/v acetic acid; B—water : methanol (5 : 95 + 1.5% (v/v acetic acid; and C—chloroform. Detection of the impurities and the active substance was performed by an evaporative light-scattering detector. The method was validated for selectivity, system precision, method precision, limit of detection, and response rates. The proposed method can be used to detect impurities in the liposomal formulation of azelaic acid. The method enables separation of azelaic acid from the identified and unidentified impurities and from the excipients used in the drug form.
Simulation of multiple scattering background in heavy ion backscattering spectrometry
International Nuclear Information System (INIS)
Li, M.M.; O'Connor, D.J.
1999-01-01
With the development of heavy ion backscattering spectrometry (HIBS) for the detection of trace quantities of heavy-atom impurities on Si surfaces, it is necessary to quantify the multiple scattering contribution to the spectral background. In the present work, the Monte Carlo computer simulation program TRIM has been used to study the backscattering spectrum and the multiple scattering background features for heavy ions C, Ne, Si, Ar and Kr impinging on four types of targets: (1) a single ultra-thin (free standing) Au film of 10 A thickness, (2) a 10 A Au film on a 50 A Si surface, (3) a 10 A Au film on an Si substrate (10 000 A), and (4) a thick target (10 000 A) of pure Si. The ratio of the signal from the Au thin layer to the background due to multiple scattering has been derived by fitting the simulation results. From the simulation results, it is found that the Au film contributes to the background which the Si plays a role in developing due to the ion's multiple scattering in the substrate. Such a background is generated neither by only the Au thin layer nor by the pure Si substrate independently. The corresponding mechanism of multiple scattering in the target can be explained as one large-angle scattering in the Au layer and subsequently several small angle scatterings in the substrate. This study allows an appropriate choice of incident beam species and energy range when the HIBS is utilized to analyse low level impurities in Si wafers
Integrable quantum impurity models
International Nuclear Information System (INIS)
Eckle, H.P.
1998-01-01
By modifying some of the local L operators of the algebraic form of the Bethe Ansatz inhomogeneous one dimensional quantum lattice models can be constructed. This fact has recently attracted new attention, the inhomogeneities being interpreted as local impurities. The Hamiltonians of the so constructed one-dimensional quantum models have a nearest neighbour structure except in the vicinity of the local impurities which involve three-site interactions. The pertinent feature of these models is the absence of backscattering at the impurities: the impurities are transparent. (Copyright (1998) World Scientific Publishing Co. Pte. Ltd)
International Nuclear Information System (INIS)
Chen Zuhui; Jie Binbin; Sah Chihtang
2010-01-01
Impurity deionization on the direct-current current-voltage characteristics from electron-hole recombination (R-DCIV) at SiO 2 /Si interface traps in MOS transistors is analyzed using the steady-state Shockley-Read-Hall recombination kinetics and the Fermi distributions for electrons and holes. Insignificant distortion is observed over 90% of the bell-shaped R-DCIV curves centered at their peaks when impurity deionization is excluded in the theory. This is due to negligible impurity deionization because of the much lower electron and hole concentrations at the interface than the impurity concentration in the 90% range. (invited papers)
Electrical manipulation of dynamic magnetic impurity and spin texture of helical Dirac fermions
Wang, Rui-Qiang; Zhong, Min; Zheng, Shi-Han; Yang, Mou; Wang, Guang-Hui
2016-05-01
We have theoretically investigated the spin inelastic scattering of helical electrons off a high-spin nanomagnet absorbed on a topological surface. The nanomagnet is treated as a dynamic quantum spin and driven by the spin transfer torque effect. We proposed a mechanism to electrically manipulate the spin texture of helical Dirac fermions rather than by an external magnetic field. By tuning the bias voltage and the direction of impurity magnetization, we present rich patterns of spin texture, from which important fingerprints exclusively associated with the spin helical feature are obtained. Furthermore, it is found that the nonmagnetic potential can create the resonance state in the spin density with different physics as the previously reported resonance of charge density.
Effective Kα x-ray excitation rates for plasma impurity measurements
International Nuclear Information System (INIS)
Hill, K.W.; Bitter, M.; von Goeler, S.; Hiroe, S.; Hulse, R.; Ramsey, A.T.; Sesnic, S.; Shimada, M.; Stratton, B.C.
1986-06-01
Metal impurity concentrations are measured by the Pulse-Height-Analyzer (PHA) diagnostic from Kα x-ray peak intensities by use of an averaged excitation rate . Low-Z impurity concentrations are inferred from the continuum enhancement (relative to a pure plasma) minus the enhancement due to metals. Since the PHA does not resolve lines from different charge states, is a weighted sum of rates; coronal equilibrium is usually assumed. The used earlier omitted the intercombination and forbidden lines from the dominant helium-like state. The result was an overestimate of metals and an underestimate of low-Z impurities in cases where metals were significant. Improved values of using recent calculations for H-, He-, and Li-like Fe range from 10 to 50% larger than the earlier rates and yield metal concentrations in better agreement with those from VUV spectroscopy
Effect of ionization of impurity centres by electric field on the conductivity of superlattice
International Nuclear Information System (INIS)
Mensah, S.Y.; Allotey, F.K.A.; Clement, A.
1994-11-01
The study of the effect of ionization of impurity centres by electric field E 0 on the conductivity of superlattice (SL) has been studied theoretically. It is observed that as the field E 0 increases the current rises reaches a maximum then falls off i.e. show a negative differential conductivity (NDC). Further increase in E 0 leads to an exponential rise of the current. This occur around E 0 = 3 x 10 4 V cm -1 . Hence the current density field shows a ''N'' shape characteristics as against the ''n'' shape characteristics in the absence of impurity. (author). 23 refs, 3 figs
Impurity contamination effects on the interaction of Li and Sn Films on W (poly)
Fasoranti, Oluseyi; Koel, Bruce
2016-10-01
Plasma-solid interactions under fusion divertor conditions lead to continuous material erosion and may result in performance degradation of the plasma-facing components. Liquid metals such as Li and Sn may help to circumvent this issue due to their ability for self-recovery and heat-flux management. This has driven interest in understanding plasma-liquid metal interactions. We have shown in our lab that surface science experiments can examine discrete aspects of plasma-surface interactions by enabling clean and controlled deposition of metal films. We will review our recent results on the thermal stability of ultrathin Li and Sn films on a polycrystalline W surface using surface diagnostic methods such as Temperature Programmed Desorption, Auger Electron Spectroscopy, and Ion Scattering Spectroscopy. These studies examine Li-W and Sn-W interfaces and investigate the impact of impurities. We will discuss relevant issues such as the differences in oxygen uptake between solid and liquid lithium films and the effects of post-oxidation, as well as pre-adsorbed surface oxygen and carbon, on the thermal stability of these films. We plan to present additional studies of deuterium ion uptake and retention on Li and Sn films. Support was provided through U.S. Department of Energy, Office of Science/Fusion Energy Sciences under Award Number DE-SC0012890.
Thermal Conductivity of Nanotubes: Effects of Chirality and Isotope Impurity
Gang, Zhang; Li, Baowen
2005-01-01
We study the dependence of thermal conductivity of single walled nanotubes (SWNT) on chirality and isotope impurity by nonequilibrium molecular dynamics method with accurate potentials. It is found that, contrary to electronic conductivity, the thermal conductivity is insensitive to the chirality. The isotope impurity, however, can reduce the thermal conductivity up to 60% and change the temperature dependence behavior. We also study the dependence of thermal conductivity on tube length for t...
Interpretation of plasma impurity deposition probes. Analytic approximation
Stangeby, P. C.
1987-10-01
Insertion of a probe into the plasma induces a high speed flow of the hydrogenic plasma to the probe which, by friction, accelerates the impurity ions to velocities approaching the hydrogenic ion acoustic speed, i.e., higher than the impurity ion thermal speed. A simple analytic theory based on this effect provides a relation between impurity fluxes to the probe Γimp and the undisturbed impurity ion density nimp, with the hydrogenic temperature and density as input parameters. Probe size also influences the collection process and large probes are found to attract a higher flux density than small probes in the same plasma. The quantity actually measured, cimp, the impurity atom surface density (m-2) net-deposited on the probe, is related to Γimp and thus to nimp by taking into account the partial removal of deposited material caused by sputtering and the redeposition process.
Ul Haq, Bakhtiar
2014-08-01
Stimulation of novel features in ZnO by impurity electrons has attracted a remarkable attention of researchers from the past decade. Consequently, ZnO has found several applications in the field of spintronics and optoelectronics. We report, the effect of 3d-(V, Ag) electrons on the properties of ZnO in stable wurtzite (WZ) and metastable zincblende (ZB) phase using the density functional theory. Introduction of V-3d electrons was found to induce a high magnetic moment value of 5.22 in WZ and 3.26 in the ZB phase, and moreover transform the semiconductor character of ZnO into a metallic nature. Ag-d electrons result in the p-type half-metallic nature of ZnO with a weak ferromagnetic background. Our calculations for ground-state magnetic ordering show that ZnO in the presence of impure 3d-(V, Ag) electrons favors ferromagnetic ordering, and obey the double exchange mechanism. However, impurity atoms have very marginal effect on the lattice parameters of ZnO, thereby exposing its potential to absorb the impurity atoms in high concentration. © 2014 Elsevier B.V. All rights reserved.
Xu, H.; Wen, C.; Liu, H.; Li, Z. P.; Shen, W. Z.
2013-03-01
We have fully investigated the correlation of microstructure properties and oxygen impurities in hydrogenated nanocrystalline silicon photovoltaic films. The achievement has been realized through a series of different hydrogen dilution ratio treatment by plasma enhanced chemical vapor deposition system. Raman scattering, x-ray diffraction, and ultraviolet-visible transmission techniques have been employed to characterize the physical structural characterization and to elucidate the structure evolution. The bonding configuration of the oxygen impurities was investigated by x-ray photoelectron spectroscopy and the Si-O stretching mode of infrared-transmission, indicating that the films were well oxidized in SiO2 form. Based on the consistence between the proposed structure factor and the oxygen content, we have demonstrated that there are two dominant disordered structure regions closely related to the post-oxidation contamination: plate-like configuration and clustered microvoids.
Dobre, M.; Peruzzi, A.; Kalemci, M.; Van Geel, J.; Maeck, M.; Uytun, A.
2018-05-01
Recent international comparisons showed that there is still room for improvement in triple point of water (TPW) realization uncertainty. Large groups of cells manufactured, maintained and measured in similar conditions still show a spread in the realized TPW temperature that is larger than the best measurement uncertainties (25 µK). One cause is the time-dependent concentration of dissolved impurities in water. The origin of such impurities is the glass/quartz envelope dissolution during a cell lifetime. The effect is a difference in the triple point temperature proportional to the impurities concentration. In order to measure this temperature difference and to investigate the effect of different types of impurities, we manufactured doped cells with different concentrations of silicon (Si), boron (B), sodium (Na) and potassium (K), the glass main chemical components. To identify any influence of the filling process, two completely independent manufacturing procedures were followed in two different laboratories, both national metrology institutes (VSL, Netherlands and UME, Turkey). Cells glass and filling water were also different while the doping materials were identical. Measuring the temperature difference as a function of the liquid fraction is a method to obtain information about impurities concentrations in TPW. Only cells doped with 1 µmol·mol-1 B, Na and K proved to be suitable for measurements at different liquid fractions. We present here the results with related uncertainties and discuss the critical points in this experimental approach.
Using 3.05 MeV resonance for determination of oxygen impurities
International Nuclear Information System (INIS)
Burkova, I.E.; Polyanskij, V.N.; Yatis, A.A.
1983-01-01
The method of determining oxygen impurities behind thin films using the isolated resonance in the 16 O(α, α) 16 O reaction at E=3.048 MeV with the width GITA approximately 20 keV, is considered. Cross section in resonance is σsUb(R) = 0.95 b apd it increases cross section of Rutherford scattering by the factor of 25. The conclusion is made on the possibility of using 3.048 MeV resonance when investigating Me-Si film structures
Effect of limiter recycling on measured poloidal impurity emission profiles in Tore Supra
International Nuclear Information System (INIS)
Hogan, J.; DeMichelis, C.; Monier-Garbet, P.; Becoulet, M.; Bush, C.; Ghendrih, P.; Guirlet, R.; Hess, W.; Mattioli, M.; Vallet, J.C.
2001-01-01
Poloidal impurity emission profiles measured with the Tore Supra grazing incidence duochromator exhibit a complex spatial structure during ergodic divertor operation with an outboard poloidal guard limiter. As previous measurements with inboard-wall limited plasmas have shown that these profiles give important information about the ergodic field structure, so the contribution of local neon recycling from the limiter-induced plume has been modeled. This permits a discrimination of edge and core transport effects. The BBQ 3D scrape-off layer code calculates the asymmetric contribution to the emission and MIST 1D simulation gives the symmetric part. A systematic increase is observed in the decay rate of neon emission after injection as the ergodic divertor strength is increased. The calculations permit identification of the limiter plume contribution to the profile structure, and, with this identification, the effect of the divertor to enhance impurity efflux can be seen from the decay data
Merker, L.; Costi, T. A.
2012-08-01
We introduce a method to obtain the specific heat of quantum impurity models via a direct calculation of the impurity internal energy requiring only the evaluation of local quantities within a single numerical renormalization group (NRG) calculation for the total system. For the Anderson impurity model we show that the impurity internal energy can be expressed as a sum of purely local static correlation functions and a term that involves also the impurity Green function. The temperature dependence of the latter can be neglected in many cases, thereby allowing the impurity specific heat Cimp to be calculated accurately from local static correlation functions; specifically via Cimp=(∂Eionic)/(∂T)+(1)/(2)(∂Ehyb)/(∂T), where Eionic and Ehyb are the energies of the (embedded) impurity and the hybridization energy, respectively. The term involving the Green function can also be evaluated in cases where its temperature dependence is non-negligible, adding an extra term to Cimp. For the nondegenerate Anderson impurity model, we show by comparison with exact Bethe ansatz calculations that the results recover accurately both the Kondo induced peak in the specific heat at low temperatures as well as the high-temperature peak due to the resonant level. The approach applies to multiorbital and multichannel Anderson impurity models with arbitrary local Coulomb interactions. An application to the Ohmic two-state system and the anisotropic Kondo model is also given, with comparisons to Bethe ansatz calculations. The approach could also be of interest within other impurity solvers, for example, within quantum Monte Carlo techniques.
Directory of Open Access Journals (Sweden)
Xuan-Ting Ji
2017-10-01
Full Text Available Recent experiments on Weyl semimetals reveal that charged impurities may play an important role. We use a screened Coulomb disorder to model the charged impurities, and study the magneto-transport in a two-node Weyl semimetal. It is found that when the external magnetic field is applied parallel to the electric field, the calculated longitudinal magnetoconductivity shows positive in the magnetic field, which is just the negative longitudinal magnetoresistivity (LMR observed in experiments. When the two fields are perpendicular to each other, the transverse magnetoconductivities are measured. It is found that the longitudinal (transverse magnetoconductivity is suppressed (enhanced sensitively with increasing the screening length. This feature makes it hardly to observe the negative LMR in Weyl semimetals experimentally owing to a small screening length. Our findings gain insight into further understanding on recently actively debated magneto-transport behaviors in Weyl semimetals. Furthermore we studied the relative weight of the inter-valley scattering and the intra-valley scattering. It shows that the former is as important as the latter and even dominates in the case of strong magnetic fields and small screening length. We emphasize that the discussions on inter-valley scattering is out of the realm of one-node model which has been studied.
Quantum one dimensional spin systems. Disorder and impurities
International Nuclear Information System (INIS)
Brunel, V.
1999-01-01
This thesis presents three studies that are respectively the spin-1 disordered chain, the non magnetic impurities in the spin-1/2 chain and the reaction-diffusion process. The spin-1 chain of weak disorder is performed by the Abelian bosonization and the renormalization group. This allows to take into account the competition between the disorder and the interactions and predicts the effects of various spin-1 anisotropy chain phases under many different disorders. A second work uses the non magnetic impurities as local probes of the correlations in the spin-1/2 chain. When the impurities are connected to the chain boundary, the author predicts a temperature dependence of the relaxation rate (1/T) of the nuclear spin impurities, different from the case of these impurities connected to the whole chain. The last work deals with one dimensional reaction-diffusion problem. The Jordan-Wigner transformation allows to consider a fermionic field theory that critical exponents follow from the renormalization group. (A.L.B.)
Scattering of light at the growing solid-melt interface
International Nuclear Information System (INIS)
Gontijo, I.
1987-12-01
The scattering of light at the growing solid-melt interface of biphenyl and naphthalene was studied using the Photon Correlation Spectroscopy technique. The origin of this light scattering remained without a satisfactory explanation since its discovery at the ice-water interface in 1978. Recently, a model based on the segregation of gaseous impurities at the interface and subsequent precipitation of microbubbles was proposed to explain this phenomenon. We report here the first experimental results that confirm the microbbubles hypothesis. (author)
Effect of biogenic fermentation impurities on lactic acid hydrogenation to propylene glycol.
Zhang, Zhigang; Jackson, James E; Miller, Dennis J
2008-09-01
The effect of residual impurities from glucose fermentation to lactic acid (LA) on subsequent ruthenium-catalyzed hydrogenation of LA to propylene glycol (PG) is examined. Whereas refined LA feed exhibits stable conversion to PG over carbon-supported ruthenium catalyst in a trickle bed reactor, partially refined LA from fermentation shows a steep decline in PG production over short (<40 h) reaction times followed by a further slow decay in performance. Addition of model impurities to refined LA has varying effects: organic acids, sugars, or inorganic salts have little effect on conversion; alanine, a model amino acid, results in a strong but reversible decline in conversion via competitive adsorption between alanine and LA on the Ru surface. The sulfur-containing amino acids cysteine and methionine irreversibly poison the catalyst for LA conversion. Addition of 0.1 wt% albumin as a model protein leads to slow decline in rate, consistent with pore plugging or combined pore plugging and poisoning of the Ru surface. This study points to the need for integrated design and operation of biological processes and chemical processes in the biorefinery in order to make efficient conversion schemes viable.
Quasibound states and transport characteristics of Au chains with a substitutional S impurity
International Nuclear Information System (INIS)
Wawrzyniak-Adamczewska, M; Kostyrko, T
2013-01-01
Electronic transport properties of short gold atom chains with a single sulfur impurity were studied using density functional theory. It is found that the role of the impurity atom in the transport properties is twofold. First, it acts as a scattering center in the dominating 6s-orbital transmission channel and generally leads to a decrease of the transmission function in a wide energy region around the Fermi level. Second, it gives rise to a quasibound state manifesting as a peak near the Fermi level both in the partial density of states as well as in the transmission function. Because of the hybridization of the sulfur 3p and gold 5d orbitals in its formation, the quasibound state moves locally upward in the gold 5d transmission channel and brings about an enhancement of the transmission function in a narrow energy region near the Fermi level. The height of the peak of the quasibound state in the transmission function depends significantly on the position of the impurity in the chain and its energy varies with the bias voltage. The current–voltage (I–V) characteristics become asymmetric with a departure of the impurity from the central position in the chain and they are nonlinear for small values of the voltage (V < 0.1 V). It is proposed that a careful analysis of the I–V characteristics or the voltage dependence of the differential conductance may be used for unambiguous location of the light impurity in experiments with gold chains. (paper)
Non-eikonal effects in high-energy scattering IV. Inelastic scattering
International Nuclear Information System (INIS)
Gurvitz, S.A.; Kok, L.P.; Rinat, A.S.
1978-01-01
Amplitudes of inelastically scattered high-energy projections were calculated. In the scattering on 12 C(Tsub(P)=1 GeV) sizeable non-eikonal corrections in diffraction extrema even for relatively small q 2 are demonstrated. At least part of the anomaly in the 3 - distribution may be due to these non-eikonal effects. (B.G.)
Induced Compton-scattering effects in radiation-transport approximations
International Nuclear Information System (INIS)
Gibson, D.R. Jr.
1982-02-01
The method of characteristics is used to solve radiation transport problems with induced Compton scattering effects included. The methods used to date have only addressed problems in which either induced Compton scattering is ignored, or problems in which linear scattering is ignored. Also, problems which include both induced Compton scattering and spatial effects have not been considered previously. The introduction of induced scattering into the radiation transport equation results in a quadratic nonlinearity. Methods are developed to solve problems in which both linear and nonlinear Compton scattering are important. Solutions to scattering problems are found for a variety of initial photon energy distributions
International Nuclear Information System (INIS)
Maneeratankul, S.; Tang, I.M.
1987-01-01
The decrease in the transition temperature and the jump in the specific heat at T/sub c/ of proximity effect sandwiches containing nonmagnetic Anderson impurities in the normal layer are studied. The effects of the resonant scattering by the impurities are treated in the same manner as that used by Kaiser in his study of the effects of resonant scattering on the properties of bulk superconductors. Numerical calculations of the decrease in T/sub c/ and the jump in the specific heat at T/sub c/ as a function of the thickness of the normal layer are presented
Energy Technology Data Exchange (ETDEWEB)
Cha, Gil Yong; Kim, Soon Young [RADCORE, Daejeon (Korea, Republic of); Lee, Jae Min [TUV Rheinland Korea, Seoul (Korea, Republic of); Kim, Yong Soo [Hanyang University, Seoul (Korea, Republic of)
2016-06-15
The neutron activation inventories in reactor vessel and its internals, and bio-shield of a PWR nuclear power plant were calculated to evaluate the effect of impurity elements contained in the structural materials on the activation inventory. Carbon steel is, in this work, used as the reactor vessel material, stainless steel as the reactor vessel internals, and ordinary concrete as the bio-shield. For stainless steel and carbon steel, one kind of impurity concentration was employed, and for ordinary concrete five kinds were employed in this study using MCNP5 and FISPACT for the calculation of neutron flux and activation inventory, respectively. As the results, specific activities for the cases with impurity elements were calculated to be more than twice than those for the cases without impurity elements in stainless and carbon steel. Especially, the specific activity for the concrete material with impurity elements was calculated to be 30 times higher than that without impurity. Neutron induced reactions and activation inventories in each material were also investigated, and it is noted that major radioactive nuclide in steel material is Co-60 from cobalt impurity element, and, in concrete material, Co-60 and Eu-152 from cobalt and europium impurity elements, respectively. The results of this study can be used for nuclear decommissioning plan during activation inventory assessment and regulation, and it is expected to be used as a reference in the design phase of nuclear power plant, considering the decommissioning of nuclear power plants or nuclear facilities.
A Calibration to Predict Concentrations of Impurities in Plutonium Oxide by Prompt Gamma Analysis
International Nuclear Information System (INIS)
Narlesky, J.E.; Kelly, E.J.; Foster, L.A.
2005-01-01
Prompt gamma (PG) analysis has been used to identify the presence of certain impurities in plutonium oxide, which has been stored in 3013 containers. A regression analysis was used to evaluate the trends between the count rates obtained from PG analysis and the concentration of the impurities in plutonium oxide samples measured by analytical chemistry techniques. The results of the analysis were used to obtain calibration curves, which may be used to predict the concentration of Al, Be, Cl, F, Mg, and Na in the 3013 containers. The scatter observed in the data resulted from several factors including sample geometry, error in sampling for chemical assay, statistical counting error, and intimacy of mixing of impurities and plutonium. Standards prepared by mixing plutonium oxide with CaF 2 , NaCl, and KCl show that intimacy mixing and sampling error have the largest influence on the results. Although these factors are difficult to control, the calibrations are expected to yield semiquantitative results that are sufficient for the purpose of ordering or ranking
Effects of Impurity on the Corrosion Behavior of Alloy 617 in the Helium Environment
International Nuclear Information System (INIS)
Jung, Sujin; Kim, Dong Jin; Lee, Gyeong Geun
2013-01-01
The helium coolant in the primary circuit inevitably includes minor impurities such as H 2 , CO, CH 4 , and H 2 O under operating condition. Material degradation is aggravated through oxidation, carburization, and decarburization under the impure helium environment. In this study, high-temperature corrosion tests were carried out at 850-950 .deg. C in the impure helium environment. The mass changes of the specimens were measured and the microstructures were analyzed quantitatively. In addition, all corrosion tests were conducted in the pure helium environment and the results were compared to the results under the impure helium. Alloy 617 specimens showed a parabolic oxidation behavior at all temperatures under the impure helium environment. All specimens had similar microstructure in the outer Cr-oxide layers, internal Al-oxides, and carbide-depleted zone. The weight increase of the corroded specimens in the pure helium was relatively reduced. Microstructure result, oxide layer and carbide depleted zone were hardly ever observed. The impurity in helium affected the corrosion behavior of Alloy 617 and may cause a decrease in the mechanical properties. Therefore, the control of minor impurities in VHTR helium is necessary for the application of Alloy 617 to the IHX material of a VHTR
Impurities block the alpha to omega martensitic transformation in titanium.
Hennig, Richard G; Trinkle, Dallas R; Bouchet, Johann; Srinivasan, Srivilliputhur G; Albers, Robert C; Wilkins, John W
2005-02-01
Impurities control phase stability and phase transformations in natural and man-made materials, from shape-memory alloys to steel to planetary cores. Experiments and empirical databases are still central to tuning the impurity effects. What is missing is a broad theoretical underpinning. Consider, for example, the titanium martensitic transformations: diffusionless structural transformations proceeding near the speed of sound. Pure titanium transforms from ductile alpha to brittle omega at 9 GPa, creating serious technological problems for beta-stabilized titanium alloys. Impurities in the titanium alloys A-70 and Ti-6Al-4V (wt%) suppress the transformation up to at least 35 GPa, increasing their technological utility as lightweight materials in aerospace applications. These and other empirical discoveries in technological materials call for broad theoretical understanding. Impurities pose two theoretical challenges: the effect on the relative phase stability, and the energy barrier of the transformation. Ab initio methods calculate both changes due to impurities. We show that interstitial oxygen, nitrogen and carbon retard the transformation whereas substitutional aluminium and vanadium influence the transformation by changing the d-electron concentration. The resulting microscopic picture explains the suppression of the transformation in commercial A-70 and Ti-6Al-4V alloys. In general, the effect of impurities on relative energies and energy barriers is central to understanding structural phase transformations.
Impurity solitons with quadratic nonlinearities
DEFF Research Database (Denmark)
Clausen, Carl A. Balslev; Torres, Juan P-; Torner, Lluis
1998-01-01
We fmd families of solitary waves mediated by parametric mixing in quadratic nonlinear media that are localized at point-defect impurities. Solitons localized at attractive impurities are found to be dynamically stable. It is shown that localization at the impurity modifies strongly the soliton...
Induced Compton scattering effects in radiation transport approximations
International Nuclear Information System (INIS)
Gibson, D.R. Jr.
1982-01-01
In this thesis the method of characteristics is used to solve radiation transport problems with induced Compton scattering effects included. The methods used to date have only addressed problems in which either induced Compton scattering is ignored, or problems in which linear scattering is ignored. Also, problems which include both induced Compton scattering and spatial effects have not been considered previously. The introduction of induced scattering into the radiation transport equation results in a quadratic nonlinearity. Methods are developed to solve problems in which both linear and nonlinear Compton scattering are important. Solutions to scattering problems are found for a variety of initial photon energy distributions
Dzhumanov, S.; Karimboev, E. X.
2014-07-01
In this paper, we show that the pseudogap in the excitation spectra of high-Tc cuprates together with the impurity phase and charge inhomogeneity plays key roles in determining the essential features of their anomalous specific heat properties observed above Tc. We consider the doped cuprate superconductor as a multi-carrier model system (which consists of intrinsic and extrinsic polarons and pre-formed bosonic Cooper pairs) and study the competing pseudogap and impurity effects on the normal-state electronic specific heat of high-Tc cuprates taking into account charge inhomogeneities. We argue that unconventional electron-phonon interactions are responsible for the precursor Cooper pairing in the polaronic band below a mean-field temperature T∗ and the existence of a pseudogap above Tc in the cuprates. The electronic specific heat Ce(T) of doped cuprates below T∗ is calculated taking into account three contributions coming from the excited components of Cooper pairs, the ideal Bose-gas of incoherent Cooper pairs and the unpaired carriers in the impurity band. Above T∗, two contributions to Ce(T) coming from the unpaired intrinsic and extrinsic polarons are calculated within the two-component degenerate Fermi-gas model. By comparing our results with the experimental Ce(T) data obtained for La- and Y-based cuprates, we find that the observed behaviors of Ce(T) (below and above T∗) are similar to the calculated results for Ce(T) and the BCS-type jumps of Ce(T) at T∗ may be depressed by the impurity effects and may become more or less pronounced BCS-type anomalies in Ce(T) .
Impurities in the atmospheres of towns and their effects upon vegetation
Energy Technology Data Exchange (ETDEWEB)
Ruston, A G; Crowther, C
1910-01-01
The atmospheric impurities in different parts of the city of Leeds have been investigated by collecting samples of rain for a period of twelve months (November 1907 to October 1908). Similar results are given of the rainfall at the Manor Farm, Garforth, about seven and a half miles due east of the main industrial quarter of Leeds. The samples were collected with funnels twelve inches in diameter, and were representative of the whole of the atmospheric impurities, both soluble and insoluble, whether actually brought down by the rain or deposited soluble and insoluble, whether actually brought down by the rain or deposited at other times. Further investigations have been made as to the influence of the suspended impurities upon the amount and intensity of the light penetrating the atmosphere at the different stations.
Effect of Impurities on the Josephson Current through Helical Metals: Exploiting a Neutrino Paradigm
Ghaemi, Pouyan; Nair, V. P.
2016-01-01
In this Letter we study the effect of time-reversal symmetric impurities on the Josephson supercurrent through two-dimensional helical metals such as on a topological insulator surface state. We show that, contrary to the usual superconducting-normal metal-superconducting junctions, the suppression of the supercurrent in the superconducting-helical metal-superconducting junction is mainly due to fluctuations of impurities in the junctions. Our results, which are a condensed matter realization of a part of the Mikheyev-Smirnov-Wolfenstein effect for neutrinos, show that the relationship between normal state conductance and the critical current of Josephson junctions is significantly modified for Josephson junctions on the surface of topological insulators. We also study the temperature dependence of the supercurrent and present a two fluid model which can explain some of the recent experimental results in Josephson junctions on the edge of topological insulators.
Spectroscopic Measurements of Impurity Spectra on the EAST Tokamak
International Nuclear Information System (INIS)
Fu Jia; Li Yingying; Shi Yuejiang; Wang Fudi; Zhang Wei; Lv Bo; Huang Juan; Wan Baonian; Zhou Qian
2012-01-01
Ultraviolet (UV) and visible impurity spectra (200∼750 nm) are commonly used to study plasma and wall interactions in magnetic fusion plasmas. Two optical multi-channel analysis (OMA) systems have been installed for the UV-visible spectrum measurement on EAST. These two OMA systems are both equipped with the Czerny-Turner (C-T) type spectrometer. The upper vacuum vessel and inner divertor baffle can be viewed simultaneously through two optical lenses. The OMA1 system is mainly used for multi-impurity lines radiation measurement. A 280 nm wavelength range can be covered by a 300 mm focal length spectrometer equipped with a 300 grooves/mm grating. The Dα/Hα line shapes can be resolved by the OMA2 system. The focal length is 750 mm. The spectral resolution can be up to 0.01 nm using a 1800 grooves/mm grating. The impurity behaviour and hydrogen ratio evolution after boroniztion, lithium coating, and siliconization are compared. Lithium coating has shown beneficial effects on the reduction of edge recycling and low Z impurity (C, O) influx. The impurity expelling effect of the divertor configuration is also briefly discussed through multi-channels observation of OMA1 system. (magnetically confined plasma)
Nakai, K.; Hamada, K.; Satoh, Y.; Yoshiie, T.
2011-01-01
The growth and shrinkage of interstitial clusters on {113} planes were investigated in electron irradiated Czochralski grown silicon (Cz-Si), floating-zone silicon (Fz-Si), and impurity-doped Fz-Si (HT-Fz-Si) using a high voltage electron microscope. In Fz-Si, {113} interstitial clusters were formed only near the beam incident surface after a long incubation period, and shrank on subsequent irradiation from the backside of the specimen. In Cz-Si and HT-Fz-Si, {113} interstitial clusters nucleated uniformly throughout the specimen without incubation, and began to shrink under prolonged irradiation at higher electron beam intensity. At lower beam intensity, however, the {113} interstitial cluster grew stably. These results demonstrate that the {113} interstitial cluster cannot grow without a continuous supply of impurities during electron irradiation. Detailed kinetics of {113} interstitial cluster growth and shrinkage in silicon, including the effects of impurities, are proposed. Then, experimental results are analyzed using rate equations based on these kinetics.
International Nuclear Information System (INIS)
Ivanov, S.N.; Kotelyanskij, I.M.; Medved', V.V.
1983-01-01
The experimental results of investigations of the influence of substitution impurities in the yttrium-aluminium garnet lattice on absorption of high-frequency acoustic waves are presented. It is shown that the phonon-impurity relaxation processses affect at most the wave absorption and have resonance character when the acoustic wave interacts with the thermal phonon group in the vicinity of the perturbed part of the phonon spectrum caused by the impurity. The differences of time values between inelastic and elastic thermal phonons relaxations determined from the data on longitudinal and shear waves in pure and impurity garnet crystals are discussed
Effects of impurities and magnetic divertors on high-temperature tokamaks
International Nuclear Information System (INIS)
Meade, D.M.; Furth, H.P.; Rutherford, P.H.; Seidl, F.G.P.; Duechs, D.F.
1974-10-01
A one-dimensional tokamak plasma transport code has been adapted to include impurity influx, stripping, radiation, and diffusion, as well as the usual processes of hydrogen plasma and heat transport, recycling at the boundary, and multigeneration charge-exchange. Neutral-beam heating, adiabatic compression, and divertor boundary conditions are included as optional features. Illustrative computations are given for present-day and next-generation tokamaks. The problems of impurity control are discussed, and two technical approaches are examined in greater detail: the transient cold-plasma shield, and the poloidal divertor. (auth)
Kondo Effect of U Impurities in Dilute (YU)2Zn17
Takagi, Shigeru; Suzuki, Hiroyuki; Anzai, Kousuke
2001-10-01
Extending previous work on single-site properties of U ions in (LaU)2Zn17, we have investigated, from ρ(T), χ(T) and Cp(T) on single crystals, (Y1-xUx)2Zn17 with x=0.025 and 0.050, which has almost the same unit-cell volume as an antiferromagnetic heavy-electron compound U2Zn17. Remarkable features in the dilute-impurity limit have been clarified, which include Kondo behavior of ρ(T), large and almost isotropic χimp(T), and strongly enhanced Cimp(T)/T with gigantic γimp=2.02 2.05 J/K2·mole-U as T→0 due to a low characteristic energy-scale of the system. It is shown that gross features of the data are explained in terms of the conventional Kondo effect in the presence of the crystal field with the U3+ \\varGamma6 doublet ground state. It is also shown that the variation of γ with the unit-cell volume in related systems is not explained as a volume effect on TK and that even the behavior of fictitious “paramagnetic” U2Zn17 is not described as a collection of U impurities in dilute (YU)2Zn17.
Impurity investigations in the boundary layer of the DITE tokamak
International Nuclear Information System (INIS)
McCracken, G.M.; Partridge, J.W.; Erents, S.K.; Sofield, C.J.; Ferguson, S.M.
1982-01-01
The results obtained in the present investigation show large fluctuations both during discharges and from one discharge to the next. The radial density gradient of impurities in the boundary is not large. It is clear that the density and in particular dn/dt can have a strong effect on the impurity level. However there are apparently a number of other factors causing changes in impurity level which have not been well controlled in the present experiments. Possibilities include flaking from the walls, and changes in the level of the light impurities, oxygen and carbon, in the discharges. (orig./RW)
Impurity dynamics in stellarator W7-AS plasmas
International Nuclear Information System (INIS)
Igitkhanov, Yuri; Beidler, Craig D.; Burhenn, Reiner; Polunovsky, Eduard; Yamazaki, Kozo
2006-01-01
Numerical efforts to understand the neoclassical transport of impurities in stellarator plasmas have been undertaken. The new code solves the radial continuity equations for each ionization stage of the impurity ions for given background plasma profiles and magnetic configuration. An analytic description of the neoclassical transport coefficients based on numerical results from the DKES (Drift Kinetic Equation Solver) code and monoenergetic Monte-Carlo calculation (C.D. Beidler et al., EPS 1994), is here applied for impurity transport coefficients. The transition between the different charge states due to the ionization and recombination in balance equation is described by using the ADAS (Atomic Data and Analysis Structure) database. The impurity behavior in some typical discharges from W7-AS with moderate (NC) and improved energy confinement (HDH) has been considered. It is shown that the spatial distribution results from the competition between the radial electric field and the thermal force (which together produce a convective flux), and the diffusive term, which flattens the radial impurity distribution. The impurity ions are localized at the radial position where the convective flux goes through zero. It is also shown that for typical stellarator discharges there is no pronounced temperature screening effect as in tokamak plasmas. (author)
Study of impurity effects on CFETR steady-state scenario by self-consistent integrated modeling
Shi, Nan; Chan, Vincent S.; Jian, Xiang; Li, Guoqiang; Chen, Jiale; Gao, Xiang; Shi, Shengyu; Kong, Defeng; Liu, Xiaoju; Mao, Shifeng; Xu, Guoliang
2017-12-01
Impurity effects on fusion performance of China fusion engineering test reactor (CFETR) due to extrinsic seeding are investigated. An integrated 1.5D modeling workflow evolves plasma equilibrium and all transport channels to steady state. The one modeling framework for integrated tasks framework is used to couple the transport solver, MHD equilibrium solver, and source and sink calculations. A self-consistent impurity profile constructed using a steady-state background plasma, which satisfies quasi-neutrality and true steady state, is presented for the first time. Studies are performed based on an optimized fully non-inductive scenario with varying concentrations of Argon (Ar) seeding. It is found that fusion performance improves before dropping off with increasing {{Z}\\text{eff}} , while the confinement remains at high level. Further analysis of transport for these plasmas shows that low-k ion temperature gradient modes dominate the turbulence. The decrease in linear growth rate and resultant fluxes of all channels with increasing {{Z}\\text{eff}} can be traced to impurity profile change by transport. The improvement in confinement levels off at higher {{Z}\\text{eff}} . Over the regime of study there is a competition between the suppressed transport and increasing radiation that leads to a peak in the fusion performance at {{Z}\\text{eff}} (~2.78 for CFETR). Extrinsic impurity seeding to control divertor heat load will need to be optimized around this value for best fusion performance.
Magnetic field effect on pentacene-doped sexithiophene diodes
Pham, Song-Toan; Fayolle, Marine; Ohto, Tatsuhiko; Tada, Hirokazu
2017-11-01
We studied the effect of impurities on the magnetoresistance of sexithiophene-based diodes using impedance spectroscopy. The impurities were introduced by doping pentacene molecules into a sexithiophene film through a co-evaporation process. The pentacene molecules act as charge-scattering centers, which trigger the negative magnetoresistance of the device. This makes it possible to tune the value of magnetoresistance from positive to negative by increasing the applied voltage. The beneficial properties induced by impurities suggest a potential route to integrate additional functions into organic devices.
Study by nuclear techniques of the impurity-defect interaction in implanted metals
International Nuclear Information System (INIS)
Thome, Lionel.
1978-01-01
The properties of out equilibrium alloys formed by impurity implantation are strongly influenced by radiation damage created during implantation. This work presents a study, via hyperfine interaction and lattice location experiments, of the impurity-defect interaction in ion implanted metals. When the impurity and defect concentrations in the implanted layer are small, i.e. when impurities are uniformly recoil implanted in the whole crystal volume following a nuclear reaction (Aq In experiments), the impurity interacts with its own damage cascade. In this case, a vacancy is found to be trapped by a fraction of impurities during an athermal process. The value of this fraction does not seem to depend critically on impurity and host. When the impurity and defect concentrations are such that defect cascades interact, i.e. when impurities are implanted with an isotope separator (Fe Yb experiments), the observed impurity-vacancy (or vacancy cluster) interactions depend then strongly on the nature of impurity and host. An empirical relation, which indicates the importance of elastic effects, has been found between the proportion of impurities interacting with defects and the difference between impurity and host atom radii. At implantation temperature such that vacancies are mobile, the impurity-defect interaction depends essentially on vacancy migration. A model based on chemical kinetics has been developed to account for the variation with temperature of measured quantities [fr
Low Z impurity transport in tokamaks
International Nuclear Information System (INIS)
Hawryluk, R.J.; Suckewer, S.; Hirshman, S.P.
1978-10-01
Low Z impurity transport in tokamaks was simulated with a one-dimensional impurity transport model including both neoclassical and anomalous transport. The neoclassical fluxes are due to collisions between the background plasma and impurity ions as well as collisions between the various ionization states. The evaluation of the neoclassical fluxes takes into account the different collisionality regimes of the background plasma and the impurity ions. A limiter scrapeoff model is used to define the boundary conditions for the impurity ions in the plasma periphery. In order to account for the spectroscopic measurements of power radiated by the lower ionization states, fluxes due to anomalous transport are included. The sensitivity of the results to uncertainties in rate coefficients and plasma parameters in the periphery are investigated. The implications of the transport model for spectroscopic evaluation of impurity concentrations, impurity fluxes, and radiated power from line emission measurements are discussed
Low-Z impurity transport in DIII-D - observations and implications
International Nuclear Information System (INIS)
Wade, M.R.; Houlberg, W.A.; Baylor, L.R.; West, W.P.; Baker, D.R.
2001-01-01
Impurity transport studies on DIII-D have revealed transport phenomena that are qualitatively consistent with that expected from turbulence transport theory in some cases and neoclassical transport theory in other cases. The transport model proposed here, which assumes that the total impurity transport is a linear sum of turbulence-driven transport and neoclassical transport, is shown to reproduce many of these observed features. This transport model is then applied to burn condition calculations, revealing that profile effects associated with neoclassical transport have a large effect on the maximum allowable impurity fraction in machines based on achieving neoclassical transport levels
The impurity transport in HT-6B tokamak
International Nuclear Information System (INIS)
Huang Rong; Xie Jikang; Li Linzhong; He Yexi; Wang Shuya; Deng Chuanbao; Li Guoxiang; Qiu Lijian
1992-06-01
The quasi-stationary profiles of the impurity ionization stages in HT-6B tokamak were determined by monitoring the VUV (vacuum ultraviolet) and visible line emissions from impurities. An impurity transport code was set up. The impurity transport coefficients and other parameters of impurities in that device were simulated and determined. From the measurement of impurity emission profiles and simulation analysis, it is concluded that the impurity confinement is improved and the impurity recycling is reduced by the slow magnetic compression. Some characteristics of impurity transport in that device are also discussed
Complex scattering dynamics and the quantum Hall effects
International Nuclear Information System (INIS)
Trugman, S.A.
1994-01-01
We review both classical and quantum potential scattering in two dimensions in a magnetic field, with applications to the quantum Hall effect. Classical scattering is complex, due to the approach of scattering states to an infinite number of dynamically bound states. Quantum scattering follows the classical behavior rather closely, exhibiting sharp resonances in place of the classical bound states. Extended scatterers provide a quantitative explanation for the breakdown of the QHE at a comparatively small Hall voltage as seen by Kawaji et al., and possibly for noise effects
Yavari, H.; Mokhtari, M.; Tamaddonpour, M.
2013-10-01
The combined effect of nonmagnetic and magnetic impurities on the spin susceptibility of a noncentrosymmetrical superconductor by considering a Cooper pairing model with a two-component order parameter composed of spin-singlet and spin-triplet pairing components is investigated. For clean superconductor CePt3Si, the low-temperature dependence (T →0) of spin susceptibility is linear which suggests that the gap function has line nodes, consistent with our gap model. We will show that in the presence of magnetic impurities the susceptibility does not vanish even in the absence of spin orbit coupling and in the region where the energy gap still is finite, and in the low concentration of magnetic impurities the spin susceptibility at zero temperature is proportional to impurity concentration.
Impurities of oxygen in silicon
International Nuclear Information System (INIS)
Gomes, V.M.S.
1985-01-01
The electronic structure of oxygen complex defects in silicon, using molecular cluster model with saturation by watson sphere into the formalism of Xα multiple scattering method is studied. A systematic study of the simulation of perfect silicon crystal and an analysis of the increasing of atom number in the clusters are done to choose the suitable cluster for the calculations. The divacancy in three charge states (Si:V 2 + , Si:V 2 0 , Si:V 2 - ), of the oxygen pair (Si:O 2 ) and the oxygen-vacancy pair (Si:O.V) neighbours in the silicon lattice, is studied. Distortions for the symmetry were included in the Si:V 2 + and Si:O 2 systems. The behavior of defect levels related to the cluster size of Si:V 2 0 and Si:O 2 systems, the insulated oxygen impurity of silicon in interstitial position (Si:O i ), and the complexes involving four oxygen atoms are analysed. (M.C.K.) [pt
Effect of heat treatment and impurity concentration on some mechanical properties V-15Cr-5Ti alloy
International Nuclear Information System (INIS)
Loomis, B.A.; Kestel, B.J.; Diercks, D.R.
1986-03-01
The effects of heat treatment and O, N, C, Si, and S impurity level on the yield strength, ductility, and fracture mode for specimens from four different heats of the V-15Cr-5Ti alloy are presented. The heat treatments for the alloy consisted of annealing as-rolled material for one hour at either 950, 1050, 1125, or 1200 0 C. The total oxygen, nitrogen, and carbon impurity concentration ranged from 400 to 1200 wppm. The Si concentration ranged from 300 to 1050 wppm, and the S concentration ranged from 440 to 1100 wppm. The yield strength and ductility for the alloy, regardless of impurity concentration, exhibited minimum and maximum values, respectively, for the 1125 0 C anneal. The primary mode of failure for the tensile specimens was transgranular fracture
Energy Technology Data Exchange (ETDEWEB)
Etzkorn, Markus; Eltschka, Matthias; Jaeck, Berthold; Topp, Andreas; Ast, Christian R. [Max-Planck-Institute for Solid State Research, 70569 Stuttgart (Germany); Kern, Klaus [Max-Planck-Institute for Solid State Research, 70569 Stuttgart (Germany); Ecole Polytechnique Federale de Lausanne, 1015 Lausanne (Switzerland)
2016-07-01
The interaction of a local magnetic impurity with a superconductor causes the formation of Yu-Shiba-Rusinov (YSR)states in the vicinity of the impurity. These have recently received increasing attention in the context of Majorana Fermions and other exotic states that might be created from the mutual interplay. YSR states have been extensively studied by scanning tunneling microscopy and so far have been discussed mainly in the limit of point scattering impurities. Here we present our investigations of the local properties of single magnetic Copper-Phthalocynane molecules on the (5x1) reconstructed, superconducting V(100) surface measured at 15 mK temperature. We find very intense YSR states with energies that depend on the precise absorbtion geometry of the molecule. At the same time we find no indication of a local suppression of the superconducting gap around the impurity. We follow the state evolution in real space for about 3 nm corresponding to about three orders of magnitude in spectral intensity. The spectra display rich structure with local variations in the electron-hole asymmetries. The observed intensity changes in the spectra can not be described on the basis of a single point like scattering potential.
Impurity gettering in semiconductors
Sopori, Bhushan L.
1995-01-01
A process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device. The process comprises hydrogenating the substrate or device at the back side thereof with sufficient intensity and for a time period sufficient to produce a damaged back side. Thereafter, the substrate or device is illuminated with electromagnetic radiation at an intensity and for a time period sufficient to cause the impurities to diffuse to the back side and alloy with a metal there present to form a contact and capture the impurities. The impurity gettering process also can function to simultaneously passivate defects within the substrate or device, with the defects likewise diffusing to the back side for simultaneous passivation. Simultaneously, substantially all hydrogen-induced damage on the back side of the substrate or device is likewise annihilated. Also taught is an alternate process comprising thermal treatment after hydrogenation of the substrate or device at a temperature of from about 500.degree. C. to about 700.degree. C. for a time period sufficient to cause the impurities to diffuse to the damaged back side thereof for subsequent capture by an alloying metal.
Directory of Open Access Journals (Sweden)
Samuel Simon Araya
2012-10-01
Full Text Available In this work the effects of reformate gas impurities on a H3PO4-doped polybenzimidazole (PBI membrane-based high temperature proton exchange membrane fuel cell (HT-PEMFC are studied. A unit cell assembly with a BASF Celtec®-P2100 high temperature membrane electrode assembly (MEA of 45 cm2 active surface area is investigated by means of impedance spectroscopy. The concentrations in the anode feed gas of all impurities, unconverted methanol-water vapor mixture, CO and CO2 were varied along with current density according to a multilevel factorial design of experiments. Results show that all the impurities degrade the performance, with CO being the most degrading agent and CO2 the least. The factorial analysis shows that there is interdependence among the effects of the different factors considered. This interdependence suggests, for example, that tolerances to concentrations of CO above 2% may be compromised by the presence in the anode feed of CO2. Methanol has a poisoning effect on the fuel cell at all the tested feed ratios, and the performance drop is found to be proportional to the amount of methanol in feed gas. The effects are more pronounced when other impurities are also present in the feed gas, especially at higher methanol concentrations.
Upper critical magnetic field of superconducting films with magnetic impurities
International Nuclear Information System (INIS)
Lemberger, T.R.
1978-01-01
The upper critical magnetic field, H/sub c2/(T), of In-Mn and Pb-Mn alloy films was measured. H/sub c2/ was determined from the resistance of the films. The results were compared with the theory of Fulde and Maki. This theory assumes that the electron-phonon coupling is weak, and that the interaction between the impurity spins and the conduction electron spins is weak. The theory predicts that the pair-breaking effect of the magnetic impurities is temperature-independent, and that the pair-breaking effects of the magnetic impurities and the applied magnetic field are additive. Furthermore, it predicts explicitly the temperature dependence of H/sub c2/. The temperature dependence of H/sub c2/ for the In-Mn alloy films is well described by the Fulde-Maki theory, despite the moderately strong electron-phonon coupling and the strong interaction between the impurity spins and the conduction electron spins. The temperature dependence of H/sub c2/ for the Pb-Mn alloy films is not well described by the Fulde-Maki theory, probably due to the strong electron-phonon coupling in Pb. However, even without a quantitatively correct theory, one can conclude from the Pb-Mn data that the pair-breaking effect of the magnetic impurities is temperature independent, and that the pair-breaking effects of the magnetic impurities and the applied magnetic field are additive. For some of the Pb-Mn alloy films, there was a region of positive curvature in H/sub c2/(T) near the zero-field transition temperature. This positive curvature is not understood
Effects of ECRH power and safety factor on laser blow-off injected impurity confinement in TCV
International Nuclear Information System (INIS)
Scavino, E; Bakos, J; Weisen, H
2004-01-01
Evidence from injection into the TCV device of laser ablated, non-recycling silicon impurities shows that the transport of impurities confinement can be remarkably different from that of energy. The ratio of impurity to energy confinement times ranges from near unity in Ohmic discharges to 5 in the presence of high power ECCD. In Ohmic discharges in deuterium, above a threshold of density and of safety factor near q 95 = 4.5, the impurity confinement time increases abruptly by a factor of 2 and is sometimes accompanied by indefinite retention of non-recycling impurities within the sawtooth mixing radius
The lineshape of inelastic neutron scattering in the relaxor ferroelectrics
International Nuclear Information System (INIS)
Ivanov, M.A.; Kozlovski, M.; Piesiewicz, T.; Stephanovich, V.A.; Weron, A.; Wymyslowski, A.
2005-01-01
The possibilities of theoretical and experimental investigations of relaxor ferroelectrics by inelastic neutron scattering method are considered. The simple model to description of the peculiarities of inelastic neutron scattering lineshapes in ferroelectric relaxors is suggested. The essence of this model is to consider the interaction of the phonon subsystem of relaxor ferroelectrics with the ensemble of defects and impurities. The modification of the Latin Hypercube Sampling (LHS) method is presented. The optimization of planning of experiment by the modified LHS method is considered [ru
Magnetic sheath effect on the gross and net erosion rates due to impurities
Mellet, N.; Pégourié, B.; Martin, C.; Gunn, J. P.; Bufferand, H.; Roubin, P.
2016-02-01
Simulations of impurity trajectories in deuterium plasmas in the vicinity of the surface are performed by taking into account the magnetic sheath in conditions relevant for ITER and WEST. We show that the magnetic sheath has a strong effect on the average impact angle of impurities in divertor conditions and that it can lead to an increase of ≈ 60% at the gross erosion maximum for neon (Ne+4) compared to the case when only the cyclotron motion is considered. The evaluation of the net erosion has been undertaken by retaining local redeposition of tungsten (W). We investigate how it is affected by the sheath magnetic potential profile. The largest effect is however observed when an energy distribution is considered. In this case the number of particles that manage to exit the sheath is larger as it is dominated by the more energetic particles. The comparison with other work is also discussed. The application to a scenario of the WEST project is finally performed, which exhibits a moderate, however non negligible, erosion of the plasma facing components.
Finite-temperature behavior of an impurity in the spin-1/2 XXZ chain
International Nuclear Information System (INIS)
Yahagi, Ryoko; Deguchi, Tetsuo; Sato, Jun
2014-01-01
We study the zero- and the finite-temperature behavior of the integrable spin-1/2 XXZ periodic chain with an impurity by the algebraic and thermal Bethe ansatz methods. We evaluate the local magnetization on the impurity site at zero temperature analytically and derive the impurity susceptibility exactly from it. In the graphs of the impurity specific heat versus temperature, we show how the impurity spin becomes more liberated from the bulk many-body effect as the exchange coupling between the impurity spin and other spins decreases and that at low temperature it couples strongly to them such as in the Kondo effect. Thus, we observe not only the crossover behavior from the high- to the low-temperature regime, but another from the N-site chain to the (N − 1)-site chain with a free impurity spin. We also show that the estimate of the Wilson ratio at a given low temperature is independent of the impurity parameter if its absolute value is small enough with respect to the temperature and the universality class is described by the XXZ anisotropy in terms of the dressed charge. (paper)
Study on impurity screening in stochastic magnetic boundary of the Large Helical Device
International Nuclear Information System (INIS)
Kobayashi, M.; Morita, S.; Feng, Y.
2008-10-01
The impurity transport characteristics in the scrape-off layer associated with a stochastic magnetic boundary of LHD are analyzed. The remnant islands with very small internal field line pitch in the stochastic region play a key role in reducing the impurity influx. The thermal force driven impurity influx is significantly suppressed when the perpendicular energy flux exceeds the parallel one inside the islands due to the small pitch. Application of the 3D edge transport code, EMC3-EIRENE, confirmed the impurity retention (screening) effect in the edge region. It is also found that the edge surface layers are the most effective region to retain (screen) impurities because of the flow acceleration and plasma cooling via short flux tubes. The carbon emission obtained in experiments is in good agreement with the modelling results, showing the impurity retention (screening) potential of the stochastic magnetic boundary. (author)
Low-Field Mobility and Galvanomagnetic Properties of Holes in Germanium with Phonon Scattering
DEFF Research Database (Denmark)
Lawætz, Peter
1968-01-01
acoustic scattering, no overall consistency is found between available galvanomagnetic data and deformation potentials derived directly from experiments on strained Ge. The discrepancies may be ascribed to ionized-impurity scattering, but at higher temperatures where optical phonon scattering is operative......A theoretical calculation of the low-field galvanomagnetic properties of holes in Ge has been carried out incorporating all relevant details of the band structure. The scattering is limited to acoustic and optical phonons and is described by the deformation potentials a, b, d, and d0. For pure......, the deviations are still appreciable. We are led to conclude that the deformation-potential theory of phonon scattering needs reconsideration, and a nontrivial correction is pointed out....
The Aharonov–Bohm effect in scattering theory
International Nuclear Information System (INIS)
Sitenko, Yu.A.; Vlasii, N.D.
2013-01-01
The Aharonov–Bohm effect is considered as a scattering event with nonrelativistic charged particles of the wavelength which is less than the transverse size of an impenetrable magnetic vortex. The quasiclassical WKB method is shown to be efficient in solving this scattering problem. We find that the scattering cross section consists of two terms, one describing the classical phenomenon of elastic reflection and another one describing the quantum phenomenon of diffraction; the Aharonov–Bohm effect is manifested as a fringe shift in the diffraction pattern. Both the classical and the quantum phenomena are independent of the choice of a boundary condition at the vortex edge, providing that probability is conserved. We show that a propagation of charged particles can be controlled by altering the flux of a magnetic vortex placed on their way. -- Highlights: •Aharonov–Bohm effect as a scattering event. •Impenetrable magnetic vortex of nonzero transverse size. •Scattering cross section is independent of a self-adjoint extension employed. •Classical phenomenon of elastic reflection and quantum phenomenon of diffraction. •Aharonov–Bohm effect as a fringe shift in the diffraction pattern
Effects of gas phase impurities on the topochemical-kinetic behaviour of uranium hydride development
International Nuclear Information System (INIS)
Bloch, J.; Brami, D.; Kremner, A.; Mintz, M.H.; Ben-Gurion Univ. of the Negev, Beersheba
1988-01-01
The hydriding kinetics of bulk uranium and U-0.1 wt.% Cr, in the presence of oxidizing gaseous impurities (oxygen and CO), were studied by combined rate measurements and metallographic examinations of partially reacted samples. The effect of the gaseous impurity (type and concentration) was examined metallographically, and the kinetic data were discussed in relation to these examinations. Below about 100 0 C the reaction of uranium with pure hydrogen consists of the following sequence of steps: (i) Surface nucleation; (ii) homogeneous growth (pitting); (iii) relatively fast lateral growth leading to the formation of a reaction front which penetrates into the sample at a constant rate. The effects of oxygen and CO on the hydriding kinetics were related to their abilities to block hydrogen penetration into the uranium. Thus, it was found that oxygen affects only the penetration through the oxide layer, whereas CO affects the penetration through both the oxide and hydride layers. (orig.)
International Nuclear Information System (INIS)
Nagata, A.; Ashida, H.; Okamoto, M.; Hirano, K.
1981-03-01
Two dimentional fluid simulation code ''TOPICS'' is developed for the STP-2, the shock heated screw pinch at Nagoya. It involves the effects of impurity ions and neutral atoms. In order to estimate the radiation losses, the impurity continuity equations with ionizations and recombinations are solved simultaneously with the plasma fluid equations. The results are compared with the coronal equilibrium model. It is found that the coronal equilibrium model underestimates the radiation losses from shock heated pinch plasmas in its initial dynamic phase. The present calculations including impurities and neutrals show the importance of the radiation losses from the plasma of the STP-2. Introducing the anomalous resistivity caused by the ion acoustic instability, the observed magnetic field penetration is explained fairly well. (author)
Quenching of overcompensated Kondo impurities via channel asymmetry
International Nuclear Information System (INIS)
Schlottmann, P.; Lee, K.
1996-01-01
We consider a spin-1/2 impurity interacting with conduction electrons in two different orbital channels via an isotropic spin exchange. The exchange is the same for both channels, but a crystalline field breaks the symmetry between the orbital channels. This corresponds to a splitting of the conduction electron Γ 8 into two doublets in the quadrupolar Kondo effect and to the application of an external magnetic field in the electron assisted tunneling of an atom in a double-well potential. We study the ground-state properties of the impurity as a function of the magnetic and crystalline fields. The crystalline field quenches the critical behavior of the overcompensated fixed point: The impurity ground state is a singlet. (orig.)
Purification of simple substances by distillation with impurity hydrothermal oxidation
International Nuclear Information System (INIS)
Kalashnik, O.N.; Nisel'son, L.A.
1987-01-01
A possibility of applying distillation method in water vapours for purification of simple substances from impurities is studied. Based on thermodynamic analysis of interaction processes in E-H 2 O system, conducted using a computer, it is as certained that SS, Se, Te, As, Cd, Hg can be purified from the majority of the impurities analysed by distillation in a water vapour flow. Behaviour of Zn, C, Ge, Al, Sb characteristic impurities under cadmium, arsenic and tellurium distillation is studied. Experiments on cadmium, arsenic and tellurium purification have confirmed, that distillation with hydrothermal oxidation of Zn, C, Ge impurities sometimes appears to be a more effective method as compared to distillation in a hydrogen flow
International Nuclear Information System (INIS)
Stuchbery, A.E.; Bezakova, E.
1998-01-01
Static magnetic hyperfine fields acting on impurities recoil-implanted into ferromagnetic hosts following heavy-ion induced reactions have been studied using the implantation perturbed angular correlation (IMPAC) technique to determine the magnetic moments of subnanosecond excited states in neutron-deficient nuclei. Problems, which in time-integral measurements cannot always be treated independently were studied and include: (i) corrections for the transient field effect, (ii) whether the hyperfine field is parallel to the applied field, (iii) whether the implanted nuclei all experience the same magnetic interaction, (iv) the time the static field takes to reach equilibrium after implantation. The focus here is on pre-equilibrium phenomena associated with the implantation process and the direction of the internal magnetic field at implanted impurities after equilibrium is reached. It was found that the internal field does become increasingly misaligned with respect to external field direction at fields below 0.08 T. This is due to the incomplete saturation of the foil and not to the microscopic effect as proposed by Aharoni
Energy Technology Data Exchange (ETDEWEB)
Correa, J. D. [Departamento de Ciencias Básicas, Universidad de Medellín, Medellín (Colombia); Mora-Ramos, M. E., E-mail: memora@uaem.mx [Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, CP 62209 Cuernavaca, Morelos (Mexico); Duque, C. A. [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia)
2014-06-07
We report a study on the optical absorption coefficient associated to hydrogenic impurity interstate transitions in zinc-blende GaN quantum wires of cylindrical shape taking into account the effects of externally applied static electric and magnetic fields. The electron states emerge within the effective mass approximation, via the exact diagonalization of the donor-impurity Hamiltonian with parabolic confinement and external field effects. The nonlinear optical absorption is calculated using a recently derived expression for the dielectric susceptibility, obtained via a nonperturbative solution of the density-matrix Bloch equation. Our results show that this treatment eliminates not only the intensity-dependent bleaching effect but also the change in sign of the nonlinear contribution due to the combined effect of asymmetric impurity location and the applied electric field.
Yang, Fann-Wei; Chen, Yu-Yu; Feng, Shih-Wei; Sun, Qian; Han, Jung
2016-12-01
In this study, effects of the thickness of a low temperature (LT) buffer and impurity incorporation on the characteristics of Nitrogen (N)-polar GaN are investigated. By using either a nitridation or thermal annealing step before the deposition of a LT buffer, three N-polar GaN samples with different thicknesses of LT buffer and different impurity incorporations are prepared. It is found that the sample with the thinnest LT buffer and a nitridation step proves to be the best in terms of a fewer impurity incorporations, strong PL intensity, fast mobility, small biaxial strain, and smooth surface. As the temperature increases at ~10 K, the apparent donor-acceptor-pair band is responsible for the decreasing integral intensity of the band-to-band emission peak. In addition, the thermal annealing of the sapphire substrates may cause more impurity incorporation around the HT-GaN/LT-GaN/sapphire interfacial regions, which in turn may result in a lower carrier mobility, larger biaxial strain, larger bandgap shift, and stronger yellow luminescence. By using a nitridation step, both a thinner LT buffer and less impurity incorporation are beneficial to obtaining a high quality N-polar GaN.
Spin relaxation through Kondo scattering in Cu/Py lateral spin valves
Batley, J. T.; Rosaond, M. C.; Ali, M.; Linfield, E. H.; Burnell, G.; Hickey, B. J.
Within non-magnetic metals it is reasonable to expect the Elliot-Yafet mechanism to govern spin-relaxation and thus the temperature dependence of the spin diffusion length might be inversely proportional to resistivity. However, in lateral spin valves, measurements have found that at low temperatures the spin diffusion length unexpectedly decreases. We have fabricated lateral spin valves from Cu with different concentrations of magnetic impurities. Through temperature dependent charge and spin transport measurements we present clear evidence linking the presence of the Kondo effect within Cu to the suppression of the spin diffusion length below 30 K. We have calculated the spin-relaxation rate and isolated the contribution from magnetic impurities. At very low temperatures electron-electron interactions play a more prominent role in the Kondo effect. Well below the Kondo temperature a strong-coupling regime exists, where the moments become screened and the magnetic dephasing rate is reduced. We also investigate the effect of this low temperature regime (>1 K) on a pure spin current. This work shows the dominant role of Kondo scattering, even in low concentrations of order 1 ppm, within pure spin transport.
International Nuclear Information System (INIS)
Posske, Thore Hagen
2016-01-01
Topological insulators are electronic phases that insulate in the bulk and accommodate a peculiar, metallic edge liquid with a spin-dependent dispersion. They are regarded to be of considerable future use in spintronics and for quantum computation. Besides determining the intrinsic properties of this rather novel electronic phase, considering its combination with well-known physical systems can generate genuinely new physics. In this thesis, we report on such combinations including topological insulators. Specifically, we analyze an attached Rashba impurity, a Kondo dot in the two channel setup, magnetic impurities on the surface of a strong three-dimensional topological insulator, the proximity coupling of the latter system to a superconductor, and hybrid systems consisting of a topological insulator and a semimetal. Let us summarize our primary results. Firstly, we determine an analytical formula for the Kondo cloud and describe its possible detection in current correlations far away from the Kondo region. We thereby rely on and extend the method of refermionizable points. Furthermore, we find a class of gapless topological superconductors and semimetals, which accommodate edge states that behave similarly to the ones of globally gapped topological phases. Unexpectedly, we also find edge states that change their chirality when affected by sufficiently strong disorder. We regard the presented research helpful in future classifications and applications of systems containing topological insulators, of which we propose some examples.
Energy Technology Data Exchange (ETDEWEB)
Posske, Thore Hagen
2016-02-26
Topological insulators are electronic phases that insulate in the bulk and accommodate a peculiar, metallic edge liquid with a spin-dependent dispersion. They are regarded to be of considerable future use in spintronics and for quantum computation. Besides determining the intrinsic properties of this rather novel electronic phase, considering its combination with well-known physical systems can generate genuinely new physics. In this thesis, we report on such combinations including topological insulators. Specifically, we analyze an attached Rashba impurity, a Kondo dot in the two channel setup, magnetic impurities on the surface of a strong three-dimensional topological insulator, the proximity coupling of the latter system to a superconductor, and hybrid systems consisting of a topological insulator and a semimetal. Let us summarize our primary results. Firstly, we determine an analytical formula for the Kondo cloud and describe its possible detection in current correlations far away from the Kondo region. We thereby rely on and extend the method of refermionizable points. Furthermore, we find a class of gapless topological superconductors and semimetals, which accommodate edge states that behave similarly to the ones of globally gapped topological phases. Unexpectedly, we also find edge states that change their chirality when affected by sufficiently strong disorder. We regard the presented research helpful in future classifications and applications of systems containing topological insulators, of which we propose some examples.
Neo-classical impurity transport
International Nuclear Information System (INIS)
Stringer, T.E.
The neo-classical theory for impurity transport in a toroidal plasma is outlined, and the results discussed. A general account is given of the impurity behaviour and its dependence on collisionality. The underlying physics is described with special attention to the role of the poloidal rotation
Measuring and controlling method for organic impurities
International Nuclear Information System (INIS)
Aizawa, Motohiro; Igarashi, Hiroo
1995-01-01
The present invention concerns measurement and control for organic impurities contained in ultrapurified water for use in a nuclear power plant. A specimen containing organic impurities leached out of anionic exchange resins and cationic exchange resins is introduced to an organic material decomposing section to decompose organic impurities into organic carbon and other decomposed products. Sulfate ions, nitrate ions, nitrite ions and carbon dioxide are produced by the decomposition of the organic impurities. As a next step, carbon dioxide in the decomposed products is separated by deaerating with a nitrogen gas or an argon gas and then a TOC concentration is measured by a non-dispersion-type infrared spectrometer. Further, a specimen from which carbon dioxide was separated is introduced to a column filled with ion exchange resins and, after concentrating inorganic ion impurities, the inorganic ion impurities are identified by using a measuring theory of an ion chromatographic method of eluting and separating inorganic ion impurities and detecting them based on the change of electroconductivity depending on the kinds of the inorganic ion impurities. Organic impurities can be measured and controlled, to improve the reliability of water quality control. (N.H.)
First-principles thermodynamic calculations of diffusion characteristics of impurities in γ-iron
International Nuclear Information System (INIS)
Tsuru, T.; Kaji, Y.
2013-01-01
Because solute impurities have an effect on embrittlement through segregation under irradiation, solute stability and the influence of irradiation on the diffusion characteristics of impurities become prominent due to several acceleration effects of high irradiance circumstances in irradiated materials. In this study, the diffusion characteristics of several impurities in non-magnetic fcc iron are investigated using first-principles density functional theory (DFT) calculations. In accordance with classical diffusion and transition state theories, we nonempirically evaluated the contribution to properties of the binding energy between vacancy and each impurity and the migration enthalpy. The migration energy was calculated using the nudged elastic band method with DFT. The vacancy formation energy, including the entropic contributions to free energies in γ-iron, was evaluated by considering vibrational phonon frequencies based on frozen phonons employing the harmonic approximation for the lattice dynamics. Consequently, we confirmed that the binding energy between large-radius impurities and vacancies is larger than that with an equivalent size of the solvent element, and that the migration enthalpies of these impurities are quite small compared with self diffusion. This finding may indicate that the electronic binding states at the saddle point have a large influence on the migration of impurities
International Nuclear Information System (INIS)
Emery, V.J.; Kivelson, S.A.
1993-01-01
In the past few years there has been a resurgence of interest in dynamical impurity problems, as a result of developments in the theory of correlated electron systems. The general dynamical impurity problem is a set of conduction electrons interacting with an impurity which has internal degrees of freedom. The simplest and earliest example, the Kondo problem, has attracted interest since the mid-sixties not only because of its physical importance but also as an example of a model displaying logarithmic divergences order by order in perturbation theory. It provided one of the earliest applications of the renormalization group method, which is designed to deal with just such a situation. As we shall see, the antiferromagnetic Kondo model is controlled by a strong-coupling fixed point, and the essence of the renormalization group solution is to carry out the global renormalization numerically starting from the original (weak-coupling) Hamiltonian. In these lectures, we shall describe an alternative route in which we identify an exactly solvable model which renormalizes to the same fixed point as the original dynamical impurity problem. This approach is akin to determining the critical behavior at a second order phase transition point by solving any model in a given universality class
Energy Technology Data Exchange (ETDEWEB)
Emery, V.J. [Brookhaven National Lab., Upton, NY (United States); Kivelson, S.A. [California Univ., Los Angeles, CA (United States). Dept. of Physics
1993-12-31
In the past few years there has been a resurgence of interest in dynamical impurity problems, as a result of developments in the theory of correlated electron systems. The general dynamical impurity problem is a set of conduction electrons interacting with an impurity which has internal degrees of freedom. The simplest and earliest example, the Kondo problem, has attracted interest since the mid-sixties not only because of its physical importance but also as an example of a model displaying logarithmic divergences order by order in perturbation theory. It provided one of the earliest applications of the renormalization group method, which is designed to deal with just such a situation. As we shall see, the antiferromagnetic Kondo model is controlled by a strong-coupling fixed point, and the essence of the renormalization group solution is to carry out the global renormalization numerically starting from the original (weak-coupling) Hamiltonian. In these lectures, we shall describe an alternative route in which we identify an exactly solvable model which renormalizes to the same fixed point as the original dynamical impurity problem. This approach is akin to determining the critical behavior at a second order phase transition point by solving any model in a given universality class.
Isotope effect with energy-dependent density of states and impurities
International Nuclear Information System (INIS)
Williams, P.J.; Carbotte, J.P.
1992-01-01
We have calculated the total isotope coefficient β in a model where there is energy-dependent structure in the electronic density of states. We model the structure with a simple Lorentzian. In our calculation, doping has the effect of shifting the Fermi level and broadening the structure in the density of states. We have treated the dopants both as normal and as magnetic impurities. The asymmetry observed in the experimental data is found in our results. However, the complete range of values observed is difficult to reproduce. We question also whether the shifts in Fermi level required in such models are reasonable
Nonlinearity and disorder: Classification and stability of nonlinear impurity modes
DEFF Research Database (Denmark)
Sukhorukov, Andrey A.; Kivshar, Yuri S.; Bang, Ole
2001-01-01
We study the effects produced by competition of two physical mechanisms of energy localization in inhomogeneous nonlinear systems. As an example, we analyze spatially localized modes supported by a nonlinear impurity in the generalized nonlinear Schrödinger equation and describe three types of no...... the case of a power-law nonlinearity in detail. We discuss several scenarios of the instability-induced dynamics of the nonlinear impurity modes, including the mode decay or switching to a new stable state, and collapse at the impurity site....
International Nuclear Information System (INIS)
Bahner, C.T.; Shoun, R.R.; McDowell, W.J.
1977-09-01
Dihexyl[(diethylcarbamoyl)methyl]phosphonate (DHDECMP) in diethylbenzene extracts actinides well from 6 M nitric acid solution, but commercially available DHDECMP contains impurities which interfere with stripping the actinides from the organic extract. DHDECMP purified by molecular distillation does not contain these impurities, but the pot residue contains increased concentrations of them. Heating the purified DHDECMP causes the formation of products which interfere with stripping in the same way, suggesting that high temperatures employed in the manufacture of DHDECMP may produce the offending impurities. These impurities can be separated from the heat-decomposed material or the pot residues by dilution with a large volume of hexanes (causing part of the impurities to separate as a second liquid phase) followed by equilibration of the hexane solution with dilute alkali. After the treatment with hexane and dilute alkali, the DHDECMP is readily recovered and functions well in the actinide extraction process. Dibutyl[(dibutylcarbamoyl)methyl]-phosphonate (DBDBCMP) and di(2-ethylhexyl)[(diethylcarbamoyl)-methyl]phosphonate (DEHDECMP) are purified less effectively by these methods. Similar separation methods using diethylbenzene or CCl 4 as solvent do not remove impurities as completely as the hexane process. Impurities can also be removed from a benzene solution of the DHDECMP pot residue by passing it through a column packed with silica gel or diethylaminoethyl cellulose. These impurities have been separated into fractions for analytical examination by use of various solvents and by column chromatography. Hexyl hydrogen [(diethylcarbamoyl)methyl]-phosphonate has been identified tentatively as a principal objectionable impurity. Dihexyl phosphoric acid and possibly dihexylphosphonate have been identified in other fractions
International Nuclear Information System (INIS)
Tangarife, E.; Duque, C.A.
2011-01-01
This work is concerned with the theoretical study of the combined effects of applied electric field and hydrostatic pressure on the binding energy and impurity polarizability of a donor impurity in laterally coupled double InAs/GaAs quantum-well wires. Calculations have been made in the effective mass and parabolic band approximations and using a variational method. The results are reported for different configurations of wire and barriers widths, impurity position, and electric field and hydrostatic pressure strengths. Our results show that for symmetrical structures the binding energy is an even function of the impurity position along the growth direction of the structure. Also, we found that for hydrostatic pressure strength up to 38 kbar, the binding energy increases linearly with hydrostatic pressure, while for larger values of hydrostatic pressure the binding energy has a non-linear behavior. Finally, we found that the hydrostatic pressure can increase the coupling between the two parallel quantum-well wires. -- Research highlights: → Binding energy for donor impurity in coupled wires strongly depends on the confinement potential. → Polarizability for donor impurity in coupled wires strongly depends on the confinement potential. → Binding energy strongly depends on the direction of the applied electric field. → Polarizability strongly depends on the direction of the applied electric field. → The coupling between the two parallel wires increases with the hydrostatic pressure.
Raman scattering signatures of the unusual vibronic interaction of molecules in liquid helium-3
Energy Technology Data Exchange (ETDEWEB)
Tehver, I., E-mail: imbi.tehver@ut.ee [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia); Benedek, G. [Donostia International Physics Center (DIPC) and University of the Basque Country (EHU), Paseo de Lardizabal 4, 20018 Donostia/San Sebastian (Spain); Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi 53, 20125 Milano (Italy); Hizhnyakov, V. [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia)
2015-10-16
Highlights: • Theory of resonance Raman scattering (RRS) of molecules in {sup 3}He liquid is proposed. • Fermi excitations give essential contribution to RRS. • RRS spectra of glyoxal molecule in {sup 3}He droplets are calculated. - Abstract: Light scattering in quantum liquid helium-3 may involve a unique mechanism – the creation and annihilation of atom excitations across the Fermi level. The density of states of particle–hole excitations in the low-energy limit is strongly enhanced as compared to that of collective excitations of phonons in helium-3. This makes possible to directly observe Fermi excitations in the resonant Raman scattering (RRS) by {sup 3}He droplets doped by impurity molecules. The RRS spectra essentially depend on the excitation frequency. In case of excitation in the anti-Stokes side of absorption the first order RRS is directly determined by the particle–hole excitations in the vicinity of the impurity molecule and the contribution of phonons mainly given by the localized spherical vibration. The calculations are made for a {sup 3}He droplet doped by a glyoxal molecule.
Hu, Min; Wang, Hailong; Gong, Qian; Wang, Shumin
2018-04-01
Within the framework of effective-mass envelope-function theory, the ground state binding energy of a hydrogenic donor impurity is calculated in the InGaAsP/InP concentric double quantum rings (CDQRs) using the plane wave method. The effects of geometry, impurity position, external electric field and alloy composition on binding energy are considered. It is shown that the peak value of the binding energy appears in two rings with large gap as the donor impurity moves along the radial direction. The binding energy reaches the peak value at the center of ring height when the donor impurity moves along the axial direction. The binding energy shows nonlinear variation with the increase of ring height. With the external electric field applied along the z-axis, the binding energy of the donor impurity located at zi ≥ 0 decreases while that located at zi < 0 increases. In addition, the binding energy decreases with increasing Ga composition, but increases with the increasing As composition.
Identification and characterization of potential impurities of donepezil.
Krishna Reddy, K V S R; Moses Babu, J; Kumar, P Anil; Chandrashekar, E R R; Mathad, Vijayavitthal T; Eswaraiah, S; Reddy, M Satyanarayana; Vyas, K
2004-09-03
Five unknown impurities ranging from 0.05 to 0.2% in donepezil were detected by a simple isocratic reversed-phase high performance liquid chromatography (HPLC). These impurities were isolated from crude sample of donepezil using isocratic reversed-phase preparative high performance liquid chromatography. Based on the spectral data (IR, NMR and MS), the structures of these impurities were characterised as 5,6-dimethoxy-2-(4-pyridylmethyl)-1-indanone (impurity I), 4-(5,6-dimethoxy-2,3-dihydro-1H-2-indenylmethyl) piperidine (impurity II), 2-(1-benzyl-4-piperdylmethyl)-5,6-dimethoxy-1-indanol (impurity III) 1-benzyl-4(5,6-dimethoxy-2,3-dihydro-1H-2-indenylmethyl) piperidine (impurity IV) and 1,1-dibenzyl-4(5,6-dimethoxy-1-oxo-2,3-dihydro-2H-2-indenylmethyl)hexahydropyridinium bromide (impurity V). The synthesis of these impurities and their formation was discussed.
International Nuclear Information System (INIS)
Yoshida, Hiroshi; Konishi, Satoshi; Katsuta, Hiroji; Naruse, Yuji
1982-02-01
Palladium alloy membrane method is considered to be a useful technique for fusion reactor fuel purification process. To study the feasibility of this method, the effects of impurities on permeation characteristics of palladium alloy membrane were examined. Experiments were carried out at practical conditions: pressure; 120 - 1200 kPa, temperature; about 700 K. No poisoning effect on hydrogen permeability of commercial Pd-Ag (Au.Ru) alloy was observed for impurities such as NH 3 , CH 4 , CO, CO 2 , O 2 and N 2 , which were mixed with hyper-pure H 2 at low concentration level (10 - 10000 ppm). Deterioration occurred by contamination with oil vapor. However, regeneration of the membrane was easily performed by air baking followed by hydrogen reduction. Chemical reactions in the permeation cell were also examined. (author)
Impurity monitoring by laser-induced fluorescence techniques
International Nuclear Information System (INIS)
Gelbwachs, J.A.
1984-01-01
Laser-induced fluorescence spectroscopy can provide a highly sensitive and selective means of detecting atomic and ionic impurities. Because the photodetector can be physically isolated from the laser-excited region, these techniques can be applied to monitoring in hostile environments. The basic concepts behind fluorescence detection are reviewed. Saturated optical excitation is shown to maximize impurity atom emission yield while mitigating effects of laser intensity fluctuations upon absolute density calibration. Monitoring in high- and low-pressure monitoring environments is compared. Methods to improve detection sensitivity by luminescence background suppression are presented
Classical impurity ion confinement in a toroidal magnetized fusion plasma.
Kumar, S T A; Den Hartog, D J; Caspary, K J; Magee, R M; Mirnov, V V; Chapman, B E; Craig, D; Fiksel, G; Sarff, J S
2012-03-23
High-resolution measurements of impurity ion dynamics provide first-time evidence of classical ion confinement in a toroidal, magnetically confined plasma. The density profile evolution of fully stripped carbon is measured in MST reversed-field pinch plasmas with reduced magnetic turbulence to assess Coulomb-collisional transport without the neoclassical enhancement from particle drift effects. The impurity density profile evolves to a hollow shape, consistent with the temperature screening mechanism of classical transport. Corroborating methane pellet injection experiments expose the sensitivity of the impurity particle confinement time to the residual magnetic fluctuation amplitude.
Vapor Delivery Systems for the Study of the Effects of Reformate Gas Impurities in HT-PEM Fuel Cells
DEFF Research Database (Denmark)
Araya, Samuel Simon; Kær, Søren Knudsen; Andreasen, Søren Juhl
2011-01-01
, impurities in the reformate gas produced from methanol steam reforming can affect the performance and durability of fuel cells. In this paper different vapor delivery systems, intended to assist in the study of the effects of some of the impurities, are described and compared with each other. A system based...... on a pump and electrically heated evaporator was found to be more suitable for the typical flow rates involved in the anode feed of an H3PO4/PBI based HT-PEMFC unit cell assembly. Test stations composed of vapor delivery systems and mass flow controllers for testing the effects of methanol slip, water vapor...
Studies of impurity recycling by the collector probe technique
International Nuclear Information System (INIS)
Hildebrandt, D.; Grote, H.; Herrmann, A.; Laux, M.; Pech, P.; Reiner, H.D.; Wolff, H.
1987-01-01
In order to study recycling effects of the nonintrinsic impurity Li discharges with and without LiD-pellet injection were investigated. The observed maximum impurity level of Li in the SOL plasma of discharges without injection reaches less than 10% of that observed in discharges with injection. The measurements offer the possibility to distinguish between influxes from the wall and those which reach the collector probe via the core plasma. The time evolution, orientation and radial dependence of the impurity fluxes are characteristic features of their origin. The consideration of all these features facilitates a better understanding of collector probe measurements in the SOL-plasma. (orig.)
Impurity transport and plasma rotation in the ISX-B tokamak
International Nuclear Information System (INIS)
Isler, R.C.; Murray, L.E.; Crume, E.C.
1983-01-01
Recent calculations have shown that when external momentum sources and plasma rotation are included in the neoclassical theory, the standard results for impurity transport can be strongly altered. Under appropriate conditions, inward convection is reduced by co-injection and enhanced by counter-injection. In order to examine the theoretical predictions, several observations of impurity transport have been made in the ISX-B tokamak during neutral-beam injection for comparison with the transport seen with Ohmic heating alone. Both intrinsic contaminants and deliberately introduced test impurities display a behaviour that is in qualitative agreement with the predicted beam-driven effects. These correlations are particularly noticeable when the comparisons are made for deuterium when the impurity transport in the Ohmically heated discharges exhibits neoclassical-like characteristics, i.e. accumulation and long confinement times. Similar but smaller effects are observed in beam-heated hydrogen discharges; neoclassical-like behaviour is not seen in Ohmically heated hydrogen sequences. Emphasis has been placed on measuring toroidal plasma rotation, and semiquantitative comparisons with the theories of beam-induced impurity transport have been made. It is possible that radial electric fields other than those associated with momentum transfer and increased anomalous processes during injection could also play a role. (author)
Influence of impurities on the surface morphology of the TIBr crystal semiconductor
International Nuclear Information System (INIS)
Santos, Robinson A. dos; Silva, Julio B. Rodrigues da; Martins, Joao F.T.; Ferraz, Caue de M.; Costa, Fabio E. da; Mesquita, Carlos H. de; Hamada, Margarida M.; Gennari, Roseli F.
2013-01-01
The impurity effect in the surface morphology quality of TlBr crystals was evaluated, aiming a future application of these crystals as room temperature radiation semiconductor detectors. The crystals were purified and grown by the Repeated Bridgman technique. Systematic measurements were carried out for determining the stoichiometry, structure orientation, surface morphology and impurity of the crystal. A significant difference in the crystals impurity concentration was observed for almost all impurities, compared to those found in the raw material. The crystals wafer grown twice showed a surface roughness and grains which may be due to the presence of impurities on the surface, while those obtained with crystals grown three times presented a more uniform surface: even though, a smaller roughness was still observed. It was demonstrated that the impurities affect strongly the surface morphology quality of crystals. (author)
Anodization of Zr-Nb-Cu alloy in mandelic acid - effect of solvent and anionic impurities
International Nuclear Information System (INIS)
Lavanya, A.; Raghunath Reddy, G.; Ch Anjaneyulu
2004-01-01
Anodization of zirconium-niobium-copper (ZNC) alloy in 0.1 M mandelic acid has been carried out. The effect of solvent (ethylene glycol) and added anionic impurities (sulphates, phosphates and carbonates) showed better kinetic results (formation rate, current efficiency and differential field of formation). (author)
Impurities in air and their effect on plant life
Energy Technology Data Exchange (ETDEWEB)
Balasubramanyam, P
1957-01-01
Air is said to be polluted when it contains an unusual amount of contaminants. The fact that several of these impurities influence plant life has been fairly well established. Damage caused to agriculture and forestry has been a subject of economic interest in the highly industrialized countries of Europe and America for more than a century now. Germany was the pioneer in this aspect of study and as early as in 1842. Researchers described the poisoning of elm trees. England's history records that the smoke and fume has been one of concern to its citizens ever since the days of the Industrial Revolution. As early as in 1848, the Government initiated a study of the harmful gases to vegetation. The subject attracted the attention of United States of America by about 1900. The writings of one researcher from 1906 to 1916 give evidence of the frequent instances of injuries to trees in New England, attributed to the escape of illuminating gas. Extensive research has followed the periodic concern regarding localized or general pollution. Similar attention has also been paid in Italy and Austria to the effect of impurities of air on vegetation. However, in India the problem attracted the attention of administrators, plant pathologists and chemists only very recently. The vicinity of industrial plants in many places has been responsible for litigation, setting up of commissions and regulation of acts in several countries. The purpose of the present contribution is to bring out the salient features of research work done so far on this subject. 30 references.
Coherent scattering and matrix correction in bone-lead measurements
International Nuclear Information System (INIS)
Todd, A.C.
2000-01-01
The technique of K-shell x-ray fluorescence of lead in bone has been used in many studies of the health effects of lead. This paper addresses one aspect of the technique, namely the coherent conversion factor (CCF) which converts between the matrix of the calibration standards and those of human bone. The CCF is conventionally considered a constant but is a function of scattering angle, energy and the elemental composition of the matrices. The aims of this study were to quantify the effect on the CCF of several assumptions which may not have been tested adequately and to compare the CCFs for plaster of Paris (the present matrix of calibration standards) and a synthetic apatite matrix. The CCF was calculated, using relativistic form factors, for published compositions of bone, both assumed and assessed compositions of plaster, and the synthetic apatite. The main findings of the study were, first, that impurities in plaster, lead in the plaster or bone matrices, coherent scatter from non-bone tissues and the individual subject's measurement geometry are all minor or negligible effects; and, second, that the synthetic apatite matrix is more representative of bone mineral than is plaster of Paris. (author)
Magnetic impurity coupled to interacting conduction electrons
International Nuclear Information System (INIS)
Schork, T.
1996-01-01
We consider a magnetic impurity which interacts by hybridization with a system of weakly correlated electrons and determine the energy of the ground state by means of a 1/N f expansion. The correlations among the conduction electrons are described by a Hubbard Hamiltonian and are treated to the lowest order in the interaction strength. We find that their effect on the Kondo temperature, T K , in the Kondo limit is twofold: first, the position of the impurity level is shifted due to the reduction of charge fluctuations, which reduces T K . Secondly, the bare Kondo exchange coupling is enhanced as spin fluctuations are enlarged. In total, T K increases. Both corrections require intermediate states beyond the standard Varma-Yafet ansatz. This shows that the Hubbard interaction does not just provide quasiparticles, which hybridize with the impurity, but also renormalizes the Kondo coupling. copyright 1996 The American Physical Society
Mikheyev-Smirnov-Wolfenstein effect in electron-neutrino scattering experiments
International Nuclear Information System (INIS)
Bahcall, J.N.; Gelb, J.M.; Rosen, S.P.
1987-01-01
We calculate the influence of resonant neutrino scattering [the Mikheyev-Smirnov-Wolfenstein (MSW) effect] in the Sun and in the Earth on measurable quantities in solar-neutrino--electron scattering experiments. The MSW effect reduces the expected rate for 8 B-neutrino--electron scattering by a factor that ranges from --0.8 to --0.2 if resonant scattering is the correct explanation for the discrepancy between observation and calculation in the /sup 37/Cl experiment. The Earth can produce a significant diurnal effect for certain values of the neutrino mixing angle and mass difference
On impurities transport in a tokamak
International Nuclear Information System (INIS)
Rozhanskij, V.A.
1980-01-01
Transport of impurity ions is analitically analized in the case when main plasma is in plateau or banana regimes but impurity ions - in the Pfirsch-Schlutter mode. It is shown that in the large region of parameters the impUrity transport represents a drift in a p oloidal electric field, averaged from magnetic surface with provision for disturbance of concentration on it. Therefore, transport velocity does not depend on Z value and impurity type, as well as collision frequency both in the plateau and banana regimes. A value of flows is determined by the value of poloidal rotation velocity. At the rotation velocity corresponding to the electric field directed from the centre to periphery impurities are thrown out of a discharge, in the reverse case the flow is directed inside. Refusal from the assumption that Zsub(eff) > approximately 2, does not considerably change the results of work. The approach developed in the process of work can be applied to the case when impurity ions are in the plateau or banana modes
Mechanisms of impurity diffusion in rutile
International Nuclear Information System (INIS)
Peterson, N.L.; Sasaki, J.
1984-01-01
Tracer diffusion of 46 Sc, 51 Cr, 54 Mn, 59 Fe, 60 Co, 63 Ni, and 95 Zr, was measured as functions of crystal orientation, temperature, and oxygen partial pressure in rutile single crystals using the radioactive tracer sectioning technique. Compared to cation self-diffusion, divalent impurities (e.g., Co and Ni) diffuse extremely rapidly in TiO 2 and exhibit a large anisotropy in the diffusion behavior; divalent-impurity diffusion parallel to the c-axis is much larger than it is perpendicular to the c-axis. The diffusion of trivalent impurity ions (Sc and Cr) and tetravalent impurity ions (Zr) is similar to cation self-diffusion, as a function of temperature and of oxygen partial pressure. The divalent impurity ions Co and Ni apparently diffuse as interstitial ions along open channels parallel to the c-axis. The results suggest that Sc, Cr, and Zr ions diffuse by an interstitialcy mechanism involving the simultaneous and cooperative migration of tetravalent interstitial titanium ions and the tracer-impurity ions. Iron ions diffused both as divalent and as trivalent ions. 8 figures
Impurity production and transport at limiters
International Nuclear Information System (INIS)
Matthews, G.F.
1989-01-01
This paper concentrates on the description and evaluation of experiments on the DITE tokamak. These are designed to characterise the processes involved in the production and transport of neutral and ionised impurities near carbon limiters. The need for good diagnostics in the scrape-off layer is highlighted. Langmuir probes are used to provide input data for models of impurity production at limiters. Observations of the radial profiles of carbon and oxygen impurities are compared with the code predictions. Changeover experiments involving hydrogen and helium plasmas are used as a means for investigating the role of the atomic physics and chemistry. The impurity control limiter (ICL) experiment is described which shows how geometry plays an important role in determining the spatial distributions of the neutral and ionised carbon. New diagnostics are required to study the flux and charge state distribution of impurities in the boundary. Preliminary results from an in-situ plasma ion mass-spectrometer are presented. The role of oxygen and the importance of evaluating the wall sources of impurity are emphasised. (orig.)
Effects of surface and interface scattering on anomalous Hall effect in Co/Pd multilayers
Guo, Zaibing
2012-09-27
In this paper, we report the results of surface and interface scattering on anomalous Hall effect in Co/Pd multilayers with perpendicular magnetic anisotropy. The surface scattering effect has been extracted from the total anomalous Hall effect. By scaling surface scattering contribution with ρAHs∼ργss, the exponent γ has been found to decrease with the increase of surface scattering resistivity, which could account for the thickness-dependent anomalous Hall effect. Interface diffusion induced by rapid thermal annealing modifies not only the magnetization and longitudinal resistivity but also the anomalous Hall effect; a large exponent γ ∼ 5.7 has been attributed to interface scattering-dominated anomalous Hall effect.
The effect of ICRF antenna phasing on metal impurities in TFTR
International Nuclear Information System (INIS)
Stevens, J.E.; Bush, C.; Colestock, P.L.; Oak Ridge National Lab., TN; AN Ukrainskoj SSR, Kharkov
1989-07-01
ICRF power levels of up to 2.8 MW were achieved during the 1988 experimental run on TFTR. Metal impurity concentrations (Ti, Cr, Fe, Ni) and Z eff were monitored during ICRF heating by x-ray pulse height analysis and uv spectroscopy. Antenna phasing was the key variable affecting ICRF performance. No increase in metallic impurities was observed for P rf approx lt 2.8 MW with the antenna straps 0-Π, while a measurable increase in titanium (Faraday screen material) was observed for P rf approx gt 1.0 MW with 0-0 phasing. 18 refs., 8 figs
Instability of homogeneous distribution of charged substitutional impurity in semiconductors
International Nuclear Information System (INIS)
Vasilevskij, M.I.; Ershov, S.N.; Panteleev, V.A.
1985-01-01
A mechanism is suggested of instability of uniform impurity distribution in a semiconductor. The mechanism is associated with the vacancy wind effect and deflection from local neutrality in case of impurity concentration fluctuation occurrence. It is shown that the mechanism can be realized by irradiation of silicon doped with group-3 and group 5 elements
Pfirsch–Schlüter neoclassical heavy impurity transport in a rotating plasma
International Nuclear Information System (INIS)
Belli, E A; Candy, J; Angioni, C
2014-01-01
In this work, we extend previous analytic theories for the neoclassical transport of a trace heavy impurity in a rotating plasma in the Pfirsch–Schlüter regime. The complete diffusive and convective components of the ambipolar particle flux are derived. The solution is valid for arbitrary impurity charge and impurity Mach number and for general geometry. Inclusion of finite main-ion temperature gradient effects is shown in the small ion Mach number limit. A simple interpolation formula is derived for the case of high impurity charge and circular geometry. While an enhancement of the diffusion coefficient is found for order one impurity Mach number, a reduction due to the rotation-driven poloidal asymmetry in the density occurs for very large Mach number. (paper)
Effects of density asymmetries on heavy-impurity transport in a rotating tokamak-plasma
International Nuclear Information System (INIS)
Romanelli, M.; Ottaviani, M.
1997-12-01
The transport equations of heavy trace-impurities in a Tokamak plasma with strong toroidal rotation have been studied analytically in the collisional regime. It is found that the poloidal asymmetry of the impurity-density, which occurs because of the rotation, brings about a large enhancement of the diffusivity and indeed of the pinch velocity above the conventional Pfirsh-Schlueter values. (author)
BWR water chemistry impurity studies
International Nuclear Information System (INIS)
Ljungberg, L.G.; Korhonen, S.; Renstroem, K.; Hofling, C.G.; Rebensdorff, B.
1990-03-01
Laboratory studies were made on the effect of water impurities on environmental cracking in simulated BWR water of stainless steel, low alloy steel and nickel-base alloys. Constant elongation rate tensile (CERT) tests were run in simulated normal water chemistry (NWC), hydrogen water chemistry (HWC), or start-up environment. Sulfate, chloride and copper with chloride added to the water at levels of a fraction of a ppM were found to be extremely deleterious to all kinds of materials except Type 316 NG. Other detrimental impurities were fluoride, silica and some organic acids, although acetic acid was beneficial. Nitrate and carbon dioxide were fairly inoccuous. Corrosion fatigue and constant load tests on compact tension specimens were run in simulated normal BWR water chemistry (NWC) or hydrogen water chemistry (HWC), without impurities or with added sulfate or carbon dioxide. For sensitized Type 304 SS in NWC, 0.1 ppM sulfate increased crack propagation rates in constant load tests by up to a factor of 100, and in fatigue tests up to a factor of 10. Also, cracking in Type 316 nuclear grade SS and Alloy 600 was enhanced, but to a smaller degree. Carbon dioxide was less detrimental than sulfate. 3 figs., 4 tabs
Sensitivity of graphene flakes and nanorings to impurities
Energy Technology Data Exchange (ETDEWEB)
Konobeeva, N.N., E-mail: yana_nn@volsu.ru [Volgograd State University, University Avenue 100, Volgograd 400062 (Russian Federation); Belonenko, M.B. [Volgograd State University, University Avenue 100, Volgograd 400062 (Russian Federation); Volgograd Institute of Business, Uzhno-Ukrainskaya Str., Volgograd 400048 (Russian Federation)
2017-06-01
In this paper, we consider the influence of impurity on the graphene flakes and nanorings conductance. Based on the jumping Hamiltonian for graphene electrons with its direct diagonalization, we obtain the density of states. Further, the tunneling current is calculated for the following contacts: graphene flake-metal, graphene flake-quantum dots, graphene nanoring-quantum dots. We analyze the effect of the flake dimensions and the positions of the adsorbed molecule of impurity on the characteristic properties of the tunneling current.
Effects of quenched impurities on surface diffusion, spreading, and ordering of O/W(110)
DEFF Research Database (Denmark)
Nikunen, P.; Vattulainen, Ilpo Tapio; Ala-Nissila, T.
2002-01-01
We study how quenched impurities affect the surface diffusion and ordering of strongly interacting adsorbate atoms on surfaces. To this end, we carry out Monte Carlo simulations for a lattice-gas model of O/W(110), including small concentrations of immobile impurities which block their adsorption...
Zeroth order phase transition in a holographic superconductor with single impurity
Zeng, Hua Bi; Zhang, Hai-Qing
We investigate the single normal impurity effect in a superconductor by the holographic method. When the size of impurity is much smaller than the host superconductor, we can reproduce the Anderson theorem, which states that a conventional s-wave superconductor is robust to a normal (non-magnetic)
International Nuclear Information System (INIS)
Hinnov, E.; Suckewer, S.; Bol, K.; Hawryluk, R.; Hosea, J.; Meservey, E.
1977-11-01
Low-Z impurities concentrations (oxygen and carbon) have been measured in different discharges in PLT. The contribution to Z/sub eff/, influx rates and radiation losses by oxygen and carbon were obtained. An inverse correlation was found between the low-Z impurity density (and also the edge ion temperature) and the high-Z impurity (tungsten) density. A one-dimensional computer transport model has been used to calculate the spatial profiles of different oxygen and carbon ionization states. This model predicts that fully stripped oxygen and carbon ions should exist near the plasma periphery
Interaction between impurities in Ag dilute alloys
International Nuclear Information System (INIS)
Krolas, K.; Wodniecka, B.; Wodniecki, P.; Uniwersytet Jagiellonski, Krakow
1977-01-01
Time dependent perturbed angular correlation measurements of gamma radiation in 111 Cd after 111 In decay were performed in AgPd and AgPt alloys. The concentration of Pd or Pt atoms being the nearest neighbours to the probe atoms is much higher than that one deduced from random impurity distribution. This effect results from the attractive interaction between the In probe atoms and Pt or Pd impurity atoms in silver host lattice. The binding energy of InPd and InPt complexes was measured as 135 +- 9 meV and 171 +- 9 meV, respectively. (author)
International Nuclear Information System (INIS)
Montoya, R.; Escudero, M.L.; García-Alonso, M.C.
2011-01-01
Highlights: ► Degradation of Mg due to the presence of impurities by finite element method. ► A thin film of electrolyte causes galvanic corrosion focused only close on impurities. ► A thick layer of electrolyte provokes galvanic corrosion extended the whole surface. ► A higher number of impurities causes galvanic corrosion on the Mg surface independently of electrolyte thickness. ► The electrolyte thickness is an important variable that affects the in vivo degradation. - Abstract: The aim of this work is to study the degradation of magnesium due to the presence of impurities, by finite element method (FEM), when different thickness of physiological medium bathes the surface. The electrochemical experimental data obtained from polarization curves are used to model mathematically the corrosion process by solving the Laplace equation and the proper boundary conditions by means of FEM. The results show that when Mg is covered by a thin film of electrolyte, galvanic corrosion is focused only on the areas located really close to the cathodic sites, and far from the impurities, the Mg matrix remains near to its corrosion potential with a natural corrosion process. However, if the Mg matrix is completely covered by a thick layer of electrolyte the potentials obtained in the Mg surface far from the impurity are higher than its corrosion potential, so the Mg suffers more severe galvanic corrosion. On the other hand, when a higher number of impurities is considered, the Mg matrix is anodically polarized and it suffers severe galvanic corrosion, independently of h. The thickness of the electrolyte h must be considered as an important variable that affects the in vivo degradation.
The role of annealing: effect on CaSO4:Dy phosphor with manganese and sodium impurities
International Nuclear Information System (INIS)
Li, S.-H.; Hsu, P.-C.
1990-01-01
The effect of the annealing treatment on the CaSO 4 :Dy phosphor with Mn and Na impurities was studied at different annealing temperatures from 100 0 C to 800 0 C. Doping with or without impurity caused no difference in the properties for temperatures less than 400 0 C. An annealing temperature greater than 400 0 C brings a reduction in low temperature peak intensities of CaSO 4 :Dy with Na only. The high temperature peak intensities increase as the temperature increases from 400 0 C to 600 0 C. However, annealing at a temperature greater than 600 0 C brings a drastic reduction in high temperature peak intensities as well as TL output. (author)
Kumar, Sunil; Verma, N. K.; Bhatti, H. S.
Zinc sulphide phosphors doped with Ba, as well as killer impurities of Fe, Co and Ni, having variable concentrations, were synthesized; and using an ultraviolet laser as the excitation source, decay-curve analyses were done. Various strong emissions in these phosphors were detected and the corresponding excited-state life times were measured at liquid nitrogen temperature. Studies were carried out to see the effect of killer impurities on the phosphorescence excited-state life times. Excited-state life times were found to decrease appreciably (microsecond to nanosecond) with the addition of quenchers. These studies are quite useful and find applications in areas such as optical memories, sensors, luminescent screens, laser-beam detection and alignment, color displays, printing, etc.
THE EFFICIENCY OF IMPURITIES EXTRACTION DURING THE PROCESS OF ETHANOL EPURATION
Directory of Open Access Journals (Sweden)
S. Yu. Nikitina
2015-01-01
Full Text Available The static model of the hydroselection column that describes the concentration variation of the main components was proposed. The purpose of this work is an optimization of the shared mixture input-position and evaluation of efficiency of the digestion and the impurity compound concentration during the epuration process. To this end, the author developed a static model of epuration columns, which allows to reveal the dependence of the degree of digestion and the degree of concentration of the main impurities in the column of the number of plates in each of these parts. It’s proved that with the increasing of theoretical plates number in the concentration part of the column the concentration effect tends to the limit value. The effects of the head impurities digestion increase indefinitely with the growth of exhausting part. The proportion of the output from the condenser impurities depends more from the digestion effect than from the condensation effect. The effect of alcohol cleaning from the fusel oil components depends strongly from the ratio of the number of plates in the digestion and concentration parts (the optimal ratio for isopropanol, isoamyl, butanol is 1.5, for the propanol, isobutanol is 0.45.
Modeling of the Microchemistry for Diffusion of Selected Impurities in Uranium
International Nuclear Information System (INIS)
Kirkpatrick, J. R.; Bullock, J.S. IV
2001-01-01
Unalloyed metallic uranium used in some work done at Y-12 contains small quantities of impurities, the three most significant of which are carbon, iron, and silicon. During metallurgical processing, as the metal cools from a molten condition towards room temperature, the metallic matrix solution becomes supersaturated in each of the impurities whose concentration exceeds the solubility limit. Many impurity atoms form compounds with uranium that precipitate out of the solution, thus creating and growing inclusions. The objective of the present work is to study the distribution of impurity atoms about some of the inclusions, with a view toward examining the effect of the interaction between inclusions on the impurity atom distribution. The method used is time-dependent mass diffusion from the supersaturated solution to the surfaces of the inclusions. Micrographs of metal samples suggest that the inclusions form in successive stages. After each inclusion forms, it begins to draw impurity atoms from its immediate vicinity, thus altering the amounts and distributions of impurity atoms available for formation and growth of later inclusions. In the present work, a one-dimensional spherical approximation was used to simulate inclusions and their regions of influence. A first set of calculations was run to simulate the distribution of impurity atoms about the largest inclusions. Then, a second set of calculations was run to see how the loss of impurity atoms to the largest inclusions might affect the distribution of impurity atoms around the next stage of inclusions. Plots are shown for the estimated distributions of impurity atoms in the region of influence about the inclusions for the three impurities studied. The authors believe that these distributions are qualitatively correct. However, there is enough uncertainty about precisely when inclusions nucleate and begin to grow that one should not put too much reliance on the quantitative results. This work does provide a
Fuel clean-up: poisoning of palladium-silver membranes by gaseous impurities
International Nuclear Information System (INIS)
Chabot, J.; Lecomte, J.; Grumet, C.; Sannier, J.
1988-01-01
The feasibility of a permeation process using a palladium-silver alloy membrane, to separate deuterium and tritium from fusion reactor gaseous wastes needs demonstration owing to poisoning effects of impurities. A parametric investigation of the poisoning by the most important expected gaseous impurities (C0, C0 2 and CH 4 ) is carried out with the loop PALLAS, in function of membrane temperature (100 to 450 0 C), H 2 pressure (0.3 to 14 kPa) and impurity concentration (0.2 to 9.5 vol. %). The poisoning effect of C0 is a concern for the process while C0 2 and CH 4 appear to have no practical effect on the permeation rate. Depending on C0 concentration optimal operating temperatures of the membrane should lie between 250 and 375 0 C limits
Determining factors for the presence of impurities in selectively collected biowaste.
Puig-Ventosa, Ignasi; Freire-González, Jaume; Jofra-Sora, Marta
2013-05-01
The presence of impurities in biodegradable waste (biowaste) causes problems with the management of waste, among which are additional costs derived from the need to improve pre-treatment of biowaste, loss of treatment capacity and the difficulty selling treated biowaste as compost owing to its low quality. When treated biowaste is used for soil conditioning it can also cause soil pollution. Understanding the reasons why impurities are in biowaste and the factors affecting the percentage of impurities present can be used to determine ways to minimise these negative effects. This article attempts to identify the main causes for the presence of impurities in biowaste. In order to do so, it carries out an empirical analysis of the level of impurities in biowaste from municipal waste collection in two steps. First, a bivariate analysis focuses on significant correlations between the presence of impurities and several variables. Second, the construction of an explanatory model based on the significant relations obtained in the first step, and on literature research, are used to check the stated hypothesis. The estimates demonstrate that the collection system, the global levels of separate collection, the urban density of the municipality and the requirement to use compostable bags may be the main drivers of impurity levels in biowaste.
International Nuclear Information System (INIS)
Sivakami, A.; Mahendran, M.
2010-01-01
The binding energy of a shallow hydrogenic impurity in a spherical quantum dot under hydrostatic pressure with square well potential is calculated using a variational approach within the effective mass approximation. The effect of conduction band non-parabolicity on these energies is also estimated. The binding energy is computed for GaAs spherical quantum dot as a function of dot size, hydrostatic pressure both in the presence and absence of the band non-parabolicity effect. Our results show that (i) the hydrostatic pressure increases the impurity binding energy when dot radius increases for a given pressure, (ii) the hydrostatic pressure with the band non-parabolicity effect effectively increases the binding energy such that the variation is large for smaller dots and (iii) the maximum contribution by the non-parabolicity effect is about 15% for narrow dots. Our results are in good agreement with Perez-Merchancano et al. [J. Phys. Condens. Matter 19 (2007) 026225] who have not considered the conduction band non-parabolicity effect.
Impurity energy level in the Haldane gap
International Nuclear Information System (INIS)
Wang Wei; Lu Yu
1995-11-01
An impurity bond J' in a periodic 1D antiferromagnetic spin 1 chain with exchange J is considered. Using the numerical density matrix renormalization group method, we find an impurity energy level in the Haldane gap, corresponding to a bound state near the impurity bond. When J' J. The impurity level appears only when the deviation dev = (J'- J)/J' is greater than B c , which is close to 0.3 in our calculation. (author). 15 refs, 4 figs
Diffusive charge transport in graphene on SiO 2
Chen, J.-H.; Jang, C.; Ishigami, M.; Xiao, S.; Cullen, W. G.; Williams, E. D.; Fuhrer, M. S.
2009-07-01
We review our recent work on the physical mechanisms limiting the mobility of graphene on SiO 2. We have used intentional addition of charged scattering impurities and systematic variation of the dielectric environment to differentiate the effects of charged impurities and short-range scatterers. The results show that charged impurities indeed lead to a conductivity linear in density ( σ(n)∝n) in graphene, with a scattering magnitude that agrees quantitatively with theoretical estimates; increased dielectric screening reduces the scattering from charged impurities, but increases the scattering from short-range scatterers. We evaluate the effects of the corrugations (ripples) of graphene on SiO 2 on transport by measuring the height-height correlation function. The results show that the corrugations cannot mimic long-range (charged impurity) scattering effects, and have too small an amplitude-to-wavelength ratio to significantly affect the observed mobility via short-range scattering. Temperature-dependent measurements show that longitudinal acoustic phonons in graphene produce a resistivity that is linear in temperature and independent of carrier density; at higher temperatures, polar optical phonons of the SiO 2 substrate give rise to an activated, carrier density-dependent resistivity. Together the results paint a complete picture of charge carrier transport in graphene on SiO 2 in the diffusive regime.
Multi-impurity polarons in a dilute Bose-Einstein condensate
International Nuclear Information System (INIS)
Santamore, D H; Timmermans, Eddy
2011-01-01
We describe the ground state of a large, dilute, neutral atom Bose-Einstein condensate (BEC) doped with N strongly coupled mutually indistinguishable, bosonic neutral atoms (referred to as ‘impurity’) in the polaron regime where the BEC density response to the impurity atoms remains significantly smaller than the average density of the surrounding BEC. We find that N impurity atoms with N ≠ 1 can self-localize at a lower value of the impurity-boson interaction strength than a single impurity atom. When the ‘bare’ short-range impurity-impurity repulsion does not play a significant role, the self-localization of multiple bosonic impurity atoms into the same single particle orbital (which we call co-self-localization) is the nucleation process of the phase separation transition. When the short-range impurity-impurity repulsion successfully competes with co-self-localization, the system may form a stable liquid of self-localized single impurity polarons. (paper)
The effect of resonant magnetic perturbations on the impurity transport in TEXTOR-DED plasmas
International Nuclear Information System (INIS)
Greiche, Albert Josef
2009-01-01
Thermonuclear fusion provides a new mechanism for the generation of electrical power which has the perspective to serve humanity for several millions of years. One possibility to implement fusion on earth is to magnetically confine hot deuterium tritium plasmas in so called tokamaks. The fusion reactions take place in the hot plasma core. Each of the fusion reactions between deuterium and tritium yields 17.6 MeV which can be used in the process of generating electrical power. Impurities contaminate the plasma which then is cooled down and diluted. This leads to a reduction of the fusion reactions and in consequence the energy yield. The transport behaviour of the impurities in the plasma is not fully understood up to now. Nevertheless, experiments have shown that the application of resonant magnetic perturbations (RMP) can control the impurity content in the plasma. The dynamic ergodic divertor (DED) on the tokamak Textor is able to induce static and dynamic RMPs. During the application of RMPs transient impurity transport experiments with argon have been performed and the time evolution of the impurity concentrations have been monitored. The line emission intensity of the impurities in the plasma is measured in the vacuum ultraviolet (VUV) and in the soft X-ray (SXR) with the absolutely calibrated VUV spectrometer Hexos and SXR PIN diodes, respectively. The analysis of the transient impurity transport experiments is performed with the help of the transport code Strahl. The impurity flows in Strahl are described by a combination of a diffusive and a convective flow. In the computing process the code solves the coupled set of continuity equations of each of the ionization stages of an impurity. With this method the time evolution of the impurity ion densities and the line emission intensities of the ionization stages can be computed. The adaption to the experimental measurements is performed with the help of the diffusion coefficient and the drift velocity which
Collision of impurities with Bose–Einstein condensates
Lingua, F.; Lepori, L.; Minardi, F.; Penna, V.; Salasnich, L.
2018-04-01
Quantum dynamics of impurities in a bath of bosons is a long-standing problem in solid-state, plasma, and atomic physics. Recent experimental and theoretical investigations with ultracold atoms have focused on this problem, studying atomic impurities immersed in an atomic Bose–Einstein condensate (BEC) and for various relative coupling strengths tuned by the Fano‑Feshbach resonance technique. Here, we report extensive numerical simulations on a closely related problem: the collision between a bosonic impurity consisting of a few 41K atoms and a BEC of 87Rb atoms in a quasi one-dimensional configuration and under a weak harmonic axial confinement. For small values of the inter-species interaction strength (regardless of its sign), we find that the impurity, which starts from outside the BEC, simply causes the BEC cloud to oscillate back and forth, but the frequency of oscillation depends on the interaction strength. For intermediate couplings, after a few cycles of oscillation the impurity is captured by the BEC, and strongly changes its amplitude of oscillation. In the strong interaction regime, if the inter-species interaction is attractive, a local maximum (bright soliton) in the BEC density occurs where the impurity is trapped; if, instead, the inter-species interaction is repulsive, the impurity is not able to enter the BEC cloud and the reflection coefficient is close to one. However, if the initial displacement of the impurity is increased, the impurity is able to penetrate the cloud, leading to the appearance of a moving hole (dark soliton) in the BEC.
Assessment of Embrittlement of VHTR Structural Alloys in Impure Helium Environments
Energy Technology Data Exchange (ETDEWEB)
Crone, Wendy; Cao, Guoping; Sridhara, Kumar
2013-05-31
The helium coolant in high-temperature reactors inevitably contains low levels of impurities during steady-state operation, primarily consisting of small amounts of H{sub 2}, H{sub 2}O, CH{sub 4}, CO, CO{sub 2}, and N{sub 2} from a variety of sources in the reactor circuit. These impurities are problematic because they can cause significant long-term corrosion in the structural alloys used in the heat exchangers at elevated temperatures. Currently, the primary candidate materials for intermediate heat exchangers are Alloy 617, Haynes 230, Alloy 800H, and Hastelloy X. This project will evaluate the role of impurities in helium coolant on the stress-assisted grain boundary oxidation and creep crack growth in candidate alloys at elevated temperatures. The project team will: • Evaluate stress-assisted grain boundary oxidation and creep crack initiation and crack growth in the temperature range of 500-850°C in a prototypical helium environment. • Evaluate the effects of oxygen partial pressure on stress-assisted grain boundary oxidation and creep crack growth in impure helium at 500°C, 700°C, and 850°C respectively. • Characterize the microstructure of candidate alloys after long-term exposure to an impure helium environment in order to understand the correlation between stress-assisted grain boundary oxidation, creep crack growth, material composition, and impurities in the helium coolant. • Evaluate grain boundary engineering as a method to mitigate stress-assisted grain boundary oxidation and creep crack growth of candidate alloys in impure helium. The maximum primary helium coolant temperature in the high-temperature reactor is expected to be 850-1,000°C.Corrosion may involve oxidation, carburization, or decarburization mechanisms depending on the temperature, oxygen partial pressure, carbon activity, and alloy composition. These corrosion reactions can substantially affect long-term mechanical properties such as crack- growth rate and fracture
El Haouari, M.; Feddi, E.; Dujardin, F.; Restrepo, R. L.; Mora-Ramos, M. E.; Duque, C. A.
2017-11-01
The ground state of a conduction electron coupled to an off-center impurity donor in a AlAS/GaAs spherical core/shell quantum dot is investigated theoretically. The image-charge effect and the influence of the electron-polar-LO-phonon interaction are considered. The electron-impurity binding energy is calculated via a variational procedure and is reported both as a function of the shell width and of the radial position of the donor atom. The polaronic effects on this quantity are particularly discussed.
Energy Technology Data Exchange (ETDEWEB)
Montoya, R., E-mail: rodrigo.montoya@cenim.csic.es [Centro Nacional de Investigaciones Metalurgicas, CENIM, CSIC, Avda. Gregorio del Amo 8, 28040 Madrid (Spain); Departamento de Matematicas, Facultad de Quimica, Universidad Nacional Autonoma de Mexico, UNAM, Ciudad Universitaria, 04510 Mexico D.F. (Mexico); Departamento de Ingenieria Metalurgica, Facultad de Quimica, Universidad Nacional Autonoma de Mexico, UNAM, Ciudad Universitaria, 04510 Mexico D.F. Mexico (Mexico); Escudero, M.L., E-mail: escudero@cenim.csic.es [Centro Nacional de Investigaciones Metalurgicas, CENIM, CSIC, Avda. Gregorio del Amo 8, 28040 Madrid (Spain); Garcia-Alonso, M.C., E-mail: crisga@cenim.csic.es [Centro Nacional de Investigaciones Metalurgicas, CENIM, CSIC, Avda. Gregorio del Amo 8, 28040 Madrid (Spain)
2011-12-15
Highlights: Black-Right-Pointing-Pointer Degradation of Mg due to the presence of impurities by finite element method. Black-Right-Pointing-Pointer A thin film of electrolyte causes galvanic corrosion focused only close on impurities. Black-Right-Pointing-Pointer A thick layer of electrolyte provokes galvanic corrosion extended the whole surface. Black-Right-Pointing-Pointer A higher number of impurities causes galvanic corrosion on the Mg surface independently of electrolyte thickness. Black-Right-Pointing-Pointer The electrolyte thickness is an important variable that affects the in vivo degradation. - Abstract: The aim of this work is to study the degradation of magnesium due to the presence of impurities, by finite element method (FEM), when different thickness of physiological medium bathes the surface. The electrochemical experimental data obtained from polarization curves are used to model mathematically the corrosion process by solving the Laplace equation and the proper boundary conditions by means of FEM. The results show that when Mg is covered by a thin film of electrolyte, galvanic corrosion is focused only on the areas located really close to the cathodic sites, and far from the impurities, the Mg matrix remains near to its corrosion potential with a natural corrosion process. However, if the Mg matrix is completely covered by a thick layer of electrolyte the potentials obtained in the Mg surface far from the impurity are higher than its corrosion potential, so the Mg suffers more severe galvanic corrosion. On the other hand, when a higher number of impurities is considered, the Mg matrix is anodically polarized and it suffers severe galvanic corrosion, independently of h. The thickness of the electrolyte h must be considered as an important variable that affects the in vivo degradation.
Determination of Impurities of Atrazine by HPLP-MS
Energy Technology Data Exchange (ETDEWEB)
Canping, Pan [Department of Applied Chemistry, China Agricultural University Beijing (China)
2009-07-15
The determination of the main impurities of the herbicide atrazine by GC/FID, GC/MS and LC/MS is described. The most relevant technical impurities were synthesized and characterized by IR and UV spectroscopy as well. The impurity profiles of different technical grade formulated products were tested and the typical impurities identified. (author)
Influence of iron impurities on defected graphene
Energy Technology Data Exchange (ETDEWEB)
Faccio, Ricardo; Pardo, Helena [Centro NanoMat, Cryssmat-Lab, DETEMA, Polo Tecnológico de Pando, Facultad de Química, Universidad de la República, Cno. Saravia s/n, CP 91000 Pando (Uruguay); Centro Interdisciplinario en Nanotecnología, Química y Física de Materiales, Espacio Interdisciplinario, Universidad de la República, Montevideo (Uruguay); Araújo-Moreira, Fernando M. [Materials and Devices Group, Department of Physics, Universidade Federal de São Carlos, SP 13565-905 (Brazil); Mombrú, Alvaro W., E-mail: amombru@fq.edu.uy [Centro NanoMat, Cryssmat-Lab, DETEMA, Polo Tecnológico de Pando, Facultad de Química, Universidad de la República, Cno. Saravia s/n, CP 91000 Pando (Uruguay); Centro Interdisciplinario en Nanotecnología, Química y Física de Materiales, Espacio Interdisciplinario, Universidad de la República, Montevideo (Uruguay)
2015-03-01
Highlights: • The interaction among a multivacancy graphene system and iron impurities is studied. • The studied iron impurities were single atom and tetrahedral and octahedral clusters. • DFT calculations using the VASP code were performed. • The embedding of Fe affects the structure and electronic behavior in the graphene. • Half metal or semimetal behavior can be obtained, depending on the Fe impurities. - Abstract: The aim of this work is to study the interaction of selected iron cluster impurities and a multivacancy graphene system, in terms of the structural distortion that the impurities cause as well as their magnetic response. While originally, the interaction has been limited to vacancies and isolated metallic atoms, in this case, we consider small iron clusters. This study was undertaken using Density Functional Theory (DFT) calculations. The influence of the iron impurities in the electronic structure of the vacant graphene system is discussed. The main conclusion of this work is that the presence of iron impurities acts lowering the magnetic signal due to the occurrence of spin pairing between carbon and iron, instead of enhancing the possible intrinsic carbon magnetism.
Influence of iron impurities on defected graphene
International Nuclear Information System (INIS)
Faccio, Ricardo; Pardo, Helena; Araújo-Moreira, Fernando M.; Mombrú, Alvaro W.
2015-01-01
Highlights: • The interaction among a multivacancy graphene system and iron impurities is studied. • The studied iron impurities were single atom and tetrahedral and octahedral clusters. • DFT calculations using the VASP code were performed. • The embedding of Fe affects the structure and electronic behavior in the graphene. • Half metal or semimetal behavior can be obtained, depending on the Fe impurities. - Abstract: The aim of this work is to study the interaction of selected iron cluster impurities and a multivacancy graphene system, in terms of the structural distortion that the impurities cause as well as their magnetic response. While originally, the interaction has been limited to vacancies and isolated metallic atoms, in this case, we consider small iron clusters. This study was undertaken using Density Functional Theory (DFT) calculations. The influence of the iron impurities in the electronic structure of the vacant graphene system is discussed. The main conclusion of this work is that the presence of iron impurities acts lowering the magnetic signal due to the occurrence of spin pairing between carbon and iron, instead of enhancing the possible intrinsic carbon magnetism
Timmermans, Eddy; Blinova, Alina; Boshier, Malcolm
2013-05-01
Polarons (particles that interact with the self-consistent deformation of the host medium that contains them) self-localize when strongly coupled. Dilute Bose-Einstein condensates (BECs) doped with neutral distinguishable atoms (impurities) and armed with a Feshbach-tuned impurity-boson interaction provide a unique laboratory to study self-localized polarons. In nature, self-localized polarons come in two flavors that exhibit qualitatively different behavior: In lattice systems, the deformation is slight and the particle is accompanied by a cloud of collective excitations as in the case of the Landau-Pekar polarons of electrons in a dielectric lattice. In natural fluids and gases, the strongly coupled particle radically alters the medium, e.g. by expelling the host medium as in the case of the electron bubbles in superfluid helium. We show that BEC-impurities can self-localize in a bubble, as well as in a Landau-Pekar polaron state. The BEC-impurity system is fully characterized by only two dimensionless coupling constants. In the corresponding phase diagram the bubble and Landau-Pekar polaron limits correspond to large islands separated by a cross-over region. The same BEC-impurity species can be adiabatically Feshbach steered from the Landau-Pekar to the bubble regime. This work was funded by the Los Alamos LDRD program.
Characterization of impurities in biogas before and after upgrading to vehicle fuel
Energy Technology Data Exchange (ETDEWEB)
Arrhenius, Karine; Johansson, Ulrika [SP Technical Research Institute of Sweden, Boraas (Sweden)
2012-01-15
Biogases produced by digesting organic wastes, residual sludge from waste water treatment, energy crops,byproducts from industry or in landfills contain impurities which can be harmful for components that will be in contact with the biogas during its utilization. In this project, the impurities present in biogases have been mapped out depending upon which feedstock is digested. P-cymene och D-limonene, two terpenes, have been found to be characteristics for biogases produced from the digestion of waste including household wastes while an 'oil' fraction containing alkanes with 9 to 13 carbon atoms is characteristic for biogases produced at waste water treatment plants. Ketones and sulfur compounds are found in biogases produced from the digestion of food industry wastes or energy crops. It was not possible to characterize impurities in biogases produced in farm plants digesting manure because not enough samples were analyzed from these plants. In order to understand the relation between the feedstock and the impurities present in the biogas, an extensive study on feedstock characterization must be conducted. One question to be answered is if these impurities only originate from the volatilization from the feedstock and in this case, why only these specific compounds are found at significant concentrations. In this study we have also studied how effective purification/upgrading techniques are to remove impurities that have been identified in biogases. En general comment is that the upgraded gas still contains a part of the characteristic impurities which have been identified for each feedstock at different levels of concentration depending on which technique has been used. The results show that activated carbon filters are more or less effective. Some of them can remove more than 90 % of the impurities while others remove less that 10 %. Results show also that the amine scrubber have very moderate effects on the impurities composition. In that case, the
Effective string theory and QCD scattering amplitudes
International Nuclear Information System (INIS)
Makeenko, Yuri
2011-01-01
QCD string is formed at distances larger than the confinement scale and can be described by the Polchinski-Strominger effective string theory with a nonpolynomial action, which has nevertheless a well-defined semiclassical expansion around a long-string ground state. We utilize modern ideas about the Wilson-loop/scattering-amplitude duality to calculate scattering amplitudes and show that the expansion parameter in the effective string theory is small in the Regge kinematical regime. For the amplitudes we obtain the Regge behavior with a linear trajectory of the intercept (d-2)/24 in d dimensions, which is computed semiclassically as a momentum-space Luescher term, and discuss an application to meson scattering amplitudes in QCD.
Hydrogenic impurity in double quantum dots
International Nuclear Information System (INIS)
Wang, X.F.
2007-01-01
The ground state binding energy and the average interparticle distances for a hydrogenic impurity in double quantum dots with Gaussian confinement potential are studied by the variational method. The probability density of the electron is calculated, too. The dependence of the binding energy on the impurity position is investigated for GaAs quantum dots. The result shows that the binding energy has a minimum as a function of the distance between the two quantum dots when the impurity is located at the center of one quantum dot or at the center of the edge of one quantum dot. When the impurity is located at the center of the two dots, the binding energy decreases monotonically
Quasi-regular impurity distribution driven by charge-density wave
International Nuclear Information System (INIS)
Baldea, I.; Badescu, M.
1991-09-01
The displacive motion of the impurity distribution immersed into the one-dimensional system has recently been studied in detail as one kind of quasi-regularity driven by CDW. As a further investigation of this problem we develop here a microscopical model for a different kind of quasi-regular impurity distribution driven by CDW, consisting of the modulation in the probability of occupied sites. The dependence on impurity concentration and temperature of relevant CDW quantities is obtained. Data reported in the quasi-1D materials NbSe 3 and Ta 2 NiSe 7 (particularly, thermal hysteresis effects at CDW transition) are interpreted in the framework of the present model. Possible similarities to other physical systems are also suggested. (author). 38 refs, 7 figs
Impurity production and transport in the boundary layer of tokamaks
International Nuclear Information System (INIS)
McCracken, G.M.
1987-01-01
The processes by which impurities are produced and enter the discharge are discussed. Emphasis is placed on sputtering at the limiter and an analytical global model is described which incorporates the self-stabilizing effects whch control the edge temperature. Predictions of the scaling of edge temperature and of total radiated power are compared with experimental data from JET and other tokamaks operating with limiters. Under many conditions the scaling of the edge conditions and of the radiated power is accurately predicted. Impurity transport in the boundary and the question of how to control the boundary layer is then discussed. The example of the Impurity Control Limiter on DITE is described. (author)
Modeling of ELM events and their effect on impurity enrichment
International Nuclear Information System (INIS)
Hogan, J.; Colchin, R.; Coster, D.; Baylor, L.; Fenstermacher, M.; Groth, M.; Wade, M.
2003-01-01
Modeling of transient impurity transport during large ELMs is used to explore basic processes which may determine ELM-averaged enrichment. The b2-Eirene code (solps4), used for DIII-D geometry, suggests that a complex sequence can occur during an ELM cycle in which a transiently detached phase, with relatively low enrichment, can occur even under nominally attached conditions. A slower recovery phase then follows, in which the effect of induced scrape-off layer flows can increase in importance. The model results are compared with available fast time-scale measurements. The observed increased enrichment with higher Z is similar to trends in basic particle reflection properties. Neon recycling processes may thus introduce a significant history effect, as illustrated by analysis of continuous, unforced neon accumulation in a DIII-D discharge with a well-characterized operational history
Effect of Fe, Co, Si and Ge impurities on optical properties of graphene sheet
International Nuclear Information System (INIS)
Kheyri, A.; Nourbakhsh, Z.; Darabi, E.
2016-01-01
The electronic and linear optical properties of pure graphene and impurity-graphene (with Fe, Co, Si and Ge impurities) sheets are investigated by using the full potential linear augmented plane wave plus local orbital (FPLAPW + lo) in the framework of the density functional theory (DFT). The calculated results are obtained within the generalized gradient approximation using the Perdew–Burke–Ernzerhof scheme in the presence of spin-orbit interaction. The band structure, partial electron density of states, dielectric function, absorption coefficient, optical conductivity, extinction index, energy loss function, reflectivity and the refraction index of these sheets for parallel and perpendicular electromagnetic wave polarization to sheet are investigated. The optical conductivity of Si-graphene and Ge-graphene sheets for the parallel electromagnetic wave polarization to the sheet starts with a gap about 0.4 eV confirms that these sheets have semiconductor behavior. Also the optical spectra of these sheets are anisotropic along these two wave polarizations. The dielectric function in the static limit of pure graphene sheet for perpendicular electromagnetic wave polarization to sheet does not significant change in the presence of Si, Ge, Fe and Co impurities. The static refractive index of Fe-graphene and Co-graphene sheets for parallel electromagnetic wave polarization to sheet is much larger than the corresponding value of pure graphene sheet. - Highlights: • Graphene sheet with Fe and Co impurities is metal. • Graphene sheet with Si and Ge impurities is semiconductor with 0.2 eV energy band gap. • These sheets optical spectra have metallic behavior for perpendicular polarization. • These sheets optical spectra have semiconductor behavior for parallel polarization. • Graphene sheet with Si and Ge impurities can use for optoelectronic devices.
Effect of Fe, Co, Si and Ge impurities on optical properties of graphene sheet
Energy Technology Data Exchange (ETDEWEB)
Kheyri, A. [Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran (Iran, Islamic Republic of); Nourbakhsh, Z., E-mail: z.nourbakhsh@sci.ui.ac.ir [Physics Department, Faculty of Science, University of Isfahan, Isfahan (Iran, Islamic Republic of); Darabi, E. [Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran (Iran, Islamic Republic of)
2016-08-01
The electronic and linear optical properties of pure graphene and impurity-graphene (with Fe, Co, Si and Ge impurities) sheets are investigated by using the full potential linear augmented plane wave plus local orbital (FPLAPW + lo) in the framework of the density functional theory (DFT). The calculated results are obtained within the generalized gradient approximation using the Perdew–Burke–Ernzerhof scheme in the presence of spin-orbit interaction. The band structure, partial electron density of states, dielectric function, absorption coefficient, optical conductivity, extinction index, energy loss function, reflectivity and the refraction index of these sheets for parallel and perpendicular electromagnetic wave polarization to sheet are investigated. The optical conductivity of Si-graphene and Ge-graphene sheets for the parallel electromagnetic wave polarization to the sheet starts with a gap about 0.4 eV confirms that these sheets have semiconductor behavior. Also the optical spectra of these sheets are anisotropic along these two wave polarizations. The dielectric function in the static limit of pure graphene sheet for perpendicular electromagnetic wave polarization to sheet does not significant change in the presence of Si, Ge, Fe and Co impurities. The static refractive index of Fe-graphene and Co-graphene sheets for parallel electromagnetic wave polarization to sheet is much larger than the corresponding value of pure graphene sheet. - Highlights: • Graphene sheet with Fe and Co impurities is metal. • Graphene sheet with Si and Ge impurities is semiconductor with 0.2 eV energy band gap. • These sheets optical spectra have metallic behavior for perpendicular polarization. • These sheets optical spectra have semiconductor behavior for parallel polarization. • Graphene sheet with Si and Ge impurities can use for optoelectronic devices.
Orbit effects on impurity transport in a rotating tokamak plasma
International Nuclear Information System (INIS)
Wong, K.L.; Cheng, C.Z.
1988-05-01
Particle orbits in a rotating tokamak plasma are calculated from the equation of motion in the frame that rotates with the plasma. It is found that heavy particles in a rotating plasma can drift away from magnetic surfaces significantly faster with a higher bounce frequency, resulting in a diffusion coefficient much larger than that for a stationary plasma. Particle orbits near the surface of a rotating tokamak are also analyzed. Orbit effects indicate that more impurities can penetrate into a plasma rotating with counter-beam injection. Particle simulation is carried out with realistic experimental parameters and the results are in qualitative agreement with some experimental observations in the Tokamak Fusion Test Reactor (TFTR). 19 refs., 15 figs
Device for removing impurities from liquid metals
International Nuclear Information System (INIS)
Naito, Kesahiro; Yokota, Norikatsu; Shimoyashiki, Shigehiro; Takahashi, Kazuo; Ishida, Tomio.
1984-01-01
Purpose: To attain highly reliable and efficient impurity removal by forming temperature distribution the impurity removing device thereby providing the function of corrosion product trap, nuclear fission product trap and cold trap under the conditions suitable to the impurity removing materials. Constitution: The impurity removing device comprises a container containing impurity removing fillers. The fillers comprise material for removing corrosion products, material for removing nuclear fission products and material for removing depositions from liquid sodium. The positions for the respective materials are determined such that the materials are placed under the temperature conditions easy to attain their function depending on the temperature distribution formed in the removing device, whereby appropriate temperature condition is set to each of the materials. (Yoshino, Y.)
Directory of Open Access Journals (Sweden)
Shenyu Dai
2018-03-01
Full Text Available The structural, electrical and mid-infrared optical properties of wurtzite structured ZnSe nanowires with different Chromium impurity distribution are investigated using first-principles calculation based on density-functional theory (DFT. The formation energies have been calculated to study the relative stabilities of different Cr doping positions. It is shown that when the Cr doping position shifted from the center to the edge, the splitting energy between 5T2 and 5E levels of Cr d-orbitals is decreased and a redshift is observed in the calculated infrared absorption spectra. A probable reason for these effects of the impurity distribution is discussed. Keywords: First-principles, Nanowires, Impurity distribution, Cr-doped ZnSe
Impurity effects in neutron-irradiated simple oxides: Implications for fusion devices
International Nuclear Information System (INIS)
Gonzalez, R.; Chen, Y.; Caceres, D.; Vergara, I.
2006-01-01
Radiation damage induced by neutron irradiation was studied in undoped MgO crystals and in MgO doped with either iron, hydrogen or lithium impurities. The oxygen-vacancy concentration produced by irradiation increases with neutron fluence. The net production rates resulting from irradiations with 14.8 MeV neutrons are about twice those produced by fission neutrons. In nominally pure crystals, the oxygen-vacancy concentration incurred by the fission-neutron irradiation is higher in crystals with a larger number of inherent impurities (such as iron) due to trapping of interstitials by impurities. Suppression of these defects is observed in MgO:H crystals and attributed to migration of oxygen vacancies to microcavities filled with H 2 gas. In MgO:Li crystals irradiated with neutron fluences below 10 18 n/cm 2 , most of the oxygen vacancies are camouflaged as hydride ions. Nanoindentation experiments show that hardness increases with neutron fluence and is independent of the presence of lithium in the crystal. Comparison between a neutron-irradiated and a thermochemically reduced crystal containing similar concentrations of oxygen vacancies shows that 70% of the neutron-irradiation hardening is produced by interstitials, 30% by oxygen vacancies and a negligible amount by higher-order point defects
Resolution effects and analysis of small-angle neutron scattering data
DEFF Research Database (Denmark)
Pedersen, J.S.
1993-01-01
A discussion of the instrumental smearing effects for small-angle neutron scattering (SANS) data sets is given. It is shown that these effects can be described by a resolution function, which describes the distribution of scattering vectors probed for the nominal values of the scattering vector...
Parametric dependences of impurity transport in the Tore Supra tokamak
International Nuclear Information System (INIS)
Parisot, Th.
2007-09-01
During this Ph.D. work, a full setup of tools for an experimental investigation of impurity transport has been developed on the Tore Supra tokamak. It includes a laser blow-off system for metallic impurity injections and developments for ITC (Impurity Transport Code), a transport code which allows the extraction of the experimental impurity transport coefficients (diffusion and convection velocity). This tool has been used to perform and analyse several experiments, to evidence parametric dependences of impurity transport. In a first experiment, a confinement time law for nickel in Tore Supra has been obtained as a function of collisionality ν * and normalized Larmor radius ρ * . Then the impurity charge Z role has been investigated in various conditions: ohmic regime with or without sawteeth, and sawtooth less L-mode with LH power. No Z effect is observed, consistently with theoretical predictions, whether neoclassical (NCLASS) or for turbulent transport with both non linear gyro-fluid (TRB) and quasilinear gyrokinetic (QuaLiKiz) simulations. An exception is found for LH heated plasmas where the confinement time seems to decrease for the heaviest impurities. This is not explained by any model available. The observed transport is close to neoclassical between sawtooth relaxations, in the centre (r q-1 ) of ohmic plasmas, turbulent outside. Without sawteeth, it is turbulent in the whole plasma, for ohmic or L mode discharges. The profile shape of the diffusion coefficient is here qualitatively different, with a stronger and deeper transition between the low diffusion central region and a more turbulent peripheral region for LH heated plasmas. (author)
Orbital effect of the magnetic field in dynamical mean-field theory
Acheche, S.; Arsenault, L.-F.; Tremblay, A.-M. S.
2017-12-01
The availability of large magnetic fields at international facilities and of simulated magnetic fields that can reach the flux-quantum-per-unit-area level in cold atoms calls for systematic studies of orbital effects of the magnetic field on the self-energy of interacting systems. Here we demonstrate theoretically that orbital effects of magnetic fields can be treated within single-site dynamical mean-field theory with a translationally invariant quantum impurity problem. As an example, we study the one-band Hubbard model on the square lattice using iterated perturbation theory as an impurity solver. We recover the expected quantum oscillations in the scattering rate, and we show that the magnetic fields allow the interaction-induced effective mass to be measured through the single-particle density of states accessible in tunneling experiments. The orbital effect of magnetic fields on scattering becomes particularly important in the Hofstadter butterfly regime.
Mobile impurities in ferromagnetic liquids
Kantian, Adrian; Schollwoeck, Ulrich; Giamarchi, Thierry
2011-03-01
Recent work has shown that mobile impurities in one dimensional interacting systems may exhibit behaviour that differs strongly from that predicted by standard Tomonaga-Luttinger liquid theory, with the appearance of power-law divergences in the spectral function signifying sublinear diffusion of the impurity. Using time-dependent matrix product states, we investigate a range of cases of mobile impurities in systems beyond the analytically accessible examples to assess the existence of a new universality class of low-energy physics in one-dimensional systems. Correspondence: Adrian.Kantian@unige.ch This work was supported in part by the Swiss SNF under MaNEP and division II.
Impurity coupled to an artificial magnetic field in a Fermi gas in a ring trap
Ünal, F. Nur; Hetényi, B.; Oktel, M. Ã.-.
2015-05-01
The dynamics of a single impurity interacting with a many-particle background is one of the central problems of condensed-matter physics. Recent progress in ultracold-atom experiments makes it possible to control this dynamics by coupling an artificial gauge field specifically to the impurity. In this paper, we consider a narrow toroidal trap in which a Fermi gas is interacting with a single atom. We show that an external magnetic field coupled to the impurity is a versatile tool to probe the impurity dynamics. Using a Bethe ansatz, we calculate the eigenstates and corresponding energies exactly as a function of the flux through the trap. Adiabatic change of flux connects the ground state to excited states due to flux quantization. For repulsive interactions, the impurity disturbs the Fermi sea by dragging the fermions whose momentum matches the flux. This drag transfers momentum from the impurity to the background and increases the effective mass. The effective mass saturates to the total mass of the system for infinitely repulsive interactions. For attractive interactions, the drag again increases the effective mass which quickly saturates to twice the mass of a single particle as a dimer of the impurity and one fermion is formed. For excited states with momentum comparable to number of particles, effective mass shows a resonant behavior. We argue that standard tools in cold-atom experiments can be used to test these predictions.
Scattering effect on entanglement propagation in RCFTs
Energy Technology Data Exchange (ETDEWEB)
Numasawa, Tokiro [Yukawa Institute for Theoretical Physics, Kyoto University,Kitashirakawa Oiwakecho, Sakyo-ku, Kyoto, 606-8502 (Japan); Kavli Institute for Theoretical Physics, University of California Santa Barbara,Santa Barbara, CA, 93106 (United States)
2016-12-14
In this paper we discuss the scattering effect on entanglement propagation in RCFTs. In our setup, we consider the time evolution of excited states created by the insertion of many local operators. Our results show that because of the finiteness of quantum dimension, entanglement is not changed after the scattering in RCFTs. In this mean, entanglement is conserved after the scattering event in RCFTs, which reflects the integrability of the system. Our results are also consistent with the free quasiparticle picture after the global quenches.
The effect of Compton scattering on quantitative SPECT imaging
International Nuclear Information System (INIS)
Beck, J.W.; Jaszczak, R.J.; Starmer, C.F.
1982-01-01
A Monte Carlo code has been developed to simulate the response of a SPECT system. The accuracy of the code has been verified and has been used in this research to study and illustrate the effects of Compton scatter on quantitative SPECT measurements. The effects of Compton scattered radiation on gamma camera response have been discussed by several authors, and will be extended to rotating gamma camera SPECT systems. The unique feature of this research includes the pictorial illustration of the Compton scattered and the unscattered components of the photopeak data on SPECT imaging by simulating phantom studies with and without Compton scatter
Determination of multiple scattering effects
International Nuclear Information System (INIS)
Langevin, M.
1981-01-01
The integration of Sigmund and Winterbon numerical values is extended to the reduced thickness tau=2000. The diagram obtained allows a simple determination of the multiple scattering effect for different targets and projectiles [fr
EUV impurity study of the Alcator tokamak
International Nuclear Information System (INIS)
Terry, J.L.; Chen, K.I.; Moos, H.W.; Marmar, E.S.
1978-01-01
The intensity of resonance line radiation from oxygen, nitrogen, carbon and molybdenum impurities has been measured in the high-field (80kG), high-density (6x10 14 cm -3 ) discharges of the Alcator Tokamak, using a 0.4-m normal-incidence monochromator (300-1300A) with its line of sight fixed along a major radius. Total light-impurity concentrations of a few tenths of a percent have been estimated by using both a simple model and a computer code which included Pfirsch-Schlueter impurity diffusion. The resulting values of Zsub(eff), including the contributions due to both the light impurities and molybdenum, were close to one. The power lost through the impurity line radiation from the lower ionization states accounted for approximately 10% of the total Ohmic input power at high densities. (author)
Interactions of impurities with a moving grain boundary
Energy Technology Data Exchange (ETDEWEB)
Bauer, C L [Carnegie-Mellon Univ., Pittsburgh, Pa. (USA)
1975-01-01
Most theories developed to explain interaction of impurities with a moving grain boundary involve a uniform excess impurity concentration distributed along a planar grain boundary. As boundary velocity increases, the excess impurities exert a net drag force on the boundary until a level is reached whereat the drag force no longer can balance the driving force and breakaway of the boundary from these impurities occurs. In this investigation, assumptions of a uniform lateral impurity profile and a planar grain boundary shape are relaxed by allowing both forward and lateral diffusion of impurities in the vicinity of a grain boundary. It is found that the two usual regions (drag of impurities by, and breakaway of a planar grain boundary) are separated by an extensive region wherein a uniform lateral impurity profile and a planar grain boundary shape are unstable. It is suspected that, in this unstable region, grain boundaries assume a spectrum of more complex morphologies and that elucidation of these morphologies can provide the first definitive description of the breakaway process and insight to more complex phenomena such as solid-solution strengthening, grain growth and secondary recrystallization.
Lattice dynamics of impurity clusters : application to pairs
International Nuclear Information System (INIS)
Chandralekha Devi, N.; Behera, S.N.
1979-01-01
A general solution is obtained for the lattice dynamics of a cluster of n-impurity atoms using the double-time Green's function formalism. The cluster is characterized by n-mass defect and m-force constant change parameters. It is shown that this general solution for the Green's function for the n-impurity cluster can also be expressed in terms of the Green's function for the (n-1)-impurity cluster. As an application, the cluster impurity modes for a pair are calculated using the Debye model for the host lattice dynamics. The splitting of the high frequency local modes and nearly zero frequency resonant modes due to pairs show an oscillatory behaviour on varying the distance of separation between the two impurity atoms. These oscillations are most prominent for two similar impurities and get damped for two dissimilar impurities or if one of the impurities produces a force constant change. The predictions of the calculation provide qualitative explanation of the data obtained from the infrared measurements of the resonant modes in mixed crystal system of KBrsub(1-c)Clsub(c):Lisup(+) and KBrsub(1-c)Isub(c):Lisup(+). (author)
Demixing of impurities and hydrogen as deduced from Zeff profiles in the boronized ASDEX
International Nuclear Information System (INIS)
Steuer, K.H.; Roehr, H.; Engelhardt, W.; Fussmann, G.; Kallenbach, A.; Kurzan, B.; Murmann, H.D.
1990-01-01
Substantial progress towards fusion has been made in the confinement, stability and heating of tokamak plasmas. The transport behaviour of magnetically confined plasmas, however, is still an unsolved problem. The transport mechanisms of hydrogen and of impurities are known to be different, leading to phenomena such as impurity accumulation on axis, especially in good confinement regimes, and more generally to demixing of the various species. Besides energy losses from impurity radiation, one has to be concerned about dilution of the fuel-ion density, and about effects that impurities may have on the main ion and electron transport. To understand the transport behaviour of the different plasma species, one needs their spatial density profiles. It is convenient to represent the various impurities by a characteristic impurity ion with a density n z and a fictive charge Z (Z = Σn i Z i 2 / Σn i Z i ; i ≥ 2). A typical value for Z is 7, indicating that light impurities are dominating. Comparing the different profiles, we find characteristic differences in the electron, proton and impurity transport behaviour. (orig./AH)
Directory of Open Access Journals (Sweden)
Saeedeh Ghafourian
2011-01-01
Full Text Available Single wall carbon nanotubes (SWCNT extensively are attractive from both theoretical and experimental point of view, due to its technological applications such as nano electronics devises. SWCNT are created by rolling a graphen sheet into a cyclindrical form. We have investigated the possibility of making a ferromagnetic semiconductor zigzag SWCNT by doping magnetic impurities. We found by increasing magnetic impurities doping on a zigzag SWCNT, average magnetization is increased and one can make a ferromagnetic semiconductor
Uranium analysis. Impurities determination by spark mass spectrometry
International Nuclear Information System (INIS)
Anon.
Determination of impurities in uranium, suitable for atomic content greater than 10 -8 , particularly adapted for a low content. The method is quantitative for metallic impurities and qualitative for non metallic impurities [fr
Fluid and gyrokinetic simulations of impurity transport at JET
DEFF Research Database (Denmark)
Nordman, H; Skyman, A; Strand, P
2011-01-01
Impurity transport coefficients due to ion-temperature-gradient (ITG) mode and trapped-electron mode turbulence are calculated using profile data from dedicated impurity injection experiments at JET. Results obtained with a multi-fluid model are compared with quasi-linear and nonlinear gyrokinetic...... simulation results obtained with the code GENE. The sign of the impurity convective velocity (pinch) and its various contributions are discussed. The dependence of the impurity transport coefficients and impurity peaking factor −∇nZ/nZ on plasma parameters such as impurity charge number Z, ion logarithmic...
Fermi-edge transmission resonance in graphene driven by a single Coulomb impurity.
Karnatak, Paritosh; Goswami, Srijit; Kochat, Vidya; Pal, Atindra Nath; Ghosh, Arindam
2014-07-11
The interaction between the Fermi sea of conduction electrons and a nonadiabatic attractive impurity potential can lead to a power-law divergence in the tunneling probability of charge through the impurity. The resulting effect, known as the Fermi edge singularity (FES), constitutes one of the most fundamental many-body phenomena in quantum solid state physics. Here we report the first observation of FES for Dirac fermions in graphene driven by isolated Coulomb impurities in the conduction channel. In high-mobility graphene devices on hexagonal boron nitride substrates, the FES manifests in abrupt changes in conductance with a large magnitude ≈e(2)/h at resonance, indicating total many-body screening of a local Coulomb impurity with fluctuating charge occupancy. Furthermore, we exploit the extreme sensitivity of graphene to individual Coulomb impurities and demonstrate a new defect-spectroscopy tool to investigate strongly correlated phases in graphene in the quantum Hall regime.
Modelling of impurity transport in ergodic layer of LHD
International Nuclear Information System (INIS)
Feng, Y.; Masuzaki, S.; Morisaki, T.; Ohyabu, N.; Yamada, H.; Komori, A.; Motojima, O.; Kobayashi, M.
2008-01-01
The impurity transport properties in the ergodic layer of LHD are analyzed by the 3D edge transport code as well as 1D simple model, which is used to illustrate the essential transport terms in the analysis. It is found that as the plasma density increases the edge surface layers, very edge region of the ergodic layer, enters friction dominant regime, resulting in impurity retention. It is considered that the cause for the retention is both temperature drop and the flow acceleration in the edge surface layers. The edge surface layers can provide effective retention of impurities coming from divertor as well as the first wall, because of the geometrical advantage of the edge region of LHD. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Continuous-time quantum Monte Carlo impurity solvers
Gull, Emanuel; Werner, Philipp; Fuchs, Sebastian; Surer, Brigitte; Pruschke, Thomas; Troyer, Matthias
2011-04-01
representations of quantum dots and molecular conductors and play an increasingly important role in the theory of "correlated electron" materials as auxiliary problems whose solution gives the "dynamical mean field" approximation to the self-energy and local correlation functions. Solution method: Quantum impurity models require a method of solution which provides access to both high and low energy scales and is effective for wide classes of physically realistic models. The continuous-time quantum Monte Carlo algorithms for which we present implementations here meet this challenge. Continuous-time quantum impurity methods are based on partition function expansions of quantum impurity models that are stochastically sampled to all orders using diagrammatic quantum Monte Carlo techniques. For a review of quantum impurity models and their applications and of continuous-time quantum Monte Carlo methods for impurity models we refer the reader to [2]. Additional comments: Use of dmft requires citation of this paper. Use of any ALPS program requires citation of the ALPS [1] paper. Running time: 60 s-8 h per iteration.
Anomalous Hall effect scaling in ferromagnetic thin films
Grigoryan, Vahram L.
2017-10-23
We propose a scaling law for anomalous Hall effect in ferromagnetic thin films. Our approach distinguishes multiple scattering sources, namely, bulk impurity, phonon for Hall resistivity, and most importantly the rough surface contribution to longitudinal resistivity. In stark contrast to earlier laws that rely on temperature- and thickness-dependent fitting coefficients, this scaling law fits the recent experimental data excellently with constant parameters that are independent of temperature and film thickness, strongly indicating that this law captures the underlying physical processes. Based on a few data points, this scaling law can even fit all experimental data in full temperature and thickness range. We apply this law to interpret the experimental data for Fe, Co, and Ni and conclude that (i) the phonon-induced skew scattering is unimportant as expected; (ii) contribution from the impurity-induced skew scattering is negative; (iii) the intrinsic (extrinsic) mechanism dominates in Fe (Co), and both the extrinsic and intrinsic contributions are important in Ni.
Anomalous Hall effect scaling in ferromagnetic thin films
Grigoryan, Vahram L.; Xiao, Jiang; Wang, Xuhui; Xia, Ke
2017-01-01
We propose a scaling law for anomalous Hall effect in ferromagnetic thin films. Our approach distinguishes multiple scattering sources, namely, bulk impurity, phonon for Hall resistivity, and most importantly the rough surface contribution to longitudinal resistivity. In stark contrast to earlier laws that rely on temperature- and thickness-dependent fitting coefficients, this scaling law fits the recent experimental data excellently with constant parameters that are independent of temperature and film thickness, strongly indicating that this law captures the underlying physical processes. Based on a few data points, this scaling law can even fit all experimental data in full temperature and thickness range. We apply this law to interpret the experimental data for Fe, Co, and Ni and conclude that (i) the phonon-induced skew scattering is unimportant as expected; (ii) contribution from the impurity-induced skew scattering is negative; (iii) the intrinsic (extrinsic) mechanism dominates in Fe (Co), and both the extrinsic and intrinsic contributions are important in Ni.
Determinant method and quantum simulations of many-body effects in a single impurity Anderson model
International Nuclear Information System (INIS)
Gubernatis, J.E.; Olson, T.; Scalapino, D.J.; Sugar, R.L.
1985-01-01
A short description is presented of a quantum Monte Carlo technique, often referred to as the determinant method, that has proved useful for simulating many-body effects in systems of interacting fermions at finite temperatures. Preliminary results using this technique on a single impurity Anderson model are reported. Examples of such many-body effects as local moment formation, Kondo behavior, and mixed valence phenomena found in the simulations are shown. 10 refs., 3 figs
Method for detecting trace impurities in gases
Freund, S.M.; Maier, W.B. II; Holland, R.F.; Beattie, W.H.
A technique for considerably improving the sensitivity and specificity of infrared spectrometry as applied to quantitative determination of trace impurities in various carrier or solvent gases is presented. A gas to be examined for impurities is liquefied and infrared absorption spectra of the liquid are obtained. Spectral simplification and number densities of impurities in the optical path are substantially higher than are obtainable in similar gas-phase analyses. Carbon dioxide impurity (approx. 2 ppM) present in commercial Xe and ppM levels of Freon 12 and vinyl chloride added to liquefied air are used to illustrate the method.
Process and system for removing impurities from a gas
Henningsen, Gunnar; Knowlton, Teddy Merrill; Findlay, John George; Schlather, Jerry Neal; Turk, Brian S
2014-04-15
A fluidized reactor system for removing impurities from a gas and an associated process are provided. The system includes a fluidized absorber for contacting a feed gas with a sorbent stream to reduce the impurity content of the feed gas; a fluidized solids regenerator for contacting an impurity loaded sorbent stream with a regeneration gas to reduce the impurity content of the sorbent stream; a first non-mechanical gas seal forming solids transfer device adapted to receive an impurity loaded sorbent stream from the absorber and transport the impurity loaded sorbent stream to the regenerator at a controllable flow rate in response to an aeration gas; and a second non-mechanical gas seal forming solids transfer device adapted to receive a sorbent stream of reduced impurity content from the regenerator and transfer the sorbent stream of reduced impurity content to the absorber without changing the flow rate of the sorbent stream.
Ionic Impurity in a Bose-Einstein Condensate at Submicrokelvin Temperatures
Kleinbach, K. S.; Engel, F.; Dieterle, T.; Löw, R.; Pfau, T.; Meinert, F.
2018-05-01
Rydberg atoms immersed in a Bose-Einstein condensate interact with the quantum gas via electron-atom and ion-atom interaction. To suppress the typically dominant electron-neutral interaction, Rydberg states with a principal quantum number up to n =190 are excited from a dense and tightly trapped micron-sized condensate. This allows us to explore a regime where the Rydberg orbit exceeds the size of the atomic sample by far. In this case, a detailed line shape analysis of the Rydberg excitation spectrum provides clear evidence for ion-atom interaction at temperatures well below a microkelvin. Our results may open up ways to enter the quantum regime of ion-atom scattering for the exploration of charged quantum impurities and associated polaron physics.
International Nuclear Information System (INIS)
Cecchi, J.L.
1980-06-01
The control of impurities in TFTR will be a particularly difficult problem due to the large energy and particle fluxes expected in the device. As part of the TFTR Flexibility Modification (TEM) project, a program has been implemented to address this problem. Transport code simulations are used to infer an impurity limit criterion as a function of the impurity atomic number. The configurational designs of the limiters and associated protective plates are discussed along with the consideration of thermal and mechanical loads due to normal plasma operation, neutral beams, and plasma disruptions. A summary is given of the materials-related research, which has been a collaborative effort involving groups at Argonne National Laboratory, Sandia Laboratories, and Princeton Plasma Physics Laboratory. Conceptual designs are shown for getterng systems capable of regenerating absorbed tritium. Research on this topic by groups at the previously mentioned laboratories and SAES Research Laboratory is reviewed
Local chemistry of Al and P impurities in silica
DEFF Research Database (Denmark)
Lægsgaard, Jesper; Stokbro, Kurt
2000-01-01
The local structure around Al and P impurities in silica is investigated using density-functional theory. Two distinct cases are considered: impurities substituting for a Si atom in alpha quartz, and impurities implanted in a stoichiometric alpha-quartz crystal. Both impurity elements are found t...
Marbler, H.; Erickson, K. P.; Schmidt, M.; Lempp, Ch.; Pöllmann, H.
2012-04-01
An experimental study of the behaviour of reservoir sandstones from deep saline aquifers during the injection and geological storage of CO2 with the inherent impurities SOX and NOX is part of the German national project COORAL*. Sample materials were taken from outcrops of possible reservoir formations of Rotliegend and Bunter Sandstones from the North German Basin. A combination of mineralogical alteration experiments and geomechanical tests was carried out on these rocks to study the potential effects of the impurities within the CO2 pore fluid. Altered rock samples after the treatment with CO2 + SOX/NOX in an autoclave system were loaded in a triaxial cell under in-situ pressure and temperature conditions in order to estimate the modifications of the geomechanical rock properties. Mineralogical alterations were observed within the sandstones after the exposure to impure supercritical (sc)CO2 and brine, mainly of the carbonatic, but also of the silicatic cements, as well as of single minerals. Besides the partial solution effects also secondary carbonate and minor silicate mineral precipitates were observed within the pore space of the treated sandstones. These alterations affect the grain structure of the reservoir rock. Results of geomechanical experiments with unaltered sandstones show that the rock strength is influenced by the degree of rock saturation before the experiment and the chemical composition of the pore fluid (scCO2 + SOX + NOX). After long-term autoclave treatment with impure scCO2, the sandstone samples exhibit modified strength parameters and elastic deformation behaviour as well as changes in porosity compared to untreated samples. Furthermore, the injected fluid volume into the pore space of sandstones from the same lithotype varies during triaxial loading depending on the chemistry of the pore fluid. CO2 with NOX and SOX bearing fluid fills a significantly larger proportion of the sandstone pore space than brine with pure scCO2. * The
Predictions for impurity-induced Tc suppression in the high-temperature superconductors
International Nuclear Information System (INIS)
Radtke, R.J.; Levin, K.; Schuettler, H.; Norman, M.R.
1993-01-01
We address the question of whether anisotropic superconductivity is compatible with the evidently weak sensitivity of the critical temperature T c to sample quality in the high-T c copper oxides. We examine this issue quantitatively by solving the strong-coupling Eliashberg equations numerically as well as analytically for s-wave impurity scattering within the second Born approximation. For pairing interactions with a characteristically low energy scale, we find an approximately universal dependence of the d-wave superconducting transition temperature on the planar residual resistivity which is independent of the details of the microscopic pairing. These results, in conjunction with future systematic experiments, should help elucidate the symmetry of the order parameter in the cuprates
Impurity transport in internal transport barrier discharges on JET
International Nuclear Information System (INIS)
Dux, R.; Giroud, C.; Zastrow, K.-D.
2004-01-01
Impurity behaviour in JET internal transport barrier (ITB) discharges with reversed shear has been investigated. Metallic impurities accumulate in cases with too strong peaking of the main ion density profile. The accumulation is due to inwardly directed drift velocities inside the ITB radius. The strength of the impurity peaking increases with the impurity charge and is low for the low-Z elements C and Ne. Transport calculations show that the observed behaviour is consistent with dominant neoclassical impurity transport inside the ITB. In some cases, MHD events in the core flatten the radial profile of the metallic impurity. (author)
Effect of divalent impurities on some physical properties of LiF and NaF
International Nuclear Information System (INIS)
Laj, C.
1969-05-01
The ionic thermo-currents technique is applied to the study of impurity vacancy dipoles in LiF and NaF doped with several divalent cations. In LiF only one ITC band is observed whatever the impurity studied. In NaF on the contrary two ITC bands are present, one corresponding to the one observed in LiF, the other one, intense in the case of small impurities, at lower temperature. A parallel EPR study in the case of Mn 2+ doped samples shows that the band observed in LiF and the corresponding one in NaF are due to the relaxation of dipoles formed by the association of an impurity and a vacancy in the next nearest position. The knowledge of the properties of the dipoles allows to show that the room temperature ionic conductivity of LiF is conditioned by the equilibrium: M ++ □+ → M ++ + □+. It is also shown that the isolated cation vacancy originating from this dissociation is responsible for the enhancement of γ-ray coloration of LiF doped with divalent cation impurities. A paramagnetic center ascribed to the presence of Mn 0 isolated in the lattice is also studied. The value of the hyperfine interaction and its temperature dependence are in good agreement with both the theory and the other experimental results. Finally it is shown that the disappearance of dipoles by annealing is related to the formation of complexes involving OH - ions, probably of the M(OH) 2 type, with the two OH - ions occupying a single fluorine site. (author) [fr
Extended numerical modeling of impurity neoclassical transport in tokamak edge plasmas
International Nuclear Information System (INIS)
Inoue, H.; Yamoto, S.; Hatayama, A.; Homma, Y.
2016-01-01
Understanding of impurity transport in tokamaks is an important issue in order to reduce the impurity contamination in fusion core plasmas. Recently, a new kinetic numerical scheme of impurity classical/neoclassical transport has been developed. This numerical scheme makes it possible to include classical self-diffusion (CL SD), classical inward pinch (CL IWP), and classical temperature screening effect (CL TSE) of impurity ions. However, impurity neoclassical transport has been modeled only in the case where background plasmas are in the Pfirsch-Schluter (PS) regime. The purpose of this study is to extend our previous model to wider range of collisionality regimes, i.e., not only the PS regime, but also the plateau regime. As in the previous study, a kinetic model with Binary Collision Monte-Carlo Model (BMC) has been adopted. We focus on the modeling of the neoclassical self-diffusion (NC SD) and the neoclassical inward pinch (NC IWP). In order to simulate the neoclassical transport with the BCM, velocity distribution of background plasma ions has been modeled as a deformed Maxwell distribution which includes plasma density gradient. Some test simulations have been done. As for NC SD of impurity ions, our scheme reproduces the dependence on the collisionality parameter in wide range of collisionality regime. As for NC IWP, in cases where test impurity ions and background ions are in the PS and plateau regimes, parameter dependences have been reproduced. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Extended numerical modeling of impurity neoclassical transport in tokamak edge plasmas
Energy Technology Data Exchange (ETDEWEB)
Inoue, H.; Yamoto, S.; Hatayama, A. [Graduate School of Science and Technology, Keio University, Hiyoshi, Yokohama (Japan); Homma, Y. [Graduate School of Science and Technology, Keio University, Hiyoshi, Yokohama (Japan); Research Fellow of Japan Society for the Promotion of Science, Tokyo (Japan)
2016-08-15
Understanding of impurity transport in tokamaks is an important issue in order to reduce the impurity contamination in fusion core plasmas. Recently, a new kinetic numerical scheme of impurity classical/neoclassical transport has been developed. This numerical scheme makes it possible to include classical self-diffusion (CL SD), classical inward pinch (CL IWP), and classical temperature screening effect (CL TSE) of impurity ions. However, impurity neoclassical transport has been modeled only in the case where background plasmas are in the Pfirsch-Schluter (PS) regime. The purpose of this study is to extend our previous model to wider range of collisionality regimes, i.e., not only the PS regime, but also the plateau regime. As in the previous study, a kinetic model with Binary Collision Monte-Carlo Model (BMC) has been adopted. We focus on the modeling of the neoclassical self-diffusion (NC SD) and the neoclassical inward pinch (NC IWP). In order to simulate the neoclassical transport with the BCM, velocity distribution of background plasma ions has been modeled as a deformed Maxwell distribution which includes plasma density gradient. Some test simulations have been done. As for NC SD of impurity ions, our scheme reproduces the dependence on the collisionality parameter in wide range of collisionality regime. As for NC IWP, in cases where test impurity ions and background ions are in the PS and plateau regimes, parameter dependences have been reproduced. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Effects of electrostatic trapping on neoclassical transport in an impure plasma
International Nuclear Information System (INIS)
Hazeltine, R.D.; Ware, A.A.
1976-01-01
Contamination of a toroidally confined plasma by highly charged impurity ions can produce substantial variation of the electrostatic potential within a magnetic surface. The resulting electrostatic trapping and electrostatic drifts, of hydrogen ions and electrons, yields significant alterations in neoclassical transport theory. A transport theory which includes these effects is derived from the drift-kinetic equation, with an ordering scheme modeled on the parameters of recent tokamak experiments. The theory self-consistently predicts that electrostatic trapping should be fully comparable to magnetic trapping, and provides transport coefficients which, depending quadratically upon the temperature and pressure gradients, differ markedly from the standard neoclassical coefficients for a pure plasma
The effects of impurities on the properties of OFP copper specified for the copper iron canister
International Nuclear Information System (INIS)
Bowyer, W.H.
1999-09-01
A brief literature study has addressed the effects of impurities on OF copper to which 50 ppm of phosphorus has been added. This copper is the candidate material for the corrosion resistant coating to be applied to the container under development by SKB for the disposal of high level nuclear waste. The levels of impurities expected in this grade of copper and the final use have controlled the focus of the work. It is concluded that the impurities of greatest importance in the context of the proposed application are sulphur, phosphorus, bismuth and lead. The addition of 50 ppm of phosphorus should ensure very low oxygen content in the copper such that, As, Ni, Mn, Cr, Fe, Sn, Zn, Si, Al, Sb and Cd present as impurities all remain in solution in the copper at all temperatures of interest. In this state they will exert no material effect on the fitness for purpose of the material. Sulphur is expected to be present in amounts exceeding the solubility limit such that it will occur as grain boundary films or particles. Such segregation can cause embrittlement and it will be more serious as grain size increases. There is no evidence to support the assertion that the phosphorus addition modifies the segregation behaviour of sulphur. There is evidence that sulphur will combine with V, Zr, or Ti, even when they are present at extremely low levels, but there is no indication of the likely effects of these combinations on the segregation behaviour or embrittling effects. There is clear evidence that when creep failure occurs by intergranular cracking, sulphur causes the creep strain to fracture to be reduced to less than 1%. The amount of sulphur required for this is very low (i.e. less than the amount permitted in the specification) and dependant on grain size. The transition from transgranular to intergranular failure in creep is influenced by temperature, stress, grain size, and composition. The addition of phosphorus increases the temperature at which the transition occurs
The effects of impurities on the properties of OFP copper specified for the copper iron canister
Energy Technology Data Exchange (ETDEWEB)
Bowyer, W.H. [Meadow End Farm, Farnham (United Kingdom)
1999-09-01
A brief literature study has addressed the effects of impurities on OF copper to which 50 ppm of phosphorus has been added. This copper is the candidate material for the corrosion resistant coating to be applied to the container under development by SKB for the disposal of high level nuclear waste. The levels of impurities expected in this grade of copper and the final use have controlled the focus of the work. It is concluded that the impurities of greatest importance in the context of the proposed application are sulphur, phosphorus, bismuth and lead. The addition of 50 ppm of phosphorus should ensure very low oxygen content in the copper such that, As, Ni, Mn, Cr, Fe, Sn, Zn, Si, Al, Sb and Cd present as impurities all remain in solution in the copper at all temperatures of interest. In this state they will exert no material effect on the fitness for purpose of the material. Sulphur is expected to be present in amounts exceeding the solubility limit such that it will occur as grain boundary films or particles. Such segregation can cause embrittlement and it will be more serious as grain size increases. There is no evidence to support the assertion that the phosphorus addition modifies the segregation behaviour of sulphur. There is evidence that sulphur will combine with V, Zr, or Ti, even when they are present at extremely low levels, but there is no indication of the likely effects of these combinations on the segregation behaviour or embrittling effects. There is clear evidence that when creep failure occurs by intergranular cracking, sulphur causes the creep strain to fracture to be reduced to less than 1%. The amount of sulphur required for this is very low (i.e. less than the amount permitted in the specification) and dependant on grain size. The transition from transgranular to intergranular failure in creep is influenced by temperature, stress, grain size, and composition. The addition of phosphorus increases the temperature at which the transition occurs
Yavari, H.; Mokhtari, M.
2014-03-01
The effects of impurity and Bose-Fermi interactions on the transition temperature of a dipolar Bose-Einstein condensation in trapped Bose-Fermi mixture, by using the two-fluid model, are investigated. The shift of the transition temperature consists of four contributions due to contact, Bose-Fermi, dipole-dipole, and impurity interactions. We will show that in the presence of an anisotropic trap, the Bose-Fermi correction to the shift of transition temperature due to the excitation spectra of the thermal part is independent of anisotropy factor. Applying our results to trapped Bose-Fermi mixtures shows that, by knowing the impurity effect, the shift of the transition temperature due to Bose-Fermi interaction could be measured for isotropic trap (dipole-dipole contributions is zero) and Feshbach resonance technique (contact potential contribution is negligible).
Local order dependent impurity levels in alloy semiconductors
International Nuclear Information System (INIS)
Silva, C.E.T.G. da; Ecole Normale Superieure, 75 - Paris
1981-01-01
We develop a one band/may sites model for an isoelectronic impurity in a semiconductor alloy. The cluster-Bethe-lattice approximation is used to study the dependence of the impurity energy level upon the short range order (SRO) of the alloy. The Kikuchi parametrization is used to describe the latter. We take into account diagonal disorder only, with possible off-diagonal relaxation around the impurity site. All the inequivalent clusters of the impurity site and its first nearest neighbours are considered, thus including the important short range alloy potential fluctuations. Results are presented for the local density of impurity states, for different degrees of SRO in the alloy. (Author) [pt
Study of multiple scattering effects in heavy ion RBS
Energy Technology Data Exchange (ETDEWEB)
Fang, Z.; O`Connor, D.J. [Newcastle Univ., NSW (Australia). Dept. of Physics
1996-12-31
Multiple scattering effect is normally neglected in conventional Rutherford Backscattering (RBS) analysis. The backscattered particle yield normally agrees well with the theory based on the single scattering model. However, when heavy incident ions are used such as in heavy ion Rutherford backscattering (HIRBS), or the incident ion energy is reduced, multiple scattering effect starts to play a role in the analysis. In this paper, the experimental data of 6MeV C ions backscattered from a Au target are presented. In measured time of flight spectrum a small step in front of the Au high energy edge is observed. The high energy edge of the step is about 3.4 ns ahead of the Au signal which corresponds to an energy {approx} 300 keV higher than the 135 degree single scattering energy. This value coincides with the double scattering energy of C ion undergoes two consecutive 67.5 degree scattering. Efforts made to investigate the origin of the high energy step observed lead to an Monte Carlo simulation aimed to reproduce the experimental spectrum on computer. As a large angle scattering event is a rare event, two consecutive large angle scattering is extremely hard to reproduce in a random simulation process. Thus, the simulation has not found a particle scattering into 130-140 deg with an energy higher than the single scattering energy. Obviously faster algorithms and a better physical model are necessary for a successful simulation. 16 refs., 3 figs.
Study of multiple scattering effects in heavy ion RBS
Energy Technology Data Exchange (ETDEWEB)
Fang, Z; O` Connor, D J [Newcastle Univ., NSW (Australia). Dept. of Physics
1997-12-31
Multiple scattering effect is normally neglected in conventional Rutherford Backscattering (RBS) analysis. The backscattered particle yield normally agrees well with the theory based on the single scattering model. However, when heavy incident ions are used such as in heavy ion Rutherford backscattering (HIRBS), or the incident ion energy is reduced, multiple scattering effect starts to play a role in the analysis. In this paper, the experimental data of 6MeV C ions backscattered from a Au target are presented. In measured time of flight spectrum a small step in front of the Au high energy edge is observed. The high energy edge of the step is about 3.4 ns ahead of the Au signal which corresponds to an energy {approx} 300 keV higher than the 135 degree single scattering energy. This value coincides with the double scattering energy of C ion undergoes two consecutive 67.5 degree scattering. Efforts made to investigate the origin of the high energy step observed lead to an Monte Carlo simulation aimed to reproduce the experimental spectrum on computer. As a large angle scattering event is a rare event, two consecutive large angle scattering is extremely hard to reproduce in a random simulation process. Thus, the simulation has not found a particle scattering into 130-140 deg with an energy higher than the single scattering energy. Obviously faster algorithms and a better physical model are necessary for a successful simulation. 16 refs., 3 figs.
Quantitative considerations in medium energy ion scattering depth profiling analysis of nanolayers
Energy Technology Data Exchange (ETDEWEB)
Zalm, P.C.; Bailey, P. [International Institute for Accelerator Applications, University of Huddersfield, Queensgate, Huddersfield HD1 3DH (United Kingdom); Reading, M.A. [Physics and Materials Research Centre, University of Salford, Salford M5 4WT (United Kingdom); Rossall, A.K. [International Institute for Accelerator Applications, University of Huddersfield, Queensgate, Huddersfield HD1 3DH (United Kingdom); Berg, J.A. van den, E-mail: j.vandenberg@hud.ac.uk [International Institute for Accelerator Applications, University of Huddersfield, Queensgate, Huddersfield HD1 3DH (United Kingdom)
2016-11-15
The high depth resolution capability of medium energy ion scattering (MEIS) is becoming increasingly relevant to the characterisation of nanolayers in e.g. microelectronics. In this paper we examine the attainable quantitative accuracy of MEIS depth profiling. Transparent but reliable analytical calculations are used to illustrate what can ultimately be achieved for dilute impurities in a silicon matrix and the significant element-dependence of the depth scale, for instance, is illustrated this way. Furthermore, the signal intensity-to-concentration conversion and its dependence on the depth of scattering is addressed. Notably, deviations from the Rutherford scattering cross section due to screening effects resulting in a non-coulombic interaction potential and the reduction of the yield owing to neutralization of the exiting, backscattered H{sup +} and He{sup +} projectiles are evaluated. The former mainly affects the scattering off heavy target atoms while the latter is most severe for scattering off light target atoms and can be less accurately predicted. However, a pragmatic approach employing an extensive data set of measured ion fractions for both H{sup +} and He{sup +} ions scattered off a range of surfaces, allows its parameterization. This has enabled the combination of both effects, which provides essential information regarding the yield dependence both on the projectile energy and the mass of the scattering atom. Although, absolute quantification, especially when using He{sup +}, may not always be achievable, relative quantification in which the sum of all species in a layer adds up to 100%, is generally possible. This conclusion is supported by the provision of some examples of MEIS derived depth profiles of nanolayers. Finally, the relative benefits of either using H{sup +} or He{sup +} ions are briefly considered.
International Nuclear Information System (INIS)
Knoll, R.W.; Gilbert, E.R.
1987-11-01
The purposes of this report are to (1) identify the sources of impurity gases in spent fuel storage casks; (2) identify the expected concentrations and types of reactive impurity gases from these sources over an operating lifetime of 40 years; and (3) determine whether these impurities could significantly degrade cladding or exposed fuel during this period. Four potential sources of impurity gases in the helium cover gas in operating casks were identified and evaluated. Several different bounding cases have been considered, where the reactive gas inventory is either assumed to be completely gettered by the cladding or where all oxygen is assumed to react completely with the exposed fuel. It is concluded that the reactive gas inventory will have no significant effect on the cladding unless all available oxygen reacts with the UO 2 fuel to produce U 3 O 8 at one or two cladding breaches. Based on Zircaloy oxidation data, the oxygen inventory in a fully loaded pressurized water reactor cask such as the Castor-V/21 will be gettered by the Zircaloy cladding in about 1 year if the peak cladding temperature within the task is ≥300 0 C. Only a negligible decrease in the thickness of the cladding would result. 24 refs., 4 tabs
A model of magnetic impurities within the Josephson junction of a phase qubit
Energy Technology Data Exchange (ETDEWEB)
Erickson, R P; Pappas, D P [National Institute of Standards and Technology, Boulder, CO 80305 (United States)
2010-02-15
We consider a superconducting phase qubit consisting of a monocrystalline sapphire Josephson junction with its symmetry axis perpendicular to the junction interfaces. Via the London gauge, we present a theoretical model of Fe{sup 3+} magnetic impurities within the junction that describes the effect of a low concentration of such impurities on the operation of the qubit. Specifically, we derive an interaction Hamiltonian expressed in terms of angular momentum states of magnetic impurities and low-lying oscillator states of a current-biased phase qubit. We discuss the coupling between the qubit and impurities within the model near resonance. When the junction is biased at an optimal point for acting as a phase qubit, with a phase difference of {pi}/2 and impurity concentration no greater than 0.05%, we find only a slight decrease in the Q factor of less than 0.01%.
Zhang, Gang; Li, Baowen
2004-01-01
We study the dependence of thermal conductivity of single walled nanotubes (SWNT) on chirality, isotope impurity, tube length and temperature by nonequilibrium molecular dynamics method with accurate potentials. It is found that, contrary to electronic conductivity, the thermal conductivity is insensitive to the chirality. The isotope impurity, however, can reduce the thermal conductivity up to 60% and change the temperature dependence behavior. We also found that the tube length dependence o...
Impurity model for mixed-valent Mn3+/Mn4+ ions
International Nuclear Information System (INIS)
Schlottmann, P.; Lee, K.
1997-01-01
Intermediate valent tri- and tetravalent manganese ions play an important role in LaMnO 3 -based systems. We consider a Mn impurity with five orbitals in cubic symmetry which hybridize with conduction electrons. The exchange interaction in the d shell maximizes the impurity spin. We study the valence of the Mn impurity as a function of the splitting of the e g to t 2g orbitals in zero magnetic field and for the totally spin-polarized state. The lifting of the degeneracy of the e g levels due to a small quadrupolar field, related to the Mn-O bond length or a Jahn-Teller effect, is also investigated. Possible implications on the magnetoresistance are discussed. copyright 1997 The American Physical Society
Tellier, CR; Siddall, G
1982-01-01
A complete and comprehensive study of transport phenomena in thin continuous metal films, this book reviews work carried out on external-surface and grain-boundary electron scattering and proposes new theoretical equations for transport properties of these films. It presents a complete theoretical view of the field, and considers imperfection and impurity effects.
Du, Huarong; Wang, Zheng-Xiong; Dong, J. Q.; Liu, S. F.
2014-05-01
The coupling of ion temperature gradient (ITG or ηi) mode and trapped electron mode (TEM) in the presence of impurity ions is numerically investigated in toroidal collisionless plasmas, using the gyrokinetic integral eigenmode equation. A framework for excitations of the ITG modes and TEMs with respect to their driving sources is formulated first, and then the roles of impurity ions played in are analyzed comprehensively. In particular, the characteristics of the ITG and TEM instabilities in the presence of impurity ions are emphasized for both strong and weak coupling (hybrid and coexistent) cases. It is found that the impurity ions with inwardly (outwardly) peaked density profiles have stabilizing (destabilizing) effects on the hybrid (namely the TE-ITG) modes in consistence with previous works. A new finding of this work is that the impurity ions have stabilizing effects on TEMs in small ηi (ηi≤1) regime regardless of peaking directions of their density profiles whereas the impurity ions with density gradient Lez=Lne/Lnz>1 (LezTEMs in large ηi (ηi≥1) regime. In addition, the dependences of the growth rate, real frequency, eigenmode structure, and wave spectrum on charge concentration, charge number, and mass of impurity ions are analyzed in detail. The necessity for taking impurity ion effects on the features of turbulence into account in future transport experimental data analyses is also discussed.
Lattice site location of electrical dopant impurities in group-III nitrides
Amorim, Lígia; Temst, Kristiaan; Wahl, Ulrich
Dopants are impurities introduced in semiconductors in small quantities to tailor the material characteristics, the effects of which depend on the exact site the dopant occupies in the crystal lattice. The lattice location of impurities is, thus, crucial for the overall understanding of the semiconductor characteristics. In general, several techniques can be used to investigate the lattice site of an impurity, the most accurate and dedicated being emission channeling. However, a characteristic of this technique is that it requires the implantation of radioactive probes, usually created and accelerated in a radioactive ion beam facility. In some cases, emission channeling might however be the only technique capable to investigate the lattice sites occupied by the impurity atoms, provided an appropriate isotope for this technique can be used. For instance, the use of other methods such as Rutherford backscattering spectrometry, perturbed angular correlations, Mössbauer spectroscopy and extended X-ray absorptio...
Non-Fermi-liquid behavior: Exact results for ensembles of magnetic impurities
Zvyagin, A A
2002-01-01
In this work we consider several exactly solvable models of magnetic impurities in critical quantum antiferromagnetic spin chains and multichannel Kondo impurities. Their ground state properties are studied and the finite set of nonlinear integral equations, which exactly describe the thermodynamics of the models, is constructed. We obtain several analytic low-energy expressions for the temperature, magnetic field, and frequency dependences of important characteristics of exactly solvable disordered quantum spin models and disordered multichannel Kondo impurities with essential many-body interactions. We show that the only low-energy parameter that gets renormalized is the velocity of the low-lying excitations (or the effective crossover scale connected with each impurity); the others appear to be universal. In our study several kinds of strong disorder important for experiments were used. Some of them produce low divergences in certain characteristics of our strongly disordered critical systems (compared wit...
Resonance effects in neutron scattering lengths
Energy Technology Data Exchange (ETDEWEB)
Lynn, J.E.
1989-06-01
The nature of neutron scattering lengths is described and the nuclear effects giving rise to their variation is discussed. Some examples of the shortcomings of the available nuclear data base, particularly for heavy nuclei, are given. Methods are presented for improving this data base, in particular for obtaining the energy variation of the complex coherent scattering length from long to sub-/angstrom/ wave lengths from the available sources of slow neutron cross section data. Examples of this information are given for several of the rare earth nuclides. Some examples of the effect of resonances in neutron reflection and diffraction are discussed. This report documents a seminar given at Argonne National Laboratory in March 1989. 18 refs., 18 figs.
Resonance effects in neutron scattering lengths
International Nuclear Information System (INIS)
Lynn, J.E.
1989-01-01
The nature of neutron scattering lengths is described and the nuclear effects giving rise to their variation is discussed. Some examples of the shortcomings of the available nuclear data base, particularly for heavy nuclei, are given. Methods are presented for improving this data base, in particular for obtaining the energy variation of the complex coherent scattering length from long to sub-angstrom wave lengths from the available sources of slow neutron cross section data. Examples of this information are given for several of the rare earth nuclides. Some examples of the effect of resonances in neutron reflection and diffraction are discussed. This report documents a seminar given at Argonne National Laboratory in March 1989. 18 refs., 18 figs
Anomalous Hall effect in semiconductor quantum wells in proximity to chiral p -wave superconductors
Yang, F.; Yu, T.; Wu, M. W.
2018-05-01
By using the gauge-invariant optical Bloch equation, we perform a microscopic kinetic investigation on the anomalous Hall effect in chiral p -wave superconducting states. Specifically, the intrinsic anomalous Hall conductivity in the absence of the magnetic field is zero as a consequence of Galilean invariance in our description. As for the extrinsic channel, a finite anomalous Hall current is obtained from the impurity scattering with the optically excited normal quasiparticle current even at zero temperature. From our kinetic description, it can be clearly seen that the excited normal quasiparticle current is due to an induced center-of-mass momentum of Cooper pairs through the acceleration driven by ac electric field. For the induced anomalous Hall current, we show that the conventional skew-scattering channel in the linear response makes the dominant contribution in the strong impurity interaction. In this case, our kinetic description as a supplementary viewpoint mostly confirms the results of Kubo formalism in the literature. Nevertheless, in the weak impurity interaction, this skew-scattering channel becomes marginal and we reveal that an induction channel from the Born contribution dominates the anomalous Hall current. This channel, which has long been overlooked in the literature, is due to the particle-hole asymmetry by nonlinear optical excitation. Finally, we study the case in the chiral p -wave superconducting state with a transverse conical magnetization, which breaks the Galilean invariance. In this situation, the intrinsic anomalous Hall conductivity is no longer zero. Comparison of this intrinsic channel with the extrinsic one from impurity scattering is addressed.
Observation of impurity accumulation and concurrent impurity influx in PBX
International Nuclear Information System (INIS)
Sesnic, S.S.; Fonck, R.J.; Ida, K.; Couture, P.; Kaita, R.; Kaye, S.; Kugel, H.; LeBlanc, B.; Okabayashi, M.; Paul, S.; Powell, E.T.; Reusch, M.; Takahashi, H.; Gammel, G.; Morris, W.
1987-01-01
Impurity studies in L- and H-mode discharges in PBX have shown that both types of discharges can evolve into either an impurity accumulative or nonaccumulative case. In a typical accumulative discharge, Z eff peaks in the center to values of about 5. The central metallic densities can be high, n met /n e ≅ 0.01, resulting in central radiated power densities in excess of 1 W/cm 3 , consistent with bolometric estimates. The radial profiles of metals obtained independently from the line radiation in the soft X-ray and the VUV regions are very peaked. Concurrent with the peaking, an increase in the impurity influx coming from the edge of the plasma is observed. At the beginning of the accumulation phase the inward particle flux for titanium has values of 6x10 10 and 10x10 10 particles/cm 2 s at minor radii of 6 and 17 cm. At the end of the accumulation phase, this particle flux is strongly increased to values of 3x10 12 and 1x10 12 particles/cm 2 s. This increased flux is mainly due to influx from the edge of the plasma and to a lesser extent due to increased convective transport. Using the measured particle flux, an estimate of the diffusion coefficient D and the convective velocity v is obtained. (orig.)
Role of impurities in magnetically confined high temperature plasmas
International Nuclear Information System (INIS)
Barnett, C.F.
1976-01-01
A summary is given of the atomic physics concerned with plasma cooling by impurities and the limiting effect that impurities may have on heating of plasmas by neutral injection. A general description is given of the tokamak concept and the present and next generation experiments are described. The time and spatial behavior of O and Mo multicharged ions in present hydrogen plasmas is presented. This is followed by a discussion of the power loss from a plasma containing one percent Fe. Finally, the limitation of plasma heating by energetic H or D injection is summarized
Effects of impurities on PZT ceramics
Energy Technology Data Exchange (ETDEWEB)
Song, Y J; Kim, H N
1982-01-01
The grain growth, dielectric constants, piezoelectric properties, and resistivity of Pb(Zr/sub 0.52/ Ti/sub 0.48/)+0.008La/sub 2/O/sub 3/ (or Nb/sub 2/.O/sub 5/)+xFe/sub 2/O/sub 3/ ceramics have been investigated as a function of Fe/sub 2/O/sub 3/ content. The grain size decreases up to 0.05 (or 0.1) mole % Fe/sub 2/O/sub 3/, but increases in the further region. This can be interpreted as such that the grain growth is not retarded by those impurities when the Fe/sub 2/O/sub 3/ content approaches the La/sub 2/O/sub 3/ (or Nb/sub 2/O/sub 5/) content because of the formation of La/sup 3 +/ (or Nb/sup 5 +/)-Fe/sup 3 +/ ion pairs. The dielectric constant has a maximum at 0.2 mole % Fe/sub 2/O/sub 3/ and decreases as the Fe/sub 2/O/sub 3/ content increases from that composition. The grain size effect is dominant in the variation of dielectric constant up 0.2 mole % Fe/sub 2/O/sub 3/. The resistivity of the ceramics of which the Fe/sub 2/O/sub 3/ content is 0.8 mole % shows the same tendency as that of the pure PZT ceramics, and it can be concluded that complete compensation of the donor and the acceptor has occurred.
A Non-Perturbative Treatment of Quantum Impurity Problems in Real Lattices
Allerdt, Andrew C.
Historically, the RKKY or indirect exchange, interaction has been accepted as being able to be described by second order perturbation theory. A typical universal expression is usually given in this context. This approach, however, fails to incorporate many body effects, quantum fluctuations, and other important details. In Chapter 2, a novel numerical approach is developed to tackle these problems in a quasi-exact, non-perturbative manner. Behind the method lies the main concept of being able to exactly map an n-dimensional lattice problem onto a 1-dimensional chain. The density matrix renormalization group algorithm is then employed to solve the newly cast Hamiltonian. In the following chapters, it is demonstrated that conventional RKKY theory does not capture the crucial physics. It is found that the Kondo effect, i.e. the screening of an impurity spin, tends to dominate over a ferromagnetic interaction between impurity spins. Furthermore, it is found that the indirect exchange interaction does not decay algebraically. Instead, there is a crossover upon increasing JK, where impurities favor forming their own independent Kondo states after just a few lattice spacings. This is not a trivial result, as one may naively expect impurities to interact when their conventional Kondo clouds overlap. The spin structure around impurities coupled to the edge of a 2D topological insulator is investigated in Chapter 7. Modeled after materials such as silicine, germanene, and stanene, it is shown with spatial resolution of the lattice that the specific impurity placement plays a key role. Effects of spin-orbit interactions are also discussed. Finally, in the last chapter, transition metal complexes are studied. This really shows the power and versatility of the method developed throughout the work. The spin states of an iron atom in the molecule FeN4C 10 are calculated and compared to DFT, showing the importance of inter-orbital coulomb interactions. Using dynamical DMRG, the
Low Z impurity transport in tokamaks. [Neoclassical transport theory
Energy Technology Data Exchange (ETDEWEB)
Hawryluk, R.J.; Suckewer, S.; Hirshman, S.P.
1978-10-01
Low Z impurity transport in tokamaks was simulated with a one-dimensional impurity transport model including both neoclassical and anomalous transport. The neoclassical fluxes are due to collisions between the background plasma and impurity ions as well as collisions between the various ionization states. The evaluation of the neoclassical fluxes takes into account the different collisionality regimes of the background plasma and the impurity ions. A limiter scrapeoff model is used to define the boundary conditions for the impurity ions in the plasma periphery. In order to account for the spectroscopic measurements of power radiated by the lower ionization states, fluxes due to anomalous transport are included. The sensitivity of the results to uncertainties in rate coefficients and plasma parameters in the periphery are investigated. The implications of the transport model for spectroscopic evaluation of impurity concentrations, impurity fluxes, and radiated power from line emission measurements are discussed.
Light impurity production in tokamaks
International Nuclear Information System (INIS)
Philipps, V.; Vietzke, E.; Erdweg, M.
1989-01-01
A review is given of the different erosion processes of carbon materials with special emphasis on conditions relevant to plasma surface interactions. New results on the chemical erosion and radiation enhanced sublimation of boron-carbon layers are presented. The chemical hydrocarbon formation produced by the interaction of the TEXTOR scrape-off plasma with a carbon target has been investigated up to temperatures of 1500K using a Sniffer probe. The chemical interaction of the plasma with the carbon walls in TEXTOR is also analysed by measuring the hydrocarbon and CO and CO 2 partial pressures built up on the surrounding walls during the discharges. The recycling of oxygen impurities in an all carbon surrounding occurs predominantly in the form of CO and Co 2 molecules and the analysis of both neutral pressures during the discharges has been used as an additional diagnostic for the oxygen impurity situation in TEXTOR. These data are discussed in view of spectroscopic measurements on the influx of carbon and oxygen atoms from the walls and impurity line radiation. CD-band spectroscopy in addition is employed to identify the hydrocarbon chemical carbon erosion. Our present understanding of the oxygen impurity recycling and the oxygen sources are described. Particle induced release of CO molecules from the entire first wall is believed to be the dominant influx process of oxygen in the SOL of plasmas with carbon facing materials. The influence of coating the TEXTOR first wall with a boron-carbon film (B/C ≅1) on the light impurity behaviour is shown. (author)
Kinetic neoclassical calculations of impurity radiation profiles
Directory of Open Access Journals (Sweden)
D.P. Stotler
2017-08-01
Full Text Available Modifications of the drift-kinetic transport code XGC0 to include the transport, ionization, and recombination of individual charge states, as well as the associated radiation, are described. The code is first applied to a simulation of an NSTX H-mode discharge with carbon impurity to demonstrate the approach to coronal equilibrium. The effects of neoclassical phenomena on the radiated power profile are examined sequentially through the activation of individual physics modules in the code. Orbit squeezing and the neoclassical inward pinch result in increased radiation for temperatures above a few hundred eV and changes to the ratios of charge state emissions at a given electron temperature. Analogous simulations with a neon impurity yield qualitatively similar results.
Complex scattering dynamics and the integer quantum Hall effect
International Nuclear Information System (INIS)
Trugman, S.A.; Waugh, F.R.
1987-01-01
The effect of a magnetic field on potential scattering is investigated microscopically. A magnetic field renders the scattering of a classical charged particle far more complex than previously suspected. Consequences include possible 1/f noise and an explanation of the observed breakdown of the quantum Hall effect at large currents. A particular scatterer is described by a discontinuous one dimensional Hamiltonian map, a class of maps that has not previously been studied. A renormalization group analysis indicates that singular behavior arises from the interplay of electron orbits that are periodic and orbits that are quasiperiodic
Impurity features in Ni-YSZ-H_{2}-H_{2}O electrodes
DEFF Research Database (Denmark)
Utz, A.; Hansen, Karin Vels; Norrman, Kion
2011-01-01
-of-flight secondary ion mass spectrometry). This analysis yields comprehensive information on composition and lateral distribution of impurity species as well as the size of impurity features. Small impurity striations are found at the triple phase boundary (TPB) as well as on the former electrode......–electrolyte interface and the impurity features were found to be influenced by the electrode configuration and the initial behavior of the Ni electrode during thermal exposure (creep or shrinkage).Furthermore, the electrochemical performance (the line specific resistance LSR) was compared to data reported for Ni point...... anodes. Good agreement was obtained for data with comparable impurity features.Additionally, an order of magnitude estimation of the effect of SiO2 content on surface coverage with an impurity film is performed for different electrode designs (point, patterned and cermet anode) and shows different...
Energy Technology Data Exchange (ETDEWEB)
Dubuit, N
2006-10-15
This work deals with the transport of impurities in magnetically confined thermonuclear plasmas. The accumulation of impurities in the core of the plasma would imply dramatic losses of energy that may lead to the extinction of the plasma. On the opposite, the injection of impurities in the plasma edge is considered as an efficient means to extract heat without damaging the first wall. The balance between these 2 contradictory constraints requires an accurate knowledge of the impurity transport inside the plasma. The effect of turbulence, the main transport mechanism for impurities is therefore a major issue. In this work, the complete formula of a turbulent flow of impurities for a given fluctuation spectrum has been inferred. The origin and features of the main accumulation processes have been identified. The main effect comes from the compressibility of the electrical shift speed in a plane perpendicular to the magnetic field. This compressibility appears to be linked to the curvature of the magnetic field. A less important effect is a thermal-diffusion process that is inversely proportional to the number of charges and then disappears for most type of impurities except the lightest. This effect implies an impurity flux proportional to the temperature gradient and its direction can change according to the average speed of fluctuations. A new version of the turbulence code TRB has been developed. This new version allows the constraints of the turbulence not by the gradients but by the flux which is more realistic. The importance of the processes described above has been confirmed by a comparison between calculation and experimental data from Tore-supra and the Jet tokamak. The prevailing role of the curvature of the magnetic field in the transport impurity is highlighted. (A.C.)
Control Strategy for Small Molecule Impurities in Antibody-Drug Conjugates.
Gong, Hai H; Ihle, Nathan; Jones, Michael T; Kelly, Kathleen; Kott, Laila; Raglione, Thomas; Whitlock, Scott; Zhang, Qunying; Zheng, Jie
2018-04-01
Antibody-drug conjugates (ADCs) are an emerging class of biopharmaceuticals. As such, there are no specific guidelines addressing impurity limits and qualification requirements. The current ICH guidelines on impurities, Q3A (Impurities in New Drug Substances), Q3B (Impurities in New Drug Products), and Q6B (Specifications: Test Procedures and Acceptance Criteria for Biotechnological/Biological Products) do not adequately address how to assess small molecule impurities in ADCs. The International Consortium for Innovation and Quality in Pharmaceutical Development (IQ) formed an impurities working group (IWG) to discuss this issue. This white paper presents a strategy for evaluating the impact of small molecule impurities in ADCs. This strategy suggests a science-based approach that can be applied to the design of control systems for ADC therapeutics. The key principles that form the basis for this strategy include the significant difference in molecular weights between small molecule impurities and the ADC, the conjugation potential of the small molecule impurities, and the typical dosing concentrations and dosing schedule. The result is that exposure to small impurities in ADCs is so low as to often pose little or no significant safety risk.
Optimalization study for ion-temperature measurements by means of Rutherford scattering
International Nuclear Information System (INIS)
Donne, A.J.H.; Barbian, E.P.
1986-03-01
Small-angle Rutherford scattering of energetic neutrals by plasma ions is governed by energy and momentum conservation. The FWHM of the scattering distibution reveals the ion temperature of the plasma. A feasibility study is performed to optimize the parameters in case Rutherford-scattering technique is applied to a medium-sized tokamak experiment. Together with a time-of-flight analyser with a high energy resolution of about 100, a 20 keV helium probing beam with a neutral current density of 10 A/m 2 can provide a detailed spectrum within 3 ms, from which the ion temperature can be extracted with an accuracy of better than 10%. The influence of plasma impurities and resonant charge exchange on the scattering process is discussed in detail. The good spatial resolution makes the method very suitable to investigate energy deposition profiles in the case of ion-cyclotron radiation applied to the plasma for the purpose of plasma heating. (orig.)
Impurity transport in internal transport barrier discharges on JET
International Nuclear Information System (INIS)
Dux, R.
2002-01-01
In JET plasmas with internal transport barrier (ITB) the behaviour of metallic and low-Z impurities (C, Ne) was investigated. In ITB discharges with reversed shear, the metallic impurities accumulate in cases with too strong peaking of the density profile, while the concentration of low-Z elements C and Ne is only mildly peaked. The accumulation might be so strong, that the central radiation approximately equals the central heating power followed by a radiative collapse of the transport barrier. The radial location with strong impurity gradients (convective barrier) was identified to be situated inside (not at!) the heat flux barrier. Calculations of neo-classical transport were performed for these discharges, including impurity-impurity collisions. It was found, that the observed Z-dependence of the impurity peaking and the location of the impurity 'barrier' can be explained with neo-classical transport. ITB discharges with monotonic shear show less inward convection and seem to be advantageous with respect to plasma purity. (author)
Observations of long impurity confinement times in the ISX tokamak
Energy Technology Data Exchange (ETDEWEB)
Burrell, K H; Wong, S K; Muller, III, C H; Hacker, M P [General Atomic Co., San Diego, CA (USA); Ketterer, H E; Isler, R C; Lazarus, E A [Oak Ridge National Lab., TN (USA)
1981-08-01
The transport of small amounts of silicon and aluminium injected into plasmas in the Impurity Study Experiment (ISX) tokamak is studied. By monitoring the time behaviour of ultra-violet spectral lines emitted by various charge states of those impurities and comparing this behaviour to the predictions of a multi-species impurity transport code, it is found that both impurity penetration times and impurity containment times are consistent with neoclassical predictions. The observed impurity containment times, which are greater than three times the energy containment time, are consistent with the inward convection predicted by neoclassical theory.
Solution of the effective Hamiltonian of impurity hopping between two sites in a metal
Ye, Jinwu
1997-07-01
We analyze in detail all the possible fixed points of the effective Hamiltonian of a nonmagnetic impurity hopping between two sites in a metal obtained by Moustakas and Fisher (MF). We find a line of non-Fermi liquid fixed points which continuously interpolates between the two-channel Kondo fixed point (2CK) and the one-channel, two-impurity Kondo (2IK) fixed point. There is one relevant direction with scaling dimension 12 and one leading irrelevant operator with dimension 32. There is also one marginal operator in the spin sector moving along this line. The marginal operator, combined with the leading irrelevant operator, will generate the relevant operator. For the general position on this line, the leading low-temperature exponents of the specific heat, the hopping susceptibility and the electron conductivity Cimp,χhimp,σ(T) are the same as those of the 2CK, but the finite-size spectrum depends on the position on the line. No universal ratios can be formed from the amplitudes of the three quantities except at the 2CK point on this line where the universal ratios can be formed. At the 2IK point on this line, σ(T)~2σu(1+aT3/2), no universal ratio can be formed either. The additional non-Fermi-liquid fixed point found by MF has the same symmetry as the 2IK, it has two relevant directions with scaling dimension 12, and is therefore also unstable. The leading low-temperature behaviors are Cimp~T,χhimp~lnT,σ(T)~2σu(1+aT3/2) no universal ratios can be formed. The system is shown to flow to a line of Fermi-liquid fixed points which continuously interpolates between the noninteracting fixed point and the two-channel spin-flavor Kondo fixed point discussed by the author previously. The effect of particle-hole symmetry breaking is discussed. The effective Hamiltonian in the external magnetic field is analyzed. The scaling functions for the physical measurable quantities are derived in the different regimes; their predictions for the experiments are given. Finally
Numerical studies of impurities in fusion plasmas
International Nuclear Information System (INIS)
Hulse, R.A.
1982-09-01
The coupled partial differential equations used to describe the behavior of impurity ions in magnetically confined controlled fusion plasmas require numerical solution for cases of practical interest. Computer codes developed for impurity modeling at the Princeton Plasma Physics Laboratory are used as examples of the types of codes employed for this purpose. These codes solve for the impurity ionization state densities and associated radiation rates using atomic physics appropriate for these low-density, high-temperature plasmas. The simpler codes solve local equations in zero spatial dimensions while more complex cases require codes which explicitly include transport of the impurity ions simultaneously with the atomic processes of ionization and recombination. Typical applications are discussed and computational results are presented for selected cases of interest
Yang, Huan; Wang, Zhenyu; Fang, Delong; Deng, Qiang; Wang, Qiang-Hua; Xiang, Yuan-Yuan; Yang, Yang; Wen, Hai-Hu
2013-01-01
The origin of superconductivity in the iron pnictides remains unclear. One suggestion is that superconductivity in these materials has a magnetic origin, which would imply a sign-reversal s± pairing symmetry. Another suggests it is the result of orbital fluctuations, which would imply a sign-equal s++ pairing symmetry. There is no consensus yet which of these two distinct and contrasting pairing symmetries is the right one in iron pnictide superconductors. Here we explore the nature of the pairing symmetry in the superconducting state of Na(Fe0.97−xCo0.03Cux)As by probing the effect of scattering of Cooper pairs by non-magnetic Cu impurities. Using scanning tunnelling spectroscopy, we identify the in-gap quasiparticle states induced by the Cu impurities, showing signatures of Cooper pair breaking by these non-magnetic impurities–a process that is only consistent with s± pairing. This experiment provides strong evidence for the s± pairing. PMID:24248097
Energy Technology Data Exchange (ETDEWEB)
Gonzalez, J.W.; Duque, C.A. [Instituto de Fisica, Universidad de Antioquia, AA 1226, Medellin (Colombia); Lopez, S.Y. [Facultad de Educacion, Universidad de Antioquia, AA 1226, Medellin (Colombia); Rodriguez, A.H. [Instituto de Fisica, Universidad Nacional Autonoma de Mexico (UNAM), Apdo. Postal 20-364, San Angel 01000, Mexico DF (Mexico); Porras-Montenegro, N. [Departamento de Fisica, Universidad del Valle, AA 25360, Cali (Colombia)
2007-01-15
Using a variational procedure within the effective mass approximation, we have calculated the influence of an applied electric field and hydrostatic pressure on the shallow-impurity-related optical properties in a rectangular-transverse section GaAs-Ga{sub 1-x}Al{sub x}As quantum well wire. The electric field is applied in the plane of the transverse section of the wire and different angular directions have been considered. The results presented are for the impurity binding energy, its corresponding density of impurity states, and impurity-related transition energy and polarizability. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Impurity study of TMX using ultraviolet spectroscopy
International Nuclear Information System (INIS)
Allen, S.L.; Strand, O.T.; Moos, H.W.; Fortner, R.J.; Nash, T.J.; Dietrich, D.D.
1981-01-01
An extreme ultraviolet (EUV) study of the emissions from intrinsic and injected impurities in TMX is presented. Two survey spectrographs were used to determine that the major impurities present were oxygen, nitrogen, carbon, and titanium. Three absolutely-calibrated monochromators were used to measure the time histories and radial profiles of these impurity emissions in the central cell and each plug. Two of these instruments were capable of obtaining radial profiles as a function of time in a single shot
Toroidal asymmetries in divertor impurity influxes in NSTX
Directory of Open Access Journals (Sweden)
F. Scotti
2017-08-01
Full Text Available Toroidal asymmetries in divertor carbon and lithium influxes were observed in NSTX, due to toroidal differences in surface composition, tile leading edges, externally-applied three-dimensional (3D fields and toroidally-localized edge plasma modifications due to radio frequency heating. Understanding toroidal asymmetries in impurity influxes is critical for the evaluation of total impurity sources, often inferred from measurements with a limited toroidal coverage. The toroidally-asymmetric lithium deposition induced asymmetries in divertor lithium influxes. Enhanced impurity influxes at the leading edge of divertor tiles were the main cause of carbon toroidal asymmetries and were enhanced during edge localized modes. Externally-applied 3D fields led to strike point splitting and helical lobes observed in divertor impurity emission, but marginal changes to the toroidally-averaged impurity influxes. Power coupled to the scrape-off layer SOL plasma during radio frequency (RF heating of H-mode discharges enhanced impurity influxes along the non-axisymmetric divertor footprint of flux tubes connecting to plasma in front of the RF antenna.
Effects of Scattering of Radiation on Wormholes
Directory of Open Access Journals (Sweden)
Alexander Kirillov
2018-02-01
Full Text Available Significant progress in the development of observational techniques gives us the hope to directly observe cosmological wormholes. We have collected basic effects produced by the scattering of radiation on wormholes, which can be used in observations. These are the additional topological damping of cosmic rays, the generation of a diffuse background around any discrete source, the generation of an interference picture, and distortion of the cosmic microwave background (CMB spectrum. It turns out that wormholes in the leading order mimic perfectly analogous effects of the scattering of radiation on the standard matter (dust, hot electron gas, etc.. However, in higher orders, a small difference appears, which allows for disentangling effects of wormholes and ordinary matter.
Influence of negative substrate bias voltage on the impurity concentrations in Zr films
International Nuclear Information System (INIS)
Lim, J.-W.; Bae, J.W.; Mimura, K.; Isshiki, M.
2006-01-01
Zr films were deposited on Si(1 0 0) substrates without a substrate bias voltage and with substrate bias voltages of -50 V and -100 V using a non-mass separated ion beam deposition system. Secondary ion mass spectrometry and glow discharge mass spectrometry were used to determine the impurity concentrations in a Zr target and Zr films. It was found that the total amount of impurities in the Zr film deposited at the substrate bias voltage of -50 V was much lower than that in the Zr film deposited without the substrate bias voltage. It means that applying a negative bias voltage to the substrate can suppress the increase in impurities of Zr films. Furthermore, it was confirmed that dominant impurity elements such as C, N and O have a considerable effect on the purity of Zr films and these impurities can be remarkably reduced by applying the negative substrate bias voltage
Thermal-neutron multiple scattering: critical double scattering
International Nuclear Information System (INIS)
Holm, W.A.
1976-01-01
A quantum mechanical formulation for multiple scattering of thermal-neutrons from macroscopic targets is presented and applied to single and double scattering. Critical nuclear scattering from liquids and critical magnetic scattering from ferromagnets are treated in detail in the quasielastic approximation for target systems slightly above their critical points. Numerical estimates are made of the double scattering contribution to the critical magnetic cross section using relevant parameters from actual experiments performed on various ferromagnets. The effect is to alter the usual Lorentzian line shape dependence on neutron wave vector transfer. Comparison with corresponding deviations in line shape resulting from the use of Fisher's modified form of the Ornstein-Zernike spin correlations within the framework of single scattering theory leads to values for the critical exponent eta of the modified correlations which reproduce the effect of double scattering. In addition, it is shown that by restricting the range of applicability of the multiple scattering theory from the outset to critical scattering, Glauber's high energy approximation can be used to provide a much simpler and more powerful description of multiple scattering effects. When sufficiently close to the critical point, it provides a closed form expression for the differential cross section which includes all orders of scattering and has the same form as the single scattering cross section with a modified exponent for the wave vector transfer
A study on the measurement of effective energy of scattering X-rays
International Nuclear Information System (INIS)
Oogama, Noboru; Fujimoto, Nobuhisa; Nishitani, Motohiro; Yamada, Katsuhiko
1995-01-01
Only a few studies have been reported on the measurement and evaluation of the effective energy of scattering X-rays using an ionization chamber. The reason for this is due to the difficulty in accurately measuring attenuation curve in scattering X-rays lacking any directional properties. We could come up with a new method for calculating the effective energy of scattering X-rays by utilizing their spectra data. First, for analysing the accuracy of our calculation method with using primary X-rays, a comparison was made of calculated values of the effective energy obtained by our calculation method with the measurement values obtained using an ionization chamber. The results gave the calculated values agreeing with the measurement values within a maximum error of 2%, and this method was very helpful in measuring the effective energy of the scattering X-rays. Consequently, this method was capable of measuring the effective energy of scattering X-rays in the following parameters: X-ray tube voltage, scattering angle and size of scatterer. In conclusion, it is considered that our method could solve the present difficulty regarding the measurement of effective energy of the scattering X-rays, and provided a useful procedure concerning the study of radiation protection. (author)
Search for impurities of counting gases in ionization chambers
International Nuclear Information System (INIS)
Hofmann, T.
1992-03-01
In order to reach for the gas detectors applied at the ALADIN spectrometer of the GSI an as good as possible and timely remaining gas purity, a study on the kind and effects of impurities in different counting gases was performed. The gas purity was observed via the signal height of an α source after a drift path of the electrons of 50 cm. A steady decrease of the α-signals was measures, the steepness of which decreases slowly as function of the time. The half-life lies in the range of weeks, which lets conclude on a slow outgassing from the materials of the arrangement. By a gas chromatography and mass spectroscopy these impurities could be determined. Beside impurities by polar molecules as water and oxygen from the atmosphere, which are deposed in microscopical capillaries of the chamber materials and then outgassed in the samples after several days so-called softeners could be observed. Because these impurities in the arrangement at the ALADIN spectrometer cannot be avoided, a purification system in the flow-through operation was constructed and its effect tested. The gas quality can by this over several days be kept in the mean constant. In this dynamical process the fluctuations of the signal heights lie at ±0.7%. A ionization chamber as monitor for the gas purity was constructed and tested with different gas mixtures concerning observables like signal height and drift time. By this calibrated monitor in the experiment at the ALADIN spectrometer the gas quality can be independently determined. (orig.) [de
Transic time measures in scattering theory
International Nuclear Information System (INIS)
MacMillan, L.W.; Osborn, T.A.
1980-01-01
This paper studies the time evolution of state vectors that are the solutions of the time-dependent Schroedinger equation, characterized by a Hamiltonian h. We employ trace-theorem methods to prove that the transit time of state vectors through a finite space region, Σ, may be used to construct a family in the energy variable, epsilon, of unique, positive, trace-class operators. The matrix elements of these operators, give the transit time of any vector through Σ, It is proved that the trace of these operators, for a fixed energy epsilon, provide a function which simultaneously gives the sum of all orbital transit times through region Σ and represents the state density of all vectors that have support on Σ and energy epsilon. We use the transit-time operators to recover the usual theory of time delay for single-channel scattering systems. In the process we extend the known results on time delay to include scattering by fixed impurities in a periodic medium
Kaneko, Tomoaki; Ohno, Takahisa
2018-03-01
We investigate the electronic structure and the transport properties of graphene adsorbed onto h-BN with carbon impurities or atomic vacancies using density functional theory and the non-equilibrium Green's function method. We find that the transport properties are degraded due to carrier doping and scattering off of localized defect states in h-BN. When graphene is doped by introducing defects in h-BN, the transmission spectra become asymmetric owing to the reduction of the electronic density of states, which contributes significantly to the degradation of graphene transport properties as compared with the effect of defect levels.
International Nuclear Information System (INIS)
Shirke, A.K.; Pode, R.B.; Deshmukh, B.T.
1996-01-01
Photodecomposition of pure and doped KI powder (KI:KOH; KI:KCN; Impurity concentration, 100, 300, 500, 700 and 1000 ppm) to produce free I 2 molecules during gamma irradiation is studied with the help of absorption and IR measurements. Large number of I 2 molecules are formed in pure KI as compared to the doped samples. Hydroxide impurity increases the rate of liberation of I 2 molecules whereas the cyanide impurity decreases the rate of liberation of I 2 molecules. (Author)
Dielectric effects on Thomson scattering in a relativistic magnetized plasma
DEFF Research Database (Denmark)
Bindslev, H.
1991-01-01
The effects of the dielectric properties of a relativistic magnetized plasma on the scattering of electromagnetic radiation by fluctuations in electron density are investigated. The origin of the density fluctuations is not considered. Expressions for the scattering cross-section and the scattered...... power accepted by the receiving antenna are derived for a plasma with spatial dispersion. The resulting expressions allow thermal motion to be included in the description of the plasma and remain valid for frequencies of the probing radiation in the region of omega(p) and omega(ce), provided...... the absorption is small. Symmetry between variables relating to incident and scattered fields is demonstrated and shown to be in agreement with the reciprocity relation. Earlier results are confirmed in the cold plasma limit. Significant relativistic effects, of practical importance to the scattering...
On impurity handling in high performance stellarator/heliotron plasmas
International Nuclear Information System (INIS)
Burhenn, R.; Feng, Y.; Ida, K.
2008-10-01
The Large Helical Device (LHD) and Wendelstein 7-X (W7-X, under construction) are experiments specially designed to demonstrate long pulse (quasi steady-state) operation, which is an intrinsic property of Stellarators and Heliotrons. Significant progress was made in establishment of high performance plasmas. A crucial point is the increasing impurity confinement towards high density as observed at several machines (TJ-II, W7-AS, LHD) which can lead to impurity accumulation and early pulse termination by radiation collapse at high density. In addition, theoretical predictions for non-axisymmetric configurations prognosticate the absence of impurity screening by ion temperature gradients in standard ion root plasmas. Nevertheless, scenarios were found where impurity accumulation was successfully avoided in LHD and/or W7-AS by the onset of drag forces in the high density and low temperature scrape-off-layer, the generation of magnetic islands at the plasma boundary and to a certain degree also by ELMs, flushing out impurities and reducing the net-impurity influx into the core. Additionally, a reduction of impurity core confinement was observed in the W7-AS High Density H-mode (HDH) regime and by application of sufficient ECRH heating power. The exploration of such purification mechanisms is a demanding task for successful steady-state operation. The impurity transport at the plasma edge/SOL was identified to play a major role for the global impurity behaviour in addition to the core confinement. (author)
Transport of light, trace impurities in Alcator C-Mod
Rowan, W. L.; Bespamyatnov, I. O.; Liao, K. T.; Horton, W.; Fu, X. R.; Hughes, J. W.
2012-10-01
Light impurity profiles for boron were measured in ITB, H-mode, L-mode, and I-mode discharges in Alcator C-Mod. Within this wide range of modes, the profiles varied from peaked to hollow to flat. Specifically, hollow profiles are often observed in H-mode, while ITBs produce strong peaking, and L-mode produces moderate peaking. I-mode discharges are characterized by flat impurity profiles. For the study reported here, the profiles were measured with charge exchange recombination spectroscopy. The dependences of Rv/D were sought on dimensionless quantities including ion density scale length, effective charge, collisionality, and temperature scale length. We find that neoclassical transport consistently underestimates the measured transport. The excess measured transport is assumed to be turbulent. The strongest dependence of Rv/D is with temperature scale length. In addition, the measured transport was compared with the prediction of an analytical theory of drift wave turbulence that identifies transport implications for drift waves driven by ion and impurity density gradients.
Strong-coupling effects in superfluid 3He in aerogel
International Nuclear Information System (INIS)
Aoyama, Kazushi; Ikeda, Ryusuke
2007-01-01
Effects of impurity scatterings on the strong-coupling (SC) contribution, stabilizing the ABM (axial) pairing state, to the quartic term of the Ginzburg-Landau free energy of superfluid 3 He are theoretically studied to examine recent observations suggestive of an anomalously small SC effect in superfluid 3 He in aerogels. To study the SC corrections, two approaches are used. One is based on a perturbation in the short-range repulsive interaction, and the other is a phenomenological approach used previously for the bulk liquid by Sauls and Serene [Phys. Rev. B 24, 183 (1981)]. It is found that the impurity scattering favors the BW pairing state and shrinks the region of the ABM pairing state in the T-P phase diagram. In the phenomenological approach, the resulting shrinkage of the ABM region is especially substantial and, if assuming an anisotropy over a large scale in aerogel, leads to justifying the phase diagrams determined experimentally
Quantum phase transitions in multi-impurity and lattice Kondo systems
International Nuclear Information System (INIS)
Nejati, Ammar
2017-01-01
The main purpose of this dissertation is to provide a detailed development of a self-consistent perturbative renormalization group (RG) method to investigate the quantum phases and quantum phase transitions of multi-impurity Kondo systems (e.g., two impurities or a lattice of impurities). The essence of the RG method is an extension of the standard ''poor man's scaling'' by including the dynamical effects of the magnetic fluctuations in the Kondo vertex. Such magnetic fluctuations arise due to the indirect carrier-mediated exchange interaction (RKKY interaction) between the impurities and compete with the Kondo effect to determine the ground-state. The aim is to take the most 'economic' route and avoid intensive numerical computations as far as possible. In general, it is shown in detail how a relatively small amount of such magnetic fluctuations can suppress and ultimately, destroy the Kondo-screened phase in a universal manner, and without incurring a magnetic instability in the system. The renormalization group method and its extensions are further applied to several distinct experimental realization of the multi-impurity Kondo effect; namely, Kondo adatoms studied via scanning tunneling spectroscopy, a highly-tunable double-quantum-dot system based on semiconducting heterostructures, and finally, the heavy fermionic compounds as Kondo lattices. We demonstrate the qualitative and quantitative agreement of the RG theory with the experimental findings, which supports the validity of the method. In the case of Kondo lattices, we further include the possibility of a magnetic ordering in the lattice to see whether a magnetic ordering can happen simultaneously with or before the Kondo breakdown (or even prevent it altogether). In the last chapter, we consider the fate of the local moments in the absence of full Kondo screening while Kondo fluctuations are still present. This partially-screened phase needs itself an extensive study
Quantum phase transitions in multi-impurity and lattice Kondo systems
Energy Technology Data Exchange (ETDEWEB)
Nejati, Ammar
2017-01-16
The main purpose of this dissertation is to provide a detailed development of a self-consistent perturbative renormalization group (RG) method to investigate the quantum phases and quantum phase transitions of multi-impurity Kondo systems (e.g., two impurities or a lattice of impurities). The essence of the RG method is an extension of the standard ''poor man's scaling'' by including the dynamical effects of the magnetic fluctuations in the Kondo vertex. Such magnetic fluctuations arise due to the indirect carrier-mediated exchange interaction (RKKY interaction) between the impurities and compete with the Kondo effect to determine the ground-state. The aim is to take the most 'economic' route and avoid intensive numerical computations as far as possible. In general, it is shown in detail how a relatively small amount of such magnetic fluctuations can suppress and ultimately, destroy the Kondo-screened phase in a universal manner, and without incurring a magnetic instability in the system. The renormalization group method and its extensions are further applied to several distinct experimental realization of the multi-impurity Kondo effect; namely, Kondo adatoms studied via scanning tunneling spectroscopy, a highly-tunable double-quantum-dot system based on semiconducting heterostructures, and finally, the heavy fermionic compounds as Kondo lattices. We demonstrate the qualitative and quantitative agreement of the RG theory with the experimental findings, which supports the validity of the method. In the case of Kondo lattices, we further include the possibility of a magnetic ordering in the lattice to see whether a magnetic ordering can happen simultaneously with or before the Kondo breakdown (or even prevent it altogether). In the last chapter, we consider the fate of the local moments in the absence of full Kondo screening while Kondo fluctuations are still present. This partially-screened phase needs itself an extensive study
Recent trends in the impurity profile of pharmaceuticals
Directory of Open Access Journals (Sweden)
Kavita Pilaniya
2010-01-01
Full Text Available Various regulatory authorities such as the International Conference on Harmonization (ICH, the United States Food and Drug administration (FDA, and the Canadian Drug and Health Agency (CDHA are emphasizing on the purity requirements and the identification of impurities in Active Pharmaceutical Ingredients (APIs. The various sources of impurity in pharmaceutical products are - reagents, heavy metals, ligands, catalysts, other materials like filter aids, charcoal, and the like, degraded end products obtained during \\ after manufacturing of bulk drugs from hydrolysis, photolytic cleavage, oxidative degradation, decarboxylation, enantiomeric impurity, and so on. The different pharmacopoeias such as the British Pharmacopoeia, United State Pharmacopoeia, and Indian Pharmacopoeia are slowly incorporating limits to allowable levels of impurities present in APIs or formulations. Various methods are used to isolate and characterize impurities in pharmaceuticals, such as, capillary electrophoresis, electron paramagnetic resonance, gas-liquid chromatography, gravimetric analysis, high performance liquid chromatography, solid-phase extraction methods, liquid-liquid extraction method, Ultraviolet Spectrometry, infrared spectroscopy, supercritical fluid extraction column chromatography, mass spectrometry, Nuclear magnetic resonance (NMR spectroscopy, and RAMAN spectroscopy. Among all hyphenated techniques, the most exploited techniques for impurity profiling of drugs are Liquid Chromatography (LC-Mass Spectroscopy (MS, LC-NMR, LC-NMR-MS, GC-MS, and LC-MS. This reveals the need and scope of impurity profiling of drugs in pharmaceutical research.
Zhang, Qiang
2017-12-26
The effect of interfacial scattering on anisotropic magnetoresistance (AMR) and anomalous Hall effect (AHE) was studied in the (Ta12n/Fe36n)n multilayers, where the numbers give the thickness in nanometer and n is an integer from 1 to 12. The multilayer structure has been confirmed by the XRR spectra and STEM images of cross-sections. The magneto-transport properties were measured by four-point probe method in Hall bar shaped samples in the temperature range of 5 - 300 K. The AMR increases with n, which could be ascribed to the interfacial spin-orbit scattering. At 5 K, the longitudinal resistivity (ρ) increases by 6.4 times and the anomalous Hall resistivity (ρ) increases by 49.4 times from n =1 to n =12, indicative of the interfacial scattering effect. The skew-scattering, side-jump and intrinsic contributions to the AHE were separated successfully. As n increases from 1 to 12, the intrinsic contribution decreases because of the decaying crystallinity or finite size effect and the intrinsic contribution dominated the AHE for all samples. The side jump changes from negative to positive because the interfacial scattering and intralayer scattering in Fe layers both contribute to side jump in the AHE but with opposite sign.
Monte Carlo method for magnetic impurities in metals
Hirsch, J. E.; Fye, R. M.
1986-01-01
The paper discusses a Monte Carlo algorithm to study properties of dilute magnetic alloys; the method can treat a small number of magnetic impurities interacting wiith the conduction electrons in a metal. Results for the susceptibility of a single Anderson impurity in the symmetric case show the expected universal behavior at low temperatures. Some results for two Anderson impurities are also discussed.
Rajan, Sharmila; Sonoda, Junichiro; Tully, Timothy; Williams, Ambrose J; Yang, Feng; Macchi, Frank; Hudson, Terry; Chen, Mark Z; Liu, Shannon; Valle, Nicole; Cowan, Kyra; Gelzleichter, Thomas
2018-04-13
bFKB1 is a humanized bispecific IgG1 antibody, created by conjoining an anti-Fibroblast Growth Factor Receptor 1 (FGFR1) half-antibody to an anti-Klothoβ (KLB) half-antibody, using the knobs-into-holes strategy. bFKB1 acts as a highly selective agonist for the FGFR1/KLB receptor complex and is intended to ameliorate obesity-associated metabolic defects by mimicking the activity of the hormone FGF21. An important aspect of the biologics product manufacturing process is to establish meaningful product specifications regarding the tolerable levels of impurities that copurify with the drug product. The aim of the current study was to determine acceptable levels of product-related impurities for bFKB1. To determine the tolerable levels of these impurities, we dosed obese mice with bFKB1 enriched with various levels of either HMW impurities or anti-FGFR1-related impurities, and measured biomarkers for KLB-independent FGFR1 signaling. Here, we show that product-related impurities of bFKB1, in particular, high molecular weight (HMW) impurities and anti-FGFR1-related impurities, when purposefully enriched, stimulate FGFR1 in a KLB-independent manner. By taking this approach, the tolerable levels of product-related impurities were successfully determined. Our study demonstrates a general pharmacology-guided approach to setting a product specification for a bispecific antibody whose homomultimer-related impurities could lead to undesired biological effects. Copyright © 2018. Published by Elsevier Inc.
Application of laser resonance scattering to the study of high-temperature plasma-wall interaction
International Nuclear Information System (INIS)
Maeda, Mitsuo; Muraoka, Katsunori; Hamamoto, Makoto; Akazaki, Masanori; Miyazoe, Yasushi
1981-01-01
Studies on laser resonance scattering and its application to the study of high-temperature plasma-wall interaction are reviewed. The application of dye laser beam to resonant scattering method has been developed. This method is able to detect low density atoms. The fluorescent photon counts can be estimated for a two-level system and a three-level system. The S/N ratio, Which is in close connection with the detection limit, has been estimated. The doppler effect due to the thermal motion of atoms is taken into consideration. The calibration of the absolute number of atoms is necessary. Tunable coherent light is used as the light source for resonance scattering method. This is able to excite atoms strongly and to increase the detection efficiency. As dye lasers, a N 2 laser, a YAG laser, and a KrF excimer laser have been studied. In VUV region, rare gas or rare gas halide lasers can be used. The strong output power can be expected when the resonance lines of atoms meet the synchronizing region of the excimer laser. The resonance scattering method is applied to the detection of impurity metal atoms in plasma. The studies of laser systems for the detection of hydrogen atoms are also in progress. (Kato, T.)
Effect of neutron anisotropic scattering in fast reactor analysis
International Nuclear Information System (INIS)
Chiba, Gou
2004-01-01
Numerical tests were performed about an effect of a neutron anisotropic scattering on criticality in the Sn transport calculation. The simplest approximation, the consistent P approximation and the extended transport approximation were compared with each other in one-dimensional slab fast reactor models. JAERI fast set which has been used for fast reactor analyses is inadequate to evaluate the effect because it doesn't include the scattering matrices and the self-shielding factors to calculate the group-averaged cross sections weighted by the higher-order moment of angular flux. In the present study, the sub-group method was used to evaluate the group-averaged cross sections. Results showed that the simplest approximation is inadequate and the transport approximation is effective for evaluating the anisotropic scattering. (author)
Impurity dependence of superconductivity in niobium
International Nuclear Information System (INIS)
Laa, C.
1984-04-01
Jump temperatures, the critical fields Hsubc and Hsubc 2 and specific heats were measured on niobium samples where the impurity content was systematically varied by loading with nitrogen. Quantities could thus be extrapolated to lattice perfection and absolute purity. Comparisons with theories were made and some parameters extracted. Agreement was found with Gorkov theory for small impurities. A new value of the Ginsburg-Landau parameter Ko was determined to be just above 1/sqrt2 which proves that niobium is an elementary Type II semiconductor. By comparisons with the BCS and the CLAC theory the values of the mean Fermi velocity, the London penetration depth, the BCS coherence length and the impurity parameter were extracted. (G.Q.)
International Nuclear Information System (INIS)
Leite, R.V.; Oliveira Filho, L.O. de; Milton Pereira, J.; Cottam, M.G.; Costa Filho, R.N.
2009-01-01
A Green's function method is used to obtain the spectrum of spin excitations associated with a linear array of magnetic impurities implanted in a ferromagnetic thin film. The equations of motion for the Green's functions of the anisotropic film are written in the framework of the Ising model in a transverse field. The frequencies of localized modes are calculated as a function of the interaction parameters for the exchange coupling between impurity-spin pairs, host-spin pairs, and impurity-host neighbors, as well as the effective field parameter at the impurity sites.
Effects of multiple scattering on radiative properties of soot fractal aggregates
International Nuclear Information System (INIS)
Yon, Jérôme; Liu, Fengshan; Bescond, Alexandre; Caumont-Prim, Chloé; Rozé, Claude; Ouf, François-Xavier; Coppalle, Alexis
2014-01-01
The in situ optical characterization of smokes composed of soot particles relies on light extinction, angular static light scattering (SLS), or laser induced incandescence (LII). These measurements are usually interpreted by using the Rayleigh–Debye–Gans theory for Fractal Aggregates (RDG-FA). RDG-FA is simple to use but it completely neglects the impact of multiple scattering (MS) within soot aggregates. In this paper, based on a scaling approach that takes into account MS effects, an extended form of the RDG-FA theory is proposed in order to take into account these effects. The parameters of this extended theory and their dependency on the number of primary sphere inside the aggregate (1 p <1006) and on the wavelength (266nm<λ<1064nm) are evaluated thanks to rigorous calculations based on discrete dipole approximation (DDA) and generalized multi-sphere Mie-solution (GMM) calculations. This study shows that size determination by SLS is not distorted by MS effect. On the contrary, it is shown that fractal dimension can be misinterpreted by light scattering experiments, especially at short wavelengths. MS effects should be taken into account for the interpretation of absorption measurements that are involved in LII or extinction measurements. -- Highlights: • We incorporate multiple scattering effects in a scaling approach for fractal aggregates. • A generalized structure factor is introduced for implementation in RDG-FA theory. • Forward scattering is affected by multiple scattering as well as power law regime. • Absorption cross sections are affected by multiple scattering. • Absorption cross sections are 11% higher than that for forward scattering
On neoclassical impurity transport in stellarator geometry
International Nuclear Information System (INIS)
García-Regaña, J M; Kleiber, R; Beidler, C D; Turkin, Y; Maaßberg, H; Helander, P
2013-01-01
The impurity dynamics in stellarators has become an issue of moderate concern due to the inherent tendency of the impurities to accumulate in the core when the neoclassical ambipolar radial electric field points radially inwards (ion root regime). This accumulation can lead to collapse of the plasma due to radiative losses, and thus limit high performance plasma discharges in non-axisymmetric devices. A quantitative description of the neoclassical impurity transport is complicated by the breakdown of the assumption of small E × B drift and trapping due to the electrostatic potential variation on a flux surface Φ-tilde compared with those due to the magnetic field gradient. This work examines the impact of this potential variation on neoclassical impurity transport in the Large Helical Device heliotron. It shows that the neoclassical impurity transport can be strongly affected by Φ-tilde . The central numerical tool used is the δf particle in cell Monte Carlo code EUTERPE. The Φ-tilde used in the calculations is provided by the neoclassical code GSRAKE. The possibility of obtaining a more general Φ-tilde self-consistently with EUTERPE is also addressed and a preliminary calculation is presented. (paper)
Enhanced electron/fuel-ion equilibration through impurity ions: Studies applicable to NIF and Omega
Petrasso, R. D.; Sio, H.; Kabadi, N.; Lahmann, B.; Simpson, R.; Parker, C.; Frenje, J.; Gatu Johnson, M.; Li, C. K.; Seguin, F. H.; Rinderknecht, H.; Casey, D.; Grabowski, P.; Graziani, F.; Taitano, W.; Le, A.; Chacon, L.; Hoffman, N.; Kagan, G.; Simakov, A.; Zylstra, A.; Rosenberg, M.; Betti, R.; Srinivasan, B.; Mancini, R.
2017-10-01
In shock-driven exploding-pushers, a platform used extensively to study multi-species and kinetic effects, electrons and fuel ions are far out of equilibrium, as reflected by very different temperatures. However, impurity ions, even in small quantities, can couple effectively to the electrons, because of a Z2 dependence, and in turn, impurity ions can then strongly couple to the fuel ions. Through this mechanism, electrons and fuel-ions can equilibrate much faster than they otherwise would. This is a quantitative issue, depending upon the amount and Z of the impurity. For NIF and Omega, we consider the role of this process. Coupled non-linear equations, reflecting the temperatures of the three species, are solved for a range of conditions. Consideration is also given to ablatively driven implosions, since impurities can similarly affect the equilibration. This work was supported in part by DOE/NNSA DE-NA0002949 and DE-NA0002726.
Simulated impurity transport in LHD from MIST
Energy Technology Data Exchange (ETDEWEB)
Rice, J.E. [National Inst. for Fusion Science, Toki, Gifu (Japan)
1998-05-01
The impurity transport code MIST and atomic physics package LINES are used to calculate the time evolution of charge state density profiles, individual line emissivity profiles and total radiated power profiles for impurities in LHD plasmas. Three model LHD plasmas are considered; a high density, low temperature case, a low density, high temperature case and the initial LHD start-up plasma (500 kW ECH), using impurity transport coefficient profiles from Heliotron E. The elements oxygen, neon, scandium, iron, nickel and molybdenum are considered, both injected and in steady state. (author)
Park, Yongchan; Choi, Byoungyoung; Shinn, Youngjae
2015-04-01
Captured CO2 streams contain various levels of impurities which vary depending on the combustion technology and CO2 sources such as a power plant and iron and steel production processes. Common impurities or contaminants are non-condensable gases like nitrogen, oxygen and hydrogen, and are also air pollutants like sulphur and nitrogen oxides. Specifically for geological storage, the non-condensable gases in CO2 streams are not favourable because they can decrease density of the injected CO2 stream and can affect buoyancy of the plume. However, separation of these impurities to obtain the CO2 purity higher than 99% would greatly increase the cost of capture. In 2010, the Korean Government announced a national framework to develop CCS, with the aim of developing two large scale integrated CCS projects by 2020. In order to achieve this goal, a small scale injection project into Pohang basin near shoreline has begun which is seeking the connection with a capture project, especially at a steel company. Any onshore sites that are suitable for the geological storage are not identified by this time so we turned to the shallow offshore Pohang basin where is close to a large-scale CO2 source. Currently, detailed site surveys are being undertaken and the collected data were used to establish a geological model of the basin. In this study, we performed preliminary modelling study on the effect of impurities on the geological storage using the geological model. Using a potential compositions of impurities in CO2 streams from the steel company, we firstly calculated density and viscosity of CO2 streams as a function of various pressure and temperature conditions with CMG-WINPROP and then investigated the effect of the non-condensable gases on storage capacity, injectivity and plume migrations with CMG-GEM. Further simulations to evaluate the areal and vertical sweep efficiencies by impurities were perform in a 2D vertical cross section as well as in a 3D simulation grid. Also
CT-QMC-simulations on the single impurity Anderson model with a superconducting bath
Energy Technology Data Exchange (ETDEWEB)
Sohn, Florian; Pruschke, Thomas [Institut fuer theoretische Physik, Universitaet Goettingen, Friedrich-Hund-Platz 1, 37077 Goettingen (Germany)
2016-07-01
Coupling a heavy fermion impurity to a superconducting lead induces a competition between the Kondo effect and superconductivity in the low temperature regime. This situation has been modeled with a single impurity Anderson model, where the normal state bath is replaced by a BCS-type superconducting bath in mean field approximation. We study this model using a continuous-time quantum Monte Carlo hybridization expansion algorithm. Results include the impurity Green's functions as well as the corresponding spectral functions obtained from analytic continuation. Two side bands are observed which we discuss in the light of Yu-Shiba-Rusinov states.
Role of impurity molecules in radiation-initiated processes in solid carbohydrates
International Nuclear Information System (INIS)
Kavetskii, V.G.; Yudin, I.V.
1992-01-01
Extension of the use of ionizing radiation for sterilization of medicinal preparations is stimulating the study of radiation-initiated processes in solid polyhydroxyl matrixes containing impurities of various organic substances. Such investigations make it possible to establish common characteristics of the effect of impurity molecules on the radiolysis of organic crystals. The materials of the investigation were lactose and rhamnose, precipitated by slow evaporation of the solvent from saturated aqueous solutions with different dihydroxyacetone contents. 4 refs., 1 fig
Effective polarization in quasi-free scattering
Maris, Theodor August Johannes; Teodoro, Maria Ribeiro; Veit, Eliane Angela
1980-01-01
A simple relation, involving only experimental quantmes, for the effective polarizations m quasi-free (p, 2p) scattering on closed shell nuclei IS tested for recent TRIUMF (p, 2p) experiments with 200 MeV polanzed protons.
Chemical binding effects in resonance - potential interference scattering for harmonic crystals
International Nuclear Information System (INIS)
Kuwaifi, A.; Summerfield, G.C.
1991-01-01
The neutron scattering cross section which is the quantity directly measured in experiments is given by the absolute square of the scattering amplitude. For energies near a resonance, this yields three terms: potential, resonant and interference. In this paper we deal with the interference neutron scattering cross section which is written in terms of a three-point correlation function. This function is calculated for the ideal gas and harmonic crystal models. For short collision times, the interference result for harmonic crystals is the same as the ideal gas but it has an effective temperature. This is the same effective temperature as was previously found for absorption and pure resonant processes. Therefore, the interference scattering cross section can be treated in the same way as resonant scattering and absorption are treated using an ideal gas result with the usual effective temperature. (author)
Direction of Impurity Pinch and Auxiliary Heating in Tokamak Plasmas
International Nuclear Information System (INIS)
Angioni, C.; Peeters, A.G.
2006-01-01
A mechanism of particle pinch for trace impurities in tokamak plasmas, arising from the effect of parallel velocity fluctuations in the presence of a turbulent electrostatic potential, is identified analytically by means of a reduced fluid model and verified numerically with a gyrokinetic code for the first time. The direction of such a pinch reverses as a function of the direction of rotation of the turbulence in agreement with the impurity pinch reversal observed in some experiments when moving from dominant auxiliary ion heating to dominant auxiliary electron heating
Multiple scattering effects in depth resolution of elastic recoil detection
International Nuclear Information System (INIS)
Wielunski, L.S.; Harding, G.L.
1998-01-01
Elastic Recoil Detection (ERD) is used to profile hydrogen and other low mass elements in thin films at surface and interfaces in a similar way that Rutherford Backscattering Spectroscopy (RBS) is used to detect and profile heavy elements. It is often assumed that the depth resolutions of these two techniques are similar. However, in contrast to typical RBS, the depth resolution of ERD is limited substantially by multiple scattering. In experimental data analysis and/or spectra simulations of a typical RBS measurement multiple scattering effects are often ignored. Computer programs used in IBA, such as RUMP, HYPRA or RBX do not include multiple scattering effects at all. In this paper, using practical thin metal structures with films containing intentionally introduced hydrogen, we demonstrate experimental ERD depth resolution and sensitivity limitations. The effects of sample material and scattering angle are also discussed. (authors)
Breatherlike impurity modes in discrete nonlinear lattices
DEFF Research Database (Denmark)
Hennig, D.; Rasmussen, Kim; Tsironis, G. P.
1995-01-01
We investigate the properties of a disordered generalized discrete nonlinear Schrodinger equation, containing both diagonal and nondiagonal nonlinear terms. The equation models a Linear host lattice doped with nonlinear impurities. We find different types of impurity states that form itinerant...
Incorporation, diffusion and segregation of impurities in polycrystalline silicon
Energy Technology Data Exchange (ETDEWEB)
Deville, J.P.; Soltani, M.L. (Universite Louis Pasteur, 67 - Strasbourg (France)); Quesada, J. (Laboratoire de Metallurgie-Chimie des Materiaux, E.N.S.A.I.S., 67 - Strasbourg (France))
1982-01-01
We studied by means of X-Ray photoelectron Spectroscopy the nature, distribution and, when possible, the chemical bond of impurities at the surface of polycrystalline silicon samples grown on a carbon ribbon. Besides main impurities (carbon and oxygen), always present at concentrations around their limit of solubility in silicon, metal impurities have been found: their nature varies from one sample to another. Their spatial distribution is not random: some are strictly confined at the surface (sodium), whereas others are in the superficial oxidized layer (calcium, magnesium) or localized at the oxide-bulk silicon interface (iron). Metal impurities are coming from the carbon ribbon and are incorporated to silicon during the growth process. It is not yet possible to give a model of diffusion processes of impurities since they are too numerous and interact one with the other. However oxygen seems to play a leading role in the spatial distribution of metal impurities.
Impurity injection into tokamak plasmas by erosion probes
International Nuclear Information System (INIS)
Hildebrandt, D.; Bakos, J.S.; Buerger, G.; Paszti, F.; Petravich, G.
1987-08-01
Exposing special erosion probes into the edge plasma of MT-1 the impurities Li and Ti were released and contaminated the plasma. By the use of collector probes the torodial transport of these impurities were investigated. The results indicate a preferential impurity flow into codirection of the plasma current. However, the asymmetric component of this flow is much larger than expected from the toroidal drift correlated to the plasma current. (author)
Li, Jun; Ji, Min; Schwarz, Tobias; Ke, Xiaoxing; Van Tendeloo, Gustaaf; Yuan, Jie; Pereira, Paulo J; Huang, Ya; Zhang, Gufei; Feng, Hai-Luke; Yuan, Ya-Hua; Hatano, Takeshi; Kleiner, Reinhold; Koelle, Dieter; Chibotaru, Liviu F; Yamaura, Kazunari; Wang, Hua-Bing; Wu, Pei-Heng; Takayama-Muromachi, Eiji; Vanacken, Johan; Moshchalkov, Victor V
2015-07-03
The determination of the pairing symmetry is one of the most crucial issues for the iron-based superconductors, for which various scenarios are discussed controversially. Non-magnetic impurity substitution is one of the most promising approaches to address the issue, because the pair-breaking mechanism from the non-magnetic impurities should be different for various models. Previous substitution experiments demonstrated that the non-magnetic zinc can suppress the superconductivity of various iron-based superconductors. Here we demonstrate the local destruction of superconductivity by non-magnetic zinc impurities in Ba0.5K0.5Fe2As2 by exploring phase-slip phenomena in a mesoscopic structure with 119 × 102 nm(2) cross-section. The impurities suppress superconductivity in a three-dimensional 'Swiss cheese'-like pattern with in-plane and out-of-plane characteristic lengths slightly below ∼1.34 nm. This causes the superconducting order parameter to vary along abundant narrow channels with effective cross-section of a few square nanometres. The local destruction of superconductivity can be related to Cooper pair breaking by non-magnetic impurities.
Fractal growth in impurity-controlled solidification in lipid monolayers
DEFF Research Database (Denmark)
Fogedby, Hans C.; Sørensen, Erik Schwartz; Mouritsen, Ole G.
1987-01-01
A simple two-dimensional microscopic model is proposed to describe solidifcation processes in systems with impurities which are miscible only in the fluid phase. Computer simulation of the model shows that the resulting solids are fractal over a wide range of impurity concentrations and impurity...... diffusional constants. A fractal-forming mechanism is suggested for impurity-controlled solidification which is consistent with recent experimental observations of fractal growth of solid phospholipid domains in monolayers. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....
Transport and re-deposition of limiter-released metal impurities
International Nuclear Information System (INIS)
Claasen, H.A.; Repp, H.
1983-01-01
The transport parallel B-vector and re-deposition of limiter- (or divertor-target-)released metal impurities in a given counter-streaming scrape-off layer plasma is studied analytically by using a kinetic approach. Electron impact ionization, Coulomb collisions with the hydrogen ions, and impurity ion acceleration in a pre-sheath electric field are accounted for. The friction and electric-field forces provide the driving forces for impurity re-cycling in front of the limiter. Both hydrogen ion sputtering and self-sputtering are included (the latter for impurity emission perpendicular to the limiter surface). The analytical formulas are numerically evaluated for the example of sputtered iron impurities, assuming a simple model for a scrape-off layer plasma in contact with a stainless-steel poloidal ring limiter. (author)
Transitions and excitations in a superfluid stream passing small impurities
Pinsker, Florian
2014-05-08
We analyze asymptotically and numerically the motion around a single impurity and a network of impurities inserted in a two-dimensional superfluid. The criticality for the breakdown of superfluidity is shown to occur when it becomes energetically favorable to create a doublet—the limiting case between a vortex pair and a rarefaction pulse on the surface of the impurity. Depending on the characteristics of the potential representing the impurity, different excitation scenarios are shown to exist for a single impurity as well as for a lattice of impurities. Depending on the lattice characteristics it is shown that several regimes are possible: dissipationless flow, excitations emitted by the lattice boundary, excitations created in the bulk, and the formation of large-scale structures.
Impurity concentration limits and activation in fusion reactor structural materials
International Nuclear Information System (INIS)
Zucchetti, M.
1991-01-01
This paper examines waste management problems related to impurity activation in first-wall, shield, and magnet materials for fusion reactors. Definitions of low activity based on hands-on recycling, remote recycling, and shallow land burial waste management criteria are discussed. Estimates of the impurity concentration in low-activation materials (elementally substituted stainless steels and vanadium alloys) are reported. Impurity activation in first-wall materials turns out to be critical after a comparison of impurity concentration limits and estimated levels. Activation of magnet materials is then considered: Long-term activity is not a concern, while short-term activity is. In both cases, impurity activation is negligible. Magnet materials, and all other less flux-exposed materials, have no practical limitation on impurities in terms of induced radioactivity
Transitions and excitations in a superfluid stream passing small impurities
Pinsker, Florian; Berloff, Natalia G.
2014-01-01
We analyze asymptotically and numerically the motion around a single impurity and a network of impurities inserted in a two-dimensional superfluid. The criticality for the breakdown of superfluidity is shown to occur when it becomes energetically favorable to create a doublet—the limiting case between a vortex pair and a rarefaction pulse on the surface of the impurity. Depending on the characteristics of the potential representing the impurity, different excitation scenarios are shown to exist for a single impurity as well as for a lattice of impurities. Depending on the lattice characteristics it is shown that several regimes are possible: dissipationless flow, excitations emitted by the lattice boundary, excitations created in the bulk, and the formation of large-scale structures.
The origin of metal impurities in DIVA
International Nuclear Information System (INIS)
Ohasa, Kazumi; Sengoku, Seio; Maeda, Hikosuke; Ohtsuka, Hideo; Yamamoto, Shin
1978-10-01
The origin of metal impurities in DIVA (JFT-2a Tokamak) has been studied experimentally. Three processes of metal impurity release from the first wall were identified; i.e. ion sputtering, evaporation, and arcing. Among of these, ion sputtering is the predominant process in the quiet phase of the discharge, which is characterized by no spikes in the loop voltage and no localized heat flux concentrations on the first wall. ''Cones'' formation due to the sputtering is observed on the gold protection plate (guard limiter) exposed to about 10,000 discharges by scanning electron micrograph. In the SEM photographs, the spacial distribution of cones on the shell surface due to the ion sputtering coincides with the spacial distribution of intensity of Au-I line radiation. Gold is the dominant metal impurity in DIVA. The honeycomb structure can decrease release of the metal impurity. (author)
Excited-states of hydrogenic-like impurities in InGaN–GaN spherical QD: Electric field effect
Energy Technology Data Exchange (ETDEWEB)
El Ghazi, Haddou, E-mail: hadghazi@gmail.com [LPS, Faculty of Sciences, Dhar EL Mehrez, B.P 1796 Atlas Fez (Morocco); Special Mathematics, CPGE Kénitra (Morocco); Jorio, Anouar [LPS, Faculty of Sciences, Dhar EL Mehrez, B.P 1796 Atlas Fez (Morocco)
2013-12-01
By means of a traditional Ritz variational method within the effective-mass and single parabolic band approximations, the excited-states energy with and without the existence of the impurity is performed. Externally applied electric field and system radius effects are considered in wurtzite (In,Ga)N–GaN spherical quantum dot with finite potential barrier. The normalized binding energy is also reported. Compared to the previous theoretical findings, a good agreement is shown.
Excited-states of hydrogenic-like impurities in InGaN–GaN spherical QD: Electric field effect
International Nuclear Information System (INIS)
El Ghazi, Haddou; Jorio, Anouar
2013-01-01
By means of a traditional Ritz variational method within the effective-mass and single parabolic band approximations, the excited-states energy with and without the existence of the impurity is performed. Externally applied electric field and system radius effects are considered in wurtzite (In,Ga)N–GaN spherical quantum dot with finite potential barrier. The normalized binding energy is also reported. Compared to the previous theoretical findings, a good agreement is shown
Impurities in the heavy-fermion superconductor UBe13 (invited)
International Nuclear Information System (INIS)
Smith, J.L.; Fisk, Z.; Willis, J.O.; Batlogg, B.; Ott, H.R.
1984-01-01
Small amounts of Sc, Lu, Gd, Np, Ce, Th, La, and Ba have been substituted for uranium in UBe 13 to observe their effects on the superconducting and normal state properties. The thorium, which was the most complete study, resulted in an extremely unusual nonmonotonic depression of the transition temperature for a nonmagnetic impurity. This comes from an interplay that exists between the lowest temperature resistivity peak and the transition temperature, as the peak is depressed. These results suggest that heavy Fermion superconductivity is only one of the possible ground states for heavy mass electron systems. All of the impurities tested resulted in a transition temperature depression
Energy Technology Data Exchange (ETDEWEB)
Sagawa, H. [Center for Mathematical Science, University of Aizu, Aizu-Wakamatsu, Fukushima 965 (Japan); Van Giai Nguyen [Theoretical Physics Division, Inst. de Physique Nucleaire, Paris-11 Univ., 91 - Orsay (France); Suzuki, T. [Department of Physics, Nihon University, Tokyo 156 (Japan)
1999-10-01
We study the effect of isospin impurity on the super-allowed Fermi {beta} decay using microscopic HF and RPA (or TDA) model taking into account CSB and CIB interactions. It is found that the isospin impurity of N = Z nuclei gives enhancement of the sum rule of Fermi transition probabilities. On the other hand, the super-allowed transitions between odd-odd J = 0 nuclei and even-even J = 0 nuclei are quenched because on the cancellation of the isospin impurity effects of mother and daughter nuclei. An implication of the calculated Fermi transition rate on the unitarity of Cabbibo-Kobayashi-Maskawa mixing matrix is also discussed. (authors) 3 refs., 1 fig.
International Nuclear Information System (INIS)
Orsitto, F.
1992-11-01
In a previous investigation the possibility of measuring the bulk ion temperature was considered in detail, in the context of the proposed Thomson scattering diagnostic for fast ions and alpha particles in the Joint European Torus project. In this report we give an affirmative answer to the question of whether good precision can be obtained in the simultaneous determination of the temperatures and densities of plasma ions from a collective scattering experiment provided some conditions are satisfied. (Author)
Symmetry effects in neutron scattering from isotopically enriched Se isotopes
Energy Technology Data Exchange (ETDEWEB)
Lachkar, J.; Haouat, G.; McEllistrem, M. T.; Patin, Y.; Sigaud, J.; Cocu, F.
1975-06-01
Differential cross sections for neutron elastic and inelastic scattering from {sup 76}Se, {sup 78}Se, {sup 80}Se and {sup 82}Se, have been measured at 8-MeV incident neutron energy and from {sup 76}Se and {sup 82}Se at 6- and 10-MeV incident energies. The differences observed in the elastic scattering cross sections are interpretable as the effects of isospin term in the scattering potentials. A full analysis of the elastic scattering data are presented.
Multiple scattering effects in depth resolution of elastic recoil detection
Energy Technology Data Exchange (ETDEWEB)
Wielunski, L.S.; Harding, G.L. [Commonwealth Scientific and Industrial Research Organisation (CSIRO), Lindfield, NSW (Australia). Telecommunications and Industrial Physics; Szilagyi, E. [KFKI Research Institute for Particle and Nuclear Physics, Budapest, (Hungary)
1998-06-01
Elastic Recoil Detection (ERD) is used to profile hydrogen and other low mass elements in thin films at surface and interfaces in a similar way that Rutherford Backscattering Spectroscopy (RBS) is used to detect and profile heavy elements. It is often assumed that the depth resolutions of these two techniques are similar. However, in contrast to typical RBS, the depth resolution of ERD is limited substantially by multiple scattering. In experimental data analysis and/or spectra simulations of a typical RBS measurement multiple scattering effects are often ignored. Computer programs used in IBA, such as RUMP, HYPRA or RBX do not include multiple scattering effects at all. In this paper, using practical thin metal structures with films containing intentionally introduced hydrogen, we demonstrate experimental ERD depth resolution and sensitivity limitations. The effects of sample material and scattering angle are also discussed. (authors). 19 refs., 4 figs.
Impurities in radioactive solutions for gamma spectroscopy
International Nuclear Information System (INIS)
Delgado, J.U.
1990-01-01
The absolute and relative methods for radioactive sources calibration, like 4 Πβ-γ and 4Πγ ionization chamber respectively, allows to reach 0,1% of exactiness in activity measurement, but cannot distinguish radioactive impurities that interfere in the activity. Then, one of the problems associated to a quality control of calibrated sources furnished to users is the identification and quantification of the impurities. In this work, a routine technical procedure, using the facilities of gamma spectrometry method that allows to identify and to determine the impurities relative contribution to the source main radionuclide activity, is described. (author) [pt
Habit modification of potassium acid phthalate (KAP) single crystals by impurities
Murugakoothan, P.; Mohan Kumar, R.; Ushasree, P. M.; Jayavel, R.; Dhanasekaran, R.; Ramasamy, P.
1999-12-01
Nonlinear optical materials potassium dihydrogen phosphate (KDP), urea and L-arginine phosphate (LAP)-doped KAP crystals were grown by the slow cooling method. The LAP-doped crystals show pronounced habit modification compared to KDP and urea doping. The effect of these impurities on growth kinetics, surface morphology, habit modification, structure, optical and mechanical properties have been studied. Among the three impurities, urea doping yields high mechanical stability and optical transmission and for KDP and LAP doping there is a decrease in optical transmission.
International Nuclear Information System (INIS)
Doan Nhat Quang; Nguyen Nhu Dat; Dinh Van An
1993-07-01
A theory is developed of the electron density of states (DOS) in slightly compensated heavily doped semiconductors which undergo a thermal treatment. The calculation is carried out within the semiclassical approach to the random impurity field, taking adequately into account high-temperature correlation among the impurities and low temperature screening due to the free carriers as well. Then, a simple analytic expression for the DOS is obtained which exhibits the same energy dependence as in the case of a random impurity distribution, but now with some correlation-induced changes in the coefficients. A numerical estimation on non-compensated n-type sample of GaAs at a doping level of 5 x 10 18 cm -3 shows that in the tail region the correlated DOS turns out to be somewhat larger and cut less sharply than the random one. (author). 45 refs, 2 figs, 1 tab
EUV impurity study of the Alcator tokamak
International Nuclear Information System (INIS)
Terry, J.L.; Chen, K.I.; Moos, H.W.; Marmar, E.S.
1977-06-01
The intensity of resonance line radiation from oxygen, nitrogen, carbon and molybdenum impurities has been measured in the high field (80 kG), high density (6 x 10 14 cm -3 ) discharges of the Alcator tokamak, using a 0.4 m normal incidence monochromator (300 to 1300 A) with its line of sight fixed along a major radius. The total light impurity concentrations were 2 x 10 -3 , 7 x 10 -4 , and 3 x 10 -3 at central electron densities of 4.5 x 10 13 cm -3 (burnout), 4.0 x 10 13 (low density plateau) and 6.0 x 10 14 (high density plateau). Both a simple model and a computer code which included Pfirsch-Schluter impurity diffusion were used to estimate oxygen influxes of 1.6 x 10 13 cm -2 sec -1 and 1.5 x 10 14 cm -2 sec -1 at the plasma edge in the low and high density emission plateaus. The resulting values of Z/sub eff/, including the contributions due to both the light impurities and molybdenum, were close to one. The power lost through the impurity line radiation accounted for approximately equal to 7 percent of the total ohmic input power at high densities
Transport of impurities during H-mode pulses in JET
International Nuclear Information System (INIS)
Giannella, R.; Gottardi, N.; Mompean, F.; Mori, H.; Pasini, D.; Stork, D.; Barnsley, R.; Hawkes, N.C.; Lawson, K.
1990-01-01
The transport of impurities during the H-mode is very different from that observed in the other regimes. This is clearly evident in the quiescent discharges where the confinement time of impurities τ I are measured in all the quiescent H-mode discharges in spite of the variety of impurity behavior observed corresponding to different plasma parameters and operating scenarios. The condition of the machine has an influence on the role played by the various impurities, but this does not seem to affect the flow patterns of these ions substantially. In particular oxygen, which was often detected as the dominant radiator, can be reduced to a negligible fraction by He conditioning of the carbon X-point tiles or limiters or by evaporating beryllium in the vacuum vessel. Nevertheless the behaviour of the residual impurities in otherwise similar discharges remains substantially unchanged. The transport patterns appear in fact to be affected by the plasma parameters and their profiles. In particular, two extreme transport regimes are presented in the following. These discharges have been modelled with the aid of a recently developed fully time-dependent impurity transport code using heuristic profiles for the impurity diffusion D and the convection velocity v. (author) 4 refs., 5 figs
Dissipative-drift wave instability in the presence of impurity radiation
International Nuclear Information System (INIS)
Bharuthram, R.; Shukla, P.K.
1992-01-01
It is believed that electrostatic fluctuations in edge plasmas are usually triggered by micro and macroscopic plasma instabilities. The latter involve dissipative-drift waves as well as tearing and rippling modes in nonuniform plasmas. However, if the plasma edge contains impurity radiation, then the radiative condensation instability could be the cause of nonthermal fluctuations. The radiative condensation instabilities have been extensively investigated in a homogeneous plasma by many authors. The effect of equilibrium density and electron temperature inhomogeneities in the study of radiative condensation instabilities has been examined by Shukla and Yu. They found new drift-like modes driven by the combined effect of impurity radiation loss and the equilibrium density and temperature gradients. The analyses of Shukla and Yu is, however, limited to low-frequency, long wavelength collisionless drift waves. Since the edge plasma of toroidal devices is highly collisional, the results of collisionless theories cannot be directly applied to explain the origin of nonthermal fluctuations. In this paper, we study the influence of impurity radiation on the dissipative-drift wave instability in a collision-dominated nonuniform plasma embedded in a homogeneous magnetic field. (author) 6 refs
International Nuclear Information System (INIS)
Radzhabov, T.D.; Iskanderova, Z.A.; Arutyunova, E.O.; Samigulin, K.R.
1982-01-01
Theoretical study of capture of impurity gas atoms with defects during ion introduction of the impurity in the process of film growth with simultaneous diffusion has been carried out. Concentration profiles of forned impurity-defect complexes have been calculated analytically and numerically by means of a computer in film depth and in a substrate; basic peculiarities of impurity component formation captured with defects in a wide range of changing basic experimental parameters have been revealed. Effect of impurity capture with defects on amount and distribution of total concentration of impurity atoms and intensity of complete absorption of bombarding ions in films have been analyzed. Shown is a possibility for producing films with a high concentration level and almost uniform distribution of the impurity-defect complexes for real, achievable an experiment, values of process parameters as well as a possibility for increasing complete absorption of gaseous impurity wiht concentration growth of capture defects-traps
Moving discrete breathers in a Klein-Gordon chain with an impurity
International Nuclear Information System (INIS)
Cuevas, J; Palmero, F; Archilla, J F R; Romero, F R
2002-01-01
We analyse the influence of an impurity in the evolution of moving discrete breathers in a Klein-Gordon chain with non-weak nonlinearity. Three different types of behaviour can be observed when moving breathers interact with the impurity: they pass through the impurity continuing their direction of movement; they are reflected by the impurity; they are trapped by the impurity, giving rise to chaotic breathers, as their Fourier power spectra show. Resonance with a breather centred at the impurity site is conjectured to be a necessary condition for the appearance of the trapping phenomenon. This paper establishes a difference between the resonance condition of the non-weak nonlinearity approach and the resonance condition with the linear impurity mode in the case of weak nonlinearity
Donor impurity in nanotube with two GaAs/GaAlAs quantum wells: Magnetic field effects
Energy Technology Data Exchange (ETDEWEB)
Gonzalez, J D; Escorcia, R; Sierra-Ortega, J, E-mail: jdavid0831@gmail.co [Grupo de Investigacion en teorIa de la Materia Condensada, Universidad del Magdalena, A.A. 731, Santa Marta (Colombia)
2009-05-01
Micro-tubes containing two GaAs/GaAlAs quantum wells (QWs) in a section of the tube layer has been fabricated and optical properties of the embedded QWs has been studied. The ground state binding energy of an off-axis donor in a cylindrical nanotube, containing two GaAs/GaAlAs quantum wells (QWs) in the presence of a uniform magnetic field is calculated as a function of the donor location as well as the density of states. A trial function for describing the asymmetric electron charge distribution is taken as a product of the combination of 1s and 2p{sub x,y} subband wave functions and an unknown function that depends only on electron-ion separation. We found that the increasing the magnetic field the increasing the binding energy while the impurity is located in the QW1, whereas the opposite occurs when the impurity is located in the QW2. Two peaks in the curves of the binding energy, as a function of the impurity position, are also found as well as in the density of impurity states.
Energy Technology Data Exchange (ETDEWEB)
Crowther, C; Ruston, A G
1911-01-01
The investigtions recorded constitute a rough survey of the influence of atmospheric impurities upon the growth of plants. They do show clearly that this influence, even outside the towns, may under certain conditions have appreciable bearing upon farm economy. The atmosphere in and around a large industrial city such as Leeds is relatively highly charged with impurities, many of which exert a marked deleterious effect upon plant growth. The impurities are most abundant in the industrial quarters of the city, but are disseminated over very large areas, especially in the direction of the prevailing winds. The rain falling through such a polluted atmosphere becomes notably rich in suspended matters, chlorides, sulphates (often also other sulphur compounds, such as SO/sub 2/), nitrogenous compounds (notably ammonia) and free acid. The suspended matters in the air impede the growth of plants not only by their deposition upon the leaves and consequent hindrance to the free passage of gases into and out of the leaves, but also by reducing the intensity of illumination of the leaves, such reduction amounting in the worst case investigated to fully 40 per cent of the maximum light available. The presence of free acid in the atmosphere exercises a detrimental influence upon plant growth: (a) by direct action upon the leaves indirectly by reducing the activity not only of the necessary ammoniacal fermentation of the soil humus, but even more of the beneficial nitrifying and nitrogen-fixing organisms in the soil. The experiment with the perennial meadow grass, timothy, indicates that with the continued application to the soil of acid rain the produce becomes distinctly poorer in protein and richer in crude fiber, and consequently less nutritious.
Energy Technology Data Exchange (ETDEWEB)
Lee, H.Y., E-mail: brbbebbero@snu.ac.kr [Seoul National University, Seoul (Korea, Republic of); Yang, J.; Kim, Y.G.; Yang, S.M.; Kim, Y.S.; Lee, K.H. [Seoul National University, Seoul (Korea, Republic of); An, Y.H. [National Fusion Research Institute, Daejon (Korea, Republic of); Chung, K.J.; Na, Y.S. [Seoul National University, Seoul (Korea, Republic of); Hwang, Y.S., E-mail: yhwang@snu.ac.kr [Seoul National University, Seoul (Korea, Republic of)
2016-11-01
Highlights: • The baking for partial wall heating and H{sub 2}/He GDC systems are developed in VEST. • The RGA and OES systems for monitoring impurities are constructed in VEST. • The partial baking and He GDC show limited effects on plasma characteristics. • H{sub 2} GDC above 4 h enables the longer plasma current duration up to ∼15 ms. • After H{sub 2} GDC, the discharge should be conducted within 3 h from treatment. - Abstract: Wall conditioning and impurity monitoring systems are developed in Versatile Experiment Spherical Torus (VEST). As a wall conditioning system, a baking system covering the vacuum vessel wall partially and a glow discharge cleaning (GDC) system using two electrodes with dc and 50 kHz power supplies are installed. The GDC system operates with hydrogen and helium gases for both chemical and physical desorption. The impurity monitoring system with residual gas analyzer (RGA), operating at <10{sup −5} Torr with a differential pumping system, is installed along with the optical emission spectroscopy (OES) system to monitor the hydrogen and impurity radiation lines. Effects of these wall conditioning techniques are investigated with the impurity monitoring system for ohmic discharges of VEST. The partial baking and He GDC show limited effects on plasma characteristics but sufficient H{sub 2} GDC above 4 h enables the longer plasma current duration up to ∼15 ms within 3 h from the end of treatment.
International Nuclear Information System (INIS)
Lee, H.Y.; Yang, J.; Kim, Y.G.; Yang, S.M.; Kim, Y.S.; Lee, K.H.; An, Y.H.; Chung, K.J.; Na, Y.S.; Hwang, Y.S.
2016-01-01
Highlights: • The baking for partial wall heating and H_2/He GDC systems are developed in VEST. • The RGA and OES systems for monitoring impurities are constructed in VEST. • The partial baking and He GDC show limited effects on plasma characteristics. • H_2 GDC above 4 h enables the longer plasma current duration up to ∼15 ms. • After H_2 GDC, the discharge should be conducted within 3 h from treatment. - Abstract: Wall conditioning and impurity monitoring systems are developed in Versatile Experiment Spherical Torus (VEST). As a wall conditioning system, a baking system covering the vacuum vessel wall partially and a glow discharge cleaning (GDC) system using two electrodes with dc and 50 kHz power supplies are installed. The GDC system operates with hydrogen and helium gases for both chemical and physical desorption. The impurity monitoring system with residual gas analyzer (RGA), operating at <10"−"5 Torr with a differential pumping system, is installed along with the optical emission spectroscopy (OES) system to monitor the hydrogen and impurity radiation lines. Effects of these wall conditioning techniques are investigated with the impurity monitoring system for ohmic discharges of VEST. The partial baking and He GDC show limited effects on plasma characteristics but sufficient H_2 GDC above 4 h enables the longer plasma current duration up to ∼15 ms within 3 h from the end of treatment.