Electron density of states in a one-dimensional distorted system with impurities: Coherent potential approximation

International Nuclear Information System (INIS)

Bulka, B.R.

1982-04-01

A tight-binding one-dimensional distorted system with impurities is considered and the electron density of states is calculated in the coherent potential approximation. It is shown that two types of impurities, an impurity built in a chain and a domain wall (a soliton), play the essential role and a drastic reduction of the energy gap is observed for a few per cent of impurities. The experimental situation in polyacetylene is also discussed. (author)

Modification of the electronic transport in Au by prototypical impurities and interlayers

KAUST Repository

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

KAUST Repository

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.

Hydrogen impurity in SrTiO{sub 3}: structure, electronic properties and migration

Energy Technology Data Exchange (ETDEWEB)

Villamagua, Luis [Grupo de Fisica de Cristales, Escuela de Electronica y Telecomunicaciones, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador); Barreto, Rafael [Facultad de IngenierIa Civil, Escuela Politecnica Nacional, Apartado 14-01-2759, Quito (Ecuador); Procel, Luis Miguel [Departamento de Quimica, Colegio Politecnico, Universidad San Francisco de Quito, Apartado 17-12-841, Quito (Ecuador); Stashans, Arvids [Grupo de Fisica de Cristales, Escuela de Electronica y Telecomunicaciones, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador)

2007-03-15

The present paper reports a computational investigation of the geometry and electronic structure as well as the migration of a hydrogen impurity in the cubic SrTiO{sub 3} crystal. The study is done using an approach based on the Hartree-Fock theory and developed for periodic systems. It is found that the H impurity forms the so-called OH group at the equilibrium. Analysis of electron density within the defective region implies the enhancement in covalent chemical bonding. A possible defect migration has been also investigated.

Use of nonlocal helium microplasma for gas impurities detection by the collisional electron spectroscopy method

Energy Technology Data Exchange (ETDEWEB)

Kudryavtsev, Anatoly A., E-mail: akud@ak2138.spb.edu [St. Petersburg State University, 7-9 Universitetskaya nab., 199034 St. Petersburg (Russian Federation); Stefanova, Margarita S.; Pramatarov, Petko M. [Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee blvd., 1784 Sofia (Bulgaria)

2015-10-15

The collisional electron spectroscopy (CES) method, which lays the ground for a new field for analytical detection of gas impurities at high pressures, has been verified. The CES method enables the identification of gas impurities in the collisional mode of electron movement, where the advantages of nonlocal formation of the electron energy distribution function (EEDF) are fulfilled. Important features of dc negative glow microplasma and probe method for plasma diagnostics are applied. A new microplasma gas analyzer design is proposed. Admixtures of 0.2% Ar, 0.6% Kr, 0.1% N{sub 2}, and 0.05% CO{sub 2} are used as examples of atomic and molecular impurities to prove the possibility for detecting and identifying their presence in high pressure He plasma (50–250 Torr). The identification of the particles under analysis is made from the measurements of the high energy part of the EEDF, where maxima appear, resulting from the characteristic electrons released in Penning reactions of He metastable atoms with impurity particles. Considerable progress in the development of a novel miniature gas analyzer for chemical sensing in gas phase environments has been made.

Effect of impurities on the growth of {113} interstitial clusters in silicon under electron irradiation

Science.gov (United States)

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.

The effect of magnetic field and donor impurity on electron spectrum in spherical core-shell quantum dot

Science.gov (United States)

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.

Electronic structure and magnetic properties of dilute U impurities in metals

Science.gov (United States)

Mohanta, S. K.; Cottenier, S.; Mishra, S. N.

2016-05-01

The electronic structure and magnetic moment of dilute U impurity in metallic hosts have been calculated from first principles. The calculations have been performed within local density approximation of the density functional theory using Augmented plane wave+local orbital (APW+lo) technique, taking account of spin-orbit coupling and Coulomb correlation through LDA+U approach. We present here our results for the local density of states, magnetic moment and hyperfine field calculated for an isolated U impurity embedded in hosts with sp-, d- and f-type conduction electrons. The results of our systematic study provide a comprehensive insight on the pressure dependence of 5f local magnetism in metallic systems. The unpolarized local density of states (LDOS), analyzed within the frame work of Stoner model suggest the occurrence of local moment for U in sp-elements, noble metals and f-block hosts like La, Ce, Lu and Th. In contrast, U is predicted to be nonmagnetic in most transition metal hosts except in Sc, Ti, Y, Zr, and Hf consistent with the results obtained from spin polarized calculation. The spin and orbital magnetic moments of U computed within the frame of LDA+U formalism show a scaling behavior with lattice compression. We have also computed the spin and orbital hyperfine fields and a detail analysis has been carried out. The host dependent trends for the magnetic moment, hyperfine field and 5f occupation reflect pressure induced change of electronic structure with U valency changing from 3+ to 4+ under lattice compression. In addition, we have made a detailed analysis of the impurity induced host spin polarization suggesting qualitatively different roles of f-band electrons on moment stability. The results presented in this work would be helpful towards understanding magnetism and spin fluctuation in U based alloys.

Characterization of light element impurities in ultrathin silicon-on-insulator layers by luminescence activation using electron irradiation

International Nuclear Information System (INIS)

Nakagawa-Toyota, Satoko; Tajima, Michio; Hirose, Kazuyuki; Ohshima, Takeshi; Itoh, Hisayoshi

2009-01-01

We analyzed light element impurities in ultrathin top Si layers of silicon-on-insulator (SOI) wafers by luminescence activation using electron irradiation. Photoluminescence (PL) analysis under ultraviolet (UV) light excitation was performed on various commercial SOI wafers after the irradiation. We detected the C-line related to a complex of interstitial carbon and oxygen impurities and the G-line related to a complex of interstitial and substitutional carbon impurities in the top Si layer with a thickness down to 62 nm after electron irradiation. We showed that there were differences in the impurity concentration depending on the wafer fabrication methods and also that there were variations in these concentrations in the respective wafers. Xenon ion implantation was used to activate top Si layers selectively so that we could confirm that the PL signal under the UV light excitation comes not from substrates but from top Si layers. The present method is a very promising tool to evaluate the light element impurities in top Si layers. (author)

Magnetic properties of metallic impurities with strongly correlated electrons

Czech Academy of Sciences Publication Activity Database

Janiš, Václav; Ringel, Matouš

2009-01-01

Roč. 115, č. 1 (2009), s. 30-35 ISSN 0587-4246 R&D Projects: GA ČR GA202/07/0644 Institutional research plan: CEZ:AV0Z10100520 Keywords : And erson impurity * strong electron correlations * spin-polarized solution * three-channel parquet equations * magnetic field Subject RIV: BE - Theoretical Physics Impact factor: 0.433, year: 2009 http://przyrbwn.icm.edu.pl/APP/ABSTR/115/a115-1-5.html

MOS Capacitance—Voltage Characteristics II. Sensitivity of Electronic Trapping at Dopant Impurity from Parameter Variations

International Nuclear Information System (INIS)

Jie Binbin; Sah Chihtang

2011-01-01

Low-frequency and high-frequency Capacitance—Voltage (C—V) curves of Metal—Oxide—Semiconductor Capacitors (MOSC), including electron and hole trapping at the dopant donor and acceptor impurities, are presented to illustrate giant trapping capacitances, from > 0.01C OX to > 10C OX . Five device and materials parameters are varied for fundamental trapping parameter characterization, and electrical and optical signal processing applications. Parameters include spatially constant concentration of the dopant-donor-impurity electron trap, N DD , the ground state electron trapping energy level depth measured from the conduction band edge, E C –E D , the degeneracy of the trapped electron at the ground state, g D , the device temperature, T, and the gate oxide thickness, x OX . (invited papers)

GGA+U investigations of impurity d-electrons effects on the electronic and magnetic properties of ZnO

KAUST Repository

Ul Haq, Bakhtiar; Ahmed, Rashid; Shaari, Amiruddin; Goumri-Said, Souraya

2014-01-01

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

IMPURITY SEGREGATION OF STAINLESS STEEL STUDIED BY ATOM-PROBE AND AUGER ELECTRON SPECTROSCOPY

OpenAIRE

Koguchi , Y.; Takahashi , K.; Ishikawa , Y.

1987-01-01

The surface compositions of type 304 stainless steel heated in vacuum at 600-900°C were determined by an atom-probe and Auger electron spectroscopic analysis. In addition to enrichment and depletion of alloying elements in the surface of the stainless steel, segregation of impurity elements such as carbon, nitrogen, phosphorus and sulfur is known to occur. In this paper the atom-probe was used to measure the impurity segregation in the grains as well as in the grain boundary while the AES was...

A Study of the Vacancy-Impurity Interaction in Dilute Nickel Alloys by Core Electron Annihilation

Science.gov (United States)

Arbuzov, V. L.; Danilov, S. E.; Druzhkov, A. P.

1997-08-01

It is shown that the angular correlation of annihilation radiation can be used to identify vacancy-impurity complexes in dilute alloys. Annihilation of trapped positrons with core electrons bears information about the chemical environment of a vacancy defect. The method is especially effective for d-matrices doped with sp-impurities since annihilation parameters of positrons with d- and sp-shell electrons differ considerably. The potentialities of the method of core-electron annihilation of positrons are demonstrated taking electron-irradiated dilute Ni-P and Ni-Si alloys as an example. It is shown that the interaction between the vacancies, which migrate at the III stage of annealing, and P atoms in Ni-P causes a considerable change in the annihilation parameters of positrons with core electrons compared to pure Ni. In Ni-Si alloys the annihilation parameters of trapped positrons with core electrons do not differ from those in Ni. This fact is an evidence that Si atoms do not interact with vacancies in Ni.

Experimental study of electron temperature gradient influence on impurity turbulent transport in fusion plasmas

International Nuclear Information System (INIS)

Villegas, D.

2010-01-01

Understanding impurity transport is a key to an optimal regime for a future fusion device. In this thesis, the theoretical and experimental influence of the electron temperature gradient R/L Te on heavy impurity transport is analyzed both in Tore Supra and ASDEX Upgrade. The electron temperature profile is modified locally by heating the plasma with little ECRH power deposited at two different radii. Experimental results have been obtained with the impurity transport code (ITC) which has been completed with a genetic algorithm allowing to determine the transport coefficient profiles with more accuracy. Transport coefficient profiles obtained by a quasilinear gyrokinetic code named QuaLiKiz are consistent with the experimental ones despite experimental uncertainties on gradients. In the core dominated by electron modes, the lower R/L Te the lower the nickel diffusion coefficient. The latter tends linearly to the neoclassical level when the instability threshold is approached. The experimental threshold is in agreement with the one computed by QuaLiKiz. Further out, where the plasma is dominated by ITG, which are independent of R/L Te , both experimental and simulated results show no modification in the diffusion coefficient profile. Furthermore, the convection velocity profile is not modified. This is attributed to a very small contribution of the thermodiffusion (1/Z dependence) in the total convection. On ASDEX, the preliminary results, very different from the Tore Supra ones, show a internal transport barrier for impurities located at the same radius as the strong ECRH power deposit. (author) [fr

Effect of impurity inhomogeneity of CdS and CdSe monocrystalline semiconductors on electron absorption of piezoactive ultrasonic waves

International Nuclear Information System (INIS)

Ketis, B.P.; Krivka, I.

1986-01-01

Relation of observed anomalies (deviations from predictions of theory for homogeneous piezosemiconductor) of electronic absorption coefficient (EAC) of volume, piezoactive acoustic waves (with 15 MHz frequency) in CdS and CdSe hexagonal crystals with electrical heterogeneity is shown experimentally. Results of electron microanalysis of CdS and CdSe piezosemiconductors confirmed their impurity heterogeneity are presented as well as data of investigations into high-frequency conduction and electronic absorption of ultrasonic waves pointing out to volume nature of impurity and electric heterogeneities of monocrystals investigated. Correlation between EAC anomalies and surface density of impurity aggregates (IA) is noted as well as coincidence of impurity and electrical heterogeneities in CdS and CdSe crystals. In CdS crystals the observed anisotropy of high-frequency conduction and volume radioactive ultrasonic waves EAC is attributed to high density and anisotropy of IA space distribution and shape. To explain EAC anomalies, a crystal is simulated with heterogeneous grid of resistances and condensators

Impurity with two electrons in the spherical quantum dot with Unite confinement potential

International Nuclear Information System (INIS)

Baghdasaryan, D A; Ghaltaghchyan, H Ts; Kazaryan, E M; Sarkisyan, H A

2016-01-01

Two-electron states in a spherical QD with the hydrogenic impurity located in the center and with a finite height confinement potential barrier are investigated. The effective mass mismatch have been taken into account. The dependence of ground state energy and Coulomb electron-electron interaction energy correction on the QD size is studied. The problem of the state exchange time control in QD is discussed, taking into account the spins of the electrons in the Russell-Saunders approximation. The effect of quantum emission has been shown. (paper)

On use of beryllium in fusion reactors: Resources, impurities and necessity of detritiation after irradiation

Energy Technology Data Exchange (ETDEWEB)

Kolbasov, B.N., E-mail: b.kolbasov@yandex.ru; Khripunov, V.I., E-mail: Khripunov_VI@nrcki.ru; Biryukov, A.Yu.

2016-11-01

Highlights: • Potential needs in Be for fusion power engineering may exceed Be resources. • Be recycling after its operation in a fusion power plant (FPP) seems inevitable. • U impurity in Be seriously impairs environmental properties of fusion power plants. • Upon burial of irradiated Be the main problems are caused by U and {sup 3}H impurities. • Clearance of Be extracted from a FPP is impossible due to U impurity. - Abstract: Worldwide identified resources of beryllium somewhat exceed 80 000 t. Beryllium production in all the countries of the world in 2012 was about 230 t. At the same time, some conceptual designs of fusion power reactors envisage utilization of several hundred tons of this metal. Therefore return of beryllium into the production cycle (recycling) will be necessary. The beryllium ore from some main deposits has uranium content inadmissible for fusion reactors. This fact raises a question on the need to develop and apply an economically acceptable technology for beryllium purification from the uranium. Practically any technological procedure with beryllium used in fusion reactors requires its detritiation. A study of tritium and helium release from irradiated beryllium at different temperatures and rates of temperature increase was performed at Kurchatov Institute.

Electronic structures and magnetic properties of 3d and 4d transition-metal impurities in ferromagnetic Fe

CERN Document Server

Park, J H; Min, B I; Cho, H S

2000-01-01

Employing the self-consistent local approach, the tight-binding linear-muffin-tin orbital recursion method, we have investigated the electronic structures and the magnetic properties of 3d and 4d transition-metal (TM) impurities in ferromagnetic bcc Fe. In both 3d and 4d TM impurities, virtual bound states appear and are characterized by a high density of states in the energy spectrum. The characters of the states are studied by calculating the bond order between interaction orbitals. For early TM impurities, the states at the impurity sites have more antibonding characters, while the states at neighboring Fe sites have more bonding characters. For late TM impurities, the situation is reversed. late TM impurities of both the 3d and the 4d TM series have the same magnetic ordering as the host Fe atoms whereas early TM impurities have magnetic moments antiparallel to that of the host. As for the Mn impurity, an inward relaxation of neighboring Fe atoms stabilizes the antiferromagnetic ordering with respect to t...

Electron tunneling into superconducting indium and lead films containing the magnetic impurity manganese

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

Donor-impurity-related optical response and electron Raman scattering in GaAs cone-like quantum dots

Science.gov (United States)

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.

Isotope effects of trapped electron modes in the presence of impurities in tokamak plasmas

Science.gov (United States)

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

Electronic structure of light impurities in α-Fe and V

International Nuclear Information System (INIS)

Gong Xingao; Zeng Zhi; Zheng Wingqi

1987-07-01

The electronic structure of α-Fe and V with hydrogen and carbon as impurities is calculated using the embedded cluster models in the framework of self-consistent local density theory. The results obtained reveal that the charge transfer between the H atom and the host atom is small, but the magnetic moments of neighbouring Fe atoms are reduced. The total energy implies that hydrogen in α-Fe is more easily found to occupy the octahedral interstitial site. On the other hand, there is a charge transfer between the C atom and the host atoms. The distance between the carbon and the nearest neighbour iron atoms is 23% elongated. The interaction between the hydrogen and the carbon impurities was studied using a set of clusters of Fe 10 CH in which the atoms were located in five kinds of configuration. The energy of clusters with hydrogen on octahedral interstitial site is lower than that on the tetrahedral interstitial site. (author). 10 refs, 6 figs, 2 tabs

Moessbauer Studies of Implanted Impurities in Solids

CERN Multimedia

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...

Thermal phonon scattering in silicon doped with Li, P and Li-O; influence of the electronic structure of the impurities

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

Coupling of ion temperature gradient and trapped electron modes in the presence of impurities in tokamak plasmas

Science.gov (United States)

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.

The electronic, magnetic and optical properties of ZnO doped with doubles impurities (Cr, Fe): An LDA-SIC and Monte Carlo study

Energy Technology Data Exchange (ETDEWEB)

Salmani, El Mehdi, E-mail: elmehdisalmani@gmail.com [LMPHE, Faculté des Sciences, Université Mohammed V, Rabat (Morocco); Laghrissi, Ayoub; Lamouri, Rachida; Ez-Zahraouy, Hamid [LMPHE, Faculté des Sciences, Université Mohammed V, Rabat (Morocco); Benyoussef, Abdelilah [Institute for Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Académie Hassan II des Sciences et Techniques, Rabat (Morocco)

2017-01-15

Electronic structure, magnetic and optical properties of ZnO doped with single and double impurities Zn{sub 1−x}Cr{sub x}O, Zn{sub 1−x}Fe{sub x}O, and Zn{sub 1−2x}Cr{sub x}Fe{sub x}O (x=0.03 and 0.06) are investigated using first-principles calculations. Based on the Korringa–Kohn–Rostoker method combined with the coherent potential approximation, we investigated the half-metallic ferromagnetic behavior of doubles impurities (Cr, Fe) doped ZnO. To support our results, we apply the self-interaction-corrected local density approximation (SIC-LDA) to study the electronic structure, optical and magnetic properties of Co-doped ZnO with doubles impurities (Cr, Fe) showing that the half-metallic ferromagnetic state still persists. The stability of the ferromagnetic state compared with the spin-glass state is investigated by comparing their total energies. The exchange interactions obtained from first principle calculations and used in a classical Ising model by a Monte Carlo approach resulted in ferromagnetic states with high Neel temperature. - Highlights: • The electronic structure calculations for ZnO doped with doubles impurities (Cr, Fe) have been discussed. • The half-metallic aspect was proven to take place for doubles impurities (Cr, Fe) codoped ZnO. • The doubles impurities (Cr, Fe)impurities are shown to introduce the necessary magnetic moment that makes ZnO good candidates for spintronic applications.

Influence of molybdenum impurity on the electronic properties of refractory phases

International Nuclear Information System (INIS)

Ivanovskij, A.L.

1992-01-01

Results of calculations of electronic structure modification of refractory phases - TiC, TiN - during dissolution in their volume of molybdenum as the element, dominating in the processes of formation of ring transition area (K-phase) are presented. It is shown that reconstruction of local state density (LSD) of Mo in the system Ni:Mo reflects the effects of impurity state and nickel valency area hybridization. LSD of Mo in MoC, MoN acquires quite a new form

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.

Dynamical impurity problems

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

Dynamical impurity problems

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.

Density of Electronic States in Impurity-Doped Quantum Well Wires

Science.gov (United States)

Sierra-Ortega, J.; Mikhailov, I. D.

2003-03-01

We analyze the electronic states in a cylindrical quantum well-wire (QWW) with randomly distributed neutral, D^0 and negatively charged D^- donors. In order to calculate the ground state energies of the off-center donors D^0 and D^- as a function of the distance from the axis of the QWW, we use the recently developed fractal dimension method [1]. There the problems are reduced to those similar for a hydrogen-like atom and a negative-hydrogen-like ion respectively, in an isotropic effective space with variable fractional dimension. The numerical trigonometric sweep method [2] and the three-parameter Hylleraas-type trial function are used to solve these problems. Novel curves for the density of impurity states in cylindrical QWWs with square-well, parabolic and soft-edge barrier potentials are present. Additionally we analyze the effect of the repulsive core on the density of the impurity states. [1] I.D. Mikhailov, F. J. Betancur, R. Escorcia and J. Sierra-Ortega, Phys. Stat. Sol., 234(b), 590 (2002) [2] F. J. Betancur, I. D. Mikhailov and L. E. Oliveira, J. Appl. Phys. D, 31, 3391(1998)

Behaviour of the electron density near an impurity with exchange and correlation

International Nuclear Information System (INIS)

Adawi, I.; Godwin, V.E.

1982-09-01

The behaviour of the electron density n(r) and potential energy V(r) near an impurity of charge Z is studied in the linear response theory of metals with exchange and correlation. The leading two terms in nsub(odd)(r) and the first three terms in Vsub(odd)(r) are the same as in the Lindhard theory, but corrections appear in the higher terms of the odd powers expansions of these functions. In all quantum linear response theories, the derivative n'(0)=-2Zn 0 /a 0 where n 0 is the free electron gas density and a 0 is the Bohr radius. (author)

Impurity segregation behavior in polycrystalline silicon ingot grown with variation of electron-beam power

Science.gov (United States)

Lee, Jun-Kyu; Lee, Jin-Seok; Jang, Bo-Yun; Kim, Joon-Soo; Ahn, Young-Soo; Cho, Churl-Hee

2014-08-01

Electron beam melting (EBM) systems have been used to improve the purity of metallurgical grade silicon feedstock for photovoltaic application. Our advanced EBM system is able to effectively remove volatile impurities using a heat source with high energy from an electron gun and to continuously allow impurities to segregate at the top of an ingot solidified in a directional solidification (DS) zone in a vacuum chamber. Heat in the silicon melt should move toward the ingot bottom for the desired DS. However, heat flux though the ingot is changed as the ingot becomes longer due to low thermal conductivity of silicon. This causes a non-uniform microstructure of the ingot, finally leading to impurity segregation at its middle. In this research, EB power irradiated on the silicon melt was controlled during the ingot growth in order to suppress the change of heat flux. EB power was reduced from 12 to 6.6 kW during the growth period of 45 min with a drop rate of 0.125 kW/min. Also, the silicon ingot was grown under a constant EB power of 12 kW to estimate the effect of the drop rate of EB power. When the EB power was reduced, the grains with columnar shape were much larger at the middle of the ingot compared to the case of constant EB power. Also, the present research reports a possible reason for the improvement of ingot purity by considering heat flux behaviors.

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

Electron exchange between neutral and ionized impurity iron centers in vitreous arsenic selenide

Energy Technology Data Exchange (ETDEWEB)

Marchenko, A. V. [Herzen State Pedagogical University of Russia (Russian Federation); Terukov, E. I. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Egorova, A. Yu. [St.-Petersburg Mining University (Russian Federation); Kiselev, V. S.; Seregin, P. P., E-mail: ppseregin@mail.ru [Herzen State Pedagogical University of Russia (Russian Federation)

2017-04-15

Impurity iron atoms in vitreous arsenic-selenide As{sub 2}Se{sub 3} films modified by iron form one-electron donor centers with an ionization energy of 0.24 (3) eV (the energy is counted from the conduction-band bottom). The Fermi level is shifted with an increase in the iron concentration from the mid-gap to the donorlevel position of iron due to the filling of one-electron states of the acceptor type lying below the Fermi level. At an iron concentration of ≥3 at %, the electron-exchange process is observed between neutral and ionized iron centers resulting in a change both in the electron density and in the tensor of the electric-field gradient at iron-atom nuclei with increasing temperature above 350 K.

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

Impurity bubbles in a BEC

Science.gov (United States)

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.

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

Electronic structure and optical properties of triangular GaAs/AlGaAs quantum dots: Exciton and impurity states

International Nuclear Information System (INIS)

Tiutiunnyk, A.; Akimov, V.; Tulupenko, V.; Mora-Ramos, M.E.; Kasapoglu, E.; Ungan, F.; Sökmen, I.

2016-01-01

Electronic structure and optical properties in equilateral triangular GaAs/Al_0_._3Ga_0_._7As quantum dots are studied extensively. The effects of donor and acceptor impurity atoms positioned in the orthocenter of the triangle, as well as of the external DC electric field are taken into account. Binding energies of the impurity, exciton energies, interband photoluminescence peak positions as well as linear and non-linear optical properties in THz range caused by transitions between excitonic states are calculated and discussed.

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.)

Effect of impurities on the growth of {113} interstitial clusters in silicon under electron irradiation

OpenAIRE

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 nucle...

The role of electronic dopant on full band in-plane RKKY coupling in armchair graphene nanoribbons-magnetic impurity system

Science.gov (United States)

Hoi, Bui Dinh; Yarmohammadi, Mohsen

2018-05-01

Motivated by the growing interest in solving the obstacles of spintronics applications, we study the Ruderman-Kittel-Kasuya-Yosida (RKKY) effective pairwise interaction between magnetic impurities interacting through the π -electrons embedded in both electronically doped-semiconducting and metallic armchair graphene nanoribbons. In terms of the Green's function formalism, treated in a tight-binding approximation with hopping beyond Dirac cone approximation, the RKKY coupling is an attraction or a repulsion depending on the magnetic impurities distances. Our results show that the RKKY coupling in semiconducting nanoribbons is much more affected by doping than metallic ones. Furthermore, we found that the RKKY coupling increases with ribbon width, while there exist some critical electronic concentrations in RKKY interaction oscillations. On the other hand, we find an unusual incoming wave-vector direction for electrons which describes more clearly the ferro- and antiferromagnetic spin configurations in such system. Also, the RKKY coupling at low and high-temperature regions has been addressed for both ferro- and antiferromagnetic spin arrangements.

Electronic structure and optical properties of triangular GaAs/AlGaAs quantum dots: Exciton and impurity states

Energy Technology Data Exchange (ETDEWEB)

Tiutiunnyk, 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); Department of Physics, Donbass State Engineering Academy, Shkadinova 72, 84313 Kramatorsk (Ukraine); Akimov, V. [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); Department of Physics, Donbass State Engineering Academy, Shkadinova 72, 84313 Kramatorsk (Ukraine); Universidad de Medellín, Carrera 87 No 30-65 Medellín (Colombia); Tulupenko, V. [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); Department of Physics, Donbass State Engineering Academy, Shkadinova 72, 84313 Kramatorsk (Ukraine); Mora-Ramos, M.E. [Centro de Investigación en Ciencias, Instituto de Investigación en Ciencias Básicas y Aplicadas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, CP 62209 Cuernavaca, Morelos (Mexico); Kasapoglu, E. [Cumhuriyet University, Physics Department, 58140 Sivas (Turkey); Ungan, F. [Cumhuriyet University, Faculty of Technology, Deparment of Optical Engineering, 58140 Sivas (Turkey); Sökmen, I. [Department of Physics, Dokuz Eylül University, 35160 Buca, İzmir (Turkey); and others

2016-03-01

Electronic structure and optical properties in equilateral triangular GaAs/Al{sub 0.3}Ga{sub 0.7}As quantum dots are studied extensively. The effects of donor and acceptor impurity atoms positioned in the orthocenter of the triangle, as well as of the external DC electric field are taken into account. Binding energies of the impurity, exciton energies, interband photoluminescence peak positions as well as linear and non-linear optical properties in THz range caused by transitions between excitonic states are calculated and discussed.

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...

Impurity band Mott insulators: a new route to high Tc superconductivity

Directory of Open Access Journals (Sweden)

Ganapathy Baskaran

2008-01-01

Full Text Available Last century witnessed the birth of semiconductor electronics and nanotechnology. The physics behind these revolutionary developments is certain quantum mechanical behaviour of 'impurity state electrons' in crystalline 'band insulators', such as Si, Ge, GaAs and GaN, arising from intentionally added (doped impurities. The present article proposes that certain collective quantum behaviour of these impurity state electrons, arising from Coulomb repulsions, could lead to superconductivity in a parent band insulator, in a way not suspected before. Impurity band resonating valence bond theory of superconductivity in boron doped diamond, recently proposed by us, suggests possibility of superconductivity emerging from impurity band Mott insulators. We use certain key ideas and insights from the field of high-temperature superconductivity in cuprates and organics. Our suggestion also offers new possibilities in the field of semiconductor electronics and nanotechnology. The current level of sophistication in solid state technology and combinatorial materials science is very well capable of realizing our proposal and discover new superconductors.

Geometry and electronic structure of an impurity-trapped exciton in the Cs2GeF6 crystal doped with U4+. The 5f17s1 manifold

International Nuclear Information System (INIS)

Ordejon, B.; Seijo, L.; Barandiaran, Z.

2007-01-01

Complete text of publication follows: Excitons trapped at impurity centres in highly ionic crystals were first described by McClure and Pedrini [Phys. Rev. B 32, 8465 (1985)] as excited states consisting of a bound electron-hole pair with the hole localized on the impurity and the electron on nearby lattice sites, and a very short impurity-ligand bond length. In this work we present a detailed microscopic characterization of an impurity - trapped exciton in Cs 2 GeF 6 doped with U 4+ . Its electronic structure has been studied by means of CASSCF/CASPT2/SOCI relativistic ab initio model potential (AIMP) embedded-cluster calculations on (UF 6 ) 2- and (UF 6 Cs 8 ) 6+ clusters embedded in Cs 2 GeF 6 . The local geometry of the impurity-trapped exciton, the potential energy curves, and the multi electronic wavefunctions, have been obtained as direct, non-empirical results of the methods. The calculated excited states appear to be significantly delocalized outside the UF 6 volume and their U-F bond length turns out to be very short, closer to that of a pentavalent uranium defect than to that of a tetravalent uranium defect. The wavefunctions of these excited states show a dominant U 5f 1 7s 1 configuration character. This result has never been anticipated by simpler models and reveals the unprecedented ability of diffuse orbitals of f-element impurities to act as electron traps in ionic crystals

Electronic Resource Management and Design

Science.gov (United States)

Abrams, Kimberly R.

2015-01-01

We have now reached a tipping point at which electronic resources comprise more than half of academic library budgets. Because of the increasing work associated with the ever-increasing number of e-resources, there is a trend to distribute work throughout the library even in the presence of an electronic resources department. In 2013, the author…

Monte Carlo method for magnetic impurities in metals

Science.gov (United States)

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.

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

Morphological and Chemical Analysis of Impurities in Ice Using the Environmental Scanning Electron Microscopy and Fluorescence Spectroscopy

Czech Academy of Sciences Publication Activity Database

Neděla, Vilém; Runštuk, Jiří; Krausko, J.; Klán, P.; Heger, D.

2015-01-01

Roč. 21, S3 (2015), s. 1699-1700 ISSN 1431-9276 R&D Projects: GA ČR(CZ) GA14-22777S Institutional support: RVO:68081731 Keywords : Ice * ESEM * impurities * morphology Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 1.730, year: 2015

Investigation of energy levels of Er-impurity centers in Si by the method of ballistic electron emission spectroscopy

International Nuclear Information System (INIS)

Filatov, D. O.; Zimovets, I. A.; Isakov, M. A.; Kuznetsov, V. P.; Kornaukhov, A. V.

2011-01-01

The method of ballistic electron emission spectroscopy is used for the first time to study the energy spectrum of Er-impurity complexes in Si. The features are observed in the ballistic electron spectra of mesa diodes based on p + -n + Si structures with a thin (∼30 nm) p + -Si:Er surface layer in the region of ballistic-electron energies eV t lower than the conduction-band-edge energy E c in this layer. They are associated with the tunnel injection of ballistic electrons from the probe of the scanning tunnel microscope to the deep donor levels of the Er-impurity complexes in the p + -Si:Er layer with subsequent thermal excitation into the conduction band and the diffusion to the p + -n + junction and the direct tunneling in it. To verify this assumption, the ballistic-electron transport was simulated in the system of the Pt probe, native-oxide layer SiO 2 -p + -Si:Er-n + , and Si substrate. By approximating the experimental ballistic-electron spectra with the modeling spectra, the ground-state energy of the Er complex in Si was determined: E d ≈ E c − 0.27 eV. The indicated value is consistent with the data published previously and obtained from the measurements of the temperature dependence of the free-carrier concentration in Si:Er layers.

Spectroscopical studies of impurities in the belt pinch HECTOR

International Nuclear Information System (INIS)

Singethan, J.

1981-04-01

In this paper UV-line-intensity measurements of impurities are presented, which have been performed in the belt-pinch HECTOR. From the line-intensities impurity concentrations and information on the radiation losses is be obtained. At temperatures below 100 eV, the energy loss due to line emission of oxygen and carbon impurities is one of the most important electron energy loss mechanisms. Thus the measurement and calculation of the radiation losses is of particular relevance. Furthermore the electron temperature time dependence can be obtained by comparing the line intensity time dependence with the solution of the respective rate equations. (orig./HT) [de

Impurity Deionization Effects on Surface Recombination DC Current-Voltage Characteristics in MOS Transistors

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)

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

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.

Topological phase, electronic, magnetic and optical properties of ScPdBi compound with Gd, Np and Cm impurities

Energy Technology Data Exchange (ETDEWEB)

Narimani, Mitra; Nourbakhsh, Zahra, E-mail: z.nourbakhsh@sci.ui.ac.ir

2017-07-15

Highlights: • Gd, Np and Cm impurities induce the magnetic moment in ScPdBi compound. • ScPdBi compound with Gd, Np and Cm impurities has normal band order. • The ε(0) and R(0) increase by increasing the atomic number of X atom. - Abstract: The electronic, magnetic and optical properties of X-doped ScPdBi (X = Gd, Np, Cm) are investigated in the framework of density functional theory. The exchange-correlation potential is treated using generalized gradient approximation with Coulomb interaction parameter. The band order and energy band gap of X-doped ScPdBi are investigated by calculation of band structure. The effect of doping impurity on magnetic properties of ScPdBi compound is studied by calculation of total and partial magnetic moments of X-doped ScPdBi compound. Furthermore, the optical properties of X-doped ScPdBi are calculated and compared in the energy range of 0–25 eV.

Helium like impurity in CdTe/ Cd1-xMnxTe semimagnetic semiconductors under magnetic field: Dimensionality effect on electron - Electron interaction

Science.gov (United States)

Kalpana, Panneer Selvam; Jayakumar, Kalyanasundaram

2017-11-01

We study the effect of magnetic field on the Coulomb interaction between the two electrons confined inside a CdTe/Cd1-xMnxTe Quantum Well (QW), Quantum Well Wire (QWW) and Quantum Dot (QD) for the composition of Mn2+ ion, x = 0.3. The two particle Schrodinger equation has been solved using variational technique in the effective mass approximation. The results show that the applied magnetic field tremendously alters the Coulomb interaction of the electrons and their binding to the donor impurity by shrinking the spatial extension of the two particle wavefunction and leads to tunnelling through the barrier. The qualitative phenomenon involved in such variation of electron - electron interaction with the magnetic field has also been explained through the 3D - plot of the probability density function.

Stacking change in MoS2 bilayers induced by interstitial Mo impurities.

Science.gov (United States)

Cortés, Natalia; Rosales, Luis; Orellana, Pedro A; Ayuela, Andrés; González, Jhon W

2018-02-01

We use a theoretical approach to reveal the electronic and structural properties of molybdenum impurities between MoS 2 bilayers. We find that interstitial Mo impurities are able to reverse the well-known stability order of the pristine bilayer, because the most stable form of stacking changes from AA' (undoped) into AB' (doped). The occurrence of Mo impurities in different positions shows their split electronic levels in the energy gap, following octahedral and tetrahedral crystal fields. The energy stability is related to the accommodation of Mo impurities compacted in hollow sites between layers. Other less stable configurations for Mo dopants have larger interlayer distances and band gaps than those for the most stable stacking. Our findings suggest possible applications such as exciton trapping in layers around impurities, and the control of bilayer stacking by Mo impurities in the growth process.

Electron stripping cross sections for light impurity ions in colliding with atomic hydrogens relevant to fusion research

International Nuclear Information System (INIS)

Tawara, H.

1992-04-01

Electron stripping (ionization) cross sections for impurity (carbon) ions with various charge states in collisions with atomic hydrogens have been surveyed. It has been found that these data are relatively limited both in collision energy and charge state and, in particular those necessary for high energy neutral beam injection (NBI) heating in fusion plasma research are scarce. Some relevant cross sections for carbon ions, C q+ (q = 0-5) have been estimated, based upon the existing data, empirical behavior and electron impact ionization data. (author)

A crystalline cluster method for deep impurities in insulators

International Nuclear Information System (INIS)

Guimaraes, P.S.

1983-01-01

An 'ab initio' self-consistent-field crystalline-cluster approach to the study of deep impurity states in insulators is proposed. It is shown that, in spite of being a cluster calculation, the interaction of the impurity with the crystal environment is fully taken into account. It is also shown that the present representation of the impurity states is, at least, as precise as the crystalline cluster representation of the pure crystal electronic structure. The procedure has been tested by performing the calculation of the electronic structure of the U center in a sodium chloride crystal, and it has been observed that the calculated GAMMA 1 - GAMMA 15 absorption energy is in good agreement with experiment. (Author) [pt

A crystalline cluster method for deep impurities in insulators

International Nuclear Information System (INIS)

Guimaraes, P.S.

1983-01-01

An ''ab initio'' self-consistent-field crysttalline-cluster approach to the study of deep impurity states in insulators is proposed. It is shown that, in spite of being a cluster calculation, the interaction of the impurity with the crystal environment is fully taken into account. It is also shown that the present representation of the impurity states is, at least, as precise as the crystalline cluster representation of the pure crystal electronic structure. The procedure has been tested by performing the calculation of the electronic structure of the U center in a sodium chloride crystal, and it has been observed that the calculated γ 1 - γ 15 absorption energy is in good agreement with experiment. (author) [pt

Dynamic conductivity modified by impurity resonant states in doping three-dimensional Dirac semimetals

Science.gov (United States)

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.

Impurity-induced states in superconducting heterostructures

Science.gov (United States)

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.

Electron exchange between tin impurity U{sup –} centers in PbS{sub z}Se{sub 1–z} alloys

Energy Technology Data Exchange (ETDEWEB)

Marchenko, A. V. [Alexander Herzen State Pedagogical University of Russia (Russian Federation); Terukov, E. I. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Seregin, P. P., E-mail: ppseregin@mail.ru; Rasnjuk, A. N.; Kiselev, V. S. [Alexander Herzen State Pedagogical University of Russia (Russian Federation)

2016-07-15

Using emission {sup 119mm}Sn({sup 119m}Sn) and {sup 119}Sb({sup 119m}Sn) Mössbauer spectroscopy, it is shown that impurity tin atoms in PbS{sub z}Se{sub 1–z} alloys substitute lead atoms and are two-electron donors with negative correlation energy (U{sup –} centers). It is found that the energy levels related to impurity tin atoms are in the lower half of the band gap at z ≥ 0.5 against the background of allowed valence-band states at z ≤ 0.4. The electron exchange between neutral and doubly ionized tin U{sup –} centers in partially compensated Pb{sub 0.99}Sn{sub 0.005}Na{sub 0.005}S{sub z}Se{sub 1–z} alloys is studied. The activation energy of this process decreases from 0.111(5) eV for a composition with z = 1 to 0.049(5) eV for compositions with c ≤ 0. For all z, the exchange is implemented via the simultaneous transfer of two electrons using delocalized valence-band states.

Boron, nitrogen, and nickel impurities in GeC nanoribbons: A first-principles investigation

Energy Technology Data Exchange (ETDEWEB)

Xu, Zhuo; Li, Yangping, E-mail: liyp@nwpu.edu.cn; Liu, Zhengtang

2017-07-01

Highlights: • The impurities preferentially substitutes the Ge atom at the ribbon edge. • The impurities could result in a reduction of the band gap of 7-AGeCNR. • The impurities turns the metallic behavior of 4-ZGeCNR into semiconductor. • The impurities could change the magnetic moment of 4-ZGeCNR. • The impurities could introduce magnetic moments into the non-magnetic 7-AGeCNR. - Abstract: Using first-principles calculations based on the density functional theory we investigated the structural, electronic and magnetic properties of substitutional boron, nitrogen, and nickel impurities in germanium carbide (GeC) nanoribbons. Hydrogen terminated GeC ribbons with armchair and zigzag edges are considered here. We observed that all three impurities preferentially substitutes the Ge atom at the ribbon edge. In addition, the electronic band structures of the doped systems indicate that (i) the impurities could introduce impurity bands in the band gap and resulting in a reduction of the band gap of 7-AGeCNR, (ii) the metallic behavior of 4-ZGeCNR turns into semiconductor because of the incorporation of the impurities, (iii) the impurities could change the magnetic moment of 4-ZGeCNR and even introduce magnetic moment into the non-magnetic 7-AGeCNR.

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)

An Impurity Emission Survey in the near UV and Visible Spectral Ranges of Electron Cyclotron Heated (ECH) Plasma in the TJ-II Stellarator

International Nuclear Information System (INIS)

McCarthy, K. J.; Zurro, B.; Baciero, A.

2001-01-01

We report on a near-ultraviolet and visible spectroscopic survey (220-600 nm) of electron cyclotron resonance (ECR) heated plasmas created in the TJ-II stellarator, with central electron temperatures up to 2 keV and central electron densities up to 1.7 x 10 ''19 m''-3. Approximately 1200 lines from thirteen elements have been identified. The purpose of the work is to identify the principal impurities and spectral lines present in TJ-II plasmas, as well as their possible origin to search for transitions from highly ionised ions. This work will act as a base for identifying suitable transitions for following the evolution of impurities under different operating regimens and multiplet systems for line polarisation studies. It is intended to use the database creates as a spectral line reference for comparing spectra under different operating and plasma heating regimes. (Author)

Electron-beam-induced current study of hydrogen passivation on grain boundaries in multicrystalline silicon: Influence of GB character and impurity contamination

International Nuclear Information System (INIS)

Chen Jun; Yang Deren; Xi Zhenqiang; Sekiguchi, Takashi

2005-01-01

The impacts of grain boundary (GB) character and impurity contamination level on the hydrogen passivation of GBs in multicrystalline silicon (mc-Si) were studied by means of an electron-beam-induced current (EBIC) technique. In mc-Si with a low contamination of Fe, the 300K EBIC contrast of all kinds of GBs in the H-passivated state was weak and similar to that in the as-grown state. The 100K EBIC contrast of Σ (Σ=3, 9, and 27) GBs decreased about 75-80%, whereas that of random and small-angle GBs decreased about 35-40%. Due to the different impurity gettering ability of different GBs, the variation in 100K EBIC contrast has suggested that the effect of H-passivation depends on both the GB character and impurity contamination level. In the mc-Si with heavy contamination of Fe, at both 300 and 100K, the EBIC contrast of both Σ (Σ=3) and random GBs decreased but the ratio was <40%, suggesting that the H-passivation is mainly affected by the impurity contamination level. on

Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

Science.gov (United States)

Jung, Han Sae; Tsai, Hsin-Zon; Wong, Dillon; Germany, Chad; Kahn, Salman; Kim, Youngkyou; Aikawa, Andrew S.; Desai, Dhruv K.; Rodgers, Griffin F.; Bradley, Aaron J.; Velasco, Jairo; Watanabe, Kenji; Taniguchi, Takashi; Wang, Feng; Zettl, Alex; Crommie, Michael F.

2015-01-01

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene’s charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene's electronic structure in the presence of a charged impurity. The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene’s electronic properties.1-8 Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge2 and/or molecular5 states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.2-5 These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices. PMID:26273961

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

Valence change in rare earth semiconductors in many-impurity Anderson model

International Nuclear Information System (INIS)

Kocharyan, A.N.

1986-01-01

Green functions averaged over point impurity localization are found out in the simplest many-impurity model of rare earth semiconductor taking into account local Coulomb repulsion and hybridization of s- and f-electrons. Analytical expressions for s- and f-electron states density are obtained in the appoximation linear in can centration. Behaviour of a state density nearly the continuous spectrum edge and in the vicinity of the f-level is studied as a function of electron parameters. A comparison with the Anderson one-impurity model is performed. It is shown that essential energy spectrum conversion occurs in the case of a great number of impurities close to the continuous spectrum. Continuous spectrum boundaries are found out, and conditions are defined, at which the forbidden energy gap occurs in the continuous spectrum nearly a f-level. Effect of the coherent conversion of spectrum on behaviour of valence in changing f-level position is analyzed. It is shown that in the lack of electron-lattice interaction the phase transition with valence change occurs in a smooth manner as in the model with strictly periodic Andersen lattice

Electronic Resource Management Systems

Directory of Open Access Journals (Sweden)

Mark Ellingsen

2004-10-01

Full Text Available Computer applications which deal with electronic resource management (ERM are quite a recent development. They have grown out of the need to manage the burgeoning number of electronic resources particularly electronic journals. Typically, in the early years of e-journal acquisition, library staff provided an easy means of accessing these journals by providing an alphabetical list on a web page. Some went as far as categorising the e-journals by subject and then grouping the journals either on a single web page or by using multiple pages. It didn't take long before it was recognised that it would be more efficient to dynamically generate the pages from a database rather than to continually edit the pages manually. Of course, once the descriptive metadata for an electronic journal was held within a database the next logical step was to provide administrative forms whereby that metadata could be manipulated. This in turn led to demands for incorporating more information and more functionality into the developing application.

Calculation technique of free and impurity ion electronic structures

International Nuclear Information System (INIS)

Kulagin, N.A.; Sviridov, D.T.

1986-01-01

The monograph deals with calculation technique of free and impurity ion spectra with completed nl N -shell. The principles of the theory of irreducible tensor operators, genealogical coefficients, calculation technique of angular and radial parts of matrix elements operators are stated. The correlation accounting methods in free ions are considered in detail. The principles of the theory of crystal field and ligand field, the method of self-consistent field for impurity ions are reported. The technique efficiency based on example of lanthanum and actinium group ions is shown. Experimental data by nf N -ion spectra are given. The tables of angular coefficients, energy values of X-ray lines of rare earth ions and genealogical coefficients are given in the appendix

Electronic Resources Management Project Presentation 2012

KAUST Repository

Ramli, Rindra M.

2012-11-05

This presentation describes the electronic resources management project undertaken by the KAUST library. The objectives of this project is to migrate information from MS Sharepoint to Millennium ERM module. One of the advantages of this migration is to consolidate all electronic resources into a single and centralized location. This would allow for better information sharing among library staff.

Investigations of impurity control in JET using fuelling, and interpretation of experiments using the LIM impurity code

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 doping effects on the orbital thermodynamic properties of hydrogenated graphene, graphane, in Harrison model

Science.gov (United States)

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.

Role of Sn impurity on electronic topological transitions in 122 Fe-based superconductors

Energy Technology Data Exchange (ETDEWEB)

Ghosh, Haranath, E-mail: hng@rrcat.gov.in [Homi Bhabha National Institute, Anushaktinagar, Mumbai 400 094 (India); Indus Synchrotrons Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Sen, Smritijit [Homi Bhabha National Institute, Anushaktinagar, Mumbai 400 094 (India); Indus Synchrotrons Utilization Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India)

2016-08-25

We show that only a few percentage of Sn doping at the Ba site on BaFe{sub 2}As{sub 2}, can cause electronic topological transition, namely, the Lifshitz transition. A hole like d{sub xy} band of Fe undergoes electron like transition due to 4% Sn doping. Lifshitz transition is found in BaFe{sub 2}As{sub 2} system around all the high symmetry points. Our detailed first principles simulation predicts absence of any Lifshitz transition in other 122 family compounds like SrFe{sub 2}As{sub 2}, CaFe{sub 2}As{sub 2} in agreement with experimental observations. This work bears practical significance due to the facts that a few percentage of Sn impurity is in-built in tin-flux grown single crystals method of synthesizing 122 materials and inter-relationship among the Lifshitz transition, magnetism and superconductivity. - Highlights: • Electronic topological transition due to Sn contamination in BaFe{sub 2}As{sub 2}. • Hole like Fe-d{sub xy} band converts into electron like in 3% Sn contaminated BaFe{sub 2}As{sub 2}. • Electron like Fe-d{sub xz}, d{sub yz} bands moves above Fermi Level at X,Y points. • No Lifshitz transition found in Sn-contaminated Sr-122, Ca-122 systems.

Power balance and characterization of impurities in the Maryland Spheromak

International Nuclear Information System (INIS)

Cote, C.

1993-01-01

The Maryland Spheromak is a medium size magnetically confined plasma of toroidal shape. Low T e and higher n e than expected contribute to produce a radiation dominated short-lived spheromak configuration. A pyroelectric radiation detector and a VUV spectrometer have been used for space and time-resolved measurements of radiated power and impurity line emission. Results from the bolometry and VUV spectroscopy diagnostics have been combined to give the absolute concentrations of the major impurity species together with the electron temperature. The large amount of oxygen and nitrogen ions in the plasma very early in the discharge is seen to be directly responsible for the abnormally high electron density. The dominant power loss mechanisms are found to be radiation (from impurity line emission) and electron convection to the end walls during the formation phase of the spheromak configuration, and radiation only during the decay phase

Power balance and characterization of impurities in the Maryland Spheromak

Energy Technology Data Exchange (ETDEWEB)

Cote, Claude [Univ. of Maryland, College Park, MD (United States)

1993-01-01

The Maryland Spheromak is a medium size magnetically confined plasma of toroidal shape. Low T_e and higher n_e than expected contribute to produce a radiation dominated short-lived spheromak configuration. A pyroelectric radiation detector and a VUV spectrometer have been used for space and time-resolved measurements of radiated power and impurity line emission. Results from the bolometry and VUV spectroscopy diagnostics have been combined to give the absolute concentrations of the major impurity species together with the electron temperature. The large amount of oxygen and nitrogen ions in the plasma very early in the discharge is seen to be directly responsible for the abnormally high electron density. The dominant power loss mechanisms are found to be radiation (from impurity line emission) and electron convection to the end walls during the formation phase of the spheromak configuration, and radiation only during the decay phase.

Impurity-induced anisotropic semiconductor-semimetal transition in monolayer biased black phosphorus

Science.gov (United States)

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.

Energy levels and far-infrared optical absorption of impurity doped semiconductor nanorings: Intense laser and electric fields effects

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.

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)

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)

PRINCIPLES OF CONTENT FORMATION EDUCATIONAL ELECTRONIC RESOURCE

Directory of Open Access Journals (Sweden)

О Ю Заславская

2017-12-01

Full Text Available The article considers modern possibilities of information and communication technologies for the design of electronic educational resources. The conceptual basis of the open educational multimedia system is based on the modular architecture of the electronic educational resource. The content of the electronic training module can be implemented in several versions of the modules: obtaining information, practical exercises, control. The regularities in the teaching process in modern pedagogical theory are considered: general and specific, and the principles for the formation of the content of instruction at different levels are defined, based on the formulated regularities. On the basis of the analysis, the principles of the formation of the electronic educational resource are determined, taking into account the general and didactic patterns of teaching.As principles of the formation of educational material for obtaining information for the electronic educational resource, the article considers: the principle of methodological orientation, the principle of general scientific orientation, the principle of systemic nature, the principle of fundamentalization, the principle of accounting intersubject communications, the principle of minimization. The principles of the formation of the electronic training module of practical studies in the article include: the principle of systematic and dose based consistency, the principle of rational use of study time, the principle of accessibility. The principles of the formation of the module for monitoring the electronic educational resource can be: the principle of the operationalization of goals, the principle of unified identification diagnosis.

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

Implementing CORAL: An Electronic Resource Management System

Science.gov (United States)

Whitfield, Sharon

2011-01-01

A 2010 electronic resource management survey conducted by Maria Collins of North Carolina State University and Jill E. Grogg of University of Alabama Libraries found that the top six electronic resources management priorities included workflow management, communications management, license management, statistics management, administrative…

Impurity sublattice localization in ZnO revealed by li marker diffusion

DEFF Research Database (Denmark)

Azarov, A.Yu.; Knutsen, K.E.; Neuvonen, P.T.

2013-01-01

Sublattice localization of impurities in compound semiconductors, e.g., ZnO, determines their electronic and optical action. Despite that the impurity position may be envisaged based on charge considerations, the actual localization is often unknown, limiting our understanding of the incorporation...... and possible doping mechanisms. In this study, we demonstrate that the preferential sublattice occupation for a number of impurities in ZnO can be revealed by monitoring Li diffusion. In particular, using ion implantation, the impurity incorporation into the Zn sublattice (holds for, B, Mg, P, Ag, Cd, and Sb...

Radiation losses from oxygen and iron impurities in a high temperature plasma

International Nuclear Information System (INIS)

Breton, C.; Michelis, C. de; Mattioli, M.

1976-06-01

Radiation and ionization losses due to impurities present in a high temperature plasma have been calculated for a light element (oxygen), which is completely stripped in the core of existing Tokamak discharges, and a heavy one (iron), which is only partially stripped. Two extreme cases have been treated: in the first one coronal equilibrium is reached; the radiated power is then equal to the product of the electron density, the impurity density, and a function of the electron temperature; in the second one impurities recycle with a constant radial velocity v 0 in a background plasma; radiation and ionization losses are proportional to the impurity flux and are a decreasing function of the diffusion velocity. The results presented can be used to evaluate losses in a practical case [fr

Negative compressibility observed in graphene containing resonant impurities

International Nuclear Information System (INIS)

Chen, X. L.; Wang, L.; Li, W.; Wang, Y.; He, Y. H.; Wu, Z. F.; Han, Y.; Zhang, M. W.; Xiong, W.; Wang, N.

2013-01-01

We observed negative compressibility in monolayer graphene containing resonant impurities under different magnetic fields. Hydrogenous impurities were introduced into graphene by electron beam (e-beam) irradiation. Resonant states located in the energy region of ±0.04 eV around the charge neutrality point were probed in e-beam-irradiated graphene capacitors. Theoretical results based on tight-binding and Lifshitz models agreed well with experimental observations of graphene containing a low concentration of resonant impurities. The interaction between resonant states and Landau levels was detected by varying the applied magnetic field. The interaction mechanisms and enhancement of the negative compressibility in disordered graphene are discussed.

Managing electronic resources a LITA guide

CERN Document Server

Weir, Ryan O

2012-01-01

Informative, useful, current, Managing Electronic Resources: A LITA Guide shows how to successfully manage time, resources, and relationships with vendors and staff to ensure personal, professional, and institutional success.

Non-Fermi-liquid theory of a compactified Anderson single-impurity model

International Nuclear Information System (INIS)

Zhang, G.; Hewson, A.C.

1996-01-01

We consider a version of the symmetric Anderson impurity model (compactified) which has a non-Fermi-liquid weak-coupling regime. We find that in the Majorana fermion representation the perturbation theory can be conveniently developed in terms of Pfaffian determinants and we use this formalism to calculate the impurity free energy, self-energies, and vertex functions. We derive expressions for the impurity and the local conduction-electron charge and spin-dynamical susceptibilities in terms of the impurity self-energies and vertex functions. In the second-order perturbation theory, a linear temperature dependence of the electrical resistivity is obtained, and the leading corrections to the impurity specific heat are found to behave as TlnT. The impurity static susceptibilities have terms in lnT to zero, first, and second order, and corrections of ln 2 T to second order as well. The conduction-electron static susceptibilities, and the singlet superconducting paired static susceptibility at the impurity site, have second-order corrections lnT, which indicate that a singlet conduction-electron pairing resonance forms at the Fermi level (the chemical potential). When the perturbation theory is extended to third order logarithmic divergences are found in the only vertex function Γ 0,1,2,3 (0,0,0,0), which is nonvanishing in the zero-frequency limit. We use the multiplicative renormalization-group (RG) method to sum all the leading-order logarithmic contributions. This gives a weak-coupling low-temperature energy scale T c =Δexp[-(1/9)(πΔ/U) 2 ], which is the combination of the two independent coupling parameters. The RG scaling equation is derived and shows that the dimensionless coupling constant bar U=U/πΔ is increased as the high-energy scale Δ is reduced, so our perturbational results can be justified in the regime T approx-gt T c

Quenching of orbital momentum by crystalline fields in a multichannel Kondo impurity

International Nuclear Information System (INIS)

Schlottmann, P.; Lee, K.

1995-01-01

We consider an impurity of spin S interacting via an isotropic spin exchange with conduction electrons of spin 1/2. The conduction electrons can be in n different orbital channels. We assume that crystalline fields split the orbital degrees of freedom into two multiplets, the one with lower energy consisting of n * orbitals and the one of higher energy of n-n * orbitals. The exchange coupling is the same for all channels. We derive the thermodynamic Bethe ansatz equations for this model and discuss the ground-state properties of the impurity as a function of the spin S and the magnetic field. The solution of the ground-state Bethe ansatz equations is obtained numerically. Three situations have to be distinguished when the magnetic field is small compared to the Kondo temperature: (i) If S=n/2 or S=n * /2 the conduction electrons exactly compensate the impurity spin into a singlet ground state, (ii) if S>n/2 the impurity is undercompensated, i.e., only partially compensated leaving an effective spin S-n/2 at low temperatures, and (iii) in all other cases the impurity spin is overcompensated giving rise to critical behavior. The quenching of the orbits by the crystalline field dramatically affects the cases S * /2

Impurity transport calculations for the limiter shadow region of a tokamak

International Nuclear Information System (INIS)

Claassen, H.A.; Repp, H.

1981-01-01

Impurity transport calculations are presented for the scrape-off layer of a tokamak with a poloidal ring limiter. The theory is based on the drift-kinetic equations for the impurity ions in their different ionization states. It is developed in the limit of low impurity concentrations under due consideration of electron impact ionization, Coulomb collisions with hydrogen ions streaming onto a neutralizing surface, a convection along the magnetic field, and a radial drift. The background plasma and the impurity sources at the walls enter the theory as input parameters. Numerical results are given for the radial profiles of density, temperature, particle flux, and energy flux of wall-released impurity ions as well as for the screening efficiency of the scrape-off layer neglecting impurity re-emission from the limiter. (author)

Quasilinear Carbon Transport In An Impurity Hole Plasma In LHD

Energy Technology Data Exchange (ETDEWEB)

Mikkelsen, David R. [PPPL; Tanaka, K. [NIFS; Nunami, M. [NIFS; Watanabe, T-H. [Nagoya University; Sugama, H. [NIFS; Yoshinuma, M. [NIFS; Suzuki, Y. [NIFS; Goto, M. [NIFS; Morita, S. [NIFS; Wieland, B. [NIFS; Yamada, I. [NIFS; Yashura, R. [NIFS; Akiyama, T. [NIFS; Pablant, Novimir A. [PPPL

2014-04-01

Comprehensive electrostatic gyrokinetic linear stability calculations for ion-scale microinstabilities in an LHD plasma with an ion-ITB and carbon "impurity hole" are used to make quasilinear estimates of particle flux to explore whether microturbulence can explain the observed outward carbon fluxes that flow "up" the impurity density gradient. The ion temperature is not stationary in the ion-ITB phase of the simulated discharge, during which the core carbon density decreases continuously. To fully sample these varying conditions the calculations are carried out at three radial locations and four times. The plasma parameter inputs are based on experimentally measured profiles of electron and ion temperature, as well as electron and carbon density. The spectroscopic line-average ratio of hydrogen and helium densities is used to set the density of these species. Three ion species (H,He,C) and the electrons are treated kinetically, including collisions. Electron instability drive does enhance the growth rate significantly, but the most unstable modes have characteristics of ion temperature gradient (ITG) modes in all cases. As the carbon density gradient is scanned between the measured value and zero, the quasilinear carbon flux is invariably inward when the carbon density profile is hollow, so turbulent transport due to the instabilities considered here does not explain the observed outward flux of impurities in impurity hole plasmas. The stiffness of the quasilinear ion heat flux is found to be 1.7-2.3, which is lower than several estimates in tokamaks.

Spin-1 two-impurity Kondo problem on a lattice

Science.gov (United States)

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.

Refractometry of TGS crystals doped with L-threonine impurity under uniaxial pressure

Energy Technology Data Exchange (ETDEWEB)

Stadnyk, V. I., E-mail: vasylstadnyk@ukr.net; Kiryk, Yu. I. [Lviv National University (Ukraine)

2013-07-15

The temperature and spectral dependences of the refractive indices of triglycine sulphate (TGS) crystals doped with L-threonine impurity have been investigated. It is established that the introduction of an impurity weakens the temperature dependence of refractive indices. The electronic polarizability, refractions, and parameters of UV oscillators of mechanically deformed impurity crystals are calculated. The temperature coefficients of the phase transition shift are determined.

Refractometry of TGS crystals doped with L-threonine impurity under uniaxial pressure

International Nuclear Information System (INIS)

Stadnyk, V. I.; Kiryk, Yu. I.

2013-01-01

The temperature and spectral dependences of the refractive indices of triglycine sulphate (TGS) crystals doped with L-threonine impurity have been investigated. It is established that the introduction of an impurity weakens the temperature dependence of refractive indices. The electronic polarizability, refractions, and parameters of UV oscillators of mechanically deformed impurity crystals are calculated. The temperature coefficients of the phase transition shift are determined

Controlling Thermodynamic Properties of Ferromagnetic Group-IV Graphene-Like Nanosheets by Dilute Charged Impurity

Science.gov (United States)

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.

Impurity production and acceleration in CTIX

Energy Technology Data Exchange (ETDEWEB)

Buchenauer, D. [Sandia National Laboratories, MS-9161, P.O. Box 969, Livermore, CA 94550 (United States)], E-mail: dabuche@sandia.gov; Clift, W.M. [Sandia National Laboratories, MS-9161, P.O. Box 969, Livermore, CA 94550 (United States); Klauser, R.; Horton, R.D. [CTIX Group, University of California at Davis, Davis, CA 95616 (United States); Howard, S.J. [General Fusion Inc., Burnaby, BC V5A 3H4 (Canada); Brockington, S.J. [HyperV Technologies Corp., Chantilly, VA 20151 (United States); Evans, R.W.; Hwang, D.Q. [CTIX Group, University of California at Davis, Davis, CA 95616 (United States)

2009-06-15

The Compact Toroid Injection Experiment (CTIX) produces a high density, high velocity hydrogen plasma that maintains its configuration in free space on a MHD resistive time scale. In order to study the production and acceleration of impurities in the injector, several sets of silicon collector probes were exposed to spheromak-like CT's exiting the accelerator. Elemental analysis by Auger Electron Spectroscopy indicated the presence of O, Al, Fe, and Cu in films up to 200 A thickness (1000 CT interactions). Using a smaller number of CT interactions (10-20), implantation of Fe and Cu was measured by Auger depth profiling. The amount of impurities was found to increase with accelerating voltage and number of CT interactions while use of a solenoidal field reduced the amount. Comparison of the implanted Fe and Cu with TRIM simulations indicated that the impurities were traveling more slowly than the hydrogen CT.

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)

Donor impurity-related photoionization cross section in GaAs cone-like quantum dots under applied electric field

Science.gov (United States)

Iqraoun, E.; Sali, A.; Rezzouk, A.; Feddi, E.; Dujardin, F.; Mora-Ramos, M. E.; Duque, C. A.

2017-06-01

The donor impurity-related electron states in GaAs cone-like quantum dots under the influence of an externally applied static electric field 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 uncorrelated Schrödinger-like electron states are obtained in quasi-analytical form and the entire electron-impurity correlated states are used to calculate the photoionisation cross section. Results for the electron state energies and the photoionisation cross section are reported as functions of the main geometrical parameters of the cone-like structures as well as of the electric field strength.

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.

Plasma impurity-control studies in CTX

International Nuclear Information System (INIS)

Barnes, C.W.; Henins, I.; Hoida, H.W.; Jarboe, T.R.; Linford, R.K.; Marshall, J.; Sherwood, A.R.; Tuszewski, M.

1981-01-01

In the past, magnetized coaxial gun generated Compact Toroids (CTs) have exhibited magnetic field and density lifetimes of about 250 to 350 μs and electron temperatures of about 10 eV. In recent experiments, after hydrogen discharge cleaning the gun and flux conserver surfaces, the lifetimes have been extended to 550 μs. This improvement in lifetime, together with spectroscopic and bolometric measurements, are consistent with the interpretation that the CT plasma losses are impurity dominated and that discharge cleaning is reducing the impurities. Details of these measurements are described as well as successful experiments which led to a more open flux conserver

Plasma impurity-control studies in CTX

Energy Technology Data Exchange (ETDEWEB)

Barnes, C.W.; Henins, I.; Hoida, H.W.; Jarboe, T.R.; Linford, R.K.; Marshall, J.; Sherwood, A.R.; Tuszewski, M.

1981-01-01

In the past, magnetized coaxial gun generated Compact Toroids (CTs) have exhibited magnetic field and density lifetimes of about 250 to 350 ..mu..s and electron temperatures of about 10 eV. In recent experiments, after hydrogen discharge cleaning the gun and flux conserver surfaces, the lifetimes have been extended to 550 ..mu..s. This improvement in lifetime, together with spectroscopic and bolometric measurements, are consistent with the interpretation that the CT plasma losses are impurity dominated and that discharge cleaning is reducing the impurities. Details of these measurements are described as well as successful experiments which led to a more open flux conserver.

Spin polarization of electrons in a magnetic impurity doped ...

Indian Academy of Sciences (India)

Abstract. A theoretical model is presented in this paper for degree of spin polarization in a light emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different ...

Spin polarization of electrons in a magnetic impurity doped ...

Indian Academy of Sciences (India)

A theoretical model is presented in this paper for degree of spin polarization in alight emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different temperatures and ...

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

Nonlinear excitations in two-dimensional molecular structures with impurities

DEFF Research Database (Denmark)

Gaididei, Yuri Borisovich; Rasmussen, Kim; Christiansen, Peter Leth

1995-01-01

We study the nonlinear dynamics of electronic excitations interacting with acoustic phonons in two-dimensional molecular structures with impurities. We show that the problem is reduced to the nonlinear Schrodinger equation with a varying coefficient. The latter represents the influence...... of the impurity. Transforming the equation to the noninertial frame of reference coupled with the center of mass we investigate the soliton behavior in the close vicinity of the impurity. With the help of the lens transformation we show that the soliton width is governed by an Ermakov-Pinney equation. We also...... excitations. Analytical results are in good agreement with numerical simulations of the nonlinear Schrodinger equation....

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.

Wetting layer effect on impurity-related electronic properties of different (In,Ga)N QD-shapes

Science.gov (United States)

El Ghazi, Haddou; Jorio, Anouar; Zorkani, Izeddine; Feddi, El Mustapha; El Mouchtachi, Ahmed

2018-05-01

In this paper, we have investigated the electronic properties of (In,Ga)N/GaN coupled wetting layer-quantum dot system using the numerical approach. The finite element method code is used to solve the Schrödinger equation, in the presence of the impurity. In our model, parallelepiped-shape, circular and square based-pyramidal and their wetting layers embedded in GaN matrix were considered. Based on the single band parabolic and the effective mass approximations, the envelop function and its corresponding energy eigenvalue are obtained assuming a finite potential barrier. Our results reveal that: (1) the wetting layer has a great influence on the electronic properties especially for a small quantum dot and acts in the opposite sense of the geometrical confinement, (2) a wetting layer-dependent critical QD-size is obtained limiting two different behaviors and (3) its effect is strongly-dependent on the quantum dot-shape.

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

The behaviour of impurities in a steady-state DT gas-blanket reactor

International Nuclear Information System (INIS)

Markvoort, J.A.

1975-11-01

A four-fluid model of a cylindrical steady-state DT gas-blanket reactor is analysed. The four fluids are electrons, deuterium-tritium, helium and a high -Z impurity. The behaviour of the plasma is described by the multifluid MHD-equations which are numerically solved with the aid of a Runge Kutta method. Whether impurities tend to concentrate on the axis is found to depend on how, in the collision term, the Nernst effect is taken into account. In order to show the influence of the Nernst terms arising from electron-ion collisions and the Nernst terms due to ion-ion collisions separately, the thermal force is dealt with in two ways. In model A, only the contribution from electron-ion collisions was considered. The computer calculations show that the impurities have their maximum concentration on the axis. A theoretical analysis explains this result. In model B, which is more realistic, these ion-ion collisions are included. The computer calculations as well as the theoretical analysis show that the influence of the thermoforce due to ion-ion collisions on the density profiles dominates over the force due to electron collisions, and lead to a minimum in the impurity density on the axis. As in model A, the analytical analysis yields relationships between the various density profiles and the temperature profile

Deposition probe measurements of impurities injected into a tokamak plasma

International Nuclear Information System (INIS)

Hildebrandt, D.; Grote, H.; Herrmann, A.

1985-01-01

Impurity confinement behaviour has been studied by using a deposition probe in conjunction with pellet injection. Generally, an exponential decay of the impurity efflux and nearly symmetric ion/electron side toroidal flows have been observed. During phases of strong plasma disturbances, asymmetric flow is seen, indicative of edge transport and prompt recycling from local sources. The application of ECRH may cause such disturbances. (author)

Microscopic insight into properties and electronic instabilities of impurities in cubic and lower symmetry insulators: the influence of pressure

International Nuclear Information System (INIS)

Moreno, M; Barriuso, M T; Aramburu, J A; GarcIa-Fernandez, P; GarcIa-Lastra, J M

2006-01-01

This article reviews the microscopic origin of properties due to transition-metal (TM) impurities, M, in insulator materials. Particular attention is paid to the influence of pressure upon impurity properties. Basic concepts such as the electronic localization in an MX N complex, the electrostatic potential, V R , arising from the rest of the lattice ions or the elastic coupling of the complex to the host lattice are initially exposed. The dependence of optical and magnetic parameters on the impurity-ligand distance, R, in cubic lattices is discussed in a first step. Emphasis is put on the actual origin of the R dependence of 10Dq. Examples revealing that laws for strict cubic symmetry cannot in general be transferred to lower symmetries are later given. This relevant fact is shown to come from allowed hybridizations like nd-(n+1)s as well as the influence of V R . As a salient feature the different colour in ruby and emerald is stressed to arise from distinct V R potentials in Al 2 O 3 and Be 3 Si 6 Al 2 O 18 . The last part of this review deals with electronic instabilities. The phenomena associated with the Jahn-Teller (JT) effect in cubic lattices, the origin of the energy barrier among equivalent minima and the existence of coherent tunnelling in systems like MgO:Cu 2+ are discussed. An increase of elastic coupling is pointed out to favour a transition from an elongated to a compressed equilibrium conformation. Interestingly the equilibrium geometry of JT ions in non-cubic lattices is shown to be controlled by mechanisms different to those in cubic systems, V R playing again a key role. The relevance of first principles calculations for clarifying the subtle mechanisms behind off-centre instabilities is also pointed out. Examples concern monovalent and divalent TM impurities in lattices with the CaF 2 structure. The instability due to the transition from the ground to an excited state is finally considered. For complexes with significant elastic coupling

Microscopic insight into properties and electronic instabilities of impurities in cubic and lower symmetry insulators: the influence of pressure.

Science.gov (United States)

Moreno, M; Barriuso, M T; Aramburu, J A; García-Fernández, P; García-Lastra, J M

2006-05-03

This article reviews the microscopic origin of properties due to transition-metal (TM) impurities, M, in insulator materials. Particular attention is paid to the influence of pressure upon impurity properties. Basic concepts such as the electronic localization in an MX(N) complex, the electrostatic potential, V(R), arising from the rest of the lattice ions or the elastic coupling of the complex to the host lattice are initially exposed. The dependence of optical and magnetic parameters on the impurity-ligand distance, R, in cubic lattices is discussed in a first step. Emphasis is put on the actual origin of the R dependence of 10Dq. Examples revealing that laws for strict cubic symmetry cannot in general be transferred to lower symmetries are later given. This relevant fact is shown to come from allowed hybridizations like nd-(n+1)s as well as the influence of V(R). As a salient feature the different colour in ruby and emerald is stressed to arise from distinct V(R) potentials in Al(2)O(3) and Be(3)Si(6)Al(2)O(18). The last part of this review deals with electronic instabilities. The phenomena associated with the Jahn-Teller (JT) effect in cubic lattices, the origin of the energy barrier among equivalent minima and the existence of coherent tunnelling in systems like MgO:Cu(2+) are discussed. An increase of elastic coupling is pointed out to favour a transition from an elongated to a compressed equilibrium conformation. Interestingly the equilibrium geometry of JT ions in non-cubic lattices is shown to be controlled by mechanisms different to those in cubic systems, V(R) playing again a key role. The relevance of first principles calculations for clarifying the subtle mechanisms behind off-centre instabilities is also pointed out. Examples concern monovalent and divalent TM impurities in lattices with the CaF(2) structure. The instability due to the transition from the ground to an excited state is finally considered. For complexes with significant elastic coupling

Gender Analysis Of Electronic Information Resource Use: The Case ...

African Journals Online (AJOL)

Based on the findings the study concluded that access and use of electronic information resources creates a “social digital divide” along gender lines. The study ... Finally, the library needs to change its marketing strategies on the availability of electronic information resources to increase awareness of these resources.

Theoretical study of impurity effects in iron-based superconductors

Science.gov (United States)

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.

Users satisfaction with electronic information resources and services ...

African Journals Online (AJOL)

This study investigated users satisfaction on the use of electronic information resources and services in MTN Net libraries in ABU & UNIBEN. Two objectives and one null hypotheses were formulated and tested with respect to the users' satisfaction on electronic information resources and services in MTN Net libraries in ...

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)

Interactions of structural defects with metallic impurities in multicrystalline silicon

International Nuclear Information System (INIS)

McHugo, S.A.; Thompson, A.C.; Hieslmair, H.

1997-01-01

Multicrystalline silicon is one of the most promising materials for terrestrial solar cells. It is critical to getter impurities from the material as well as inhibit contamination during growth and processing. Standard processing steps such as, phosphorus in-diffusion for p-n junction formation and aluminum sintering for backside ohmic contact fabrication, intrinsically possess gettering capabilities. These processes have been shown to improve L n values in regions of multicrystalline silicon with low structural defect densities but not in highly dislocated regions. Recent Deep Level Transient Spectroscopy (DLTS) results indirectly reveal higher concentrations of iron in highly dislocated regions while further work suggests that the release of impurities from structural defects, such as dislocations, is the rate limiting step for gettering in multicrystalline silicon. The work presented here directly demonstrates the relationship between metal impurities, structural defects and solar cell performance in multicrystalline silicon. Edge-defined Film-fed Growth (EFG) multicrystalline silicon in the as-grown state and after full solar cell processing was used in this study. Standard solar cell processing steps were carried out at ASE Americas Inc. Metal impurity concentrations and distributions were determined by use of the x-ray fluorescence microprobe (beamline 10.3.1) at the Advanced Light Source, Lawrence Berkeley National Laboratory. The sample was at atmosphere so only elements with Z greater than silicon could be detected, which includes all metal impurities of interest. Structural defect densities were determined by preferential etching and surface analysis using a Scanning Electron Microscope (SEM) in secondary electron mode. Mapped areas were exactly relocated between the XRF and SEM to allow for direct comparison of impurity and structural defect distributions

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

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

Insulator-semimetallic transition in quasi-1D charged impurity-infected armchair boron-nitride nanoribbons

Science.gov (United States)

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.

Continuous-time quantum Monte Carlo impurity solvers

Science.gov (United States)

Gull, Emanuel; Werner, Philipp; Fuchs, Sebastian; Surer, Brigitte; Pruschke, Thomas; Troyer, Matthias

2011-04-01

Continuous-time quantum Monte Carlo impurity solvers are algorithms that sample the partition function of an impurity model using diagrammatic Monte Carlo techniques. The present paper describes codes that implement the interaction expansion algorithm originally developed by Rubtsov, Savkin, and Lichtenstein, as well as the hybridization expansion method developed by Werner, Millis, Troyer, et al. These impurity solvers are part of the ALPS-DMFT application package and are accompanied by an implementation of dynamical mean-field self-consistency equations for (single orbital single site) dynamical mean-field problems with arbitrary densities of states. Program summaryProgram title: dmft Catalogue identifier: AEIL_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEIL_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: ALPS LIBRARY LICENSE version 1.1 No. of lines in distributed program, including test data, etc.: 899 806 No. of bytes in distributed program, including test data, etc.: 32 153 916 Distribution format: tar.gz Programming language: C++ Operating system: The ALPS libraries have been tested on the following platforms and compilers: Linux with GNU Compiler Collection (g++ version 3.1 and higher), and Intel C++ Compiler (icc version 7.0 and higher) MacOS X with GNU Compiler (g++ Apple-version 3.1, 3.3 and 4.0) IBM AIX with Visual Age C++ (xlC version 6.0) and GNU (g++ version 3.1 and higher) compilers Compaq Tru64 UNIX with Compq C++ Compiler (cxx) SGI IRIX with MIPSpro C++ Compiler (CC) HP-UX with HP C++ Compiler (aCC) Windows with Cygwin or coLinux platforms and GNU Compiler Collection (g++ version 3.1 and higher) RAM: 10 MB-1 GB Classification: 7.3 External routines: ALPS [1], BLAS/LAPACK, HDF5 Nature of problem: (See [2].) Quantum impurity models describe an atom or molecule embedded in a host material with which it can exchange electrons. They are basic to nanoscience as

Thermal Conductivity of Nanotubes: Effects of Chirality and Isotope Impurity

OpenAIRE

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...

Impurities in chromium deposits produced by electroplating and physical vapor deposition

Energy Technology Data Exchange (ETDEWEB)

Dini, J.W.

1994-05-01

Impurity contents in electrodeposited (hexavalent and trivalent) chromium deposits and physically vapor deposited (thermal evaporation, electron beam evaporation and rf-sputtering) were compared. Oxygen is the key impurity obtained in electrodeposited films but it can be minimized in hexavalent plating solutions by operating at high temperature, e. g., 85 C. Electrodeposits produced in trivalent chromium plating solutions and physically vapor deposited films have much higher oxygen contents than electrodeposits produced in hexavalent chromium solutions operated at temperatures around 85 C. Depending on the target material used for physically vapor deposited films, these films can also have high amounts of other impurities.

Donors in Semiconductors - are they Understood in Electronic Era?

International Nuclear Information System (INIS)

Dmochowski, Janusz E

2007-01-01

The physics of semiconductors and contemporary electronics cannot be understood without impurities. The hydrogen-like shallow donor (and acceptor) state of electron (hole) bound by Coulomb electrostatic force of excess charge of impurity is used to control conductivity of semiconductors and construct semiconductor diodes, transistors and numerous types of semiconductor electronic and optoelectronic devices, including lasers. Recently, surprisingly, the physics of impurity donors appeared to be much reacher. Experimental evidence has been provided for universal existence of other types of electronic states of the same donor impurity: i) mysterious, deep, DX-type state resulting in metastability - slow hysteresis phenomena - understood as two-electron, acceptor-like state of donor impurity, formed upon large lattice distortion or rearrangement around impurity and accompanying capture of second electron, resulting in negative electron correlation energy U; ii) deep, localized, fully symmetric, A1, one-electron donor state of substitutional impurity. The latter state can be formed from the 'ordinary' shallow hydrogen-like state in the process of strong localization of electron by short range, local potential of impurity core, preserving full (A 1 ) symmetry of the substitutional impurity in the host lattice. The 'anticrossing' of the two A 1 (shallow hydrogenic and deep localized) energy levels upon transformation is observed. All types of electronic states of impurity can be universally observed for the same donor impurity and mutual transformation between different states occur upon changing experimental conditions. The knowledge about existence and properties of these n ew , molecular type, donor states in semiconductors seems still await general recognition and positive application in contemporary material and device science and engineering

Organizational matters of competition in electronic educational resources

Directory of Open Access Journals (Sweden)

Ирина Карловна Войтович

2015-12-01

Full Text Available The article examines the experience of the Udmurt State University in conducting competitions of educational publications and electronic resources. The purpose of such competitions is to provide methodological support to educational process. The main focus is on competition of electronic educational resources. The technology of such contests is discussed through detailed analysis of the main stages of the contest. It is noted that the main task of the preparatory stage of the competition is related to the development of regulations on competition and the definition of criteria for selection of the submitted works. The paper also proposes a system of evaluation criteria of electronic educational resources developed by members of the contest organizing committee and jury members. The article emphasizes the importance of not only the preparatory stages of the competition, but also measures for its completion, aimed at training teachers create quality e-learning resources.

Impurity effects on electrical conductivity of doped bilayer graphene in the presence of a bias voltage

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)

CHALLENGES OF ELECTRONIC INFORMATION RESOURCES IN ...

African Journals Online (AJOL)

This paper discusses the role of policy for proper and efficient library services in the electronic era. It points out some of the possible dangers of embarking in electronic resources without a proper focus at hand. Thus, it calls for today's librarians and policy makers to brainstorm and come up with working policies suitable to ...

Interplay of antiferromagnetism and superconductivity in cuprates with impurity effect and d-wave pairing

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.

Interplay of antiferromagnetism and superconductivity in cuprates with impurity effect and d-wave pairing

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

Mn and Fe Impurities in Si$_{1-x}$ Ge$_{x}$ alloys

CERN Multimedia

2002-01-01

Following our investigations of Mn and Fe impurities in elemental semiconductors and in silicon in particular by means of on-line $^{57}$Fe Mössbauer spectroscopy, utilizing radioactive $^{57}$Mn$^{+}$ ion beams at ISOLDE, we propose to extend these studies to bulk and epitaxially-grown Si$_{1-x}$Ge$_{x}$ alloys. In these materials, although already successfully employed in electronic devices, little is known about point defects and important harmful 3d impurities. The experiments aim to determine a variety of fundamental properties: The lattice location of ion-implanted Mn/Fe, the electronic and vibrational properties of dilute Fe impurities in different lattice sites, the charge-state and composition dependence of the diffusivity of interstitial Fe on an atomic scale, the reactions and formation of complexes with lattice defects created by the $^{57}$Mn implantation or by the recoil effect in the nuclear decay to the Mössbauer state of $^{57m}$Fe. Feasibility studies in 2003 indicate that these aims can b...

Microscopic insight into properties and electronic instabilities of impurities in cubic and lower symmetry insulators: the influence of pressure

Energy Technology Data Exchange (ETDEWEB)

Moreno, M [Departamento de Ciencias de la Tierra y Fisica de la Materia Condensada, Universidad de Cantabria, 39005 Santander (Spain); Barriuso, M T [Departamento de Fisica Moderna, Universidad de Cantabria, 39005 Santander (Spain); Aramburu, J A [Departamento de Ciencias de la Tierra y Fisica de la Materia Condensada, Universidad de Cantabria, 39005 Santander (Spain); GarcIa-Fernandez, P [Departamento de Ciencias de la Tierra y Fisica de la Materia Condensada, Universidad de Cantabria, 39005 Santander (Spain); GarcIa-Lastra, J M [Departamento de Fisica Moderna, Universidad de Cantabria, 39005 Santander (Spain)

2006-05-03

This article reviews the microscopic origin of properties due to transition-metal (TM) impurities, M, in insulator materials. Particular attention is paid to the influence of pressure upon impurity properties. Basic concepts such as the electronic localization in an MX{sub N} complex, the electrostatic potential, V{sub R}, arising from the rest of the lattice ions or the elastic coupling of the complex to the host lattice are initially exposed. The dependence of optical and magnetic parameters on the impurity-ligand distance, R, in cubic lattices is discussed in a first step. Emphasis is put on the actual origin of the R dependence of 10Dq. Examples revealing that laws for strict cubic symmetry cannot in general be transferred to lower symmetries are later given. This relevant fact is shown to come from allowed hybridizations like nd-(n+1)s as well as the influence of V{sub R}. As a salient feature the different colour in ruby and emerald is stressed to arise from distinct V{sub R} potentials in Al{sub 2}O{sub 3} and Be{sub 3}Si{sub 6}Al{sub 2}O{sub 18}. The last part of this review deals with electronic instabilities. The phenomena associated with the Jahn-Teller (JT) effect in cubic lattices, the origin of the energy barrier among equivalent minima and the existence of coherent tunnelling in systems like MgO:Cu{sup 2+} are discussed. An increase of elastic coupling is pointed out to favour a transition from an elongated to a compressed equilibrium conformation. Interestingly the equilibrium geometry of JT ions in non-cubic lattices is shown to be controlled by mechanisms different to those in cubic systems, V{sub R} playing again a key role. The relevance of first principles calculations for clarifying the subtle mechanisms behind off-centre instabilities is also pointed out. Examples concern monovalent and divalent TM impurities in lattices with the CaF{sub 2} structure. The instability due to the transition from the ground to an excited state is finally

Role of potential scattering in the Shiba-Rusinov theory of the magnetic impurities in superconductors

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

Use of Electronic Resources in a Private University in Nigeria ...

African Journals Online (AJOL)

The study examined awareness and constraints in the use of electronic resources by lecturers and students of Ajayi Crowther University, Oyo, Nigeria. It aimed at justifying the resources expended in the provision of electronic resources in terms of awareness, patronage and factors that may be affecting awareness and use ...

High-frequency EPR of surface impurities on nanodiamond

Science.gov (United States)

Peng, Zaili; Stepanov, Viktor; Takahashi, Susumu

Diamond is a fascinating material, hosting nitrogen-vacancy (NV) defect centers with unique magnetic and optical properties. There have been many reports that suggest the existence of paramagnetic impurities near surface of various kinds of diamonds. Electron paramagnetic resonance (EPR) investigation of mechanically crushed nanodiamonds (NDs) as well as detonation NDs revealed g 2 like signals that are attributed to structural defects and dangling bonds near the diamond surface. In this presentation, we investigate paramagnetic impurities in various sizes of NDs using high-frequency (HF) continuous wave (cw) and pulsed EPR spectroscopy. Strong size dependence on the linewidth of HF cw EPR spectra reveals the existence of paramagnetic impurities in the vicinity of the diamond surface. We also study the size dependence of the spin-lattice and spin-spin relaxation times (T1 and T2) of single substitutional nitrogen defects in NDs Significant deviations from the temperature dependence of the phonon-assisted T1 process were observed in the ND samples, and were attributed to the contribution from the surface impurities. This work was supported by the Searle Scholars Program and the National Science Foundation (DMR-1508661 and CHE-1611134).

Electronic Resources Management System: Recommendation Report 2017

KAUST Repository

Ramli, Rindra M.

2017-05-01

This recommendation report provides an overview of the selection process for the new Electronic Resources Management System. The library has decided to move away from Innovative Interfaces Millennium ERM module. The library reviewed 3 system as potential replacements namely: Proquest 360 Resource Manager, Ex Libris Alma and Open Source CORAL ERMS. After comparing and trialling the systems, it was decided to go for Proquest 360 Resource Manager.

Fermi-edge transmission resonance in graphene driven by a single Coulomb impurity.

Science.gov (United States)

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.

Defect-impurity interactions in irradiated germanium

International Nuclear Information System (INIS)

Cleland, J.W.; James, F.J.; Westbrook, R.D.

1975-07-01

Results of experiments are used to formulate a better model for the structures of lattice defects and defect-impurity complexes in irradiated n-type Ge. Single crystals were grown by the Czochralski process from P, As, or Sb-doped melts, and less than or equal to 10 15 to greater than or equal to 10 17 oxygen cm -3 was added to the furnace chamber after approximately 1 / 3 of the crystal had been solidified. Hall coefficient and resistivity measurements (at 77 0 K) were used to determine the initial donor concentration due to the dopant and clustered oxygen, and infrared absorption measurements (at 11.7 μ) were used to determine the dissociated oxygen concentration. Certain impurity and defect-impurity interactions were then investigated that occurred as a consequence of selected annealing, quenching, Li diffusion, and irradiation experiments at approximately 300 0 K with 60 Co photons, 1.5 to 2.0 MeV electrons, or thermal energy neutrons. Particular attention was given to determining the electrical role of the irradiation produced interstitial and vacancy, and to look for any evidence from electrical and optical measurements of vacancy--oxygen, lithium--oxygen, and lithium--vacancy interactions. (U.S.)

Impurity doping: a novel strategy for controllable synthesis of functional lanthanide nanomaterials.

Science.gov (United States)

Chen, Daqin; Wang, Yuansheng

2013-06-07

Many technological nanomaterials are intentionally 'doped' by introducing appropriate amounts of foreign elements into hosts to impart electronic, magnetic and optical properties. In fact, impurity doping was recently found to have significant influence on nucleation and growth of many functional nanocrystals (NCs), and provide a fundamental approach to modify the crystallographic phase, size, morphology, and electronic configuration of nanomaterials. In this feature article, we provide an overview of the most recent progresses in doping-induced control of phase structures, sizes, shapes, as well as performances of functional nanomaterials for the first time. Two kinds of impurity doping strategies, including the homo-valence ion doping and hetero-valence ion doping, are discussed in detail. We lay emphases on impurity doping induced modifications of microstructures and optical properties of upconversion (UC) lanthanide (Ln(3+)) NCs, but do not limit to them. In addition, we also illustrate the control of Ln(3+) activator distribution in the core@shell architecture, which has recently provided scientists with new opportunities for designing and tuning the multi-color emissions of Ln(3+)-doped UC NCs. Finally, the challenges and future perspectives of this novel impurity doping strategy are pointed out.

Effect of normal impurities on anisotropic superconductors with variable density of states

Science.gov (United 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.

Trace impurity analyzer

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

use of electronic resources by graduate students of the department

African Journals Online (AJOL)

respondent's access electronic resources from the internet via Cybercafé .There is a high ... KEY WORDS: Use, Electronic Resources, Graduate Students, Cybercafé. INTRODUCTION ... Faculty of Education, University of Uyo, Uyo. Olu Olat ...

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

TOPICAL REVIEW: Microscopic insight into properties and electronic instabilities of impurities in cubic and lower symmetry insulators: the influence of pressure

Science.gov (United States)

Moreno, M.; Barriuso, M. T.; Aramburu, J. A.; García-Fernández, P.; García-Lastra, J. M.

2006-05-01

This article reviews the microscopic origin of properties due to transition-metal (TM) impurities, M, in insulator materials. Particular attention is paid to the influence of pressure upon impurity properties. Basic concepts such as the electronic localization in an MXN complex, the electrostatic potential, VR, arising from the rest of the lattice ions or the elastic coupling of the complex to the host lattice are initially exposed. The dependence of optical and magnetic parameters on the impurity-ligand distance, R, in cubic lattices is discussed in a first step. Emphasis is put on the actual origin of the R dependence of 10Dq. Examples revealing that laws for strict cubic symmetry cannot in general be transferred to lower symmetries are later given. This relevant fact is shown to come from allowed hybridizations like nd-(n+1)s as well as the influence of VR. As a salient feature the different colour in ruby and emerald is stressed to arise from distinct VR potentials in Al2O3 and Be3Si6Al2O18. The last part of this review deals with electronic instabilities. The phenomena associated with the Jahn-Teller (JT) effect in cubic lattices, the origin of the energy barrier among equivalent minima and the existence of coherent tunnelling in systems like MgO:Cu2+ are discussed. An increase of elastic coupling is pointed out to favour a transition from an elongated to a compressed equilibrium conformation. Interestingly the equilibrium geometry of JT ions in non-cubic lattices is shown to be controlled by mechanisms different to those in cubic systems, VR playing again a key role. The relevance of first principles calculations for clarifying the subtle mechanisms behind off-centre instabilities is also pointed out. Examples concern monovalent and divalent TM impurities in lattices with the CaF2 structure. The instability due to the transition from the ground to an excited state is finally considered. For complexes with significant elastic coupling vibrational frequencies

Dressed topological insulators. Rashba impurity, Kondo effect, magnetic impurities, proximity-induced superconductivity, hybrid systems

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.

Dressed topological insulators. Rashba impurity, Kondo effect, magnetic impurities, proximity-induced superconductivity, hybrid systems

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.

Gold and Platinum in Silicon - Isolated Impurities Complexes

CERN Multimedia

Mcglynn, P

2002-01-01

%IS357 :\\\\ \\\\ Gold and platinum impurities in silicon are exploited for the control of minority carrier lifetimes, and this important feature has resulted in sustained research interest over several decades. Although the properties of isolated substitutional Au~atoms are well understood, this is not the case for Pt. Considerable uncertainty exists regarding the nature of several Pt related defects observed in Electron Paramagnetic Resonance~(EPR) and Photo~Luminescence~(PL). One of the objectives of this experiment is to exploit the transformation of radioactive Au isotopes as a means of producing specific Pt centres, and to use our thorough knowledge of Au in silicon to guide in the interpretation of data obtained for the centres when they transform to Pt.\\\\ \\\\ In addition to isolated impurities, the experiment also addresses the question of pairs of atoms formed by Au and Pt. Studies of these impurity pairs have been reported, but the benefits of a direct comparison of the defects in both the Au and Pt form...

Probe measurements for impurity transport in the scrape-off layer of JIPP T-II

International Nuclear Information System (INIS)

Mohri, M.; Satake, T.; Hashiba, H.; Yamashina, T.; Amemiya, S.

1982-05-01

Impurity transport processes in the scrape-off layer of the JIPP T-II device have been studied by a probe method. A cubical silicon probe was inserted and exposed to 20 identical tokamak discharges in the scrape-off region. Deposited impurities were analyzed with use of AES, RBS and PIXE equipments. The main metallic impurities were molybdenum and iron whose deposition behavior was almost the same on any side of the probe, and their fluxes were observed to be 1.2 x 10 13 /cm 2 .discharge on the electron drift side and 5.2 x 10 13 /cm 2 .discharge on the ion drift side, respectively at the distance of 18.3 cm from the center line of the plasma. The mean transport energy of the impurities striking the probe surface was estimated from the depth concentration profile applying the LSS theory for iron as 90 eV on the electron drift side and 250 eV on the ion drift side, respectively. The e-folding length of the scrape-off plasma density was measured by the radial distribution of a deposited tantalum amount to be 0.64 cm on the electron drift side and 1.73 cm on the ion drift side, respectively. (author)

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

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.

Electronic resource management practical perspectives in a new technical services model

CERN Document Server

Elguindi, Anne

2012-01-01

A significant shift is taking place in libraries, with the purchase of e-resources accounting for the bulk of materials spending. Electronic Resource Management makes the case that technical services workflows need to make a corresponding shift toward e-centric models and highlights the increasing variety of e-formats that are forcing new developments in the field.Six chapters cover key topics, including: technical services models, both past and emerging; staffing and workflow in electronic resource management; implementation and transformation of electronic resource management systems; the ro

Satellite NMR in Cu doped with transition impurities

International Nuclear Information System (INIS)

Slichter, C.P.

1979-01-01

Measurements were made of the conduction electron spin magnetization density, M/sub sigma/(R vector) near iron group atoms (Sc through Ni) in Cu. M/sub sigma/(R vector) produces an additional effective local field which shifts the NMR frequency of nearby shells of Cu nuclei relative to Cu nuclei far from all impurities. Resonances of nearby shells appear as weak satellites to the strong resonance of distant Cu nuclei (the main line). M/sub sigma/(R vector) at a given site is proportional through know constants to the splitting of the satellite from the main line. The shell was identified giving rise to the satellite in many cases by use of single crystals. A good approximation M/sub sigma/(R vector) is proportional to the spin susceptibility chi/sub s/ of the impurity. For CuCr we find a large temperature independent chi/sub s/, in contrast to CuMn and CuFe. The results lead to a picture of the electronic structure of Cr, Mn, and Fe along the lines of Schrieffer and Hirst as ions with integral numbers of d-electrons, possessing crystal field and spin-orbit couplings

Impurities block the alpha to omega martensitic transformation in titanium.

Science.gov (United States)

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.

Utilization of electronic information resources by academic staff at ...

African Journals Online (AJOL)

The study investigated the utilization of Electronic Information resources by the academic staff of Makerere University in Uganda. It examined the academic staff awareness of the resources available, the types of resources provided by the Makerere University Library, the factors affecting resource utilization. The study was ...

Ab initio study of the EFG tensor at Cd impurities in Sc2O3 semiconductor

International Nuclear Information System (INIS)

Munoz, E.L.; Richard, D.; Errico, L.A.; Renteria, M.

2009-01-01

We present an ab initio study of diluted Cd impurities localized at both cation sites of the semiconductor Sc 2 O 3 . The electric-field-gradient (EFG) tensor at Cd impurities located at both cationic sites of the host structure was determined from the calculation of the electronic structure of the doped system. Calculations were performed with the full-potential augmented-plane wave plus local orbitals (APW+lo) method within the framework of the density functional theory. We studied the atomic structural relaxations and the perturbation of the electronic charge density induced by the impurities in the host system in a fully self-consistent way. We showed that the Cd impurity introduces an increase of 8% in the nearest oxygen neighbors bond-lengths, changing the EFG sign for probes located at the asymmetric cation site. The APW+lo predictions for the charged state of the Cd impurity were compared with EFG results existent in the literature, coming from time-differential γ-γ perturbed-angular-correlations experiments performed on 111 Cd-implanted Sc 2 O 3 powder samples. From the excellent agreement between theory and experiment, we can strongly suggest that the Cd acceptor impurities are ionized at room temperature. Finally, we showed that simple calculations like those performed within the point-charge model with antishielding factors do not correctly describe the problem of a Cd impurity in Sc 2 O 3 .

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

Simulation of iron impurity in BaTiO3 crystals

International Nuclear Information System (INIS)

Stashans, Arvids; Castillo, Darwin

2009-01-01

Iron-doped barium titanate (BaTiO 3 ) has been simulated taking into account cubic and tetragonal crystallographic lattices of the crystal. A quantum-chemical method based on the Hartree-Fock formalism has been used throughout the study. The calculated equilibrium structures of Fe-doped crystals reveal the defect-inward displacements of the Ti and O atoms whereas the shifts for the Ba atoms are encountered to be away with respect to the Fe impurity. According to the analysis of electron density population and electron band structure it is found that some unusual chemical bonding might take place between the Fe atom and its six adjacent O atoms. The role of Fe impurity in the ferroelectric polarization of the tetragonal BaTiO 3 crystal has been discussed too.

The role of metallic impurities in oxide semiconductors: first-principles calculations and PAC experiments

Energy Technology Data Exchange (ETDEWEB)

Errico, L.A.; Fabricius, G.; Renteria, M. [Departamento de Fisica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata (Argentina)

2004-08-01

We report an ab-initio comparative study of the electric-field-gradient tensor (EFG) and structural relaxations introduced by acceptor (Cd) and donor (Ta) impurities when they replace cations in a series of binary oxides: TiO{sub 2}, SnO{sub 2}, and In{sub 2}O{sub 3}. Calculations were performed with the Full-Potential Linearized-Augmented Plane Waves method that allows us to treat the electronic structure and the atomic relaxations in a fully self-consistent way. We considered different charge states for each impurity and studied the dependence on these charge states of the electronic properties and the structural relaxations. Our results are compared with available data coming from PAC experiments and previous calculations, allowing us to obtain a new insight on the role that metal impurities play in oxide semiconductors. It is clear from our results that simple models can not describe the measured EFGs at impurities in oxides even approximately. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Electronic Resources Management Project Presentation 2012

KAUST Repository

Ramli, Rindra M.

2012-01-01

This presentation describes the electronic resources management project undertaken by the KAUST library. The objectives of this project is to migrate information from MS Sharepoint to Millennium ERM module. One of the advantages of this migration

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

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

Effect of impurity modes with quasilocal and local frequencies on the superconducting transition temperature

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)

Electromagnetic effects on trace impurity transport in tokamak plasmas

Science.gov (United States)

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.

FP-LAPW Calculations of the EFG at Cd Impurities in Rutile SnO2

International Nuclear Information System (INIS)

Errico, L. A.; Fabricius, G.; Renteria, M.

2001-01-01

We report an ab initio study of the electric-field gradient (EFG) at Cd impurities located at the cation site in the semiconductor SnO 2 (rutile phase). The study was performed with the WIEN97 implementation of the FP-LAPW method. In order to simulate the diluted Cd-impurity in the SnO 2 host and to calculate the electronic structure of the system we used a 72-atoms super-cell, studying the relaxation introduced by the impurity in the lattice. The free-relaxation process performed shows that the relaxations of the oxygen nearest-neighbors of the impurity are not isotropic. Our prediction for the EFG tensor are compared with experimental results and point-charge model predictions

Investigation of impurity confinement in lower hybrid wave heated plasma on EAST tokamak

Science.gov (United States)

Xu, Z.; Wu, Z. W.; Zhang, L.; Gao, W.; Ye, Y.; Chen, K. Y.; Yuan, Y.; Zhang, W.; Yang, X. D.; Chen, Y. J.; Zhang, P. F.; Huang, J.; Wu, C. R.; Morita, S.; Oishi, T.; Zhang, J. Z.; Duan, Y. M.; Zang, Q.; Ding, S. Y.; Liu, H. Q.; Chen, J. L.; Hu, L. Q.; Xu, G. S.; Guo, H. Y.; the EAST Team

2018-01-01

The transient perturbation method with metallic impurities such as iron (Fe, Z  =  26) and copper (Cu, Z  =  29) induced in plasma-material interaction (PMI) procedure is used to investigate the impurity confinement characters in lower hybrid wave (LHW) heated EAST sawtooth-free plasma. The dependence of metallic impurities confinement time on plasma parameters (e.g. plasma current, toroidal magnetic field, electron density and heating power) are investigated in ohmic and LHW heated plasma. It is shown that LHW heating plays an important role in the reduction of the impurity confinement time in L-mode discharges on EAST. The impurity confinement time scaling is given as 42IP0.32Bt0.2\\overline{n}e0.43Ptotal-0.4~ on EAST, which is close to the observed scaling on Tore Supra and JET. Furthermore, the LHW heated high-enhanced-recycling (HER) H-mode discharges with ~25 kHz edge coherent modes (ECM), which have lower impurity confinement time and higher energy confinement time, provide promising candidates for high performance and steady state operation on EAST.

Occurrence and Characterization Microstructure of Iron Impurities in Halloysite.

Science.gov (United States)

Liu, Rong; Yan, Chunjie; Wang, Hongquan; Xiao, Guoqi; Tu, Dong

2015-09-01

The quality of the clays and over all halloysite are mostly associated with minor amounts of ferruginous impurities content, since this element gives an undesirable reddish color to the halloysite mineral. Hence, finding out the modes of occurrence of iron in halloysite is of prime importance in the value addition and optimum utilization of halloysite. In order to analyze the occurrence of iron impurities in halloysite, Transmission Electron Microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were combined with wet chemical analysis methods to study the low-grade halloysite. The results indicated that the mineral phases of iron impurities in the concentrates are mainly composed of amounts of magnetite, goethite and hematite. Two types of occurrences for iron impurities have been found. One is single crystalline mineral consist in the halloysite, which contains three different phases of Goethite FeO(OH) (44.75%), Magnetite Fe3O4 (27.43%) and Hematite Fe2O3 (31.96%). The other is amorphous Fe-Al-Si glial materials. This study is of significance in the theoretical research on the halloysite mineralogy and in the developmental practice of halloysite in coal measures.

Electron beam treatment of industrial wastewater

International Nuclear Information System (INIS)

Han, Bumsoo; Kim, JinKyu; Kim, Yuri

2004-01-01

For industrial wastewater with low impurity levels such as contaminated ground water, cleaning water and etc., purification only with electron beam is possible, but it should be managed carefully with reducing required irradiation doses as low as possible. Also for industrial wastewater with high impurity levels such as dyeing wastewater, leachate and etc., purification only with electron beam requires high amount of doses and far beyond economies. Electron beam treatment combined with conventional purification methods such as coagulation, biological treatment, etc. is suitable for reduction of non-biodegradable impurities in wastewater and will extend the application area of electron beam. A pilot plant with electron beam for treating 1,000 m 3 /day of wastewater from dyeing industries has constructed and operated continuously since Oct 1998. Electron beam irradiation instead of chemical treatment shows much improvement in removing impurities and increases the efficiency of biological treatment. Actual plant is under consideration based upon the experimental results. (author)

Practical guide to electronic resources in the humanities

CERN Document Server

Dubnjakovic, Ana

2010-01-01

From full-text article databases to digitized collections of primary source materials, newly emerging electronic resources have radically impacted how research in the humanities is conducted and discovered. This book, covering high-quality, up-to-date electronic resources for the humanities, is an easy-to-use annotated guide for the librarian, student, and scholar alike. It covers online databases, indexes, archives, and many other critical tools in key humanities disciplines including philosophy, religion, languages and literature, and performing and visual arts. Succinct overviews of key eme

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

Utilisation of Electronic Information Resources By Lecturers in ...

African Journals Online (AJOL)

This study assesses the use of information resources, specifically, electronic databases by lecturers/teachers in Universities and Colleges of Education in South Western Nigeria. Information resources are central to teachers' education. It provides lecturers/teachers access to information that enhances research and ...

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

Multi-photon Rabi oscillations in high spin paramagnetic impurity

International Nuclear Information System (INIS)

Bertaina, S; Groll, N; Chen, L; Chiorescu, I

2011-01-01

We report on multiple photon monochromatic quantum oscillations (Rabi oscillations) observed by pulsed EPR (Electron Paramagnetic Resonance) of Mn 2+ (S = 5/2) impurities in MgO. We find that when the microwave magnetic field is similar or large than the anisotropy splitting, the Rabi oscillations have a spectrum made of many frequencies not predicted by the S = l/2 Rabi model. We show that these new frequencies come from multiple photon coherent manipulation of the multi-level spin impurity. We develop a model based on the crystal field theory and the rotating frame approximation, describing the observed phenomenon with a very good agreement.

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)

Discipline, availability of electronic resources and the use of Finnish National Electronic Library - FinELib

Directory of Open Access Journals (Sweden)

Sanna Torma

2004-01-01

Full Text Available This study elaborated relations between digital library use by university faculty, users' discipline and the availability of key resources in the Finnish National Electronic Library (FinELib, Finnish national digital library, by using nationwide representative survey data. The results show that the perceived availability of key electronic resources by researchers in FinELib was a stronger predictor of the frequency and purpose of use of its services than users' discipline. Regardless of discipline a good perceived provision of central resources led to a more frequent use of FinELib. The satisfaction with the services did not vary with the discipline, but with the perceived availability of resources.

Reversal of local spins in transport of electrons through a one-dimensional chain

International Nuclear Information System (INIS)

Hu, D.-S.; Xiong, S.-J.

2003-01-01

We investigate the spin reversal of two coupled magnetic impurities in the transport processes of electrons in a one-dimensional chain. The impurities are side coupled to the chain and the electrons are injected and tunneling through it. The transmission coefficient of electrons and the polarization of impurities are calculated by the use of the equivalent single-particle network method for the correlated system. It is found that both the transmission coefficient and the polarization of impurities depend on the initial state of impurities and the impurity spins can be converted into the direction of electron spin if the injected electrons are polarized and the number of electrons is large enough. The evolution of the spin-reversal processes is studied in details

The Role of the Acquisitions Librarian in Electronic Resources Management

Science.gov (United States)

Pomerantz, Sarah B.

2010-01-01

With the ongoing shift to electronic formats for library resources, acquisitions librarians, like the rest of the profession, must adapt to the rapidly changing landscape of electronic resources by keeping up with trends and mastering new skills related to digital publishing, technology, and licensing. The author sought to know what roles…

Impurity transport studies by means of tracer-encapsulated solid pellet injection in neutral beam heated plasmas on LHD

International Nuclear Information System (INIS)

Tamura, N; Sudo, S; Khlopenkov, K V; Kato, S; Sergeev, V Yu; Muto, S; Sato, K; Funaba, H; Tanaka, K; Tokuzawa, T; Yamada, I; Narihara, K; Nakamura, Y; Kawahata, K; Ohyabu, N; Motojima, O

2003-01-01

The quantitative properties of impurity transport in large helical device (LHD) plasmas heated by neutral beam injection have been investigated by means of tracer-encapsulated solid pellet (TESPEL) injection. In the case of a titanium (Ti) tracer, the behaviour of the emission lines from the highly ionized Ti impurity, Ti Kα(E He-like ∼ 4.7 keV) and Ti XIX (λ = 16.959 nm), has been observed clearly by a soft x-ray pulse height analyzer and a vacuum ultraviolet spectrometer, respectively. A fairly longer decay time of the Ti Kα emission lines is obtained above the value of a line-averaged electron density, 3.0x10 19 m -3 . The dependence of the behaviour of the Ti tracer impurity on the line-averaged electron density below the value of that, 3.5x10 19 m -3 is in qualitative agreement with the characteristics obtained from the observation of the behaviour of an intrinsic metallic impurity in neutral beam heated plasmas on LHD. In order to estimate the properties of the Ti impurity transport quantitatively, the one-dimensional impurity transport code, MIST has been used. As a result of the transport analysis with the MIST code, even an small inward convection should be necessary to account for the experimental results with the value of the line-averaged electron density, 3.5x10 19 m -3 . In order to examine the experimentally obtained transport coefficients, neoclassical analysis with respect to the radial impurity flux has been performed. The inferred rise of the inward convection cannot be explained solely by neoclassical impurity transport. Therefore, in order to account for the inward convection, the effect of a radial electric field and/or some other effect must be taken into account additionally

Optical coefficients in a semiconductor quantum ring: Electric field and donor impurity effects

Science.gov (United States)

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.

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

Analysis of Pedagogic Potential of Electronic Educational Resources with Elements of Autodidactics

Directory of Open Access Journals (Sweden)

Igor A.

2018-03-01

Full Text Available Introduction: in recent years didactic properties of electronic educational resources undergo considerable changes, nevertheless, the question of studying of such complete phenomenon as “an electronic educational resource with autodidactics elements” remains open, despite sufficient scientific base of researches of the terms making this concept. Article purpose – determination of essence of electronic educational resources with autodidactics elements. Materials and Methods: the main method of research was the theoretical analysis of the pedagogical and psychological literature on the problem under study. We used the theoretical (analysis, synthesis, comparison and generalization methods, the method of interpretation, pedagogical modeling, and empirical methods (observation, testing, conversation, interview, analysis of students’ performance, pedagogical experiment, peer review. Results: we detected the advantages of electronic educational resources in comparison with traditional ones. The concept of autodidactics as applied to the subject of research is considered. Properties of electronic educational resources with a linear and nonlinear principle of construction are studied.The influence of the principle of construction on the development of the learners’ qualities is shown. We formulated an integral definition of electronic educational resources with elements of autodidactics, namely, the variability, adaptivity and cyclicity of training. A model of the teaching-learning process with electronic educational resources is developed. Discussion and Conclusions: further development of a problem will allow to define whether electronic educational resources with autodidactics elements pedagogical potential for realization of educational and self-educational activity of teachers have, to modify technological procedures taking into account age features of students, their specialties and features of the organization of process of training of

Preservation and conservation of electronic information resources of ...

African Journals Online (AJOL)

The major holdings of the broadcast libraries of the Nigerian Television Authority (NTA) are electronic information resources; therefore, providing safe places for general management of these resources have aroused interest in the industry in Nigeria for sometimes. The need to study the preservation and conservation of ...

Electric-field gradients at Ta impurities in Sc{sub 2}O{sub 3} semiconductor

Energy Technology Data Exchange (ETDEWEB)

Richard, Diego, E-mail: richard@fisica.unlp.edu.ar [Departamento de Fisica e Instituto de Fisica La Plata (IFLP, CONICET La Plata), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina. (Argentina); Munoz, Emiliano L. [Departamento de Fisica e Instituto de Fisica La Plata (IFLP, CONICET La Plata), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina. (Argentina); Errico, Leonardo A. [Departamento de Fisica e Instituto de Fisica La Plata (IFLP, CONICET La Plata), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina. (Argentina); Universidad Nacional del Noroeste Bonaerense (UNNOBA), Monteagudo 2772, 2700 Pergamino, Argentina. (Argentina); Renteria, Mario [Departamento de Fisica e Instituto de Fisica La Plata (IFLP, CONICET La Plata), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina. (Argentina)

2012-08-15

In this work we present an ab initio study of Ta-doped Sc{sub 2}O{sub 3} semiconductor. Calculations were performed at dilute Ta impurities located at both cationic sites of the host structure, using the Augmented Plane Wave plus Local Orbitals (APW+lo) method. The structural atomic relaxations and the electric-field gradients (EFG) were studied for different charge states of the cell in order to simulate different ionization states of the double-donor Ta impurity. From the results for the EFG tensor at Ta impurity sites and the comparison with experimental results obtained using the Time-Differential {gamma}-{gamma} Perturbed-Angular-Correlations technique we could determined the structural distortions induced by the Ta impurity and the electronic structure of the doped-semiconductor.

Transport of wall released impurities in the limiter scrape-off layer of a tokamak

International Nuclear Information System (INIS)

Claassen, H.A.; Repp, H.

1978-01-01

A collisional theory for the transport of heavy wall released impurities in the plasma scrape-off layer is developed, which to zero order approximation considers electron impact ionization and Coulomb collisions with the plasma ions. Impurity ion convection parallel to the magnetic field and radial drift motion are treated as first order correction terms. The theory, which under certain restrictions to the integral coefficients of the Fokker-Planck collision operator is independent of the special form of the plasma ion distribution, is applied to the calculation of the impurity ion fluxes in the scrape-off layer. Preliminary numerical results are presented for a model plasma ion distribution of the loss ellipse type and a half-maxwellian distribution of the wall released impurity atoms. (Auth.)

Studying metal impurities (Mn2+, Cu2+, Fe3+) in calcium phosphates by electron paramagnetic resonance

Science.gov (United States)

Iskhakova, K.; Murzakhanov, F.; Mamin, G.; Putlyaev, V.; Klimashina, E.; Fadeeva, I.; Fomin, A.; Barinov, S.; Maltsev, A.; Bakhteev, S.; Yusupov, R.; Gafurov, M.; Orlinskii, S.

2018-05-01

Calcium phosphates (CaP) are exploited in many fields of science, including geology, chemistry, biology and medicine due to their abundance in the nature and presence in the living organism. Various analytical and biochemical methods are used for controlling their chemical content, structure, morphology, etc. Unfortunately, magnetic resonance techniques are usually not even considered as necessary tools for CaP inspection. Some aspects of application of the commercially realized electron paramagnetic resonance (EPR) approaches for characterization of CaP powders and ceramics (including the nanosized materails) such as hydroxyapatite and tricalcium phosphates of biogenic and synthetic origins containing intrinsic impurities or intentional dopants are demonstrated. The key features and advantages of the EPR techniques for CaP based materials characterization that could compliment the data obtained with the recognized analytical methods are pointed out.

Building an electronic resource collection a practical guide

CERN Document Server

Lee, Stuart D

2004-01-01

This practical book guides information professionals step-by-step through building and managing an electronic resource collection. It outlines the range of electronic products currently available in abstracting and indexing, bibliographic, and other services and then describes how to effectively select, evaluate and purchase them.

Hydrogenic-Donor Impurity Binding Energy Dependence of the Electric Field in GaAs/AlxGa1−xAs Quantum Rings

Directory of Open Access Journals (Sweden)

Guangxin Wang

2013-01-01

Full Text Available Using a variational method with two-parameter trial wave function and the effective mass approximation, the binding energy of a donor impurity in GaAs/AlxGa1−xAs cylindrical quantum ring (QR subjected to an external field is calculated. It is shown that the donor impurity binding energy is highly dependent on the QR structure parameters (radial thickness and height, impurity position, and external electric field. The binding energy increases inchmeal as the QR parameters (radial thickness and height decrease until a maximum value for a central impurity and then begins to drop quickly. The applied electric field can significantly modify the spread of electronic wave function in the QR and shift electronic wave function from the donor position and then leads to binding energy changes. In addition, results for the binding energies of a hydrogenic donor impurity as functions of the impurity position and applied electric field are also presented.

Analysis of Human Resources Management Strategy in China Electronic Commerce Enterprises

Science.gov (United States)

Shao, Fang

The paper discussed electronic-commerce's influence on enterprise human resources management, proposed and proved the human resources management strategy which electronic commerce enterprise should adopt from recruitment strategy to training strategy, keeping talent strategy and other ways.

Simulation of iron impurity in BaTiO{sub 3} crystals

Energy Technology Data Exchange (ETDEWEB)

Stashans, Arvids, E-mail: arvids@utpl.edu.e [Grupo de Fisicoquimica de Materiales, Instituto de Quimica Aplicada, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador); Castillo, Darwin [Grupo de Fisicoquimica de Materiales, Instituto de Quimica Aplicada, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador); Escuela de Electronica y Telecomunicaciones, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador)

2009-05-01

Iron-doped barium titanate (BaTiO{sub 3}) has been simulated taking into account cubic and tetragonal crystallographic lattices of the crystal. A quantum-chemical method based on the Hartree-Fock formalism has been used throughout the study. The calculated equilibrium structures of Fe-doped crystals reveal the defect-inward displacements of the Ti and O atoms whereas the shifts for the Ba atoms are encountered to be away with respect to the Fe impurity. According to the analysis of electron density population and electron band structure it is found that some unusual chemical bonding might take place between the Fe atom and its six adjacent O atoms. The role of Fe impurity in the ferroelectric polarization of the tetragonal BaTiO{sub 3} crystal has been discussed too.

Using XML Technologies to Organize Electronic Reference Resources

OpenAIRE

Huser, Vojtech; Del Fiol, Guilherme; Rocha, Roberto A.

2005-01-01

Provision of access to reference electronic resources to clinicians is becoming increasingly important. We have created a framework for librarians to manage access to these resources at an enterprise level, rather than at the individual hospital libraries. We describe initial project requirements, implementation details, and some preliminary results.

Dynamics of impurity modes and electron–phonon interaction in Heavy Fermion (HF) systems

International Nuclear Information System (INIS)

Shadangi, N.; Sahoo, J.; Mohanty, S.; Nayak, P.

2014-01-01

A theoretical explanation is provided to understand the effect of small concentration of impurities characterized by change in mass and nearest neighbor force constants on the phonon spectrum as well as on the electron–phonon interaction in some Heavy Fermion (HF) systems in the normal state within theoretical framework of the Periodic Anderson Model (PAM). Three different mechanisms of the electron–phonon interactions, namely, the usual interaction between the phonons with the electrons in the f-bands, electrons arising from that of hybridization term of PAM and the local electron–phonon coupling at the impurity sites are considered. Coherent Potential Approximation (CPA) is used to evaluate the configuration averaged self–energy and the total Green function. For simplicity of calculation the CPA self–energy is evaluated in Average t -matrix Approximation (ATA). The analytical analysis is carried out for finite T in the long wavelength limit. The influence of impurity mass parameter λ and other system parameters such as d, the position of f-level, the effective coupling strength g on the calculated re-normalized phonon frequency and the excitation spectrum through the spectral function is studied. The numerical analysis of the results does show the influence of impurities as evident from different plots in this paper.

Electronic Resources and Mission Creep: Reorganizing the Library for the Twenty-First Century

Science.gov (United States)

Stachokas, George

2009-01-01

The position of electronic resources librarian was created to serve as a specialist in the negotiation of license agreements for electronic resources, but mission creep has added more functions to the routine work of electronic resources such as cataloging, gathering information for collection development, and technical support. As electronic…

Numerical calculation of impurity charge state distributions

International Nuclear Information System (INIS)

Crume, E.C.; Arnurius, D.E.

1977-09-01

The numerical calculation of impurity charge state distributions using the computer program IMPDYN is discussed. The time-dependent corona atomic physics model used in the calculations is reviewed, and general and specific treatments of electron impact ionization and recombination are referenced. The complete program and two examples relating to tokamak plasmas are given on a microfiche so that a user may verify that his version of the program is working properly. In the discussion of the examples, the corona steady-state approximation is shown to have significant defects when the plasma environment, particularly the electron temperature, is changing rapidly

Effect of impurities and processing on silicon solar cells. Volume 1: Characterization methods for impurities in silicon and impurity effects data base

Science.gov (United States)

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.

Numerical renormalization group calculation of impurity internal energy and specific heat of quantum impurity models

Science.gov (United States)

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.

Plasma response on impurity injection in W7-AS

International Nuclear Information System (INIS)

Hildebrandt, D.; Brakel, R.; Elsner, A.; Grigull, P.; Hacker, H.; Burhenn, R.; Fiedler, S.; Giannone, L.; Goerner, C.; Hartfuss, H.J.; Herre, G.; Herrmann, A.; Hofmann, J.V.; Kuehner, G.; Naujoks, D.; Sardei, F.; Weller, A.; Wolf, R.

1997-01-01

In order to study impurity transport and radiation behavior nitrogen has been injected into the scrape-off plasma of limiter-dominated discharges by gas puffing or into natural magnetic islands at the plasma edge of separatrix-dominated discharges by a reciprocating erosion probe. Strong radiative plasma edge cooling with a reduction of the power flux to the limiter could be obtained. The accompanied degradation of the energy confinement and the observed decrease of the central electron temperature can partly be explained by the reduction of the effective heating power. At high plasma densities and sufficiently strong impurity injection phenomena well known from tokamaks, like plasma shrinking, plasma detachment from the limiters and MARFE's were transiently observed. (orig.)

Plasma response on impurity injection in W7-AS

Energy Technology Data Exchange (ETDEWEB)

Hildebrandt, D [Euratom Assoc., Berlin (Germany). Max-Planck-Inst. of Plasma Phys.; Brakel, R; Elsner, A; Grigull, P; Hacker, H; Burhenn, R; Fiedler, S; Giannone, L.; Goerner, C; Hartfuss, H J; Herre, G; Herrmann, A; Hofmann, J V; Kuehner, G; Naujoks, D; Sardei, F; Weller, A; Wolf, R

1997-02-01

In order to study impurity transport and radiation behavior nitrogen has been injected into the scrape-off plasma of limiter-dominated discharges by gas puffing or into natural magnetic islands at the plasma edge of separatrix-dominated discharges by a reciprocating erosion probe. Strong radiative plasma edge cooling with a reduction of the power flux to the limiter could be obtained. The accompanied degradation of the energy confinement and the observed decrease of the central electron temperature can partly be explained by the reduction of the effective heating power. At high plasma densities and sufficiently strong impurity injection phenomena well known from tokamaks, like plasma shrinking, plasma detachment from the limiters and MARFE`s were transiently observed. (orig.).

Environment sensitive embedding energies of impurities, and grain boundary stability in tantalum

International Nuclear Information System (INIS)

Krasko, G.L.

1996-01-01

Metalloid impurities have a very low solubility in tantalum, and therefore prefer to segregate at the grain boundaries (GBs). In order to analyze the energetics of the impurities on the tantalum GB, the LMTO calculations were performed on a simple 8-atom supercell emulating a typical (capped trigonal prism) GB environment. The so-called environment-sensitive embedding energies were calculated for hydrogen, boron, carbon, nitrogen, oxygen, phosphorus, and sulphur, as a function of the electron charge density due to the host atoms at the impurity site. The calculations showed that, at the electron density typical of a GB, carbon has the lowest energy (followed by Nitrogen and Boron) and thus would compete with the other impurities for the site on the GB, tending to displace them from the GB. The above energies were then used in a modified Finnis-Sinclair embedded atom approach for calculating the cohesive energies and the equilibrium interplanar distances in the vicinity of a (111) Σ3 tilt GB plane, both for the clean GB and that with an impurity. These distances were found to oscillate, returning to the value corresponding to the equilibrium spacing between (111) planes in bulk BCC tantalum by the 10th--12th plane off the GB. Carbon, nitrogen and boron somewhat dampen the deformation wave (making the oscillations less than in the clean GB), while oxygen, phosphorus and sulphur result in an increase of the oscillations. The cohesive energies follow the same trend, the GB with carbon being the most stable. Thus, carbon, nitrogen and boron may be thought of as being cohesion enhancers, while oxygen, phosphorus and sulphur result in decohesion effects

Self-consistent modeling of plasma response to impurity spreading from intense localized source

International Nuclear Information System (INIS)

Koltunov, Mikhail

2012-07-01

Non-hydrogen impurities unavoidably exist in hot plasmas of present fusion devices. They enter it intrinsically, due to plasma interaction with the wall of vacuum vessel, as well as are seeded for various purposes deliberately. Normally, the spots where injected particles enter the plasma are much smaller than its total surface. Under such conditions one has to expect a significant modification of local plasma parameters through various physical mechanisms, which, in turn, affect the impurity spreading. Self-consistent modeling of interaction between impurity and plasma is, therefore, not possible with linear approaches. A model based on the fluid description of electrons, main and impurity ions, and taking into account the plasma quasi-neutrality, Coulomb collisions of background and impurity charged particles, radiation losses, particle transport to bounding surfaces, is elaborated in this work. To describe the impurity spreading and the plasma response self-consistently, fluid equations for the particle, momentum and energy balances of various plasma components are solved by reducing them to ordinary differential equations for the time evolution of several parameters characterizing the solution in principal details: the magnitudes of plasma density and plasma temperatures in the regions of impurity localization and the spatial scales of these regions. The results of calculations for plasma conditions typical in tokamak experiments with impurity injection are presented. A new mechanism for the condensation phenomenon and formation of cold dense plasma structures is proposed.

Cr{sup 3+} in layered perovskites: do the electron paramagnetic resonance parameters only depend on the impurity-ligand distances?

Energy Technology Data Exchange (ETDEWEB)

Garcia-Lastra, J M [Nano-Bio Spectroscopy Group and European Theoretical Spectroscopy Facility (ETSF), Departamento Fisica de Materiales UPV/EHU, Apartado 1072, 20018 San Sebastian (Spain); Barriuso, M T [Departamento de Fisica Moderna, Universidad de Cantabria, E-39005 Santander (Spain); Aramburu, J A; Moreno, M, E-mail: scpgalaj@ehu.e [Departamento de Ciencias de la Tierra y Fisica de la Materia Condensada, Universidad de Cantabria, E-39005 Santander (Spain)

2010-04-21

The actual value of axial, R{sub ax}, and equatorial, R{sub eq}, impurity-ligand distances for Cr{sup 3+} embedded in tetragonal K{sub 2}MgX{sub 4} (X = F, Cl) lattices has been explored by means of density functional theory (DFT) calculations on clusters involving up to 69 ions using two different functionals. For K{sub 2}MgF{sub 4}:Cr{sup 3+} R{sub eq} and R{sub ax} are found to be coincident within only 0.5 pm. When the g tensor of K{sub 2}MgF{sub 4}:Cr{sup 3+} is derived considering only the CrF{sub 6}{sup 3-} unit in vacuo at the calculated equilibrium geometry the g{sub perpendicular}-g{sub ||} quantity fails to reproduce the experimental value by one order of magnitude. In contrast, when the active electrons localized in the CrX{sub 6}{sup 3-} complex (X = F, Cl) are allowed to feel the anisotropic electric field coming from the rest of the lattice ions the splitting in the first excited state, {sup 4}T{sub 2}, increases by one order of magnitude. The present results thus show that the g tensor anisotropy and the zero-field splitting constant, D, observed for K{sub 2}MgX{sub 4}:Cr{sup 3+} (X = F, Cl) are not mainly due to a local deformation of the CrX{sub 6}{sup 3-} octahedron but to the action of the internal electric field, often ignored when seeking the microscopic origin of electronic properties due to impurities in insulating lattices. Accordingly, serious doubts on the validity of the superposition model are cast by the present work.

Edge and Core Impurity Transport Study with Spectroscopic Instruments in LHD

International Nuclear Information System (INIS)

Morita, Shigeru; Goto, Motoshi; Kobayashi, Masahiro; Muto, Sadatsugu; Chowdhuri, Malay Bikas; Chunfeng, Dong; Hangyu, Zhou; Zhengying, Cui; Fujii, Keisuke; Hasuo, Masahiro; Iwamae, Atsushi; Furuzawa, Akihiro; Sakurai, Ikuya; Tawara, Yuzuru; Yinxian, Jie; Baonian, Wan; Zhenwei, Wu; Koubiti, Mohammed; Yamaguchi, Naohiro

2009-01-01

Impurity transport was investigated at both edge and core regions in large helical device (LHD) with developed spectroscopic instruments which can measure one- and two-dimensional distributions of impurities. The edge impurity behavior was studied recently using four carbon resonant transitions in different ionization stages of CIII (977A), CIV (1548A), CV (40.3A) and CVI (33.7A). When the line-averaged electron density, n e , is increased from 1 to 6 x 10 13 cm -3 , the ratio of (CIII+CIV)/n e increases while the ratio of (CV+CVI)/n e decreases. Here, CIII+CIV (CV+CVI) expresses the sum of CIII (CV) and CIV (CVI) intensities. The CIII+CIV indicates the carbon influx and the CV+CVI indicates the emissions through the transport in the ergodic layer. The result thus gives experimental evidence on the impurity screening by the ergodic layer in LHD, which is also supported by a three-dimensional edge particle simulation. The core impurity behavior is also studied in high-density discharges (n e ≤ 1x 10 15 cm -3 ) with multi H 2 -pellets injection. It is found that the ratio of V/D (V: convection velocity, D: diffusion coefficient) decreases after pellet injection and Z eff profile shows a flat one at values of 1.1-1.2. These results confirm no impurity accumulation occurs in high-density discharges. As a result, the iron density, n Fe , is analyzed to be 6 x 10 -7 ( = n Fe /n e ) of which the amount can be negligible as radiation source even in such high-density discharges. One- and two-dimensional impurity distributions from space-resolved VUV and EUV spectrometers newly developed for further impurity transport study are also presented with their preliminary results. (magnetically confined plasma)

Electronic Resources Management System: Recommendation Report 2017

KAUST Repository

Ramli, Rindra M.

2017-01-01

This recommendation report provides an overview of the selection process for the new Electronic Resources Management System. The library has decided to move away from Innovative Interfaces Millennium ERM module. The library reviewed 3 system

Thermal Conductivity of Nanotubes Revisited: Effects of Chirality, Isotope Impurity, Tube Length, and Temperature

OpenAIRE

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...

FP-LAPW Calculations of the EFG at Cd Impurities in Rutile SnO{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Errico, L. A.; Fabricius, G.; Renteria, M. [Universidad Nacional de La Plata, Instituto de Fisica La Plata (IFLP-CONICET) - Departamento de Fisica, Facultad de Ciencias Exactas (Argentina)

2001-11-15

We report an ab initio study of the electric-field gradient (EFG) at Cd impurities located at the cation site in the semiconductor SnO{sub 2}(rutile phase). The study was performed with the WIEN97 implementation of the FP-LAPW method. In order to simulate the diluted Cd-impurity in the SnO{sub 2} host and to calculate the electronic structure of the system we used a 72-atoms super-cell, studying the relaxation introduced by the impurity in the lattice. The free-relaxation process performed shows that the relaxations of the oxygen nearest-neighbors of the impurity are not isotropic. Our prediction for the EFG tensor are compared with experimental results and point-charge model predictions.

Density and impurity profile behaviours in HL-2A tokamak with different gas fuelling methods

International Nuclear Information System (INIS)

Zheng-Ying, Cui; Yan, Zhou; Wei, Li; Bei-Bin, Feng; Ping, Sun; Chun-Feng, Dong; Yi, Liu; Wen-Yu, Hong; Qing-Wei, Yang; Xuan-Tong, Ding; Xu-Ru, Duan

2009-01-01

The electron density profile peaking and the impurity accumulation in the HL-2A tokamak plasma are observed when three kinds of fuelling methods are separately used at different fuelling particle locations. The density profile becomes more peaked when the line-averaged electron density approaches the Greenwald density limit n G and, consequently, impurity accumulation is often observed. A linear increase regime in the density range n e G and a saturation regime in n e > 0.6n G are obtained. There is no significant difference in achieved density peaking factor f ne between the supersonic molecular beam injection (SMBI) and gas puffing into the plasma main chamber. However, the achieved f ne is relatively low, in particular, in the case of density below 0.7n G , when the working gas is puffed into the divertor chamber. A discharge with a density as high as 1.2n G , i.e. n e = 1.2n G , can be achieved by SMBI just after siliconization as a wall conditioning. The metallic impurities, such as iron and chromium, also increase remarkably when the impurity accumulation happens. The mechanism behind the density peaking and impurity accumulation is studied by investigating both the density peaking factor versus the effective collisionality and the radiation peaking versus density peaking. (fluids, plasmas and electric discharges)

Investigation Effects of Magnetetic Impurity Doping on Average Magnetization of Semiconducting Carbon Nanotubes

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

Impurity studies and discharge cleaning in Doublet III

Energy Technology Data Exchange (ETDEWEB)

Marcus, F.B.

1979-10-01

The goal of present and next generation tokamak experiments is to produce high-density, high-purity plasmas during high-power, extended-duration discharges. Plasma discharges with Z/sub eff/ values near unity and low concentrations of medium and high-Z metallic impurities have been obtained in Doublet III using a combination of low-power hydrogen discharge cleaning, gas puffing, precise plasma shape and position control, and high-Z limiters. Analysis of the first wall surface and residual gas impurities confirmed that clean conditions have been achieved. The high-Z limiters showed very limited amounts of melting or arcing. The progress of the wall cleaning process was monitored by three diagnostic techniques: Auger electron spectroscopy of metallic samples at the vessel wall, residual gas analysis, and the resistivity of full power discharges.

Impurity studies and discharge cleaning in Doublet III

International Nuclear Information System (INIS)

Marcus, F.B.

1979-10-01

The goal of present and next generation tokamak experiments is to produce high-density, high-purity plasmas during high-power, extended-duration discharges. Plasma discharges with Z/sub eff/ values near unity and low concentrations of medium and high-Z metallic impurities have been obtained in Doublet III using a combination of low-power hydrogen discharge cleaning, gas puffing, precise plasma shape and position control, and high-Z limiters. Analysis of the first wall surface and residual gas impurities confirmed that clean conditions have been achieved. The high-Z limiters showed very limited amounts of melting or arcing. The progress of the wall cleaning process was monitored by three diagnostic techniques: Auger electron spectroscopy of metallic samples at the vessel wall, residual gas analysis, and the resistivity of full power discharges

Evaluation of determinative methods for sodium impurities

International Nuclear Information System (INIS)

Molinari, Marcelo; Guido, Osvaldo; Botbol, Jose; Ares, Osvaldo

1988-01-01

Sodium, universally accepted as heat transfer fluid in fast breeder reactors, requires a special technology for every operation involved in any applicable methodology, due to its well known chemical reactivity. The purpose of this work is: a) to study the sources and effects of chemical species which, as traces, accompany sodium used in the nuclear field; b) to classify, taking into account, the present requirements and resources of the National Atomic Energy Commission (CNEA), the procedures found in the literature for determination of the most important impurities which exist in experimental liquid sodium systems and c) to describe the principles of the methods and to evaluate them in order to make a selection. It was concluded the convenience to develop, as a first stage, laboratory procedures to determine carbon, oxygen, hydrogen and non-volatile impurities, which besides serving present needs, will be referential for direct methods with undeferred response. The latter are needed in liquid sodium experimental loops and require, primarily, more complex and extended development. Additionally, a description is made of experimental work performed up-to-now in this laboratory, consisting of a transfer device for sodium sampling and a sodium distillation device, adapted from a previous design, with associated vacuum and inert gas systems. It is intended as a separative technique for indirect determination of oxygen and non-volatile impurities. (Author) [es

Measurements of impurity spectra using UV/visible spectroscopic system in a GAMMA 10 plasma

International Nuclear Information System (INIS)

Matama, K.; Yoshikawa, M.; Kobayashi, T.; Kubota, Y.; Cho, T.

2006-01-01

Impurity spectra have been measured and identified using a newly designed ultraviolet and visible (UV/visible) spectroscopic system in the tandem mirror GAMMA 10. It is constructed using two spectrometers to obtain an entire wavelength range of UV/visible impurity spectra with a high wavelength resolution in one plasma shot. We successfully obtained the emission intensities of the radiation spectra in detail and information on the time-varying population densities of the impurities. We evaluate radiation loss from the GAMMA 10 plasma in the UV/visible range; further we estimate the electron density and temperature after applying the measured spectral intensity to a collisional-radiative model

FLAPW Study of the EFG Tensor at Cd Impurities in In2O3

International Nuclear Information System (INIS)

Errico, L. A.; Renteria, M.; Fabricius, G.; Darriba, G. N.

2004-01-01

We report an ab initio study of the electric-field gradient tensor (EFG) at Cd impurities located at both nonequivalent cationic sites in the semiconductor In 2 O 3 . Calculations were performed with the FLAPW method that allows us to treat the electronic structure of the doped system and the atomic relaxations introduced by the impurities in the host in a fully self-consistent way. From our results for the EFG (in excellent agreement with the experiments), it is clear that the problem of the EFG at Cd impurities in In 2 O 3 cannot be described by the point-charge model and antishielding factors.

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...

The Internet School of Medicine: use of electronic resources by medical trainees and the reliability of those resources.

Science.gov (United States)

Egle, Jonathan P; Smeenge, David M; Kassem, Kamal M; Mittal, Vijay K

2015-01-01

Electronic sources of medical information are plentiful, and numerous studies have demonstrated the use of the Internet by patients and the variable reliability of these sources. Studies have investigated neither the use of web-based resources by residents, nor the reliability of the information available on these websites. A web-based survey was distributed to surgical residents in Michigan and third- and fourth-year medical students at an American allopathic and osteopathic medical school and a Caribbean allopathic school regarding their preferred sources of medical information in various situations. A set of 254 queries simulating those faced by medical trainees on rounds, on a written examination, or during patient care was developed. The top 5 electronic resources cited by the trainees were evaluated for their ability to answer these questions accurately, using standard textbooks as the point of reference. The respondents reported a wide variety of overall preferred resources. Most of the 73 responding medical trainees favored textbooks or board review books for prolonged studying, but electronic resources are frequently used for quick studying, clinical decision-making questions, and medication queries. The most commonly used electronic resources were UpToDate, Google, Medscape, Wikipedia, and Epocrates. UpToDate and Epocrates had the highest percentage of correct answers (47%) and Wikipedia had the lowest (26%). Epocrates also had the highest percentage of wrong answers (30%), whereas Google had the lowest percentage (18%). All resources had a significant number of questions that they were unable to answer. Though hardcopy books have not been completely replaced by electronic resources, more than half of medical students and nearly half of residents prefer web-based sources of information. For quick questions and studying, both groups prefer Internet sources. However, the most commonly used electronic resources fail to answer clinical queries more than half

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

Impurity-generated non-Abelions

Science.gov (United States)

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

Phonon-impurity relaxation and acoustic wave absorption in yttrium-aluminium garnet crystals with impurities

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

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)

Ab initio study of the EFG tensor at Cd impurities in Sc{sub 2}O{sub 3} semiconductor

Energy Technology Data Exchange (ETDEWEB)

Munoz, E.L.; Richard, D. [Departamento de Fisica and IFLP (CONICET-UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata (Argentina); Errico, L.A. [Departamento de Fisica and IFLP (CONICET-UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata (Argentina); Universidad Nacional del Noroeste Bonaerense (UNNOBA), Monteagudo 2772, Pergamino, CP 2700 Buenos Aires (Argentina); Renteria, M., E-mail: renteria@fisica.unlp.edu.a [Departamento de Fisica and IFLP (CONICET-UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 67, 1900 La Plata (Argentina)

2009-10-01

We present an ab initio study of diluted Cd impurities localized at both cation sites of the semiconductor Sc{sub 2}O{sub 3}. The electric-field-gradient (EFG) tensor at Cd impurities located at both cationic sites of the host structure was determined from the calculation of the electronic structure of the doped system. Calculations were performed with the full-potential augmented-plane wave plus local orbitals (APW+lo) method within the framework of the density functional theory. We studied the atomic structural relaxations and the perturbation of the electronic charge density induced by the impurities in the host system in a fully self-consistent way. We showed that the Cd impurity introduces an increase of 8% in the nearest oxygen neighbors bond-lengths, changing the EFG sign for probes located at the asymmetric cation site. The APW+lo predictions for the charged state of the Cd impurity were compared with EFG results existent in the literature, coming from time-differential gamma-gamma perturbed-angular-correlations experiments performed on {sup 111}Cd-implanted Sc{sub 2}O{sub 3} powder samples. From the excellent agreement between theory and experiment, we can strongly suggest that the Cd acceptor impurities are ionized at room temperature. Finally, we showed that simple calculations like those performed within the point-charge model with antishielding factors do not correctly describe the problem of a Cd impurity in Sc{sub 2}O{sub 3}.

Graphene plasmons: Impurities and nonlocal effects

Science.gov (United States)

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.

Effects of hydrogen-like impurity and electromagnetic field on quantum transition of an electron in a Gaussian potential with QD thickness

Science.gov (United States)

Xin, Wei; Zhao, Yu-Wei; Sudu; Eerdunchaolu

2018-05-01

Considering Hydrogen-like impurity and the thickness effect, the eigenvalues and eigenfunctions of the electronic ground and first exited states in a quantum dot (QD) are derived by using the Lee-Low-Pins-Pekar variational method with the harmonic and Gaussian potentials as the transverse and longitudinal confinement potentials, respectively. A two-level system is constructed on the basis of those two states, and the electronic quantum transition affected by an electromagnetic field is discussed in terms of the two-level system theory. The results indicate the Gaussian potential reflects the real confinement potential more accurately than the parabolic one; the influence of the thickness of the QD on the electronic transition probability is interesting and significant, and cannot be ignored; the electronic transition probability Γ is influenced significantly by some physical quantities, such as the strength of the electron-phonon coupling α, the electric-field strength F, the magnetic-field cyclotron frequency ωc , the barrier height V0 and confinement range L of the asymmetric Gaussian potential, suggesting the transport and optical properties of the QD can be manipulated further though those physical quantities.

ANALYTICAL REVIEW OF ELECTRONIC RESOURCES FOR THE STUDY OF LATIN

Directory of Open Access Journals (Sweden)

Olena Yu. Balalaieva

2014-04-01

Full Text Available The article investigates the current state of development of e-learning content in the Latin language. It is noted that the introduction of ICT in the educational space has expanded the possibility of studying Latin, opened access to digital libraries resources, made it possible to use scientific and educational potential and teaching Latin best practices of world's leading universities. A review of foreign and Ukrainian information resources and electronic editions for the study of Latin is given. Much attention was paid to the didactic potential of local and online multimedia courses of Latin, electronic textbooks, workbooks of interactive tests and exercises, various dictionaries and software translators, databases and digital libraries. Based on analysis of the world market of educational services and products the main trends in the development of information resources and electronic books are examined. It was found that multimedia courses with interactive exercises or workbooks with interactive tests, online dictionaries and translators are the most widely represented and demanded. The noticeable lagging of Ukrainian education and computer linguistics in quantitative and qualitative measures in this industry is established. The obvious drawback of existing Ukrainian resources and electronic editions for the study of Latin is their noninteractive nature. The prospects of e-learning content in Latin in Ukraine are outlined.

Nonlinear optical response in a zincblende GaN cylindrical quantum dot with donor impurity center

Energy Technology Data Exchange (ETDEWEB)

Hoyos, Jaime H. [Departamento de Ciencias Básicas, Universidad de Medellín, Cra. 87 No. 30-65, Medellín (Colombia); Correa, J.D., E-mail: jcorrea@udem.edu.co [Departamento de Ciencias Básicas, Universidad de Medellín, Cra. 87 No. 30-65, Medellín (Colombia); Mora-Ramos, M.E. [Centro de Investigación en Ciencias, Instituto de Investigación en Ciencias Básicas y Aplicadas, 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)

2016-03-01

We calculate the nonlinear optical absorption coefficient of a cylindrical zincblende GaN-based quantum dot. For this purpose, we consider Coulomb interactions between electrons and an impurity ionized donor atom. The electron-donor-impurity spectrum and the associated quantum states are calculated using the effective mass approximation with a parabolic potential energy model describing both the radial and axial electron confinement. We also include the effects of the hydrostatic pressure and external electrostatic fields. The energy spectrum is obtained through an expansion of the eigenstates as a linear combination of Gaussian-type functions which reduces the computational effort since all the matrix elements are obtained analytically. Therefore, the numerical problem is reduced to the direct diagonalization of the Hamiltonian. The obtained energies are used in the evaluation of the dielectric susceptibility and the nonlinear optical absorption coefficient within a modified two-level approach in a rotating wave approximation. This quantity is investigated as a function of the quantum dot dimensions, the impurity position, the external electric field intensity and the hydrostatic pressure. The results of this research could be important in the design and fabrication of zincblende GaN-quantum-dot-based electro-optical devices.

Nonlinear optical response in a zincblende GaN cylindrical quantum dot with donor impurity center

International Nuclear Information System (INIS)

Hoyos, Jaime H.; Correa, J.D.; Mora-Ramos, M.E.; Duque, C.A.

2016-01-01

We calculate the nonlinear optical absorption coefficient of a cylindrical zincblende GaN-based quantum dot. For this purpose, we consider Coulomb interactions between electrons and an impurity ionized donor atom. The electron-donor-impurity spectrum and the associated quantum states are calculated using the effective mass approximation with a parabolic potential energy model describing both the radial and axial electron confinement. We also include the effects of the hydrostatic pressure and external electrostatic fields. The energy spectrum is obtained through an expansion of the eigenstates as a linear combination of Gaussian-type functions which reduces the computational effort since all the matrix elements are obtained analytically. Therefore, the numerical problem is reduced to the direct diagonalization of the Hamiltonian. The obtained energies are used in the evaluation of the dielectric susceptibility and the nonlinear optical absorption coefficient within a modified two-level approach in a rotating wave approximation. This quantity is investigated as a function of the quantum dot dimensions, the impurity position, the external electric field intensity and the hydrostatic pressure. The results of this research could be important in the design and fabrication of zincblende GaN-quantum-dot-based electro-optical devices.

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

Elektronik Bilgi Kaynaklarının Seçimi / Selection of Electronic Information Resources

Directory of Open Access Journals (Sweden)

Pınar Al

2003-04-01

Full Text Available For many years, library users have used only from the printed media in order to get the information that they have needed. Today with the widespread use of the Web and the addition of electronic information resources to library collections, the use of information in the electronic environment as well as in printed media is started to be used. In time, such types of information resources as, electronic journals, electronic books, electronic encyclopedias, electronic dictionaries and electronic theses have been added to library collections. In this study, selection criteria that can be used for electronic information resources are discussed and suggestions are provided for libraries that try to select electronic information resources for their collections.

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.

Polarizability of a crystal with impurities

International Nuclear Information System (INIS)

Goettig, S.

1985-09-01

The expression for the complex frequency- and wavevector-dependent longitudinal electronic polarizability due to the presence of a weak static disorder (e.g. impurities) in a crystal with an arbitrary band structure is derived. The quantum kinetic equation in the self-consistent-field approximation is solved, expanding the one-particle density operator in powers of the screened static imperfection field and a weak perturbing electric field. The polarizability is determined by the induced electronic charge density quadratic in the imperfection field and linear in the perturbing field, averaged over the statistical distribution of imperfections. The obtained expression, which accounts properly for the collective effects in the electronic plasma, takes also into account the polar coupling of the plasma with longitudinal optical phonons. The conductivity in the optical limit (q-vector→O) is calculated, and the correspondence with one-band effective-mass approximation is established. (author)

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

Access to electronic resources by visually impaired people

Directory of Open Access Journals (Sweden)

Jenny Craven

2003-01-01

Full Text Available Research into access to electronic resources by visually impaired people undertaken by the Centre for Research in Library and Information Management has not only explored the accessibility of websites and levels of awareness in providing websites that adhere to design for all principles, but has sought to enhance understanding of information seeking behaviour of blind and visually impaired people when using digital resources.

COREDIV modelling of JET ILW discharges with different impurity seeding: nitrogen, neon, argon and krypton

Directory of Open Access Journals (Sweden)

Ivanova-Stanik Irena

2017-03-01

Full Text Available Numerical simulations with the COREDIV code of JET H-mode discharges with 25 MW of auxiliary heating in the ITER-like wall (ILW configuration with different impurity seedings – nitrogen (N, neon (Ne, argon (Ar and krypton (Kr – are presented. All simulations have been performed with the same transport model and input discharge parameters like auxiliary heating, volume average plasma density, confinement factor. Only the seeded impurity puff rate was changed in the calculations. It appears that for the considered heating power of 25 MW and relatively low volume electron average density = 6.2 × 1019 m−3, impurity seeding is necessary. It has been found that for every gas at the maximum level of the seeding rate, allowed by the code convergence, the power to the plate is reduced up to 2–4 MW, with electron temperature at the plate of about 2 eV, indicating semi-detached conditions in the divertor region. It should be noted, however, that in cases with low and medium Z impurity (N, Ne and Ar, tungsten radiation is a significant part of radiation losses and stays above 22–32% of the total energy losses, but for high Z impurity (Kr it is reduced up to 10% of the total losses. The maximum of the Kr radiation is between the pedestal region and separatrix, showing that radiative mantle can be created, which might have a strong influence on the plasma parameters in the pedestal region.

Effective equations for the precession dynamics of electron spins and electron–impurity correlations in diluted magnetic semiconductors

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)

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.

Hole trapping at Al impurities in silica: A challenge for density functional theories

DEFF Research Database (Denmark)

Lægsgaard, Jesper; Stokbro, Kurt

2001-01-01

The atomic geometry and electronic structure around a neutral substitutional Al impurity in silica is investigated using either the unrestricted Hartree-Fock (UHF) approximation, or Beckes three-parameter hybrid functional (B3LYP). It is found that the B3LYP functional fails to describe...... the structural distortions around the Al impurity, while the UHF results are consistent with experimental information. We argue that the failure of the B3LYP functional is caused by the incomplete self-interaction cancellation usually present in density functional theories....

Behavior of impurity ion velocities during the pulsed poloidal current drive in the Madison symmetric torus reversed-field pinch

International Nuclear Information System (INIS)

Sakakita, Hajime; Craig, Darren; Anderson, Jay K.; Chapman, Brett E.; Den-Hartog, Daniel J.; Prager, Stewart C.; Biewer, Ted M.; Terry, Stephen D.

2003-01-01

We report on passive measurements of impurity ion velocities during the pulsed poloidal current drive (PPCD) in the Madison Symmetric Torus reversed-field pinch. During PPCD, the electron temperature increased and a sudden reduction of magnetic fluctuations was observed. For this change, we have studied whether plasma velocity is affected. Plasma rotation is observed to decrease during PPCD. From measurements of line intensities for several impurities at 10 poloidal chords, it is found that the impurity line emission shifts outward. The ion temperature of impurities is reasonably connected to that measured by charge exchange recombination spectroscopy from core to edge. (author)

Ab-initio study of C and O impurities in uranium nitride

International Nuclear Information System (INIS)

Lopes, Denise Adorno; Claisse, Antoine; Olsson, Pär

2016-01-01

Uranium nitride (UN) has been considered a potential fuel for Generation IV (GEN-IV) nuclear reactors as well as a possible new fuel for Light Water Reactors (LWR), which would permit an extension of the fuel residence time in the reactor. Carbon and oxygen impurities play a key role in the UN microstructure, influencing important parameters such as creep, swelling, gas release under irradiation, compatibility with structural steel and coolants, and thermal stability. In this work, a systematic study of the electronic structure of UN containing C and O impurities using first-principles calculations by the Density Functional Theory (DFT) method is presented. In order to describe accurately the localized U 5f electrons, the DFT + U formalism was adopted. Moreover, to avoid convergence toward metastable states, the Occupation Matrix Control (OMC) methodology was applied. The incorporation of C and O in the N-vacancy is found to be energetically favorable. In addition, only for O, the incorporation in the interstitial position is energetically possible, showing some degree of solubility for this element in this site. The binding energies show that the pairs (C−N_v_a_c) and (O−N_v_a_c) interact much further than the other defects, which indicate the possible occurrence of vacancy drag phenomena and clustering of these impurities in grain boundaries, dislocations and free surfaces. The migration energy of an impurity by single N-vacancy show that C and O employ different paths during diffusion. Oxygen migration requires significantly lower energy than carbon. This fact is due to flexibility in the U−O chemical bonds, which bend during the diffusion forming a pseudo UO_2 coordination. On the other hand, C and N have a directional and inflexible chemical bond with uranium; always requiring the octahedral coordination. These findings provide detailed insight into how these impurities behave in the UN matrix, and can be of great interest for assisting the development

Ab-initio study of C and O impurities in uranium nitride

Energy Technology Data Exchange (ETDEWEB)

Lopes, Denise Adorno; Claisse, Antoine; Olsson, Pär, E-mail: polsson@kth.se

2016-09-15

Uranium nitride (UN) has been considered a potential fuel for Generation IV (GEN-IV) nuclear reactors as well as a possible new fuel for Light Water Reactors (LWR), which would permit an extension of the fuel residence time in the reactor. Carbon and oxygen impurities play a key role in the UN microstructure, influencing important parameters such as creep, swelling, gas release under irradiation, compatibility with structural steel and coolants, and thermal stability. In this work, a systematic study of the electronic structure of UN containing C and O impurities using first-principles calculations by the Density Functional Theory (DFT) method is presented. In order to describe accurately the localized U 5f electrons, the DFT + U formalism was adopted. Moreover, to avoid convergence toward metastable states, the Occupation Matrix Control (OMC) methodology was applied. The incorporation of C and O in the N-vacancy is found to be energetically favorable. In addition, only for O, the incorporation in the interstitial position is energetically possible, showing some degree of solubility for this element in this site. The binding energies show that the pairs (C−N{sub vac}) and (O−N{sub vac}) interact much further than the other defects, which indicate the possible occurrence of vacancy drag phenomena and clustering of these impurities in grain boundaries, dislocations and free surfaces. The migration energy of an impurity by single N-vacancy show that C and O employ different paths during diffusion. Oxygen migration requires significantly lower energy than carbon. This fact is due to flexibility in the U−O chemical bonds, which bend during the diffusion forming a pseudo UO{sub 2} coordination. On the other hand, C and N have a directional and inflexible chemical bond with uranium; always requiring the octahedral coordination. These findings provide detailed insight into how these impurities behave in the UN matrix, and can be of great interest for assisting the

Impurity gettering in semiconductors

Science.gov (United States)

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.

Library training to promote electronic resource usage

DEFF Research Database (Denmark)

Frandsen, Tove Faber; Tibyampansha, Dativa; Ibrahim, Glory

2017-01-01

Purpose: Increasing the usage of electronic resources is an issue of concern for many libraries all over the world. Several studies stress the importance of information literacy and instruction in order to increase the usage. Design/methodology/approach: The present article presents the results...

Why and How to Measure the Use of Electronic Resources

Directory of Open Access Journals (Sweden)

Jean Bernon

2008-11-01

Full Text Available A complete overview of library activity implies a complete and reliable measurement of the use of both electronic resources and printed materials. This measurement is based on three sets of definitions: document types, use types and user types. There is a common model of definitions for printed materials, but a lot of questions and technical issues remain for electronic resources. In 2006 a French national working group studied these questions. It relied on the COUNTER standard, but found it insufficient and pointed out the need for local tools such as web markers and deep analysis of proxy logs. Within the French national consortium COUPERIN, a new working group is testing ERMS, SUSHI standards, Shibboleth authentication, along with COUNTER standards, to improve the counting of the electronic resources use. At this stage this counting is insufficient and its improvement will be a European challenge for the future.

CUSTOM RELAXATION INDUCED IMPURITY PHOTOCONDUCTIVITY IN THE UNITED AII BVI and AIII BV

Directory of Open Access Journals (Sweden)

L. B. Atlukhanova

2016-01-01

Full Text Available Two types of non-standard relaxation induced impurity photoconductivity (IIP observed in photoconductors CdS, ZnSe, GaAs and others, depending on the kinetic characteristics of the traps are described. In one case, at the stage of post flashing monotonic decay which is typical for relaxation associated with slow traps (the ratio of the speed of the electron capture to the recombination rate (R << 1, the photo response is experiencing vibrations of low frequency (f =0.03-0.3Hz. Relaxation of the second type characterized by rapid photoelectric traps (R >> 1: measurement alternating signal (f > 20 Hz relaxation curves take the form of curves usual impurity photoconductivity. Electronic processes responsible for relaxation of non-standard IIP are analyzed. For example, fast-centers, which include the characteristic AIIBVI donor Agi0, for the first time in semiconductors experimentally, investigated the dependence of the cross section of electron capture by traps energy released during localization.

Scattering Theory on Surface Majorana Fermions by an Impurity in ^{3}He-B.

Science.gov (United States)

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.

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

Trends on 3d transition metal impurities in diamond

International Nuclear Information System (INIS)

Assali, L.V.C.; Machado, W.V.M.; Justo, J.F.

2009-01-01

We carried out a first principles investigation on the electronic properties and chemical trends of 3d transition metal related impurities in diamond. In terms of formation energy, the interstitial site is considerably more unfavorable than the substitutional or divacancy ones. Going from Ti to Ni, the 3d-related energy levels in the gap become deeper toward the valence band in all three sites. However, in the divacancy one, those levels cross with the divacancy-related ones, such that the electronic property of the center depends on the character of the highest occupied level.

Polaronic effects on the off-center donor impurity in AlAs/GaAs/SiO2 spherical core/shell quantum dots

Science.gov (United States)

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.

Magnetic hyperfine field at a Cd impurity diluted in RCo{sub 2} at finite temperatures

Energy Technology Data Exchange (ETDEWEB)

Oliveira, A.L. de, E-mail: alexandre.oliveira@ifrj.edu.br [Instituto Federal de Educação, Ciência e Tecnologia do Rio de Janeiro, Campus Nilópolis – RJ (Brazil); Chaves, C.M., E-mail: cmch@cbpf.br [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro (Brazil); Oliveira, N.A. de [Instituto de Física Armando Dias Tavares, Universidade do Estado do Rio de Janeiro, Rio de Janeiro (Brazil); Troper, A. [Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro (Brazil)

2015-06-15

The local magnetic moments and the magnetic hyperfine fields at an s–p Cd impurity diluted in inter-metallic Laves phase compounds RCo{sub 2} (R=Gd, Tb) at finite temperatures are calculated. For other rare earth elements (light or heavy) the pure compounds display a magnetic first order transition and are not describable by our formalism. The host has two coupled lattices (R and Co) both having itinerant d electrons but only the rare earth lattice has localized f electrons. They all contribute to the magnetization of the host and also to the local moment and to the magnetic hyperfine field at the impurity. The investigation of magnetic hyperfine field in these materials then provides valuable information on the d-itinerant electrons and also on the localized (4f) magnetic moments. For the d–d electronic interaction we use the Hubbard–Stratonovich identity thus allowing the employment of functional integral in the static saddle point approximation. Our model reproduces quite well the experimental data. - Highlights: • A functional integral method in the static limit, producing site disorder, is used. • The site disorder is treated with the coherent potential approximation (CPA) • A Friedel sum rule gives a self-consistency condition for the impurity energy. • The experimental curve of hyperfine fields×temperature is very well reproduced.

Nuclear orientation of rare earth impurities in ferromagnetic host metals

International Nuclear Information System (INIS)

Keus, H.E.

1981-01-01

Experiments are described investigating the behaviour of the metals Nd and Lu as impurities in a ferromagnetic host metal - iron, cobalt and nickel. The systems have been studied with the aid of nuclear orientation, making use of the interactions between the atom nuclei and the electrons - the so called hyperfine interactions. (C.F.)

Runaway electrons during tokamak startup

International Nuclear Information System (INIS)

Sharma, A.S.; Jayakumar, R.

1988-01-01

Runaway electrons significantly affect the plasma and impurity evolution during tokamak startup. During its rise, a runaway pulse stores magnetic flux inductively; this is then released during the decay phase of the runaway pulse. This process affects plasma formation, current initiation and current buildup. Because of their relativistic velocities the runaway electrons have higher ionization and excitation rates than the plasma electrons. This leads to a significant modification of the impurity behaviour and consequently the plasma evolution. (author). 20 refs, 8 figs

Control of edge localized modes by pedestal deposited impurity in the HL-2A tokamak

Science.gov (United States)

Zhang, Y. P.; Mazon, D.; Zou, X. L.; Zhong, W. L.; Gao, J. M.; Zhang, K.; Sun, P.; Dong, C. F.; Cui, Z. Y.; Liu, Yi; Shi, Z. B.; Yu, D. L.; Cheng, J.; Jiang, M.; Xu, J. Q.; Isobe, M.; Xiao, G. L.; Chen, W.; Song, S. D.; Bai, X. Y.; Zhang, P. F.; Yuan, G. L.; Ji, X. Q.; Li, Y. G.; Zhou, Y.; Delpech, L.; Ekedahl, A.; Giruzzi, G.; Hoang, T.; Peysson, Y.; Song, X. M.; Song, X. Y.; Li, X.; Ding, X. T.; Dong, J. Q.; Yang, Q. W.; Xu, M.; Duan, X. R.; Liu, Y.; the HL-2A Team

2018-04-01

Effect of the pedestal deposited impurity on the edge-localized mode (ELM) behaviour has been observed and intensively investigated in the HL-2A tokamak. Impurities have been externally seeded by a newly developed laser blow-off (LBO) system. Both mitigation and suppression of ELMs have been realized by LBO-seeded impurity. Measurements have shown that the LBO-seeded impurity particles are mainly deposited in the pedestal region. During the ELM mitigation phase, the pedestal density fluctuation is significantly increased, indicating that the ELM mitigation may be achieved by the enhancement of the pedestal transport. The transition from ELM mitigation to ELM suppression was triggered when the number of the LBO-seeded impurity exceeds a threshold value. During the ELM suppression phase, a harmonic coherent mode (HCM) is excited by the LBO-seeded impurity, and the pedestal density fluctuation is significantly decreased, the electron density is continuously increased, implying that HCM may reduce the pedestal turbulence, suppress ELMs, increase the pedestal pressure, thus extending the Peeling-Ballooning instability limit. It has been found that the occurance of the ELM mitigation and ELM suppression closely depends on the LBO laser spot diameter.

Light impurity transport in JET ILW L-mode plasmas

Science.gov (United States)

Bonanomi, N.; Mantica, P.; Giroud, C.; Angioni, C.; Manas, P.; Menmuir, S.; Contributors, JET

2018-03-01

A series of experimental observations of light impurity profiles was carried out in JET (Joint European Torus) ITER-like wall (ILW) L-mode plasmas in order to investigate their transport mechanisms. These discharges feature the presence of 3He, Be, C, N, Ne, whose profiles measured by active Charge Exchange diagnostics are compared with quasi-linear and non-linear gyro-kinetic simulations. The peaking of 3He density follows the electron density peaking, Be and Ne are also peaked, while the density profiles of C and N are flat in the mid plasma region. Gyro-kinetic simulations predict peaked density profiles for all the light impurities studied and at all the radial positions considered, and fail predicting the flat or hollow profiles observed for C and N at mid radius in our cases.

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)

Competing pseudogap and impurity effects on the normal-state specific heat properties of cuprate superconductors

Science.gov (United States)

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) .

Evaluation of soft x-ray average recombination coefficient and average charge for metallic impurities in beam-heated plasmas

International Nuclear Information System (INIS)

Sesnic, S.S.; Bitter, M.; Hill, K.W.; Hiroe, S.; Hulse, R.; Shimada, M.; Stratton, B.; von Goeler, S.

1986-05-01

The soft x-ray continuum radiation in TFTR low density neutral beam discharges can be much lower than its theoretical value obtained by assuming a corona equilibrium. This reduced continuum radiation is caused by an ionization equilibrium shift toward lower states, which strongly changes the value of the average recombination coefficient of metallic impurities anti γ, even for only slight changes in the average charge, anti Z. The primary agent for this shift is the charge exchange between the highly ionized impurity ions and the neutral hydrogen, rather than impurity transport, because the central density of the neutral hydrogen is strongly enhanced at lower plasma densities with intense beam injection. In the extreme case of low density, high neutral beam power TFTR operation (energetic ion mode) the reduction in anti γ can be as much as one-half to two-thirds. We calculate the parametric dependence of anti γ and anti Z for Ti, Cr, Fe, and Ni impurities on neutral density (equivalent to beam power), electron temperature, and electron density. These values are obtained by using either a one-dimensional impurity transport code (MIST) or a zero-dimensional code with a finite particle confinement time. As an example, we show the variation of anti γ and anti Z in different TFTR discharges

Theoretical study of the dependence of single impurity Anderson model on various parameters within distributional exact diagonalization method

Science.gov (United States)

Syaina, L. P.; Majidi, M. A.

2018-04-01

Single impurity Anderson model describes a system consisting of non-interacting conduction electrons coupled with a localized orbital having strongly interacting electrons at a particular site. This model has been proven successful to explain the phenomenon of metal-insulator transition through Anderson localization. Despite the well-understood behaviors of the model, little has been explored theoretically on how the model properties gradually evolve as functions of hybridization parameter, interaction energy, impurity concentration, and temperature. Here, we propose to do a theoretical study on those aspects of a single impurity Anderson model using the distributional exact diagonalization method. We solve the model Hamiltonian by randomly generating sampling distribution of some conducting electron energy levels with various number of occupying electrons. The resulting eigenvalues and eigenstates are then used to define the local single-particle Green function for each sampled electron energy distribution using Lehmann representation. Later, we extract the corresponding self-energy of each distribution, then average over all the distributions and construct the local Green function of the system to calculate the density of states. We repeat this procedure for various values of those controllable parameters, and discuss our results in connection with the criteria of the occurrence of metal-insulator transition in this system.

Impurity toroidal rotation and transport in Alcator C-Mod ohmic high confinement mode plasmas

International Nuclear Information System (INIS)

Rice, J. E.; Goetz, J. A.; Granetz, R. S.; Greenwald, M. J.; Hubbard, A. E.; Hutchinson, I. H.; Marmar, E. S.; Mossessian, D.; Pedersen, T. Sunn; Snipes, J. A.

2000-01-01

Central toroidal rotation and impurity transport coefficients have been determined in Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] Ohmic high confinement mode (H-mode) plasmas from observations of x-ray emission following impurity injection. Rotation velocities up to 3x10 4 m/sec in the co-current direction have been observed in the center of the best Ohmic H-mode plasmas. Purely ohmic H-mode plasmas display many characteristics similar to ion cyclotron range of frequencies (ICRF) heated H-mode plasmas, including the scaling of the rotation velocity with plasma parameters and the formation of edge pedestals in the electron density and temperature profiles. Very long impurity confinement times (∼1 sec) are seen in edge localized mode-free (ELM-free) Ohmic H-modes and the inward impurity convection velocity profile has been determined to be close to the calculated neoclassical profile. (c) 2000 American Institute of Physics

Analysis of Sulfidation Routes for Processing Weathered Ilmenite Concentrates Containing Impurities

Science.gov (United States)

Ahmad, Sazzad; Rhamdhani, M. Akbar; Pownceby, Mark I.; Bruckard, Warren J.

Rutile is the preferred feedstock for producing high-grade TiO2 pigment but due to decreasing resources, alternative materials such as ilmenite is now used to produce a synthetic rutile (SR) feedstock. This requires removal of impurities (e.g. Fe, Mg, Mn) which, for a primary ilmenite is straightforward process. Processing of weathered ilmenite however, is complex, especially when chrome-bearing impurities are present since minor chromium downgrades the SR market value as it imparts color to the final TiO2 pigment, Chrome-bearing spinels are a problem in weathered ilmenites from the Murray Basin, Australia as their physical and chemical properties overlap with ilmenite making separation difficult. In this paper, different sulfidation process routes for weathered ilmenites are analyzed for their applicability to Murray Basin deposits as a mean of remove chrome spinel impurities. Thermodynamic and experimental studies indicated that selective sulfidation of chrome-bearing spinel can be achieved under controlled pO2 and pS2 processing conditions thereby making them amenable to separation.

Euler European Libraries and Electronic Resources in Mathematical Sciences

CERN Document Server

The Euler Project. Karlsruhe

The European Libraries and Electronic Resources (EULER) Project in Mathematical Sciences provides the EulerService site for searching out "mathematical resources such as books, pre-prints, web-pages, abstracts, proceedings, serials, technical reports preprints) and NetLab (for Internet resources), this outstanding engine is capable of simple, full, and refined searches. It also offers a browse option, which responds to entries in the author, keyword, and title fields. Further information about the Project is provided at the EULER homepage.

The influence of impurities on the recovery of radiation defects in niobium

International Nuclear Information System (INIS)

Petzold, J.

1986-01-01

Pure niobium and doped niobium are irradiated with electrons (3 MeV) at a temperature of 7-8 K. During annealing the influence of the different impurities and of their doping concentration on the recovery of the electric conductivity are investigated. (BHO)

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

Effects of Electronic Information Resources Skills Training for Lecturers on Pedagogical Practices and Research Productivity

Science.gov (United States)

Bhukuvhani, Crispen; Chiparausha, Blessing; Zuvalinyenga, Dorcas

2012-01-01

Lecturers use various electronic resources at different frequencies. The university library's information literacy skills workshops and seminars are the main sources of knowledge of accessing electronic resources. The use of electronic resources can be said to have positively affected lecturers' pedagogical practices and their work in general. The…

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.)

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.

Tunneling spectroscopy of a phosphorus impurity atom on the Ge(111)-(2 × 1) surface

Energy Technology Data Exchange (ETDEWEB)

Savinov, S. V.; Oreshkin, A. I., E-mail: oreshkin@spmlab.phys.msu.su, E-mail: oreshkin@spmlab.ru [Moscow State University (Russian Federation); Oreshkin, S. I. [Moscow State University, Sternberg Astronomical Institute (Russian Federation); Haesendonck, C. van [Laboratorium voor Stoffysica en Magnetisme (Belgium)

2015-06-15

We numerically model the Ge(111)-(2 × 1) surface electronic properties in the vicinity of a P donor impurity atom located near the surface. We find a notable increase in the surface local density of states (LDOS) around the surface dopant near the bottom of the empty surface state band π*, which we call a split state due to its limited spatial extent and energetic position inside the band gap. We show that despite the well-established bulk donor impurity energy level position at the very bottom of the conduction band, a surface donor impurity on the Ge(111)-(2 × 1) surface might produce an energy level below the Fermi energy, depending on the impurity atom local environment. It is demonstrated that the impurity located in subsurface atomic layers is visible in a scanning tunneling microscope (STM) experiment on the Ge(111)-(2 × 1) surface. The quasi-1D character of the impurity image, observed in STM experiments, is confirmed by our computer simulations with a note that a few π-bonded dimer rows may be affected by the presence of the impurity atom. We elaborate a model that allows classifying atoms on the experimental low-temperature STM image. We show the presence of spatial oscillations of the LDOS by the density-functional theory method.

FLAPW Study of the EFG Tensor at Cd Impurities in In{sub 2}O{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Errico, L. A., E-mail: errico@fisica.unlp.edu.ar; Renteria, M.; Fabricius, G.; Darriba, G. N. [Universidad Nacional de La Plata, Departamento de Fisica, Facultad de Ciencias Exactas (Argentina)

2004-11-15

We report an ab initio study of the electric-field gradient tensor (EFG) at Cd impurities located at both nonequivalent cationic sites in the semiconductor In{sub 2}O{sub 3}. Calculations were performed with the FLAPW method that allows us to treat the electronic structure of the doped system and the atomic relaxations introduced by the impurities in the host in a fully self-consistent way. From our results for the EFG (in excellent agreement with the experiments), it is clear that the problem of the EFG at Cd impurities in In{sub 2}O{sub 3} cannot be described by the point-charge model and antishielding factors.

Discrete impurity band from surface danging bonds in nitrogen and phosphorus doped SiC nanowires

Science.gov (United States)

Li, Yan-Jing; Li, Shu-Long; Gong, Pei; Li, Ya-Lin; Cao, Mao-Sheng; Fang, Xiao-Yong

2018-04-01

The electronic structure and optical properties of the nitrogen and phosphorus doped silicon carbide nanowires (SiCNWs) are investigated using first-principle calculations based on density functional theory. The results show doping can change the type of the band gap and improve the conductivity. However, the doped SiCNWs form a discrete impurity levels at the Fermi energy, and the dispersion degree decreases with the diameter increasing. In order to reveal the root of this phenomenon, we hydrogenated the doped SiCNWs, found that the surface dangling bonds were saturated, and the discrete impurity levels are degeneracy, which indicates that the discrete impurity band of the doped SiCNWs is derived from the dangling bonds. The surface passivation can degenerate the impurity levels. Therefore, both doping and surface passivation can better improve the photoelectric properties of the SiCNWs. The result can provide additional candidates in producing nano-optoelectronic devices.

Numerical simulation of runaway electrons: 3-D effects on synchrotron radiation and impurity-based runaway current dissipation

Science.gov (United States)

del-Castillo-Negrete, D.; Carbajal, L.; Spong, D.; Izzo, V.

2018-05-01

Numerical simulations of runaway electrons (REs) with a particular emphasis on orbit dependent effects in 3-D magnetic fields are presented. The simulations were performed using the recently developed Kinetic Orbit Runaway electron Code (KORC) that computes the full-orbit relativistic dynamics in prescribed electric and magnetic fields including radiation damping and collisions. The two main problems of interest are synchrotron radiation and impurity-based RE dissipation. Synchrotron radiation is studied in axisymmetric fields and in 3-D magnetic configurations exhibiting magnetic islands and stochasticity. For passing particles in axisymmetric fields, neglecting orbit effects might underestimate or overestimate the total radiation power depending on the direction of the radial shift of the drift orbits. For trapped particles, the spatial distribution of synchrotron radiation exhibits localized "hot" spots at the tips of the banana orbits. In general, the radiation power per particle for trapped particles is higher than the power emitted by passing particles. The spatial distribution of synchrotron radiation in stochastic magnetic fields, obtained using the MHD code NIMROD, is strongly influenced by the presence of magnetic islands. 3-D magnetic fields also introduce a toroidal dependence on the synchrotron spectra, and neglecting orbit effects underestimates the total radiation power. In the presence of magnetic islands, the radiation damping of trapped particles is larger than the radiation damping of passing particles. Results modeling synchrotron emission by RE in DIII-D quiescent plasmas are also presented. The computation uses EFIT reconstructed magnetic fields and RE energy distributions fitted to the experimental measurements. Qualitative agreement is observed between the numerical simulations and the experiments for simplified RE pitch angle distributions. However, it is noted that to achieve quantitative agreement, it is necessary to use pitch angle

Identification and characterization of potential impurities of donepezil.

Science.gov (United States)

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.

Theory of Raman scattering in coupled electron-phonon systems

Science.gov (United States)

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.

Coulomb Impurity Problem of Graphene in Strong Coupling Regime in Magnetic Fields.

Science.gov (United States)

Kim, S C; Yang, S-R Eric

2015-10-01

We investigate the Coulomb impurity problem of graphene in strong coupling limit in the presence of magnetic fields. When the strength of the Coulomb potential is sufficiently strong the electron of the lowest energy boundstate of the n = 0 Landau level may fall to the center of the potential. To prevent this spurious effect the Coulomb potential must be regularized. The scaling function for the inverse probability density of this state at the center of the impurity potential is computed in the strong coupling regime. The dependence of the computed scaling function on the regularization parameter changes significantly as the strong coupling regime is approached.

Impurity Induced Phase Competition and Supersolidity

Science.gov (United States)

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.

Plasma-wall impurity experiments in ISX-A

International Nuclear Information System (INIS)

Colchin, R.J.; Bush, C.E.; Edmonds, P.H.; England, A.; Hill, K.W.; Isler, R.C.; Jernigan, T.C.; King, P.W.; Langley, R.A.; McNeill, D.H.; Murakami, M.; Neidigh, R.V.; Neilson, C.H.; Simpkins, J.E.; Wilgen, J.; DeBoo, J.C.; Burrell, K.H.; Ensberg, E.S.

1978-01-01

The ISX-A was a tokamak designed for studying plasma-wall interactions and plasma impurities. It fulfilled this role quite well, producing reliable and reproducible plasmas which had currents up to 175 kA and energy containment times up to 30 ms. With discharge precleaning, Zsub(eff) was as low as 1.6; with titanium evaporation. Zsub(eff) approached 1.0. Values of Zsub(eff) > approximately 2.0 were found to be proportional to residual impurity gases in the vacuum system immidiately following a discharge. However, there was no clear dependence of Zsub(eff) on base pressure. Stainless steel limiters were used in most of the ISX-A experiments. Upon introducing carbon limiters into the vacuum system, Zsub(eff) increased to 5.6. After twelve days of clean-up with tokamak discharges, during which time Zsub(eff) steadily decreased, the carbon limiters tended to give slightly higher values of Zsub(eff) than stainless steel limiters. Injection of 16 atoms of tungsten into discharges caused the power incident on the wall to double and the electron temperature profile to become hollow. (Auth.)

Tuning magnetocrystalline anisotropy of α″-Fe{sub 16}N{sub 2} by interstitial impurity doping: A first principles study

Energy Technology Data Exchange (ETDEWEB)

Khan, Imran; Hong, Jisang, E-mail: hongj@pknu.ac.kr

2017-07-01

Highlights: • The electronic structure and magnetic properties of 2s and 2p elements doped α″-Fe{sub 16}N{sub 2} were investigated. • The impurity doping induced local lattice distortions near the impurity site. • The local lattice distortion mainly contributed to enhance the magnetocrystalline anisotropy. • Almost 16% enhancement was achieved in coercive field due to enhancement of the magnetic anisotropy. • The maximum energy product was also enhanced due to impurity doping. - Abstract: The electronic structure and the magnetocrystalline anisotropy of impurity (Li, Be, B, C, and N) doped α″-Fe{sub 16}N{sub 2} were studied by using full potential linearized augmented plane wave method (FLAPW). From the formation energy calculations, it was evident that the 2s and 2p elements except Li could be easily doped into pure α″-Fe{sub 16}N{sub 2}. The impurity doping induced local lattice distortions near the impurity site and the magnetic moment near the impurity atom was substantially suppressed. However, the volume of the cell and the total magnetic moment of the doped systems were weakly suppressed compared to the pure α″-Fe{sub 16}N{sub 2}. Despite this relatively weak suppression in magnetization, the local distortion contributed to enhancing the magnetocrystalline anisotropy. Due to this enhancement in the anisotropy, the coercive field was also enhanced about 12–16% compared with that in pure structure. Along with the enlarged coercive field, the energy product was also increased. These results may suggest that impurity doped α″-Fe{sub 16}N{sub 2} can be used as potential rare earth free permanent magnet.

Electronic Commerce Resource Centers. An Industry--University Partnership.

Science.gov (United States)

Gulledge, Thomas R.; Sommer, Rainer; Tarimcilar, M. Murat

1999-01-01

Electronic Commerce Resource Centers focus on transferring emerging technologies to small businesses through university/industry partnerships. Successful implementation hinges on a strategic operating plan, creation of measurable value for customers, investment in customer-targeted training, and measurement of performance outputs. (SK)

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

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

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.)

Behaviour of impurities during the H-mode in JET

International Nuclear Information System (INIS)

Gianella, R.; Behringer, K.; Denne, B.; Gottardi, N.; Hellermann, M. von; Morgan, P.D.; Pasini, D.; Stamp, M.F.

1989-01-01

In additionally-heated tokamak discharges, the H-mode phases are reported to display, together with a better energy confinement, a longer global containment time for particles. In particular, steep gradients of electron density and temperature are sustained in the outer region of the plasma column. This enhanced performance is observed especially in discharges in which the activity of edge localized modes (ELMs) is low or absent. High confinement and accumulation of metallic impurities, which quickly give raise to terminal disruptions have been described under similar conditions. In JET H-modes very long impurity confinement times are also observed. However the experimental condition is somewhat more favourable since quiescent H-modes are obtained lasting much longer than the energy confinement times and the radiation from metals is generally negligible. The dominant impurities are normally carbon and oxygen, the latter generally accounting for half or more of the power radiated from the bulk plasma. During the X-point operation the effective influx of carbon into the discharge, which is normally in close correlation with that of deuterium, is substantially reduced while the influx of oxygen, whose production mechanisms is believed to be of a chemical nature, does not show significant variations. (author) 5 refs., 4 figs

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

Impurity incorporation, deposition kinetics, and microstructural evolution in sputtered Ta films

Science.gov (United States)

Whitacre, Jay Fredric

There is an increasing need to control the microstructure in thin sputtered Ta films for application as high-temperature coatings or diffusion barriers in microelectronic interconnect structures. To this end, the relationship between impurity incorporation, deposition kinetics, and microstructural evolution was examined for room-temperature low growth rate DC magnetron sputtered Ta films. Impurity levels present during deposition were controlled by pumping the chamber to various base pressures before growth. Ar pressures ranging from 2 to 20 mTorr were used to create contrasting kinetic environments in the sputter gas. This affected both the distribution of adatom kinetic energies at the substrate as well as the rate of impurity desorption from the chamber walls: at higher Ar pressures adatoms has lower kinetic energies, and there was an increase in impurity concentration. X-ray diffraction, high-resolution transmission electron microscopy (HREM), transmission electron diffraction (TED), scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS), and x-ray photoelectron. spectroscopy (XPS) were used to examine film crystallography, microstructure, and composition. A novel laboratory-based in-situ x-ray diffractometer was constructed. This new set-up allowed for the direct observation of microstructural evolution during growth. Films deposited at increasingly higher Ar pressures displayed a systematic decrease in grain size and degree of texturing, while surface morphology was found to vary from a nearly flat surface to a rough surface with several length scales of organization. In-situ x-ray results showed that the rate of texture evolution was found to be much higher in films grown using lower Ar pressures. These effects were studied in films less than 200 A thick using high resolution x-ray diffraction in conjunction with a synchrotron light source (SSRL B.L. 7-2). Films grown using higher Ar pressures (above 10 mTorr) with a pre-growth base

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

On the role of impurity radiation on edge turbulence in the TJ-1 Tokamak

International Nuclear Information System (INIS)

Ochando, M.A.; Pedrosa, M.A.; Balbin, R.; Garcia-Cortes, I.; Hidalgo, C.

1994-01-01

The correlation between edge radiation and electron temperature and density fluctuations has been studied in the vicinity of the upper poloidal limiter of the TJ-I tokamak. When edge impurity radiation is strongly raked in the proximity of the limiter radius, electron temperature fluctuations are notably higher than density fluctuations. Results provide experimental evidence of edge turbulence driven by thermal instabilities

Optical-absorption spectra associated with shallow donor impurities in GaAs-(Ga,Al)As quantum-dots

International Nuclear Information System (INIS)

Silva Valencia, J.

1995-08-01

The binding energy of a hydrogenic donor impurity and the optical-absorption spectra associated with transitions between the n=1 valence level and the donor-impurity band were calculated for infinite barrier-well spherical GaAs-(Ga,Al)As quantum-dots of different radii, using the effective mass approximation within a variational scheme. An absorption peak associated with transitions involving impurities at the center of the well and a peak related with impurities at the edge of the dot were the main features observed for the different radii of the dots considered in the calculations. Also as a result of the higher electronic confinement in a quantum- dot, we found a much wider energy range of the absorption spectra when compared to infinite GaAs-(Ga,Al)As quantum-wells and quantum-well wires of width and diameter comparable to the diameter of the quantum dot. (author). 13 refs, 3 figs

Low-Z impurities in PLT

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

Influence of complex impurity centres on radiation damage in wide-gap metal oxides

Energy Technology Data Exchange (ETDEWEB)

Lushchik, A., E-mail: aleksandr.lushchik@ut.ee [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia); Lushchik, Ch. [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia); Popov, A.I. [Institute of Solid State Physics, University of Latvia, Kengaraga 8, Riga LV-1063 (Latvia); Schwartz, K. [GSI Helmholtzzentrum für Schwerionenforschung (GSI), Planckstr. 1, 64291 Darmstadt (Germany); Shablonin, E.; Vasil’chenko, E. [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia)

2016-05-01

Different mechanisms of radiation damage of wide-gap metal oxides as well as a dual influence of impurity ions on the efficiency of radiation damage have been considered on the example of binary ionic MgO and complex ionic–covalent Lu{sub 3}Al{sub 5}O{sub 12} single crystals. Particular emphasis has been placed on irradiation with ∼2 GeV heavy ions ({sup 197}Au, {sup 209}Bi, {sup 238}U, fluence of 10{sup 12} ions/cm{sup 2}) providing extremely high density of electronic excitations within ion tracks. Besides knock-out mechanism for Frenkel pair formation, the additional mechanism through the collapse of mobile discrete breathers at certain lattice places (e.g., complex impurity centres) leads to the creation of complex defects that involve a large number of host atoms. The experimental manifestations of the radiation creation of intrinsic and impurity antisite defects (Lu|{sub Al} or Ce|{sub Al} – a heavy ion in a wrong cation site) have been detected in LuAG and LuAG:Ce{sup 3+} single crystals. Light doping of LuAG causes a small enhancement of radiation resistance, while pair impurity centres (for instance, Ce|{sub Lu}–Ce|{sub Al} or Cr{sup 3+}–Cr{sup 3+} in MgO) are formed with a rise of impurity concentration. These complex impurity centres as well as radiation-induced intrinsic antisite defects (Lu|{sub Al} strongly interacting with Lu in a regular site) tentatively serve as the places for breathers collapse, thus decreasing the material resistance against dense irradiation.

The influence of alkali metal impurities on the uranium dioxide hydrofluorination reaction

International Nuclear Information System (INIS)

Ponelis, A.A.

1989-01-01

The effect alkali metal impurities (sodium and potassium) in the uranium dioxide (UO 2 ) feed material have on the conversion to uraniumtetrafluoride (UF 4 ) was examined. A direct correlation exists between impurity level and sintering with concomitant reduced conversion. The sintering mechanism is attributable to decreased specific surface area. The typical 'die-off' of reaction or conversion can be explained in terms of increased particle growth rather than an arbitray zero porosity function. Hydrofluorination temperatures varied from 250 to 650 degrees C using pellets varying in size from 0.42 mm to 10 mm. Scanning electron microscope photographs show clearly the particle or grain growth in the pellet as well as the increased size with impurity level. A new dimensionless constant, N KP , is defined to facilitate explanation of the reaction as a function of pellet radius. N KP is defined as the ratio of pellet diffusion resistance to particle diffusion resistance of the reacting HF gas. At high values of this number (N KP >40) the conversion is limited to the outer periphery of the pellet while at low values (N KP KP at higher reaction temperatures which means that the particle diffusion resistance increases with increasing impurity level and results in easier sintering of these materials. 53 refs., 206 figs., 94 tabs

Impurity Correction Techniques Applied to Existing Doping Measurements of Impurities in Zinc

Science.gov (United States)

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.

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

The electrical conductivity of an interacting electron gas

International Nuclear Information System (INIS)

Kojima, D.Y.

1977-01-01

A manybody theory by the propagator method developed by Montroll and Ward for the equilibrium statistical mechanics, is reformulated to describe the electrical conductivity for an electron gas system containing impurity. The theory includes electron-impurity interaction to the infinite order and electron-electron interaction to the first order exchange effect. The propagator used by Montroll and Ward is separated into two propagators, each of which satisfies either Bloch or Schroedinger equation, to utilize the perturbation method. Correct counting of graphs are presented. Change in the relaxation time due to the electron-electron interaction is explicity shown and compared with recent works [pt

Spectroscopic system for impurity measurements in the TJ-1 Tokamak of JEN

International Nuclear Information System (INIS)

Navas, G.; Zurro, B.

1982-01-01

we describe a spectroscopic system with spatial resolution capability that has been configured for plasma diagnostic in the TJ-1 Tokamak of JEN. The experimental system, based on a one meter monochromator, has been absolutely calibrated using a tungsten-halogen lamp. The calibration procedures and the absolute spectral sensitivity are presented as well as its dependence with the polarization. A simplified spectroscopic model of the radiation emitted by the intrinsic plasma impurities (C, 0, . . . ) has been developed. A one dimensional model of the temporal evolution of various ionization stages in coronal equilibrium is used to predict the electron temperature and impurity concentration. This model has been applied to experimental data from several Tokamaks. (Author) 23 refs

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

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)

Collision of impurities with Bose–Einstein condensates

Science.gov (United States)

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.

Enhanced ionized impurity scattering in nanowires

Science.gov (United States)

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)].

First-principles calculations of impurity diffusion coefficients in dilute Mg alloys using the 8-frequency model

International Nuclear Information System (INIS)

Ganeshan, S.; Hector, L.G.; Liu, Z.-K.

2011-01-01

Research highlights: → Implemented the eight frequency model for impurity diffusion in hexagonal metals. → Model inputs were energetics/vibrational properties from first princples. → Predicted diffusion coefficients for Al, Ca, Zn and Sn impurity diffusion in Mg. → Successful prediction of partial correlation factors and jump frequencies. → Good agreement between calculated and experimental results. - Abstract: Diffusion in dilute Mg-X alloys, where X denotes Al, Zn, Sn and Ca impurities, was investigated with first-principles density functional theory in the local density approximation. Impurity diffusion coefficients were computed as a function of temperature using the 8-frequency model which provided the relevant impurity and solvent (Mg) jump frequencies and correlation factors. Minimum energy pathways for impurity diffusion and associated saddle point structures were computed with the climbing image nudged elastic band method. Vibrational properties were obtained with the supercell (direct) method for lattice dynamics. Calculated diffusion coefficients were compared with available experimental data. For diffusion between basal planes, we find D Mg-Ca > D Mg-Zn > D Mg-Sn > D Mg-Al, where D is the diffusion coefficient. For diffusion within a basal plane, the same trend holds except that D Mg-Zn overlaps with D Mg-Al at high temperatures and D Mg-Sn at low temperatures. These trends were explored with charge density contours in selected planes of each Mg-X alloy, the variation of the activation energy for diffusion with the atomic radius of each impurity and the electronic density of states. The theoretical methodology developed herein can be applied to impurity diffusion in other hexagonal materials.

Rotation characteristics of main ions and impurity ions in H-mode tokamak plasma

International Nuclear Information System (INIS)

Kim, J.; Burrell, K.H.; Gohil, P.; Groebner, R.J.; Kim, Y.; St. John, H.E.; Seraydarian, R.P.; Wade, M.R.

1994-01-01

Poloidal and toroidal rotation of the main ions (He 2+ ) and the impurity ions (C 6+ and B 5+ ) in H-mode helium plasmas have been measured via charge exchange recombination spectroscopy in the DIII-D tokamak. It was discovered that the main ion poloidal rotation is in the ion diamagnetic drift direction while the impurity ion rotation is in the electron diamagnetic drift direction, in qualitative agreement with the neoclassical theory. The deduced radial electric field in the edge is of the same negative-well shape regardless of which ion species is used, validating the fundamental nature of the electric field in L-H transition phenomenology

Electronic transport properties of Ti-impurity band in Si

Energy Technology Data Exchange (ETDEWEB)

Olea, J; Gonzalez-Diaz, G; Pastor, D; Martil, I [Departamento de Fisica Aplicada III (Electricidad y Electronica), Facultad de Ciencias, Fisicas, Universidad Complutense, E-28040 Madrid (Spain)

2009-04-21

In this paper we show that pulsed laser melted high dose implantation of Ti in Si, above the Mott transition, produces an impurity band (IB) in this semiconductor. Using the van der Pauw method and Hall effect measurements we find strong laminated conductivity at the implanted layer and a temperature dependent decoupling between the Ti implanted layer (TIL) and the substrate. The conduction mechanism from the TIL to the substrate shows blocking characteristics that could be well explained through IB theory. Using the ATLAS code we can estimate the energetic position of the IB at 0.36 eV from the conduction band, the density of holes in this band which is closely related to the Ti atomic density and the hole mobility in this band. Band diagrams of the structure at low and high temperatures are also simulated in the ATLAS framework. The simulation obtained is fully coherent with experimental results.

Electronic transport properties of Ti-impurity band in Si

International Nuclear Information System (INIS)

Olea, J; Gonzalez-Diaz, G; Pastor, D; Martil, I

2009-01-01

In this paper we show that pulsed laser melted high dose implantation of Ti in Si, above the Mott transition, produces an impurity band (IB) in this semiconductor. Using the van der Pauw method and Hall effect measurements we find strong laminated conductivity at the implanted layer and a temperature dependent decoupling between the Ti implanted layer (TIL) and the substrate. The conduction mechanism from the TIL to the substrate shows blocking characteristics that could be well explained through IB theory. Using the ATLAS code we can estimate the energetic position of the IB at 0.36 eV from the conduction band, the density of holes in this band which is closely related to the Ti atomic density and the hole mobility in this band. Band diagrams of the structure at low and high temperatures are also simulated in the ATLAS framework. The simulation obtained is fully coherent with experimental results.

On the Role of Impurity Radiation on Edge Turbulence in the TJ-I Tokamak

International Nuclear Information System (INIS)

Ochando, M. A.; Pedrosa, M. A.; Balbin, R.; Garcia-Cortes, I.; Hidalgo, C.

1994-01-01

The correlation between edge radiation and electron temperature and density fluctuations has been studied in the vicinity of the upper poloidal limiter of the TJ-I tokamak. When edge impurity radiation is strongly peaked in the proximity of the limiter radius, electron temperature fluctuations are notably higher than density fluctuations. Results provide experimental evidence of edge turbulence driven by thermal instabilities. (Author) 16 refs

On the Role of Impurity Radiation on Edge Turbulence in the TJ-I Tokamak

Energy Technology Data Exchange (ETDEWEB)

Ochando, M A; Pedrosa, M A; Balbin, R; Garcia-Cortes, I; Hidalgo, C

1994-07-01

The correlation between edge radiation and electron temperature and density fluctuations has been studied in the vicinity of the upper poloidal limiter of the TJ-I tokamak. When edge impurity radiation is strongly peaked in the proximity of the limiter radius, electron temperature fluctuations are notably higher than density fluctuations. Results provide experimental evidence of edge turbulence driven by thermal instabilities. (Author) 16 refs.

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)

Impurity bound states in mesoscopic topological superconducting loops

Science.gov (United States)

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.

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

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.)

Plasma-wall impurity experiments in ISX-A

International Nuclear Information System (INIS)

Colchin, R.J.; Bush, C.E.; Edmonds, P.H.

1978-08-01

The ISX-A was a tokamak designed for studying plasma-wall interactions and plasma impurities. It fulfilled this role quite well, producing reliable and reproducible plasmas which had currents up to 175 kA and energy containment times up to 30 msec. With discharge precleaning, Z/sub eff/ was as low as 1.6; with titanium evaporation, Z/sub eff/ approached 1.0. Values of Z/sub eff/ greater than or equal to 2.0 were found to be proportional to residual impurity gases in the vacuum system immediately following a discharge. However, there was no clear dependence of Z/sub eff/ on base pressure. Stainless steel limiters were used in most of the ISX-A experiments. When carbon limiters were introduced into the vacuum system, Z/sub eff/ increased to 5.6. After twelve days of cleanup with tokamak discharges, during which time Z/sub eff/ steadily decreased, the carbon limiters tended to give slightly higher values of Z/sub eff/ than stainless steel limiters. Injection of less than 10 16 atoms of tungsten into discharges caused the power incident on the wall to double and the electron temperature profile to become hollow

Methane impurity production in the fusion reactor environment

International Nuclear Information System (INIS)

Dawson, P.T.

1984-11-01

Fusion requires temperatures of the order of 10 8 degrees C. In order to attain the required temperature it will be essential to minimise the energy losses from the plasma. Impurities are a major cause of plasma cooling. Ionization of impurity species in the plasma leads to a subsequent decay and emission of radiation. The most common low Z contaminants to be consideed are water and methane produced by reaction of hydrogen isotopes with oxygen and carbon. This review focuses on the methane production problem. We will be concerned with the sources of carbon in the reactor and also with the reactivity of carbon with hydrogen molecules, atoms and ions and the synergistic effects which can arise from coincident fluxes of electrons and photons and the effects of radiation-induced damage of the materials involved. While the reactor first wall will provide the most hostile environment for methane producton, most of the reactions discussed can occur in breeder blankets and also in other tritium facilities such as fuel handling, purification and storage facilities

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

USE OF ELECTRONIC EDUCATIONAL RESOURCES WHEN TRAINING IN WORK WITH SPREADSHEETS

Directory of Open Access Journals (Sweden)

Х А Гербеков

2017-12-01

Full Text Available Today the tools for maintaining training courses based on opportunities of information and communication technologies are developed. Practically in all directions of preparation and on all subject matters electronic textbook and self-instruction manuals are created. Nevertheless the industry of computer educational and methodical materials actively develops and gets more and more areas of development and introduction. In this regard more and more urgent is a problem of development of the electronic educational resources adequate to modern educational requirements. Creation and the organization of training courses with use of electronic educational resources in particular on the basis of Internet technologies remains a difficult methodical task.In article the questions connected with development of electronic educational resources for use when studying the substantial line “Information technologies” of a school course of informatics in particular for studying of spreadsheets are considered. Also the analysis of maintenance of a school course and the unified state examination from the point of view of representation of task in him corresponding to the substantial line of studying “Information technologies” on mastering technology of information processing in spreadsheets and the methods of visualization given by means of charts and schedules is carried out.

Mobile impurities in ferromagnetic liquids

Science.gov (United States)

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 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

Science.gov (United States)

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.

Impurities, temperature, and density in a miniature electrostatic plasma and current source

International Nuclear Information System (INIS)

Den Hartog, D.J.; Craig, D.J.; Fiksel, G.; Sarff, J.S.

1996-10-01

We have spectroscopically investigated the Sterling Scientific miniature electrostatic plasma source-a plasma gun. This gun is a clean source of high density (10 19 - 10 20 m -3 ), low temperature (5 - 15 eV) plasma. A key result of our investigation is that molybdenum from the gun electrodes is largely trapped in the internal gun discharge; only a small amount escapes in the plasma flowing out of the gun. In addition, the gun plasma parameters actually improve (even lower impurity contamination and higher ion temperature) when up to 1 kA of electron current is extracted from the gun via the application of an external bias. This improvement occurs because the internal gun anode no longer acts as the current return for the internal gun discharge. The gun plasma is a virtual plasma electrode capable of sourcing an electron emission current density of 1 kA/cm 2 . The high emission current, small size (3 - 4 cm diameter), and low impurity generation make this gun attractive for a variety of fusion and plasma technology applications

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)

Effect of impurities on the performance of lithium intended for lithium/thionyl chloride battery manufacture

Energy Technology Data Exchange (ETDEWEB)

Hagan, W P; Hampson, N A; Packer, R K

1988-09-01

The elemental impurities in four different, commercially-available lithium samples have been determined. Cells consisting of these lithium samples as anodes and pressed acetylene black as cathodes were discharged at 20 C and at 70 C at a rate of 50 mA/sq cm. The passivating films remaining on the lithium surface after discharge were examined using electron microscopy and their elemental compositions determined using the surface sensitive technique of X-ray photoelectron spectroscopy. Performance characteristics (voltage and capacity) of test cells consisting, in part, of the different lithium samples are discussed in terms of impurity concentrations determined by secondary ion mass spectrometry and atomic absorption spectroscopy. The permeability and electronic conductivity of the LiCl passivating films are adduced as two possible reasons for the variations in capacity and on-load voltage of the different lithium samples. 25 references.

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)

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

Influence of argon impurities on the elastic scattering of x-rays from imploding beryllium capsules

Science.gov (United States)

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.

Conductivity of the electron-impurity system

International Nuclear Information System (INIS)

Goettig, S.

1983-09-01

The free-carrier absorption of electromagnetic radiation due to the presence of static scatterers is examined taking into account the electron-electron interaction, the plasma-phonon polar coupling and the plasma anisotropy. For the case of strong coupling in the isotropic plasma the absorption due to the collective-mode excitation processes is, for frequencies just above the plasmon-like collective mode frequency, shown to be dominant over the absorption due to single-particle excitations. The expression for the frequency-dependent absorptive part of the conductivity due to the long-wavelength collective-mode excitations is derived for the case of multicomponent anisotropic degenerate plasma (e.g. lead chalcogenides). The results are discussed in detail and compared with available experimental data for n-PbSe. The comparison with the previous theories is also given. (author)

A computational study on tuning the field emission and electronic properties of BN nanocones by impurity atom doping

Science.gov (United States)

Ahmadi, S.; Delir Kheirollahi Nezhad, P.; Hosseinian, A.; Vessally, E.

2018-06-01

We have inspected the effect of substituting a boron or nitrogen atom of a BN nanocone (BNNC) by two impurity atoms with lower and higher atomic numbers based on the density functional theory calculations. Our results explain the experimental observations in a molecular level. Orbital and partial density of states analyses show that the doping processes increase the electrical conductivity by creating new states within the gap of BNNC as follows: BeB > ON > CB > CN. The electron emission current from the surface of BNNC is improved after the CB and BeB dopings, and it is decreased by CN and ON dopings. The BeB and CN dopings make the BNNC a p-type semiconductor and the CB and ON dopings make it an n-type one in good agreement with the experimental results. The ON and BeB doping processes are suggested for the field emission current, and electrical conductivity enhancement, respectively.

Effect of iodine impurity on relaxation of photoexcited silver chloride

International Nuclear Information System (INIS)

Vostrikova, Yu. V.; Klyuev, V. G.

2008-01-01

The time and temperature dependences of relaxation of excited AgCl and AgCl:I crystals is studied by the method of photostimulated flash of luminescence. The presence of iodine impurity in silver chloride gives rise to hole recombination (luminescence) centers and hole traps in the band gap. It is shown that the main contribution to the decrease in the concentration of electrons localized at deep traps is made by the recombination of electrons with holes released thermally from shallow localization levels (iodine-related centers). Estimation of activation energy for the relaxation process showed that these energies for the AgCl and AgCl:I samples under study are the same within the experimental error and are equal to E rel1 = 0.01 ± 0.0005 eV for the initial stage of relaxation and E rel2 = 0.09 ± 0.005 eV for the final state. This fact indicates that the majority of hole traps involved in the relaxation process in AgCl are related to iodine impurity. In the course of thermal relaxation in AgCl, relocalization of nonequilibrium charge carriers from shallow levels to deep levels is observed. The depth of the corresponding trap is E arl = 0.174 ± 0.03 eV.

Method for detecting trace impurities in gases

Science.gov (United States)

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

Science.gov (United States)

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.

Impurity control in TFTR

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...

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)

Analytical Study of Usage of Electronic Information Resources at Pharmacopoeial Libraries in India

Directory of Open Access Journals (Sweden)

Sunil Tyagi

2014-02-01

Full Text Available The objective of this study is to know the rate and purpose of the use of e-resource by the scientists at pharmacopoeial libraries in India. Among other things, this study examined the preferences of the scientists toward printed books and journals, electronic information resources, and pattern of using e-resources. Non-probability sampling specially accidental and purposive technique was applied in the collection of primary data through administration of user questionnaire. The sample respondents chosen for the study consists of principle scientific officer, senior scientific officer, scientific officer, and scientific assistant of different division of the laboratories, namely, research and development, pharmaceutical chemistry, pharmacovigilance, pharmacology, pharmacogonosy, and microbiology. The findings of the study reveal the personal experiences and perceptions they have had on practice and research activity using e-resource. The major findings indicate that of the total anticipated participants, 78% indicated that they perceived the ability to use computer for electronic information resources. The data analysis shows that all the scientists belonging to the pharmacopoeial libraries used electronic information resources to address issues relating to drug indexes and compendia, monographs, drugs obtained through online databases, e-journals, and the Internet sources—especially polices by regulatory agencies, contacts, drug promotional literature, and standards.

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

Page 170 Use of Electronic Resources by Undergraduates in Two ...

African Journals Online (AJOL)

undergraduate students use electronic resources such as NUC virtual library, HINARI, ... web pages articles from magazines, encyclopedias, pamphlets and other .... of Nigerian university libraries have Internet connectivity, some of the system.

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.)

Influence of impurities on the crystallization of dextrose monohydrate

Science.gov (United States)

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.

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.

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)

Model of e-learning with electronic educational resources of new generation

Directory of Open Access Journals (Sweden)

A. V. Loban

2017-01-01

Full Text Available Purpose of the article: improving of scientific and methodical base of the theory of the е-learning of variability. Methods used: conceptual and logical modeling of the е-learning of variability process with electronic educational resource of new generation and system analysis of the interconnection of the studied subject area, methods, didactics approaches and information and communication technologies means. Results: the formalization complex model of the е-learning of variability with electronic educational resource of new generation is developed, conditionally decomposed into three basic components: the formalization model of the course in the form of the thesaurusclassifier (“Author of e-resource”, the model of learning as management (“Coordination. Consultation. Control”, the learning model with the thesaurus-classifier (“Student”. Model “Author of e-resource” allows the student to achieve completeness, high degree of didactic elaboration and structuring of the studied material in triples of variants: modules of education information, practical task and control tasks; the result of the student’s (author’s of e-resource activity is the thesaurus-classifier. Model of learning as management is based on the principle of personal orientation of learning in computer environment and determines the logic of interaction between the lecturer and the student when determining the triple of variants individually for each student; organization of a dialogue between the lecturer and the student for consulting purposes; personal control of the student’s success (report generation and iterative search for the concept of the class assignment in the thesaurus-classifier before acquiring the required level of training. Model “Student” makes it possible to concretize the learning tasks in relation to the personality of the student and to the training level achieved; the assumption of the lecturer about the level of training of a

An S=1/2 impurity spin in the antiferromagnetic S=1 bond-alternating chain

Energy Technology Data Exchange (ETDEWEB)

Ogawa, Nobuyuki [Gifu National College of Technology, Dept. of Fundamental Science, Gifu (Japan); Hikihara, Toshiya [National Inst. for Materials Science, Computational Material Research Group, Tsukuba, Ibaraki (Japan); Kaburagi, Makoto [Kobe Univ., Faculty of Cross-Cultural Studies, Kobe, Hyogo (Japan); Tonegawa, Takashi [Fukui Univ. of Technology, Dept. of Mechanical Engineering, Fukui (Japan)

2002-06-01

We explore low-lying excited states as well as the ground state of the antiferromagnetic S=1 bond-alternating chain with an S=1/2 impurity spin. For the case where the ground-state phase of the host system is the Haldane phase, we review a numerical analysis of the electron-spin-resonance experimental results on the NENP: Cu{sup 2+} system. For the case where the ground-state phase of the host system is the dimer phase, on the other hand, we calculate, using the exact-diagonalization method, the dependences of the energy differences between the ground and low-lying excited states upon both the impurity-host exchange constant and the single-ion-type anisotropy constant, and also calculate, using the density-matrix renormalization-group method, the external-magnetic-field dependence of the impurity-spin magnetization in the ground state. In these calculations, we keep the NTENP: Cu{sup 2+} system in mind to choose the value of the bond-alternation parameter. We find that a few low-lying excited states which are expected from the valence-bond-solid picture appear as the impurity states in the energy gap between the singlet ground and triplet first-excited states (the dimer gap). Furthermore, for certain values of the above constants, we find that the impurity-spin magnetization shows a clear jump at a magnetic field which is in the dimer-gap region or in the magnetization-plateau region of the host system, and also that the impurity-spin magnetization has a magnetic-field region where it decreases as a function of the magnetic field. (author)

Spectroscopic investigation of heavy impurity behaviour during ICRH with the JET ITER-like wall

Energy Technology Data Exchange (ETDEWEB)

Czarnecka, A. [Institute of Plasma Physics and Laser Microfusion, Association EURATOM-IPPLM, Hery 23 Str., 01-497 Warsaw (Poland); Bobkov, V.; Maggi, C.; Pütterich, T. [Max-Planck-Institut für Plasmaphysik, EURATOM-Association, D-85748 Garching (Germany); Coffey, I. H. [Department of Physics, Queen' s University, Belfast, BT7 1NN, Northern Ireland (United Kingdom); Colas, L. [CEA, IRFM, F-13108 Saint-Paul-Lez-Durance (France); Jacquet, P.; Lawson, K. D. [Euratom/CCFE Association, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Lerche, E.; Van Eester, D. [Association EURATOM - Belgian State, ERM-KMS, TEC Partner (Belgium); Mayoral, M.-L. [Euratom/CCFE Association, Culham Science Centre, Abingdon, OX14 3DB, UK and EFDA Close Support Unit, Garching (Germany); Collaboration: JET-EFDA Contributors

2014-02-12

Magnetically confined plasmas, such as those produced in the tokamak JET, contain measurable amounts of impurity ions produced during plasma-wall interactions (PWI) from the plasma-facing components and recessed wall areas. The impurities, including high- and mid-Z elements such as tungsten (W) from first wall tiles and nickel (Ni) from Inconel structure material, need to be controlled within tolerable limits, to ensure they do not significantly affect the performance of the plasma. This contribution focuses on documenting W and Ni impurity behavior during Ion Cyclotron Resonance Heating (ICRH) operation with the new ITER-Like Wall (ILW). Ni- and W-concentration were derived from VUV spectroscopy and the impact of applied power level, relative phasing of the antenna straps, plasma separatrix - antenna strap distance, IC resonance position, edge density and different plasma configuration, on the impurity release during ICRH are presented. For the same ICRH power the Ni and W concentration was lower with dipole phasing than in the case of −π/2 phasing. The Ni concentration was found to increase with ICRH power and for the same NBI power level, ICRH-heated plasmas were characterized by two times higher Ni impurity content. Both W and Ni concentrations increased strongly with decreasing edge density which is equivalent to higher edge electron temperatures and more energetic ions responsible for the sputtering. In either case higher levels were found in ICRH than in NBI heated discharges. When the central plasma temperature was similar, ICRH on-axis heating resulted in higher core Ni impurity concentration in comparison to off-axis ICRH in L-mode. It was also found that the main core radiation during ICRH came from W.

Effect of impurity correlation on the density of states in slightly compensated heavily doped semiconductors

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

Radiated Power and Impurity Concentrations in the EXTRAP-T2R Reversed-Field Pinch

Science.gov (United States)

Corre, Y.; Rachlew, E.; Cecconello, M.; Gravestijn, R. M.; Hedqvist, A.; Pégourié, B.; Schunke, B.; Stancalie, V.

2005-01-01

A numerical and experimental study of the impurity concentration and radiation in the EXTRAP-T2R device is reported. The experimental setup consists of an 8-chord bolometer system providing the plasma radiated power and a vacuum-ultraviolet spectrometer providing information on the plasma impurity content. The plasma emissivity profile as measured by the bolometric system is peaked in the plasma centre. A one dimensional Onion Skin Collisional-Radiative model (OSCR) has been developed to compute the density and radiation distributions of the main impurities. The observed centrally peaked emissivity profile can be reproduced by OSCR simulations only if finite particle confinement time and charge-exchange processes between plasma impurities and neutral hydrogen are taken into account. The neutral hydrogen density profile is computed with a recycling code. Simulations show that recycling on metal first wall such as in EXTRAP-T2R (stainless steel vacuum vessel and molybdenum limiters) is compatible with a rather high neutral hydrogen density in the plasma centre. Assuming an impurity concentration of 10% for oxygen and 3% for carbon compared with the electron density, the OSCR calculation including lines and continuum emission reproduces about 60% of the total radiated power with a similarly centrally peaked emissivity profile. The centrally peaked emissivity profile is due to low ionisation stages and strongly radiating species in the plasma core, mainly O4+ (Be-like) and C3+ Li-like.

Radiated Power and Impurity Concentrations in the EXTRAP-T2R Reversed-Field Pinch

International Nuclear Information System (INIS)

Corre, Y.; Rachlew, E.; Gravestijn, R.M.; Hedqvist, A.; Stancalie, V.

2005-01-01

A numerical and experimental study of the impurity concentration and radiation in the EXTRAP-T2R device is reported. The experimental setup consists of an 8-chord bolometer system providing the plasma radiated power and a vacuum ultraviolet spectrometer providing information on the plasma impurity content. The plasma emissivity profile as measured by the bolometric system is peaked in the plasma centre. A one dimensional Onion Skin Collisional-Radiative model (OSCR) has been developed to compute the density and radiation distributions of the main impurities. The observed centrally peaked emissivity profile can be reproduced by OSCR simulations only if finite particle confinement time and charge-exchange processes between plasma impurities and neutral hydrogen are taken into account. The neutral hydrogen density profile is computed with a recycling code. Simulations show that recycling on metal first wall such as in EXTRAP-T2R (stainless steel vacuum vessel and molybdenum limiters) is compatible with a rather high neutral hydrogen density in the plasma centre. Assuming an impurity concentration of 10% for oxygen and 3% for carbon compared with the electron density, the OSCR calculation including lines and continuum emission reproduces about 60% of the total radiated power with a similarly centrally peaked emissivity profile. The centrally peaked emissivity profile is due to low ionisation stages and strongly radiating species in the plasma core, mainly O 4+ (Be-like) and C 3+ (Li-like)

A survey of the use of electronic scientific information resources among medical and dental students

Directory of Open Access Journals (Sweden)

Aarnio Matti

2006-05-01

Full Text Available Abstract Background To evaluate medical and dental students' utilization of electronic information resources. Methods A web survey sent to 837 students (49.9% responded. Results Twenty-four per cent of medical students and ninteen per cent of dental students searched MEDLINE 2+ times/month for study purposes, and thiry-two per cent and twenty-four per cent respectively for research. Full-text articles were used 2+ times/month by thirty-three per cent of medical and ten per cent of dental students. Twelve per cent of respondents never utilized either MEDLINE or full-text articles. In multivariate models, the information-searching skills among students were significantly associated with use of MEDLINE and full-text articles. Conclusion Use of electronic resources differs among students. Forty percent were non-users of full-text articles. Information-searching skills are correlated with the use of electronic resources, but the level of basic PC skills plays not a major role in using these resources. The student data shows that adequate training in information-searching skills will increase the use of electronic information resources.

Influence of an ergodic magnetic limiter on the impurity content in a tokamak

International Nuclear Information System (INIS)

Engelhardt, W.; Feneberg, W.

1978-01-01

This work deals with the properties of an ergodic magnetic limiter and presents calculations concerning the reduction of the impurity rate in a tokamak by a boundary sheath with decreased confinement time. The layer is produced by resonant helical windings superposed on an equilibrium magnetic field with closed magnetic surfaces. The transport coefficients in the boundary layer, which yield the temperature and density distribution, are obtained from the movement of particles along a stochastic magnetic field. The resulting line density can be made a factor of ten higher than is expected for a poloidal divertor experiment. From this it is concluded that all impurities coming from the wall will be ionized in the boundary layer. The concentration of the impurities in the plasma center is calculated according to a model which uses an anomalous diffusion coefficient being consistent with the ergodization in the boundary layer. The resulting concentration can be reduced proportional to the factor (nsub(e)Dsub(e)) -1 where nsub(e) and Dsub(e) are electron density and diffusion coefficient in the boundary layer. (Auth.)

The effect of impurities on the performance of lithium intended for lithium/thionyl chloride battery manufacture

Science.gov (United States)

Hagan, W. P.; Hampson, N. A.; Packer, R. K.

The elemental impurities in four different, commercially-available lithium samples have been determined. Cells consisting of these lithium samples as anodes and pressed acetylene black as cathodes were discharged at 20 °C and at 70 °C at a rate of 50 mA cm -2. The passivating films remaining on the lithium surface after discharge were examined using electron microscopy and their elemental compositions determined using the surface sensitive technique of X-ray photoelectron spectroscopy. Performance characteristics (voltage and capacity) of test cells consisting, in part, of the different lithium samples are discussed in terms of impurity concentrations determined by secondary ion mass spectrometry and atomic absorption spectroscopy. The permeability and electronic conductivity of the LiCl passivating films are adduced as two possible reasons for the variations in capacity and on-load voltage of the different lithium samples.

Access to electronic information resources by students of federal ...

African Journals Online (AJOL)

The paper discusses access to electronic information resources by students of Federal Colleges of Education in Eha-Amufu and Umunze. Descriptive survey design was used to investigate sample of 526 students. Sampling technique used was a Multi sampling technique. Data for the study were generated using ...

Adoption and use of electronic information resources by medical ...

African Journals Online (AJOL)

This study investigated the adoption and use of electronic information resources by medical science students of the University of Benin. The descriptive survey research design was adopted for the study and 390 students provided the data. Data collected were analysed with descriptive Statistics(Simple percentage and ...

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)

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.)

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.

Analyzing the Radiation Properties of High-Z Impurities in High-Temperature Plasmas

International Nuclear Information System (INIS)

Reinke, M. L.; Ince-Cushman, A.; Podpaly, Y.; Rice, J. E.; Bitter, M.; Hill, K. W.; Fournier, K. B.; Gu, M. F.

2009-01-01

Most tokamak-based reactor concepts require the use of noble gases to form either a radiative mantle or divertor to reduce conductive heat exhaust to tolerable levels for plasma facing components. Predicting the power loss necessary from impurity radiation is done using electron temperature-dependent 'cooling-curves' derived from ab initio atomic physics models. We present here a technique to verify such modeling using highly radiative, argon infused discharges on Alcator C-Mod. A novel x-ray crystal imaging spectrometer is used to measure spatially resolved profiles of line-emissivity, constraining impurity transport simulations. Experimental data from soft x-ray diodes, bare AXUV diodes and foil bolometers are used to determine the local emissivity in three overlapping spectral bands, which are quantitatively compared to models. Comparison of broadband measurements show agreement between experiment and modeling in the core, but not over the entire profile, with the differences likely due to errors in the assumed radial impurity transport outside of the core. Comparison of Ar 16+ x-ray line emission modeling to measurements suggests an additional problem with the collisional-radiative modeling of that charge state.

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)

Where Do Electronic Books Fit in the College Research Arsenal of Resources?

Science.gov (United States)

Barbier, Patricia

2007-01-01

Student use of electronic books has become an accepted supplement to traditional resources. Student use and satisfaction was monitored through an online course discussion board. Increased use of electronic books indicate this service is an accepted supplement to the print book collection.

TEM study of impurity segregations in beryllium pebbles

Energy Technology Data Exchange (ETDEWEB)

Klimenkov, M., E-mail: michael.klimenkov@kit.edu [Institute for Applied Materials – Applied Materials Physics, Karlsruhe Institute of Technology, Hermann-von-Helmholz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Chakin, V.; Moeslang, A. [Institute for Applied Materials – Applied Materials Physics, Karlsruhe Institute of Technology, Hermann-von-Helmholz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Rolli, R. [Institute for Applied Materials – Materials and Biomechanics, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)

2014-12-15

Beryllium is planned to be used as a neutron multiplier in the Helium-cooled Pebble Bed European concept of a breeding blanket of demonstration power reactor DEMO. In order to evaluate the irradiation performance, individual pebbles and constrained pebble beds were neutron-irradiated at temperatures typical of fusion blankets. Beryllium pebbles 1 mm in diameter produced by the rotating electrode method were subjected to a TEM study before and after irradiation at High Flux Reactor, Petten, Netherlands at 861 K. The grain size varied in a wide range from sub-micron size up to several tens of micrometers, which indicated formation bimodal grain size distribution. Based on the application of combined electron energy loss spectroscopy and energy dispersive X-ray spectroscopy methods, we suggest that impurity precipitates play an important role in controlling the mechanical properties of beryllium. The impurity elements were present in beryllium at a sub-percent concentration form beryllide particles of a complex (Fe/Al/Mn/Cr)B composition. These particles are often ordered along dislocations lines, forming several micron-long chains. It can be suggested that fracture surfaces often extended along these chains in irradiated material.

Impurity magnetopolaron in a parabolic quantum dot: the squeezed-state variational approach

International Nuclear Information System (INIS)

Kandemir, B S; Cetin, A

2005-01-01

We present a calculation of the ground-state binding energy of an impurity magnetopolaron confined in a three-dimensional (3D) parabolic quantum dot potential, in the framework of a variational approach based on two successive canonical transformations. First, we apply a displaced-oscillator type unitary transformation to diagonalize the relevant Froehlich Hamiltonian. Second, a single-mode squeezed-state transformation is introduced to deal with bilinear terms arising from the first transformation. Finally, the parameters of these transformations together with the parameters included in the electronic trial wavefunction are determined variationally to obtain the ground-state binding energy of an impurity magnetopolaron confined in a 3D parabolic quantum dot potential. Our approach has two advantages: first, the displaced-oscillator transformation allows one to obtain results valid for whole range of electron-phonon coupling strength since it is a special combination of Lee-Low-Pines and Huybrechts (LLP-H) canonical transformations, and second, the later transformation improves all-coupling results. It has been shown that the effects of quadratic terms arising from the all-coupling approach are very important and should be taken into account in studying the size-dependent physical properties of nanostructured materials

Control Strategy for Small Molecule Impurities in Antibody-Drug Conjugates.

Science.gov (United States)

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.

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.

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

Interleaved numerical renormalization group as an efficient multiband impurity solver

Science.gov (United States)

Stadler, K. M.; Mitchell, A. K.; von Delft, J.; Weichselbaum, A.

2016-06-01

Quantum impurity problems can be solved using the numerical renormalization group (NRG), which involves discretizing the free conduction electron system and mapping to a "Wilson chain." It was shown recently that Wilson chains for different electronic species can be interleaved by use of a modified discretization, dramatically increasing the numerical efficiency of the RG scheme [Phys. Rev. B 89, 121105(R) (2014), 10.1103/PhysRevB.89.121105]. Here we systematically examine the accuracy and efficiency of the "interleaved" NRG (iNRG) method in the context of the single impurity Anderson model, the two-channel Kondo model, and a three-channel Anderson-Hund model. The performance of iNRG is explicitly compared with "standard" NRG (sNRG): when the average number of states kept per iteration is the same in both calculations, the accuracy of iNRG is equivalent to that of sNRG but the computational costs are significantly lower in iNRG when the same symmetries are exploited. Although iNRG weakly breaks SU(N ) channel symmetry (if present), both accuracy and numerical cost are entirely competitive with sNRG exploiting full symmetries. iNRG is therefore shown to be a viable and technically simple alternative to sNRG for high-symmetry models. Moreover, iNRG can be used to solve a range of lower-symmetry multiband problems that are inaccessible to sNRG.

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

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

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.

Impurity trapped excitons under high hydrostatic pressure

Science.gov (United States)

Grinberg, Marek

2013-09-01

Paper summarizes the results on pressure effect on energies of the 4fn → 4fn and 4fn-15d1 → 4fn transitions as well as influence of pressure on anomalous luminescence in Lnα+ doped oxides and fluorides. A model of impurity trapped exciton (ITE) was developed. Two types of ITE were considered. The first where a hole is localized at the Lnα+ ion (creation of Ln(α+1)+) and an electron is attracted by Coulomb potential at Rydberg-like states and the second where an electron captured at the Lnα+ ion (creation of Ln(α-1)+) and a hole is attracted by Coulomb potential at Rydberg-like states. Paper presents detailed analysis of nonlinear changes of energy of anomalous luminescence of BaxSr1-xF2:Eu2+ (x > 0.3) and LiBaF3:Eu2+, and relate them to ITE-4f65d1 states mixing.

Single-site properties of U impurities doped in La2Zn17 (abstract)

Science.gov (United States)

Suzuki, H.; Anzai, K.; Takagi, S.

1997-04-01

Thermodynamic and transport properties of heavy Fermion (HF) U compounds show similar behavior to HF Ce compounds. Although most of the magnetic properties of HF Ce compounds can be qualitatively understood on the basis of the impurity Kondo model, no such consensus for HF U compounds has been reached. In addition to this, the single-site properties of U impurities are not understood so well, in contrast to the case of Ce impurities. Recent works for dilute U systems reported new features as are not seen in dilute Ce systems. We have investigated a dilute-U2Zn17 system of (La1-zUz)2Zn17 in order to reveal the single U ion site properties of this system by preparing single crystals. The impurity contributions to various physical quantities such as ρimp(T), χimp(T), and Cimp(T) can be scaled by the U concentration between z=0.025 and 0.05, and the system is considered as in the dilute limit still for z=0.05. The electrical resistivity shows the typical impurity-Kondo upturn at low temperatures. The electronic specific-heat coefficient is strongly enhanced (γimp≈1.5 J/K2 mole U) and about 4 times as large as that for dense U2Zn17. Suppressions of the Kondo effect by the magnetic field are seen in γimp(H) and magnetoresistance. The relatively large anisotropy in χimp(T) indicates an existence of the crystal field. These features of this system will be explained in terms of the Kondo effect in the presence of the crystal field.

Strain field due to transition metal impurities in Ni and Pd

Indian Academy of Sciences (India)

1 2. 28 1 π. ¯h2r3 2. dH mr5. (44). In eqs (41) to (44), ∆φFE(r), ∆φc(r) and ∆φb(r) are impurity induced changes in the po- tential due to free electron, s–d hybridization and d-bandwidth contributions respectively. 3. Calculations and results. The above formalism is used to calculate the atomic displacements in Ni and Pd dilute.

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

Strategic Planning for Electronic Resources Management: A Case Study at Gustavus Adolphus College

Science.gov (United States)

Hulseberg, Anna; Monson, Sarah

2009-01-01

Electronic resources, the tools we use to manage them, and the needs and expectations of our users are constantly evolving; at the same time, the roles, responsibilities, and workflow of the library staff who manage e-resources are also in flux. Recognizing a need to be more intentional and proactive about how we manage e-resources, the…

The influence of impurities on the coefficients of transportation

International Nuclear Information System (INIS)

Selmi, Aloine

2011-01-01

The goal of this Masters project was to build a water filtration plant using a Micromegas detector. (You need to explain at least how Micromegas can be used in filtration plants, and to filtrate what.) This new generation of devices have good resolution, low background, fast response with the highest efficiency and good sensitivity in the range of natural radioactivity. The central part of this work was to describe the development of a detection plane. A small Micomegas prototype, was built in CNSTN (Tunisia), and is devoted to study electron transport properties in a gas. This manuscript describes the development of a filtration plant using a Micromegas gas detector. This detector must be filled with Xenon 98 pour cent and C F 4 2 pour cent at pressure varying between 1 and 4 bar. I realized the need to have a rigorously high purity gas; I studied in depth the influence of impurities on the parameters characterizing the detector: drift velocity of electron in the gas, their longitudinal and transverse diffusion and the gas gain, the electron attachment while varying the proportions of impurities and the gas pressure. These studies have been done using a simulation program called M agboltz . Another simulation program G EANT4 w as used to better understand the interactions and radiation field. I also used two other programs, G arfield a nd M axwell , to simulate the electric field in the detector. I reached the stage of near completion of this treatment plant but the necessary equipment could not be purchased, simply because its cost was too high. To complete my masters, I started the design of a gamma camera filled by Xenon gas at high pressure and based on Micromegas - micro pattern.

REVIEW OF MOODLE PLUGINS FOR DESIGNING MULTIMEDIA ELECTRONIC EDUCATIONAL RESOURCES FROM LANGUAGE DISCIPLINES

Directory of Open Access Journals (Sweden)

Anton M. Avramchuk

2015-09-01

Full Text Available Today the problem of designing multimedia electronic educational resources from language disciplines in Moodle is very important. This system has a lot of different, powerful resources, plugins to facilitate the learning of students with language disciplines. This article presents an overview and comparative analysis of the five Moodle plugins for designing multimedia electronic educational resources from language disciplines. There have been considered their key features and functionality in order to choose the best for studying language disciplines in the Moodle. Plugins are compared by a group of experts according to the criteria: efficiency, functionality and easy use. For a comparative analysis of the plugins it is used the analytic hierarchy process.

MOS Capacitance—Voltage Characteristics III. Trapping Capacitance from 2-Charge-State Impurities

International Nuclear Information System (INIS)

Jie Binbin; Sah Chihtang

2011-01-01

Low-frequency and high-frequency capacitance—voltage curves of Metal—Oxide—Semiconductor Capacitors are presented to illustrate giant electron and hole trapping capacitances at many simultaneously present two-charge-state and one-trapped-carrier, or one-energy-level impurity species. Models described include a donor electron trap and an acceptor hole trap, both donors, both acceptors, both shallow energy levels, both deep, one shallow and one deep, and the identical donor and acceptor. Device and material parameters are selected to simulate chemically and physically realizable capacitors for fundamental trapping parameter characterizations and for electrical and optical signal processing applications. (invited papers)

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)

Striped morphologies induced by magnetic impurities in d-wave superconductors

Science.gov (United States)

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.

Understanding of impurity poloidal distribution in the edge pedestal by modelling

Science.gov (United States)

Rozhansky, V.; Kaveeva, E.; Molchanov, P.; Veselova, I.; Voskoboynikov, S.; Coster, D.; Fable, E.; Puetterich, T.; Viezzer, E.; Kukushkin, A. S.; Kirk, A.; the ASDEX Upgrade Team

2015-07-01

Simulation of an H-mode ASDEX Upgrade shot with boron impurity was done with the B2SOLPS5.2 transport code. Simulation results were compared with the unique experimental data available for the chosen shot: radial density, electron and ion temperature profiles in the equatorial midplanes, radial electric field profile, radial profiles of the parallel velocity of impurities at the low-field side (LFS) and high-field side (HFS), radial density profiles of impurity ions at LHS and HFS. Simulation results reproduce all available experimental data simultaneously. In particular strong poloidal HFS-LFS asymmetry of B5+ ions was predicted in accordance with the experiment. The simulated HFS B5+ density inside the edge transport barrier is twice larger than that at LFS. This is consistent with the experimental observations where even larger impurity density asymmetry was observed. A similar effect was predicted in the simulation done for the MAST H-mode. Here the HFS density of He2+ is predicted to be 4 times larger than that at LHS. Such a large predicted asymmetry is connected with a larger ratio of HFS and LFS magnetic fields which is typical for spherical tokamaks. The HFS/LFS asymmetry was not measured in the experiment, however modelling qualitatively reproduces the observed change of sign of He+parallel velocity to the counter-current direction at LFS. The understanding of the asymmetry is based on neoclassical effects in plasma with strong gradients. It is demonstrated that simulation results obtained with account of sources of ionization, realistic geometry and turbulent transport are consistent with the simplified analytical approach. Difference from the standard neoclassical theory is emphasized.

Modern ICT Tools: Online Electronic Resources Sharing Using Web ...

African Journals Online (AJOL)

Modern ICT Tools: Online Electronic Resources Sharing Using Web 2.0 and Its Implications For Library And Information Practice In Nigeria. ... The PDF file you selected should load here if your Web browser has a PDF reader plug-in installed (for example, a recent version of Adobe Acrobat Reader). If you would like more ...

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.)

Interpretation of plasma impurity deposition probes. Analytic approximation

Science.gov (United States)

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.

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.

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

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)

Non-ionic contributions to the electric-field gradient at 111Cd/181Ta impurities in bixbyites

International Nuclear Information System (INIS)

Renteria, Mario; Freitag, Kristian; Errico, Leonardo A.

1999-01-01

The electric-field-gradient (EFG) tensor at both cation sites of the bixbyite structure in 181 Hf-implanted Lu- and Sm-sesquioxides was determined by the PAC technique. The cumulated EFG data at Ta-impurity sites in binary oxides enable us to discuss the 'universal' character of the empirical correlation between local and ionic contributions to the EFG in these systems. An EFG factorization in terms of the electronic characteristics of the probe and the geometry of the cation coordination is proposed, which explains the experimental EFG results at Ta/Cd impurity sites in bixbyites and agrees with a simplified decomposition of the EFG valence contribution coming from ab-initio calculations

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)

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

THE MODEL OF LINGUISTIC TEACHERS’ COMPETENCY DEVELOPMENT ON DESIGNING MULTIMEDIA ELECTRONIC EDUCATIONAL RESOURCES IN THE MOODLE SYSTEM

Directory of Open Access Journals (Sweden)

Anton M. Avramchuk

2017-10-01

Full Text Available The article is devoted to the problem of developing the competency of teachers of language disciplines on designing multimedia electronic educational resources in the Moodle system. The concept of "the competence of teachers of language disciplines on designing multimedia electronic educational resources in the Moodle system" is justified and defined. Identified and characterized the components by which the levels of the competency development of teachers of language disciplines on designing multimedia electronic educational resources in the Moodle system should be assessed. Developed a model for the development of the competency of teachers of language disciplines on designing multimedia electronic educational resources in the Moodle system, which is based on the main scientific approaches, used in adult education, and consists of five blocks: target, informative, technological, diagnostic and effective.

Scattering of waves by impurities in precompressed granular chains.

Science.gov (United States)

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.

Developing Humanities Collections in the Digital Age: Exploring Humanities Faculty Engagement with Electronic and Print Resources

Science.gov (United States)

Kachaluba, Sarah Buck; Brady, Jessica Evans; Critten, Jessica

2014-01-01

This article is based on quantitative and qualitative research examining humanities scholars' understandings of the advantages and disadvantages of print versus electronic information resources. It explores how humanities' faculty members at Florida State University (FSU) use print and electronic resources, as well as how they perceive these…

Ionic Impurity in a Bose-Einstein Condensate at Submicrokelvin Temperatures

Science.gov (United States)

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.

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...

Child-Langmuir flow in a planar diode filled with charged dust impurities

International Nuclear Information System (INIS)

Tang Xiaoyan; Shukla, Padma Kant

2008-01-01

The Child-Langmuir (CL) flow in a planar diode in the presence of stationary charged dust particles is studied. The limiting electron current density and other diode properties, such as the electrostatic potential, the electron flow speed, and the electron number density, are calculated analytically. A comparison of the results with the case without dust impurities reveals that the diode parameters mentioned above decrease with the increase of the dust charge density. Furthermore, it is found that the classical scaling of D -2 (the gap spacing D) for the CL current density remains exactly valid, while the scaling of V 3/2 (the applied gap voltage V) can be a good approximation for low applied gap voltage and for low dust charge density

The influence of impurity and particle control on TMX-U [Tandem Mirror Experiment Upgrade] plasma operation

International Nuclear Information System (INIS)

Allen, S.L.; Yu, T.L.; Foote, J.H.; Pickles, W.L.

1985-11-01

A variety of techniques are used in TMX-U to control impurities and reflux: repeated plasma pulses, glow discharge cleaning (GDC), and gettering. A series of experiments under three different plasma-wall conditions was performed: no wall conditioning after a machine maintenance cycle, a glow-discharge-cleaned wall, and a gettered wall. Several plasma diagnostics to determine the effect of these procedures on TMX-U plasma parameters were used. Spectroscopic measurements indicated that GDC reduced impurities and increased the electron temperature, enabling full-duration beam-sustained plasma operation without a large number of repeated plasma pulses. Gettering further reduced the impurities and the neutral pressure, and this improved condition persisted for several shots after gettering was stopped. Measurements from residual gas analyzers and an end-loss ion spectrometer indicated that hydrogen is present in the plasma during the initial deuterium operation after pumpdown; the hydrogen level decreased after plasma operation with gettering, indicating reduced wall recycling

Resonant States in High-Temperature Superconductors with Impurities

CERN Document Server

Kovacevic, Z L; Hayn, R

2002-01-01

A microscopic theory of resonant states for the Zn-doped CuO_2 plane in superconducting phase is formulated within the effective t-J model. In the model derived from the original p-d model Zn impurities are considered as vacancies for the d states on Cu sites. In the superconducting phase in addition to the local static perturbation induced by the vacancy a dynamical perturbation appears which results in frequency-dependent perturbation matrix. By employing the T-matrix formalism for the Green functions in terms of the Hubbard operators the local density of electronic states with d-, p- and s-symmetry is calculated.

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.

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.)

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)

Spin-relaxation time in the impurity band of wurtzite semiconductors

Science.gov (United States)

Tamborenea, Pablo I.; Wellens, Thomas; Weinmann, Dietmar; Jalabert, Rodolfo A.

2017-09-01

The spin-relaxation time for electrons in the impurity band of semiconductors with wurtzite crystal structure is determined. The effective Dresselhaus spin-orbit interaction Hamiltonian is taken as the source of the spin relaxation at low temperature and for doping densities corresponding to the metallic side of the metal-insulator transition. The spin-flip hopping matrix elements between impurity states are calculated and used to set up a tight-binding Hamiltonian that incorporates the symmetries of wurtzite semiconductors. The spin-relaxation time is obtained from a semiclassical model of spin diffusion, as well as from a microscopic self-consistent diagrammatic theory of spin and charge diffusion in doped semiconductors. Estimates are provided for particularly important materials. The theoretical spin-relaxation times compare favorably with the corresponding low-temperature measurements in GaN and ZnO. For InN and AlN we predict that tuning of the spin-orbit coupling constant induced by an external potential leads to a potentially dramatic increase of the spin-relaxation time related to the mechanism under study.

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....

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

Transitions and excitations in a superfluid stream passing small impurities

KAUST Repository

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

KAUST Repository

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.

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

Temperature dependence of the magnetic hyperfine field at an s–p impurity diluted in RNi_2

International Nuclear Information System (INIS)

Oliveira, A.L. de; Chaves, C.M.; Oliveira, N.A. de; Troper, A.

2016-01-01

We study the formation of local magnetic moments and magnetic hyperfine fields at an s–p impurity diluted in intermetallic Laves phase compounds RNi_2 (R=Nd, Sm, Gd, Tb, Dy) at finite temperatures. We start with a clean host and later the impurity is introduced. The host has two-coupled (R and Ni) sublattice Hubbard Hamiltonians but the Ni sublattice can be disregarded because its d band, being full, is magnetically ineffective. Also, the effect of the 4f electrons of R is represented by the polarization they produce on the d band. This leaves us with a lattice of effective rare earth R-ions with polarized electrons. For the dd electronic interaction we use the Hubbard–Stratonovich identity in a functional integral approach in the static saddle point approximation. - Highlights: • Functional integral method in the static limit, producing site disorder, is used. • The site disorder is treated with the Coherent Potential Approximation (CPA). • Non magnetic Ni generates an effective lattice with only a polarized R d band. • The effective R lattice differ from the pure R metal: Results and Discussions. • The experimental curve of hyperfine fields × temperature are very well reproduced.

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)

EPR OF Mn2+ IMPURITIES IN CALCITE: A DETAILED STUDY PERTINENT TO MARBLE PROVENANCE DETERMINATION

DEFF Research Database (Denmark)

Weihe, H.; Piligkos, S.; Barra, A.L.

2009-01-01

We demonstrate that the electron paramagnetic resonance spectrum of Mn2+ impurities in calcite, and therefore also in marble, may be accurately reproduced by a traditional spin Hamiltonian formalism. The success of such a treatment, however, very much depends on the spin Hamiltonian parameters...... having the correct signs as well as magnitudes. We present data that determine the sign of the axial anisotropy parameter and thereby facilitate future quantum mechanical characterizations of marble electron paramagnetic resonance spectra that supplement provenance determination....

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...

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

First principles density functional calculation of magnetic moment and hyperfine fields of dilute transition metal impurities in Gd host

International Nuclear Information System (INIS)

Mohanta, S.K.; Mishra, S.N.; Srivastava, S.K.

2014-01-01

We present first principles calculations of electronic structure and magnetic properties of dilute transition metal (3d, 4d and 5d) impurities in a Gd host. The calculations have been performed within the density functional theory using the full potential linearized augmented plane wave technique and the GGA+U method. The spin and orbital contributions to the magnetic moment and the hyperfine fields have been computed. We find large magnetic moments for 3d (Ti–Co), 4d (Nb–Ru) and 5d (Ta–Os) impurities with magnitudes significantly different from the values estimated from earlier mean field calculation [J. Magn. Magn. Mater. 320 (2008) e446–e449]. The exchange interaction between the impurity and host Gd moments is found to be positive for early 3d elements (Sc–V) while in all other cases an anti-ferromagnetic coupling is observed. The trends for the magnetic moment and hyperfine field of d-impurities in Gd show qualitative difference with respect to their behavior in Fe, Co and Ni. The calculated total hyperfine field, in most cases, shows excellent agreement with the experimental results. A detailed analysis of the Fermi contact hyperfine field has been made, revealing striking differences for impurities having less or more than half filled d-shell. The impurity induced perturbations in host moments and the change in the global magnetization of the unit cell have also been computed. The variation within each of the d-series is found to correlate with the d–d hybridization strength between the impurity and host atoms. - Highlights: • Detailed study of transition metal impurities in ferromagnetic Gd has been carried out. • The trends in impurity magnetic moment are qualitatively different from Fe, Co and Ni. • The variation within each of the d-series is found to correlate with the d–d hybridization strength between the impurity and host atoms. • Experimental trend in a hyperfine field has been reproduced successfully

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

Spectroscopic methods for detection of impurities in water

Science.gov (United States)

Strashnikova, Natalia V.; Papiashvili, Nona; Cohen-Luria, Rivka; Mark, Shlomo; Shilon, Guy; Khankin, Daniel; Kalisky, Yehoshua; Kalisky, Ofra; Parola, Abraham H.

2011-11-01

Optical photoluminescence spectroscopic method for detection of impurities, hazardous materials, pesticides, and pollutants in water resources, both qualitatively and quantitatively, is presented. The method is based on synchronous fluorescence spectroscopy (SFS) of organic aromatic compounds, or poly-aromatic hydrocarbons (PAH), and is carried out by following simultaneously their excitation and emission spectra. The full excitation emission matrix (EEM) generated in this way provides a 2-D and 3-D fluorescence map of the tested sample and the diagonals through the axes origin provide the synchronous fluorescence spectra at a constant wavelengths differences between the emission and excitation wavelengths, thus enabling multitude components identification. This map contains all the relevant spectroscopic information of the tested sample, and serves as a unique "fingerprint" with a very specific and accurate identification. When compared with pre-determined spectra and calibration curves from a "databank", there is a one-toone correspondence between the image and the specific compound, and it can be identified accurately both qualitatively and quantitatively. This method offers several significant advantages, and it provides a sensitive (ppm detection level), accurate and simple spectroscopic tool to monitor impurities and pollutants in water. The design and performance of the spectrofluorimeter prototype, as well as the software development and analysis of chemical organic compounds and mixtures in water will be discussed in this paper.

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

Electronic resource management systems a workflow approach

CERN Document Server

Anderson, Elsa K

2014-01-01

To get to the bottom of a successful approach to Electronic Resource Management (ERM), Anderson interviewed staff at 11 institutions about their ERM implementations. Among her conclusions, presented in this issue of Library Technology Reports, is that grasping the intricacies of your workflow-analyzing each step to reveal the gaps and problems-at the beginning is crucial to selecting and implementing an ERM. Whether the system will be used to fill a gap, aggregate critical data, or replace a tedious manual process, the best solution for your library depends on factors such as your current soft

Impurity-defect complexes in hydrogenated amorphous silicon

International Nuclear Information System (INIS)

Yang, L.H.; Fong, C.Y.; Nichols, C.S.

1991-01-01

The two most outstanding features observed for dopants in hydrogenated amorphous silicon (a-Si:H)-a shift in the Fermi level accompanied by an increase in the defect density and an absence of degenerate doping have previously been postulated to stem from the formation of substitutional dopant-dangling bond complexes. Using first-principles self-consistent pseudopotential calculations in conjunction with a supercell model for the amorphous network and the ability of network relaxation from the first-principles results. The authors have studied the electronic and structural properties of substitutional fourfold-coordinated phosphorus and boron at the second neighbor position to a dangling bond defect. This paper demonstrates that such impurity-defect complexes can account for the general features observed experimentally in doped a-Si:H

Electronic Resource Management System. Vernetzung von Lizenzinformationen

Directory of Open Access Journals (Sweden)

Michaela Selbach

2014-12-01

Full Text Available In den letzten zehn Jahren spielen elektronische Ressourcen im Bereich der Erwerbung eine zunehmend wichtige Rolle: Eindeutig lässt sich hier ein Wandel in den Bibliotheken (fort vom reinen Printbestand zu immer größeren E-Only-Beständen feststellen. Die stetig wachsende Menge an E-Ressourcen und deren Heterogenität stellt Bibliotheken vor die Herausforderung, die E-Ressourcen effizient zu verwalten. Nicht nur Bibliotheken, sondern auch verhandlungsführende Institutionen von Konsortial- und Allianzlizenzen benötigen ein geeignetes Instrument zur Verwaltung von Lizenzinformationen, welches den komplexen Anforderungen moderner E-Ressourcen gerecht wird. Die Deutsche Forschungsgemeinschaft (DFG unterstützt ein Projekt des Hochschulbibliothekszentrums des Landes Nordrhein-Westfalen (hbz, der Universitätsbibliothek Freiburg, der Verbundzentrale des Gemeinsamen Bibliotheksverbundes (GBV und der Universitätsbibliothek Frankfurt, in dem ein bundesweit verfügbares Electronic Ressource Managementsystem (ERMS aufgebaut werden soll. Ein solches ERMS soll auf Basis einer zentralen Knowledge Base eine einheitliche Nutzung von Daten zur Lizenzverwaltung elektronischer Ressourcen auf lokaler, regionaler und nationaler Ebene ermöglichen. Statistische Auswertungen, Rechteverwaltung für alle angeschlossenen Bibliotheken, kooperative Datenpflege sowie ein über standardisierte Schnittstellen geführter Datenaustausch stehen bei der Erarbeitung der Anforderungen ebenso im Fokus wie die Entwicklung eines Daten- und Funktionsmodells. In the last few years the importance of electronic resources in library acquisitions has increased significantly. There has been a shift from mere print holdings to both e- and print combinations and even e-only subscriptions. This shift poses a double challenge for libraries: On the one hand they have to provide their e-resource collections to library users in an appealing way, on the other hand they have to manage these

Defect-impurity interactions in ion-implanted metals

International Nuclear Information System (INIS)

Turos, A.

1986-01-01

An overview of defect-impurity interactions in metals is presented. When point defects become mobile they migrate towards the sinks and on the way can be captured by impurity atoms forming stable associations so-called complexes. In some metallic systems complexes can also be formed athermally during ion implantation by trapping point defects already in the collision cascade. An association of a point defect with an impurity atom leads to its displacement from the lattice site. The structure and stability of complexes are strongly temperature dependent. With increasing temperature they dissociate or grow by multiple defect trapping. The appearance of freely migrating point defects at elevated temperatures, due to ion bombardment or thermal annealing, causes via coupling with defect fluxes, important impurity redistribution. Because of the sensitivity of many metal-in-metal implanted systems to radiation damage the understanding of this processes is essential for a proper interpretation of the lattice occupancy measurements and the optimization of implantation conditions. (author)

Glycolic acid physical properties and impurities assessment

Energy Technology Data Exchange (ETDEWEB)

Lambert, D. P. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Pickenheim, B. R. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); Hay, M. S. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL); BIBLER, N. E. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

2017-08-09

This document has been revised to add analytical data for fresh, 1 year old, and 4 year old glycolic acid as recommended in Revision 2 of this document. This was needed to understand the concentration of formaldehyde and methoxyacetic acid, impurities present in the glycolic acid used in Savannah River National Laboratory (SRNL) experiments. Based on this information, the concentration of these impurities did not change during storage. These impurities were in the glycolic acid used in the testing included in this report and in subsequent testing using DuPont (now called Chemours) supplied Technical Grade 70 wt% glycolic acid. However, these impurities were not reported in the first two versions of this report. The Defense Waste Processing Facility (DWPF) is planning to implement a nitric-glycolic acid flowsheets to increase attainment to meet closure commitment dates during Sludge Batch 9. In fiscal year 2009, SRNL was requested to determine the physical properties of formic and glycolic acid blends.

Complexity of Quantum Impurity Problems

Science.gov (United States)

Bravyi, Sergey; Gosset, David

2017-12-01

We give a quasi-polynomial time classical algorithm for estimating the ground state energy and for computing low energy states of quantum impurity models. Such models describe a bath of free fermions coupled to a small interacting subsystem called an impurity. The full system consists of n fermionic modes and has a Hamiltonian {H=H_0+H_{imp}}, where H 0 is quadratic in creation-annihilation operators and H imp is an arbitrary Hamiltonian acting on a subset of O(1) modes. We show that the ground energy of H can be approximated with an additive error {2^{-b}} in time {n^3 \\exp{[O(b^3)]}}. Our algorithm also finds a low energy state that achieves this approximation. The low energy state is represented as a superposition of {\\exp{[O(b^3)]}} fermionic Gaussian states. To arrive at this result we prove several theorems concerning exact ground states of impurity models. In particular, we show that eigenvalues of the ground state covariance matrix decay exponentially with the exponent depending very mildly on the spectral gap of H 0. A key ingredient of our proof is Zolotarev's rational approximation to the {√{x}} function. We anticipate that our algorithms may be used in hybrid quantum-classical simulations of strongly correlated materials based on dynamical mean field theory. We implemented a simplified practical version of our algorithm and benchmarked it using the single impurity Anderson model.

Self-sustaining thin films as a means of reducing first wall erosion and plasma impurity influx

International Nuclear Information System (INIS)

Krauss, A.R.; Gruen, D.M.

1982-01-01

Neutral impurities ejected from Tokamak wall and limiter surfaces may travel several cm before being ionized very quickly upon entering the plasma edge. The influence of the unipolar sheath potential is exerted only within a very short distance of the surface and has no effect on neutral impurity atoms within a very short distance of the surface and has no effect on neutral impurity atoms which are subsequently ionized by charge-exchange collisions or electron impact ionization. However, secondary ions emanating from the limiter surfaces with kinetic energies less than the sheath potential will have essentially zero probability of traveling more than a few Debye lengths before being redeposited. Similarly, secondary ions originating at the first wall are redeposited as a result of the deflection produced by the magnetic field. Impurity influx resulting from sputtering would therefore be substantially reduced for surfaces which produce a very high ion/neutral ratio when sputtered. It has been previously shown that the high secondary ion yield associated with the alkali metal potassium does not apply to the bulk metal but pertains to ionic compounds and thin (mono-layer) films. Two processes are discussed as a means of producing these films in a self-sustaining manner compatible with the fusion reactor environment. (orig.)

Impurity and particle control for INTOR

International Nuclear Information System (INIS)

Post, D.

1985-02-01

The INTOR impurity control system studies have been focused on the development of an impurity control system which would be able to provide the necessary heat removal and He pumping while satisfying the requirements for (1) minimum plasma contamination by impurities, (2) reasonable component lifetime (approx. 1 year), and (3) minimum size and cost. The major systems examined were poloidal divertors and pumped limiters. The poloidal divertor was chosen as the reference option since it offered the possibility of low sputtering rates due to the formation of a cool, dense plasma near the collector plates. Estimates of the sputtering rates associated with pumped limiters indicated that they would be too high for a reasonable system. Development of an engineering design concept was done for both the poloidal divertor and the pumped limiter

The Electron Microscopy Outreach Program: A Web-based resource for research and education.

Science.gov (United States)

Sosinsky, G E; Baker, T S; Hand, G; Ellisman, M H

1999-01-01

We have developed a centralized World Wide Web (WWW)-based environment that serves as a resource of software tools and expertise for biological electron microscopy. A major focus is molecular electron microscopy, but the site also includes information and links on structural biology at all levels of resolution. This site serves to help integrate or link structural biology techniques in accordance with user needs. The WWW site, called the Electron Microscopy (EM) Outreach Program (URL: http://emoutreach.sdsc.edu), provides scientists with computational and educational tools for their research and edification. In particular, we have set up a centralized resource containing course notes, references, and links to image analysis and three-dimensional reconstruction software for investigators wanting to learn about EM techniques either within or outside of their fields of expertise. Copyright 1999 Academic Press.

Metal impurity transport control in JET H-mode plasmas with central ion cyclotron radiofrequency power injection

DEFF Research Database (Denmark)

Valisa, M.; Carraro, L.; Predebon, I.

2011-01-01

The scan of ion cyclotron resonant heating (ICRH) power has been used to systematically study the pump out effect of central electron heating on impurities such as Ni and Mo in H-mode low collisionality discharges in JET. The transport parameters of Ni and Mo have been measured by introducing...

Technical Communicator: A New Model for the Electronic Resources Librarian?

Science.gov (United States)

Hulseberg, Anna

2016-01-01

This article explores whether technical communicator is a useful model for electronic resources (ER) librarians. The fields of ER librarianship and technical communication (TC) originated and continue to develop in relation to evolving technologies. A review of the literature reveals four common themes for ER librarianship and TC. While the…

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

Scaling laws for trace impurity confinement: a variational approach

International Nuclear Information System (INIS)

Thyagaraja, A.; Haas, F.A.

1990-01-01

A variational approach is outlined for the deduction of impurity confinement scaling laws. Given the forms of the diffusive and convective components to the impurity particle flux, we present a variational principle for the impurity confinement time in terms of the diffusion time scale and the convection parameter, which is a non-dimensional measure of the size of the convective flux relative to the diffusive flux. These results are very general and apply irrespective of whether the transport fluxes are of theoretical or empirical origin. The impurity confinement time scales exponentially with the convection parameter in cases of practical interest. (orig.)

Zirconium analysis. Impurities determination by spark mass specrometry

International Nuclear Information System (INIS)

Anon.

Determination of impurities in zirconium, suitable for atomic content greater than 10 -8 but particularly adapted for low contents. The method is quantitative only if a reference sample is available (metallic impurities) [fr

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)

Dynamics of impurities in the scrape-off layer

International Nuclear Information System (INIS)

Stangeby, P.C.; Commission of the European Communities, Abingdon

1988-01-01

Impurity modelling of the Scrape-Off Layer, SOL, is reviewed. Simple analytic models are sometimes adequate for relating central impurity levels to edge plasma conditions and for explaining the patterns of net erosion/deposition found on limiters. More sophisticated approaches, which are also necessary, are categorized and reviewed. A plea is made for the acquisition of a more comprehensive data base of edge plasma properties since reliable impurity modelling appears to be dependent on more extensive use of experimental input. (author)

The optimisation of limiter geometry to reduce impurity influx in tokamaks

International Nuclear Information System (INIS)

Matthews, G.F.; McCracken, G.M.; Sewell, P.; Goodall, D.H.J.; Stangeby, P.C.; Pitcher, C.S.

1987-01-01

Conventional limiters are designed to withstand large power loadings and hence are constructed with surfaces at grazing angles to the toroidal magnetic field. As a result any impurities released from the limiter surface are projected towards the centre of the plasma and are poorly screened from it. The impurity control limiter (ICL), an alternative concept which has an inverted geometry is discussed. The ICL shape is designed to direct the impurities towards the wall. Results are presented from a two-dimensional neutral particle code which maps the ionisation of carbon physically sputtered by deuterons from a carbon limiter. This ionisation source is coupled to a one-dimensional impurity transport code which calculates the implied central impurity density. The results demonstrate that the ICL achieves impurity control in two ways. Firstly, many of the sputtered impurities directed towards the wall are not ionised and return to the wall as neutrals. Secondly, much of the ionisation which does occur is located in the scrape-off layer. Here there is a strong ion sink which may also be enhanced by the flow of hydrogenic ions entraining impurity ions created close to the limiter surface. We conclude that a reduction in central impurity density of a factor of 10 is possible in a Tokamak such as DITE provided that the limiter is the main source of impurities. (author)

Effects of an Intense Laser Field and Hydrostatic Pressure on the Intersubband Transitions and Binding Energy of Shallow Donor Impurities in a Quantum Well

International Nuclear Information System (INIS)

Yesilgul, U.; Ungan, F.; Kasapoglu, E.; Sari, H.; Sökmen, I.

2011-01-01

We have calculated the intersubband transitions and the ground-state binding energies of a hydrogenic donor impurity in a quantum well in the presence of a high-frequency laser field and hydrostatic pressure. The calculations are performed within the effective mass approximation, using a variational method. We conclude that the laser field amplitude and the hydrostatic pressure provide an important effect on the electronic and optical properties of the quantum wells. According to the results obtained from the present work, it is deduced that (i) the binding energies of donor impurity decrease as the laser field increase, (ii) the binding energies of donor impurity increase as the hydrostatic pressure increase, (iii) the intersubband absorption coefficients shift toward lower energies as the hydrostatic pressure increases, (iv) the magnitude of absorption coefficients decrease and also shift toward higher energies as the laser field increase. It is hopeful that the obtained results will provide important improvements in device applications. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Direct evidence for As as a Zn-site impurity in ZnO

CERN Document Server

Wahl, Ulrich; Correia, J G; Lourenço-Santana-Marques, Ana Claudia; Alves, E; Carvalho-Soares, José

2005-01-01

Arsenic has been reported in the literature as one of the few p-type dopants in the technologically promising II-VI semiconductor ZnO. However, there is an ongoing debate whether the p-type character is due to As simply replacing O atoms or to the formation of more complicated defect complexes, possibly involving As on Zn sites. We have determined the lattice location of implanted As in ZnO by means of conversion electron emission channeling from radioactive $^{73}$As. In contrast to what one might expect from its nature as a group V element, we find that As does not occupy substitutional O sites but in its large majority substitutional Zn sites. Arsenic in ZnO (and probably also in GaN) is thus an interesting example for an impurity in a semiconductor where the major impurity lattice site is determined by atomic size and electronegativity rather than its position in the periodic system.

Anomalous temperature behavior of Sn impurities