WorldWideScience

Sample records for blocked impurity band

  1. An Implant-Passivated Blocked Impurity Band Germanium Detector for the Far Infrared Project

    Data.gov (United States)

    National Aeronautics and Space Administration — We propose to fabricate a germanium blocked-impurity-band (BIB) detector using a novel process which will enable us to: 1- fabricate a suitably-doped active layer...

  2. An Implant-Passivated Blocked Impurity Band Germanium Detector for the Far Infrared Project

    Data.gov (United States)

    National Aeronautics and Space Administration — We propose to investigate the feasibility of fabricating a germanium blocked-impurity-band (BIB) detector using a novel process which will enable us to: 1-...

  3. Cold performance tests of blocked-impurity-band Si:As detectors developed for DARWIN

    OpenAIRE

    Birkmann, Stephan M.; Stegmaier, Jutta; Groezinger, Ulrich; Krause, Oliver; Souverijns, Tim; Putzeys, Jan; Tezcan, Deniz Sabuncuoglu; De Munck, Koen; Fiorini, Paolo; Minoglou, Kiki; Merken, Patrick; Van Hoof, Chris; De Moor, Piet

    2008-01-01

    We report first results of laboratory tests of Si:As blocked-impurity-band (BIB) mid-infrared (4 to 28 um) detectors developed by IMEC. These prototypes feature 88 pixels hybridized on an integrated cryogenic readout electronics (CRE). They were developed as part of a technology demonstration program for the future DARWIN mission. In order to be able to separate detector and readout effects, a custom build TIA circuitry was used to characterize additional single pixel detectors. We used a new...

  4. GaAs Blocked-Impurity-Band Detectors for Far-Infrared Astronomy

    Energy Technology Data Exchange (ETDEWEB)

    Cardozo, Benjamin Lewin

    2004-12-21

    High-purity and doped GaAs films have been grown by Liquid-phase epitaxy (LPE) for development of a blocked impurity band (BIB) detector for far-infrared radiation. The film growth process developed has resulted in the capability to grow GaAs with a net active impurity concentration below 1 x 10{sup 13} cm{sup -3}, ideal for the blocking layer of the BIB detector. The growth of n-type LPE GaAs films with donor concentrations below the metal-insulator transition, as required for the absorbing layer of a BIB detector, has been achieved. The control of the donor concentration, however, was found to be insufficient for detector production. The growth by LPE of a high-purity film onto a commercially grown vapor-phase epitaxial (VPE) n-type GaAs doped absorbing layer resulted in a BIB device that showed a significant reduction in the low-temperature dark current compared to the absorbing layer only. Extended optical response was not detected, most likely due to the high compensation of the commercially grown GaAs absorbing layer, which restricts the depletion width of the device.

  5. Liquid phase epitaxial growth and characterization of germanium far infrared blocked impurity band detectors

    Energy Technology Data Exchange (ETDEWEB)

    Bandaru, Jordana

    2001-05-12

    Germanium Blocked Impurity Band (BIB) detectors require a high purity blocking layer (< 10{sup 13} cm{sup -3}) approximately 1 mm thick grown on a heavily doped active layer ({approx} 10{sup 16} cm{sup -3}) approximately 20 mm thick. Epilayers were grown using liquid phase epitaxy (LPE) of germanium out of lead solution. The effects of the crystallographic orientation of the germanium substrate on LPE growth modes were explored. Growth was studied on substrates oriented by Laue x-ray diffraction between 0.02{sup o} and 10{sup o} from the {l_brace}111{r_brace} toward the {l_brace}100{r_brace}. Terrace growth was observed, with increasing terrace height for larger misorientation angles. It was found that the purity of the blocking layer was limited by the presence of phosphorus in the lead solvent. Unintentionally doped Ge layers contained {approx}10{sup 15} cm{sup -3} phosphorus as determined by Hall effect measurements and Photothermal Ionization Spectroscopy (PTIS). Lead purification by vacuum distillation and dilution reduced the phosphorus concentration in the layers to {approx} 10{sup 14} cm{sup -3} but further reduction was not observed with successive distillation runs. The graphite distillation and growth components as an additional phosphorus source cannot be ruled out. Antimony ({approx}10{sup 16} cm{sup -3}) was used as a dopant for the active BIB layer. A reduction in the donor binding energy due to impurity banding was observed by variable temperature Hall effect measurements. A BIB detector fabricated from an Sb-doped Ge layer grown on a pure substrate showed a low energy photoconductive onset ({approx}6 meV). Spreading resistance measurements on doped layers revealed a nonuniform dopant distribution with Sb pile-up at the layer surface, which must be removed by chemomechanical polishing. Sb diffusion into the pure substrate was observed by Secondary Ion Mass Spectroscopy (SIMS) for epilayers grown at 650 C. The Sb concentration at the interface

  6. Liquid phase epitaxial growth and characterization of germanium far infrared blocked impurity band detectors

    International Nuclear Information System (INIS)

    Germanium Blocked Impurity Band (BIB) detectors require a high purity blocking layer ( and lt; 10(sup 13) cm(sup -3)) approximately 1 mm thick grown on a heavily doped active layer ((approx) 10(sup 16) cm(sup -3)) approximately 20 mm thick. Epilayers were grown using liquid phase epitaxy (LPE) of germanium out of lead solution. The effects of the crystallographic orientation of the germanium substrate on LPE growth modes were explored. Growth was studied on substrates oriented by Laue x-ray diffraction between 0.02(sup o) and 10(sup o) from the(lbrace)111(rbrace) toward the(lbrace)100(rbrace). Terrace growth was observed, with increasing terrace height for larger misorientation angles. It was found that the purity of the blocking layer was limited by the presence of phosphorus in the lead solvent. Unintentionally doped Ge layers contained(approx)10(sup 15) cm(sup -3) phosphorus as determined by Hall effect measurements and Photothermal Ionization Spectroscopy (PTIS). Lead purification by vacuum distillation and dilution reduced the phosphorus concentration in the layers to(approx) 10(sup 14) cm(sup -3) but further reduction was not observed with successive distillation runs. The graphite distillation and growth components as an additional phosphorus source cannot be ruled out. Antimony ((approx)10(sup 16) cm(sup -3)) was used as a dopant for the active BIB layer. A reduction in the donor binding energy due to impurity banding was observed by variable temperature Hall effect measurements. A BIB detector fabricated from an Sb-doped Ge layer grown on a pure substrate showed a low energy photoconductive onset ((approx)6 meV). Spreading resistance measurements on doped layers revealed a nonuniform dopant distribution with Sb pile-up at the layer surface, which must be removed by chemomechanical polishing. Sb diffusion into the pure substrate was observed by Secondary Ion Mass Spectroscopy (SIMS) for epilayers grown at 650 C. The Sb concentration at the interface dropped

  7. Cold performance tests of blocked-impurity-band Si:As detectors developed for DARWIN

    CERN Document Server

    Birkmann, Stephan M; Groezinger, Ulrich; Krause, Oliver; Souverijns, Tim; Putzeys, Jan; Tezcan, Deniz Sabuncuoglu; De Munck, Koen; Fiorini, Paolo; Minoglou, Kiki; Merken, Patrick; Van Hoof, Chris; De Moor, Piet

    2008-01-01

    We report first results of laboratory tests of Si:As blocked-impurity-band (BIB) mid-infrared (4 to 28 um) detectors developed by IMEC. These prototypes feature 88 pixels hybridized on an integrated cryogenic readout electronics (CRE). They were developed as part of a technology demonstration program for the future DARWIN mission. In order to be able to separate detector and readout effects, a custom build TIA circuitry was used to characterize additional single pixel detectors. We used a newly designed test setup at the MPIA to determine the relative spectral response, the quantum efficiency, and the dark current. All these properties were measured as a function of operating temperature and detector bias. In addition the effects of ionizing radiation on the detector were studied. For determining the relative spectral response we used a dual-grating monochromator and a bolometer with known response that was operated in parallel to the Si:As detectors. The quantum efficiency was measured by using a custom-buil...

  8. Initial testing of a Si:As blocked-impurity-band (BIB) trap detector

    Science.gov (United States)

    Woods, Solomon I.; Kaplan, Simon G.; Jung, Timothy M.; Carter, Adriaan C.; Proctor, James E.

    2012-06-01

    We discuss the design, construction, and initial test results of a Si:As blocked-impurity-band (BIB) trap detector. The trap consists of two rectangular BIB devices configured in a v-shaped geometry. This trapping geometry is designed to ideally yield a minimum of 7 bounces before exit for incident light within an f/4 cone with 3 mm clear aperture. The individual BIB devices consist of 70 μm thick active layers with As doping near 1.7×1018 cm-3, and have dark currents of approximately 100 nA at an operating temperature of 9 K. A simple ray-tracing model of the trap, along with data on the quantum yield of typical BIB detector elements, indicates that it is possible to achieve an external quantum efficiency of > 0.99 over the 4 μm to 28 μm spectral range and significant suppression of the etalon fringes present in the spectral responsivity of a single element. We have made initial responsivity measurements of the trap compared to a calibrated 5 mm diameter pyroelectric detector over the 3 μm to 17 μm spectral range using the fiber-coupled output of a Fourier-transform spectrometer. We also discuss the results of comparison measurements between the trap detector and an absolute cryogenic radiometer viewing the output of a calibrated blackbody source at discrete filter bands from 5 μm to 11 μ. In initial testing the performance of the trap is limited by the poor performance of the individual BIB detectors, but the advantages of boosted quantum efficiency and suppressed etalon are realized by the trap.

  9. Advanced far infrared blocked impurity band detectors based on germanium liquid phase epitaxy

    Science.gov (United States)

    Olsen, C. S.

    1998-01-01

    This research has shown that epilayers with residual impurity concentrations of 5 x 10(sup 13) cm(exp -3) can be grown by producing the purest Pb available in the world. These epilayers have extremely low minority acceptor concentrations, which is ideal for fabrication of IR absorbing layers. The Pb LPE growth of Ge also has the advantageous property of gettering Cu from the epilayer and the substrate. Epilayers have been grown with intentional Sb doping for IR absorption on lightly doped substrates. This research has proven that properly working Ge BIB detectors can be fabricated from the liquid phase as long as pure enough solvents are available. The detectors have responded at reach minimum wavenumbers. Optimization of the Sb doping concentration should further decrease the photoionization energy of these detectors. Ge BIB detectors have been fabricated that respond to 60 cm(exp -1) with low responsivity. Through reduction of the minority residual impurities, detector performance has reached responsivities of 1 A/W. These detectors have exhibited quantum efficiency and NEP values that rival conventional photoconductors and are expected to provide a much more sensitive tool for new scientific discoveries in a number of fields, including solid state studies, astronomy, and cosmology.

  10. Advanced far infrared blocked impurity band detectors based on germanium liquid phase epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Olsen, C S [Lawrence Berkeley National Lab., CA (United States). Engineering Div.

    1998-05-01

    This research has shown that epilayers with residual impurity concentrations of 5 x 10{sup 13} cm{sup {minus}3} can be grown by producing the purest Pb available in the world. These epilayers have extremely low minority acceptor concentrations, which is ideal for fabrication of IR absorbing layers. The Pb LPE growth of Ge also has the advantageous property of gettering Cu from the epilayer and the substrate. Epilayers have been grown with intentional Sb doping for IR absorption on lightly doped substrates. This research has proven that properly working Ge BIB detectors can be fabricated from the liquid phase as long as pure enough solvents are available. The detectors have responded at proper wavelengths when reversed biased even though the response did not quite reach minimum wavenumbers. Optimization of the Sb doping concentration should further decrease the photoionization energy of these detectors. Ge BIB detectors have been fabricated that respond to 60 cm{sup {minus}1} with low responsivity. Through reduction of the minority residual impurities, detector performance has reached responsivities of 1 A/W. These detectors have exhibited quantum efficiency and NEP values that rival conventional photoconductors and are expected to provide a much more sensitive tool for new scientific discoveries in a number of fields, including solid state studies, astronomy, and cosmology.

  11. The effect of high magnetic field on the photoresponse of Si:B structures with blocked conductivity in the impurity band

    International Nuclear Information System (INIS)

    The dependence of photoconductivity on the magnetic field has been studied for Si:B blocked-impurity-band (BIB) structures with the boron impurity concentration of ∼1018 cm-3 in the active layer. Measurements were performed in the magnetic field B up to 30 T with the pulse length of 0.8 s in the temperature range T = 4.2-9 K, under irradiation of structures with the room-temperature background with ∼1016 photons/(cm2 s) intensity. It is established that, in the longitudinal configuration and with the magnetic field parallel to the electric field, the photocurrent decreases as B increases, mainly due to a decrease in the hole multiplication factor M in the magnetic field and/or an increase in the activation energy for hopping conductivity in the active layer. At T = 4.2 K, the photocurrent can drop by a factor of several tens. At the same time, at low bias voltage Vb, when M ∼ 1, and at higher temperatures, T ∼ 9 K, the photocurrent decreases no more than twofold in the field of ∼30 T. It is found also that in the transverse configuration (with the magnetic field perpendicular to the electric field), the effect of the magnetic field on the photoresponse of a structure significantly increases (more than by an order of magnitude at T = 4.2 K). This fact can be explained by the accumulation of carriers in the blocking (undoped) layer of a BIB structure, which is related to increasing time of the hole flight across this layer due to high mobility of holes and strong bending of their trajectories in the transverse configuration

  12. Development of Blocked-Impurity-Band-Type Ge Detectors Fabricated with the Surface-Activated Wafer Bonding Method for Far-Infrared Astronomy

    Science.gov (United States)

    Hanaoka, M.; Kaneda, H.; Oyabu, S.; Yamagishi, M.; Hattori, Y.; Ukai, S.; Shichi, K.; Wada, T.; Suzuki, T.; Watanabe, K.; Nagase, K.; Baba, S.; Kochi, C.

    2016-07-01

    We report the current status of the development of our new detectors for far-infrared (FIR) astronomy. We develop Blocked-Impurity-Band (BIB)-type Ge detectors to realize large-format compact arrays covering a wide FIR wavelength range up to 200 \\upmu m. We fabricated Ge junction devices of different physical parameters with a BIB-type structure, using the room temperature, surface-activated wafer bonding (SAB) method. We measured the absolute responsivity and the spectral response curve of each device at low temperatures, using an internal blackbody source in a cryostat and a Fourier transform spectrometer, respectively. The results show that the SAB Ge junction devices have significantly higher absolute responsivities and longer cut-off wavelengths of the spectral response than the conventional bulk Ge:Ga device. Based upon the results, we discuss the optimum parameters of SAB Ge junction devices for FIR detectors. We conclude that SAB Ge junction devices possess a promising applicability to next-generation FIR detectors covering wavelengths up to ˜ 200 \\upmu m with high responsivity. As a next step, we plan to fabricate a BIB-type Ge array device in combination with a low-power cryogenic readout integrated circuit.

  13. Development for Germanium Blocked Impurity Band Far-Infrared Image Sensors with Fully-Depleted Silicon-On-Insulator CMOS Readout Integrated Circuit

    Science.gov (United States)

    Wada, T.; Arai, Y.; Baba, S.; Hanaoka, M.; Hattori, Y.; Ikeda, H.; Kaneda, H.; Kochi, C.; Miyachi, A.; Nagase, K.; Nakaya, H.; Ohno, M.; Oyabu, S.; Suzuki, T.; Ukai, S.; Watanabe, K.; Yamamoto, K.

    2016-07-01

    We are developing far-infrared (FIR) imaging sensors for low-background and high-sensitivity applications such as infrared astronomy. Previous FIR monolithic imaging sensors, such as an extrinsic germanium photo-conductor (Ge PC) with a PMOS readout integrated circuit (ROIC) hybridized by indium pixel-to-pixel interconnection, had three difficulties: (1) short cut-off wavelength (120 \\upmu m), (2) large power consumption (10 \\upmu W/pixel), and (3) large mismatch in thermal expansion between the Ge PC and the Si ROIC. In order to overcome these difficulties, we developed (1) a blocked impurity band detector fabricated by a surface- activated bond technology, whose cut-off wavelength is longer than 160 \\upmu m, (2) a fully-depleted silicon-on-insulator CMOS ROIC which works below 4 K with 1 \\upmu W/pixel operating power, and (3) a new concept, Si-supported Ge detector, which shows tolerance to thermal cycling down to 3 K. With these new techniques, we are now developing a 32 × 32 FIR imaging sensor.

  14. Germanium blocked impurity band far infrared detectors

    International Nuclear Information System (INIS)

    The infrared portion of the electromagnetic spectrum has been of interest to scientist since the eighteenth century when Sir William Herschel discovered the infrared as he measured temperatures in the sun's spectrum and found that there was energy beyond the red. In the late nineteenth century, Thomas Edison established himself as the first infrared astronomer to look beyond the solar system when he observed the star Arcturus in the infrared. Significant advances in infrared technology and physics, long since Edison's time, have resulted in many scientific developments, such as the Infrared Astronomy Satellite (IRAS) which was launched in 1983, semiconductor infrared detectors for materials characterization, military equipment such as night-vision goggles and infrared surveillance equipment. It is now planned that cooled semiconductor infrared detectors will play a major role in the ''Star Wars'' nuclear defense scheme proposed by the Reagan administration

  15. Spin susceptibility of Anderson impurities in arbitrary conduction bands

    Science.gov (United States)

    Fang, Tie-Feng; Tong, Ning-Hua; Cao, Zhan; Sun, Qing-Feng; Luo, Hong-Gang

    2015-10-01

    Spin susceptibility of Anderson impurities is a key quantity in understanding the physics of Kondo screening. Traditional numerical renormalization group (NRG) calculation of the impurity contribution χimp to susceptibility, defined originally by Wilson in a flat wide band, has been generalized before to structured conduction bands. The results brought about non-Fermi-liquid and diamagnetic Kondo behaviors in χimp, even when the bands are not gapped at the Fermi energy. Here, we use the full density-matrix (FDM) NRG to present high-quality data for the local susceptibility χloc and to compare them with χimp obtained by the traditional NRG. Our results indicate that those exotic behaviors observed in χimp are unphysical. Instead, the low-energy excitations of the impurity in arbitrary bands only without gap at the Fermi energy are still a Fermi liquid and paramagnetic. We also demonstrate that unlike the traditional NRG yielding χloc less accurate than χimp, the FDM method allows a high-precision dynamical calculation of χloc at much reduced computational cost, with an accuracy at least one order higher than χimp. Moreover, artifacts in the FDM algorithm to χimp and origins of the spurious non-Fermi-liquid and diamagnetic features are clarified. Our work provides an efficient high-precision algorithm to calculate the spin susceptibility of impurity for arbitrary structured bands, while negating the applicability of Wilson's definition to such cases.

  16. Sunlight loss for femtosecond microstructured silicon with two impurity bands

    International Nuclear Information System (INIS)

    Black silicon, produced by irradiating the surface of a silicon wafer with femtosecond laser pulses in the presence of a sulfur-bearing gas, is widely believed to be a potential material for efficient multi-intermediate-band silicon solar cells. Taking chalcogen as an example, we analyse the loss of sunlight for silicon with two impurity bands and we find that loss of the sunlight can be minimized to 0.332 when Te0(0.307 eV) and Te+(0.411 eV) are doped into microstructured silicon. Finally, problems needed to be resolved in analysing the relationship between conversion efficiency of the ideal four-band silicon solar cell and the position of the introduced two intermediated bands in silicon according to detailed balance theory are pointed out with great emphasis. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

  17. Strongly correlated impurity band superconductivity in diamond: X-ray spectroscopic evidence

    Directory of Open Access Journals (Sweden)

    G. Baskaran

    2006-01-01

    Full Text Available In a recent X-ray absorption study in boron doped diamond, Nakamura et al. have seen a well isolated narrow boron impurity band in non-superconducting samples and an additional narrow band at the chemical potential in a superconducting sample. We interpret the beautiful spectra as evidence for upper Hubbard band of a Mott insulating impurity band and an additional metallic 'mid-gap band' of a conducting 'self-doped' Mott insulator. This supports the basic framework of a recent theory of the present author of strongly correlated impurity band superconductivity (impurity band resonating valence bond, IBRVB theory in a template of a wide-gap insulator, with no direct involvement of valence band states.

  18. Hyperspectral band selection based on parallel particle swarm optimization and impurity function band prioritization schemes

    Science.gov (United States)

    Chang, Yang-Lang; Liu, Jin-Nan; Chen, Yen-Lin; Chang, Wen-Yen; Hsieh, Tung-Ju; Huang, Bormin

    2014-01-01

    In recent years, satellite imaging technologies have resulted in an increased number of bands acquired by hyperspectral sensors, greatly advancing the field of remote sensing. Accordingly, owing to the increasing number of bands, band selection in hyperspectral imagery for dimension reduction is important. This paper presents a framework for band selection in hyperspectral imagery that uses two techniques, referred to as particle swarm optimization (PSO) band selection and the impurity function band prioritization (IFBP) method. With the PSO band selection algorithm, highly correlated bands of hyperspectral imagery can first be grouped into modules to coarsely reduce high-dimensional datasets. Then, these highly correlated band modules are analyzed with the IFBP method to finely select the most important feature bands from the hyperspectral imagery dataset. However, PSO band selection is a time-consuming procedure when the number of hyperspectral bands is very large. Hence, this paper proposes a parallel computing version of PSO, namely parallel PSO (PPSO), using a modern graphics processing unit (GPU) architecture with NVIDIA's compute unified device architecture technology to improve the computational speed of PSO processes. The natural parallelism of the proposed PPSO lies in the fact that each particle can be regarded as an independent agent. Parallel computation benefits the algorithm by providing each agent with a parallel processor. The intrinsic parallel characteristics embedded in PPSO are, therefore, suitable for parallel computation. The effectiveness of the proposed PPSO is evaluated through the use of airborne visible/infrared imaging spectrometer hyperspectral images. The performance of PPSO is validated using the supervised K-nearest neighbor classifier. The experimental results demonstrate that the proposed PPSO/IFBP band selection method can not only improve computational speed, but also offer a satisfactory classification performance.

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

    OpenAIRE

    Ganapathy Baskaran

    2008-01-01

    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 ...

  20. Band structures of ZnTe:O alloys with isolated oxygen and with clustered oxygen impurities

    International Nuclear Information System (INIS)

    Highlights: • Band structures of ZnTe:O alloy highly depends on the status of oxygen. • Clustered oxygen lowers the bandgap while isolated oxygen increases the bandgap. • The solar adsorption efficiency of ZnTe:O can be improved by oxygen clustering. -- Abstract: First-principles calculations reveal that band structures of ZnTe:O alloys highly depend on the configuration of oxygen in the alloy. For alloys with isolated oxygen, the calculated band structure shows the formation of intermediate states between valence and conduction band and the shift of conduction band to higher energy level. It expands the gap between valence and conduction band. For alloys with clustered oxygen, the formation of intermediate band is still observed, while the gap between valence and conduction band is decreased. For alloys with oxygen impurities adjacent to Zn vacancy, the band structure only shows the decrease of the gap between valence and conduction band without the formation of any intermediate band. These results suggest the critical role of Zn–O bonding in determining the energy level of the impurity states. On the basis of our results, a possible band engineering approach is suggested in order to improve the performance of ZnTe:O alloy as intermediate band solar adsorbent

  1. 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.

  2. Sequential tunneling in doped superlattices: Fingerprints of impurity bands and photon-assisted tunneling

    DEFF Research Database (Denmark)

    Wacker, Andreas; Jauho, Antti-Pekka; Zeuner, S.;

    1997-01-01

    We report a combined theoretical and experimental study of electrical transport in weakly coupled doped superlattices. Our calculations exhibit negative differential conductivity at sufficiently high electric fields for all dopings. In low-doped samples the presence of impurity bands modifies the...

  3. Impurity effects on the band structure of one-dimensional photonic crystals: experiment and theory

    International Nuclear Information System (INIS)

    We study the effects of single impurities on the transmission in microwave realizations of the photonic Kronig-Penney model, consisting of arrays of Teflon pieces alternating with air spacings in a microwave guide. As only the first propagating mode is considered, the system is essentially one-dimensional (1D) obeying the Helmholtz equation. We derive analytical closed form expressions from which the band structure, frequency of defect modes and band profiles can be determined. These agree very well with experimental data for all types of single defects considered (e.g. interstitial and substitutional) and show that our experimental set-up serves to explore some of the phenomena occurring in more sophisticated experiments. Conversely, based on the understanding provided by our formulae, information about the unknown impurity can be determined by simply observing certain features in the experimental data for the transmission. Further, our results are directly applicable to the closely related quantum 1D Kronig-Penney model

  4. Impurity effects on the band structure of one-dimensional photonic crystals: Experiment and theory

    CERN Document Server

    Luna-Acosta, G A; Kuhl, U; Stoeckmann, H -J

    2007-01-01

    We study the effects of single impurities on the transmission in microwave realizations of the photonic Kronig-Penney model, consisting of arrays of Teflon pieces alternating with air spacings in a microwave guide. As only the first propagating mode is considered, the system is essentially one dimensional obeying the Helmholtz equation. We derive analytical closed form expressions from which the band structure, frequency of defect modes, and band profiles can be determined. These agree very well with experimental data for all types of single defects considered (e. g. interstitial, substitutional) and shows that our experimental set-up serves to explore some of the phenomena occurring in more sophisticated experiments. Conversely, based on the understanding provided by our formulas, information about the unknown impurity can be determined by simply observing certain features in the experimental data for the transmission. Further, our results are directly applicable to the closely related quantum 1D Kronig-Penn...

  5. Impurity Sub-Band in Heavily Cu-Doped InAs Nanocrystal Quantum Dots Detected by Ultrafast Transient Absorption.

    Science.gov (United States)

    Yang, Chunfan; Faust, Adam; Amit, Yorai; Gdor, Itay; Banin, Uri; Ruhman, Sanford

    2016-05-19

    The effect of Cu impurities on the absorption cross section, the rate of hot exction thermalization, and on exciton recombination processes in InAs quantum dots was studied by femtosecond transient absorption. Our findings reveal dynamic spectral effects of an emergent impurity sub-band near the bottom of the conduction band. Previously hypothesized to explain static photophysical properties of this system, its presence is shown to shorten hot carrier relaxation. Partial redistribution of interband oscillator strength to sub-band levels reduces the band edge bleach per exciton progressively with the degree of doping, even though the total linear absorption cross section at the band edge remains unchanged. In contrast, no doping effects were detected on absorption cross sections high in the conduction band, as expected due to the relatively high density of sates of the undoped QDs. PMID:26720008

  6. Magnetic behaviour of dilute Ce impurities in α-U: influence of f-band conduction electrons on moment instability

    International Nuclear Information System (INIS)

    We have measured magnetic susceptibility of dilute Ce impurities in the f-band metal α-U. The data show Curie-Weiss behaviour in the temperature range 4.2-300 K yielding a magnetic moment of ∝2μB/Ce and a spin fluctuation temperature TSF of SF value, in the small unit cell of U lattice, deviates strongly from the systematics of Ce magnetism in sp- and d-band metal hosts. The results indicate that magnetism of spin fluctuation of Ce in U is strongly influenced by the host f-band electrons. (orig.)

  7. Intense laser field and conduction band-edge nonparabolicity effects on hydrogenic impurity states of InGaN QW

    Science.gov (United States)

    El Ghazi, Haddou

    2015-09-01

    In this paper, hydrogenic impurity ground-state binding energy in unstrained wurtzite (In, Ga)N symmetric quantum well is investigated. The heterostructure is considered under the action of an intense laser field (ILF) incorporating an additional internal probe as well as the conduction band-edge nonparabolicity effect (CBENP). The variational approach is used within the framework of single band effective-mass approximation with two-parametric 1S-hydrogenic trial wavefunction. The competition effect between internal and external perturbations is also shown. Our results reveal that the binding energy is the largest for the well width around the effective Bohr radius and is strongly influenced by both parameters. Moreover, the principle effect of ILF (CBENP) is to reduce (enhance) the binding energy. It is found that the lift of the conduction band-edge can be easily eliminated by adjusting the ILF-parameter.

  8. Impurity states are the origin of yellow-band emission in GaN structures produced by epitaxial lateral overgrowth

    International Nuclear Information System (INIS)

    GaN grown by selective area epitaxy and subsequent lateral overgrowth exhibits sharply peaked anisotropic structures in the form of hexagonal pyramids and ridges. Spatially resolved optical emission from these structures, using both cathodoluminescence and collection-mode near-field scanning optical microscopy, of radiation centered near 550 nm, the so-called yellow band, indicates that the emission arises predominantly from the apex regions of the pyramids and ridges. In contrast, transmission electron microscopy shows that the apex region is nearly dislocation free and that dislocations cluster at the vertical growth core region. The spatial separation of the dislocations and optical emission indicates that the yellow-band emission has no direct relationship to dislocations. The observation of yellow-band emission strongly localized in the apical regions of both types of structures and the tendency of impurity species to concentrate in these areas argues that it arises instead from impurity states, the most likely candidate of which is a complex formed between a gallium vacancy, VGa, and Si or O. (c) 1999 American Institute of Physics

  9. The impurity optical absorption and structure of conduction band in 6H-SiC

    International Nuclear Information System (INIS)

    The investigation of absorption spectra in n-type nitrogen doped 6H-SiC crystals from the near infrared up to fundamental band region at polarization of electric field (E) of the light wave relatively the optical axis (C) for E parallel to C and E perpendicular to C has been carried out. It is for the first time that at E parallel to C a slight absorption band with maximum at 2.85 eV has been investigated. All absorption bands observed were caused by photoionization of donors (nitrogen) with electron transition in to above-lying minima of the conduction band situated at different critical points of the Brillouin zone. The analysis of data obtained and experimental data available on the photoionization of nitrogen, alongside with theoretical data on the structure of the conduction band make it possible to propose the structure and symmetry of additional extrema in Brillouin zone for 6H-SiC

  10. Development of ultra pure germanium epi layers for blocked impurity band far infrared detectors

    Energy Technology Data Exchange (ETDEWEB)

    Lutz, M.P.

    1991-05-01

    The main goals of this paper are: (1) To develop a low-pressure CVD (LPCVD) process that allows epitaxial growth at lower temperatures. Lower temperatures will allow the achievement of a sharp dopant profile at the substrate/epi-layer interface. Less out-diffusion from the substrate would allow the use of thinner epitaxial layers, which would lead to a larger depletion width in the photoactive region. LPCVD also avoids, to a great extent, gas-phase nucleation, which would cause Ge particulates to fall onto the wafer surface during growth. (2) To reduce high levels of oxygen and copper present at the wafer interface, as observed by secondary ion mass spectroscopy (SIMS). In order to achieve high-quality epitaxial layers, it is imperative that the substrate surface be of excellent quality. (3) To make and test detectors, after satisfactory epitaxial layers have been made.

  11. Development of ultra pure germanium epi layers for blocked impurity band far infrared detectors

    International Nuclear Information System (INIS)

    The main goals of this paper are: (1) To develop a low-pressure CVD (LPCVD) process that allows epitaxial growth at lower temperatures. Lower temperatures will allow the achievement of a sharp dopant profile at the substrate/epi-layer interface. Less out-diffusion from the substrate would allow the use of thinner epitaxial layers, which would lead to a larger depletion width in the photoactive region. LPCVD also avoids, to a great extent, gas-phase nucleation, which would cause Ge particulates to fall onto the wafer surface during growth. (2) To reduce high levels of oxygen and copper present at the wafer interface, as observed by secondary ion mass spectroscopy (SIMS). In order to achieve high-quality epitaxial layers, it is imperative that the substrate surface be of excellent quality. (3) To make and test detectors, after satisfactory epitaxial layers have been made

  12. Magnetic Impurities in Graphene

    OpenAIRE

    Hu, F. M.; Ma, Tianxing; Lin, Hai-Qing; Gubernatis, J. E.

    2011-01-01

    We used a quantum Monte Carlo method to study the magnetic impurity adatoms on graphene. We found that by tuning the chemical potential we could switch the values of the impurity's local magnet moment between relatively large and small values. Our computations of the impurity's spectral density found its behavior to differ significantly from that of an impurity in a normal metal and our computations of the charge-charge and spin-spin correlations between the impurity and the conduction band e...

  13. The Effects of Mode Impurity of Ka-band System Performance

    Science.gov (United States)

    Hoppe, D. J.; Imbriale, W. A.; Bhanji, A. M.

    1985-01-01

    Problems associated with spurious mode generation in the proposed Ka-Band gyroklystron transmitter tube, overmoded transmission line, and feed are discussed. A brief description of the overall problem is presented. The theory used to evaluate feed and antenna performance when spurious modes are present is given. Results for feed patterns and overall antenna patterns for various levels and types of spurious modes are presented. Worst case antenna efficiency is calculated as a function of spurious mode level. Conclusions are drawn regarding the results of this study and their application to specifications on the transmitter tube and transmission line system.

  14. Minority carrier blocking to enhance the thermoelectric figure of merit in narrow-band-gap semiconductors

    Science.gov (United States)

    Bahk, Je-Hyeong; Shakouri, Ali

    2016-04-01

    We present detailed theoretical predictions on the enhancement of the thermoelectric figure of merit by minority carrier blocking with heterostructure barriers in bulk narrow-band-gap semiconductors. Bipolar carrier transport, which is often significant in a narrow-band-gap material, is detrimental to the thermoelectric energy conversion efficiency as it suppresses the Seebeck coefficient and increases the thermal conductivity. When the minority carriers are selectively prevented from participating in conduction while the transport of majority carriers is relatively unaffected by one-sided heterobarriers, the thermoelectric figure of merit can be drastically enhanced. Thermoelectric transport properties such as Seebeck coefficient, electrical conductivity, and electronic thermal conductivity including the bipolar term are calculated with and without the barriers based on the near-equilibrium Boltzmann transport equations under the relaxation time approximation to investigate the effects of minority carrier barriers on the thermoelectric figure of merit. For this, we provide details of carrier transport modeling and fitting results of experimental data for three important material systems, B i2T e3 -based alloys, M g2S i1 -xS nx , and S i1 -xG ex , that represent, respectively, near-room-temperature (300 K-500 K), midtemperature (600 K-900 K), and high-temperature (>1000 K ) applications. Theoretical maximum enhancement of thermoelectric figure of merit that can be achieved by minority carrier blocking is quantified and discussed for each of these semiconductors.

  15. On the impact of isoelectric impurities on band bowing and disorder of compound semiconductors; Ueber den Einfluss von isoelektronischen Stoerstellen auf Bandbiegung und Unordnung in Verbindungshalbleitern

    Energy Technology Data Exchange (ETDEWEB)

    Karcher, Christian

    2012-03-16

    Isolectronic impurities and their impact on the properties of compound semiconductors is discussed in two systems: Nitrogen in Ga(As,P) quantum wells on the one hand and Sulfur and Selenium in bulk ZnTe. The properties are reduced to two experimentally observable aspects: Band Bowing, i.e. the non-linearity of the band gap of the compound semiconductor and disorder, i.e. in particular the formation of a strongly localized density of states beneath the fundamental band gap. Apart of the pure experimental studies an insight into the theoretical model of disorder-induced temperature dependent luminescence properties of the compound semiconductors by means of Monte Carlo Simulations is given.

  16. Simulation of structured 4T1→6A1 emission bands of Mn2+ impurity in Zn2SiO4: A first-principle methodology

    International Nuclear Information System (INIS)

    A sequential, fully first-principle theoretical study of the Mn2+ green emission bands in the Zn2SiO4:Mn2+ phosphor is presented for the first time. A combined approach is developed based on the modern periodic density-functional theory and cluster ab initio wave-function-based electronic structure methods, the linear response theory for lattice phonons, and generating function formalism of vibronic spectra within the displaced multi-mode harmonic oscillator model. We obtain fairly good agreement between the calculated low- and high-temperature emission band positions, widths, zero-phonon lines and phonon wings and the available experimental emission studies, with special emphasis on Mn2+ distribution over two non-equivalent Zn2+ sites in the Zn2SiO4 material. An interpretation for vibronic structure observed in the low-temperature emission spectrum of this phosphor is suggested based on the present first-principle study. - Highlights: ► First-principle methodology for simulation of vibronic bands of impurities. ► Calculation of zero phonon lines and phonon structures. ► Estimation of temperature broadening of emission bands. ► Theoretical analysis of green emission band of Zn2SiO4:Mn phosphor. ► Distribution of Mn ions over Zn sites in the host matrix.

  17. In-Band Interference Effects on UTRA LTE Uplink Resource Block Allocation

    DEFF Research Database (Denmark)

    Priyanto, Basuki Endah; Sørensen, Troels Bundgaard; Jensen, Ole Kiel

    In this paper we investigate the impact of in-band interference on the uplink multiple access of UMTS Terrestrial Radio Access, long term evolution (UTRA LTE). In- band and out-of-band interference arise as a result of transmitter imperfections. Out-of- band, or adjacent channel, interference can...

  18. Layer Combination Effect on Band Gap Shift of InGaAsP/InP MQWs by Impurity-free Vacancy Disordering

    Institute of Scientific and Technical Information of China (English)

    ZHAO Jie; WANG Yong-chen; FENG Zhe-chuan; Ferguson I

    2004-01-01

    InGaAsP/InP multiple quantum wells with quantum well intermixing have been prepared by impurity-free vacancy disordering.The luminescent characteristics were investigated using photoluminescence and photoreflectance,from which the band gap blue shift was observed.Si3N4,SiO2 and SOG were used for the dielectric layer to enhance intermixing from the outdiffusion of group III atoms.All samples were annealed by rapid thermal annealing.The results indicate that the band gap blue shift varies with the dielectric layers and the annealing temperature.The SiO2 capping with an InGaAs cladding layer was successfully used to induce larger band tuning effect in the InGaAsP/InP MQWs than the Si3N4 capping with an InGaAs cladding layer.On the other hand, samples with the Si3N4-InP cap layer combination also show larger energy shifts than that with SiO2-InP cap layer combination.

  19. 47 CFR 27.16 - Network access requirements for Block C in the 746-757 and 776-787 MHz bands.

    Science.gov (United States)

    2010-10-01

    ... 47 Telecommunication 2 2010-10-01 2010-10-01 false Network access requirements for Block C in the... § 27.16 Network access requirements for Block C in the 746-757 and 776-787 MHz bands. (a) Applicability... the devices and applications of their choice on the licensee's C Block network, except: (1) Insofar...

  20. Computing approximate blocking probability of inverse multiplexing and sub-band conversion in the flexible-grid optical networks

    Science.gov (United States)

    Gu, Yamei; You, Shanhong

    2016-07-01

    With the rapid growth of data rate, the optical network is evolving from fixed-grid to flexible-grid to provide spectrum-efficient and scalable transport of 100 Gb/s services and beyond. Also, the deployment of wavelength converter in the existing network can increase the flexibility of routing and wavelength allocation (RWA) and improve blocking performance of the optical networks. In this paper, we present a methodology for computing approximate blocking probabilities of the provision of multiclass services in the flexible-grid optical networks with sub-band spectrum conversion and inverse multiplexing respectively. Numerical calculation results based on the model are compared to the simulation results for the different cases. It is shown that the calculation results match well with the simulation results for the flexible-grid optical networks at different scenarios.

  1. Band gap control using electric field of photonic gel cells fabricated with block copolymer and hydrogel.

    Science.gov (United States)

    Lee, Sung Nam; Baek, Young Bin; Shin, Dong Myung

    2014-08-01

    Optical and electrical characteristics of the devices using photonic gel film and hydrogel electrolyte were studied. Poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) lamellar film with alternating hydrophobic block and hydrophilic polyelectrolyte block polymers (52 kg/mol-b-57 kg/mol) were prepared for the photonic gel. Poly(isobutylene-co-maleic acid) sodium salts were prepared for the hydrogel. This hydrogel fiber is common water swelling material and it owned ions for a device has conductivity. Photonic gel and hydrogel was spin coating onto Indium-tin-oxide (ITO) glass for make electric fields. The reflectance maximum wavelength of photonic crystal device shifted from 538 nm and reached to 557 nm, 585 nm and 604 nm during 30 min voltage applying time. The bandwidth variation was very limited. Loss of electrolyte was much less with hydrogel compared to the pure water. We can control color of hydrogel used photonic device by electric field with reasonable time range under moderate electric field by applying 2 V between two facing electrodes. PMID:25936055

  2. Determining impurities

    International Nuclear Information System (INIS)

    A method of determining the content of impurities in organic-origin natural fibrous materials, in which a specimen of said material is compacted to a surface density of from 0.05 to 50 g/cm2, whereupon it is exposed to the effect of a soft gamma-radiation, the mass attenuation coefficient (μ) is determined and the percentage content (Csub(A)) of impurities is assessed. The method has applications in the textile industry. (author)

  3. Donor impurity-related optical absorption spectra in GaAs-Ga{sub 1-x}Al{sub x}As quantum wells: hydrostatic pressure and {gamma}-X conduction band mixing effects

    Energy Technology Data Exchange (ETDEWEB)

    Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, C.P. 62209, Cuernavaca, MOR (Mexico); Inst. de Ciencia de Materiales de Madrid, CSIC, Sor Juana Ines de la Cruz 3, 28049 Madrid (Spain); Lopez, S.Y. [Fac. de Educacion, Universidad de Antioquia, AA 1226, Medellin (Colombia); Duque, C.A. [Inst. de Fisica, Universidad de Antioquia, AA 1226, Medellin (Colombia); Velasco, V.R. [Inst. de Ciencia de Materiales de Madrid, CSIC, Sor Juana Ines de la Cruz 3, 28049 Madrid (Spain)

    2007-07-01

    Using a variational procedure within the effective mass approximation, the mixing between the {gamma} and X conduction band valleys in GaAs-Ga{sub 1-x}Al{sub x}As quantum wells is investigated by taking into account the effect of applied hydrostatic pressure. Some optical properties such as donor and/or acceptor binding energy and impurity-related transition energies are calculated and comparisons with available experimental data are presented. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Hydrostatic pressure effects on the {gamma}-X conduction band mixing and the binding energy of a donor impurity in GaAs-Ga{sub 1-x}Al{sub x}As quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Duque, C.A. [Instituto de Fisica, Universidad de Antioquia, AA 1226, Medellin (Colombia); Lopez, S.Y. [Facultad de Educacion, Universidad de Antioquia, AA 1226, Medellin (Colombia); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, C.P. 62210, Cuernavaca (Mexico)

    2007-06-15

    Mixing between {gamma} and X valleys of the conduction band in GaAs-Ga{sub 1-x}Al{sub x}As quantum wells is investigated taken into account the effect of applied hydrostatic pressure. This effect is introduced via the pressure-dependent values of the corresponding energy gaps and the main band parameters. The mixing is considered along the lines of a phenomenological model. Variation of the confined ground state in the well as a function of the pressure is reported. The dependencies of the variationally calculated binding energy of a donor impurity with the hydrostatic pressure and well width are also presented. It is shown that the inclusion of the {gamma}-X mixing explains the non-linear behavior in the photoluminescence peak of confined exciton states that has been observed for pressures above 20 kbar. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. Optical density of states in ultradilute GaAsN alloy: Coexistence of free excitons and impurity band of localized and delocalized states

    International Nuclear Information System (INIS)

    Optically active states in liquid phase epitaxy-grown ultra-dilute GaAsN are studied. The feature-rich low temperature photoluminescence spectrum has contributions from excitonic band states of the GaAsN alloy, and two types of defect states—localized and extended. The degree of delocalization for extended states both within the conduction and defect bands, characterized by the electron temperature, is found to be similar. The degree of localization in the defect band is analyzed by the strength of the phonon replicas. Stronger emission from these localized states is attributed to their giant oscillator strength.

  6. Quantum cascade laser design based on impurity-band transitions of donors in Si/GeSi(1 1 1) heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Bekin, N.A., E-mail: nbekin@ipm.sci-nnov.r [Institute for Physics of Microstructures of RAS, GSP-105, Nizhny Novgorod 603950 (Russian Federation); Pavlov, S.G. [Institute of Planetary Research, German Aerospace Center, 12489 Berlin (Germany)

    2009-12-15

    The possibility of amplification of terahertz radiation due to optical transitions between a two-dimensional state continuum (2D) and shallow-level donor states in Si/GeSi(1 1 1) superlattices with selectively delta-doped quantum wells is analyzed theoretically. The mechanism of population inversion is based on fast ionization of donor centers by phonon-assisted tunneling into continuum of a lower subband in the neighboring quantum well. The fast tunneling is caused by hybridization of the impurity ground state and a 2D state continuum in the neighboring quantum well. It is shown that for the donor concentration of 5x10{sup 11} cm{sup -2} per period the terahertz gain can be as high as 10 cm{sup -1} in the wavelength range of 29-45 mum (6.5-10.2 THz).

  7. Elucidating the band structure and free charge carrier dynamics of pure and impurities doped CH3NH3PbI(3-x)Cl(x) perovskite thin films.

    Science.gov (United States)

    Zhang, Zhen-Yu; Chen, Xin; Wang, Hai-Yu; Xu, Ming; Gao, Bing-Rong; Chen, Qi-Dai; Sun, Hong-Bo

    2015-11-28

    CH3NH3PbI3-xClx perovskite material has been commonly used as the free charge generator and reservoir in highly efficient perovskite-based solid-state solar photovoltaic devices. However, many of the underlying fundamental photophysical mechanisms in this material such as the perovskite transition band structure as well as the dependent relationship between the carrier properties and lattice properties still lack sufficient understanding. Here, we elucidated the fundamental band structure of the pure CH3NH3PbI3-xClx pervoskite lattice, and then reported about the dependent relationship between the free charge carrier characteristic and the different CH3NH3PbI3-xClx pervoskite lattice thin films utilizing femtosecond time-resolved pump-probe technologies. The data demonstrated that the pure perovskite crystal band structure should only have one conduction and one valence band rather than dual valences, and the pure perovskite lattice could trigger more free charge carriers with a slower recombination rate under an identical pump intensity compared with the impurities doped perovskite crystal. We also investigated the perovskite film performance when exposed to moisture and water, the corresponding results gave us a dip in the optimization of the performance of perovskite based devices, and so as a priority this material should be isolated from moisture (water). This work may propose a deeper perspective on the comprehension for this material and it is useful for future optimization of applications in photovoltaic and light emission devices. PMID:26497219

  8. Scattering of Waves by Impurities in Precompressed Granular Chains

    OpenAIRE

    Martínez, Alejandro J.; YASUDA, HIROMI; Kim, Eunho; Kevrekidis, P. G.; Mason A Porter; Yang, Jinkyu

    2016-01-01

    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 ...

  9. Local order dependent impurity levels in alloy semiconductors

    International Nuclear Information System (INIS)

    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)

  10. Coulomb impurity in graphene

    CERN Document Server

    Biswas, Rudro R; Son, Dam T

    2007-01-01

    We consider the problem of screening of an electrically charged impurity in a clean graphene sheet. When electron-electron interactions are neglected, the screening charge has a sign opposite to that of the impurity, and is localized near the impurity. Interactions between electrons smear out the induced charge density to give a large-distance tail that follows approximately, but not exactly, an r^{-2} behavior and with a sign which is the same as that of the impurity.

  11. Impurity binding energy for -doped quantum well structures

    Indian Academy of Sciences (India)

    V Tulupenko; C A Duque; R Demediuk; O Fomina; V Akimov; V Belykh; T Dmitrichenko; V Poroshin

    2014-10-01

    The binding energy of an impurity delta layer situated either in the centre or at the edge of a quantum well (QW) is theoretically considered for the example of -type Si0.8Ge0.2/Si/Si0.8Ge0.2 QW doped with phosphorus. Calculations are made for the case of not so big impurity concentrations, when impurity bands are not yet formed and it is still possible to treat impurity as isolated ones. It is shown on the base of self-consistent solution of Schrödinger, Poisson and electro-neutrality equations that impurity binding energy is dependent on the degree of impurity ionization and the most noticeably for the case of edge-doped QWs.

  12. The electronic structure of impurities in semiconductors

    CERN Multimedia

    Nylandsted larsen, A; Svane, A

    2002-01-01

    The electronic structure of isolated substitutional or interstitial impurities in group IV, IV-IV, and III-V compound semiconductors will be studied. Mössbauer spectroscopy will be used to investigate the incorporation of the implanted isotopes on the proper lattice sites. The data can be directly compared to theoretical calculations using the LMTO scheme. Deep level transient spectroscopy will be used to identify the band gap levels introduced by metallic impurities, mainly in Si~and~Si$ _{x}$Ge$_{1-x}$. \\\\ \\\\

  13. SOURCES OF IMPURITIES: A REVIEW

    OpenAIRE

    Sapra Ashu; Kakkar Saloni; Narasimhan B.

    2012-01-01

    Impurity is defined as an entity of drug substance or drug product that is not chemical entity defined as drug substance, an excipient, or other additives to drug products. In Webster’s dictionary, impurity is “something that is impure or makes something else impure. In the pharmaceutical world, an impurity is generally considered as any other organic material besides the drug substance that arises out of the synthesis most of the time; inorganic contaminants are not considered as impurities ...

  14. Simulating graphene impurities

    OpenAIRE

    Marcin Szyniszewski

    2013-01-01

    We study a model of magnetic impurities deposited onto a graphene lattice, interacting via exchange of conduction electrons. Our objective is to look for the long-range ordering of the impurities, which would lead to drastic changes in the transport properties of graphene. Numerical simulations are performed and we indeed observe the ordered phase. We also estimate the critical temperature of a transition between disordered and ordered phases.

  15. SOURCES OF IMPURITIES: A REVIEW

    Directory of Open Access Journals (Sweden)

    Sapra Ashu

    2012-01-01

    Full Text Available Impurity is defined as an entity of drug substance or drug product that is not chemical entity defined as drug substance, an excipient, or other additives to drug products. In Webster’s dictionary, impurity is “something that is impure or makes something else impure. In the pharmaceutical world, an impurity is generally considered as any other organic material besides the drug substance that arises out of the synthesis most of the time; inorganic contaminants are not considered as impurities unless they are toxic, such as heavy metals or arsenic. There are numerous sources of impurities and many different common terms are used for impurities such as Intermediates, Penultimate intermediates, Byproducts, Transformation products, Interaction products, related products and Degradation products. In this review, a description of different types of impurities in relation to ICH guidelines including specific examples, are presented.

  16. Impurity control in TFTR

    International Nuclear Information System (INIS)

    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

  17. Hydrogen-impurity binding energy in vanadium and niobium

    OpenAIRE

    Mokrani, A.; Demangeat, C.

    1989-01-01

    H-H and H-substitutional impurity interaction energy are estimated by the Green operator method developed in the tight binding approximation. This electronic (or chemical) energy is split in four terms : i) the bound states (introduced by the hydrogen) contribution, ii) the band structure contribution, iii) the electron-electron interaction without charge transfer and iv) the charge transfer (between matrix and impurity) contribution. The calculations are done for the transition metal matrix ...

  18. Charged impurity scattering and mobility in gated silicon nanowires

    OpenAIRE

    Persson, Martin P.; Mera, Hector; Niquet, Yann-Michel; Delerue, Christophe; Diarra, Mamadou

    2010-01-01

    We study the effects of charged impurity scattering on the electronic transport properties of -oriented Si nanowires in a gate-all-around geometry, where the impurity potential is screened by the gate, gate oxide and conduction band electrons. The electronic structure of the doped nanowires is calculated with a tight-binding method and the transport properties with a Landauer-Buttiker Green functions approach and the linearized Boltzmann transport equation (LBTE) in the first Born approximati...

  19. 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.

  20. Modelling static impurities

    OpenAIRE

    Correia, Sebastiao; Polonyi, Janos; Richert, Jean

    2000-01-01

    A simple model is presented for the calculation of the quenched average over impurities which are rendered static by setting their mass equal to infinity. The path integral formalism of the second quantized theory contains annealed averages only. The similarity with the Gaussian quenched potential model is discussed.

  1. Dynamical impurity problems

    International Nuclear Information System (INIS)

    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

  2. Microscopic models of impurities in silicon

    International Nuclear Information System (INIS)

    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:Hi), subtitutional and interstitial iron in neutral and positive charge states (Si:Fe0,+, Si:Fe0,+) and substitutional gold in three charge states(Si,Au-,0,+). The thetraedic interstitial defect of silicon (Si:Sii) was also studied. The complex impurities: neighbour iron pair in the lattice (Si:Fe2), substitutional gold-interstitial iron pair (Si:AusFe) and substitutional boron-interstitial hydrogen pair (Si:BsHi), were analysed. (M.C.K.)

  3. Impurity solitons with quadratic nonlinearities

    DEFF Research Database (Denmark)

    Clausen, Carl A. Balslev; Torres, Juan P-; Torner, Lluis

    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...

  4. 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...

  5. A STUDY OF TIN IMPURITY ATOMS IN AMORPHOUS SILICON

    OpenAIRE

    Rabchanova, Tatiana

    2013-01-01

    Using the Mössbauer spectroscopy method for the 119 Sn isotope the state of tin impurity atoms in amorphous a-Si silicon is studied. The electrical and optical properties of tin doped films of thermally spray-coated amorphous silicon have been studied. It is shown that in contrast to the crystalline silicon where tin is an electrically inactive substitution impurity, in vacuum deposited amorphous silicon it produces an acceptor band near the valence band and a fraction of the tin atoms become...

  6. Some aspects regarding impurities profile in fipronil-HPLC method

    Directory of Open Access Journals (Sweden)

    Ana Csuma,

    2011-12-01

    Full Text Available Using a substance as active pharmaceutical ingredient in veterinary drug formulation requires the characterization of this substance as content in active compound and so in terms of impurities possiblepresent in it, the latter being a mandatory requirement for a drug application. Fipronil is a synthetic product belonging to pesticide class used in veterinary practice to manufacture of some products against fleas, given spot–on or in form of spray, in cats and dogs. The main impurities in fipronil include process related impuritiesand degradation products as a result of exposure to environmental conditions: reduction, oxidation, photolysis and hydrolysis. A HPLC method suitable for analytical separation of fipronil from its impurities was established. Separation was achieved on a reversed phase column using a mixture of methanol, acetonitrile and water as mobile phase. In the chosen chromatographic conditions the resolution between fipronil and its sulphone (the main impurity was > 3 and the tailing factor (T < 2.0. Related impurities have absorbed in thesame band of UV wavelength as the main compound fipronil. Comparing the area of impurities obtained for sample solution with the area of the main peak in diluted standard solution allowed the detection of impurities at concentration < 0.1 %. Chromatographic separation on the same analytical column and detection at 280 nm was validated for assay of the content of active substance in fipronil used as ingredient in drug formulations.

  7. Effect of impurity doping in gapped bilayer graphene

    International Nuclear Information System (INIS)

    Impurity doping plays a pivotal role in semiconductor electronics. We study the doping effect in a two-dimensional semiconductor, gapped bilayer graphene. By employing in situ deposition of calcium on the bilayer graphene, dopants are controllably introduced. Low temperature transport results show a variable range hopping conduction near the charge neutrality point persisting up to 50 K, providing evidence for the impurity levels inside the gap. Our experiment confirms a predicted peculiar effect in the gapped bilayer graphene, i.e., formation of in-gap states even if the bare impurity level lies in the conduction band. The result provides perspective on the effect of doping and impurity levels in semiconducting bilayer graphene

  8. Magnetoconductivity of Hubbard bands induced in silicon MOSFETs

    International Nuclear Information System (INIS)

    Sodium impurities are diffused electrically to the oxide-semiconductor interface of a silicon MOSFET to create an impurity band. At low temperature and at low electron density, the band is split into an upper and a lower sections under the influence of Coulomb interactions. We used magnetoconductivity measurements to provide evidence for the existence of Hubbard bands and determine the nature of States in each band

  9. Chirped-Superlattice, Blocked-Intersubband QWIP

    Science.gov (United States)

    Gunapala, Sarath; Ting, David; Bandara, Sumith

    2004-01-01

    An Al(x)Ga(1-x)As/GaAs quantum-well infrared photodetector (QWIP) of the blocked-intersubband-detector (BID) type, now undergoing development, features a chirped (that is, aperiodic) superlattice. The purpose of the chirped superlattice is to increase the quantum efficiency of the device. A somewhat lengthy background discussion is necessary to give meaning to a brief description of the present developmental QWIP. A BID QWIP was described in "MQW Based Block Intersubband Detector for Low-Background Operation" (NPO-21073), NASA Tech Briefs Vol. 25, No. 7 (July 2001), page 46. To recapitulate: The BID design was conceived in response to the deleterious effects of operation of a QWIP at low temperature under low background radiation. These effects can be summarized as a buildup of space charge and an associated high impedance and diminution of responsivity with increasing modulation frequency. The BID design, which reduces these deleterious effects, calls for a heavily doped multiple-quantum-well (MQW) emitter section with barriers that are thinner than in prior MQW devices. The thinning of the barriers results in a large overlap of sublevel wave functions, thereby creating a miniband. Because of sequential resonant quantum-mechanical tunneling of electrons from the negative ohmic contact to and between wells, any space charge is quickly neutralized. At the same time, what would otherwise be a large component of dark current attributable to tunneling current through the whole device is suppressed by placing a relatively thick, undoped, impurity-free AlxGa1 x As blocking barrier layer between the MQW emitter section and the positive ohmic contact. [This layer is similar to the thick, undoped Al(x)Ga(1-x)As layers used in photodetectors of the blocked-impurity-band (BIB) type.] Notwithstanding the aforementioned advantage afforded by the BID design, the responsivity of a BID QWIP is very low because of low collection efficiency, which, in turn, is a result of low

  10. Quasiparticle interference from magnetic impurities

    Science.gov (United States)

    Derry, Philip G.; Mitchell, Andrew K.; Logan, David E.

    2015-07-01

    Fourier transform scanning tunneling spectroscopy (FT-STS) measures the scattering of conduction electrons from impurities and defects, giving information about the electronic structure of both the host material and adsorbed impurities. We interpret such FT-STS measurements in terms of the quasiparticle interference (QPI), here investigating in detail the QPI due to single magnetic impurities adsorbed on a range of representative nonmagnetic host surfaces, and contrasting with the case of a simple scalar impurity or point defect. We demonstrate how the electronic correlations present for magnetic impurities markedly affect the QPI, showing, e.g., a large intensity enhancement due to the Kondo effect, and universality at low temperatures/scanning energies. The commonly used joint density of states interpretation of FT-STS measurements is also considered, and shown to be insufficient in many cases, including that of magnetic impurities.

  11. Evaluation and optimization of well patterns designed for banding faulted block reservoirs with extremely low permeability%条带状特低渗透断块油藏布井方案评价与优选

    Institute of Scientific and Technical Information of China (English)

    齐亚东; 雷群; 杨正明; 王学武; 于荣泽; 周舒

    2011-01-01

    注采井网优化是特低渗透断块油藏有效开发的关键技术之一.针对条带状特低渗透断块油藏,从其几何特征及规模出发,设计了13种布井方案,并借鉴花17断块的地质参数及生产制度,应用自主研制的特低渗透油藏非线性渗流数值模拟软件,对各种布井方案进行了评价,最终优选出3种最佳方案.优选结果显示:可部署3排直井的条带状断块,以2排油井夹1排水井的交错布井方式为最优;可部署两排直井的条带状断块,宜选用井网单元呈“上”形的一注对三采的布井方式;直井—水平并联合布井的条带状断块,注水直井布置在水平采油井的趾尖外侧一定距离时,开发效果最佳.%Flooding patterns optimization is one of the key technologies for developing faulted block oilfields with extremely low permeability effectively. Considering the geometric characteristics and the size of banding faulted block oilfields, 13 well patterns were designed. Referring to the geologic parameters and production performance in Block Hual7, all of the 13 well patterns were evaluated by applying the nonlinear flow numerical simulation software which designed for such kind of reservoir, and by comparison 3 optimal patterns were provided. The optimization results indicated that: for the banding faulted block reservoirs which could accommodate 3 rows of vertical wells, the optimal pattern was one row of injection wells between two rows of production wells; for the reservoirs which can accommodate 2 rows of vertical wells, the optimal pattern was the one with one injection well working for 3 production wells aver-agely; and for vertical-horizontal-combined patterns, the optimal location of the vertical injection well is the periphery of the horizontal production well's hoe.

  12. Holographic impurities and Kondo effect

    CERN Document Server

    Erdmenger, J; Hoyos, C; Newrzella, M-N; O'Bannon, A; Wu, J

    2015-01-01

    Magnetic impurities are responsible for many interesting phenomena in condensed matter systems, notably the Kondo effect and quantum phase transitions. Here we present a holographic model of a magnetic impurity that captures the main physical properties of the large-spin Kondo effect. We estimate the screening length of the Kondo cloud that forms around the impurity from a calculation of entanglement entropy and show that our results are consistent with the g-theorem.

  13. Understanding impurity retention by divertors

    International Nuclear Information System (INIS)

    Simple, 1-D fluid model prescriptions are developed to predict under what circumstances impurities released at divertor targets would be expected to leak to the main plasma. The prescriptions are tested by comparison with results using the DIVIMP (divertor impurity) Monte Carlo code and are found to be well satisfied under strongly collisional conditions. The transition to collisionlessness degrades the agreement with the simple model. Usually, the simple model predicts a more-or-less catastrophic buildup of impurities outside the divertor. This, however, is an artificial result arising from the assumption of strictly one-dimensional, along B, motion; even weak cross-field transport can stop such impurity accumulation. ((orig.))

  14. The impact of snow impurity assumption on snow parameters retrieved from satellite data

    Science.gov (United States)

    Li, W.; Huang, F.; Chen, N.; Tanikawa, T.; Stamnes, K. H.

    2011-12-01

    The snow reflectance depends primarily on snow grain size and snow impurity. Snow impurity plays an important role in the visible part of the spectrum. Usually snow contaminants consist of dust, soot and algae. Different snow impurity types have different impacts on the snow reflectance. Due to the limitation of available satellite bands, it is difficult to retrieve all types of impurity at the same time. A sensitivity study has been carried out to explore how the snow reflectance depends on dust and soot impurities in the snow. The reflectances due to either dust or soot impurities will be quantified, and the implications for remote sensing of snow grain size and impurity concentration will be discussed. In particular, an attempt will be made to answer the question: what is the consequence of assuming that the impurity consists either of dust or soot when retrieving snow properties from remote sensing data when in reality both types of impurities may be present? In this study MODIS images will be used to retrieve the snow grain size and impurity concentration assuming either a soot or dust scenario, and field match-up data will be used for validation purposes. The potential for simultaneous retrieval of both dust and soot impurities will assessed by exploring what kind of spectral resolution would be required for such retrievals.

  15. Polarizability of a crystal with impurities

    International Nuclear Information System (INIS)

    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)

  16. Microscopic theory of impurity pumping

    International Nuclear Information System (INIS)

    Neoclassical transport coefficients for ion and impurity species in the plateau to Pfirsch--Schlueter regime are calculated using sources of particles and heat as driving forces. In the Pfirsch--Schlueter regime, such sources can lead to a reversal of the usual inward flux of impurities

  17. Neo-classical impurity transport

    International Nuclear Information System (INIS)

    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

  18. Drug impurities: problems and regulations.

    Science.gov (United States)

    Pifferi, G; Mannucci, A

    1999-11-01

    The matter of impurities is a frequently debated issue, mainly focused on the validation of the analytical methods and on the toxicology of potential impurities. In the first part of the review, the classification, the source and the chemical aspects of impurities are briefly considered according to the current international regulations. A special attention is given to the analytical control, in both qualitative and quantitative terms, of unexpected impurities arising from changes in the manufacturing process or by degradation. The thresholds for identification and qualification of impurities in new drug substances and in new drug products are examined together with the safety studies, when required. Finally, the acceptance limits for four classes of residual solvents are also reported. PMID:10765465

  19. 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.

  20. Effect of Nitrogen Impurity on Electronic Properties of Boron Nanotubes

    Directory of Open Access Journals (Sweden)

    Sandeep Kumar Jain

    2014-01-01

    Full Text Available For the first time we present electronic band structure and density of states for nitrogen doped hexagonal ultrathin boron nanotubes in the framework of density functional theory. The considered models of nanotubes below 5 Å diameter are armchair (3,3, zigzag (5,0, and chiral (4,2. The impurity chosen for the study is nitrogen and concentration of impurity atoms is limited to two. The study reveals that (3,3 BNT retains its metallic nature after nitrogen doping. However, metallicity gets increased which is attributed by the excess electrons of nitrogen. Further, it also brings out that (5,0 BNT which is originally metal transforms into semiconductor after nitrogen interaction and the band gap at G point increases with the impurity. Moreover, the band gap of (4,2 BNT reduces significantly and turns into semimetal for nitrogen doping. Thus, the nitrogen impurity has the predominant effect on the electronic properties of BNTs and therefore can be regarded as suitable candidates for nanoelectronic and field emission devices.

  1. Local measurement of transport parameters for laser injected trace impurities

    Energy Technology Data Exchange (ETDEWEB)

    Giannella, R.; Lauro-Taroni, L. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking

    1994-07-01

    A procedure has been developed that determines local measurements of transport parameters`s profiles for injected impurities. The measured profiles extend from the plasma centre up to a certain radial position (usually {rho} = 0.6-0.7). In the outer region of the plasma the procedure supplies ``most suitable extensions`` up to the plasma edge of the measured transport profiles. The procedure intrinsically assures consistency and excellent agreement between the simulated and experimental data of local broad band soft X-ray emissivity and intensities of individual emission lines from different ion states of the injected impurities. 4 refs., 3 figs.

  2. Elastoresistivity of impurities in copper

    International Nuclear Information System (INIS)

    Among the numerous techniques used to observe impurities or defects in metals, elasto-resistivity has been relatively little used. Uniaxial elasto-resistivity due to substitutional impurities in copper, measured at 4.2 K, decreases when the impurity content increases. It is then possible to define a specific uniaxial elasto-resistivity of a given impurity in copper. Measurements have been extended to different temperatures, different rates of cold work (i.e. different dislocation concentrations) and different doses of irradiation (neutron irradiations at 20 K). The elasto-resistivity of pure copper at 4.2 K does not depend on the cold work performed at 300 K. A rule similar to Matthiessen's rule has been established when two types of defects are present. A correlation between our experiments of uniaxial elasto-resistivity and KONCZYKOWSKI'S measurements of hydrostatic piezoresistivity allows us to give a simple phenomenological description of the behavior of the impurities in the stress: the impurities get longer along the same direction as the elastic matrix. A simple evaluation shows that the elasto-resistivity and the thermo-electric power of an impurity are related

  3. Impurity screening in Tore Supra

    International Nuclear Information System (INIS)

    Ergodic divertor (ED) experiments in helium plasmas with carbonized and boronized wall conditions have been performed in Tore Supra. The intrinsic impurity decontamination effect (as well as the screening of purposely injected nitrogen impurities), previously observed in deuterium plasmas, has been confirmed also for conditions where the electron density in the confined (unperturbed) bulk plasma remains practically constant. Inward displacements of the plasma 0.10-0.15 m away from the ED modules result in the magnetic perturbation having little or no effect on impurities. (orig.)

  4. 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.

  5. Random Magnetic Impurities and the $\\delta$ Impurity Problem

    OpenAIRE

    Desbois, Jean; Furtlehner, Cyril; Ouvry, Stéphane; Théorique, Division de Physique; IPN; Fr-91406, Orsay

    1994-01-01

    One considers the effect of disorder on the 2-dimensional density of states of an electron in a constant magnetic field superposed onto a Poissonnian random distribution of point vortices. If one restricts the electron Hilbert space to the lowest Landau level of the total average magnetic field, the random magnetic impurity problem is mapped onto a contact $\\delta$ impurity problem. A brownian motion analysis of the model, based on brownian probability distributions for arithmetic area windin...

  6. Hyperfine Fields of Light Interstitial Impurities in Ni

    International Nuclear Information System (INIS)

    The magnetic hyperfine interaction of light interstitial impurities in Ni have been studied by means of the Korringa-Kohn-Rostoker (KKR) band structure method. This method allows to deal with the impurity problem by solving the corresponding Dyson equation for the Green's function. It also allows to account for lattice relaxations. For this purpose a new technique was developed that allows to handle in principle arbitrary lattice distortions. Corresponding calculations have been performed for the magnetic hyperfine fields of the light interstitial impurities H to Ne in Ni. By minimising the force on the nearest neighbour host atoms their equilibrium position was determined. The resulting hyperfine fields for the equilibrium configuration are found to be in rather good agreement with available experimental data.

  7. Impurity Influence on Nitride LEDs

    Directory of Open Access Journals (Sweden)

    O.I. Rabinovich

    2014-07-01

    Full Text Available Light emitting diodes (LEDs are widely used nowadays. They are used in major parts of our life. But it is still necessary to improve their characteristics. In this paper the impurity and Indium atoms influence on the LEDs characteristics is investigated by computer simulation. Simulation was carried out in Sim Windows. The program was improved for this purpose by creating new files for AlGaInN heterostructure and devices including more than 25 basic parameters. It was found that characteristics depend on impurity and indium atoms changes a lot. The optimum impurity concentration for doping barriers between quantum wells was achieved. By varying impurity and Indium concentration the distribution in AlGaInN heterostructure LEDs characteristics could be improved.

  8. Impurities confined in quantum structures

    CERN Document Server

    Holtz, Per Olof

    2004-01-01

    The introduction of impurities, even in very small concentrations, in a semiconductor can change its optical and electrical properties entirely. This attribute of the semiconductor is utilized in the manifoldness of their applications. In this book, the progress on elucidating the physical properties of impurities confined in quantum structures are reviewed with an emphasis on the experimental aspects. The major results of various kinds of characterization, such as infrared spectroscopy, Raman measurements, luminescence characterization, perturbation spectroscopy and dynamical studies of the confined impurities are reviewed, but also the theoretical basis to calculate the electronic structure of the confined donors and acceptors are presented. This monograph also describes more specific aspects of the confined impurities such as the properties in the high doping regime and the effects of hydrogen passivation.

  9. Heart Block

    Science.gov (United States)

    ... the signal causes the heart to contract and pump blood. Heart block occurs if the electrical signal is ... degree heart block limits the heart's ability to pump blood to the rest of the body. This type ...

  10. 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.

  11. Population Blocks.

    Science.gov (United States)

    Smith, Martin H.

    1992-01-01

    Describes an educational game called "Population Blocks" that is designed to illustrate the concept of exponential growth of the human population and some potential effects of overpopulation. The game material consists of wooden blocks; 18 blocks are painted green (representing land), 7 are painted blue (representing water); and the remaining…

  12. Effects of quenched impurities on surface diffusion, spreading, and ordering of O/W(110)

    DEFF Research Database (Denmark)

    Nikunen, P.; Vattulainen, Ilpo Tapio; Ala-Nissila, T.

    2002-01-01

    We study how quenched impurities affect the surface diffusion and ordering of strongly interacting adsorbate atoms on surfaces. To this end, we carry out Monte Carlo simulations for a lattice-gas model of O/W(110), including small concentrations of immobile impurities which block their adsorption...... sites. We examine the behavior of the diffusion coefficients and order parameters as a function of coverage corresponding to various ordered phases at low temperatures. The effects of impurities are examined under both equilibrium and nonequilibrium conditions, and the results are compared to recent...... studies on a completely clean surface. We find that even minute impurity concentrations affect the diffusion behavior considerably in equilibrium. The effects are strongest in ordered phases and close to phase boundaries, where quenched impurities lead to a reduction of order, which in turn leads to...

  13. Electrically Driven Spin Dynamics of Paramagnetic Impurities

    Science.gov (United States)

    Saha, D.; Siddiqui, L.; Bhattacharya, P.; Datta, S.; Basu, D.; Holub, M.

    2008-05-01

    The spin dynamics of dilute paramagnetic impurities embedded in a semiconductor GaAs channel of a conventional lateral spin valve has been investigated. It is observed that the electron spin of paramagnetic Mn atoms can be polarized electrically when driven by a spin valve in the antiparallel configuration. The transient current through the MnAs/GaAs/MnAs spin valve bears the signature of the underlying spin dynamics driven by the exchange interaction between the conduction band electrons in GaAs and the localized Mn electron spins. The time constant for this interaction is observed to be dependent on temperature and is estimated to be 80 ns at 15 K.

  14. How do Impurity Inclusions Influence the Mechanical Properties of Multicrystalline Silicon?

    OpenAIRE

    Orellana Pérez, T.; Tejado Garrido, Elena Maria; Funke, V.C.; Fütterer, W.; Riepe, S.; Möller, H. J.; Pastor Caño, Jose Ignacio

    2015-01-01

    The purpose of this research is to characterise the mechanical properties of multicrystalline silicon for photovoltaic applications that was crystallised from silicon feedstock with a high content of several types of impurities. The mechanical strength, fracture toughness and elastic modulus were measured at different positions within a multicrystalline silicon block to quantify the effect of impurity segregation on these mechanical properties. The microstructure and fracture surfaces of the ...

  15. Scandium resonant impurity level in PbTe

    International Nuclear Information System (INIS)

    We synthesize a scandium-doped PbTe single-crystal ingot and investigate the phase and the elemental composition as well as galvanomagnetic properties of Pb1-yScyTe alloys in weak magnetic fields (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) upon varying the scandium content (y ≤ 0.02). We find that all investigated samples are single-phase and n-type. The distribution of scandium impurities along the axis of the ingot is estimated to be exponential. An increase of scandium impurity content leads to a monotonous growth of the free electron concentration by four orders of magnitude (approximately from 1016 cm−3 to 1020 cm−3). In heavily doped alloys (y > 0.01), the free electron concentration at the liquid-helium temperature tends to saturation, indicating the pinning of the Fermi energy by the scandium resonant impurity level located on the background of the conduction band. Using the two-band Kane and six-band Dimmock dispersion relations for IV-VI semiconductors, dependences of the Fermi energy measured from the bottom of the conduction band Ec on the scandium impurity content are calculated and the energy of the resonant scandium level is estimated to be ESc ≈ Ec + 280 meV. Diagrams of electronic structure rearrangement of Pb1-yScyTe alloys upon doping are proposed

  16. Magnetic impurities and materials design for semiconductor spintronics

    Czech Academy of Sciences Publication Activity Database

    Sato, K.; Dederichs, P. H.; Katayama-Yoshida, H.; Kudrnovský, Josef

    340-342, - (2003), s. 863-869. ISSN 0921-4526 R&D Projects: GA AV ČR IAA1010203 Grant ostatní: RTN1-1999(XE) 00145 Institutional research plan: CEZ:AV0Z1010914 Keywords : diluted magnetic semiconductors * Zener and double-exchange models * impurity bands * Curie temperature Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.908, year: 2003

  17. 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.

  18. Impurity trapped exciton states related to rare earth ions in crystals under high hydrostatic pressure

    International Nuclear Information System (INIS)

    Emission related to rare earth ions in solids takes place usually due to 4fn → 4fn and 4fn−15d1 → 4fn internal transitions. In the case of band to band excitation the effective energy transfer from the host to optically active impurity is required. Among other processes one of the possibilities is capturing of the electron at excited state and hole at the ground state of impurity. Localization of electron or hole at the dopand site creates a long range Coulomb potential that attracts the second carrier which then occupies the localized Rydberg-like states. Such a system can be considered as impurity trapped exciton. Usually impurity trapped exciton is a short living phenomenon which decays non-radiatively leaving the impurity ion in the excited state. However, in several compounds doped with Eu2+ the impurity trapped exciton states become stable and contribute to the radiative processes though anomalous luminescence that appears apart of the 4f7 → 4f7 and 4f75d1 → 5f7 emission. In this contribution pressure effect on energies of the 4fn−15d1→5fn transitions in Ln doped oxides and fluorides as well as influence of pressure on the energy of impurity trapped exciton states is discussed. The latest results on high pressure investigations of luminescence related to Pr3+, and Eu2+ in different lattices are reviewed.

  19. 基于半带滤波分块采样的计算任务排序算法%Computing Task Sorting Algorithm Based on Half Band Filter Sub Block Sampling

    Institute of Scientific and Technical Information of China (English)

    刘彩霞

    2015-01-01

    在计算机信息管理中,需要对计算任务按优先级或复杂度进行优化排序,实现计算效益优化.研究云计算信息系统中的计算任务优化排序算法,提高数据管理和调度的效率.传统方法采用子带合成滤波方法进行任务排序,计算开销和执行时效性方面性能不好,提出一种基于带滤波分块采样的计算任务排序算法.计算在整个计算机信息管理基站的每个站点的合计成本,根据信息匹配相关度进行资源搜索,计算任务分配时半滤波分块采样的收敛函数,得到基于半滤波分块采样的任务排序二元假设检验分配模型,实现任务优先级排序优化.仿真结果表明,采用该算法对云计算信息系统中的计算任务进行排序,能有效准确地确定计算任务的优先级,减少任务冲突,提高任务执行效率,在计算机信息管理和任务分配中具有较高应用价值.%In computer information management, the need for computing tasks according to priority or complexity of the opti-mized sorting, realize the calculation efficiency optimization. The research of cloud computing optimization algorithm of computing tasks in information system, improve the efficiency of data management and scheduling. The traditional method is using the sub-band synthesis filter method for task sequencing, the computation and the execution time of the perfor-mance is not good, put forward a sort of computing tasks with filtering algorithm based on block sampling. In the calculation of total cost of each site of the whole computer information management of base station, according to the information match-ing of resources search, calculation convergence function is assigned half filter block sampling, get the distribution sort half filter block sampling of two element hypothesis test model based on task priority scheduling optimization, implementation. The simulation results show that, the cloud computing tasks in information systems are

  20. Impurity doping processes in silicon

    CERN Document Server

    Wang, FFY

    1981-01-01

    This book introduces to non-experts several important processes of impurity doping in silicon and goes on to discuss the methods of determination of the concentration of dopants in silicon. The conventional method used is the discussion process, but, since it has been sufficiently covered in many texts, this work describes the double-diffusion method.

  1. Spectroscopic studies of impurity densities and impurity transport

    Science.gov (United States)

    Behringer, K.

    1992-06-01

    Spectrometers and spectra, mainly from JET, are discussed with respect to diagnostic potential and calibration problems. Spatial scan facilities or multichord diagnostics are essential for transport investigations, and several possibilities are shown. The interpretation of spectral line radiation usually requires the availability of impurity transport codes, which calculate the ionization balance in the presence of transport, the line emissivities and the total impurity radiation. Some atomic physics prerequisites of such codes are discussed. Theoretical and experimental approaches to the transport problem are investigated using ASDEX and JET results for anomalous transport. The occasional observation of neoclassical accumulation, for example after pellet injection, is presented and respective modeling is described. Some H mode transport phenomena are mentioned.

  2. Fundamental aspects of metallic impurities and impurity interactions in silicon during device processing

    Energy Technology Data Exchange (ETDEWEB)

    Graff, K. [TEMIC, TELEFUNKEN, Heilbronn (Germany)

    1995-08-01

    A review on the behavior of metallic impurities in silicon can be considerably simplified by a restriction on pure, dislocation-free, monocrystalline silicon. In this case interactions between different impurities and between impurities and grown-in lattice defects can be reduced. This restriction is observed in Chapter 1 for discussing the general behavior of metallic impurities in silicon.

  3. Observation of impurity accumulation and concurrent impurity influx in PBX

    International Nuclear Information System (INIS)

    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, Zeff peaks in the center to values of about 5. The central metallic densities can be high, n/sub met//n/sub e/ ≅ 0.01, resulting in central radiated power densities in excess of 1 W/cm3, 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 6 x 1010 and 10 x 1010 particles/cm2s at minor radii of 6 and 17 cm. At the end of the accumulation phase, this particle flux is strongly increased to values of 3 x 1012 and 1 x 1012 particles/cm2s. 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

  4. Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes: A comparative study

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Ram Sevak, E-mail: singh915@gmail.com [Department of Physics, National Institute of TechnologyKurukshetra 136119 (Haryana) (India)

    2015-11-15

    Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes (CNTs and BNNTs) is systematically studied using first principle calculations based on density functional theory. Energy band structures and density of states of optimized zigzag (5, 0), armchair (3, 3), and chiral (4, 2) structures of CNT and BNNT are calculated. Oxygen doping in zigzag CNT exhibits a reduction in metallicity with opening of band gap in near-infrared region while metallicity is enhanced in armchair and chiral CNTs. Unlike oxygen-doped CNTs, energy bands are drastically modulated in oxygen-doped zigzag and armchair BNNTs, showing the nanotubes to have metallic behaviour. Furthermore, oxygen impurity in chiral BNNT induces narrowing of band gap, indicating a gradual modification of electronic band structure. This study underscores the understanding of different electronic properties induced in CNTs and BNNTs under oxygen doping, and has potential in fabrication of various nanoelectronic devices.

  5. Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes: A comparative study

    International Nuclear Information System (INIS)

    Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes (CNTs and BNNTs) is systematically studied using first principle calculations based on density functional theory. Energy band structures and density of states of optimized zigzag (5, 0), armchair (3, 3), and chiral (4, 2) structures of CNT and BNNT are calculated. Oxygen doping in zigzag CNT exhibits a reduction in metallicity with opening of band gap in near-infrared region while metallicity is enhanced in armchair and chiral CNTs. Unlike oxygen-doped CNTs, energy bands are drastically modulated in oxygen-doped zigzag and armchair BNNTs, showing the nanotubes to have metallic behaviour. Furthermore, oxygen impurity in chiral BNNT induces narrowing of band gap, indicating a gradual modification of electronic band structure. This study underscores the understanding of different electronic properties induced in CNTs and BNNTs under oxygen doping, and has potential in fabrication of various nanoelectronic devices

  6. Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes: A comparative study

    Directory of Open Access Journals (Sweden)

    Ram Sevak Singh

    2015-11-01

    Full Text Available Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes (CNTs and BNNTs is systematically studied using first principle calculations based on density functional theory. Energy band structures and density of states of optimized zigzag (5, 0, armchair (3, 3, and chiral (4, 2 structures of CNT and BNNT are calculated. Oxygen doping in zigzag CNT exhibits a reduction in metallicity with opening of band gap in near-infrared region while metallicity is enhanced in armchair and chiral CNTs. Unlike oxygen-doped CNTs, energy bands are drastically modulated in oxygen-doped zigzag and armchair BNNTs, showing the nanotubes to have metallic behaviour. Furthermore, oxygen impurity in chiral BNNT induces narrowing of band gap, indicating a gradual modification of electronic band structure. This study underscores the understanding of different electronic properties induced in CNTs and BNNTs under oxygen doping, and has potential in fabrication of various nanoelectronic devices.

  7. Self-pumping impurity control

    Science.gov (United States)

    Brooks, J.N.; Mattas, R.F.

    1983-12-21

    It is an object of the present invention to provide an apparatus for removing impurities from the plasma in a fusion reactor without an external vacuum pumping system. It is also an object of the present invention to provide an apparatus for removing the helium ash from a fusion reactor. It is another object of the present invention to provide an apparatus which removes helium ash and minimizes tritium recycling and inventory.

  8. A Holographic Two-Impurity Kondo Model

    CERN Document Server

    O'Bannon, Andy; Probst, Jonas

    2015-01-01

    We propose a model of a strongly-interacting two-impurity Kondo system based on the AdS/CFT correspondence, also known as holography. In a Landau Fermi Liquid, the single-impurity Kondo effect is the screening of an impurity spin at low temperature $T$. The two-impurity Kondo model then describes the competition between the Kondo interaction and the Heisenberg interaction between two impurity spins, also called the RKKY interaction. For spin-$1/2$ impurities, that competition leads to a quantum phase transition from a Kondo-screened phase to a phase in which the two impurity spins screen one another. Our holographic model is based on a $(1+1)$-dimensional CFT description of the two-impurity Kondo model, reliable for two impurities with negligible separation in space. We consider only impurity spins in a totally anti-symmetric representation of an $SU(N)$ spin symmetry. We employ a large-$N$ limit, in which both Kondo and RKKY couplings are double-trace, and both Kondo and inter-impurity screening appear as co...

  9. Impurity diffusion in transition-metal oxides

    International Nuclear Information System (INIS)

    Intrinsic tracer impurity diffusion measurements in ceramic oxides have been primarily confined to CoO, NiO, and Fe3O4. Tracer impurity diffusion in these materials and TiO2, 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 TiO2 whereas chromium ions (a smaller-sized impurity) do not. 60 references, 11 figures

  10. BWR water chemistry impurity studies

    International Nuclear Information System (INIS)

    Laboratory studies were made on the effect of water impurities on environmental cracking in simulated BWR water of stainless steel, low alloy steel and nickel-base alloys. Constant elongation rate tensile (CERT) tests were run in simulated normal water chemistry (NWC), hydrogen water chemistry (HWC), or start-up environment. Sulfate, chloride and copper with chloride added to the water at levels of a fraction of a ppM were found to be extremely deleterious to all kinds of materials except Type 316 NG. Other detrimental impurities were fluoride, silica and some organic acids, although acetic acid was beneficial. Nitrate and carbon dioxide were fairly inoccuous. Corrosion fatigue and constant load tests on compact tension specimens were run in simulated normal BWR water chemistry (NWC) or hydrogen water chemistry (HWC), without impurities or with added sulfate or carbon dioxide. For sensitized Type 304 SS in NWC, 0.1 ppM sulfate increased crack propagation rates in constant load tests by up to a factor of 100, and in fatigue tests up to a factor of 10. Also, cracking in Type 316 nuclear grade SS and Alloy 600 was enhanced, but to a smaller degree. Carbon dioxide was less detrimental than sulfate. 3 figs., 4 tabs

  11. Low Z impurity transport in tokamaks

    International Nuclear Information System (INIS)

    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

  12. Impurity-bound states and Green's function zeros as local signatures of topology

    Science.gov (United States)

    Slager, Robert-Jan; Rademaker, Louk; Zaanen, Jan; Balents, Leon

    2015-08-01

    We show that the local in-gap Green's function of a band insulator G0(ɛ ,k∥,r⊥=0 ) , with r⊥ the position perpendicular to a codimension-1 or codimension-2 impurity, reveals the topological nature of the phase. For a topological insulator, the eigenvalues of this Green's function attain zeros in the gap, whereas for a trivial insulator the eigenvalues remain nonzero. This topological classification is related to the existence of in-gap bound states along codimension-1 and codimension-2 impurities. Whereas codimension-1 impurities can be viewed as soft edges, the result for codimension-2 impurities is nontrivial and allows for a direct experimental measurement of the topological nature of two-dimensional insulators.

  13. Ghost Block

    OpenAIRE

    Webb, Neil

    2011-01-01

    Filmed on the English south coast 'Ghost Block' depicts the uncanny and eerie atmosphere at the site of a WW2 coastal defence line. The concrete cubes were used as an anti-invasion blockade against potential landing forces. This protection line now slowly decaying and becoming enmeshed into the environment still acts as a defence to repel unwanted visitors. The area is a natural reserve to nesting birds that often lay eggs directly onto the beach surface. The blocks act as a final barrier ...

  14. Towards quantum information processing with impurity spins in silicon

    International Nuclear Information System (INIS)

    The finding of algorithms for factoring and data base search that promise substantially increased computational power, as well as the expectation for efficient simulation of quantum systems have spawned an intense interest in the realization of quantum information processors [1]. Solid state implementations of quantum computers scaled to >1000 quantum bits ('qubits') promise to revolutionize information technology, but requirements with regard to sources of decoherence in solid state environments are sobering. Here, we briefly review basic approaches to impurity spin based qubits and present progress in our effort to form prototype qubit test structures. Since Kane's bold silicon based spin qubit proposal was first published in 1998 [2], several groups have taken up the challenge of fabricating elementary building blocks [3-5], and several exciting variations of single donor qubit schemes have emerged [6]. Single donor atoms, e. g. 31P, are 'natural quantum dots' in a silicon matrix, and the spins of electrons and nuclei of individual donor atoms are attractive two level systems for encoding of quantum information. The coupling to the solid state environment is weak, so that decoherence times are long (hours for nuclear spins, and ∼60 ms for electron spins of isolated P atoms in silicon [7]), while control over individual spins for one qubit operations becomes possible when individual qubits are aligned to electrodes that allow shifting of electron spin resonances in global magnetic fields by application of control voltages. Two qubit operations require an interaction that couples, and entangles qubits. The exchange interaction, J, is a prime candidate for mediation of two qubit operations, since it can be turned on and off by variation of the wave function overlap between neighboring qubits, and coherent manipulation of quantum information with the exchange interaction alone has been shown to be universal [8]. However, detailed band structure calculations and

  15. Impurity-induced divertor plasma oscillations

    International Nuclear Information System (INIS)

    Two different oscillatory plasma regimes induced by seeding the plasma with high- and low-Z impurities are found for ITER-like divertor plasmas, using computer modeling with the DUSTT/UEDGE and SOLPS4.3 plasma-impurity transport codes. The oscillations are characterized by significant variations of the impurity-radiated power and of the peak heat load on the divertor targets. Qualitative analysis of the divertor plasma oscillations reveals different mechanisms driving the oscillations in the cases of high- and low-Z impurity seeding. The oscillations caused by the high-Z impurities are excited near the X-point by an impurity-related instability of the radiation-condensation type, accompanied by parallel impurity ion transport affected by the thermal and plasma friction forces. The driving mechanism of the oscillations induced by the low-Z impurities is related to the cross-field transport of the impurity atoms, causing alteration between the high and low plasma temperature regimes in the plasma recycling region near the divertor targets. The implications of the impurity-induced plasma oscillations for divertor operation in the next generation tokamaks are also discussed

  16. Impurity-induced divertor plasma oscillations

    Energy Technology Data Exchange (ETDEWEB)

    Smirnov, R. D., E-mail: rsmirnov@ucsd.edu; Krasheninnikov, S. I.; Pigarov, A. Yu. [University of California, San Diego, La Jolla, California 92093 (United States); Kukushkin, A. S. [NRC “Kurchatov Institute”, Moscow 123182 (Russian Federation); National Research Nuclear University MEPhI, Moscow 115409 (Russian Federation); Rognlien, T. D. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)

    2016-01-15

    Two different oscillatory plasma regimes induced by seeding the plasma with high- and low-Z impurities are found for ITER-like divertor plasmas, using computer modeling with the DUSTT/UEDGE and SOLPS4.3 plasma-impurity transport codes. The oscillations are characterized by significant variations of the impurity-radiated power and of the peak heat load on the divertor targets. Qualitative analysis of the divertor plasma oscillations reveals different mechanisms driving the oscillations in the cases of high- and low-Z impurity seeding. The oscillations caused by the high-Z impurities are excited near the X-point by an impurity-related instability of the radiation-condensation type, accompanied by parallel impurity ion transport affected by the thermal and plasma friction forces. The driving mechanism of the oscillations induced by the low-Z impurities is related to the cross-field transport of the impurity atoms, causing alteration between the high and low plasma temperature regimes in the plasma recycling region near the divertor targets. The implications of the impurity-induced plasma oscillations for divertor operation in the next generation tokamaks are also discussed.

  17. Epidural block

    Science.gov (United States)

    ... Drugs & Supplements Videos & Tools Español You Are Here: Home ... It numbs or causes a loss of feeling in the lower half your body. This lessens the pain of contractions during childbirth. An epidural block may also be used to ...

  18. Impurity control in toroidal devices

    International Nuclear Information System (INIS)

    This summary report on the Technical Committee Meeting organized by the IAEA and held in Naka-Gun, Japan, 13-15 February 1989, provides an overview of the results presented. Of the twenty-three papers presented, sixteen were devoted to tokamak experiments. These presented data of plasma behavior in the scrape-off layer and divertor regions, as well as effects of impurities on the core plasma; these are summarized here. Other papers summarized deal with plasma-wall interactions, including wall material behavior. Still others deal with theoretical work on physics modelling in the edge region. Refs, figs and tabs

  19. Impurity-induced moments in underdoped cuprates

    Energy Technology Data Exchange (ETDEWEB)

    Khaliullin, G. [Max-Planck-Institut fuer Physik komplexer Systeme, Noethnitzer Str. 38, D-01187 Dresden (Germany)]|[Kazan Physicotechnical Institute of the Russian Academy of Sciences, 420029 Kazan (Russia); Kilian, R. [Max-Planck-Institut fuer Physik komplexer Systeme, Noethnitzer Str. 38, D-01187 Dresden (Germany); Krivenko, S. [Kazan Physicotechnical Institute of the Russian Academy of Sciences, 420029 Kazan (Russia); Fulde, P. [Max-Planck-Institut fuer Physik komplexer Systeme, Noethnitzer Str. 38, D-01187 Dresden (Germany)

    1997-11-01

    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} {ital 1997} {ital The American Physical Society}

  20. Impurity-induced moments in underdoped cuprates

    International Nuclear Information System (INIS)

    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

  1. 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...

  2. Microscopic analysis of the valence band and impurity band theories of (Ga,Mn)As

    Czech Academy of Sciences Publication Activity Database

    Mašek, Jan; Máca, František; Kudrnovský, Josef; Makarovský, O.; Eaves, L.; Campion, R. P.; Edmonds, K. W.; Rushforth, A.W.; Foxon, C. T.; Gallagher, B. L.; Novák, Vít; Sinova, Jairo; Jungwirth, Tomáš

    2010-01-01

    Roč. 105, č. 22 (2010), 227202/1-227202/4. ISSN 0031-9007 R&D Projects: GA ČR GA202/07/0456; GA MŠk LC510; GA AV ČR KAN400100652 Grant ostatní: EU FP7(XE) #215368; EU FP7 NAMASTE(XE) No.214499 Institutional research plan: CEZ:AV0Z10100520 Keywords : gallium arsenide * semiconductors Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 7.621, year: 2010

  3. Quantum impurities in channel mixing baths

    Science.gov (United States)

    Liu, Jin-Guo; Wang, Da; Wang, Qiang-Hua

    2016-01-01

    We propose a versatile strategy for numerical renormalization group (NRG) solution of general channel-mixing Kondo and Anderson impurity models beyond previous reach. We illustrate the strategy by investigating the quantum phase transitions in models of Anderson impurities coupled to s - and d -wave superconducting baths. We discuss the effects of nontrivial channel-mixing in such models. Our strategy opens the door toward broad applications of NRG as impurity solver in cluster dynamical mean field theory for strongly correlated electron systems.

  4. Impurity phases in beryllium oxide ceramic

    OpenAIRE

    Turnaev, S. K.; Bitsoev, G. D.; Kil'govatov, G. M.; Kiiko, V. S.

    2013-01-01

    An x-ray spectrographic method with an electron probe and a scanning electron microscope are used to study industrial ceramic specimen surface composition, distinguished by presence of a different color for both the main part, and impurity phases. BeO-ceramic specimens, having a visually differing color, are conditionally separated into three types. In reflected electron microphotographs impurities are distinguished qualitatively with respect to electrical conductivity. Iron impurity is invar...

  5. Trace organic impurities in gaseous helium

    Science.gov (United States)

    Schehl, T. A.

    1973-01-01

    A program to determine trace organic impurities present in helium has been initiated. The impurities were concentrated in a cryogenic trap to permit detection and identification by a gas chromatographic-mass spectrometric technique. Gaseous helium (GHe) exhibited 63 GC flame ionization response peaks. Relative GC peak heights and identifications of 25 major impurities by their mass spectra are given. As an aid to further investigation, identities are proposed for 16 other components, and their mass spectra are given.

  6. Impurity Effect on Spin Ladder System

    OpenAIRE

    Motome, Yukitoshi; Katoh, Nobuyuki; Furukawa, Nobuo; Imada, Masatoshi

    1996-01-01

    Effects of nonmagnetic impurity doping in a spin ladder system with a spin gap are investigated by the exact diagonalization as well as by the variational Monte Carlo calculations. Substantial changes in macroscopic properties such as enhancements in spin correlations and magnetic susceptibilities are observed in the low impurity concentration region, which are caused by the increase of low-energy states. These results suggest that small but finite amount of nonmagnetic impurity doping releva...

  7. Density Correlations of Magnetic Impurities and Disorder

    OpenAIRE

    Desbois, Jean; Furtlehner, Cyril; Ouvry, Stéphane

    1996-01-01

    We consider an electron coupled to a random distribution of point vortices in the plane (magnetic impurities). We analyze the effect of the magnetic impurities on the density of states of the test particle, when the magnetic impurities have a spatial probability distribution governed by Bose or Fermi statistic at a given temperature. Comparison is made with the Poisson distribution, showing that the zero temperature Fermi distribution corresponds to less disorder. A phase diagram describing i...

  8. Impurity penetration through the edge transport barrier

    Energy Technology Data Exchange (ETDEWEB)

    Belo, P [EURATOM/IST Fusion Association, Centro de Fusao Nuclear, Av. Rovisco Pais, 1049-001 Lisbon (Portugal); Parail, V [EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Corrigan, G [EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Heading, D [EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Houlberg, W [Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Monier-Garbet, P [Association Euratom-CEA, Cadarache 13108 Saint Paul Lez Durance (France); Ongena, J [Laboratoire de Physique des Plasmas-Laboratorium voor Plasmafysica, Association EURATOM-Belgian State, Ecole Royale Militaire-B-1000 Brussels, Koninklijke Militaire School (Belgium)

    2004-08-01

    The ELMs in H-mode plasmas manifest themselves as short bursts of increased edge transport, which expel energy and particles, including impurities from the plasma edge to the SOL and further towards target plates and limiters (Zohm H 1996 Plasma Phys. Control. Fusion 38 1213, Loarte A et al 2003 Plasma Phys. Control. Fusion 45 1549). ELMs are considered beneficial events with respect to impurities since they can prevent impurities from accumulating in the plasma core. JET has recently performed an experiment in which a controlled influx of noble gas impurities was successfully used in order to reduce the amplitude and frequency of type-I ELMs. An interesting correlation between the level of the main gas puffing and the radial redistribution of impurities has been found in this experiment: it was shown that impurities are contained near the separatrix in discharges with a relatively strong level of main gas puffing. Reduction of the puffing below a certain level leads to impurity accumulation in the core followed by thermal collapse. This paper describes the results of predictive modelling of impurity seeding experiments on JET using a coupling of the 1.5D core transport code JETTO (for the main ions) and 1D transport code SANCO (for impurities). Two sets of boundary conditions for the density and temperatures, which correspond to two different deuterium gas puffing rates, were used in the modelling. An explanation for the experimentally observed phenomenon is presented.

  9. Analytical advances in pharmaceutical impurity profiling.

    Science.gov (United States)

    Holm, René; Elder, David P

    2016-05-25

    Impurities will be present in all drug substances and drug products, i.e. nothing is 100% pure if one looks in enough depth. The current regulatory guidance on impurities accepts this, and for drug products with a dose of less than 2g/day identification of impurities is set at 0.1% levels and above (ICH Q3B(R2), 2006). For some impurities, this is a simple undertaking as generally available analytical techniques can address the prevailing analytical challenges; whereas, for others this may be much more challenging requiring more sophisticated analytical approaches. The present review provides an insight into current development of analytical techniques to investigate and quantify impurities in drug substances and drug products providing discussion of progress particular within the field of chromatography to ensure separation of and quantification of those related impurities. Further, a section is devoted to the identification of classical impurities, but in addition, inorganic (metal residues) and solid state impurities are also discussed. Risk control strategies for pharmaceutical impurities aligned with several of the ICH guidelines, are also discussed. PMID:26690047

  10. Density correlations of magnetic impurities and disorder

    Energy Technology Data Exchange (ETDEWEB)

    Desbois, J.; Furtlehner, C.; Ouvry, S. [Paris-11 Univ., 91 - Orsay (France). Inst. de Physique Nucleaire

    1996-06-01

    An electron coupled to a random distribution of point vortices in the plane (magnetic impurities) is discussed. The effect of the magnetic impurities on the density of states of the test particle, when the magnetic impurities have a spatial probability distribution governed by Bose or Fermi statistic at a given temperature is analyzed. Comparison is made with the Poisson distribution, showing that the zero temperature Fermi distribution corresponds to less disorder. A phase diagram describing isolated impurities versus Landau level oscillations is proposed. (author). 6 refs.

  11. Density correlations of magnetic impurities and disorder

    International Nuclear Information System (INIS)

    An electron coupled to a random distribution of point vortices in the plane (magnetic impurities) is discussed. The effect of the magnetic impurities on the density of states of the test particle, when the magnetic impurities have a spatial probability distribution governed by Bose or Fermi statistic at a given temperature is analyzed. Comparison is made with the Poisson distribution, showing that the zero temperature Fermi distribution corresponds to less disorder. A phase diagram describing isolated impurities versus Landau level oscillations is proposed. (author)

  12. 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.

  13. Gastric Banding

    Science.gov (United States)

    ... gastric banding before deciding to have the procedure. Advertisements for a device or procedure may not include ... feeds Follow FDA on Twitter Follow FDA on Facebook View FDA videos on YouTube View FDA photos ...

  14. Band structures of TiO2 doped with N, C and B

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    This study on the band structures and charge densities of nitrogen (N)-, carbon (C)- and boron (B)-doped titanium dioxide (TiO2) by first-principles simulation with the CASTEP code (Segall et al., 2002) showed that the three 2p bands of impurity atom are located above the valence-band maximum and below the Ti 3d bands, and that along with the decreasing of impurity atomic number, the fluctuations become more intensive. We cannot observe obvious band-gap narrowing in our result.Therefore, the cause of absorption in visible light might be the isolated impurity atom 2p states in band-gap rather than the band-gap narrowing.

  15. Eliminating Impurity Traps in the Silane Process

    Science.gov (United States)

    Coleman, L. M.

    1982-01-01

    Redistribution reaction section of silane process progressively separates heavier parts of chlorosilane feedstock until light silane product is available for pyrolysis. Small amount of liquid containing impurities is withdrawn from processing stages in which trapping occurs and passed to earlier processing stage in which impurities tend to be removed via chemical reactions.

  16. Nonlinear screening of charge impurities in graphene

    OpenAIRE

    2006-01-01

    It is shown that a ``vacuum polarization'' induced by Coulomb potential in graphene leads to a strong suppression of electric charges even for undoped case (no charge carriers). A standard linear response theory is therefore not applicable to describe the screening of charge impurities in graphene. In particular, it overestimates essentially the contributions of charge impurities into the resistivity of graphene.

  17. Cryogenic Laser Calorimetry for Impurity Analysis

    Science.gov (United States)

    Swimm, R. T.

    1985-01-01

    The results of a one-year effort to determine the applicability of laser-calorimetric spectroscopy to the study of deep-level impurities in silicon are presented. Critical considerations for impurity analysis by laser-calorimetric spectroscopy are discussed, the design and performance of a cryogenic laser calorimeter is described, and measurements of background absorption in high-purity silicon are presented.

  18. Impurity transport in plasma edge turbulence

    OpenAIRE

    Naulin, Volker; Priego Wood, Martin; Juul Rasmussen, Jens

    2004-01-01

    The turbulent transport of minority species/impurities is investigated in 2D drift-wave turbulence as well as in 3D toroidal drift-Alfven edge turbulence. The full effects of perpendicular and -- in 3D -- parallel advection are kept for the impurity species. Anomalous pinch effects are recovered and explained in terms of Turbulent EquiPartition (TEP)

  19. Impurity density derivation from bandpass soft x-ray tomography: applicability, perspectives and limitations

    International Nuclear Information System (INIS)

    Deriving impurity density from local soft x-ray (SXR) emissivity (reconstructed by background-subtracted tomography during trace injections) by line-emission modelling leads to uncertainties due to the unknown ionization balance, especially for medium-Z impurities. This paper proposes a paradigm shift in the way SXR tomography is used, from one that maximizes signal at the expense of uncertain modelling to one that relies on sharper spectral resolution used to better understand what exactly is being measured. It is indeed shown that the measured SXR emissivity of an impurity may be robust with respect to changes to its unknown ionization balance (i.e. with respect to impurity transport) under two conditions. First, the electron temperature must be above a certain threshold (typically 4–5 keV or higher for metals like Ni or Fe). Second, the spectral response of SXR detectors must have a tuneable band-pass and should focus on a specific spectral region for each considered impurity. Both these conditions aim at maximizing the Bremsstrahlung contribution, which has the weakest dependence on ion charge. Prospective applications for several impurities are discussed as well as practical limitations. Since this method offers diagnostics-designing potential, possible technological solutions are also discussed. (paper)

  20. Blocked strainers

    International Nuclear Information System (INIS)

    Thermal insulation was the cause of the blockages that shut down five BWRs in Sweden. The main culprit was mineral wool installed when the plants started up. Physical degradation of the wool over the lifetime of the plant meant it could easily be washed out of place during a loss of coolant accident and could quickly block strainers in the emergency core cooling systems. The five BWRs are almost all back on line, equipped with larger strainers and faster backwashing capability. But the incident prompted more detailed investigation into how materials in the containment would behave during an accident. One material that caused particular concern is Caposil, a material often used to insulate the reactor vessel. Composed of natural calcium, aluminium silicates and cellulose fibres, in the event of a LOCA Caposil becomes particularly hazardous. Under high pressure, or when brought into contact with high pressure water and steam, Caposil fragments into 1 cm clumps, free fibres, and ''fines''. It is these fines which cause major problems and can block a strainer extremely quickly. The successful testing of a high performance water filter which can handle Caposil is described. (4 figures) (Author)

  1. Lanczos transformation for quantum impurity problems in d-dimensional lattices: Application to graphene nanoribbons

    Science.gov (United States)

    Büsser, C. A.; Martins, G. B.; Feiguin, A. E.

    2013-12-01

    We present a completely unbiased and controlled numerical method to solve quantum impurity problems in d-dimensional lattices. This approach is based on a canonical transformation, of the Lanczos form, where the complete lattice Hamiltonian is exactly mapped onto an equivalent one-dimensional system, in the same spirit as Wilson's numerical renormalization, and Haydock's recursion method. We introduce many-body interactions in the form of a Kondo or Anderson impurity and we solve the low-dimensional problem using the density matrix renormalization group. The technique is particularly suited to study systems that are inhomogeneous, and/or have a boundary. The resulting dimensional reduction translates into a reduction of the scaling of the entanglement entropy by a factor Ld-1, where L is the linear dimension of the original d-dimensional lattice. This allows one to calculate the ground state of a magnetic impurity attached to an L×L square lattice and an L×L×L cubic lattice with L up to 140 sites. We also study the localized edge states in graphene nanoribbons by attaching a magnetic impurity to the edge or the center of the system. For armchair metallic nanoribbons we find a slow decay of the spin correlations as a consequence of the delocalized metallic states. In the case of zigzag ribbons, the decay of the spin correlations depends on the position of the impurity. If the impurity is situated in the bulk of the ribbon, the decay is slow as in the metallic case. On the other hand, if the adatom is attached to the edge, the decay is fast, within few sites of the impurity, as a consequence of the localized edge states, and the short correlation length. The mapping can be combined with ab initio band structure calculations to model the system, and to understand correlation effects in quantum impurity problems starting from first principles.

  2. Progress in nonmagnetic impurity doping studies on Fe-based superconductors

    Science.gov (United States)

    Li, Jun; Guo, Yan-Feng; Yang, Zhao-Rong; Yamaura, Kazunari; Takayama-Muromachi, Eiji; Wang, Hua-Bing; Wu, Pei-Heng

    2016-05-01

    We review the progress of nonmagnetic impurity doping studies on Fe-based superconductors. On the theoretical side, two highly promising candidates for the pairing symmetry order parameter, i.e. the multi-gap s ++ and s ± wave models, have been proposed but continuously debated. The debate arises because of the complex gap structure and exceptional magnetic and metallic behaviors of Fe-based superconductors, which may vary the influence of nonmagnetic defects in the chemical potential, impurity disorder, inter- and intra-band scattering strength, and electron localization. This creates difficulties in directly obtaining the most important information for understanding the symmetry order parameter. Experimentally, nonmagnetic impurity substitution studies have been widely carried out, which have provided very useful insights. We review herein the various nonmagnetic impurity doping experiments, including the controlled defects within the superconducting Fe2 X 2 planes through sample quality improvement, single impurity effects on the electronic state and local moment, the magnetic response of the Fe2 X 2 planes both on the macroscopic scale as the antiferromagnetic state and the local scale of moment, as well as the significant effect of modifying the transport properties. The experiments enable us to qualitatively analyze the nonmagnetic impurity effects on the superconducting state for many Fe-based superconductors. We also propose herein some strategies for nonmagnetic impurity doping study. As an important model for explaining the nonmagnetic impurity doping effects, the pair-breaking model is compared with various theoretical approaches via analysis of the pair-breaking rates of various Fe-superconductors.

  3. Vacancy-impurity nanoclusters in phase-separated solid mixtures 3He - 4He

    International Nuclear Information System (INIS)

    Vacancies in quantum crystals are delocalized and can be considered as quasiparticles (vacancions) with band-energy structure. The delocalization of a vacancy reduces the energy of the system by a half vacancion bandwidth. However, this requires a good periodical structure around it. As a result a crystalline cluster is created. It is shown that such a cluster in phase-separated 3He - 4He solid solutions with small concentration of 4He consists of 4He impurity atoms (vacancy-impurity cluster), not of host atoms with oriented spins (magnetic vacancy). The clusters created may have different structure in dependence of the vacancion parameters. (author)

  4. Blue luminescence in porous anodic alumina films: the role of the oxalic impurities

    CERN Document Server

    Gao Tao; Zhang Li

    2003-01-01

    Porous anodic alumina (PAA) films with ordered nanopore arrays have been prepared by electrochemically anodizing aluminium in oxalic acid solutions, and the role of the oxalic impurities in the optical properties of PAA films has been discussed. Photoluminescence (PL) measurements show that the PAA films obtained have a blue PL band with a peak position at around 470 nm; the oxalic impurities, incorporated in the PAA films during the anodization processes and already existing in them, could be being transformed into PL centres and hence responsible for this PL emission.

  5. Enhanced near-infrared responsivity of silicon photodetector by the impurity photovoltaic effect

    Institute of Scientific and Technical Information of China (English)

    袁吉仁; 黄海宾; 邓新华; 梁晓军; 周耐根; 周浪

    2015-01-01

    The near-infrared responsivity of a silicon photodetector employing the impurity photovoltaic (IPV) effect is inves-tigated with a numerical method. The improvement of the responsivity can reach 0.358 A/W at a wavelength of about 1200 nm, and its corresponding quantum efficiency is 41.1%. The origin of the enhanced responsivity is attributed to the absorption of sub-bandgap photons, which results in the carrier transition from the impurity energy level to the con-duction band. The results indicate that the IPV effect may provide a general approach to enhancing the responsivity of photodetectors.

  6. Luminescence of Eu and Mn impurity centers in Ga2S3(Se3) monocrystals

    International Nuclear Information System (INIS)

    The results of the investigation of the nature of Eu and Mn impurity centers in Ga2S3(Se3) and their luminescence properties are presented. Eu crystal dopping results in a complete quenching of impurity band and occurrence of europium in the green region (520-580 nm) of the spectrum. When dopping Ga2S3 with manganese (up to 0.1%), the radiation intensity of nonactivated crystals in 588 nm region decreases, and in 700 nm region-increases. A strong quenching of luminescence occurs as temperature grows from 77 to 300 K; at room temperature luminescence is practically absent

  7. Precise tuning of the Curie temperature of (Ga,Mn)As-based magnetic semiconductors by hole compensation: Support for valence-band ferromagnetism

    OpenAIRE

    Zhou, Shengqiang; Li, Lin; Yuan, Ye; Rushforth, A.W.; Chen, Lin; Wang, Yutian; Zhao, Jianhua; Edmonds, K. W.; Campion, R. P.; Gallagher, B.L.; Timm, C.; Helm, M.

    2016-01-01

    For the prototype diluted ferromagnetic semiconductor (Ga,Mn)As, there is a fundamental concern about the electronic states near the Fermi level, i.e., whether the Fermi level resides in a well-separated impurity band derived from Mn doping (impurity-band model) or in the valence band that is already merged with the Mn-derived impurity band (valence-band model). We investigate this question by carefully shifting the Fermi level by means of carrier compensation. We use helium-ion implantation,...

  8. Influence of iron impurities on defected graphene

    International Nuclear Information System (INIS)

    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

  9. 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.

  10. Influence of the impurity-defect and impurity-impurity interactions on the crystalline silicon solar cells conversion efficiency

    International Nuclear Information System (INIS)

    This study aims at understanding the influence of the impurity - defect interaction on the silicon solar cell performances. We studied first the case of single-crystalline silicon. We combined numerical simulations and experimental data providing new knowledge concerning metal impurities in silicon, to quantify the evolution of the conversion efficiency with the impurity concentration. Mainly due to the gettering effects, iron appears to be quite well tolerated. It is not the case for gold, diffusing too slowly. Hydrogenation effects were limited. We transposed then this study toward multi-crystalline silicon. Iron seems rather well tolerated, due to the gettering effects but also due to the efficiency of the hydrogenation. When slow diffusers are present, multi crystalline silicon is sensitive to thermal degradation. n-type silicon could solve this problem, this material being less sensitive to metal impurities. (author)

  11. 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)

  12. Simulated impurity transport in LHD from MIST

    International Nuclear Information System (INIS)

    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)

  13. Anderson impurity in a helical metal

    OpenAIRE

    Chen, WQ; Gao, JH; Zhang, FC; Feng, XY; Wang, QH

    2010-01-01

    We use a trial wave function to study the spin-1/2 Kondo effect of a helical metal on the surface of a three-dimensional topological insulator. While the impurity spin is quenched by conduction electrons, the spin-spin correlation of the conduction electron and impurity is strongly anisotropic in both spin and spatial spaces. As a result of strong spin-orbit coupling, the out-of-plane component of the impurity spin is found to be fully screened by the orbital angular momentum of the conductio...

  14. Impurities of oxygen in silicon

    International Nuclear Information System (INIS)

    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:V2+, Si:V20, Si:V2-), of the oxygen pair (Si:O2) and the oxygen-vacancy pair (Si:O.V) neighbours in the silicon lattice, is studied. Distortions for the symmetry were included in the Si:V2+ and Si:O2 systems. The behavior of defect levels related to the cluster size of Si:V20 and Si:O2 systems, the insulated oxygen impurity of silicon in interstitial position (Si:Oi), and the complexes involving four oxygen atoms are analysed. (M.C.K.)

  15. Computation of the Stark effect in P impurity states in silicon

    Science.gov (United States)

    Debernardi, A.; Baldereschi, A.; Fanciulli, M.

    2006-07-01

    We compute within the effective-mass theory and without adjustable parameters the Stark effect for shallow P donors in Si with anisotropic band structure. Valley-orbit coupling is taken into account in a nonperturbative way and scattering effects of the impurity core are included to properly describe low-lying impurity states. The ground-state energy slightly decreases with increasing electric field up to a critical value Ecr˜25keV/cm , at which the donor can be ionized by tunneling due to a field-induced mixing of the “ 1s -like” singlet ground state with a “ 2p0 -like” excited state in zero field. The resulting ground-state wave function at high field extends significantly outside the potential barrier surrounding the impurity. Calculations of the hyperfine splitting and of the A -shell superhyperfine coupling constants as a function of the electric field complete the work.

  16. Hydrogenic donor impurity in parallel-triangular quantum wires: Hydrostatic pressure and applied electric field effects

    Science.gov (United States)

    Restrepo, R. L.; Giraldo, E.; Miranda, G. L.; Ospina, W.; Duque, C. A.

    2009-12-01

    The combined effects of the hydrostatic pressure and in-growth direction applied electric field on the binding energy of hydrogenic shallow-donor impurity states in parallel-coupled-GaAs- Ga1-xAlxAs-quantum-well wires are calculated using a variational procedure within the effective-mass and parabolic-band approximations. Results are obtained for several dimensions of the structure, shallow-donor impurity positions, hydrostatic pressure, and applied electric field. Our results suggest that external inputs such us hydrostatic pressure and in-growth direction electric field are two useful tools in order to modify the binding energy of a donor impurity in parallel-coupled-quantum-well wires.

  17. Hydrogenic donor impurity in parallel-triangular quantum wires: Hydrostatic pressure and applied electric field effects

    Energy Technology Data Exchange (ETDEWEB)

    Restrepo, R.L.; Giraldo, E.; Miranda, G.L.; Ospina, W. [EIA-Fisica Teorica y Aplicada, Escuela de Ingenieria de Antioquia, AA 7516, Medellin (Colombia); Duque, C.A., E-mail: cduque@fisica.udea.edu.c [Instituto de Fisica, Universidad de Antioquia, AA 1226, Medellin (Colombia)

    2009-12-15

    The combined effects of the hydrostatic pressure and in-growth direction applied electric field on the binding energy of hydrogenic shallow-donor impurity states in parallel-coupled-GaAs-Ga{sub 1-x}Al{sub x}As-quantum-well wires are calculated using a variational procedure within the effective-mass and parabolic-band approximations. Results are obtained for several dimensions of the structure, shallow-donor impurity positions, hydrostatic pressure, and applied electric field. Our results suggest that external inputs such us hydrostatic pressure and in-growth direction electric field are two useful tools in order to modify the binding energy of a donor impurity in parallel-coupled-quantum-well wires.

  18. Hydrogenic donor impurity in parallel-triangular quantum wires: Hydrostatic pressure and applied electric field effects

    International Nuclear Information System (INIS)

    The combined effects of the hydrostatic pressure and in-growth direction applied electric field on the binding energy of hydrogenic shallow-donor impurity states in parallel-coupled-GaAs-Ga1-xAlxAs-quantum-well wires are calculated using a variational procedure within the effective-mass and parabolic-band approximations. Results are obtained for several dimensions of the structure, shallow-donor impurity positions, hydrostatic pressure, and applied electric field. Our results suggest that external inputs such us hydrostatic pressure and in-growth direction electric field are two useful tools in order to modify the binding energy of a donor impurity in parallel-coupled-quantum-well wires.

  19. Magnetic resonance peak and nonmagnetic impurities

    OpenAIRE

    Y. Sidis; Bourges, P.; Keimer, B.; Regnault, L. P.; Bossy, J.; Ivanov, A; Hennion, B.; Gautier-Picard, P.; Collin, G.

    2000-01-01

    Nonmagnetic Zn impurities are known to strongly suppress superconductivity. We review their effects on the spin excitation spectrum in $\\rm YBa_2Cu_3O_{7}$, as investigated by inelastic neutron scattering measurements.

  20. Numerical Studies of Impurities in Fusion Plasmas

    Science.gov (United States)

    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.

  1. DIVIMP Modeling of Impurity Transport in EAST

    International Nuclear Information System (INIS)

    Simulations of carbon impurity transport in SOL/divertor plasmas with Ohmic heating on EAST tokamak were performed using the two-dimensional (2D) Monte Carlo impurity transport code DIVIMP. The background plasmas for DIVIMP simulations were externally taken from B2.5/Eirene calculation. Besides the basic output of DIVIMP, the 2D density distributions of the carbon impurity with different ionization states and neutral carbon atoms were obtained, the 2D distributions of CII and CIII emissivities from C+1 and C+2 radiation respectively were also calculated. Comparison between the measured and calculated CIII emissivities showed favorable agreement, indicating that the impurity physics transport models, as implemented in the DIVIMP code, are suitable for the EAST tokamak plasma condition. (magnetically confined plasma)

  2. DIVIMP Modeling of Impurity Transport in EAST

    Science.gov (United States)

    Wang, Fuqiong; Chen, Yiping; Hu, Liqun

    2014-07-01

    Simulations of carbon impurity transport in SOL/divertor plasmas with Ohmic heating on EAST tokamak were performed using the two-dimensional (2D) Monte Carlo impurity transport code DIVIMP. The background plasmas for DIVIMP simulations were externally taken from B2.5/Eirene calculation. Besides the basic output of DIVIMP, the 2D density distributions of the carbon impurity with different ionization states and neutral carbon atoms were obtained, the 2D distributions of CII and CIII emissivities from C+1 and C+2 radiation respectively were also calculated. Comparison between the measured and calculated CIII emissivities showed favorable agreement, indicating that the impurity physics transport models, as implemented in the DIVIMP code, are suitable for the EAST tokamak plasma condition.

  3. Phase growth in bistable systems with impurities

    OpenAIRE

    Echeverria, C.; Tucci, K.; Cosenza, M. G.

    2007-01-01

    A system of coupled chaotic bistable maps on a lattice with randomly distributed impurities is investigated as a model for studying the phenomenon of phase growth in nonuniform media. The statistical properties of the system are characterized by means of the average size of spatial domains of equivalent spin variables that define the phases. It is found that the rate at which phase domains grow becomes smaller when impurities are present and that the average size of the resulting domains in t...

  4. Description of the impurity transport code 'STRAHL'

    International Nuclear Information System (INIS)

    'STRAHL' is an interactive, stand-alone impurity transport code which is used on JET for the interpretation of spectroscopic measurements. It calculates the impurity ionisation balance on the basis of given plasma parameters and empirical transport models, using atomic physics data sets especially compiled for that purpose. The paper explains the basic ideas and formulas behind STRAHL in order to allow potential users to design their own special version. (U.K.)

  5. Parametrically Driven Nonlinear Oscillators with an Impurity

    Institute of Scientific and Technical Information of China (English)

    张卓; 唐翌

    2002-01-01

    By virtue of the method of multiple scales, we study a chain of parametrically driven nonlinear oscillators with a mass impurity. An equation is presented to describe the nonlinear wave of small amplitude in the chain.In our derivation, the equation is applicable to any eigenmode of coupled pendulum. Our result shows that a nonpropagation soliton emerges as the lowest or highest eigenmode of coupled pendulum is excited, and the impurity tends to pin the nonpropagation soliton excitation.

  6. Transport of Impurities in Tokamak Edge Turbulence

    Czech Academy of Sciences Publication Activity Database

    Seidl, Jakub; Papřok, Richard; Krlín, Ladislav

    Vol. P212. Roma: ENEA-Fusione, 2011. s. 88-88. [European Fusion Theory Conference(EFTC)/14./. 26.09.2011-29.09.2011, Frascati] R&D Projects: GA ČR GAP205/10/2055 Institutional research plan: CEZ:AV0Z20430508 Keywords : plasma turbulence * plasma impurities * impurity transport * drift waves Subject RIV: BL - Plasma and Gas Discharge Physics http://www.fusione.enea.it/EVENTS/EFTC14/upload/abstractsgiulia/JakubSeidl.pdf

  7. Achieving Improved Ohmic Confinement via impurity injection

    International Nuclear Information System (INIS)

    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 steel 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. The remainder of this contribution is organized according to the following lines: 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 experiments in other tokamaks and some conclusions are drawn about the effects of the impurity puffing on both, the central and the edge plasma behaviour. (author) 9 refs., 2 figs

  8. Achieving improved ohmic confinement via impurity injection

    International Nuclear Information System (INIS)

    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.)

  9. Texas Experimental Tokamak impurity injection system

    International Nuclear Information System (INIS)

    Summary investigation of impurity transport and measurements of ion temperature are facilitated by injecting controlled quantities of selected impurities into tokamaks as diagnostic probes. The impurity injector now in use on the Texas Experimental Tokamak (TEXT) was designed for reliable, automatic operation. In this system, a thin film of the desired impurity is placed near the edge of the plasma. The light pulse from a Q-switched ruby laser is directed to a preselected point on the target. A small part of the impurity film evaporates and drifts into the plasma. The laser beam may be scanned to many points on the target so that enough impurity pulses can be obtained from a single target to allow a full day's operation. The scanning assembly and associated electronics are designed to operate with minimum intervention and to facilitate rapid repair and modification. The system is fully automatic but also incorporates both remote and local manual control capabilities to permit system calibration and troubleshooting. In the event of component failure, its self-diagnostic capability can indicate the area for repair. The system is demonstrating its effectiveness and reliability in the support of three different experimental programs. Engineering aspects of the system are discussed in this paper

  10. Electronic structure and local magnetism of 3d-5d impurity substituted CeFe2

    Science.gov (United States)

    Das, Rakesh; Das, G. P.; Srivastava, S. K.

    2016-04-01

    We present here a systematic first-principles study of electronic structure and local magnetic properties of Ce[Fe0.75M0.25]2 compounds, where M is a 3d, 4d or 5d transition or post-transition element, using the generalized gradient approximation of the density functional theory. The d-f band hybridizations existing in CeFe2 get modified by the impurity M in an orderly manner across a period for each impurity series: the hybridization is strongest for the Mn group impurity in the period and gets diminished on either side of it. The weakening of the d-f hybridization strength is also associated with a relative localization of the Ce 4f states with respect to the delocalized 4f states in CeFe2. The above effects are most prominent for 3d impurity series, while for 4d and 5d impurities, the hybridizations and relocalizations are relatively weak due primarily to the relatively extended nature of 4d and 5d wavefunctions. The Ce local moment is found to decrease from the CeFe2 value in proportion to the strength of relocalization, thus following almost the same orderly trend as obeyed by the d-f hybridization. Further, depending on the way the spin-up and spin-down densities of states of an impurity shift relative to the Fermi energy, the impurity local moments are highest for Mn or Fe group, reduce on either side, become zero for Ni to Ga, and are small but negative for V and Ti. The Ce hyperfine field is found to follow the M local moment in a linear fashion, and vice-versa.

  11. 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...

  12. Isolation, Synthesis and Characterization of Rosiglitazone Maleate Impurities

    OpenAIRE

    Krishna, Singamsetty Radha; Brahmeshwar Rao, Mandava Venkata Naga; Raju, Tirmalaraju Satyanaryana; Himabindu, Vurimidi; Reddy, Ghanta Mahesh

    2008-01-01

    Three unknown impurities in rosiglitazone maleate 1 bulk drug at level below 0.1% (ranging from 0.05 to 0.1%) were detected by simple reverse phase high performance liquid chromatography. These impurities were preliminarily identified with LC-MS and characterized by the mass number of the impurities. Different experiments were conducted and finally synthesized and characterized the unknown impurities.

  13. Micellization and Characterization of Block Copolymer Detergents

    DEFF Research Database (Denmark)

    Hvidt, Søren

    Triblock copolymers of the type EPE, where E and P denote ethylene oxide and propylene oxide blocks, respectively, are used widely in industry as emulsifiers, anti-foaming agents, and in delayed drug release. EPE copolymers form micelles with a core of P blocks and different micellar shapes...... depending on block length ratios and temperature. The micellization process with increasing temperature or concentration has been followed by a number of techniques including differential scanning calorimetry and surface tension measurements. The detailed micellar mechanism is not well understood and...... different models have been proposed. Results obtained by a range of liquid chromatographic methods will be shown and it will be demonstrated that commercial EPE copolymers are inhomogeneous at several levels and many of their unusual properties reflect the presence of impurities....

  14. Effect of divalent impurities on some physical properties of LiF and NaF

    International Nuclear Information System (INIS)

    The ionic thermo-currents technique is applied to the study of impurity vacancy dipoles in LiF and NaF doped with several divalent cations. In LiF only one ITC band is observed whatever the impurity studied. In NaF on the contrary two ITC bands are present, one corresponding to the one observed in LiF, the other one, intense in the case of small impurities, at lower temperature. A parallel EPR study in the case of Mn2+ doped samples shows that the band observed in LiF and the corresponding one in NaF are due to the relaxation of dipoles formed by the association of an impurity and a vacancy in the next nearest position. The knowledge of the properties of the dipoles allows to show that the room temperature ionic conductivity of LiF is conditioned by the equilibrium: M++ □+ → M++ + □+. It is also shown that the isolated cation vacancy originating from this dissociation is responsible for the enhancement of γ-ray coloration of LiF doped with divalent cation impurities. A paramagnetic center ascribed to the presence of Mn0 isolated in the lattice is also studied. The value of the hyperfine interaction and its temperature dependence are in good agreement with both the theory and the other experimental results. Finally it is shown that the disappearance of dipoles by annealing is related to the formation of complexes involving OH- ions, probably of the M(OH)2 type, with the two OH- ions occupying a single fluorine site. (author)

  15. Effect of TlBr crystal impurities for gamma-ray detector application

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Robinson A. dos; Mesquita, Carlos H. de; Costa, Fabio E. da; Martins, Joao F. Trencher; Marcondes, Renata M.; Hamada, Margarida M. [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2011-07-01

    Full text: Thallium bromide (TlBr) is a semiconductor compound with a high atomic number and wide band gap, being a very promising material to be used as room temperature radiation detectors. The performance of a radiation detector depends on several factors, such as, the carrier lifetime, the mobility, the crystallographic imperfections and the impurity concentrations of the detector. These factors may play an important role in the final performance of radiation semiconductor detectors. The TlBr crystal purity is a crucial factor for its optimal performance as a radiation detector. In this work, the commercial TlBr salts were used as the raw material for crystal growths. To reduce impurities, these salts were purified by the repeated Bridgman growth method. To evaluate the purification efficiency, measurements of the impurity concentration were made after each growth, analyzing the trace impurities by inductively coupled plasma mass spectroscopy (ICP-MS). A compartmental model defined by linear differential equations was proposed to calculate the impurity migration in the crystal during the growth. It is useful for predicting the repetitions number of Bridgman growth needed to achieve a desirable concentration value. To evaluate the crystal used as a radiation semiconductor detector, measurements of its resistivity and gamma-ray spectroscopy were carried out. The radiation response depended on the crystal purity. The repeated Bridgman technique improved the TlBr crystal quality used as a radiation semiconductor detector. (author)

  16. Simulation of the impurity-vacancy clusters in Ni

    International Nuclear Information System (INIS)

    Formation energies and atomic configuration of impurity-vacancy, impurity-divacancy complexes are investigated using mathematical simulation method. Impurity introduction was simulated by changing the impurity atomic radius as compared to matrix atomic radius R0. It is shown, that if impurity radius exceeds 1.18 R0, impurity-divacancy complex transfers into a depleted configuration in which impurity atom is placed between the two vacancies. Possessing low activity and large capture radius, this complex may become an effective center of point defect recombination

  17. Simulation of impurity-vacancy clusters in Ni

    International Nuclear Information System (INIS)

    Formation energies and atomic configurations of impurity-vacancy, impurity-divacancy complexes have been investigated by computerized simulation. Impurity introduction is simulated by changing the atomic radius of the impurity in comparison with the atomic radius, R0, of the matrix. It is shown that with the impurity radius more than 1.18 R0 the impurity-divacancy complex transforms into the splitting configuration, in which the impurity atom is in the middle between two vacancies. This complex can become an effective centre of point defect recombination, when possessing light mobility and a large radius of capture

  18. Investigation on the effect of metallic impurity Zn in solvent during photolithography process

    Science.gov (United States)

    Jeon, Byoung-Tak; Kim, Ook-Hyun; Baik, Jeong-Heon; Ha, Jeong-Hyuk; Lee, Il-Ho; Yang, Weon-Sik

    2005-05-01

    The trend toward narrower line widths in the manufacture of integrated circuits has put an increasing burden on contamination control in every aspect of semiconductor fabrication. For a deep sub micrometer device, metal contamination appearing on the device can cause fatal problems including increasing the leakage current at the p-n junction, decreasing the breakdown voltage of oxide. Many lithographic defects have been known and evaluated, however, the effects of metallic impurity (Zn) in solvent are seldom reported during lithography process. Solvents are component material for Photoresist and have been used for prewet, strippers, EBR, rinse and so on during photolithography process. Lithography plays a very important role because it is applied repeatedly onto the wafer surface during device manufacturing. Unfortunately, pattern lifting happened to well formation layer wafers that were reworked on a normal iline litho process after stripping the Photoresist with solvent (PGMEA). We also detected blocked pattern defect at 0.18 CMOS gate pattern coated with DUV resist applied solvent prewet step after BARC coating. From various investigations, we could know that pattern lifting and blocked defect were derived from solvent (PGMEA). In this paper, we show mechanism of adhesion fails and blocked defect happened by metallic impurity Zn in solvent during solvent rework and prewet on organic BARC film. It shows that proper control of metallic impurities in thinner is an important item in FAB.

  19. Optical detection of impurities and defects in detector-grade mercuric iodide vandenBerg, L.

    Science.gov (United States)

    James, R. B.; Ottesen, D. K.; Wong, D.; Schlesinger, T. E.; Schnepple, W. F.; Ortale, C.; Vandenberg, L.

    Fourier tranform infrared spectroscopy (FTIR) and low-temperature photoluminescence were used to study impurities and defects in mercuric iodide crystals. FTIR spectra of the transmittance and reflectance were obtained in the 400 to 4000 cm sup minus 1 range, and the results were found to vary for different samples due to the presence of impurities and stoichiometry deviations. The photoluminescence data were found to consist primarily of three distinct emission bands. The lowest energy band at about 680 nm (at 4.2 K) was shown to be related to the performance of nuclear radiation detectors fabricated from these samples. Further correlations between the spectral features obtained from FTIR and photoluminescence techniques and the detector response are also noted.

  20. Optical detection of impurities and defects in detector-grade mercuric iodide

    Energy Technology Data Exchange (ETDEWEB)

    James, R.B.; Ottesen, D.K.; Wong, D.; Schlesinger, T.E.; Schnepple, W.F.; Ortale, C.; van den Berg, L.

    1987-01-01

    Fourier tranform infrared spectroscopy (FTIR) and low-temperature photoluminescence were used to study impurities and defects in mercuric iodide crystals. FTIR spectra of the transmittance and reflectance were obtained in the 400 to 4000 cm/sup /minus/1/ range, and the results were found to vary for different samples due to the presence of impurities and stoichiometry deviations. The photoluminescence data were found to consist primarily of three distinct emission bands. The lowest energy band at about 680 nm (at 4.2 K) was shown to be related to the performance of nuclear radiation detectors fabricated from these samples. Further correlations between the spectral features obtained from FTIR and photoluminescence techniques and the detector response are also noted.

  1. Rydberg Impurity Probes in Ultracold Gases

    Science.gov (United States)

    Mitchison, Mark; Johnson, Tomi; Plenio, Martin; Jaksch, Dieter

    2015-03-01

    Impurities immersed in ultracold gases can act as highly sensitive, tunable and potentially non-destructive probes of their environment. In this setting, we propose the use of an atomic impurity in a Rydberg state to measure density fluctuations via Ramsey interferometry. The rapid collisional dynamics of the light Rydberg electron interacting with the heavy gas particles, combined with the capability to quickly change the state of the impurity with optical pulses, make such a probe ideal for measuring local properties of ultracold gases. Our proposed device promises angle-resolved density measurements with sub-micron spatial resolution, and with no need to integrate over the line of sight. We outline how Rydberg impurity probes could be applied to study various interesting quantum states of current experimental relevance. We also discuss the possibility of using multiple Rydberg atoms to extract the spatial pair distribution function g (2) (r). Our work is placed in the context of other recently proposed impurity-based probes.

  2. Impurities in the Lithium Tokamak Experiment

    Science.gov (United States)

    Boyle, D. P.; Bell, R. E.; Kaita, R.; Majeski, R.; Biewer, T. M.; Gray, T. K.; Tritz, K.; Widmann, K.

    2014-10-01

    The Lithium Tokamak Experiment (LTX) is designed to study the low-recycling regime through the use of close-fitting, lithium-coated, heatable shell quadrants surrounding the plasma volume. Lithium coatings can getter and bury impurities, but they can also become covered by impurity compounds. Liquefied coatings can both dissolve impurity compounds and bring them to the surface, while sputtering and evaporation rates increase strongly with temperature. Here, we use spectroscopic measurements to assess the effects of varying wall conditions on plasma impurities, mainly Li, C, and O. A passive Doppler spectroscopy system measures toroidal and poloidal impurity profiles using fixed-wavelength and variable-wavelength visible spectrometers. In addition, survey and high-resolution extreme ultraviolet spectrometers detect emission from higher charge states. Preliminary results show that fresh Li coatings generally reduced C and O emission. C emission decreased sharply following the first solid Li coatings. Inverted toroidal profiles in a discharge with solid Li coatings show peaked Li III emissivity and temperature profiles. Recently, experiments with fresh liquid coatings led to especially strong O reduction. Results from these and additional experiments will be presented. Supported by US DOE Contracts DE-AC02-09CH11466 and DE-AC05-00OR22725.

  3. Gettering of metal impurities in silicon

    Energy Technology Data Exchange (ETDEWEB)

    Schroeter, W.; Spiecker, E.; Apel, M. [Universitaet Goettingen (Germany)

    1995-08-01

    Gettering means the removal of metallic impurities from the device-active area of the wafer by transport to a predesigned region-called gettering layer (GL). We introduce an interface at z = d{sub GL}, at which the effect of the gettering mechanism on the metal impurity distribution in the wafer is quantified, e.g. by specifying currents or by interfacial reactions of metal impurities, self interstitials etc. between GL and wafer. In response metal impurities will diffuse out of the wafer into the gettering layer. Following such a concept, in general three species of the metal impurity (M) are involved in gettering: M{sub p} {l_arrow} M{sub i} {l_arrow} M{sub GL}. M{sub p} denotes immobile species in the wafer, which are precipitated into suicides or segregated at extended defects or whose diffusivity is too small to contribute noticeably to transport during the gettering procedure - like many substitutional metal species.

  4. Characterization and micellization of a poloxamer block copolymer

    DEFF Research Database (Denmark)

    Hvidt, S.; Pedersen, Walther Batsberg

    2007-01-01

    Several poloxamers that are symmetrical EPE block copolymers (E and P are ethylene and propylene oxide, respectively) have been characterized by size exclusion chromatography on Superose columns in water. The poloxamers contain between 12 and 26 wt% of smaller-size UV-absorbing impurities....... Poloxamer P94 (E28P48E28) forms micelles with increasing temperature, and micellization was investigated by eluent gel permeation chromatography (EGPC). EGPC results demonstrate that P94 impurities are not incorporated into the micelles up to 38°C. The importance of poloxamer heterogeneity for thermodynamic...

  5. Ultrasound guided supraclavicular block.

    LENUS (Irish Health Repository)

    Hanumanthaiah, Deepak

    2013-09-01

    Ultrasound guided regional anaesthesia is becoming increasingly popular. The supraclavicular block has been transformed by ultrasound guidance into a potentially safe superficial block. We reviewed the techniques of performing supraclavicular block with special focus on ultrasound guidance.

  6. Interaction-induced localization of mobile impurities in ultracold systems

    Science.gov (United States)

    Li, Jian; An, Jin; Ting, C. S.

    2013-11-01

    The impurities, introduced intentionally or accidentally into certain materials, can significantly modify their characteristics or reveal their intrinsic physical properties, and thus play an important role in solid-state physics. Different from those static impurities in a solid, the impurities realized in cold atomic systems are naturally mobile. Here we propose an effective theory for treating some unique behaviors exhibited by ultracold mobile impurities. Our theory reveals the interaction-induced transition between the extended and localized impurity states, and also explains the essential features obtained from several previous models in a unified way. Based on our theory, we predict many intriguing phenomena in ultracold systems associated with the extended and localized impurities, including the formation of the impurity-molecules and impurity-lattices. We hope this investigation can open up a new avenue for the future studies on ultracold mobile impurities.

  7. Impurity and particle control for INTOR

    International Nuclear Information System (INIS)

    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

  8. On charged impurity structures in liquid helium

    International Nuclear Information System (INIS)

    The thermoluminescence spectra of impurity-helium condensates (IHC) submerged in superfluid helium have been observed for the first time. Thermoluminescence of impurity-helium condensates submerged in superfluid helium is explained by neutralization reactions occurring in impurity nanoclusters. Optical spectra of excited products of neutralization reactions between nitrogen cations and thermoactivated electrons were rather different from the spectra observed at higher temperatures, when the luminescence due to nitrogen atom recombination dominates. New results on current detection during the IHC destruction are presented. Two different mechanisms of nanocluster charging are proposed to describe the phenomena observed during preparation and warm-up of IHC samples in bulk superfluid helium, and destruction of IHC samples out of liquid helium.

  9. Triangular Ising antiferromagnets with quenched nonmagnetic impurities.

    Science.gov (United States)

    Tang, Huai-Lei; Zhu, Yi; Yang, Guo-Hong; Jiang, Ying

    2010-05-01

    In a random spin system, the cooperation of randomness and frustration will lead to a spin-glass phase. However, in geometrically frustrated spin systems, quenched nonmagnetic impurities lift frustration locally. This makes randomness and frustration in these systems as competitors rather than cooperators. By mapping the dilute triangular Ising antiferromagnetic system to elastic array of noncrossing strings, we find that the nonmagnetic impurities in the spin system play roles of pinning centers in the string system. Calculation shows that in the ground state of this system, the spin-glass correlation is power-law decayed, quite different from the standard behavior of spin glass in which spin-glass correlation between two spins at infinite distance tends to a finite value. This indicates that triangular Ising antiferromagnets with quenched nonmagnetic impurities cannot be a spin glass. Instead, in the ground states, they present properties of vortex glass. PMID:20866185

  10. Characteristics of impurity-induced pseudogap

    Science.gov (United States)

    Numata, Yoshinori; Uto, Tatsuro; Matuda, Azusa

    2016-05-01

    We have performed STM/STS measurements on a single crystal of Bi2.1Sr1.9Ca (Cu1-xCox) 2O8+δ (Co-Bi2212), to reveal impurity effects on the pseudogap in cuprate high-Tc superconductors. We report a drastic change in the temperature dependence of a pseudogap and in the density of states (DOS) modulation with a 4a period, in a certain doping range. In the Co 4% substituted samples, the pseudogap gradually closed like a gap of a BCS superconductor for slightly overdoped and overdoped regime, while their low temperature values were enhanced due to impurity. In addition, a disappearance of a 4a periodic modulation and a development of new modulation were observed in the DOS spatial distribution. These results indicate an intimate relation between the DOS modulation and the pseudogap, and qualitative difference in the impurity enhanced pseudogap and conventional one.

  11. Removal Of Volatile Impurities From Copper Concentrates

    Energy Technology Data Exchange (ETDEWEB)

    Winkel, L.; Schuler, A.; Frei, A.; Sturzenegger, M.

    2005-03-01

    To study the removal of volatile impurities from two different copper concentrates they have been heated on a thermo balance to temperatures between 900 and 1500 C. This sample treatment revealed that both concentrates undergo strong weight losses at 500 and 700 C. They were attributed to the removal of sulfur. Elemental analyses of the residues by ICP spectrometry have shown that the thermal treatment efficiently removes the volatile impurities. Already below 900 C most of the arsenic is removed by evaporation, the largest fraction of lead and zinc is removed in the temperature interval of 1300-1500 C. It was observed that quartz in the concentrate leads to the formation of a silicon-enriched phase besides a metal rich sulfide phase. The former is interpreted as an early stage of a silicate slag. Elemental analysis showed that the formation of this distinct slag phase does not hinder the efficient removal of volatile impurities. (author)

  12. Effect of impurity radiation on tokamak equilibrium

    International Nuclear Information System (INIS)

    The energy loss from a tokamak plasma due to the radiation from impurities is of great importance in the overall energy balance. Taking the temperature dependence of this loss for two impurities characteristic of those present in existing tokamak plasmas, the condition for radial power balance is derived. For the impurities considered (oxygen and iron) it is found that the radiation losses are concentrated in a thin outer layer of the plasma and the equilibrium condition places an upper limit on the plasma paraticle number density in this region. This limiting density scales with mean current density in the same manner as is experimentally observed for the peak number density of tokamak plasmas. The stability of such equilibria is also discussed. (author)

  13. Impurity transport and control in ASDEX Upgrade

    International Nuclear Information System (INIS)

    Impurity transport parameters of Si and Ne have been determined for H-mode and improved H-mode plasmas with and without central wave heating. The diffusion coefficient D is always anomalous in the edge region and about neoclassical in the centre, when central heating powers are low. Sufficient central wave heating increases the central D and leads also to a flattening of the central density profile. Accumulation of W has been studied in improved H-mode discharges. It strongly depends on the density peaking, and can become severe for purely NBI heated discharges with peaked density profiles, while for flat density profiles, which are achieved with sufficient central wave heating, the W concentrations are flat. Extrapolations of the found impurity behaviour were used to guide a case study of particle transport for the ITER-FEAT inductive operation reference scenario. It suggests sufficient anomalous transport and thus negligible impurity accumulation in the inner plasma region. (author)

  14. The Higgs Branch of Impurity Theories

    CERN Document Server

    Kapustin, A A; Kapustin, Anton; Sethi, Savdeep

    1998-01-01

    We consider supersymmetric gauge theories with impurities in various dimensions. These systems arise in the study of intersecting branes. Unlike conventional gauge theories, the Higgs branch of an impurity theory can have compact directions. For models with eight supercharges, the Higgs branch is a hyperKahler manifold given by the moduli space of solutions of certain differential equations. These equations are the dimensional reductions of self-duality equations with boundary conditions determined by the impurities. They can also be interpreted as Nahm transforms of self-duality equations on toroidally compactified spaces. We discuss the application of our results to the light-cone formulation of Yang-Mills theories and to the solution of certain N=2 d=4 gauge theories.

  15. Analysis of impurities in beryllium, affecting evaluation of the tritium breeding ratio

    International Nuclear Information System (INIS)

    In most conceptual fusion power reactor designs, it is proposed to use beryllium as a neutron multiplier in the blanket. Detailed chemical composition of beryllium is necessary for evaluation of the tritium breeding ratio, and estimating the activation and transmutation of beryllium in the fusion reactor. In the present report, special attention was paid to a detailed analysis of impurities in beryllium, relevant to the tritium breeding ratio evaluation. Two different methods were used for the study of impurities: an analysis of the local sample by the ICP-MS method, and an integral analysis of the beryllium assembly, using the pulsed neutron method. The latter method was proposed as the most effective way of analyzing the integral effect to impurities in beryllium on production of the tritium on the lithium-6. The evaluation of the integral effect was based on time behaviour observations of the thermal neutron flux, following the injection of a burst of D-T neutrons into the beryllium assembly. Structural beryllium grade (S-200-F, Brush Wellman Inc.) was used in the study. The influence of the impurities has resulted in a smaller experimental reaction rate for production of the tritium on lithium-6, due to an increase in the parasitic neutron absorption. Experimental data was compared with the reference data and the MCNP Monte Carlo calculations using the JENDL-3.2 data set. Results indicate, that the measured absorption cross section of thermal neutrons in beryllium blocks is approximately 30% larger than the calculated value, based on the data, specified by the manufacturing company. ICP-MS analysis indicated that the impurities include elements such as Li, B, Cd and others. These elements affect the absorption cross section even if the content of impurities is less than 10 ppm. (author)

  16. Correlations between locked modes and impurity influxes

    Energy Technology Data Exchange (ETDEWEB)

    Fishpool, G.M. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Lawson, K.D. [UKAEA Culham Lab., Abingdon (United Kingdom)

    1994-07-01

    An analysis of pulses that were disturbed by medium Z impurity influxes (Cl, Cr, Fe and Ni) recorded during the 91/92 JET operations, has demonstrated that such influxes can result in MHD modes which subsequently ``lock``. A correlation is found between the power radiated by the influx and the time difference between the start of the influx and the beginning of the locked mode. The growth in the amplitude of the locked mode itself can lead to further impurity influxes. A correlation is noted between intense influxes (superior to 10 MW) and the mode ``unlocking``. (authors). 4 refs., 4 figs.

  17. The physics of Kondo impurities in graphene.

    Science.gov (United States)

    Fritz, Lars; Vojta, Matthias

    2013-03-01

    This article summarizes our understanding of the Kondo effect in graphene, primarily from a theoretical perspective. We shall describe different ways to create magnetic moments in graphene, either by adatom deposition or via defects. For dilute moments, the theoretical description is in terms of effective Anderson or Kondo impurity models coupled to graphene's Dirac electrons. We shall discuss in detail the physics of these models, including their quantum phase transitions and the effect of carrier doping, and confront this with existing experimental data. Finally, we will point out connections to other quantum impurity problems, e.g., in unconventional superconductors, topological insulators, and quantum spin liquids. PMID:23411583

  18. The physics of Kondo impurities in graphene

    International Nuclear Information System (INIS)

    This article summarizes our understanding of the Kondo effect in graphene, primarily from a theoretical perspective. We shall describe different ways to create magnetic moments in graphene, either by adatom deposition or via defects. For dilute moments, the theoretical description is in terms of effective Anderson or Kondo impurity models coupled to graphene's Dirac electrons. We shall discuss in detail the physics of these models, including their quantum phase transitions and the effect of carrier doping, and confront this with existing experimental data. Finally, we will point out connections to other quantum impurity problems, e.g., in unconventional superconductors, topological insulators, and quantum spin liquids. (review article)

  19. Impurity diffusion of niobium in nickel

    International Nuclear Information System (INIS)

    Impurity diffusion of niobium in nickel has been studied employing sandwich type diffusion couples between pure nickel (99.99%) and Ni-4.6 at % Nb alloy, in the temperature range of 1200 to 1500 K. The concentration penetration profiles across the diffusion zone have been established by using electron probe micro analyser (EPMA). The chemical diffusion coefficients have been evaluated by employing Hall's analytical solution to Fick's law. The concentration dependence of these diffusion coefficients has been established and impurity diffusion coefficient of niobium in nickel DNb has been evaluated by extrapolating these values to zero mole fraction of niobium. (author). 11 refs., 2 figs

  20. Impurity radiation from medium density plasmas

    International Nuclear Information System (INIS)

    Impurity radiation from plasmas of densities typical of tokamaks and mirrors is examined for a variety of impurity species over a wide temperature range. Calculations indicate that radiative losses are enhanced during the early phase of the stripping process and that the radiation is much greater at temperatures characteristic of many electron atoms than had been generally recognized by the plasma physics community. These results are useful in the analysis of the energy balance in tokamaks and given important constraints on the choice of wall materials

  1. Plasma impurity-control studies in CTX

    International Nuclear Information System (INIS)

    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

  2. Novel Bound States in Graphene with Impurities

    CERN Document Server

    Gupta, Kumar S

    2008-01-01

    We obtain a novel bound state spectrum of the low energy excitations near the Fermi points of graphene in the presence of a charge impurity. The effects of possible short range interactions induced by the impurity are modelled by suitable boundary conditions. The spectrum in the subcritical region of the effective Coulomb coupling is labelled by a parameter which characterizes the boundary conditions and determines the inequivalent quantizations of the system. In the supercritical region we obtain a renormalization group flow for the effective Coulomb coupling.

  3. 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.

  4. Local Magnetization in the Impure Spin 1/2 Anisotropic Ising-Heisenberg Chains

    Science.gov (United States)

    Gildenblat, Gennady

    A theory of the Friedel-type oscillations of the local magnetization in the impure antiferromagnetic spin 1/2 chains is developed using the Green function equations of motion in the pseudo-fermion representation. For the isotropic XY (XX) chain, the problem is solved exactly, while the Ising-Heisenberg model is investigated numerically within a temperature-dependent Hartree-Fock approximation. It is shown that the Hartree-Fock self consistency equations for the uniformly magnetized XXZ chain can be recovered as a particular case of the formalism developed in the present work. Comparison with the earlier perturbation theory treatment in a free-fermion approximation reveals that the magnetic field dependence of the perturbation of the local magnetization is sensitive to the formation of the localized states and the exact form of the energy dispersion law of the quasi-particles. In particular it is shown that the perturbations of the local magnetization in the impure spin 1/2 chains disappear in the absence of the external magnetic field. Using the exact solution for the XY chain it is shown that unless the localized energy levels are formed outside the pseudo-fermion energy band the singularity of the local magnetization existing in the pure chain disappears at an arbitrary distance from the single impurity spin. For the ferromagnetic chain with the ferromagnetically coupled impurity the solution of the Hartree-Fock equations at low temperatures agrees reasonably with the results of the linear spin-wave theory. If the impurity is antiferromagnetically coupled, then, in contrast with the results of the spin -wave theory, the Hartree-Fock approximation agrees with the exact result for the zero-field ground state spin defect at the impurity site. Unlike the previous methods, the technique developed in this work permits investigation of the whole temperature range and predicts the correct Curie-Weiss behavior at sufficiently large temperatures.

  5. Anomalous Micellization of Pluronic Block Copolymers

    Science.gov (United States)

    Leonardi, Amanda; Ryu, Chang Y.

    2014-03-01

    Poly(ethylene oxide) - poly(propylene oxide) - poly(ethylene oxide) (PEO-PPO-PEO) block copolymers, commercially known as Pluronics, are a unique family of amphiphilic triblock polymers, which self-assemble into micelles in aqueous solution. These copolymers have shown promise in therapeutic, biomedical, cosmetic, and nanotech applications. As-received samples of Pluronics contain low molecular weight impurities (introduced during the manufacturing and processing), that are ignored in most applications. It has been observed, however, that in semi-dilute aqueous solutions, at concentrations above 1 wt%, the temperature dependent micellization behavior of the Pluronics is altered. Anomalous behavior includes a shift of the critical micellization temperature and formation of large aggregates at intermediate temperatures before stable sized micelles form. We attribute this behavior to the low molecular weight impurities that are inherent to the Pluronics which interfere with the micellization process. Through the use of Dynamic Light Scattering and HPLC, we compared the anomalous behavior of different Pluronics of different impurity levels to their purified counterparts.

  6. Influence of samarium impurity on spectral characteristics of calcium iodide crystals

    International Nuclear Information System (INIS)

    The influence of a SmBr3 impurity on optical absorption spectra and x-ray-, photo-, and thermally stimulated luminescence of CaI2 scintillator was studied in the temperature range 90-295 K. Activation of CaI2 from the melt by SmBr3 caused absorption bands related to 4f 6 → 4f 55d electronic transitions in Sm2+ to appear in the spectra. Excitation and emission spectra of CaI2:SmBr3 (0.01 mol%) were represented mainly by bands characteristic of the matrix. The photoluminescence spectrum at 90 K upon optical excitation of the crystal in the impurity absorption region (λex = 280 nm) was approximated by individual Gaussian bands with maxima near 345, 395, 430, 470, 500, and 520 nm. The photoluminescence spectrum of CaI2:SmBr3 (0.5 mol%) at 295 K with excitation by radiation from an LGI-21 nitrogen laser (λex = 337.1 nm) was represented mainly by a band at 465 nm. The intensity of this band weakened, its maximum shifted to 470 nm, luminescence in the 520 nm region increased, and weak emission with a maximum near 585 nm was also observed upon lowering the crystal temperature to 90 K. Doping CaI2 with the Sm impurity decreased the yield and changed the spectral composition of its x-ray-luminescence. CaI2:SmBr3 stored a small light sum in shallow trapping levels upon x-ray excitation at 90 K. The nature of the emission and trapping centers in the investigated crystals was discussed. (authors)

  7. Influence of samarium impurity on spectral characteristics of calcium iodide crystals

    International Nuclear Information System (INIS)

    The influence of a SmBr3 impurity on optical absorption spectra and x-ray-, photo-, and thermally stimulated luminescence of CaI2 scintillator was studied in the temperature range 90-295 K. Activation of CaI2 from the melt by SmBr3 caused absorption bands related to 4f6-4f5 5d electronic transitions in Sm2+ to appear in the spectra. Excitation and emission spectra of CaI2:SmBr3(0.01 mol%) were represented mainly by bands characteristic of the matrix. The photoluminescence spectrum at 90 K upon optical excitation of the crystal in the impurity absorption region (λex = 280 nm) was approximated by individual Gaussian bands with maxima near 345, 395, 430, 470, 500, and 520 nm. The photoluminescence spectrum of CaI2:SmBr3(0.5 mol%) at 295 K with excitation by radiation from an LGI-21 nitrogen laser (λex = 337.1 nm) was represented mainly by a band at 465 nm. The intensity of this band weakened, its maximum shifted to 470 nm, luminescence in the 520 nm region increased, and weak emission with a maximum near 585 nm was also observed upon lowering the crystal temperature to 90 K. Doping CaI2with the Sm impurity decreased the yield and changed the spectral composition of its x-ray-luminescence. CaI2:SmBr2 stored a small light sum in shallow trapping levels upon x-ray excitation at 90 K. The nature of the emission and trapping centers in the investigated crystals was discussed. (author)

  8. Influence of samarium impurity on spectral characteristics of calcium iodide crystals

    Science.gov (United States)

    Novosad, S. S.; Novosad, I. S.

    2013-03-01

    The influence of a SmBr3 impurity on optical absorption spectra and x-ray-, photo-, and thermally stimulated luminescence of CaI2 scintillator was studied in the temperature range 90-295 K. Activation of CaI2 from the melt by SmBr3 caused absorption bands related to 4 f 6 → 4 f 55 d electronic transitions in Sm2+ to appear in the spectra. Excitation and emission spectra of CaI2:SmBr3 (0.01 mol%) were represented mainly by bands characteristic of the matrix. The photoluminescence spectrum at 90 K upon optical excitation of the crystal in the impurity absorption region (λex = 280 nm) was approximated by individual Gaussian bands with maxima near 345, 395, 430, 470, 500, and 520 nm. The photoluminescence spectrum of CaI2:SmBr3 (0.5 mol%) at 295 K with excitation by radiation from an LGI-21 nitrogen laser (λex = 337.1 nm) was represented mainly by a band at 465 nm. The intensity of this band weakened, its maximum shifted to 470 nm, luminescence in the 520 nm region increased, and weak emission with a maximum near 585 nm was also observed upon lowering the crystal temperature to 90 K. Doping CaI2 with the Sm impurity decreased the yield and changed the spectral composition of its x-ray-luminescence. CaI2:SmBr3 stored a small light sum in shallow trapping levels upon x-ray excitation at 90 K. The nature of the emission and trapping centers in the investigated crystals was discussed.

  9. Radiation effects on impurity diffusion in silicon

    International Nuclear Information System (INIS)

    Coherently combined experiments have been made in order to investigate certain parameters of the problem of diffusion under hydrogen irradiation. The physical basis of the problem (diffusion in semiconductors, particle irradiation, defect creation) is reviewed and the characterisation methods are then presented whilst laying emphasis on the way they restrict those experiments that are possible. The role of the parameters which are made to vary (temperature, current of the irradiation beam, irradiation time) is shown, using boron, arsenic or phosphorus as doping agent. The limitations of the single two-impurity model (one slow, one fast) is shown. It is also shown that with this model it is not possible to account integrally for the profiles obtained by ionic analysis. To complete the model, it was necessary to introduce defect precipitation as well as its effect on the diffusion length of the impurities. It was also possible to show the fundamental importance of the irradiation current parameter (and not of the total dose) and its interconnexion with the irradiation temperature parameter. With electric measurements an endeavour was also made to show the effect of residual defects on the conductivity and mobility of irradiated layers. The balancing of these layers led to studying the annealing of the defects and the experiments enabled the radiation enhanced to be oberved. The effect of the Fermi level position on the exo-diffusion of fast impurities was also shown, interpreted in terms of the formation and fast diffusion of a vacancy-impurity complex

  10. Impure Heisenberg systems with biquadratic interactions

    Science.gov (United States)

    Chakraborty, K. G.

    1980-08-01

    The purpose of the present paper is to study an impure Heisenberg ferromagnet governed by the Hamiltonian H=-Ji,Δ[S-->i.S-->i+Δ+α(S-->i.S-->i+Δ)2]-2J0Δ[S-->0.S-->Δ+α0(S-->0.S-->Δ)2], where J is the host-host bilinear exchange constant, 2(J+J0) is the host-impurity bilinear exchange constant, α and α0 being the corresponding biquadratic coupling parameters, and Δ, a nearest-neighbor vector. S--> and S-->0 are the host and the impurity spins, respectively. Through utilization of the Dyson transformation, it is shown that at low temperatures the effect of the biquadratic terms is simply to renormalize the bilinear exchange constants J and J0 by 1+2αS(S-1) and 1+α0(2SS0-S-S0), respectively. Some qualitative discussions on the scattering processes are presented. The method of Green's function is then employed to discuss the criteria for the existence of localized modes in the system. The situations appearing in KMnF3, RbMnF3, KNiF3, and MnF2 doped by impurities are critically examined. Some numerical estimates of the biquadratic parameters α and α0 are also made which are found to agree satisfactorily with those obtained by previous authors.

  11. Synthesis and Identification of Selected Impurities

    International Nuclear Information System (INIS)

    Non-active substances undesired, but often unavoidable compounds accompanying target active ingredients in various pesticide formulations have been synthesized for supporting product registration and evaluation of the total toxicological and physicochemical properties of formulated products. The synthesis and structural characterization of various impurities of pesticide active ingredients are described and illustrated by IR, NMR, GC and GC/MS data. (author)

  12. Block clustering with collapsed latent block models

    OpenAIRE

    Wyse, Jason; Friel, Nial

    2010-01-01

    We introduce a Bayesian extension of the latent block model for model-based block clustering of data matrices. Our approach considers a block model where block parameters may be integrated out. The result is a posterior defined over the number of clusters in rows and columns and cluster memberships. The number of row and column clusters need not be known in advance as these are sampled along with cluster memberhips using Markov chain Monte Carlo. This differs from existing work on latent bloc...

  13. Process and system for removing impurities from a gas

    Energy Technology Data Exchange (ETDEWEB)

    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.

  14. BITC - A fortran programme for impurity transport in tokamaks

    International Nuclear Information System (INIS)

    A code is described which computes the time evolution of the radial densities of impurities present in a toroidal plasma. Energy losses by radiation are also calculated. Different impurity species, with all their ionization stages, can be taken into account

  15. Photothermal Conversion of F-centres in Additively Coloured Potassium Chloride Crystals with Cationic and Anionic Impurities

    Directory of Open Access Journals (Sweden)

    Vladimirov D.A.

    2004-12-01

    Full Text Available The compensating influence of cationic (Ca++ ions and anionic (OH– ions impurities doped into additively coloured potassium chloride crystal on the process of photothermal conversion of F-centres is detected. “Brightening” in the absorption band of the F-centres is revealed that achieves 90%. It is not accompanied by the appearance of centres absorbing in the visible range. Double vacancies and the complexes Ca++(OH–2-cationic vacancy are shown to be responsible for this phenomenon. Basing on those results, a new system for holographic recording is suggested that uses the compensating effect of cationic and anionic impurities .

  16. The Crystal Structure of Impurity Centers Tm^{2+} and Eu^{2+} in SrCl2 : Ab Initio Calculations

    Science.gov (United States)

    Chernyshev, V. A.; Serdcev, A. V.; Petrov, V. P.; Nikiforov, A. E.

    2016-01-01

    Ab initio calculations of the impurity centers Tm^{2+} thulium and europium Eu^{2+} in SrCl2 and MeF2 (Me = Ca, Sr, Ba) were carried out at low (zero) temperature. The crystal structure of impurity centers was investigated. Charge density maps show that the bonds formed by the rare-earth ions have an ionic character. The crystal structures, lattice dynamics, and band structures of MeF2 and SrCl2 were calculated at low temperature. Ab initio calculations were performed in periodic CRYSTAL code within the framework of the MO LCAO approach by using hybrid DFT functionals.

  17. Analytical band Monte Carlo analysis of electron transport in silicene

    Science.gov (United States)

    Yeoh, K. H.; Ong, D. S.; Ooi, C. H. Raymond; Yong, T. K.; Lim, S. K.

    2016-06-01

    An analytical band Monte Carlo (AMC) with linear energy band dispersion has been developed to study the electron transport in suspended silicene and silicene on aluminium oxide (Al2O3) substrate. We have calibrated our model against the full band Monte Carlo (FMC) results by matching the velocity-field curve. Using this model, we discover that the collective effects of charge impurity scattering and surface optical phonon scattering can degrade the electron mobility down to about 400 cm2 V‑1 s‑1 and thereafter it is less sensitive to the changes of charge impurity in the substrate and surface optical phonon. We also found that further reduction of mobility to ∼100 cm2 V‑1 s‑1 as experimentally demonstrated by Tao et al (2015 Nat. Nanotechnol. 10 227) can only be explained by the renormalization of Fermi velocity due to interaction with Al2O3 substrate.

  18. 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 an...

  19. Impurity diagnostics in the GAMMA 10 tandem mirror

    International Nuclear Information System (INIS)

    We have constructed spectroscopic measurement systems in the wavelength range from soft X-ray to visible lights. We observed absolute impurity line intensities, Doppler line broadenings and Doppler shifts of impurity lines and time dependent radial profiles of the impurity lines in the GAMMA 10 tandem mirror. (author)

  20. Electronic properties of impurity-infected few-layer graphene nanoribbons

    International Nuclear Information System (INIS)

    Spurred by achievements in devising different multilayered graphene-based nano-systems, based on the random tight-binding Hamiltonian model and within the coherent potential approximation, the influence of varying the number of layers and the effect of doping by the boron and nitrogen impurities on the density of states of a mono- and few-layer armchair- and zigzag-edge graphene nanoribbons are theoretically investigated. When the nanoribbons are pristine, with increasing the number of layers the band gap of the armchair nanoribbons is decreased, yet the zigzag ribbons remain metallic and depending on the number of the layers few peaks are appeared around the zero-energy level. Moreover, in the presence of impurities, the band gap of the armchair nanoribbons is decreased for each number of layers. The Van-Hove singularities are steadily broadened and the density of states move to a higher (lower) value of the energy as a result of doping with boron (nitrogen) atoms. This study could provide with us to explore and devise new optoelectronic devices based on the impurity-infected graphene nanoribbons with tunable widths and edges

  1. Electronic properties of impurity-infected few-layer graphene nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Mousavi, Hamze, E-mail: hamze.mousavi@gmail.com [Department of Physics, Razi University, Kermanshah (Iran, Islamic Republic of); Nano Science and Nano Technology Research Center, Razi University, Kermanshah (Iran, Islamic Republic of); Bagheri, Mehran [Laser and Plasma Research Institute, Shahid Beheshti University, G.C., Evin, Tehran 19835-63113 (Iran, Islamic Republic of)

    2015-02-01

    Spurred by achievements in devising different multilayered graphene-based nano-systems, based on the random tight-binding Hamiltonian model and within the coherent potential approximation, the influence of varying the number of layers and the effect of doping by the boron and nitrogen impurities on the density of states of a mono- and few-layer armchair- and zigzag-edge graphene nanoribbons are theoretically investigated. When the nanoribbons are pristine, with increasing the number of layers the band gap of the armchair nanoribbons is decreased, yet the zigzag ribbons remain metallic and depending on the number of the layers few peaks are appeared around the zero-energy level. Moreover, in the presence of impurities, the band gap of the armchair nanoribbons is decreased for each number of layers. The Van-Hove singularities are steadily broadened and the density of states move to a higher (lower) value of the energy as a result of doping with boron (nitrogen) atoms. This study could provide with us to explore and devise new optoelectronic devices based on the impurity-infected graphene nanoribbons with tunable widths and edges.

  2. Nitrogen Band Assignments for Presolar and Carbonado Diamonds

    CERN Document Server

    Garai, Jozsef; Chen, Jiuhua

    2010-01-01

    Presolar and carbonado diamonds formed in hydrogen rich environment and received severe radiation dose. It is suggested that these environmental affects altered the Substitutional N0 defect to Substitutional N+H defect by ionizing the nitrogen due to irradiation and by hydrogenating the ionized nitrogen. The bands of the substitutional N+H defect are deduced by red shifting the irradiation induced N+ bands due to the mass of the additional Hydrogen. The identified six bands induced by the N+H defects are present in both the presolar and the carbonado diamond spectra. The assignment of the substitutional N+H bands identifies all of the nitrogen related bands in the spectra, which shows that presolar and carbonado diamonds contain almost exclusively single nitrogen impurities. Thus these diamonds can be classified as type Ib. The substitutional N+H induced bands can be used to identify diamonds in space.

  3. Incomplete block designs

    CERN Document Server

    Dey, Aloke

    2010-01-01

    This book presents a systematic, rigorous and comprehensive account of the theory and applications of incomplete block designs. All major aspects of incomplete block designs are considered by consolidating vast amounts of material from the literature - the classical incomplete block designs, like the balanced incomplete block (BIB) and partially balanced incomplete block (PBIB) designs. Other developments like efficiency-balanced designs, nested designs, robust designs, C-designs and alpha designs are also discussed, along with more recent developments in incomplete block designs for special t

  4. Impurities in Bose-Einstein Condensates: From Polaron to Soliton.

    Science.gov (United States)

    Shadkhoo, Shahriar; Bruinsma, Robijn

    2015-09-25

    We propose that impurities in a Bose-Einstein condensate which is coupled to a transversely laser-pumped multimode cavity form an experimentally accessible and analytically tractable model system for the study of impurities solvated in correlated liquids and the breakdown of linear-response theory [corrected]. As the strength of the coupling constant between the impurity and the Bose-Einstein condensate is increased, which is possible through Feshbach resonance methods, the impurity passes from a large to a small polaron state, and then to an impurity-soliton state. This last transition marks the breakdown of linear-response theory. PMID:26451565

  5. Power radiated from ITER and CIT by impurities

    International Nuclear Information System (INIS)

    The MIST code has been used to model impurity radiation from the edge and core plasmas in ITER and CIT. A broad range of parameters have been varied, including Zeff, impurity species, impurity transport coefficients, and plasma temperature and density profiles, especially at the edge. For a set of these parameters representative of the baseline ITER ignition scenario, it is seen that impurity radiation, which is produced in roughly equal amounts by the edge and core regions, can make a major improvement in divertor operation without compromising core energy confinement. Scalings of impurity radiation with atomic number and machine size are also discussed. 22 refs., 16 figs

  6. Magnetic field nanosensor based on Mn impurities

    Directory of Open Access Journals (Sweden)

    Daniela ENCIU

    2014-06-01

    Full Text Available Nanosensors based on graphene nanoribbon, studied in the present work, could provide a special interest in (aero space applications. More specifically, the paper proposes the construction of a nanosensor based on Mn (Manganese impurities. Different spin configurations of the Mn atoms are considered. The mathematical model used to determine the spin transport is based on Kohn-Sham equations. The spin-dependent transmission functions are calculated using the formalism of the nonequilibrium Green’s functions. The implementation of the mathematical model is performed in the SIESTA package. The spin transport properties are determined using the first principle calculations using density functional theory. The graphene nanoribbon with transition metal impurities is based on active element – the system of spins – which is influenced by the external perturbation field. Such nanostructures may serve as spatial applications. The differences between different excited states are determined and it is established that the energy range overlaps the mid-infrared wavelengths.

  7. An impurity seeded radiative mantle for ITER

    International Nuclear Information System (INIS)

    Self-consistent, coupled transport/MHD/scrape-off layer (SOL) divertor calculations indicate that a stable, radiating mantle can be maintained just inside the separatrix by iron impurity injection into the SOL in an ITER EDA model. The power flux to the divertor plate is reduced thereby by an order of magnitude or more. This reduction of the power exhausted to the divertor is predicted to be achieved without significant deleterious effect on the core power balance, without producing significant changes in the current profile that might trigger a disruptive collapse of the current channel and without inducing an H to L mode transition. These results suggest that an impurity seeded radiative mantle should be considered as part of the solution to the divertor heat load problem in ITER and other future tokamaks. (author). 34 refs, 10 figs, 1 tab

  8. Impurity effect in the quantum Nernst effect

    International Nuclear Information System (INIS)

    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)

  9. Global migration of impurities in tokamaks

    International Nuclear Information System (INIS)

    The migration of impurities in tokamaks has been studied with the help of tracer-injection (13C and 15N) experiments in JET and ASDEX Upgrade since 2001. We have identified a common pattern for the migrating particles: scrape-off layer flows drive impurities from the low-field side towards the high-field side of the vessel. Migration is also sensitive to the density and magnetic configuration of the plasma, and strong local variations in the resulting deposition patterns require 3D treatment of the migration process. Moreover, re-erosion of the deposited particles has to be taken into account to properly describe the migration process during steady-state operation of the tokamak. (paper)

  10. Divertor and gas blanket impurity control study

    International Nuclear Information System (INIS)

    A simple calculational model for the transport of particles across the scrap off region between the plasma and the wall in the presence of a divertor or a gas blanket has been developed. The model departs from previous work in including: (a) the entire impurity transport as well as its effect on the energy balance equations; (b) the recycling neutrals from the divertor, and (c) the reflected neutrals from the wall. Results obtained with this model show how the steady state impurity level in the plasma depends on the divertor parameters such as the neutral backflow from the divertor, the particle residence time and the scrape off thickness; and on the gas blanket parameters such as the neutral source strength and the gas blanket thickness. The variation of the divertor or gas blanket performance as a function of the heat and particle fluxes escaping from the plasma, the wall material and the cross field diffusion is examined and numerical examples are given

  11. On impurity segregation on dislocations in metals

    OpenAIRE

    Netchaev, Yu.; Mukhina, L.

    1993-01-01

    Thermodynamic and crystallo-chemistry considerations are given about the possibility of existing linear distribution laws for some impurities in metals between bulk solution and near-dislocation segregation regions (NDSR) with composition and structure close to the corresponding intermetallic compound. The solutions of Fe in Al are considered. NDSR composition can be close to FeAl3. The experimental data on the solubilities are treated within the model developed to determine the effective bin...

  12. Stark effect of shallow impurities in Si

    OpenAIRE

    Smit, G. D. J.; Rogge, S.; Caro, J.; Klapwijk, T. M.

    2003-01-01

    We have theoretically studied the effect of an electric field on the energy levels of shallow donors and acceptors in silicon. An analysis of the electric field dependence of the lowest energy states in donors and acceptors is presented, taking the bandstructure into account. A description as hydrogen-like impurities was used for accurate computation of energy levels and lifetimes up to large (several MV/m) electric fields. All results are discussed in connection with atomic scale electronics...

  13. Final Technical Report: Effects of Impurities on Fuel Cell Performance and Durability

    Energy Technology Data Exchange (ETDEWEB)

    James G. Goodwin, Jr.; Hector Colon-Mercado; Kitiya Hongsirikarn; and Jack Z. Zhang

    2011-11-11

    The main objectives of this project were to investigate the effect of a series of potential impurities on fuel cell operation and on the particular components of the fuel cell MEA, to propose (where possible) mechanism(s) by which these impurities affected fuel cell performance, and to suggest strategies for minimizing these impurity effects. The negative effect on Pt/C was to decrease hydrogen surface coverage and hydrogen activation at fuel cell conditions. The negative effect on Nafion components was to decrease proton conductivity, primarily by replacing/reacting with the protons on the Bronsted acid sites of the Nafion. Even though already well known as fuel cell poisons, the effects of CO and NH3 were studied in great detail early on in the project in order to develop methodology for evaluating poisoning effects in general, to help establish reproducibility of results among a number of laboratories in the U.S. investigating impurity effects, and to help establish lower limit standards for impurities during hydrogen production for fuel cell utilization. New methodologies developed included (1) a means to measure hydrogen surface concentration on the Pt catalyst (HDSAP) before and after exposure to impurities, (2) a way to predict conductivity of a Nafion membranes exposed to impurities using a characteristic acid catalyzed reaction (methanol esterification of acetic acid), and, more importantly, (3) application of the latter technique to predict conductivity on Nafion in the catalyst layer of the MEA. H2-D2 exchange was found to be suitable for predicting hydrogen activation of Pt catalysts. The Nafion (ca. 30 wt%) on the Pt/C catalyst resides primarily on the external surface of the C support where it blocks significant numbers of micropores, but only partially blocks the pore openings of the meso- and macro-pores wherein lie the small Pt particles (crystallites). For this reason, even with 30 wt% Nafion on the Pt/C, few Pt sites are blocked and, hence, are

  14. Simulation of iron impurity in BaTiO3 crystals

    International Nuclear Information System (INIS)

    Iron-doped barium titanate (BaTiO3) 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 BaTiO3 crystal has been discussed too.

  15. 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.

  16. Phase growth in bistable systems with impurities.

    Science.gov (United States)

    Echeverria, C; Tucci, K; Cosenza, M G

    2008-01-01

    A system of coupled chaotic bistable maps on a lattice with randomly distributed impurities is investigated as a model for studying the phenomenon of phase growth in nonuniform media. The statistical properties of the system are characterized by means of the average size of spatial domains of equivalent spin variables that define the phases. It is found that the rate at which phase domains grow becomes smaller when impurities are present and that the average size of the resulting domains in the inhomogeneous state of the system decreases when the density of impurities is increased. The phase diagram showing regions where homogeneous, heterogeneous, and chessboard patterns occur on the space of parameters of the system is obtained. A critical boundary that separates the regime of slow growth of domains from the regime of fast growth in the heterogeneous region of the phase diagram is calculated. The transition between these two growth regimes is explained in terms of the stability properties of the local phase configurations. Our results show that the inclusion of spatial inhomogeneities can be used as a control mechanism for the size and growth velocity of phase domains forming in spatiotemporal systems. PMID:18351923

  17. Evaluation of determinative methods for sodium impurities

    International Nuclear Information System (INIS)

    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)

  18. Electrophobic Interaction Induced Impurity Clustering in Metals

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Hong-Bo; Wang, Jin-Long; Jiang, Wei; Lu, Guang-Hong; Aguiar, Jeffery A.; Liu, Feng

    2016-10-15

    We introduce the concept of electrophobic interaction, analogous to hydrophobic interaction, for describing the behavior of impurity atoms in a metal, a 'solvent of electrons'. We demonstrate that there exists a form of electrophobic interaction between impurities with closed electron shell structure, which governs their dissolution behavior in a metal. Using He, Be and Ar as examples, we predict by first-principles calculations that the electrophobic interaction drives He, Be or Ar to form a close-packed cluster with a clustering energy that follows a universal power-law scaling with the number of atoms (N) dissolved in a free electron gas, as well as W or Al lattice, as Ec is proportional to (N2/3-N). This new concept unifies the explanation for a series of experimental observations of close-packed inert-gas bubble formation in metals, and significantly advances our fundamental understanding and capacity to predict the solute behavior of impurities in metals, a useful contribution to be considered in future material design of metals for nuclear, metallurgical, and energy applications.

  19. 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.

  20. 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.

  1. Postural heart block.

    OpenAIRE

    Seda, P E; McAnulty, J H; Anderson, C J

    1980-01-01

    A patient presented with orthostatic dizziness and syncope caused by postural heart block. When the patient was supine, atrioventricular conduction was normal and he was asymptomatic; when he was standing he developed second degree type II block and symptoms. The left bundle-branch block on his electrocardiogram and intracardiac electrophysiological study findings suggest that this heart block occurred distal to the His bundle. Orthostatic symptoms are usually presumed to be secondary to an i...

  2. Motion of a Distinguishable Impurity in the Bose Gas: Arrested Expansion Without a Lattice and Impurity Snaking

    Science.gov (United States)

    Robinson, Neil J.; Caux, Jean-Sébastien; Konik, Robert M.

    2016-04-01

    We consider the real-time dynamics of an initially localized distinguishable impurity injected into the ground state of the Lieb-Liniger model. Focusing on the case where integrability is preserved, we numerically compute the time evolution of the impurity density operator in regimes far from analytically tractable limits. We find that the injected impurity undergoes a stuttering motion as it moves and expands. For an initially stationary impurity, the interaction-driven formation of a quasibound state with a hole in the background gas leads to arrested expansion—a period of quasistationary behavior. When the impurity is injected with a finite center-of-mass momentum, the impurity moves through the background gas in a snaking manner, arising from a quantum Newton's cradlelike scenario where momentum is exchanged back and forth between the impurity and the background gas.

  3. Generalized Block Failure

    DEFF Research Database (Denmark)

    Jönsson, Jeppe

    2015-01-01

    shows that no readily available tests with a well-defined substantial eccentricity have been performed. This paper presents theoretical and experimental work leading towards generalized block failure capacity methods. Simple combination of normal force, shear force and moment stress distributions along......Block tearing is considered in several codes as a pure block tension or a pure block shear failure mechanism. However in many situations the load acts eccentrically and involves the transfer of a substantial moment in combination with the shear force and perhaps a normal force. A literature study...... yield lines around the block leads to simple interaction formulas similar to other interaction formulas in the codes....

  4. Effect of Born and unitary impurity scattering on the Kramer–Pesch shrinkage of a vortex core in an s-wave superconductor

    International Nuclear Information System (INIS)

    Highlights: ► We study non-magnetic impurity effect on a vortex in moderately clean regime. ► Impurity effect on s-wave vortex core in unitary limit is weaker than in Born one. ► Kramer–Pesch vortex core shrinkage is stronger in unitary limit than in Born one. -- Abstract: We theoretically investigate a non-magnetic impurity effect on the temperature dependence of the vortex core shrinkage (Kramer–Pesch effect) in a single-band s-wave superconductor. The Born limit and the unitary limit scattering are compared within the framework of the quasiclassical theory of superconductivity. We find that the impurity effect inside a vortex core in the unitary limit is weaker than in the Born one when a system is in the moderately clean regime, which results in a stronger core shrinkage in the unitary limit than in the Born one

  5. Effect of Born and unitary impurity scattering on the Kramer–Pesch shrinkage of a vortex core in an s-wave superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Hayashi, Nobuhiko, E-mail: n-hayashi@21c.osakafu-u.ac.jp [NanoSquare Research Center (N2RC), Osaka Prefecture University, 1-2 Gakuen-cho, Naka-ku, Sakai 599-8570 (Japan); CREST(JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Higashi, Yoichi [NanoSquare Research Center (N2RC), Osaka Prefecture University, 1-2 Gakuen-cho, Naka-ku, Sakai 599-8570 (Japan); Department of Mathematical Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531 (Japan); CREST(JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Nakai, Noriyuki; Suematsu, Hisataka [NanoSquare Research Center (N2RC), Osaka Prefecture University, 1-2 Gakuen-cho, Naka-ku, Sakai 599-8570 (Japan); CREST(JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan)

    2013-01-15

    Highlights: ► We study non-magnetic impurity effect on a vortex in moderately clean regime. ► Impurity effect on s-wave vortex core in unitary limit is weaker than in Born one. ► Kramer–Pesch vortex core shrinkage is stronger in unitary limit than in Born one. -- Abstract: We theoretically investigate a non-magnetic impurity effect on the temperature dependence of the vortex core shrinkage (Kramer–Pesch effect) in a single-band s-wave superconductor. The Born limit and the unitary limit scattering are compared within the framework of the quasiclassical theory of superconductivity. We find that the impurity effect inside a vortex core in the unitary limit is weaker than in the Born one when a system is in the moderately clean regime, which results in a stronger core shrinkage in the unitary limit than in the Born one.

  6. In situ mobile subaquatic archaeometry evaluated by non-destructive Raman microscopy of gemstones lying under impure waters

    Science.gov (United States)

    Smith, David C.

    2003-08-01

    A series of laboratory simulations have been made in order to evaluate the credibility of carrying out physico-chemical analysis of cultural heritage items by Raman spectral fingerprinting using a mobile Raman microscope in situ under natural impure water in subaquatic or submarine conditions. Three different kinds of gemstone (zircon, microcline and sodalite) were successively placed under different kinds of impure water into which a low power microscope objective was immersed to eliminate the normal aerial pathway between the objective and the object to be analysed. According to the nature of the impurities (inorganic or organic, dissolved or suspended, transparent or coloured) the results obtained variously gave Raman band intensities stronger than, similar to or weaker than those of spectra obtained without water, i.e. in air. The significant point is that after only minor spectral treatment the less good spectra nevertheless yielded exploitable data with most, if not all, of the key Raman bands being detected. Thus the problems of fluorescence or peak absences under water are of a similar degree of magnitude to the other problems inherent with the Raman spectroscopic technique in aerial conditions, e.g. relative peak intensities varying with crystal orientation; peak positions varying with chemical composition. These results indicate that even if at certain sites of submerged cities or sunken ships, the combination of animal, vegetal, mineral and microbial impurities join together to inhibit or hinder the success of subaquatic or submarine archaeometry, there will certainly be other sites where such activity is indeed credible.

  7. A review of impurity transport characteristics in the LHD

    Science.gov (United States)

    Sudo, Shigeru

    2016-04-01

    The behavior of impurities in the Large Helical Device (LHD) is reviewed based on the knowledge acquired since LHD experiments started in 1998. As a result, a consistent physical picture of impurity transport is obtained in the vast plasma parameter range. The essential points are: (1) the impurity confinement time increases monotonically as the bulk electron density increases in the plasma core; (2) the balance between the friction force and the thermal force on the impurities plays an important role in determining impurity transport in the stochastic layers; (3) a positive electric field leads to outward convection, and a negative electric field generally leads to inward convection (except for the impurity hole case); and (4) in the case of the impurity hole phenomenon, with a high ion temperature plasma and a steep ion temperature gradient, outward convection of the impurities in the plasma core is apparent in spite of the negative electric field. The mechanism for producing outward convection in the impurity hole plasma has not yet been clarified. The effects of the magnetic axis shift and the magnetic island are summarized, and some possible methods for impurity control are also discussed.

  8. Structural Identification and Characterization of Potential Impurities of Azelnidipine

    Directory of Open Access Journals (Sweden)

    Sureshbabu Kapavarapu

    2016-06-01

    Full Text Available Azelnidipine (AZL is a pale yellowish white tablet (16mg with diameter of 9.2mm and thickness of 3.3mm. A reverse phase performance liquid chromatographic method was developed for the determination of AZL in bulk and pharmaceutical dosage form. During the synthesis of bulk drug of AZL, we observed four impurities. All the impurities were detected by a gradient high performance liquid chromatographic (HPLC method. LC-MS was performed to identify the mass number of these impurities. A thorough study was carried out to characterize the impurities. These impurities were synthesized, characterized and were co-injected with the sample containing impurities and are found to be matching with the impurities present in the sample. Based on the complete spectral analysis (UV, IR, NMR and MS these impurities were characterized as 1 Azelnidipine Stage-I para impurity [Impurity 1], whose molecular formula is C14 H15 NO5 and molecular weight is 277.27, 2 Azelnidipine Intermediate [Impurity 2], whose molecular formula is C14H15NO5 and molecular weight is 277.27, 3 4-Nitro Azelnidipine [Impurity 3], whose molecular formula is C33H34N4O6 and molecular weight is 582.65 and, 4 2-Nitro Azelnidipine [Impurity 4], whose molecular formula is C33H34N4O6 and molecular weight is 582.65. The proposed method was validated as per International Conference on Harmonization (ICH guidelines. The method was accurate, precise, specific and rapid found to be suitable for the quantitative analysis of the drug and dosage form.

  9. Dynamics of thermoluminescence spectra of impurity-helium condensates containing stabilized nitrogen and oxygen atoms

    International Nuclear Information System (INIS)

    The results of investigations of thermoluminescence dynamics during destruction of neon-helium and krypton-helium condensates containing stabilized nitrogen and oxygen atoms are presented. Spectra of the thermoluminescence of a krypton-helium condensate contained bands of N and O atoms and NO molecules. The intensities of the bands in these spectra were found to increase simultaneously during destruction processes in the temperature range 1.5-15 K. Observation of the NO molecules provides clear evidence for chemical reactions in the nanoclusters comprising the sample at low temperatures. Destruction of neon-helium samples occurred in two stages. During the first stage the α-group of N atoms surrounded by Ne and N2 molecules dominated the spectra. During the second stage, the spectra contained intense bands of N and O atoms stabilized in a molecular nitrogen matrix. The unusual characteristics of the thermoluminescence spectra were observed, and their changes were explained in terms of the shell structure of impurity nanoclusters which comprised the impurity-helium condensates.

  10. Blocked randomization with randomly selected block sizes.

    Science.gov (United States)

    Efird, Jimmy

    2011-01-01

    When planning a randomized clinical trial, careful consideration must be given to how participants are selected for various arms of a study. Selection and accidental bias may occur when participants are not assigned to study groups with equal probability. A simple random allocation scheme is a process by which each participant has equal likelihood of being assigned to treatment versus referent groups. However, by chance an unequal number of individuals may be assigned to each arm of the study and thus decrease the power to detect statistically significant differences between groups. Block randomization is a commonly used technique in clinical trial design to reduce bias and achieve balance in the allocation of participants to treatment arms, especially when the sample size is small. This method increases the probability that each arm will contain an equal number of individuals by sequencing participant assignments by block. Yet still, the allocation process may be predictable, for example, when the investigator is not blind and the block size is fixed. This paper provides an overview of blocked randomization and illustrates how to avoid selection bias by using random block sizes. PMID:21318011

  11. Blocked Randomization with Randomly Selected Block Sizes

    Directory of Open Access Journals (Sweden)

    Jimmy Efird

    2010-12-01

    Full Text Available When planning a randomized clinical trial, careful consideration must be given to how participants are selected for various arms of a study. Selection and accidental bias may occur when participants are not assigned to study groups with equal probability. A simple random allocation scheme is a process by which each participant has equal likelihood of being assigned to treatment versus referent groups. However, by chance an unequal number of individuals may be assigned to each arm of the study and thus decrease the power to detect statistically significant differences between groups. Block randomization is a commonly used technique in clinical trial design to reduce bias and achieve balance in the allocation of participants to treatment arms, especially when the sample size is small. This method increases the probability that each arm will contain an equal number of individuals by sequencing participant assignments by block. Yet still, the allocation process may be predictable, for example, when the investigator is not blind and the block size is fixed. This paper provides an overview of blocked randomization and illustrates how to avoid selection bias by using random block sizes.

  12. BLOCK H-MATRICES AND SPECTRUM OF BLOCK MATRICES

    Institute of Scientific and Technical Information of China (English)

    黄廷祝; 黎稳

    2002-01-01

    The block H-matrices are studied by the concept of G-functions, several concepts of block matrices are introduced. Equivalent characters of block H-matrices are obtained. Spectrum localizations claracterized by Gfunctions for block matrices are got.

  13. Investigation of the dependence of spectral and scintillation characteristics of calcium iodide crystals with europium impurity on the conditions of their growing

    International Nuclear Information System (INIS)

    Influence of the concentration of the activating impurity Eu Cl3, thermal processing, and additional oxy chemical impurities (OI) Ca(OH)2 on the optical-luminescence and scintillation characteristics of Ca I2:Eu crystals grown by the Stockbarger method in the vacuum quartz ampoule is studied. We show that europium ions enter into calcium iodide in two valence states. Long-wave bands found in absorption and excitation spectra of Ca I2:Eu crystals are ascribed to f-d transitions in Eu2+ ions. We suppose that short-wave bands in these spectra may be caused by charge transfer. Under X-ray excitation, the electron-hole mechanism of the excitation of activator's luminescence dominates. It is shown that Ca I2:Eu crystals with optimal concentration of impurity may be used as scintillators in production of X-ray radiation detectors

  14. Magnetic impurities and materials design for semiconductor spintronics

    International Nuclear Information System (INIS)

    Curie temperatures (TC) of several diluted magnetic semiconductors are calculated from first-principles by using a mapping on a Heisenberg model in a mean field approximation. Very large TC's are obtained for V- or Cr-doped ZnSe and ZnTe and Cr-doped GaN, GaP and GaAs. Effects of additional carrier doping into (Ga, Mn)As and (Ga, Mn)N are investigated. TC of (Ga, Mn)N increases by hole doping, while (Ga, Mn)As is insensitive to hole doping. The origin of the ferromagnetism in Mn-doped III-V DMS is also discussed. It is found that if impurity bands are formed in the gap, as it is the case for (Ga, Mn)N, double exchange dominates leading to a characteristic √c dependence of TC as a function of the Mn concentration c. On the other hand, if the d-states are localized, as in (Ga, Mn)Sb, Zener's p-d exchange prevails resulting in a linear c-dependence of TC. (Ga, Mn)As is an intermediate case, showing a √c like behavior in the Local density approximation (LDA), but a nearly linear c-dependence, if the LDA+U method, with U=4 eV, is used

  15. Hydrogenic impurities in superlattices with parabolic quantum well potentials

    International Nuclear Information System (INIS)

    Parabolic quantum-wells (PQWs) in compositional GaAs/Alsub(x)Gasub(1-x)As and homogeneous doping GaAs superlattices are being built using the technique of molecular beam epitaxy. The binding energy (Esub(b)) and wave function of a hydrogenic impurity in an effective PQW are calculated variationally. The identification of the parabolic coefficient k as 8Qsub(e)ΔEsub(g)/Lsub(z)2(4πesup(z)nsub(D)epsilonsub(O)) for compositional (doping)-PQWs allows us to predict physical ranges of Esub(b).ΔEsub(g)(Qsub(e)) is the total (fraction of conduction) band discontinuity, Lsub(z) is the width of the compositional PQW; nsub(D) is the donor-doping concentration, and epsilonsub(O) is the dielectric constant of bulk GaAs. For typical compositional-PQWs, Esub(b) depends logarithmically on Qsub(e), hence appropriate experiments may be designed to confirm one of the two values (0.85 and 0.57) proposed elsewhere. Comparison with Bastard's, Green and Bajaj's, and Crowne's works indicates that 1) compositional-PQWs of typical width Lsub(z)(>or approx. 300 A) yield larger values of Esub(b) compared to those of finite or even infinite square wells of same width, and 2) doping-PQWs with linear effective potentials produce physical ranges for |Esub(b)| considerably larger than those produced by doping-PQWs. (author)

  16. Determination of the impurities in drug products containing montelukast and in silico/in vitro genotoxicological assessments of sulfoxide impurity.

    Science.gov (United States)

    Emerce, Esra; Cok, Ismet; Degim, I Tuncer

    2015-10-14

    Impurities affecting safety, efficacy, and quality of pharmaceuticals are of increasing concern for regulatory agencies and pharmaceutical industries, since genotoxic impurities are understood to play important role in carcinogenesis. The study aimed to analyse impurities of montelukast chronically used in asthma theraphy and perform genotoxicological assessment considering regulatory approaches. Impurities (sulfoxide, cis-isomer, Michael adducts-I&II, methylketone, methylstyrene) were quantified using RP-HPLC analysis on commercial products available in Turkish market. For sulfoxide impurity, having no toxicity data and found to be above the qualification limit, in silico mutagenicity prediction analysis, miniaturized bacterial gene mutation test, mitotic index determination and in vitro chromosomal aberration test w/wo metabolic activation system were conducted. In the analysis of different batches of 20 commercial drug products from 11 companies, only sulfoxide impurity exceeded qualification limit in pediatric tablets from 2 companies and in adult tablets from 7 companies. Leadscope and ToxTree programs predicted sulfoxide impurity as nonmutagenic. It was also found to be nonmutagenic in Ames MPF Penta I assay. Sulfoxide impurity was dose-dependent cytotoxic in human peripheral lymphocytes, however, it was found to be nongenotoxic. It was concluded that sulfoxide impurity should be considered as nonmutagenic and can be classified as ordinary impurity according to guidelines. PMID:26205398

  17. 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)].

  18. Classical impurities associated to high rank algebras

    International Nuclear Information System (INIS)

    Classical integrable impurities associated with high rank (glN) algebras are investigated. A particular prototype, i.e. the vector non-linear Schrödinger (NLS) model, is chosen as an example. A systematic construction of local integrals of motion as well as the time components of the corresponding Lax pairs is presented based on the underlying classical algebra. Suitable gluing conditions compatible with integrability are also extracted. The defect contribution is also examined in the case where non-trivial integrable conditions are implemented. It turns out that the integrable boundaries may drastically alter the bulk behavior, and in particular the defect contribution

  19. Improvements of metal impurities sampling and measurements

    International Nuclear Information System (INIS)

    In order to control radiation exposure and to manage water treatment systems such as condensate filter and demineralizer in BWR plants, it is required to measure metal impurities, called for crud, accurately. In Japanese BWR plants, the crud is collected continuously on a Millipore filter used by integrating crud sampling method and measured by the fluorescent X-ray spectrometer. Usually the crud concentrations vary at the same sample point, and it is considered that the causes are induced by sampling equipments, application, utilization and so on. The influences of sampling tube length, materials, probe types, and flow rate, and estimate the appropriateness of using a Millipor filter for continuous crud sampling

  20. Hubbard chain with a Kondo impurity

    OpenAIRE

    Bares, P. -A.; Grzegorczyk, K.

    1998-01-01

    A Bethe Ansatz solution of a (modified) Hubbard chain with a Kondo impurity of arbitrary spin S at a highly symmetric line of parameter space is proposed and explored. Our results confirm the existence of a strong-coupling (line of) fixed-point(s) with ferromagnetic Kondo coupling as first hypothetized by Furusaki and Nagaosa on the basis of perturbative renormalization group calculations. For on-site Hubbard repulsion and ferromagnetic Kondo exchange, the ground state has spin S-1/2, i.e., i...

  1. Numerical calculation of impurity charge state distributions

    Energy Technology Data Exchange (ETDEWEB)

    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.

  2. Classical impurities associated to high rank algebras

    Energy Technology Data Exchange (ETDEWEB)

    Doikou, Anastasia, E-mail: A.Doikou@hw.ac.uk [Department of Mathematics, Heriot–Watt University, EH14 4AS, Edinburgh (United Kingdom); Department of Computer Engineering and Informatics, University of Patras, Patras GR-26500 (Greece)

    2014-07-15

    Classical integrable impurities associated with high rank (gl{sub N}) algebras are investigated. A particular prototype, i.e. the vector non-linear Schrödinger (NLS) model, is chosen as an example. A systematic construction of local integrals of motion as well as the time components of the corresponding Lax pairs is presented based on the underlying classical algebra. Suitable gluing conditions compatible with integrability are also extracted. The defect contribution is also examined in the case where non-trivial integrable conditions are implemented. It turns out that the integrable boundaries may drastically alter the bulk behavior, and in particular the defect contribution.

  3. Spectrophotometric determination of zinc in impure solutions

    International Nuclear Information System (INIS)

    A dithizone colorimetric method is described for determining zinc concentrations of 0.001 to 5 g/l in aqueous solutions from Rio Tinto Mines, containing copper, iron and other impurities. Citrate, cyanide and bis-2hydroxyethyl)-dithiocarbamate are added to the aqueous sample of masking several metals, and zinc is extracted at pH 5 with a solution of dithizone in carbon tetrachloride. Excess of dithizone is removed with sodium sulphide, and optical density of zinc dithionate in organic solution is measured at 5.35 nm. Calibration curves obey Beer's law up to 0.5 micro Zn/ml. (Author) 5 refs

  4. Random Magnetic Impurities and the Landau Problem

    OpenAIRE

    Desbois, Jean; Furtlehner, Cyril; Ouvry, Stéphane

    1995-01-01

    The 2-dimensional density of states of an electron is studied for a Poissonian random distribution of point vortices carrying $\\alpha$ flux in unit of the quantum of flux. It is shown that, for any given density of impurities, there is a transition, when $\\alpha\\simeq 0.3-0.4$, from an "almost free" density of state -with only a depletion of states at the bottom of the spectrum characterized by a Lifschitz tail- to a Landau density of state with sharp Landau level oscillations. Several eviden...

  5. Fractional impurity moments in two-dimensional noncollinear magnets.

    Science.gov (United States)

    Wollny, Alexander; Fritz, Lars; Vojta, Matthias

    2011-09-23

    We study dilute magnetic impurities and vacancies in two-dimensional frustrated magnets with noncollinear order. Taking the triangular-lattice Heisenberg model as an example, we use quasiclassical methods to determine the impurity contributions to the magnetization and susceptibility. Most importantly, each impurity moment is not quantized but receives nonuniversal screening corrections due to local relief of frustration. At finite temperatures, where bulk long-range order is absent, this implies an impurity-induced magnetic response of Curie form, with a prefactor corresponding to a fractional moment per impurity. We also discuss the behavior in an applied magnetic field, where we find a singular linear-response limit for overcompensated impurities. PMID:22026900

  6. 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.

  7. Damping by slow relaxing rare earth impurities in Ni80Fe20.

    Science.gov (United States)

    Woltersdorf, G; Kiessling, M; Meyer, G; Thiele, J-U; Back, C H

    2009-06-26

    Doping Ni80Fe20 by heavy rare earth atoms alters the magnetic relaxation properties of this material drastically. We show that this effect can be well explained by the slow relaxing impurity mechanism. This process is a consequence of the anisotropy of the on site exchange interaction between the 4f magnetic moments and the conduction band. As expected from this model the magnitude of the damping effect scales with the anisotropy of the exchange interaction and increases by an order of magnitude at low temperatures. In addition, our measurements allow us to determine the relaxation time of the 4f electrons as a function of temperature. PMID:19659120

  8. Impurity Bound States and Greens Function Zeroes as Local Signatures of Topology

    OpenAIRE

    Slager, Robert-Jan; Rademaker, Louk; Zaanen, Jan; Balents, Leon

    2015-01-01

    We show that the local in-gap Greens function of a band insulator $\\mathbf{G}_0 (\\epsilon,\\mathbf{k}_{\\parallel},\\mathbf{r}_{\\perp}=0)$, with $\\mathbf{r}_\\perp$ the position perpendicular to a codimension-1 or -2 impurity, reveals the topological nature of the phase. For a topological insulator, the eigenvalues of this Greens function attain zeros in the gap, whereas for a trivial insulator the eigenvalues remain nonzero. This topological classification is related to the existence of in-gap b...

  9. Effects of Nb impurity on orthorhombic PbZrO{sub 3} crystals

    Energy Technology Data Exchange (ETDEWEB)

    Rivera, Richard; Stashans, Arvids [Grupo de FisicoquImica de Materiales, Instituto de Quimica Aplicada, Universidad Tecnica Particular de Loja, Apartado 11-01-608, Loja (Ecuador)], E-mail: arvids@utpl.edu.ec

    2008-10-15

    A study of Nb doping in lead zirconate (PbZrO{sub 3}) has been carried out by using a quantum-chemical method developed for crystals and a periodic supercell model. One of the Zr atoms was replaced by an Nb atom in the supercell consisting of 80 atoms. The obtained geometry optimization for the defective region points to defect-outward atomic movements, which are accompanied by some reduction of atomic charges. It is observed that an extra electron imposed by the Nb impurity is transferred to the conduction band of the material and contributes to the n-type electrical conductivity, explaining indirectly some of the experimental observations.

  10. Subsurface impurities and vacancies in a three-dimensional topological insulator

    OpenAIRE

    Black-Schaffer, Annica M.; Balatsky, Alexander V.

    2012-01-01

    Using a three-dimensional microscopic lattice model of a strong topological insulator (TI) we study potential impurities and vacancies in surface and subsurface positions. For all impurity locations we find impurity-induced resonance states with energy proportional to the inverse of the impurity strength, although the impurity strength needed for a low-energy resonance state increases with the depth of the impurity. For strong impurities and vacancies as deep as 15 layers into the material, r...

  11. Lesson Thirteen Trifascicular Block

    Institute of Scientific and Technical Information of China (English)

    鲁端; 王劲

    2005-01-01

    @@ A complete trifascicular block would result in complete AV block. The idio ventricular rhythm has a slower rate and a wide QRS complex because the pacemaker is located at the peripheral part of the conduction system distal to the sites of the block1. Such a rhythm may be difficult to differentiate from bifascicular or bundle branch block combined with complete block at a higher level such as the AV node or His bundle2. Besides a slower ventricular rate, a change in the morphology of the QRS complex from a previous known bifascicular pattern would be strongly suggestive of a trifascicular origin of the complete AV block3. A His bundle recording is required for a definitive diagnosis, however.

  12. Bound state energy of a Coulomb impurity in gapped bilayer graphene: "Hydrogen atom with a Mexican hat"

    OpenAIRE

    Skinner, Brian; Shklovskii, B. I.; Voloshin, M. B.

    2013-01-01

    Application of a perpendicular electric field induces a band gap in bilayer graphene, and it also creates a "Mexican hat" structure in the dispersion relation. This structure has unusual implications for the hydrogen-like bound state of an electron to a Coulomb impurity. We calculate the ground state energy of this hydrogen-like state as a function of the applied interlayer voltage and the effective fine structure constant. Unlike in the normal hydrogen atom, the resulting wavefunction has ma...

  13. Effect of lattice disordering on recombination emission of exciton-impurity complexes and defects in ZnxCd1-xTe

    International Nuclear Information System (INIS)

    It is shown experimentally that zinc atoms in ZnxCd1-xTe create no recombination levels in the band gap of this compound in the whole range of the composition. The concentration broadening of exciton lines and the impurity-defect bands is accounted for by the influence of the compositional fluctuation of the cationic sublattice on the energy position of hydrogen-like levels of bound excitons and defects

  14. Identification and synthesis of impurities formed during sertindole preparation

    OpenAIRE

    Hima Bindu, V; I. V. Sunil Kumar; Anjaneyulu, G S R

    2011-01-01

    Sertindole (1), an atypical anti-psychotic drug is used for the treatment of schizophrenia. During the laboratory optimization and later during its bulk synthesis the formation of various impurities was observed. The impurities formed were monitored and their structures were tentatively assigned on the basis of their fragmentation patterns in LC-MS. Most of the impurities were synthesized and their assigned constitutions confirmed by co-injection in HPLC. We describe herein the formation, syn...

  15. Recommended methods for purification of solvents and tests for impurities

    CERN Document Server

    Coetzee, J F

    1982-01-01

    Recommended Methods for Purification of Solvents and Tests for Impurities is a compilation of recommended procedures for purification of solvents and tests for solvent impurities. Ten solvents are covered: acetonitrile, sulfolane, propylene carbonate, dimethyl sulfoxide, dimethylformamide, hexamethylphosphoramide, pyridine, ethylenediamine, N-methylacetamide, and N-methylpropionamide. This book is comprised of 12 chapters and opens with an introduction to general aspects of impurity effects. The rationale for the selection of solvent is explained, and the relative reactivities of solutes in di

  16. The Kondo Effect in the Presence of Magnetic Impurities

    OpenAIRE

    Heersche, H. B.; de Groot, Z.; Folk, J. A.; Kouwenhoven, L.P. (Leo) (Professor); van der Zant, H. S. J.; Houck, A. A.; Labaziewicz, J.; Chuang, I.L.

    2005-01-01

    We measure transport through gold grain quantum dots fabricated using electromigration, with magnetic impurities in the leads. A Kondo interaction is observed between dot and leads, but the presence of magnetic impurities results in a gate-dependent zero-bias conductance peak that is split due to an RKKY interaction between the spin of the dot and the static spins of the impurities. A magnetic field restores the single Kondo peak in the case of an antiferromagnetic RKKY interaction. This syst...

  17. Block Advertisement Protocol

    OpenAIRE

    Nemirovsky, Danil

    2015-01-01

    Bitcoin, a decentralized cryptocurrency, has attracted a lot of attention from academia, financial service industry and enthusiasts. The trade-off between transaction confirmation throughput and centralization of hash power do not allow Bitcoin to perform at the same level as modern payment systems. Block Advertisement Protocol is proposed as a step to resolve this issue. The protocol allows block mining and block relaying to happen in parallel. The protocol dictates a miner to advertise the ...

  18. Steady-state organization of binary mixtures by active impurities

    DEFF Research Database (Denmark)

    Sabra, Mads Christian; Gilhøj, Henriette; Mouritsen, Ole G.

    1998-01-01

    The structural reorganization of a phase-separated binary mixture in the presence of an annealed dilution of active impurities is studied by computer-simulation techniques via a simple two-dimensional lattice-gas model. The impurities, each of which has two internal states with different affinity...... for the two species, become active by an external driving of a transition between the two impurity states, leading to an energy flow from the impurities into the binary mixture. In steady state, the drive is found to break down the phase-separated state and lead to a new finite length scale controlled...

  19. Impurity screening studies in the ALCATOR C-Mod tokamak

    International Nuclear Information System (INIS)

    Screening experiments have been undertaken in both limited and diverted discharges with a range of gaseous impurities in ohmic discharges. Measurements have been made as a function of plasma density and of the poloidal position of gas injection. It has been found that for recycling impurities such as neon and argon the number of impurities in the core plasma is proportional to the number injected. For non-recycling impurities (carbon and nitrogen) the number in the core is a function of the rate of injection. For discharges limited on the inner wall the screening is a function of the poloidal position of injection, with the injection at the inner wall giving the poorest screening. In diverted discharges with recycling impurities the position of injection does not significantly affect the screening. For non-recycling impurities the screening is typically a factor of 3 better when impurities are injected from the divertor rather than from the outside midplane. However, the best screening occurs when the impurities are injected at the inner midplane. Screening is typically a factor of 10 better for diverted than for limited discharges. Impurity transport has been modelled using the Monte Carlo code DIVIMP with a background plasma derived from experimental measurements of plasma parameters at the target and in the scrape-off layer (SOL). It is found that the code can reproduce the experimental measurements within a factor of 2. (author). 12 refs, 3 figs

  20. 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....

  1. Numerical Simulation of mobile BEC-impurity interaction

    Science.gov (United States)

    Lausch, Tobias; Grusdt, Fabian; Fleischhauer, Michael; Widera, Artur

    2016-05-01

    Cooling atoms to temperatures, where quantum effects become dominant, has become a standard in cold atom experiments. Especially interactions of quantum baths such as fermi gases and the implementation of impurities, which form fermi polarons, have been studied theoretically and experimentally in detail. However, detailed experiments on the bose polaron and the interaction between impurities and a bose gas are still elusive. We consider a model, where we immerse a single impurity into a BEC, which is described by Bogoliubov approximation. From the master equation, we derived the impurity's momentum resolved scattering and cooling dynamics for numerical simulations. Such cooling processes should enable momentum resolved radio-frequency spectroscopy of the BEC polaron.

  2. Compensation effect for impurity solubility in liquid metals

    International Nuclear Information System (INIS)

    Experimental data of different authors on impurity solubility in lead are analyzed. It is shown that the slope of compensatory dependences for Pb-Me (Me - Al, Cu, Co, Mn, Ge, U) systems is near in absolute magnitude to the melting points of corresponding impurity. The physical interpretation of compensation effect for impurity solubility in liquid metals is suggested, it is that the slope of compensatory dependence is determined by physical properties of the phase under saturation (stratification), and its shift by impurity activity coefficient in the solution

  3. Topological state engineering by potential impurities on chiral superconductors

    Science.gov (United States)

    Kaladzhyan, Vardan; Röntynen, Joel; Simon, Pascal; Ojanen, Teemu

    2016-08-01

    In this work we consider the influence of potential impurities deposited on top of two-dimensional chiral superconductors. As discovered recently, magnetic impurity lattices on an s -wave superconductor may give rise to a rich topological phase diagram. We show that a similar mechanism takes place in chiral superconductors decorated by nonmagnetic impurities, thus avoiding the delicate issue of magnetic ordering of adatoms. We illustrate the method by presenting the theory of potential impurity lattices embedded on chiral p -wave superconductors. While a prerequisite for the topological state engineering is a chiral superconductor, the proposed procedure results in vistas of nontrivial descendant phases with different Chern numbers.

  4. Gas chromatographic analysis of trace gas impurities in tungsten hexafluoride.

    Science.gov (United States)

    Laurens, J B; de Coning, J P; Swinley, J M

    2001-03-01

    Highly reactive fluorinated gaseous matrices require special equipment and techniques for the gas chromatographic analysis of trace impurities in these gases. The impurities that were analysed at the low-microg/l levels included oxygen, nitrogen, carbon dioxide, carbon monoxide, sulfur hexafluoride and hydrogen. This paper describes the use of a system utilising backflush column switching to protect the columns and detectors in the analysis of trace gas impurities in tungsten hexafluoride. Two separate channels were used for the analysis of H2, O2, N2, CO, CO2 and SF6 impurities with pulsed discharge helium ionisation detection. PMID:11269587

  5. Identification and synthesis of impurities formed during sertindole preparation

    Directory of Open Access Journals (Sweden)

    V. Hima Bindu

    2011-01-01

    Full Text Available Sertindole (1, an atypical anti-psychotic drug is used for the treatment of schizophrenia. During the laboratory optimization and later during its bulk synthesis the formation of various impurities was observed. The impurities formed were monitored and their structures were tentatively assigned on the basis of their fragmentation patterns in LC-MS. Most of the impurities were synthesized and their assigned constitutions confirmed by co-injection in HPLC. We describe herein the formation, synthesis and characterization of these impurities. Our study will be of immense help to others to obtain chemically pure sertindole.

  6. Alpha particle diagnostics using impurity pellet injection

    International Nuclear Information System (INIS)

    We have proposed using impurity injection to measure the energy distribution of the fast confined alpha particles in a reacting plasma. The ablation cloud surrounding the injected pellet is thick enough that an equilibrium fraction Fo∞(E) of the incident alphas should be neutralized as they pass through the cloud. By observing neutrals created in the large spatial region of the cloud which is expected to be dominated by the helium-like ionization state, e.g., Li+ ions, we can determine the incident alpha distribution dnHe2+/dE from the measured energy distribution of neutral helium atoms. Initial experiments were performed on TEXT in which we compared pellet penetration with our impurity pellet ablation model, and measured the spatial distribution of various ionization states in carbon pellet clouds. Experiments have recently begun on TFTR with the goal of measuring the alpha particle energy distribution during D-T operation in 1993--94. A series of preliminary experiments are planned to test the diagnostic concept. The first experiments will observe neutrals from beam-injected deuterium ions and the high energy 3He tail produced during ICH minority heating on TFTR interacting with the cloud. We will also monitor by line radiation the charge state distributions in lithium, boron, and carbon clouds

  7. Impurity transport in ohmically heated TFTR plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Stratton, B.C.; Fonck, R.J.; Hulse, R.A.; Ramsey, A.T.; Timberlake, J.; Efthimion, P.C.; Fredrickson, E.; Grek, B.; Hill, K.W.; Johnson, D.W.

    1988-11-01

    Impurity transport in ohmically heated TFTR plasmas is studied by computer modeling of VUV line emissions from impurities injected using the laser-blowoff technique. The results are sensitive to uncertainties in the ionization and recombination rates used in the modeling; as a result, only a spatially averaged diffusion coefficient and parameterized convective velocity can be measured. Measurements of these transport parameters are presented for deuterium and helium discharges with I/sub p/ = 0.8-2.5 MA, /bar n/sub e// = 0.6-6.0/times/10/sup 19/ m/sup -3/, and Z/sub eff/ = 2-6. Diffusion coefficients are found to be in the 0.5-1.5 m/sup 2//s range, considerably larger than neoclassical values. Nonzero inward convective velocities are necessary to fit the data in most cases. No dependence of the diffusion coefficient on injected element, working gas species, or plasma current is found, but at a given current, the diffusion coefficient is smaller by approximately a factor of two in plasmas near the density limit than in discharges with /bar n/sub e//<3/times/10/sup 19/ m/sup -3/. 31 refs., 9 figs., 3 tabs.

  8. Studies of impurity behavior in TFTR

    Energy Technology Data Exchange (ETDEWEB)

    Hill, K.W.; Bitter, M.; Bretz, N.L.; Diesso, M.; Efthimion, P.C.; Von Goeler, S.; Kiraly, J.; Ramsey, A.T.; Sauthoff, N.R.; Schivell, J.

    1986-03-01

    Central medium- and low-Z impurity concentrations and Z/sub eff/ have been measured by x-ray spectrometry in Tokamak Fusion Test Reactor discharges during three periods of operation. These were the (1) start-up period, (2) ohmic heating, and (3) ohmic heating portion of the two neutral beam periods, distinguished mainly by different vacuum vessel internal hardware and increasing plasma current and toroidal field capability. Plasma parameters spanned minor radius a = 0.41 - 0.83 m, major radius R = 2.1 - 3.1 m, current I/sub p = 0.25 - 2.0 MA, line-averaged electron density n-bar/sub e/ = 0.9 - 4.0 x 10/sup 19/ m/sup -3/, and toroidal magnetic field B/sub T/ = 1.8 - 4.0 T. The metal impurities came mostly from the limiter. At low densities titanium or nickel approached 1% of n/sub e/ during operation on a TiC-coated graphite or Inconel limiter, respectively. Lower levels of Cr, Fe, and Ni (less than or equal to0.1%) were observed with a graphite limiter at similarly low densities; these elements were removed mainly from stainless steel or Inconel hardware within the vacuum vessel during pulse discharge cleaning or plasma operation on an Inconel limiter and then deposited on the graphite limiter. Hardware closest to the graphite limiter contributed most to the deposits.

  9. Studies of impurity behavior in TFTR

    International Nuclear Information System (INIS)

    Central medium- and low-Z impurity concentrations and Z/sub eff/ have been measured by x-ray spectrometry in Tokamak Fusion Test Reactor discharges during three periods of operation. These were the (1) start-up period, (2) ohmic heating, and (3) ohmic heating portion of the two neutral beam periods, distinguished mainly by different vacuum vessel internal hardware and increasing plasma current and toroidal field capability. Plasma parameters spanned minor radius a = 0.41 - 0.83 m, major radius R = 2.1 - 3.1 m, current I/sub p = 0.25 - 2.0 MA, line-averaged electron density n-bar/sub e/ = 0.9 - 4.0 x 1019 m-3, and toroidal magnetic field B/sub T/ = 1.8 - 4.0 T. The metal impurities came mostly from the limiter. At low densities titanium or nickel approached 1% of n/sub e/ during operation on a TiC-coated graphite or Inconel limiter, respectively. Lower levels of Cr, Fe, and Ni (less than or equal to0.1%) were observed with a graphite limiter at similarly low densities; these elements were removed mainly from stainless steel or Inconel hardware within the vacuum vessel during pulse discharge cleaning or plasma operation on an Inconel limiter and then deposited on the graphite limiter. Hardware closest to the graphite limiter contributed most to the deposits

  10. Impurity transport in ohmically heated TFTR plasmas

    International Nuclear Information System (INIS)

    Impurity transport in ohmically heated TFTR plasmas is studied by computer modeling of VUV line emissions from impurities injected using the laser-blowoff technique. The results are sensitive to uncertainties in the ionization and recombination rates used in the modeling; as a result, only a spatially averaged diffusion coefficient and parameterized convective velocity can be measured. Measurements of these transport parameters are presented for deuterium and helium discharges with I/sub p/ = 0.8-2.5 MA, /bar n/sub e// = 0.6-6.0/times/1019 m-3, and Z/sub eff/ = 2-6. Diffusion coefficients are found to be in the 0.5-1.5 m2/s range, considerably larger than neoclassical values. Nonzero inward convective velocities are necessary to fit the data in most cases. No dependence of the diffusion coefficient on injected element, working gas species, or plasma current is found, but at a given current, the diffusion coefficient is smaller by approximately a factor of two in plasmas near the density limit than in discharges with /bar n/sub e//19 m-3. 31 refs., 9 figs., 3 tabs

  11. Particle fueling and impurity control in PDX

    International Nuclear Information System (INIS)

    Fueling requirements and impurity levels in neutral-beam-heated discharges in the PDX tokamak have been compared for plasmas formed with conventional graphite rail limiters, a particle scoop limiter, and an open or closed poloidal divertor. Gas flows necessary to obtain a given density are highest for diverted discharges and lowest for the scoop limiter. Hydrogen pellet injection provides an efficient alternate fueling technique, and a multiple pellet injector has produced high density discharges for an absorbed neutral beam power of up to 600 kW, above which higher speeds or more massive pellets are required for penetration to the plasma core. Power balance studies indicate that 30 to 40% of the total input power is radiated while approx. 15% is absorbed by the limiting surface, except in the open divertor case, where 60% flows to the neutralizer plate. In all operating configurations, Z/sub eff/ usually rises at the onset of neutral beam injection. Both open divertor plasmas and those formed on a well conditioned water-cooled limiter have Z/sub eff/ less than or equal to 2 at the end of neutral injection. A definitive comparison of divertors and limiters for impurity control purposes requires longer beam pulses or higher power levels than available on present machines

  12. Impurity control in Fusion Experimental Reactor (FER)

    International Nuclear Information System (INIS)

    Poloidal divertor system is employed as the impurity control measure in Fusion Experimental Reactor (FER). The authors will report the overall survey of impurity control physics in FER. The results obtained are as follows. (1) The triple-valued solutions of divertor plasma equilibrium are obtained as a function of incoming ion flux. Engineering design is carried out based on the stable dense and cold divertor plasma. (2) Low density and high temperature solution disappears when the geometry is extremely closed (chamber length=50cm and void width=O). (3) Plasma temperature can become slightly high on the side of exhaust duct near the plate. (4) Erosion rate on the first wall by charge-exchange neutrals is recognized to be about 1cm/year by DEGAS code that is also obtained by even our divertor code and simple order estimation. (5) Cold and dense divertor plasma could be formed during noninductive current drive phase either LHRF or NBI, if the current drive efficiency is improved

  13. Impurity and surface studies in ORMAK

    International Nuclear Information System (INIS)

    The ORMAK tokamak has been in operation since 1971, and surface impurity problems have been pursued from the beginning. Surface studies of materials removed from ORMAK have revealed the presence of C, O, and Fe. These are also the principal impurities observed spectroscopically in plasma discharges, although numerous other elements are present in lesser amounts. Spectroscopy, x-ray measurements, plasma resistance, and fast ion scattering have been used in an effort to determine Z/sub eff/, the effective nuclear charge of plasma ions. All four measurements have practical difficulties leading to relatively large experimental error limits. Oxygen discharge pre-cleaning has allowed ORMAK discharges to reach higher currents and correspondingly higher ion and electron temperatures; spectroscopic studies reveal a lower level of contaminants, particularly C and N. Power measurements indicate that most of the input power strikes the walls, mostly as radiation. By varying operating parameters it is found that Z/sub eff/ approximately I/sub p//anti n/sub e/

  14. Analysis of shear banding in twelve materials

    Science.gov (United States)

    Batra, R. C.; Kim, C. H.

    The problem of the initiation and growth of shear bands in 12 different materials, namely, OFHC copper, Cartridge brass, Nickel 200, Armco IF (interstitial free) iron, Carpenter electric iron, 1006 steel, 2024-T351 aluminum, 7039 aluminum, low alloy steel, S-7 tool steel, Tungsten alloy, and Depleted Uranium (DU -0.75 Ti) is studied with the objectives of finding out when a shear band initiates, and upon what parameters does the band width depend. The nonlinear coupled partial differential equations governing the overall simple shearing deformations of a thermally softening viscoplastic block are analyzed. It is assumed that the thermomechanical response of these materials can be adequately represented by the Johnson-Cook law, and the only inhomogeneity present in the block is the variation in its thickness. The effect of the defect size on the initiation and subsequent growth of the band is also studied. It is found that, for each one of these 12 materials, the deformation has become nonhomogeneous by the time the maximum shear stress occurs. Also the band width, computed when the shear stress has dropped to 85 percent of its peak value, does not correlate well with the thermal conductivity of the material. The band begins to grow rapidly when the shear stress has dropped to 90 percent of its maximum value.

  15. Study on effects of carbon impurities and oxygen vacancies in amorphous alumina phosphor prepared via a solution method

    International Nuclear Information System (INIS)

    The amorphous alumina phosphors without containing expensive or toxic elements were prepared via a solution method. The obtained sample indicates bluish-white emission centered at 390–430 nm by UV excitation. According to the measurement results of Electron Spin Resonance (ESR), Fourier Transform Infrared Spectroscopy (FT-IR) and organic microanalysis, it is found that the carbon impurities exist in the sample and they are essential for luminescence. On the other hand, 27Al NMR measurements indicate the presence of Al of 5-coordination. Moreover, there is good correspondence among the excitation spectra of the emission samples, the experimental optical properties of amorphous alumina, and the calculated oxygen vacancies levels in amorphous alumina model. Therefore, the new luminescence mechanism can be proposed as follows; the electrons in valence band are excited to oxygen vacancies bands by UV light and return to ground state through the carbon impurities band, being accompanied by the bluish-white emission. - Highlights: • The amorphous alumina prepared via solution method shows bluish-white emission. • According to the ESR results, carbon impurities are necessary for luminescence. • FT-IR, NMR and UV–vis measurements of the samples were conducted. • Our results indicated that oxygen vacancies play an important role. • We proposed the new luminescence mechanism for amorphous alumina phosphor

  16. Study on effects of carbon impurities and oxygen vacancies in amorphous alumina phosphor prepared via a solution method

    Energy Technology Data Exchange (ETDEWEB)

    Wakui, Yoshinori; Takahashi, Kanako [Department of Material and Environmental Chemistry, Graduate School of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya-shi, Tochigi 321-8585 (Japan); Shan, Yue Jin, E-mail: shan@cc.utsunomiya-u.ac.jp [Department of Material and Environmental Chemistry, Graduate School of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya-shi, Tochigi 321-8585 (Japan); Tezuka, Keitaro; Imoto, Hideo [Department of Material and Environmental Chemistry, Graduate School of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya-shi, Tochigi 321-8585 (Japan); Hosokawa, Shogo; Shinozaki, Norifumi [Tatsumori Ltd., 50 Minami-Kawada, Kami-Yukiai, Tamura-cho, Koriyama-shi, Fukushima 963-0724 (Japan); Ando, Mariko; Maekawa, Hideki [Graduate School of Engineering, Tohoku University, 6-6-04 Aramaki Aoba, Sendai-shi, Miyagi 980-8579 (Japan)

    2015-01-15

    The amorphous alumina phosphors without containing expensive or toxic elements were prepared via a solution method. The obtained sample indicates bluish-white emission centered at 390–430 nm by UV excitation. According to the measurement results of Electron Spin Resonance (ESR), Fourier Transform Infrared Spectroscopy (FT-IR) and organic microanalysis, it is found that the carbon impurities exist in the sample and they are essential for luminescence. On the other hand, {sup 27}Al NMR measurements indicate the presence of Al of 5-coordination. Moreover, there is good correspondence among the excitation spectra of the emission samples, the experimental optical properties of amorphous alumina, and the calculated oxygen vacancies levels in amorphous alumina model. Therefore, the new luminescence mechanism can be proposed as follows; the electrons in valence band are excited to oxygen vacancies bands by UV light and return to ground state through the carbon impurities band, being accompanied by the bluish-white emission. - Highlights: • The amorphous alumina prepared via solution method shows bluish-white emission. • According to the ESR results, carbon impurities are necessary for luminescence. • FT-IR, NMR and UV–vis measurements of the samples were conducted. • Our results indicated that oxygen vacancies play an important role. • We proposed the new luminescence mechanism for amorphous alumina phosphor.

  17. Rattling 'guest' impurities in Si and Ge clathrate semiconductors

    International Nuclear Information System (INIS)

    In addition to their ground state, diamond structure, Si, Ge and Sn can form crystalline solids called clathrates. As in the diamond structure, in the clathrates, the Group IV atoms are tetrahedrally coordinated and sp3 covalently bonded to their neighbors. However, the clathrates contain pentagonal atomic rings and have open-framework lattices containing 20-, 24- and 28-atom 'cages'. There are two clathrate lattices: Type I, a SC lattice with 46 atoms per unit cell and Type II, a FCC lattice with 136 atoms per cubic cell. The pure clathrates are semiconductors. The cages can contain weakly bound impurities ('guests'), usually alkali or alkaline earth atoms. The choice of guest may be used to tune the material properties. The guests are electronic donors, but because of their weak bonding, they have small effects on the electronic band structures. However, they can produce low frequency vibrational ('rattling') modes which can strongly affect the vibrational properties. Some guest-containing clathrates have been shown to be excellent candidates for thermoelectric applications precisely because the guests only perturb the electronic properties weakly, while strongly affecting the vibrational (heat transport) properties. For thermoelectric applications, semiconductor materials are needed. When all cages are filled, the clathrates become semi-metallic due to the excess valence electrons of the guests. To compensate for this, Group III atoms (usually Ga or In) are substituted on the framework sites. After an introduction to clathrates, the results of calculations of the vibrational properties of some experimentally relevant Si- and Ge-based Type I and Type II clathrates are presented. The calculations were carried out using a first-principles, plane wave, pseudopotential method. Results for the Si-based Type II materials Cs8Ga8Si128 and Rb8Ga8Si128, and for the Ge-based Type I materials Ba8Ga16Ge30 and Ba8Ga16Si5Ge25 will be discussed with an emphasis on the very low

  18. Interaction of light with impurities in lithium niobate crystals

    International Nuclear Information System (INIS)

    Congruent lithium niobate (LiNbO3) and 5-mol% MgO-doped LiNbO3 (MgO:LN) crystals are widely used as nonlinear-optical crystals in frequency-conversion devices due to their large nonlinear-optic coefficients. These devices usually require high optical pump powers, but absorption of photons by impurities limits their usability due to heat accumulation that leads to thermo-optic refractive index changes. These refractive index changes distort the beam shape and disturb the phase-matching condition. Furthermore pyroelectric fields can build up. In this thesis the residual optical absorption in congruent LiNbO3 (CLN) and MgO:LN crystals is studied. Absorption spectra of CLN and MgO:LN crystals between 400-2000 nm reveal a residual absorption up to 0.04 cm-1. This absorption is mainly caused by transition metal impurities. Between 2300-2800 nm unknown hydrogen absorption bands in CLN and MgO:LN are revealed on the order of 0.001 cm-1. High-temperature annealing is applied to the CLN and MgO:LN crystals, which decreases optical absorption by up to one order of magnitude. As an application, the operation of a 1550-nm pumped singly-resonant CW optical parametric oscillator, resonant around 2600 nm, using a low-loss, periodically-poled, annealed CLN crystal is demonstrated. Another issue that affects CLN is photorefractive damage (PRD), i.e. light-induced refractive index changes. In contrast, MgO:LN crystals do not suffer from PRD even at high optical intensities. However, it is shown in this thesis that PRD can occur within seconds in MgO:LN, using green laser light at light intensity levels as low as 100 mW/cm2, if the crystal is heated by several degrees Celsius during or before illumination. Photorefractive damage does not occur in CLN crystals under the same conditions. We show that the pyroelectric effect together with an elevated photoconductivity compared to that of CLN causes this beam distortion and that this effect also influences frequency conversion experiments

  19. Interaction of light with impurities in lithium niobate crystals

    Energy Technology Data Exchange (ETDEWEB)

    Schwesyg, Judith Renate Marie-Luise

    2011-06-06

    Congruent lithium niobate (LiNbO{sub 3}) and 5-mol% MgO-doped LiNbO{sub 3} (MgO:LN) crystals are widely used as nonlinear-optical crystals in frequency-conversion devices due to their large nonlinear-optic coefficients. These devices usually require high optical pump powers, but absorption of photons by impurities limits their usability due to heat accumulation that leads to thermo-optic refractive index changes. These refractive index changes distort the beam shape and disturb the phase-matching condition. Furthermore pyroelectric fields can build up. In this thesis the residual optical absorption in congruent LiNbO{sub 3} (CLN) and MgO:LN crystals is studied. Absorption spectra of CLN and MgO:LN crystals between 400-2000 nm reveal a residual absorption up to 0.04 cm{sup -1}. This absorption is mainly caused by transition metal impurities. Between 2300-2800 nm unknown hydrogen absorption bands in CLN and MgO:LN are revealed on the order of 0.001 cm{sup -1}. High-temperature annealing is applied to the CLN and MgO:LN crystals, which decreases optical absorption by up to one order of magnitude. As an application, the operation of a 1550-nm pumped singly-resonant CW optical parametric oscillator, resonant around 2600 nm, using a low-loss, periodically-poled, annealed CLN crystal is demonstrated. Another issue that affects CLN is photorefractive damage (PRD), i.e. light-induced refractive index changes. In contrast, MgO:LN crystals do not suffer from PRD even at high optical intensities. However, it is shown in this thesis that PRD can occur within seconds in MgO:LN, using green laser light at light intensity levels as low as 100 mW/cm{sup 2}, if the crystal is heated by several degrees Celsius during or before illumination. Photorefractive damage does not occur in CLN crystals under the same conditions. We show that the pyroelectric effect together with an elevated photoconductivity compared to that of CLN causes this beam distortion and that this effect also

  20. NEAR-MILLIMETER WAVE BAND-PASS FILTERS

    Energy Technology Data Exchange (ETDEWEB)

    Timusk, T.; Richards, P. L.

    1980-11-01

    We report on the properties of band-pass filters for broad band photometry in the frequency range from 3 to 12cm{sup -1}. The filters are based on a combination of capacitive grids deposited on thick Mylar substrates and are designed to have very high out-of-band rejection. Low frequencies are blocked by a "thick grill" that consists of hexagonal grid of circular holes in a thick metal plate.

  1. Impedance Matched Absorptive Thermal Blocking Filters

    CERN Document Server

    Wollack, E J; Rostem, K; U-Yen, K

    2014-01-01

    We have designed, fabricated and characterized absorptive thermal blocking filters for cryogenic microwave applications. The transmission line filter's input characteristic impedance is designed to match $50\\,\\Omega$ and its response has been validated from 0-to-50\\,GHz. The observed return loss in the 0-to-20\\,GHz design band is greater than $20\\,$dB and shows graceful degradation with frequency. Design considerations and equations are provided that enable this approach to be scaled and modified for use in other applications.

  2. MIBSA: Multi Interacting Blocks for Slope Analysis

    Science.gov (United States)

    Dattola, Giuseppe; Crosta, Giovanni; Castellanza, Riccardo; di Prisco, Claudio

    2016-04-01

    As it is well known, the slope instabilities have very important consequences in terms of human lives and activities. So predicting the evolution in time and space of slope mass movements becomes fundamental. This is even more relevant when we consider that the triggering mechanisms are a rising ground water level and the occurrence of earthquakes. Therefore, seasonal rainfall has a direct influence on the triggering of large rock and earthslide with a composite failure surface and causing differential behaviors within the sliding mass. In this contribution, a model describing the slope mass by means of an array of blocks that move on a prefixed failure surface, is defined. A shear band located at the base of each block, whose behavior is modelled via a viscous plastic model based on the Perzyna's approach, controls the slip velocity of the block. The motion of the blocks is obtained by solving the second balance equation in which the normal and tangential interaction forces are obtained by a specific interaction model. The model has been implemented in an original code and it is used to perform a parametric analysis that describes the effects of block interactions under a transient ground water oscillation. The numerical results confirm that the normal and tangential interactions between blocks can inhibit or induce the slope movements. The model is tested against some real case studies. This model is under development to add the dynamic effects generated by earthquake shaking.

  3. Block Scheduling Revisited.

    Science.gov (United States)

    Queen, J. Allen

    2000-01-01

    Successful block scheduling depends on provision of initial and ongoing instructional training. Teaching strategies should vary and include cooperative learning, the case method, the socratic seminar, synectics, concept attainment, the inquiry method, and simulations. Recommendations for maximizing block scheduling are outlined. (Contains 52…

  4. Reduced impurities and improved electrical properties of atomic-layer-deposited HfO2 film grown at a low temperature (100 °C) by Al2O3 incorporation

    Science.gov (United States)

    Park, Tae Joo; Byun, Youngchol; Wallace, Robert M.; Kim, Jiyoung

    2016-05-01

    The HfO2 films grown by atomic layer deposition (ALD) at a low temperature (100 °C) necessarily has a large amount of residual impurities due to lack of thermal energy for stable ALD reactions such as ligand removal and oxidation, which degrades various properties. However, Al2O3 incorporation into the film significantly decreased the residual impurities despite of a low growth temperature. The decrease in C impurity is attributed to the reduced oxygen vacancies by the incorporated Al2O3 phase or the high reactivity of Al precursor. Consequently, the electronic band structure of the film, and thereby the electrical properties were improved significantly.

  5. Physical properties of antiferromagnetic Mn doped ZnO samples: Role of impurity phase

    International Nuclear Information System (INIS)

    Structural, morphological, optical, and magnetic properties of nanocrystalline Zn1−xMnxO samples (x=0.01, 0.02, 0.04, 0.06, 0.08 and 0.10) prepared by the sol–gel route are studied by X-ray diffraction (XRD), Scanning electron microscopy (SEM), UV–visible absorption spectroscopy, Superconducting quantum interference device (SQUID) magnetometry and positron annihilation lifetime spectroscopy (PALS). XRD confirms formation of wurzite structure in all the Mn-substituted samples. A systematic increase in lattice constants and decrease in grain size have been observed with increase in manganese doping concentration up to 6 at% in the ZnO structure. An impurity phase (ZnMnO3) has been detected when percentage of Mn concentration is 6 at% or higher. The optical band gap of the Mn-substituted ZnO samples decrease with increase in doping concentration of manganese whereas the width of the localized states increases. The antiferromagnetic exchange interaction is strong in the samples for 2 and 4 at% of Mn doping but it reduces when the doping level increases from 6 at% and further. Positron life time components τ1 and τ2 are found to decrease when concentration of the dopant exceeds 6 at%. The changes in magnetic properties as well as positron annihilation parameters at higher manganese concentration have been assigned as due to the formation of impurity phase. - highlights: • Single phase structure has been observed up to 6 at% of Mn doping. • Impurity phase has been developed above 6 at% of Mn doping. • Antiferromagnetic and paramagnetic interactions are present in the samples. • Defect parameters show sharp fall as Mn concentration above 6 at%. • The magnetic and defect properties are modified by the formation of impurity phase

  6. Band structure of semiconductors

    CERN Document Server

    Tsidilkovski, I M

    2013-01-01

    Band Structure of Semiconductors provides a review of the theoretical and experimental methods of investigating band structure and an analysis of the results of the developments in this field. The book presents the problems, methods, and applications in the study of band structure. Topics on the computational methods of band structure; band structures of important semiconducting materials; behavior of an electron in a perturbed periodic field; effective masses and g-factors for the most commonly encountered band structures; and the treatment of cyclotron resonance, Shubnikov-de Haas oscillatio

  7. Topics in topological band systems

    Science.gov (United States)

    Huang, Zhoushen

    The discovery of integer quantum Hall effect and its subsequent theoretical formulation heralded a new paradigm of thinking in condensed matter physics, which has by now blossomed into the rapidly growing field of topological phases. In this work we investigate several mutually related topics in the framework of topological band theory. In Chapter 2, we study solutions to boundary states on a lattice and see how they are related to the bulk topology. To elicit a real space manifestation of the non-trivial topology, the presence of a physical edge is not strictly necessary. We study two other possibilities, namely the entanglement spectrum associated with an imaginary spatial boundary, and the localization centers of Wannier functions, in Chapters 3,4, and 5. Topological classification through discrete indices is so far possible only for systems described by pure quantum states---in the existing scheme, quantization is lost for systems in mixed states. In Chapter 6, we present a program through which discrete topological indices can be defined for topological band systems at finite temperature, based on Uhlmann's parallel transport of density matrices. The potential of topologocal insulators in realistic applications lies in the existence of Dirac nodes on its surface spectrum. Dirac physics, however, is not exclusive to TI surfaces. In a recently discovered class of materials known as Weyl semimetals, energy nodes which emit linear dispersions also occur in the bulk material. In Chapter 7, we study the possibility of resonance states induced by localized impurities near the nodal energy in Weyl semimetals, which will help us in understanding the stability of density-of-state suppression at the energy nodes. Finally, in Chapter 8, we apply the topological characterization developed for noninteracting particles to a class of interacting spin models in 3D, which are generalizations of Kitaev's honeycomb model, and identify several exotic quantum phases such as spin

  8. Influence of impurities on the H{sub 2}/H{sub 2}O/Ni/YSZ electrode

    Energy Technology Data Exchange (ETDEWEB)

    Hoegh, J.

    2005-05-15

    contact area and 3) The sulfur adsorption on the Ni wire. An increasing water content in the atmosphere was seen to lower the polarization resistance at OCV and at anodic overpotentials, but it had no effect at cathodic overpotentials. It was hypothesized that water changes the properties of the impurities and hereby promote the electrode reaction at OCV and anodic overpotentials. A strong cathodic polarization <-2000 mV vs. air at 700 deg. C was seen to lower the polarization resistance by a factor of 5-60. It was hypothesized that the strong cathodic polarization reduces or partly reduces the impurities from oxide to metal. Hence, the blocking influence of impurities would be diminished. (au)

  9. Magnetic 3d interactions in ZnO and In2O3 in a band-gap corrected approach

    Science.gov (United States)

    Lany, Stephan; Raebiger, H.; Zunger, A.

    2008-03-01

    The electronic and magnetic configuration of 3d transition metal (TM) impurities in wide-gap oxides like ZnO and In2O3 is misrepresented in the standard LDA and GGA approximations to density functional theory: Because the conduction band minimum lies energetically much too low, the spin-polarized impurity states wrongly occur as resonances inside the conduction band rather than as gap states. Due to spurious ``charge spilling'' from the TM impurity state into the host conduction band, the magnetic moment and the occupancy of the TM impurity state is incorrect, and the TM state becomes partially occupied, which is prone to cause overestimated ferromagnetic interactions. These errors are not corrected by the LDA+U or GGA+U methods often applied to TM-d states. In our band-gap corrected approach, we augment the GGA+U functional by empirical non-local external potentials (NLEP) for the s- and p-states of Oxygen and the cations. In this approach the correct spin and orbital configuration of the TM impurity-states is recovered. In the absence of additional doping, we find generally short-ranged magnetic interactions, and pronounced Jahn-Teller effects in case of partially occupied gap states. Additional electron-doping can lead to more long-range ferromagnetic interactions for those TM-dopants that have unoccupied d-states which hybridize strongly with the conduction band.

  10. Spectrographic determination of impurities in magnesium metal

    International Nuclear Information System (INIS)

    The spectrographic determination of trace quantities of Al, B, Cd, Co, Cr, Cu, Fe, Li, Hn, Mo, Ni and Si in magnesium metal is described. Samples are dissolved with HNO3 and calcinate into MgO. In order to avoid losses of boron NH4OH is added to the nitric solution. Except for aluminium and chromium the analysis is performed through the use of the carrier distillation technique. These two impurities are determined by burning to completion the MgO. Among the compounds studied as carriers (AgCl, AgF, CsCl, CuF2, KCl and SrF2) AgCl allows, In general, the best volatilization efficiency. Lithium determination is achieved by using KC1 or CsCl. Detection limits, on the basis of MgO, are in the range 0,1 to 30 ppm, depending on the element. (Author) 8 refs

  11. Copper thiocyanate: polytypes, defects, impurities, and surfaces

    Science.gov (United States)

    Tsetseris, Leonidas

    2016-07-01

    Copper thiocyanate (CuSCN) is an established solid state dye in solar cells and has emerged as a key material for applications in transparent conductors and solution-processed thin film transistors. Here we report the results of density-functional theory calculations on several fundamental properties related to the performance of CuSCN in the above-mentioned systems. We describe the structural and electronic properties of CuSCN phases and show that the material is prone to polytypism. We also perform a systematic study on various defects and hydrogen impurities and determine their effect on the electronic properties of the host system, particularly with respect to doping. Finally, we show that non-polar surfaces have low formation energies, suggesting easy cleavage along certain directions.

  12. Probe measurements of impurities in the plasma boundary of PLT

    International Nuclear Information System (INIS)

    Carbon probes were exposed to the plasma edge in PLT at various distances from the plasma and to different numbers [1-3, 6, 12] of overlayed discharges. The type and areal density of impurities retained were determined using ion backscattering. The principal impurities were found to be O, Fe, Cr, Ti, and Cu which had fluxes of 14, 2.8, 0.8, 0.6 and 0.2 x 1015/cm2 (+- 25%) respectively, near the radius of the wall. At the same position the deuterium flux was 2.2 +- 0.5 x 1017 D/cm2 s. Lateral spreading of the impurity deposition profile behind the probe slit allowed a lower limit to be placed on the impurity mean ion energy. Between the wall and radius of the ring limiter the impurity fluxes increased by a factor of approx. equal to2 compared to an increase in the D flux by a factor of approx. equal to5. The observed nonlinear impurity retention versus the number of discharges is consistent with the values determined for the impurity and D fluxes and the expected effects of sputtering. The observed large flux of iron at the radius of the ring limiter suggests that this may be a primary source of metal impurities in PLT. (orig.)

  13. Lattice dynamics of impurity clusters : application to pairs

    International Nuclear Information System (INIS)

    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)

  14. 40 CFR 159.179 - Metabolites, degradates, contaminants, and impurities.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 23 2010-07-01 2010-07-01 false Metabolites, degradates, contaminants.../Benefit Information § 159.179 Metabolites, degradates, contaminants, and impurities. (a) Metabolites and... degradation of less than 10 percent in a 30-day period. (b) Contaminants and impurities. The presence in...

  15. Interactions of impurities with a moving grain boundary

    International Nuclear Information System (INIS)

    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

  16. Impurity injection by use of multiple-shell pellet

    International Nuclear Information System (INIS)

    A model of the three-layered multiple-shell pellet is studied in order to apply to the impurity injection experiment. The mass dependence of the ablation is examined by employing the neutral-cloud shielding model. The localization width of the impurity is estimated. (author)

  17. Addendum to impurity radiation from medium density plasmas

    International Nuclear Information System (INIS)

    A previous treatment of impurity radiation due to plasma contaminants is extended to include low-Z materials of the type anticipated for first walls in tokamak reactor designs. In addition, analytic fits are presented for the temperature dependence of the key quantities that enter into the modeling of tokamak impurity phenomena

  18. Tight-Binding Description of Impurity States in Semiconductors

    Science.gov (United States)

    Dominguez-Adame, F.

    2012-01-01

    Introductory textbooks in solid state physics usually present the hydrogenic impurity model to calculate the energy of carriers bound to donors or acceptors in semiconductors. This model treats the pure semiconductor as a homogeneous medium and the impurity is represented as a fixed point charge. This approach is only valid for shallow impurities…

  19. Effects of impurities on growth habit of KDP crystal

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The effects of metaphosphate, boric acid and quaternary ammonium cations with different concentration on the growth habit of KDP crystal are reported. The results are analyzed and discussed, which show that the effects of different impurities on the growth habit of KDP are not the same. It is due to the different adsorption mechanism of the impurities.

  20. Intense laser effects on donor impurity in a cylindrical single and vertically coupled quantum dots under combined effects of hydrostatic pressure and applied electric field

    International Nuclear Information System (INIS)

    Using the effective mass and parabolic band approximations and a variational procedure we have calculated the combined effects of intense laser radiation, hydrostatic pressure, and applied electric field on shallow-donor impurity confined in cylindrical-shaped single and double GaAs-Ga1-xAlxAs QD. Several impurity positions and inputs of the heterostructure dimensions, hydrostatic pressure, and applied electric field have been considered. The laser effects have been introduced by a perturbative scheme in which the Coulomb and the barrier potentials are modified to obtain dressed potentials. Our findings suggest that (1) for on-center impurities in single QD the binding energy is a decreasing function of the dressing parameter and for small dot dimensions of the structures (lengths and radius) the binding energy is more sensitive to the dressing parameter, (2) the binding energy is an increasing/decreasing function of the hydrostatic pressure/applied electric field, (3) the effects of the intense laser field and applied electric field on the binding energy are dominant over the hydrostatic pressure effects, (4) in vertically coupled QD the binding energy for donor impurity located in the barrier region is smaller than for impurities in the well regions and can be strongly modified by the laser radiation, and finally (5) in asymmetrical double QD heterostructures the binding energy as a function of the impurity positions follows a similar behavior to the observed for the amplitude of probability of the noncorrelated electron wave function.

  1. Intrinsic and impurity induced emission bands in SrHfO.sub.3./sub..

    Czech Academy of Sciences Publication Activity Database

    Mihóková, Eva; Chiodini, N.; Fasoli, M.; Lauria, A.; Moretti, F.; Vedda, A.; Nikl, Martin; Jarý, Vítězslav

    Darwin : Charles Darwin University, 2010. 18O05. ISBN N. [International Conference on Excitonic and Photonic Processes in Condensed and Nano Materials /9./. 11.07.2010-15.07.2010, Brisbane] Institutional research plan: CEZ:AV0Z10100521 Keywords : hafnates * radioluminescence * scintillator Subject RIV: BM - Solid Matter Physics ; Magnetism

  2. Lattice location and magnetism of isolated Fe impurities in narrow band semiconductor InSb

    Energy Technology Data Exchange (ETDEWEB)

    Mohanta, S. K.; Mishra, S. N., E-mail: mishra@tifr.res.in [Tata Institute of Fundamental Research (India)

    2015-04-15

    Employing the time differential perturbed angular distribution method, we have measured local susceptibility and spin relaxation rate of {sup 54}Fe nuclei implanted in InSb. The magnetic response of Fe, identified to occupy the metal as well as the semi-metal atom sites, exhibit Curie-Weiss type susceptibility and Korringa like spin relaxation rate, revealing the existence of localized moments with small spin fluctuation temperature. The experimental results are supported by first principle electronic structure calculations performed within the frame work of density functional theory.

  3. Predictability of blocking

    International Nuclear Information System (INIS)

    Tibaldi and Molteni (1990, hereafter referred to as TM) had previously investigated operational blocking predictability by the ECMWF model and the possible relationships between model systematic error and blocking in the winter season of the Northern Hemisphere, using seven years of ECMWF operational archives of analyses and day 1 to 10 forecasts. They showed that fewer blocking episodes than in the real atmosphere were generally simulated by the model, and that this deficiency increased with increasing forecast time. As a consequence of this, a major contribution to the systematic error in the winter season was shown to derive from the inability of the model to properly forecast blocking. In this study, the analysis performed in TM for the first seven winter seasons of the ECMWF operational model is extended to the subsequent five winters, during which model development, reflecting both resolution increases and parametrisation modifications, continued unabated. In addition the objective blocking index developed by TM has been applied to the observed data to study the natural low frequency variability of blocking. The ability to simulate blocking of some climate models has also been tested

  4. Impurity production monitoring during RF experiments in Tore Supra

    Energy Technology Data Exchange (ETDEWEB)

    Meyer, O., E-mail: olivier.meyer@cea.f [Association Euratom-CEA, CEA/DSM/IRFM, Centre de Cadarache, 13108 Saint-Paul-Lez-Durance (France); Monier-Garbet, P.; Devynck, P.; Ekedahl, A.; Oddon, P.; Pegourie, B.; Vartanian, S. [Association Euratom-CEA, CEA/DSM/IRFM, Centre de Cadarache, 13108 Saint-Paul-Lez-Durance (France)

    2009-06-15

    Real time monitoring of edge plasma impurity content is used in a radiofrequency heated plasma scenario, to operate the tokamak safely by preventing any large increase in the impurity source, and to asses the global machine conditions after wall conditioning procedures. By means of high resolution Vacuum Ultraviolet spectroscopy, the main intrinsic impurity line brightnesses (C IV, O IV, Fe XV and Cu XIX) are routinely monitored and stored in a database along with basic plasma parameters (plasma current, electron density, injected power). The radiated power and the effective charge are also included for data consistency analysis. This paper describes the impurity monitoring technique implemented on Tore Supra (TS) and presents the main results concerning the evolution of the plasma edge impurity content for two scenarios performed on TS: high power scenario and long pulse duration scenario.

  5. Interaction between dislocation and divalent impurity in KBr single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Ohgaku, T; Matsunaga, T, E-mail: ohgaku@kenroku.kanazawa-u.ac.jp [Graduate school of Natural Science and Technology, Kanazawa University, Kakumamachi, Kanazawa 920-1192 (Japan)

    2009-07-15

    Interaction between dislocation and divalent impurity has been investigated in KBr single crystals doped with various impurities by strain rate cycling tests under ultrasonic oscillation. The interaction energy between dislocation and impurity-vacancy dipole (I-V dipole) has been obtained by fitting Barnett model to experimental results. The interaction energies between dislocation and I-V dipole were determined to be 0.51, 0.30, 0.23 and 0.36eV for Ba{sup 2+}, Sr{sup 2+}, Ca{sup 2+} and Mg{sup 2+}, respectively. The energy increases with increasing ionic radius of divalent impurity except Mg{sup 2+}. This may be because the I-V dipole is made of a divalent impurity and a nearest vacancy for Ba{sup 2+}, Sr{sup 2+} and Ca{sup 2+} but of a divalent one and a next nearest vacancy for Mg{sup 2+}.

  6. Spectroscopic analysis of impurity precipitates in CdS films

    International Nuclear Information System (INIS)

    Impurities in cadmium sulfide (CdS) films are a concern in the fabrication of copper (indium, gallium) diselenide (CIGS) and cadmium telluride (CdTe) photovoltaic devices. Devices incorporating chemical-bath-deposited (CBD) CdS are comparable in quality to devices incorporating purer CdS films grown using vacuum deposition techniques, despite the higher impurity concentrations typically observed in the CBD CdS films. In this paper, we summarize and review the results of Fourier transform infrared (FTIR). Auger, electron microprobe, and X-ray photoelectron spectroscopic (XPS) analyses of the impurities in CBD CdS films. We show that these impurities differ as a function of substrate type and film deposition conditions. We also show that some of these impurities exist as 102 micron-scale precipitates. copyright 1999 American Institute of Physics

  7. Photonic band gap materials

    International Nuclear Information System (INIS)

    An overview of the theoretical and experimental efforts in obtaining a photonic band gap, a frequency band in three-dimensional dielectric structures in which electromagnetic waves are forbidden, is presented

  8. Optical detection of impurities and defects in detector-grade mercuric iodide

    Science.gov (United States)

    James, R. B.; Ottesen, D. K.; Wong, D.; Schlesinger, T. E.; Schnepple, W. F.; Ortale, C.; Van Den Berg, L.

    1989-11-01

    We report the results of two different optical techniques, Fourier transform infrared (FTIR) spectroscopy and low-temperature photoluminescence, used to study impurities and native defects in mercuric iodide crystals and nuclear detectors. Several absorption bands associated with the presence of impurities are observed in transmission infrared spectra. Our measurements indicate that significant amounts of water are likely contained in the HgI2 crystals, and that the concentration of the water can be reduced by appropriate storage of the material. The FTIR spectra also show the existence of hydrocarbons in the bulk material. Several other weak absorption bands due to contaminants are detected in the transmission measurements. Low-temperature photoluminescence studies were also conducted on fully processed nuclear detectors to elucidate the relation between the measured luminescence and the detector response. At 78 K we observe a spectral line that appears to be correlated with the detector quality. In general, the photoluminescence results suggest that detector fabrication steps cause significant modifications to the stoichiometry in the near-surface region of the HgI2 crystals.

  9. Ferromagnetism of magnetic impurities coupled indirectly via conduction electrons: Insights from various theoretical approaches

    Science.gov (United States)

    Titvinidze, Irakli; Schwabe, Andrej; Potthoff, Michael

    2014-07-01

    The magnetic ground-state properties of the periodic Anderson model with a regular depletion of the correlated sites are analyzed within different theoretical approaches. We consider the model on the one-dimensional chain and on the two-dimensional square lattice with hopping between nearest neighbors. At half-filling and with correlated impurities present at every second site, the depleted Anderson lattice is the most simple system where the indirect magnetic coupling mediated by the conduction electrons is ferromagnetic. We discuss the underlying electronic structure and the possible mechanisms that result in ferromagnetic long-range order. To this end, different numerical and analytical concepts are applied to the depleted Anderson and also to the related depleted Kondo lattice and are contrasted with each other. This includes numerical approaches, i.e., Hartree-Fock theory, density-matrix renormalization and dynamical mean-field theory, as well as analytical concepts, namely a variant of the Lieb-Mattis theorem and the concept of flat-band ferromagnetism, and, finally, perturbative approaches, i.e., the effective RKKY exchange in the limit of weak coupling and the "inverse indirect magnetic exchange" in the limit of strong coupling between the conduction band and the impurities.

  10. Features of ZnS-powder doping with a Mn impurity during synthesis and subsequent annealing

    International Nuclear Information System (INIS)

    Luminescence, electron spin resonance, and X-ray diffraction (XRD) methods were used to investigate the features of ZnS-powder doped by Mn impurity during self-propagating high-temperature synthesis and subsequent annealing. The obtained powder consists of ZnS microcrystals with mainly hexagonal phase (80 ± 5)%. It was found, that after synthesis Mn presents not only in the form of non-uniformly distributed microscopic impurities in ZnS, but also in the form of Mn metal nanocrystals. Thermal annealing at 800°C leads to the additional doping of ZnS from metallic Mn, to the redistribution of the embedded Mn in the volume of microcrystals, and to the ZnS oxidation. At the same time, the ratio between the cubic and hexagonal phases does not change. It was shown that annealing causes a decrease in the concentration of the defects responsible for the luminescence-excitation bands, which correspond to transitions from the ground to the excited states of the Mn2+ ion. As a result of annealing, there is also a change in XRD coherent domain size. Simultaneously, the intensity of peaks in the luminescence-excitation spectrum with wavelengths of 375 and 395 nm was changed. The causes of these changes and the nature of the corresponding bands are discussed.

  11. Block Cipher Analysis

    DEFF Research Database (Denmark)

    Miolane, Charlotte Vikkelsø

    ensurethat no attack violatesthe securitybounds specifiedbygeneric attack namely exhaustivekey search and table lookup attacks. This thesis contains a general introduction to cryptography with focus on block ciphers and important block cipher designs, in particular the Advanced Encryption Standard......(AES).Wedescribe the mostgeneraltypes ofblock cipher cryptanalysis but concentrate on the algebraic attacks. While the algebraic techniques have been successful oncertainstreamcipherstheirapplicationtoblock ciphershasnot shown any significant results so far. This thesis contributes to the field of algebraic attacks on...... algebraic results on small scale variants of AES. In the final part of the thesis we present a new block cipher proposal Present and examine its security against algebraic and differential cryptanalysis in particular....

  12. Band parameters of phosphorene

    DEFF Research Database (Denmark)

    Lew Yan Voon, L. C.; Wang, J.; Zhang, Y.;

    2015-01-01

    Phosphorene is a two-dimensional nanomaterial with a direct band-gap at the Brillouin zone center. In this paper, we present a recently derived effective-mass theory of the band structure in the presence of strain and electric field, based upon group theory. Band parameters for this theory are co...

  13. Flat Band Quastiperiodic Lattices

    Science.gov (United States)

    Bodyfelt, Joshua; Flach, Sergej; Danieli, Carlo

    2014-03-01

    Translationally invariant lattices with flat bands (FB) in their band structure possess irreducible compact localized flat band states, which can be understood through local rotation to a Fano structure. We present extension of these quasi-1D FB structures under incommensurate lattices, reporting on the FB effects to the Metal-Insulator Transition.

  14. Basic and neutral route specific impurities in MDMA prepared by different synthesis methods. Comparison of impurity profiles.

    Science.gov (United States)

    Swist, M; Wilamowski, J; Parczewski, A

    2005-12-20

    In this work, the neutral and basic impurities found in the precipitate of MDMA(*)HCl are presented. MDMA.HCl was prepared by the most popular synthesis methods used in clandestine manufacture, i.e. safrole bromination, Leuckart method and reductive amination with various reducing agents: Al/Hg, NaBH(4), NaBH(3)CN. 3,4-Methylenedioxyphenyl-2-propanone (MDP-2-P), the starting material in Leuckart reaction and reductive amination, was prepared by two different synthesis methods, i.e. by isosafrole oxidation and MDP-2-nitropropene reduction. The extraction of impurities was performed under alkaline and neutral conditions. Impurity profiles were obtained using GC/MS. Each synthesis method is characterised by its own route specific impurities. The influence of pH on the extraction of synthesis markers from 3,4-methylenedioxymethamphetamine (MDMA) samples is discussed and comparison of the profiles of basic and neutral impurities is presented. PMID:16226147

  15. Block copolymer battery separator

    Energy Technology Data Exchange (ETDEWEB)

    Wong, David; Balsara, Nitash Pervez

    2016-04-26

    The invention herein described is the use of a block copolymer/homopolymer blend for creating nanoporous materials for transport applications. Specifically, this is demonstrated by using the block copolymer poly(styrene-block-ethylene-block-styrene) (SES) and blending it with homopolymer polystyrene (PS). After blending the polymers, a film is cast, and the film is submerged in tetrahydrofuran, which removes the PS. This creates a nanoporous polymer film, whereby the holes are lined with PS. Control of morphology of the system is achieved by manipulating the amount of PS added and the relative size of the PS added. The porous nature of these films was demonstrated by measuring the ionic conductivity in a traditional battery electrolyte, 1M LiPF.sub.6 in EC/DEC (1:1 v/v) using AC impedance spectroscopy and comparing these results to commercially available battery separators.

  16. Blocking in Category Learning

    OpenAIRE

    Bott, Lewis; Hoffman, Aaron B.; Murphy, Gregory L.

    2007-01-01

    Many theories of category learning assume that learning is driven by a need to minimize classification error. When there is no classification error, therefore, learning of individual features should be negligible. We tested this hypothesis by conducting three category learning experiments adapted from an associative learning blocking paradigm. Contrary to an error-driven account of learning, participants learned a wide range of information when they learned about categories, and blocking effe...

  17. Concord Housing Blocks

    OpenAIRE

    Kumaraswamy, Mohan

    2002-01-01

    One element of the CIVCAL project Web-based resources containing images, tables, texts and associated data on the construction of Concord type Housing Blocks. A high rise public housing project using prefabriction and advanced formwork systems. Both Harmony and Concord Blocks are designed on the basis of standard modular flats which permit the use of factory produced components and a construction sequence which makes extensive use of advanced formwork systems.

  18. Efficient Block Truncation Coding

    Directory of Open Access Journals (Sweden)

    K.Somasundaram,

    2010-09-01

    Full Text Available Block Truncation Coding (BTC is one of the lossy image compression techniques. The computational complexity involved in this method is very simple. In the proposed method, the feature of inter-pixel correlation is exploited to further reduce the requirement of bits to store a block. The proposed method gives very good performance in terms of bit-rate and PSNR values when compared to the conventional BTC.

  19. Selective Area Band Engineering of Graphene using Cobalt-Mediated Oxidation

    OpenAIRE

    Paul F. Bazylewski; Luan Nguyen; Robert P.C. Bauer; Hunt, Adrian H.; Eamon J. G. McDermott; Leedahl, Brett D.; Andrey I. Kukharenko; Cholakh, Seif O.; Kurmaev, Ernst Z.; Peter Blaha; Alexander Moewes; Young Hee Lee; Gap Soo Chang

    2015-01-01

    This study reports a scalable and economical method to open a band gap in single layer graphene by deposition of cobalt metal on its surface using physical vapor deposition in high vacuum. At low cobalt thickness, clusters form at impurity sites on the graphene without etching or damaging the graphene. When exposed to oxygen at room temperature, oxygen functional groups form in proportion to the cobalt thickness that modify the graphene band structure. Cobalt/Graphene resulting from this trea...

  20. Band structures of phononic crystal composed of lattices with different periodic constants

    International Nuclear Information System (INIS)

    With a square lattice mercury and water system being as the model, the band structures of nesting and compound phononic crystals with two different lattice constants were investigated using the method of the supercell plane wave expansion. It was observed that large band gaps can be achieved in low frequency regions by adjusting one of the lattice constants. Meanwhile, effects similar to interstitial impurity defects can be achieved with the increase of lattice constant of the phononic crystal. The corresponding defect modes can be stimulated in band gaps. The larger the lattice constant, the stronger the localization effect of defect modes on the wave. In addition, the change of the filling fraction of impurity exerts great influence on the frequency and localization of defect modes. Furthermore, the change of the position of impurity has notable influence on the frequency of defect modes and their localization. However, the geometry structure and orientation of impurity have little effect on the frequency of defect modes and their localization in the band gap.

  1. Impurity behavior in PBX L- and H-mode plasmas

    International Nuclear Information System (INIS)

    Intrinsic impurity behavior and transport properties in neutral-beam-heated L- and H-mode PBX tokamak plasmas were studied with a variety of impurity diagnostics. Central impurity accumulation was most often observed in H-mode discharges and sometimes resulted in a thermal collapse due to high central metallic radiation (-- 1.5 W/cm3). The accumulation was evident from peaked Z/sub eff/ and radiated power profiles and further substantiated from specific VUV and X-ray spectroscopy measurements. It is shown that impurity accumulation was neither unique nor inevitable in H-mode discharges, and it could be suppressed by sufficient gas puffing. Central accumulation was also seen in L-mode plasmas even with co-injected neutral beams. This usually occurred at high beam power and relatively low density. While there was no significant difference in the degree of accumulation between L- and H-mode discharges, the Z/sub eff/ profile itself was more peaked in the H-mode due to flatter electron density profiles in H-mode plasmas than in L-mode plasmas. The degree of accumulation increased as Z/sub eff/(0) itself increased and is qualitatively explained by neoclassical convection and diffusion driven by impurity--impurity collisions in addition to the usual impurity--plasma ion contributions in the central plasma region of interest. 44 refs., 20 figs

  2. Effect of gaseous impurities and the laser optics

    Science.gov (United States)

    Isarie, Ilie; Oprean, Constantin; Amza, Gheorghe; Petrescu, Valentin; Isarie, Claudiu

    2004-06-01

    The impurities into the volume of a material appear while the elaboration process of the considered material. If a material is non-homogenous, even if we machine this material by means of a classical technology we could remark some differences in the machining process like cutting, drilling a.s.o. even in the process of welding. The impurities may be gaseous or solid. Each kind of impurity has another effect for the classical tool, or for a non-traditional tool i.e. a kind of concentrated energy. Each kind of medium has another reaction versus laser beam, because each medium has other physical characteristics. The modifications of characteristics require modifications of photon beam parameters. Not any laser equipment is prepared to react correct to any kind of material, representing the impurity. To have a high quality machining process, we must know the nature-kind of the impurity, and in the same time, we must assure such components, which are able to react and correct to all kind of impurities which laser beam will meet. The recently generation of lasers are correct gifted, in order to work with materials presenting all kind of impurities.

  3. 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.

  4. Turbulent transport of impurities in a magnetized plasma

    International Nuclear Information System (INIS)

    This work deals with the transport of impurities in magnetically confined thermonuclear plasmas. The accumulation of impurities in the core of the plasma would imply dramatic losses of energy that may lead to the extinction of the plasma. On the opposite, the injection of impurities in the plasma edge is considered as an efficient means to extract heat without damaging the first wall. The balance between these 2 contradictory constraints requires an accurate knowledge of the impurity transport inside the plasma. The effect of turbulence, the main transport mechanism for impurities is therefore a major issue. In this work, the complete formula of a turbulent flow of impurities for a given fluctuation spectrum has been inferred. The origin and features of the main accumulation processes have been identified. The main effect comes from the compressibility of the electrical shift speed in a plane perpendicular to the magnetic field. This compressibility appears to be linked to the curvature of the magnetic field. A less important effect is a thermal-diffusion process that is inversely proportional to the number of charges and then disappears for most type of impurities except the lightest. This effect implies an impurity flux proportional to the temperature gradient and its direction can change according to the average speed of fluctuations. A new version of the turbulence code TRB has been developed. This new version allows the constraints of the turbulence not by the gradients but by the flux which is more realistic. The importance of the processes described above has been confirmed by a comparison between calculation and experimental data from Tore-supra and the Jet tokamak. The prevailing role of the curvature of the magnetic field in the transport impurity is highlighted. (A.C.)

  5. Impurity-limited resistance and phase interference of localized impurities under quasi-one dimensional nano-structures

    Science.gov (United States)

    Sano, Nobuyuki

    2015-12-01

    The impurity-limited resistance and the effect of the phase interference among localized multiple impurities in the quasi-one dimensional (quasi-1D) nanowire structures are systematically investigated under the framework of the scattering theory. We derive theoretical expressions of the impurity-limited resistance in the nanowire under the linear response regime from the Landauer formula and from the Boltzmann transport equation (BTE) with the relaxation time approximation. We show that the formula from the BTE exactly coincides with that from the Landauer approach with the weak-scattering limit when the energy spectrum of the in-coming electrons from the reservoirs is narrow and, thus, point out a possibility that the distinction of the impurity-limited resistances derived from the Landauer formula and that of the BTE could be made clear. The derived formulas are applied to the quasi-1D nanowires doped with multiple localized impurities with short-range scattering potential and the validity of various approximations on the resistance are discussed. It is shown that impurity scattering becomes so strong under the nanowire structures that the weak-scattering limit breaks down in most cases. Thus, both phase interference and phase randomization simultaneously play a crucial role in determining the impurity-limited resistance even under the fully coherent framework. When the impurity separation along the wire axis direction is small, the constructive phase interference dominates and the resistance is much greater than the average resistance. As the separation becomes larger, however, it approaches the series resistance of the single-impurity resistance due to the phase randomization. Furthermore, under the uniform configuration of impurities, the space-average resistance of multiple impurities at room temperature is very close to the series resistance of the single-impurity resistance, and thus, each impurity could be regarded as an independent scattering center. The

  6. Impurity-limited resistance and phase interference of localized impurities under quasi-one dimensional nano-structures

    Energy Technology Data Exchange (ETDEWEB)

    Sano, Nobuyuki, E-mail: sano@esys.tsukuba.ac.jp [Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan)

    2015-12-28

    The impurity-limited resistance and the effect of the phase interference among localized multiple impurities in the quasi-one dimensional (quasi-1D) nanowire structures are systematically investigated under the framework of the scattering theory. We derive theoretical expressions of the impurity-limited resistance in the nanowire under the linear response regime from the Landauer formula and from the Boltzmann transport equation (BTE) with the relaxation time approximation. We show that the formula from the BTE exactly coincides with that from the Landauer approach with the weak-scattering limit when the energy spectrum of the in-coming electrons from the reservoirs is narrow and, thus, point out a possibility that the distinction of the impurity-limited resistances derived from the Landauer formula and that of the BTE could be made clear. The derived formulas are applied to the quasi-1D nanowires doped with multiple localized impurities with short-range scattering potential and the validity of various approximations on the resistance are discussed. It is shown that impurity scattering becomes so strong under the nanowire structures that the weak-scattering limit breaks down in most cases. Thus, both phase interference and phase randomization simultaneously play a crucial role in determining the impurity-limited resistance even under the fully coherent framework. When the impurity separation along the wire axis direction is small, the constructive phase interference dominates and the resistance is much greater than the average resistance. As the separation becomes larger, however, it approaches the series resistance of the single-impurity resistance due to the phase randomization. Furthermore, under the uniform configuration of impurities, the space-average resistance of multiple impurities at room temperature is very close to the series resistance of the single-impurity resistance, and thus, each impurity could be regarded as an independent scattering center. The

  7. Modular Analysis of Almost Block Diagonal Systems of Equations

    OpenAIRE

    El-Mistikawy, Tarek M. A.

    2013-01-01

    Almost block diagonal linear systems of equations can be exemplified by two modules. This makes it possible to construct all sequential forms of band and/or block elimination methods, six old and fourteen new. It allows easy assessment of the methods on the basis of their operation counts, storage needs, and admissibility of partial pivoting. It unveils a robust partial pivoting strategy- local pivoting. Extension of modular analysis to bordered systems is also included.

  8. Lattice relaxations and hyperfine fields of heavy impurities in Fe

    OpenAIRE

    Korhonen, T.; Settels, A.; Papanikolaou, N.; Zeller, R.; Dederichs, P. H.

    2000-01-01

    We present first-principles calculations of the lattice relaxations and hyperfine fields of heavy impurities in bcc Fe. We consider impurities of the 5sp and 6sp series, containing the largest atoms in the periodic table. As an application we calculate the hyperfine fields of these impurities and in particular the effects of lattice relaxations on these fields. The calculations are based on a full-potential Korringa-Kohn-Rostoker Green's-function method for defects and employ the local spin-d...

  9. Alternating current response of carbon nanotubes with randomly distributed impurities

    Energy Technology Data Exchange (ETDEWEB)

    Hirai, Daisuke; Watanabe, Satoshi [Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Yamamoto, Takahiro [Department of Electrical Engineering and Department of Liberal Arts (Physics), Tokyo University of Science, 6-3-1 Niijuku, Katsushika, Tokyo 125-8585 (Japan)

    2014-10-27

    The increasing need for nanodevices has necessitated a better understanding of the electronic transport behavior of nanomaterials. We therefore theoretically examine the AC transport properties of metallic carbon nanotubes with randomly distributed impurities. We find that the long-range impurity scattering increases the emittance, but does not affect the DC conductance. The estimated dwell time of electrons increases with the potential amplitudes. That is, multiple scattering by the impurities increases the kinetic inductance in proportion to the dwell time, which eventually increases the emittance. We believe that our findings can contribute significantly to nanodevice development.

  10. Impurity transport and confinement in the TJ-II stellarator

    International Nuclear Information System (INIS)

    In this study, performed by injecting impurities using the laser ablation method, we address impurity transport in the TJ-II stellarator for a broad range of experimental situations in electron cyclotron heated plasmas (ECRH): i.e. for a density scan, a magnetic configuration scan, a power scan and its dependence with power deposition profile. An analysis of impurity relaxation, defined by means of a stretched exponential, is presented in order to search for systematic behaviour in the tau and beta parameters of this function. (author)

  11. Prevention of serious impurity penetration into water-steam circuits

    International Nuclear Information System (INIS)

    In consequence of reports from several power Plants concerning heavy damages due to penetrations of impurities into the water-steam circuit, the VGB Sub-Committee 'Water Chemistry in Thermal Power Plants' has established a working group to check-up how serious impurity penetration can be avoided. The lecture describes possible danger points. Suitable technical arrangements for the avoidance of penetrations, and possibilities for monitoring will be discussed. Penetration of impurities cannot be avoided with absolute reliability, even when the recommended arrangements and usual monitoring are realized. Additional measures for the protection of water steam circuits will be suggested. (orig.)

  12. Dynamics and response functions of an impurity in a BEC

    Science.gov (United States)

    Shchadilova, Yulia; Grusdt, Fabian; Schmidt, Richard; Demler, Eugene

    2016-05-01

    We discuss the non-equilibrium quantum dynamics of an impurity in an ultracold Bose gas. In our theoretical description we take into account the microscopic interactions beyond the Fröhlich approximation. We calculate the response functions of the system for weak and strong RF-driving between two hyperfine states of the impurity. We show that in the weak driving regime the population transfer of the impurity is in agreement with spectral functions obtained by the linear response calculations. This is in contrast with the strong RF regime where we observe the strong renormalization of the Rabi frequency close to the inter-species Feshbach resonance.

  13. Impact of organic impurities on steam turbine operation

    International Nuclear Information System (INIS)

    Organic impurities in steam can lower local pH in the steam turbine, and may possibly cause additional ion-specific corrosion effects. Some practical cases of organic impurities in the steam are illustrated. Limited quantities of carbon dioxide in the steam did not prove to be detrimental as long as the alkalization of the water was sufficient. Low local pH can be compensated within limits by conditioning of feedwater or steam. The possibility of specific corrosion effects for the individual organic impurities, especially for acetate deserves further research

  14. Interference of quantum states in electronic waveguides with impurities

    International Nuclear Information System (INIS)

    One investigated into effects of interference of propagating and localized states in quasi-dimensional electric waveguides containing attracting impurities (quantum points) of finite sizes. Matrix of electron scattering is calculated in terms of the Feshbach theory. It is shown that attracting impurities with finite sizes may initiate a series of the Fano asymmetric resonances in waveguide transparency. In this case, due to interference of electronic states, characteristics of resonances may oscillate at variation of impurity parameters. One determined conditions under which the effects of interference of electron waves results in collapse and swing of the Fano resonances

  15. Resonant Transmission Through Two Impurities in a Narrow Quantum Wire

    Institute of Scientific and Technical Information of China (English)

    宋小龙; 赵志云; 汪源; 施耀铭

    2003-01-01

    We study electron transmission through two impurities in a narrow quantum wire by solving Dyson's equations for single electron Green functions. We have verified that, for the delta-function potential of two impurities, the Green function can be factorized into a product of the ‘free' Green function and current transmission amplitude. Meanwhile Green function and current transmission amplitude obey Fisher-Lee's relation. An analytical expression of the electron transmission amplitude for intrasubband and intersubband is obtained as a function of Fermi energy and the distance between two impurities. The resonant behavior of the current transmission amplitude are detail discussed.

  16. Nonlinearity and disorder: Classification and stability of nonlinear impurity modes

    DEFF Research Database (Denmark)

    Sukhorukov, Andrey A.; Kivshar, Yuri S.; Bang, Ole;

    2001-01-01

    We study the effects produced by competition of two physical mechanisms of energy localization in inhomogeneous nonlinear systems. As an example, we analyze spatially localized modes supported by a nonlinear impurity in the generalized nonlinear Schrödinger equation and describe three types of no...... case of a power-law nonlinearity in detail. We discuss several scenarios of the instability-induced dynamics of the nonlinear impurity modes, including the mode decay or switching to a new stable state, and collapse at the impurity site....

  17. Impurity states in two and three dimensional disordered system S

    International Nuclear Information System (INIS)

    We investigate the microscopic structure of the impurity states in two-and three-dimensional (2D and 3D) disordered system. A cluster model is outlined for the donor impurity density of states (DIDS) of doped semiconductors. It is shown that the impurity states are very sensitive to a change in the dimensionality of the system, i.e., from 3D to 2D system. It is found that all eigenstates become localized in 2D disordered system for a large range of concentration. (author)

  18. Impurity states in two - and three-dimensional disordered systems

    International Nuclear Information System (INIS)

    We investigate the microscopic structure of the impurity states in two-and three-dimensional (2D and 3d) disordered systems. A cluster model is outlined for the donor impurity density of states (DIDS) of doped semiconductors. It is shown that the impurity states are very sensitive to a change in the dimensionality of the system, i.e from 3D to 2D system. It is found that all eigenstates become localized in 2D disordered system for a large range of concentration. (Author)

  19. Alumina Recovery from Kaolin with Mineral Impurities

    Institute of Scientific and Technical Information of China (English)

    SI Peng; QIAO Xiuchen; YU Jianguo

    2012-01-01

    The alumina recovery from low grade kaolin (K-JS) treated through thermal and mechanical methods was investigated.High grade kaolin (K-SX) was used as comparison.The optimum calcination temperatures for K-JS and K-SX were both 600 ℃,which resulted in 89.34wt% of alumina extraction from K-JS and 83.37wt% from K-SX.With the increase in calcination temperature,the chemical reactivity of calcined K-JS and K-SX to acid decreased.Mechanical treatment was much more effective in increasing the alumina extraction from activated kaolin.Around 99wt% of alumina was extracted from K-JS ground for 10 hours and 95wt% of alumina was extracted from K-SX ground for 20 hours.The IR results showed that the substitute of Al for Si occurred in calcined K-SX,however,the impurities in K-JS decreased this substitute.More alumina could be extracted from low grade kaolin than that from high grade kaolin under identical thermal or mechanical conditions.

  20. Nucleation of voids - the impurity effect

    International Nuclear Information System (INIS)

    Nucleation of voids under irradiation in multicomponent alloys remains an unsolved theoretical problem. Of particular interest are the effects of nonequilibrium solute segregation phenomena on the critical nucleus and the nucleation rate. The resolution of the multicomponent nucleation in a dissipative system also has broader implication to the field of irreversible thermodynamics. The present paper describes a recent study of solute segregation effects in void nucleation. We begin with a thermodynamic model for a nonequilibrium void with interfacial segregation. The thermodynamic model is coupled with kinetic considerations of solute/solvent diffusion under a bias, which is itself related to segregation by the coating effect, to assess the stability of void embryos. To determine nucleation rate, we develop a novel technique by extending the most probable path method in statistical mechanics for nonequilibrium steady state to simulate large fluctuation with nonlinear dissipation. The path of nucleation is determined by solving an analogous problem on particle trajectory in classical dynamics. The results of both the stability analysis and the fluctuation analysis establish the paramount significance of the impurity effect via the mechanism of nonequilibrium segregation. We conclude that over-segregation is probably the most general cause for the apparently low nucleation barriers that are responsible for nearly ubiquitous occurrence of void swelling in common metals

  1. Dynamics of impurities in ultracold Bose gas

    Science.gov (United States)

    Shchadilova, Yulia; Grusdt, Fabian; Rubtsov, Alexey; Demler, Eugene

    2015-05-01

    A system of an impurity immersed in a Bose-Einstein condensate (BEC) exhibits the polaronic effect, which is known to be an ubiquitous phenomenon in a wide range of physical systems including semiconductors, doped Mott insulators, and high-Tc superconductors. Recent analysis of the BEC-polaron problem showed that existing analytical approaches do not provide reliable results in the experimentally relevant range of parameters when tested against Monte Carlo (MC) simulations. In this contribution we demonstrate that the description of polarons at finite momentum can be done by employing an analytical class of wavefunctions based on the correlated Gaussian ansatz (CGWs). We show that CGWs show excellent agreement with known MC results for the polaron binding energy for a wide range of interactions. We discuss the properties of the polarons and atomic mixtures in systems of ultracold atoms in which polaronic effects can be observed with current experimental technology. Our CGWs predicts a specific pattern of correlations between host atoms that can be measured in time-of-flight experiments. Department of Physics, Harvard University.

  2. Impurity Trapping of Positive Muons in Metals

    CERN Multimedia

    2002-01-01

    Polarized positive muons are implanted into metal samples. In an applied magnetic field the muon spin precession is studied. The line width in the precession frequency spectrum gives information about the static and dynamic properties of muons in a metal lattice. At temperatures where the muon is immobile within its lifetime the line width gives information about the site of location. At temperatures where the muon is mobile, the line width gives information on the diffusion process. It is known from experiments on quasi-elastic neutron scattering on hydrogen in niobium that interstitial impurities like nitrogen tend to act as traps for hydrogen. These trapping effects have now been studied systematically for muons in both f.c.c. metals (aluminium and copper) and b.c.c. metals (mainly niobium). Direct information on the trapping rates and the nature of the diffusion processes can be obtained since the muonic lifetime covers a time range where many of these processes occur.\\\\ \\\\ Mathematical models are set up ...

  3. Infrared studies of impurity states and ultrafast carrier dynamics in semiconductor quantum structures

    Energy Technology Data Exchange (ETDEWEB)

    Stehr, D.

    2007-12-28

    This thesis deals with infrared studies of impurity states, ultrafast carrier dynamics as well as coherent intersubband polarizations in semiconductor quantum structures such as quantum wells and superlattices, based on the GaAs/AlGaAs material system. In the first part it is shown that the 2p{sub z} confined impurity state of a semiconductor quantum well develops into an excited impurity band in the case of a superlattice. This is studied by following theoretically the transition from a single to a multiple quantum well or superlattice by exactly diagonalizing the three-dimensional Hamiltonian for a quantum well system with random impurities. These results also require reinterpretation of previous experimental data. The relaxation dynamics of interminiband transitions in doped GaAs/AlGaAs superlattices in the mid-IR are studied. This involves single-color pump-probe measurements to explore the dynamics at different wavelengths, which is performed with the Rossendorf freeelectron laser (FEL), providing picosecond pulses in a range from 3-200 {mu}m and are used for the first time within this thesis. In these experiments, a fast bleaching of the interminiband transition is observed followed by thermalization and subsequent relaxation, whose time constants are determined to be 1-2 picoseconds. This is followed by an additional component due to carrier cooling in the lower miniband. In the second part, two-color pump-probe measurements are performed, involving the FEL as the pump source and a table-top broad-band tunable THz source for probing the transmission changes. In addition, the dynamics of excited electrons within the minibands is explored and their contribution quantitatively extracted from the measurements. Intersubband absorption experiments of photoexcited carriers in single quantum well structures, measured directly in the time-domain, i.e. probing coherently the polarization between the first and the second subband, are presented. By varying the carrier

  4. Impression block with orientator

    International Nuclear Information System (INIS)

    Tool review, namely the impression block, applied to check the shape and size of the top of fish as well as to determine the appropriate tool for fishing operation was realized. For multiple application and obtaining of the impress depth of 3 cm and more, the standard volumetric impression blocks with fix rods are used. However, the registered impress of fish is not oriented in space and the rods during fishing are in the extended position. This leads to rods deformation and sinking due to accidental impacts of impression block over the borehole irregularity and finally results in faulty detection of the top end of fishing object in hole. The impression blocks with copy rods and fixed magnetic needle allow estimating the object configuration and fix the position of magnetic needle determining the position of the top end of object in hole. However, the magnetic needle fixation is realized in staged and the rods are in extended position during fishing operations as well as it is in standard design. The most efficient tool is the impression block with copy rods which directs the examined object in the borehole during readings of magnetic needles data from azimuth plate and averaging of readings. This significantly increases the accuracy of fishing toll direction. The rods during fishing are located in the body and extended only when they reach the top of fishing object

  5. Uniaxial backfill block compaction

    International Nuclear Information System (INIS)

    The main parts of the project were: to make a literature survey of the previous uniaxial compaction experiments; do uniaxial compaction tests in laboratory scale; and do industrial scale production tests. Object of the project was to sort out the different factors affecting the quality assurance chain of the backfill block uniaxial production and solve a material sticking to mould problem which appeared during manufacturing the blocks of bentonite and cruched rock mixture. The effect of mineralogical and chemical composition on the long term functionality of the backfill was excluded from the project. However, the used smectite-rich clays have been tested for mineralogical consistency. These tests were done in B and Tech OY according their SOPs. The objective of the Laboratory scale tests was to find right material- and compaction parameters for the industrial scale tests. Direct comparison between the laboratory scale tests and industrial scale tests is not possible because the mould geometry and compaction speed has a big influence for the compaction process. For this reason the selected material parameters were also affected by the previous compaction experiments. The industrial scale tests were done in summer of 2010 in southern Sweden. Blocks were done with uniaxial compaction. A 40 tons of the mixture of bentonite and crushed rock blocks and almost 50 tons of Friedland-clay blocks were compacted. (orig.)

  6. Block diagonal and schur complement preconditioners for block-toeplitz systems with small size blocks

    OpenAIRE

    Ching, WK; Ng, MK; Wen, YW

    2007-01-01

    In this paper we consider the solution of Hermitian positive definite block-Toeplitz systems with small size blocks. We propose and study block diagonal and Schur complement preconditioners for such block-Toeplitz matrices. We show that for some block-Toeplitz matrices, the spectra of the preconditioned matrices are uniformly bounded except for a fixed number of outliers where this fixed number depends only on the size of the block. Hence, conjugate gradient type methods, when applied to solv...

  7. Computer simulation of electron states of the isoelectronic substitutional impurities in quantum wire of KCl with edge dislocation

    International Nuclear Information System (INIS)

    The electron states of quantum wires KCl, KCl : Br, and KCl : I with an edge dislocations were investigated. The main problem was in study of dislocation influence on localized electron states connected with substitutional isoelectronic impurities Br− and I− in the neighborhood of edge dislocation line. The tight-binding semi-empirical band approximation, semi-empirical and non-empirical cluster approach were used. Semi-empirical calculations were carried out in framework of model [1,2]. Besides, the algorithms for electronic levels calculations of polar nanosystems with the partial self-consistency [3] were used. The computer simulation results lead to the conclusion that the substitutional isoelectronic impurity anions Br− and I− located near the dislocation line capture the holes more efficiently than in bulk of systems without dislocations

  8. The influence of impurity on the critical thickness of the CeO2 buffer layer for coated conductors

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The lattice parameters, band structure, density of state and elastic constant of RE-doped CeO2 (RE=Sm, Gd, Dy), the buffer material for coated HTS conductors, are calculated using the plane-wave method with pseudopotentials based on the density functional theory (DFT) of first-principle. The rule and mechanism of the effect of rare earth impurity on the critical thickness of the CeO2 buffer layer are investigated. It is found that, in the range of the calculation, the changes of the lattice volume V and elastic constant E of CeO2 with the impurity are mainly determined by the increased electrons ne of the system. The relationship of the elastic constant E and increased electrons ne is established. It is indicated that the critical thickness of the CeO2 single buffer layer doped with Sm, Gd, and Dy may be enhanced by 22%, 43% and 33%, respectively.

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

    Institute of Scientific and Technical Information of China (English)

    Jie Binbin; Sah Chihtang

    2011-01-01

    Low-frequency and high-frequency Capacitance-Voltage(C V)curves of Metal OxideSemiconductor Capacitors(MOSC),including electron and hole trapping at the dopant donor and acceptor impurities,are presented to illustrate giant trapping capacitances,from > 0.01Cox to > 10Cox.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,NDD,the ground state electron trapping energy level depth measured from the conduction band edge,EC-ED,the degeneracy of the trapped electron at the ground state,gD,the device temperature,T,and the gate oxide thickness,xox.

  10. One-man band

    OpenAIRE

    Stillman, R.

    2013-01-01

    This website presents practice-based research related to solo simultaneous instrumental performance ('one-man band'). The site was conceived as a creative and widely accessible platform for music and ideas resulting from one-man band activates carried out between 2008 and 2013. Central to this project is an interest in how one-man band technique informs compositional process, including studio production. Through presentation and analysis of the author’s own creative practice, the site exp...

  11. Nymble Blocking System

    Directory of Open Access Journals (Sweden)

    Anand Joshi

    2012-05-01

    Full Text Available In order to allow users to access Internet services privately, anonymizing networks like Tor uses a series of routers to hide the client’s IP address from the server. These networks, however, have been marred by users employing this anonymity for abusive purposes such as defacing popular web sites. Usually, web site administrators rely on IP-address blocking in order to disable access to misbehaving users, but it is impractical if the abuser routes through an anonymizing network. In order to avoid this, administrators bar all known exit nodes of the anonymizing network, thereby denying anonymous access to all the users(whether misbehaving or not. To solve this issue, we introduce Nymble, a system where servers blacklist misbehaving users, thereby blocking users without affecting their anonymity. Nymble is thus agnostic to varied definitions of misbehavior. Servers can block users for any reason, and the privacy of blacklisted users is not affected in any case.

  12. Radiative instabilities in plasmas: impurity motion and recombination effects

    International Nuclear Information System (INIS)

    Radiative instabilities in an impurity-seeded plasma are investigated when the plasma is supposed to be highly but partially ionized. Since in such plasmas radiative losses strongly depend on neutral and impurity densities, their dynamics are taken into account. As a result, a new radiative-recombination instability is found and described. We show that the influence of the ionization-recombination balance on plasma stability is sufficient for plasma densities above 1014 cm-3. The effects of a finite impurity Larmor radius are not small and play a stabilizing role as well as the thermal forces. On the other hand, compressibility of the magnetic field leads to plasma destabilization. We note that this radiative-recombination instability accumulates impurities in a cold zone while cleaning other regions. (Author)

  13. Simulating the symmetron: domain walls and symmetry-restoring impurities

    CERN Document Server

    Pearson, Jonathan A

    2014-01-01

    In this paper we study the dynamics of relativistic domain walls in the presence of static symmetry-restoring impurities. The field theory is precisely the same as what is known to cosmologists as the "symmetron model", whereby the usual $\\mathbb{Z}_2$ symmetry breaking potential is appended with a space-varying mass-term (the space-variation is set by the profile of the impurity, which we take to be a "tanh"-function). After presenting the outcomes of a suite of different numerical experiments we have three main results: (1) domain walls pin to impurities, (2) domain wall necklaces can be energetically preferred configurations, and (3) impurities significantly modifies the usual ${N}_{\\rm dw}\\propto t^{-1}$ scaling law for random networks of domain walls.

  14. Parallel impurity dynamics in the TJ-II stellarator

    Science.gov (United States)

    Alonso, J. A.; Velasco, J. L.; Calvo, I.; Estrada, T.; Fontdecaba, J. M.; García-Regaña, J. M.; Geiger, J.; Landreman, M.; McCarthy, K. J.; Medina, F.; Van Milligen, B. Ph; Ochando, M. A.; Parra, F. I.; the TJ-II Team; the W7-X Team

    2016-07-01

    We review in a tutorial fashion some of the causes of impurity density variations along field lines and radial impurity transport in the moment approach framework. An explicit and compact form of the parallel inertia force valid for arbitrary toroidal geometry and magnetic coordinates is derived and shown to be non-negligible for typical TJ-II plasma conditions. In the second part of the article, we apply the fluid model including main ion-impurity friction and inertia to observations of asymmetric emissivity patterns in neutral beam heated plasmas of the TJ-II stellarator. The model is able to explain qualitatively several features of the radiation asymmetry, both in stationary and transient conditions, based on the calculated in-surface variations of the impurity density.

  15. Parallel impurity dynamics in the TJ-II stellarator

    CERN Document Server

    Alonso, J A; Estrada, T; Fontdecaba, J M; García-Regaña, J M; Geiger, J; Landreman, M; McCarthy, K J; Medina, F; Van Milligen, B Ph; Ochando, M A; Parra, F I; Velasco, J L

    2016-01-01

    We review in a tutorial fashion some of the causes of impurity density variations along field lines and radial impurity transport in the moment approach framework. An explicit and compact form of the parallel inertia force valid for arbitrary toroidal geometry and magnetic coordinates is derived and shown to be non-negligible for typical TJ-II plasma conditions. In the second part of the article, we apply the fluid model including main ion-impurity friction and inertia to observations of asymmetric emissivity patterns in neutral beam heated plasmas of the TJ-II stellarator. The model is able to explain qualitatively several features of the radiation asymmetry, both in stationary and transient conditions, based on the calculated in-surface variations of the impurity density.

  16. Analysis of radiative mantle formation by impurity seeding in ITER

    International Nuclear Information System (INIS)

    In order to reduce high heat load on divertor plate in fusion reactors, we investigated radiative mantle formation scenarios by impurity seeding into scrape off layer (SOL) in ITER using the TOTAL simulation code. The low-Z impurity, like He, could not form a radiative mantle and have almost no contribution to the reduction of divertor heat load. On the contrary, the medium-Z impurity, like Kr, can form radiative mantle definitely and can radiate about 84% (core:33% / mantle:51%) of input power inside the last closed flux surface (LCFS) without any serious changes in density and temperature profile, and without inducing back transition from H to L mode. It can reduce divertor heat load about 60% compared with the case of no impurity injection in ITER. (author)

  17. Impurity-Assisted Tunneling Magnetoresistance under a Weak Magnetic Field

    Science.gov (United States)

    Txoperena, Oihana; Song, Yang; Qing, Lan; Gobbi, Marco; Hueso, Luis E.; Dery, Hanan; Casanova, Fèlix

    2014-10-01

    Injection of spins into semiconductors is essential for the integration of the spin functionality into conventional electronics. Insulating layers are often inserted between ferromagnetic metals and semiconductors for obtaining an efficient spin injection, and it is therefore crucial to distinguish between signatures of electrical spin injection and impurity-driven effects in the tunnel barrier. Here we demonstrate an impurity-assisted tunneling magnetoresistance effect in nonmagnetic-insulator-nonmagnetic and ferromagnetic-insulator-nonmagnetic tunnel barriers. In both cases, the effect reflects on-off switching of the tunneling current through impurity channels by the external magnetic field. The reported effect is universal for any impurity-assisted tunneling process and provides an alternative interpretation to a widely used technique that employs the same ferromagnetic electrode to inject and detect spin accumulation.

  18. Runaway electron dynamics in tokamak plasmas with high impurity content

    Science.gov (United States)

    Martín-Solís, J. R.; Loarte, A.; Lehnen, M.

    2015-09-01

    The dynamics of high energy runaway electrons is analyzed for plasmas with high impurity content. It is shown that modified collision terms are required in order to account for the collisions of the relativistic runaway electrons with partially stripped impurity ions, including the effect of the collisions with free and bound electrons, as well as the scattering by the full nuclear and the electron-shielded ion charge. The effect of the impurities on the avalanche runaway growth rate is discussed. The results are applied, for illustration, to the interpretation of the runaway electron behavior during disruptions, where large amounts of impurities are expected, particularly during disruption mitigation by massive gas injection. The consequences for the electron synchrotron radiation losses and the resulting runaway electron dynamics are also analyzed.

  19. Study of impurity behaviour in non-coronal equilibrium state

    Institute of Scientific and Technical Information of China (English)

    Cheng Fa-Yin; Shi Bing-Ren

    2007-01-01

    A physical model of analysing the behaviour of impurities out of coronal equilibrium in tokamak plasmas has been proposed. Through solving the time-dependent rate equations including the effects of atomic processes and the particle transport losses, the ionization state distribution is obtained for a range of low Z impurities such as helium, carbon,oxygen and argon. By using the ionization state distribution of these impurities, the radiation rate coefficients and the mean charge state changing with plasma temperature are calculated. The results show that the mean charge stateis sensitively dependent on the parameter neτ, and this is the reason why the radiation power of impurities under non-coronal equilibrium conditions is several orders of magnitude higher than that under coronal equilibrium condition.

  20. Structure and dynamics of Lennard-Jones clusters with impurities

    International Nuclear Information System (INIS)

    Molecular dynamics simulations and Lennard-Jones potentials have been used to study binary mixed clusters. The low temperature structures, impurity solvation and the melting and freezing transitions for different values of the relative atomic size and interaction energy have been studied for A13B, A12B, A55B and A13B13 clusters. For A13B large impurities do not solvate even for high interaction energy. For A55B larger impurities remain on the surface for low interaction energies but solvate as the energy of interaction increases. The presence of the impurity very strongly affects the solid-liquid transition. Icosahedral structures remain as the minimum energy configurations for A13B13 clusters with atoms of the same size and different interaction energies. For A13B13 clusters with atoms of the same interaction energy and different size, smaller atoms go inside surrounded by the bigger surface atoms. (orig.)

  1. Trace impurities in single crystals of hexagonal lithium iodate

    International Nuclear Information System (INIS)

    The purpose of this work was to investigate the combined entry of trace impurities into a single crystal of lithium iodate grown from an aqueous solution with additions of the radioactive isotopes 59Fe, 57Co, 54Mn, and 65Zn. The study made it possible to reveal considerable nonuniformity in the distribution of trace impurities, whose content is the crystal decreases over a range of several orders of magnitude. The isomorphous character of the entry of all the cationic trace impurities investigated into lithium iodate crystals was established. The adequacy of the mathematical model describing the chemical nonuniformity of single crystals grown from solutions by the method of isothermal evaporation was demonstrated experimentally. The experimental values of the distribution constants (as defined by Derner and Hoskins) of trace impurities of iron, manganese, cobalt, and zinc (when they are present together in the mother solutions) were obtained

  2. Dimensionality effects on spin-polarized quantum beats in ferromagnetic hosts with a pair of side-coupled impurities

    Energy Technology Data Exchange (ETDEWEB)

    Guessi, L.H.; Leandro, S.C.; Seridonio, A.C.; Siqueira, E.C. [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Ilha Solteira, SP (Brazil). Dept. de Fisico Quimica; Souza, F.M.; Vernek, E. [Universidade Federal de Uberlandia (UFU), MG (Brazil). Inst. de Fisica; Yoshida, M. [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Rio Claro, SP (Brazil); Figueira, M.S. [Universidade Federal Fluminense (UFF), Niteroi, RJ (Brazil). Inst. de Fisica

    2012-07-01

    Full text: In this work, we report a theoretical description of the differential conductance in the low bias regime, for a normal scanning tunneling microscope (STM) probe in the presence of ferromagnetic (FM) hosts with impurities. The hosts are treated as a spin-polarized electron gas hybridized to a pair of side-coupled impurities. Two setups of different dimensionalities are considered, a quantum wire (QW) and a metallic surface (MS). In order to deal with the non-interacting and the Coulomb blockade regimes of these systems, the analysis is done in the framework of the two-impurity Anderson model (TIAM) in combination with the equation of motion (EOM) approach for the Hamiltonian Green functions (GFs). The Fano effect appears in such setups, due to the quantum interference between the transport channels composed by the spin-polarized conduction bands and the electron tunneling into (or out of) the impurities. Thus the conductance of the STM reveals as a function of the probe position, a Fano interference strong dependent on the host dimensionality. It leads to the emergence of spin-polarized quantum beats in the Friedel oscillations for the conductance signal, which are uniform in the QW system in opposite to those found in the MS case, characterized by a long-range damped behavior. We remark that, the energy levels of the impurities and the Coulomb repulsion, modulate these beats. As a result, they establish a scenario where the interplay between the Coulomb blockade and the ferromagnetism of a metallic environment, can be useful for future quantum computation devices. (author)

  3. Bactericidal block copolymer micelles.

    Science.gov (United States)

    Vyhnalkova, Renata; Eisenberg, Adi; van de Ven, Theo

    2011-05-12

    Block copolymer micelles with bactericidal properties were designed to deactivate pathogens such as E. coli bacteria. The micelles of PS-b-PAA and PS-b-P4VP block copolymers were loaded with biocides TCMTB or TCN up to 20 or 30 wt.-%, depending on the type of antibacterial agent. Bacteria were exposed to loaded micelles and bacterial deactivation was evaluated. The micelles loaded with TCN are bactericidal; bacteria are killed in less than two minutes of exposure. The most likely interpretation of the data is that the biocide is transferred to the bacteria by repeated micelle/bacteria contacts, and not via the solution. PMID:21275041

  4. Luminescence of impurity-bound excitons in Li6GdB3O9:Ce3+ single crystals

    International Nuclear Information System (INIS)

    The anomalous (τ 6GdB3O9 doped with trivalent cerium ions, has been revealed for the first time and investigated through the low-temperature time-resolved vacuum ultraviolet synchrotron spectroscopy. It was shown that the optical transitions at 6.2 eV are due to electron transfer from the ground 4f1 states of Ce3+ ion onto the autoionized states near the conduction band bottom of a crystal. These transitions lead to the formation of impurity-bound excitons in the form of correlated electron-hole pair, in which the hole component is localized at 4f-level of the cerium ion and an electron component is located at the conduction band bottom in the attractive potential of this hole. It is established that the direct radiative recombination of the cerium impurity-bound exciton leads to a fast broadband emission at 4.25 eV. The energy threshold for creation of the impurity-bound excitons was determined on the basis of the obtained spectroscopic data. We calculated the H(k) functions of distribution of the elementary relaxations over the reaction rate constants and explained on this basis the decay kinetics and quenching processes, not only for the anomalous emission at 4.25 eV, but for the ordinary 5d-4f luminescence at 3.0 eV in Ce3+ ions. The paper discusses the decay channels for the impurity-bound excitons and their influence on the decay kinetics and spectra of luminescence in Li6GdB3O9 crystals.

  5. Magnetized impurity states in metal with degenerate zone. Finite temperature

    International Nuclear Information System (INIS)

    A contribution of impurity atoms into heat capacity, mean magnetization and magnetic susceptibility of solid solutions of metals with a degenerate zone is analytically determined. Measured values for magnetic susceptibility (μ0) and heat capacity (Snp) have shown that in the solutions PbFe the magnetic moment of an impurity center is determined by a high g-factor rather than by a high spin

  6. Magnetic impurities on the surface of a topological insulator

    OpenAIRE

    Liu, Qin; Liu, Chao-Xing; Xu, Cenke; Qi, Xiao-Liang; Zhang, Shou-Cheng

    2008-01-01

    The surface states of a topological insulator are described by an emergent relativistic massless Dirac equation in 2+1 dimensions. In contrast to graphene, there is an odd number of Dirac points, and the electron spin is directly coupled to the momentum. We show that a magnetic impurity opens up a local gap and suppresses the local density of states. Furthermore, the Dirac electronic states mediate an RKKY interaction among the magnetic impurities which is always ferromagnetic, whenever the c...

  7. Effects of Zr impurity on microscopic behavior of Hf metal

    Science.gov (United States)

    Dey, S. K.; Dey, C. C.; Saha, S.

    2016-08-01

    Hf metal with ∼ 3 wt% Zr impurity has been reinvestigated by perturbed angular correlation (PAC) spectroscopy using a LaBr3(Ce)-BaF2 detector set up to understand the microscopic behavior of this metal with temperature. From present measurements, five quadrupole interaction frequencies have been found at room temperature where both pure hcp fraction (∼33%) with 12 nearest neighbor Hf surrounding the probe 181Hf atom and the probe-impurity fraction (∼33%) corresponding to 11 nearest neighbor Hf plus one dissimilar Zr atom are clearly distinguished. At room temperature, the results for quadrupole frequency and asymmetry parameter are found to be ωQ=51.6(4) Mrad/s, η=0.20(4) for the impurity fraction and ωQ=46.8(2) Mrad/s, η=0 for the pure fraction with values of frequency distribution width δ=0 for both components. At 77 K, only 1 NN Zr impurity (∼93%) and pure hcp (∼7%) components have been found with a value of δ ∼ 10% for the impurity fraction. A drastic change in microstructural configuration of Hf metal is observed at 473 K where the impurity fraction increases to ∼ 50% and the pure hcp fraction reduces to ∼ 15% with abrupt changes in quadrupole frequencies for both components. The pure fraction then increases with temperature and enhances to ∼50% at 973 K. In the temperature range 473-973 K, quadrupole frequencies for both components are found to decrease slowly with temperature. Using the Arrhenius relation, binding energy (B) for the probe-impurity pair and the entropy of formation are measured from temperature dependent fractions of probe-impurity and pure hcp in the temperature range 473-773 K. The three other minor components found at different temperatures are attributed to crystalline defects.

  8. Electron coherence at low temperatures: The role of magnetic impurities

    OpenAIRE

    Saminadayar, Laurent; Mohanty, Pritiraj; Webb, Richard A.; Degiovanni, Pascal; Bäuerle, Christopher

    2007-01-01

    We review recent experimental progress on the saturation problem in metallic quantum wires. In particular, we address the influence of magnetic impurities on the electron phase coherence time. We also present new measurements of the phase coherence time in ultra-clean gold and silver wires and analyse the saturation of \\tauphi in these samples, cognizant of the role of magnetic scattering. For the cleanest samples, Kondo temperatures below 1 mK and extremely-small magnetic-impurity concentrat...

  9. Phase Transition of Spin-Peierls Systems with Impurities

    Institute of Scientific and Technical Information of China (English)

    XU Bo-Wei; DING Guo-Hui; YE Fei

    2000-01-01

    The quasi-one-dimensional spin-Peierls(SP) systems with impurities are studied in their bosonized form. The spins of the dimerized state are bounded into singlets with an SP gap, while the impurities of doped systems will induce fluctuations of the coupling strength between the spins at different sites and break some pairs of spin singlets. The doping suppresses the dimerized SP state and induces a Kosterlitz-Thouless phase transition from the dimerized state into the undimerized one.

  10. Method of plasma impurity control without magnetic divertor

    International Nuclear Information System (INIS)

    A method is proposed for controlling impurity generation in a tokomak by skimming and pumping the scrape-off. This method avoids many of the complications of a magnetic divertor, such as specially configured magnetic fields, toroidal symmetry, and inefficient use of toroidal field volume. Estimates are given for operating parameters. Impurity reductions of as much as a factor of 10 should be achievable. The necessary high-capacity pump would employ either titanium gettering or cryocondensation

  11. Impurity control and corrosion resistance of magnesium-aluminum alloy

    Energy Technology Data Exchange (ETDEWEB)

    Liu, M. [GM China Lab; Song, GuangLing [ORNL

    2013-01-01

    The corrosion resistance of magnesium alloys is very sensitive to the contents of impurity elements such as iron. In this study, a series of diecast AXJ530 magnesium alloy samples were prepared with additions of Mn and Fe. Through a comprehensive phase diagram calculation and corrosion evaluation, the mechanisms for the tolerance limit of Fe in magnesium alloy are discussed. This adds a new dimension to control the alloying impurity in terms of alloying composition design and casting conditions.

  12. Lead-bismuth coolant cleaning from solid impurities using filtration

    International Nuclear Information System (INIS)

    The factors, influencing the efficiency of the circuit cleaning of the lead-bismuth coolant from the solid phase impurities through filtration, are analyzed. The choice of the filtration material is substantiated proceeding from the properties of the given coolant as a dispersion system. The results of the experiments on determining the efficiency of cleaning capacity by retained impurities, throughput and regeneration made it possible to develop the industrial filters for the NPU needs

  13. The effects of naturally occurring impurities in rock salt

    Indian Academy of Sciences (India)

    Alina-Mihaela Badescu; Alexandra Saftoiu

    2014-09-01

    In this paper we investigate the effect that naturally occurring impurities in salt mines have both on effective permittivity of the medium and on radio wave propagation at ∼200 MHz. The effective permittivity is determined based on the dielectric properties of salt and the characteristics of the main impurities. We conclude that at such frequencies the scattering is negligible compared to absorptions. The effect of trapped water in different forms is also evaluated.

  14. The effect of magnetic impurity scattering in Au films

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The magnetic impurity scattering plays an important role in the phase coherence behavior of thin films.By using the thickness and disorder dependences of the low temperature logarithmic anomaly in resistivity we are able to determine the concentration of magnetic impurities in Au films and demonstrate that the low temperature saturation or plateau in phase decoherence time is closely related with the Kondo effect.

  15. Impurity profiling of methamphetamine hydrochloride drugs seized in the Philippines.

    Science.gov (United States)

    Dayrit, Fabian M; Dumlao, Morphy C

    2004-08-11

    Methamphetamine hydrochloride is one of the most widely used illicit drugs in the Philippines. In this study, we describe the application of cluster analysis of trace impurities in the profiling of the seized methamphetamine drug samples. Thirty milligrams of a homogenized drug sample were dissolved in 1 mL of pH 10.5 buffer solution and extracted with ethyl acetate containing three internal standards. The trace impurities were identified using gas chromatography-mass spectrometry (GC-MS) and quantified by gas chromatography with a flame ionization detector (GC-FID). Following previously reported methodologies, 30 impurity peaks were selected from the GC-FID chromatograms. The peak areas and retention times were referenced to the internal standards. The peak areas of the selected peaks were then grouped for cluster analysis. In order to check for consistency of clustering, two further cluster analyses were performed using 40 and 50 impurity peaks. Changes in clustering were observed in going from 30 to 40 impurity peaks, while analyses using 40 and 50 impurity peaks gave similar results. Thus, for the seized drug samples used in this study, cluster analysis using at least 40 impurity peaks showed better consistency of clustering as compared to analysis using 30 peaks only. Ten of the impurity peaks were identified, of which four were identified for the first time in methamphetamine drug samples. These are p-bromotoluene, N-benzyl amphetamine, N-ethyl amphetamine, and N-ethyl methamphetamine. The presence of phenyl-2-propanone (P2P), N,N-dimethyl amphetamine, and N-formyl amphetamine is indicative that these casework samples were synthesized using the Leuckart method. PMID:15240018

  16. E-Block: A Tangible Programming Tool with Graphical Blocks

    OpenAIRE

    Danli Wang; Yang Zhang; Shengyong Chen

    2013-01-01

    This paper designs a tangible programming tool, E-Block, for children aged 5 to 9 to experience the preliminary understanding of programming by building blocks. With embedded artificial intelligence, the tool defines the programming blocks with the sensors as the input and enables children to write programs to complete the tasks in the computer. The symbol on the programming block's surface is used to help children understanding the function of each block. The sequence information is transfer...

  17. Poloidal asymmetries of heavy impurities in the ASDEX upgrade plasma

    International Nuclear Information System (INIS)

    For heavy and highly charged impurities multiple mechanisms exist that produce non-constant impurities densities on the flux surfaces. As for neoclassical and turbulent transport models such an asymmetry is highly importance an effort is launched to experimentally characterize the asymmetries comparing them with theoretical expectations. In the ASDEX upgrade tokamak (AUG) is routinely observed increase of outboard tungsten density in fast rotating plasma. This asymmetry is caused by the centrifugal force pushing tungsten ions outward due to its high mass. Furthermore, the high charge makes heavy impurities sensitive to poloidal variations of the plasma potential. The variation can be generated by magnetic trapped ions heated by RF heating. In such a case, the presence of an inboard asymmetry or at least the absence of an outboard asymmetry due to the centrifugal force can be observed. Finally, ion-impurity friction enhanced by the large charge of the impurity ions may cause a relatively weak up-down asymmetry of the impurity density. The aim of this poster is to show first evidence of these asymmetries in the AUG plasmas, the description of the used methodology, and to compare with theoretical models based on the parallel force balance.

  18. Effects of PEO-PPO diblock impurities on the cubic structure of aqueous PEO-PPO-PEO pluronics micelles: fcc and bcc ordered structures in F127

    DEFF Research Database (Denmark)

    Mortensen, Kell; Pedersen, Walther Batsberg; Hvidt, S.

    2008-01-01

    We report on structural properties of PEO-PPO-PEO type of triblock block copolymers (Pluronics F127) with special emphasis on the effect of diblock PEO-PPO impurities on the ordered gel phase. Commercial F127 polymers contain as received roughly 20% PEO-PPO diblock and 80% PEO-PPO-PEO triblock...... copolymers. Aqueous solutions of F127 copolymers used as received form fee ordered micellar structure. Copolymers depleted with respect to the diblock impurity, resulting in a pure PEO-PPO-PEO triblock copolymer system, form bcc ordered micelles within the major parts of the gel phase. However, close to the...... disorder-to-order transition, the purified F 127 copolymer system also forms fcc structure, thus giving rise to a novel sequence of micellar phases: disorder-fcc-bcc. This is the phase sequence predicted theoretically for pure block copolymer melts....

  19. Reconfigurable wave band structure of an artificial square ice

    Science.gov (United States)

    Iacocca, Ezio; Gliga, Sebastian; Stamps, Robert L.; Heinonen, Olle

    2016-04-01

    Artificial square ices are structures composed of magnetic nanoelements arranged on the sites of a two-dimensional square lattice, such that there are four interacting magnetic elements at each vertex, leading to geometrical frustration. Using a semianalytical approach, we show that square ices exhibit a rich spin-wave band structure that is tunable both by external magnetic fields and the magnetization configuration of individual elements. Internal degrees of freedom can give rise to equilibrium states with bent magnetization at the element edges leading to characteristic excitations; in the presence of magnetostatic interactions these form separate bands analogous to impurity bands in semiconductors. Full-scale micromagnetic simulations corroborate our semianalytical approach. Our results show that artificial square ices can be viewed as reconfigurable and tunable magnonic crystals that can be used as metamaterials for spin-wave-based applications at the nanoscale.

  20. Effects of electron- and impurity-ion-LO phonon couples on the impurity states in cylindrical quantum wires

    Institute of Scientific and Technical Information of China (English)

    Zhao Zengru; Liang Xixia

    2009-01-01

    The variational method and the effective mass approximation are used to calculate the phonon effects on the hydrogenic impurity states in a cylindrical quantum wire with finite deep potential by taking both the couplings of the electron-confined bulk longitudinal optical (LO) phonons and the impurity-ion-LO phonons into account.The binding energies and the phonon contributions are calculated as functions of the transverse dimension of the quantum wire. The results show that the polaronic effect induced by the electron-LO phonon coupling and the screening effect induced by the impurity-ion-LO phonon coupling tend to compensate each other and the total effects reduce the impurity binding energies.

  1. Effects of Block Scheduling

    Directory of Open Access Journals (Sweden)

    William R. Veal

    1999-09-01

    Full Text Available This study examined the effects of a tri-schedule on the academic achievement of students in a high school. The tri-schedule consists of traditional, 4x4 block, and hybrid schedules running at the same time in the same high school. Effectiveness of the schedules was determined from the state mandated test of basic skills in reading, language, and mathematics. Students who were in a particular schedule their freshman year were tested at the beginning of their sophomore year. A statistical ANCOVA test was performed using the schedule types as independent variables and cognitive skill index and GPA as covariates. For reading and language, there was no statistically significant difference in test results. There was a statistical difference mathematics-computation. Block mathematics is an ideal format for obtaining more credits in mathematics, but the block format does little for mathematics achievement and conceptual understanding. The results have content specific implications for schools, administrations, and school boards who are considering block scheduling adoption.

  2. Spice Blocks Melanoma Growth

    Science.gov (United States)

    Science Teacher, 2005

    2005-01-01

    Curcumin, the pungent yellow spice found in both turmeric and curry powders, blocks a key biological pathway needed for development of melanoma and other cancers, according to a study that appears in the journal Cancer. Researchers from The University of Texas M. D. Anderson Cancer Center demonstrate how curcumin stops laboratory strains of…

  3. Contaminated soil concrete blocks

    NARCIS (Netherlands)

    Korte, de A.C.J.; Brouwers, H.J.H.; Limbachiya, Mukesh C.; Kew, Hsein Y.

    2009-01-01

    According to Dutch law the contaminated soil needs to be remediated or immobilised. The main focus in this article is the design of concrete blocks, containing contaminated soil, that are suitable for large production, financial feasible and meets all technical and environmental requirements. In ord

  4. Systematic electronic-structure investigation of substitutional impurity diffusion and flux coupling in bcc iron

    Science.gov (United States)

    Messina, Luca; Nastar, Maylise; Sandberg, Nils; Olsson, Pär

    2016-05-01

    The diffusion properties of a wide range of impurities (transition metals and Al, Si, and P) in ferritic alloys are here investigated by means of a combined ab initio-atomic diffusion theory approach. The flux-coupling mechanisms and the solute-diffusion coefficients are inferred from electronic-structure calculations of solute-defect interactions and microscopic jump frequencies. All properties except the second-nearest-neighbor binding energy are found to have a characteristic bell shape as a function of the d -band filling for the 4 d and 5 d series, and an M shape for the 3 d row because of the out-of-trend behavior of Mn. The solute jump frequencies are governed by compressibility, which makes diffusion of large solutes faster, although this effect is partially compensated for by lower attempt frequencies and larger correlations with the vacancy. Diffusion coefficients are predicted in a wide temperature range, far below the experimentally accessible temperatures. In accordance with experiments, Co is found to be a slow diffuser in iron, and the same behavior is predicted for Re, Os, and Ir impurities. Finally, flux-coupling phenomena depend on the iron jump frequencies next to a solute atom, which are mainly controlled by similar electronic interactions to those determining the binding energies. Vacancy drag and solute enrichment at sinks systematically arise below a solute-dependent temperature threshold, directly correlated with the electronic-level interactions at the equilibrium and the saddle-point states. Early transition metals with repulsive second-nearest-neighbor interactions also diffuse via vacancy drag, although they show a lower temperature threshold than the late metals. This confirms that drag is the most common solute-vacancy coupling mechanism in iron at low temperatures, and this is likely to be confirmed as well for impurity diffusion in other transition metals.

  5. Development and Validation of HPLC and HPTLC Methods for Determination of Cefoperazone and Its Related Impurities.

    Science.gov (United States)

    Abdelaleem, Eglal A; Naguib, Ibrahim A; Zaazaa, Hala E; Hussein, Essraa A

    2016-02-01

    Validated sensitive and highly selective methods were developed for the quantitative determination of cefoperazone sodium (CEF) in the presence of its reported impurities; 7-aminocephalosporanic acid (7-ACA) and 5-mercapto-1-methyl-tetrazole (5-MER). Method A is high-performance liquid chromatography (HPLC), where the mixture of CEF and the reported impurities; 7-ACA and 5-MER were separated on a C8 column (5 µm ps, 250 mm × 4.6 i.d.) using methanol:0.05 M KH2PO4 buffer (22.5:77.5 v/v, pH 7.5) as a mobile phase. The three components were detected at 254 nm with a concentration range of 10-90 µg mL(-1) and the mean percentage recovery 99.67% (SD 1.465). Method B is high-performance thin layer chromatography (HPTLC), where the mixture of CEF and the reported impurities were separated on silica gel HPTLC F254 plates using (acetone:methanol:ethyl acetate:2% sodium lauryl sulfate:glacial acetic acid) (3:2:3:0.8:0.2, by volume) as a developing system and scanning at 254 nm over a concentration range of 1-10 µg per band with the mean percentage recovery 99.95% (SD 1.335). The proposed methods were statistically compared with a reported HPLC method with no significant difference regarding accuracy and precision; indicating the ability of the proposed methods to be reliable and suitable for routine analysis of drug product. The proposed HPTLC method proved to be more sensitive, while the HPLC gave more reproducible results besides saving time. PMID:26306573

  6. Local moment approach as a quantum impurity solver for the Hubbard model

    Science.gov (United States)

    Barman, Himadri

    2016-07-01

    The local moment approach (LMA) has presented itself as a powerful semianalytical quantum impurity solver (QIS) in the context of the dynamical mean-field theory (DMFT) for the periodic Anderson model and it correctly captures the low-energy Kondo scale for the single impurity model, having excellent agreement with the Bethe ansatz and numerical renormalization group (NRG) results. However, the most common correlated lattice model, the Hubbard model, has not been explored well within the LMA+DMFT framework beyond the insulating phase. Here in our work, within the framework we complete the filling-interaction phase diagram of the single band Hubbard model at zero temperature. Our formalism is generic to any particle filling and can be extended to finite temperature. We contrast our results with another QIS, namely the iterated perturbation theory (IPT) and show that the second spectral moment sum rule improves better as the Hubbard interaction strength grows stronger in LMA, whereas it severely breaks down after the Mott transition in IPT. For the metallic case, the Fermi liquid (FL) scaling agreement with the NRG spectral density supports the fact that the FL scale emerges from the inherent Kondo physics of the impurity model. We also show that, in the metallic phase, the FL scaling of the spectral density leads to universality which extends to infinite frequency range at infinite correlation strength (strong coupling). At large interaction strength, the off half-filling spectral density forms a pseudogap near the Fermi level and filling-controlled Mott transition occurs as one approaches the half-filling. As a response property, we finally study the zero temperature optical conductivity and find universal features such as absorption peak position governed by the FL scale and a doping independent crossing point, often dubbed the isosbestic point in experiments.

  7. Edit Distance with Block Deletions

    OpenAIRE

    Dana Shapira; Storer, James A.

    2011-01-01

    Several variants of the edit distance problem with block deletions are considered. Polynomial time optimal algorithms are presented for the edit distance with block deletions allowing character insertions and character moves, but without block moves. We show that the edit distance with block moves and block deletions is NP-complete (Nondeterministic Polynomial time problems in which any given solution to such problem can be verified in polynomial time, and any NP problem can be converted into...

  8. Fermion-Scalar Conformal Blocks

    CERN Document Server

    Iliesiu, Luca; Poland, David; Pufu, Silviu S; Simmons-Duffin, David; Yacoby, Ran

    2015-01-01

    We compute the conformal blocks associated with scalar-scalar-fermion-fermion 4-point functions in 3D CFTs. Together with the known scalar conformal blocks, our result completes the task of determining the so-called `seed blocks' in three dimensions. Conformal blocks associated with 4-point functions of operators with arbitrary spins can now be determined from these seed blocks by using known differential operators.

  9. Effect of impurity correlation in heavily modulation-doped quantum wires

    International Nuclear Information System (INIS)

    A theory is given of the electronic properties of modulation-doped quantum wires which undergo a thermal treatment, taking into account Coulomb interactions among the impurities in the sample preparation. The impurity correlation weakens their field and is enhanced when elevating the doping level, lowering the freezing temperature for impurity diffusion, and reducing the size of the impurity system. In the limiting case of a 1D impurity system, the ionic correlation may suppress the impurity field even at a low doping level. For a very thin impurity system, the electron mobility of the wire may be increased by up to some orders of magnitude at a high doping level. (author)

  10. Zeroth Order Phase Transition in a Holographic Superconductor with Single Impurity

    CERN Document Server

    Zeng, Hua Bi

    2014-01-01

    We studied the single normal impurity effect in superconductor by using the holographic method. When the size of impurity is much smaller compared to the host superconductor, we reproduced the Anderson theorem, which states that a conventional s-wave superconductor is robust to a normal (non-magnetic) impurity with small impurity strength or impurities with small concentration. While by increasing the size of impurity in a fixed host superconductor we also find a decrease $T_c$ of the host superconductor, the phase transition at the critical impurity strength is of zeroth order.

  11. Release of impurities from structural defects in polycrystalline silicon solar cells

    Energy Technology Data Exchange (ETDEWEB)

    McHugo, S.A. [Lawrence Berkeley National Lab., CA (United States). Advanced Light Source; Imaizumi, M. [Toyota Technological Inst., Nagoya (Japan)

    1997-04-01

    It is critical to understand the behavior of metallic impurities in polycrystalline silicon used for solar cells. These impurities significantly increase the minority carrier recombination rate and, in turn, degrade cell performance. Impurity gettering is a commonly used method to remove these impurities from the material, however, past work has suggested that impurity release from structural defects drastically limits the gettering process. Presently, there is only a limited understanding of impurity release from structural defects. In this work, a correlation between structural defects and the location of metal impurities in as-grown material is established and the release of nickel and copper from structural defects in polycrystalline silicon was studied in as-grown material and after sequential thermal treatments which dissolve the impurities into the silicon matrix. Synchrotron-based x-ray fluorescence impurity mapping with spatial resolution of {approx} 1 {micro}m, was used to determine impurity distributions after each thermal treatment.

  12. Quantum entanglement investigation on impurity effects in the transverse Ising chain

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Xuchu [Key Laboratory of Functional Materials and Devices for Special Environments of CAS, Xinjiang Technical Institute of Physics & Chemistry of CAS, 40-1 South Beijing Road, Urumqi 830011 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Si, Tieyan [Harbin Institution of Technology, 92 West Dazhi Street, Nan Gang District, Harbin 150001 (China); Yang, Zhihua, E-mail: zhyang@ms.xjb.ac.cn [Key Laboratory of Functional Materials and Devices for Special Environments of CAS, Xinjiang Technical Institute of Physics & Chemistry of CAS, 40-1 South Beijing Road, Urumqi 830011 (China)

    2015-04-01

    The impurity effects of the transverse Ising spin model with a magnetic impurity are investigated via the correlation function and entanglement on the basis of an exact solution. The non-analytical transition point from an ordered phase to a disorder phase is significantly shifted by the impurity coupling with local host spins. The maximal entanglement point which usually appears around the critical point shows strong dependence on the impurity coupling strength with local host spin and the independent transverse field upon the impurity itself. Quantum entanglement in disordered spin phase is much stronger than that in ordered spin phase. The exact concurrence of impurity spin with local host spin suddenly increases to a large value from zero at a threshold value. The maximal entanglement point between impurity and local host spin increases as the impurity coupling strength increases. So the impurity coupling strength and local transverse field on the impurity can control position of critical point and maximal entanglement point.

  13. Quantum entanglement investigation on impurity effects in the transverse Ising chain

    International Nuclear Information System (INIS)

    The impurity effects of the transverse Ising spin model with a magnetic impurity are investigated via the correlation function and entanglement on the basis of an exact solution. The non-analytical transition point from an ordered phase to a disorder phase is significantly shifted by the impurity coupling with local host spins. The maximal entanglement point which usually appears around the critical point shows strong dependence on the impurity coupling strength with local host spin and the independent transverse field upon the impurity itself. Quantum entanglement in disordered spin phase is much stronger than that in ordered spin phase. The exact concurrence of impurity spin with local host spin suddenly increases to a large value from zero at a threshold value. The maximal entanglement point between impurity and local host spin increases as the impurity coupling strength increases. So the impurity coupling strength and local transverse field on the impurity can control position of critical point and maximal entanglement point

  14. Regularizing Inverse Preconditioners for Symmetric Band Toeplitz Matrices

    Directory of Open Access Journals (Sweden)

    Lotti G

    2007-01-01

    Full Text Available Image restoration is a widely studied discrete ill-posed problem. Among the many regularization methods used for treating the problem, iterative methods have been shown to be effective. In this paper, we consider the case of a blurring function defined by space invariant and band-limited PSF, modeled by a linear system that has a band block Toeplitz structure with band Toeplitz blocks. In order to reduce the number of iterations required to obtain acceptable reconstructions, in 13 an inverse Toeplitz preconditioner for problems with a Toeplitz structure was proposed. The cost per iteration is of operations, where is the pixel number of the 2D image. In this paper, we propose inverse preconditioners with a band Toeplitz structure, which lower the cost to and in experiments showed the same speed of convergence and reconstruction efficiency as the inverse Toeplitz preconditioner.

  15. Regularizing Inverse Preconditioners for Symmetric Band Toeplitz Matrices

    Directory of Open Access Journals (Sweden)

    O. Menchi

    2007-01-01

    Full Text Available Image restoration is a widely studied discrete ill-posed problem. Among the many regularization methods used for treating the problem, iterative methods have been shown to be effective. In this paper, we consider the case of a blurring function defined by space invariant and band-limited PSF, modeled by a linear system that has a band block Toeplitz structure with band Toeplitz blocks. In order to reduce the number of iterations required to obtain acceptable reconstructions, in 13 an inverse Toeplitz preconditioner for problems with a Toeplitz structure was proposed. The cost per iteration is of O(n2logn operations, where n2 is the pixel number of the 2D image. In this paper, we propose inverse preconditioners with a band Toeplitz structure, which lower the cost to O(n2 and in experiments showed the same speed of convergence and reconstruction efficiency as the inverse Toeplitz preconditioner.

  16. Ka Band Phase Locked Loop Oscillator Dielectric Resonator Oscillator for Satellite EHF Band Receiver

    Directory of Open Access Journals (Sweden)

    S. Coco

    2008-01-01

    Full Text Available This paper describes the design and fabrication of a Ka Band PLL DRO having a fundamental oscillation frequency of 19.250 GHz, used as local oscillator in the low-noise block of a down converter (LNB for an EHF band receiver. Apposite circuital models have been created to describe the behaviour of the dielectric resonator and of the active component used in the oscillator core. The DRO characterization and measurements have shown very good agreement with simulation results. A good phase noise performance is obtained by using a very high Q dielectric resonator.

  17. Enhanced spin Hall ratios by Al and Hf impurities in Pt thin films

    Science.gov (United States)

    Nguyen, Minh-Hai; Zhao, Mengnan; Ralph, Daniel C.; Buhrman, Robert A.

    The spin Hall effect (SHE) in Pt has been reported to be strong and hence promising for spintronic applications. In the intrinsic SHE mechanism, which has been shown to be dominant in Pt, the spin Hall conductivity σSH is constant, dependent only on the band structure of the spin Hall material. The spin Hall ratio θSH =σSH . ρ , on the other hand, should be proportional to the electrical resistivity ρ of the spin Hall layer. This suggests the possibility of enhancing the spin Hall ratio by introducing additional diffusive scattering to increase the electrical resistivity of the spin Hall layer. Our previous work has shown that this could be done by increasing the surface scattering by growing thinner Pt films in contact with higher resistivity materials such as Ta. In this talk, we discuss another approach: to introduce impurities of metals with negligible spin orbit torque into the Pt film. Our PtAl and PtHf alloy samples exhibit strong enhancement of the spin Hall torque efficiency with impurity concentration due to increased electrical resistivity. Supported in part by Samsung Electronics.

  18. Vacuum ultraviolet spectroscopic study of plasma impurities in the Tokapole II poloidal divertor experiment

    International Nuclear Information System (INIS)

    The main diagnostics were two vacuum ultraviolet spectrometers, which were used to identify impurities, observe impurity behavior, and measure the line radiated power. Impurity concentrations and the effects of impurities on gross plasma characteristics were determined with an impurity doping technique. The electron temperature was estimated by a time dependent coronal model describing the time history of the oxygen ions, and the ion temperature was obtaind from Doppler broadening measurements. Energy loss processes were studied with a power balance analysis

  19. Entanglement of an impurity and conduction spins in the Kondo model

    OpenAIRE

    Oh, Sangchul; Kim, Jaewan

    2006-01-01

    Based on Yosida's ground state of the single-impurity Kondo Hamiltonian, we study three kinds of entanglement between an impurity and conduction electron spins. First, it is shown that the impurity spin is maximally entangled with all the conduction electrons. Second, a two-spin density matrix of the impurity spin and one conduction electron spin is given by a Werner state. We find that the impurity spin is not entangled with one conduction electron spin even within the Kondo screening length...

  20. The carbon impurity particle transport in ohmic discharges on the HT-7 tokamak

    Institute of Scientific and Technical Information of China (English)

    Zhou Qian; Wan Bao-Nian; Wu Zhen-Wei; Huang Juan

    2005-01-01

    The line-integrated optical measurement of impurity radiation profiles for the study of light impurity transport is performed in the HT-7 tokamak. The carbon impurity line emissivity is obtained by Abel inversion. The radial transport behaviours of carbon impurities at different central line averaged electron densities (-ne) are investigated in ohmic discharges. The diffusion coefficient Dk(r), the convection velocity Wk(r) and the total flux of the impurity densities.

  1. NCCN Evidence Blocks.

    Science.gov (United States)

    Carlson, Robert W; Jonasch, Eric

    2016-05-01

    NCCN has developed a series of Evidence Blocks: graphics that provide ratings for each recommended treatment regimen in terms of efficacy, toxicity, quality and consistency of the supporting data, and affordability. The NCCN Evidence Blocks are currently available in 10 tumor types within the NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines). At a glance, patients and providers can understand how a given treatment was assessed by the NCCN Guidelines Panel and get a sense of how a given treatment may match individual needs and preferences. Robert W. Carlson, MD, CEO of NCCN, described the reasoning behind this new feature and how the tool is used, and Eric Jonasch, MD, Professor of Genitourinary Medical Oncology at The University of Texas MD Anderson Cancer Center, and Vice Chair of the NCCN Kidney Cancer Panel, described its applicability in the management of metastatic renal cell carcinoma. PMID:27226499

  2. Right bundle branch block

    DEFF Research Database (Denmark)

    Bussink, Barbara E; Holst, Anders Gaarsdal; Jespersen, Lasse;

    2013-01-01

    AimsTo determine the prevalence, predictors of newly acquired, and the prognostic value of right bundle branch block (RBBB) and incomplete RBBB (IRBBB) on a resting 12-lead electrocardiogram in men and women from the general population.Methods and resultsWe followed 18 441 participants included in...... men vs. 0.5%/2.3% in women, P <0.001). Significant predictors of newly acquired RBBB were male gender, increasing age, high systolic blood pressure, and presence of IRBBB, whereas predictors of newly acquired IRBBB were male gender, increasing age, and low BMI. Right bundle branch block was associated...... with significantly increased all-cause and cardiovascular mortality in both genders with age-adjusted hazard ratios (HR) of 1.31 [95% confidence interval (CI), 1.11-1.54] and 1.87 (95% CI, 1.48-2.36) in the gender pooled analysis with little attenuation after multiple adjustment. Right bundle branch...

  3. SNUPPS power block modelling

    International Nuclear Information System (INIS)

    A series of models is being built and used as tools in the design of the SNUPPS Standard Power Block. The modelling programme includes both preliminary and final design models, a construction sequence mode, and additional models used to study various features of the design. The design of a standard power block unit has necessitated design definition which is more detailed than that customarily used in the design of nuclear power stations. One innovation is the use of engineering models as a primary design tool in the layout of process piping, preparation of isometric drawings, design of small components which are customarily designed in the field during construction. Development of a standard construction sequence and construction work plan is another innovation. (author)

  4. Influence of magnetic Co impurities on the optical interband transitions in ZnO

    Energy Technology Data Exchange (ETDEWEB)

    Boukortt, A. [Institut Materiaux Microelectronique Nanosciences de Provence, Faculte St. Jerome, Case 142, 13397 Marseille Cedex 20 (France); Mostaganem University, Faculty of Science and Technology, Genie Electric Department, 27000 Mostaganem (Algeria); Hayn, R.; Virot, F. [Institut Materiaux Microelectronique Nanosciences de Provence, Faculte St. Jerome, Case 142, 13397 Marseille Cedex 20 (France); Zaoui, A. [Modelling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes (Algeria)

    2011-04-15

    Density functional calculations of Co-doped ZnO and a theoretical analysis of the optical interband transitions are presented. That compound is potentially important for spintronics and magneto-optoelectronic applications. Using the full potential linearized augmented plane wave (PW) method we analyze the dielectric functions (real and imaginary part) to understand the optical interband transitions. We show that the local spin-density approximation (LSDA) has severe drawbacks like a spurious Drude-like peak and a wrong position of the 3d bands which may be repaired by the LSDA + U method. We show the appearance of new peaks in the optical conductivity related with the magnetic impurities which we analyze in detail. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  5. Tomographic imaging system for measuring impurity line emission in a field-reversed configurationa)

    Science.gov (United States)

    Roche, T.; Bolte, N.; Garate, E.; Heidbrink, W. W.; McWilliams, R.; Wessel, F.

    2012-10-01

    A 16 chord optical tomography system has been developed and implemented in the flux coil generated-field reversed configuration (FRC). The chords are arranged in two fans of eight, which cover ˜35% of the vessel area at the midplane. Each illuminate separate photomultiplier tubes (PMTs) which are fitted with narrow band-pass filters. In this case, filters are centered at 434.8 nm to measure emission from singly ionized argon. PMT crosstalk is negligible. Background noise due to electron radiation and Hγ line radiation is time-dependent, 2D emissivity profiles of the impurity ions. Analysis of these data show radial, cross-field diffusion to be in the range of 10-103 m2/s during FRC equilibrium.

  6. Origin of localized states in graphite: Indirect photoemission processes or impurities?

    Energy Technology Data Exchange (ETDEWEB)

    Davila, M.E. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas (CSIC), C/ Sor Juana Ines de la Cruz, 3, 28049 Madrid (Spain)], E-mail: mdavila@icmm.csic.es; Valbuena, M.A.; Pantin, V. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas (CSIC), C/ Sor Juana Ines de la Cruz, 3, 28049 Madrid (Spain); Avila, J. [Synchrotron SOLEIL, Orme des Merisiers, Saint Aubin BP 48, 91192 Gif sur Yvette Cedex (France); Esquinazi, P. [Department of Superconductivity and Magnetism, Leipzig University (Germany); Asensio, M.C. [Synchrotron SOLEIL, Orme des Merisiers, Saint Aubin BP 48, 91192 Gif sur Yvette Cedex (France)

    2007-10-31

    The electronic band structure of different types of graphite samples have been investigated in order to identify the origin of non-dispersive density of states recently reported in the literature. A systematic series of synchrotron radiation angle resolved photoemission spectroscopy (ARPES) measurements on graphite single crystal, highly oriented graphite (HOPG) and epitaxial grown graphite single crystal on 6H-SiC(0 0 0 1) samples, have been carried out as well as compared with theoretical tight binding calculations. Our results indicate that these localized states are present in all the graphite-investigated samples showing the same non-dispersive character and at the same binding energies. The photoemission data taken at several photon energies demonstrate that these states are not surface states nor due to indirect photoemission processes. It seems that they are closely related to the level of impurities present in the studied samples.

  7. Luminescence of Single Crystals Cadmium Bromide Doped with Impurities of Argentum

    Directory of Open Access Journals (Sweden)

    N.V. Stetsyk

    2014-06-01

    Full Text Available Temperature behaviors of X-ray luminescence (XL or RL, photoluminescence (PL, and thermoluminescence (TL were studied in CdBr2 : Ag+ single crystals from room temperature to liquid nitrogen temperature. The luminescence is practically absent in the interband (including X-rays excitation crystals CdBr2 : Ag+, but manifested in the excitation light from the region 3.68 eV. In this region of the spectrum selective absorption band of silver impurity centers is observed. It was found that the crystals CdBr2 : Ag+ are sensitive to the action of X-rays and ultraviolet light through the flow of photochemical reactions (FHR in these crystals.

  8. SUPERFICIAL CERVICAL PLEXUS BLOCK

    Directory of Open Access Journals (Sweden)

    Komang Mega Puspadisari

    2014-01-01

    Full Text Available Superficial cervical plexus block is one of the regional anesthesia in  neck were limited to thesuperficial fascia. Anesthesia is used to relieve pain caused either during or after the surgery iscompleted. This technique can be done by landmark or with ultrasound guiding. The midpointof posterior border of the Sternocleidomastoid was identified and the prosedure done on thatplace or on the level of cartilage cricoid.

  9. Growth, Endlessness, Blocks

    OpenAIRE

    Nabata, Avery Misuzu

    2014-01-01

    Growth, Endlessness, Blocks is a sculptural installation comprised of a series of wood structures of various scales. Large sections of drywall function as extensions of the gallery walls. Each structure balances a number of different physical characteristics that are tied to the act of making. Balance and presence combine in a disconcerting way giving the viewer a sense of uneasiness and a moment finely tuned by the artist. The artist seeks to embody the role of the factory fabricator as a me...

  10. A UWB Band-Pass Antenna with Triple-Notched Band Using Common Direction Rectangular Complementary Split-Ring Resonators

    OpenAIRE

    Bo Yan; Di Jiang; Ruimin Xu; Yuehang Xu

    2013-01-01

    A novel ultrawideband (UWB) antenna which has a triple-band notch function is presented. The proposed antenna can block interfering signals from C-band satellite communication systems, IEEE802.11a, and HIPERLAN/2 WLAN systems for example. The antenna is excited by using novel common direction rectangular complementary split-ring resonators (CSRR) fabricated on radiating patch of the dielectric substrate with coplanar waveguide (CPW) feed strip line. The voltage standing wave ratio (VSWR) of t...

  11. Donor impurity states and related optical response in a lateral coupled dot-ring system under applied electric field

    Energy Technology Data Exchange (ETDEWEB)

    Correa, J.D. [Departamento de Ciencias Básicas, Universidad de Medellín, Medellín (Colombia); Mora-Ramos, M.E. [Centro de Investigación en Ciencias, Instituto de Ciencias Básicas y Aplicadas, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, CP 62209 Cuernavaca, Morelos (Mexico); Duque, C.A., E-mail: cduque@fisica.udea.edu.co [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)

    2015-09-01

    A study on the effects of an externally applied electric field on the linear optical absorption and relative refractive index change associated with transitions between off-center donor impurity states in laterally coupled quantum dot-ring system is reported. Electron states are calculated within the effective mass and parabolic band approximations by means of an exact diagonalization procedure. The states and the optical response in each case show significant sensitivity to the geometrical distribution of confining energies as well as to the strength of the applied field.

  12. Donor impurity states and related optical response in a lateral coupled dot-ring system under applied electric field

    International Nuclear Information System (INIS)

    A study on the effects of an externally applied electric field on the linear optical absorption and relative refractive index change associated with transitions between off-center donor impurity states in laterally coupled quantum dot-ring system is reported. Electron states are calculated within the effective mass and parabolic band approximations by means of an exact diagonalization procedure. The states and the optical response in each case show significant sensitivity to the geometrical distribution of confining energies as well as to the strength of the applied field

  13. E-Block: A Tangible Programming Tool with Graphical Blocks

    Directory of Open Access Journals (Sweden)

    Danli Wang

    2013-01-01

    Full Text Available This paper designs a tangible programming tool, E-Block, for children aged 5 to 9 to experience the preliminary understanding of programming by building blocks. With embedded artificial intelligence, the tool defines the programming blocks with the sensors as the input and enables children to write programs to complete the tasks in the computer. The symbol on the programming block's surface is used to help children understanding the function of each block. The sequence information is transferred to computer by microcomputers and then translated into semantic information. The system applies wireless and infrared technologies and provides user with feedbacks on both screen and programming blocks. Preliminary user studies using observation and user interview methods are shown for E-Block's prototype. The test results prove that E-Block is attractive to children and easy to learn and use. The project also highlights potential advantages of using single chip microcomputer (SCM technology to develop tangible programming tools for children.

  14. Impurities in Silicon Nanocrystals: The intentional and the inherent

    Science.gov (United States)

    Rowe, David J.

    Silicon nanocrystals (SiNCs) have become an important class of materials in the fields of photovoltaics, thermoelectrics, lighting, and medicine. Impurities within SiNCs dramatically alter the electrical and optical properties of the host material, whether the impurity is intentionally added in an attempt to manipulate properties, or is inherent to the material and its natural state. Despite such remarkable changes, impurity incorporation within SiNCs remains poorly understood, since concepts applied to understanding impurities in bulk materials may not completely translate to nanomaterials. Understanding the effect of SiNC impurities requires new technologies to produce materials suitable for study combined with new insights to expound the differences in the nanoscale physics. Nonthermal plasma-assisted gas-phase synthesis provides an excellent route to producing and investigating impurities within SiNCs due to the unique chemical reaction environment of the plasma. The robustness of such a technique allows for the production of very pure SiNCs or SiNCs with added impurities simply by adding different chemicals to the plasma. The chapters in this document focus on the effect that different impurities have on the properties of SiNCs. Chapter 2 focuses on heavily P-doped SiNCs exhibiting the first known observation of a unique electrical and optical property known as localized surface plasmon resonance (LSPR) within free-standing SiNCs. Chapter 3 explains the synthesis of B- and P-doped SiGeNC alloys and their deposition into thin films for thermoelectric applications. Chapter 4 highlights research which uses P-doped SiNCs to form emitter layers for pn-junction type solar cells, including device fabrication and optical characterization. Chapter 5 examines inherent impurities in the form of dangling bond defects which may be responsible for the quenching of SiNC photoluminescence, and their evolution during the process of air-ambient oxidation. Several appendices at

  15. Ground-state of Two-dimensional Graphene in the Presence of Random Charged Impurities

    Science.gov (United States)

    Rossi, Enrico

    2009-03-01

    The low energy electronic excitations of graphene are described by a massless Dirac fermion model. In clean isolated graphene the Fermi energy lies exactly at the Dirac point where the linear chiral electron and hole bands cross each other. Close to the Dirac point the average carrier density vanishes and the density fluctuations are expected to dominate the physics of graphene. In current experiment the fluctuations are mostly due to quenched disorder. In this talk I present the Thomas-Fermi-Dirac (TFD) theory [1] to calculate the carrier density of graphene in presence of disorder. The TFD theory includes the effects of non-linear screening, exchange and correlation. The approach is independent of the disorder source and very efficient allowing the calculation of disorder-averaged quantities that can be directly compared with experiments. Recent transport results strongly suggest that in current graphene samples charge impurities are the main source of disorder. I then present the results of the TFD theory for this case. I show that close to the Dirac point the carrier density breaks-up in electron-hole puddles and is characterized by two types of inhomogeneities: wide regions of low density and sparse narrow regions of high density and a typical correlation length of 10 nm. I present detailed results that show how the disordered averaged quantities characterizing the carrier density profile depend on the experimental parameters. I show that at finite voltages the density probability distribution has a bimodal character providing direct evidence for the existence of puddles over a finite range of gate voltages. In graphene the exchange-correlation term increases with density contrary to parabolic-band electron liquids and because of this it tends to suppress density inhomogeneities. I show that this effect becomes very important close to the Dirac point, especially at low impurity densities.

  16. Particle and impurity transport in JET versus neoclassical theory

    International Nuclear Information System (INIS)

    The analysis of impurity transport in recent years has stressed the need for reliable neoclassical predictions against which the experimental data should be benchmarked. During long H-modes, the impurities seem to accumulate in a region close to the separatrix: this behaviour has been identified for metallic (Ni), but also for lighter (O, Be) impurities and has been put in relation with a neoclassical mechanism. A central zone of reduced transport has been identified in various cases and the values of diffusion and convection have been associated with neoclassical ones. The neoclassical coefficients used in the simulation programs for the comparison with the experimental results are analytical approximating expressions derived under several restrictions: the plasma is assumed to have a circular cross section and a small inverse aspect ratio and the impurity is present in the plasma as a trace, i.e. the impurity strength α = nI Z2I/niZ2iabiJ, linearly relating the fluxes to the thermodynamical forces (gradients), can be factorized in each collisionality regime into the product of two distinct terms: one depending only on the geometry (flux surface averages of quantities equilibrium-dependent) and one depending on the driving physical mechanism. (author) 10 refs., 3 figs

  17. Global effects on neoclassical transport in the pedestal with impurities

    Science.gov (United States)

    Pusztai, I.; Buller, S.; Landreman, M.

    2016-08-01

    We present a numerical study of collisional transport in a tokamak pedestal in the presence of non-trace impurities, using the radially global δ f neoclassical solver Perfect (Landreman et al 2014 Plasma Phys. Control. Fusion 56 045005). It is known that in a tokamak core with non-trace impurities present the radial impurity flux opposes the bulk ion flux to provide an ambipolar particle transport, with the electron transport being negligibly small. However, in a sharp density pedestal with sub-sonic ion flows the electron transport can be comparable to the ion and impurity flows. Furthermore, the neoclassical particle transport is not intrinsically ambipolar, and the non-ambipolarity of the fluxes extends outside the pedestal region by the radial coupling of the perturbations. The neoclassical momentum transport, which is finite in the presence of ion orbit-width scale profile variations, is significantly enhanced when impurities are present in non-trace quantities, even if the total parallel mass flow is dominated by the bulk ions.

  18. Magnetic main group impurities in CdS

    Energy Technology Data Exchange (ETDEWEB)

    Bedolla-Velazquez, Pedro; Mohn, Peter; Gruber, Christoph [Technische Universitaet Wien (Computational Materials Science) (Austria)

    2011-07-01

    With the development of magnetic semiconductors, the role of the magnetism of impurities came again into the focus of research. For d- and f-electron impurities, the situation seems to be rather clear. A new field appears when one starts to study magnetism produced by vacancies or by atoms, which usually do not carry any magnetic moments in a bulk solid. Starting from the magnetism of carbon vacancies in graphene we will present a study of CdS where S is replaced by main group elements. On the basis of ab-initio supercell calculations employing density functional theory (DFT) we investigate the behaviour of impurities (B,N,C,O,F,Al,Si,P,Ga,Ge) in wurtzite (w) and zincblende (zb) CdS lattices. It is found that the impurities prefer the sulfur position and most of them, depending on the concentration exhibit magnetic order. We find that for small concentrations (64zb/72w and 32zb atom supercells) a half metallic ferromagnetic behaviour is found. For a 16 atom supercell for both zb- and w-structure partly also unsaturated magnetic moments occur. For Si, Ge and P impurities a metamagnetic behaviour appears, which is found for the first time in p-electron systems. A field dependence of the magnetic moments in these materials may lead to new technological applications in these magnetic semiconductors as tunable spin injection materials.

  19. Impurity profile tracking for active pharmaceutical ingredients: case reports.

    Science.gov (United States)

    Zhou, Lili; Mao, Bing; Reamer, Robert; Novak, Tom; Ge, Zhihong

    2007-06-28

    Tracking the impurity profile of an active pharmaceutical ingredient (API) is a very important task for all stages of drug development. A systematic approach for tracking impurity profile of API is described. Various real pharmaceutical applications are presented through successful examples of impurity profile tracking for three different novel APIs. These include MK-0969, an M3 antagonist; MK-0677, an oral-active growth hormone secretagogue and API-A, a cathepsin K inhibitor. A general strategy including selection of a reversed phase high performance liquid chromatographic (RP-HPLC) impurity profile method based on screening various stationary phases and changing the pH of the mobile phase and elucidation of impurity structures through the utilization of LC-MS, preparative-LC and NMR is demonstrated. A series of studies were conducted on the peak purity check by using the LC-UV diode-array and LC-MS detections. The advantages and disadvantages of each technique in the evaluation of peak purity are discussed. PMID:17142001

  20. Adjacent stage impurity ratio in rare earth countercurrent extraction process

    Institute of Scientific and Technical Information of China (English)

    CHENG Fuxiang; WU Sheng; LIAO Chunsheng; YAN Chunhua

    2013-01-01

    Impurity components decrease stage by stage in a cascade of rare earth (RE) extraction separation,and adjacent stage impurity ratio (ASIR) which is defined as the ratio of an impurity's contents in the aqueous/organic phase of two adjacent stages can be used to evaluate the capacity of impurity removal for the two stages.On the basis of extraction equilibrium and mass balance,the ASIR in a two-component extraction separation was deducted and its simplified expressions were given for different process sections according to reasonable assumptions.The calculation simulation was then carried out to obtain the ASIR distribution in the cascade.The results showed that in both the extraction and scrubbing sections the ASIR principally increased with the decrease of the molar proportion of the impurity but along with a flat appearing in the purification zone located in the middle of the cascade.The ASIR intuitively exhibits the nmning status of RE extraction separation and purification,which could provide a theoretic guide for investigating the influence factors of RE extraction separation process in practical industry.

  1. Quantum one dimensional spin systems. Disorder and impurities

    International Nuclear Information System (INIS)

    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.)

  2. Effects of impurities on crystal growth in fructose crystallization

    Science.gov (United States)

    Chu, Y. D.; Shiau, L. D.; Berglund, K. A.

    1989-10-01

    The influence of impurities on the crystallization of anhydrous fructose from aqueous solution was studied. The growth kinetics of fructose crystals in the fructose-water-glucose and fructose-water-difructose dianhydrides systems were investigated using photomicroscopic contact nucleation techniques. Glucose is the major impurity likely to be present in fructose syrup formed during corn wet milling, while several difructose dianhydrides are formed in situ under crystallization conditions and have been proposed as a cause in the decrease of overall yields. Both sets of impurities were found to cause inhibition of crystal growth, but the mechanisms responsible in each case are different. It was found that the presence of glucose increases the solubility of fructose in water and thus lowers the supersaturation of the solution. This is probably the main effect responsible for the decrease of crystal growth. Since the molecular structures of difructose dianhydrides are similar to that of fructose, they are probably "tailor-made" impurities. The decrease of crystal growth is probably caused by the incorporation of these impurities into or adsorption to the crystal surface which would accept fructose molecules in the orientation that existed in the difructose dianhydride.

  3. Phonon self-energy in superconductors: Effect of vibrating impurities

    Science.gov (United States)

    Sergeev, A.; Preis, Ch.; Keller, J.

    2000-09-01

    The phonon self-energy due to the interaction with electrons is studied for superconductors with s- and d-wave pairing. Addition of impurities not only changes the electronic states, but it also generates a channel of the electron-phonon interaction due to electron scattering from vibrating impurities. Impurity-induced electron-phonon coupling results in significant modifications of the phonon self-energy. For a d-wave superconductor the phonon attenuation coefficient (the imaginary part of the phonon self-energy) has been calculated in the Born approximation and in the unitary limit for electron-impurity scattering. In the case of weak electron-impurity potential, the attenuation decreases if temperature reduces below Tc, while an increase of the attenuation in the superconducting state has been found in the unitary limit. The theory shows a good agreement with measured disorder-dependent coupling of the B1g phonon mode to superconducting electrons in high-Tc samples: the Born approximation well describes temperature dependence of the attenuation in YBaCuO single crystals, the unitary limit corresponds to polycrystals and twinned crystals.

  4. Global effects on neoclassical transport in the pedestal with impurities

    CERN Document Server

    Pusztai, I; Landreman, M

    2016-01-01

    We present a numerical study of collisional transport in a tokamak pedestal in the presence of non-trace impurities, using the radially global $\\delta f$ neoclassical solver PERFECT [M. Landreman et al. 2014 Plasma Phys. Control. Fusion 56 045005]. It is known that in a tokamak core with non-trace impurities present the radial impurity flux opposes the bulk ion flux to provide an ambipolar particle transport, with the electron transport being negligibly small. However, in a sharp density pedestal with sub-sonic ion flows the electron transport can be comparable to the ion and impurity flows. Furthermore, the neoclassical particle transport is not intrinsically ambipolar, and the non-ambipolarity of the fluxes extends outside the pedestal region by the radial coupling of the perturbations. The neoclassical momentum transport, which is finite in the presence of ion orbit-width scale profile variations, is significantly enhanced when impurities are present in non-trace quantities, even if the total parallel mass...

  5. Impurities in Illicit Drug Preparations: Amphetamine and Methamphetamine.

    Science.gov (United States)

    Verweij, A M

    1989-06-01

    In this review, attention is paid to chromatographic and mass spectral properties of already identified impurities found to be present in frequently abused drug preparations of illegal origin of amphetamine and methamphetamine. The most commonly employed methods of synthesis of drugs of this type are briefly described. Special emphasis is given to the Leuckart route, found to be the preferred method, in the illicit production of amphetamine. Furthermore, some isolation and preconcentration methods for the contaminants are discussed. The importance of identifying impurities present in amphetamine or methamphetamine cannot be overestimated. These impurities originate mostly from the improper purification in the end stage of the different syntheses used in the clandestine manufacture of the substances; it is possible to differentiate between the several kinds of illegal drug preparations, synthesized by various methods, by means of so-called "route specific" impurities. Finally, a survey is given of the impurities already known to be present in amphetamine and methamphetamine, together with their mass spectral and some chromatographic properties. PMID:26266521

  6. Remotely screened electron-impurity scattering model for nanoscale MOSFETs

    International Nuclear Information System (INIS)

    The ionized impurities within the channel of nanoscale MOSFETs are shown to be strongly remotely screened by the close proximity of the highly doped, degenerate source and drain regions due to polarization charge effects. The position of the ionized impurity within the channel region controls the strength of the remote screening due to polarization charges induced in the source and drain, which increase heavily as the channel screening length exceeds the channel length. A remotely screened ionized impurity scattering potential is calculated based on an exact solution to Poisson's equation for a model system. This scattering potential includes the polarization charge effects from the source and the drain which may contribute separately or in combination depending on the position of the ionized impurity and the channel screening length. A scattering model is developed based on a simplified form of this scattering potential that is suitable for use in Monte Carlo simulations. The resulting scattering model is analysed and is shown to increase the ionized impurity mobility in the channel by a noticeable amount

  7. Laparoscopic gastric banding

    Science.gov (United States)

    ... make the band tighter or looser any time after you have this surgery. It may be tightened or ... Having problems eating Not losing enough weight Vomiting after you eat Outlook (Prognosis) The final weight loss with ...

  8. CSF oligoclonal banding - slideshow

    Science.gov (United States)

    ... presentations/100145.htm CSF oligoclonal banding - series—Normal anatomy ... Overview The cerebrospinal fluid (CSF) serves to supply nutrients to the central nervous system (CNS) and collect waste products, as well as ...

  9. The Band Pass Filter

    OpenAIRE

    Christiano, Lawrence J.; Terry J. Fitzgerald

    1999-01-01

    The `ideal' band pass filter can be used to isolate the component of a time series that lies within a particular band of frequencies. However, applying this filter requires a dataset of infinite length. In practice, some sort of approximation is needed. Using projections, we derive approximations that are optimal when the time series representations underlying the raw data have a unit root, or are stationary about a trend. We identify one approximation which, though it is only optimal for one...

  10. Iliotibial band friction syndrome

    OpenAIRE

    Lavine, Ronald

    2010-01-01

    Published articles on iliotibial band friction syndrome have been reviewed. These articles cover the epidemiology, etiology, anatomy, pathology, prevention, and treatment of the condition. This article describes (1) the various etiological models that have been proposed to explain iliotibial band friction syndrome; (2) some of the imaging methods, research studies, and clinical experiences that support or call into question these various models; (3) commonly proposed treatment methods for ili...

  11. Potential variations around grain boundaries in impurity-doped BaSi2 epitaxial films evaluated by Kelvin probe force microscopy

    International Nuclear Information System (INIS)

    Potential variations around the grain boundaries (GBs) in antimony (Sb)-doped n-type and boron (B)-doped p-type BaSi2 epitaxial films on Si(111) were evaluated by Kelvin probe force microscopy. Sb-doped n-BaSi2 films exhibited positively charged GBs with a downward band bending at the GBs. The average barrier height for holes was approximately 10 meV for an electron concentration n ≈ 1017 cm−3. This downward band bending changed to upward band bending when n was increased to n = 1.8 × 1018 cm−3. In the B-doped p-BaSi2 films, the upward band bending was observed for a hole concentration p ≈ 1018 cm−3. The average barrier height for electrons decreased from approximately 25 to 15 meV when p was increased from p = 2.7 × 1018 to p = 4.0 × 1018 cm−3. These results are explained under the assumption that the position of the Fermi level Ef at GBs depends on the degree of occupancy of defect states at the GBs, while Ef approached the bottom of the conduction band or the top of the valence band in the BaSi2 grain interiors with increasing impurity concentrations. In both cases, such small barrier heights may not deteriorate the carrier transport properties. The electronic structures of impurity-doped BaSi2 are also discussed using first-principles pseudopotential method to discuss the insertion sites of impurity atoms and clarify the reason for the observed n-type conduction in the Sb-doped BaSi2 and p-type conduction in the B-doped BaSi2.

  12. Sn doped CdTe as candidate for intermediate-band solar cells: A first principles DFT+GW study

    Science.gov (United States)

    Flores, Mauricio A.; Menéndez-Proupin, Eduardo

    2016-05-01

    In this work, we investigate the electronic properties and defect formation energies of Sn doped CdTe combining first principles density-functional theory and many body GW calculations. Due to the Sn dopant, an isolated impurity band is formed in the middle of the forbidden band gap of CdTe allowing the absorption of sub-bandgap photons via an intermediate-band. Our results suggest CdTe:Sn as a promising candidate for the development of third-generation intermediate-band solar cells with theoretical efficiencies up to 63.2%.

  13. Collective bands in 104,106,108Mo

    International Nuclear Information System (INIS)

    We have used our analysis of γ-γ-γ data (5.7 x 1011 triples and higher folds) taken with Gammasphere from prompt γ rays emitted in the spontaneous fission of 252Cf to study the collective bands in 104,106,108Mo. The one-phonon and two-phonon γ-vibrational bands and known two-quasiparticle bands in neutron-rich 104,106Mo were extended to higher spins. The one-and two-phonon γ-vibrational bands have remarkably close energies for transitions from the same spin states and identical moments of inertia. Several new bands are observed and are proposed as quasiparticle bands in 104,106Mo, along with the first β-type vibrational band in 106Mo. The quasiparticle bands have essentially constant moments of inertia near the rigid-body value that indicate blocking of the pairing interaction. Candidates for chiral doublet bands in 106Mo are strong. These are the first reported chiral vibrational bands in an even-even nucleus

  14. Electron and donor-impurity-related Raman scattering and Raman gain in triangular quantum dots under an applied electric field

    Science.gov (United States)

    Tiutiunnyk, Anton; Akimov, Volodymyr; Tulupenko, Viktor; Mora-Ramos, Miguel E.; Kasapoglu, Esin; Morales, Alvaro L.; Duque, Carlos Alberto

    2016-04-01

    The differential cross-section of electron Raman scattering and the Raman gain are calculated and analysed in the case of prismatic quantum dots with equilateral triangle base shape. The study takes into account their dependencies on the size of the triangle, the influence of externally applied electric field as well as the presence of an ionized donor center located at the triangle's orthocenter. The calculations are made within the effective mass and parabolic band approximations, with a diagonalization scheme being applied to obtain the eigenfunctions and eigenvalues of the x- y Hamiltonian. The incident and secondary (scattered) radiation have been considered linearly-polarized along the y-direction, coinciding with the direction of the applied electric field. For the case with an impurity center, Raman scattering with the intermediate state energy below the initial state one has been found to show maximum differential cross-section more than by an order of magnitude bigger than that resulting from the scheme with lower intermediate state energy. The Raman gain has maximum magnitude around 35 nm dot size and electric field of 40 kV/cm for the case without impurity and at maximum considered values of the input parameters for the case with impurity. Values of Raman gain of the order of up to 104cm-1 are predicted in both cases.

  15. Temperature anomaly of the coefficient of ultrasonic absorption by electrons of hybridized states of cobalt impurities in mercury selenide

    Science.gov (United States)

    Zhevstovskikh, I. V.; Okulov, V. I.; Gudkov, V. V.; Mayakin, V. Yu.; Sarychev, M. N.; Andriichuk, M. D.; Paranchich, L. D.

    2015-05-01

    The effects of the interaction of ultrasound with donor d electrons of cobalt impurity atoms at low concentrations in mercury selenide crystals have been investigated. The temperature dependences of the electronic contribution to the absorption coefficient at a frequency of 53 MHz in crystals with cobalt concentrations from 1018 to 1020 cm-3 and in the undoped crystal have been observed experimentally. It has been found that crystals with impurities are characterized by an anomalous nonmonotonic temperature dependence of the absorption coefficient of the slow transverse wave in a narrow temperature range near 10 K. A smooth monotonic temperature dependence has been observed for longitudinal and fast transverse waves. Based on the developed theoretical interpretation, it has been established that the anomaly in the temperature dependence of the absorption coefficient of a slow transverse wave is associated with the hybridization of impurity d states in the conduction band of the crystal. A comparison of the theoretical and experimental dependences has made it possible to determine the parameters characterizing the hybridized electronic states.

  16. Temperature and impurity concentration effects on Mg(1-x)CoxGa2O4 photoluminescence

    International Nuclear Information System (INIS)

    Ceramic materials doped with magnetic ions that present emission in the visible and near-infrared spectral regions are very attractive due to their inherent tunability. Possible applications include their utilization as optoelectronic and display devices, as spintronic material, in signal transmission and information storage, in the fabrication of special papers, as dosimetric materials and room temperature solid state lasers. Materials doped with tetrahedrally coordinated Co2+ present wide bands originated from electronic transitions in the ionic unfilled 3d electronic shell. The Co2+ 3d electrons are outside of the ion core and therefore their optical properties are directly affected by static and dynamic properties of ligand anions. The magnesium gallate MgGa2O4 is a partially inverted spinel described as a AB2O4 material with two possible positions for A2+ and B3+ cations. Polycrystalline MgGa2O4 : Co2+ samples were produced by solid-state reactions between ultra-pure raw oxides MgO, β-Ga2O3 and the desired CoCO3 quantities. Photoluminescence data at room temperature and 77 K of MgGa2O4 polycrystalline samples doped with 0.1 and 1.0% of Co2+ are presented. The visible emission observed is attributed to the 4T1(4P) →4A2(4F) spin-allowed transition of Co2+ ions tetrahedrally coordinated by O2- ions. The photoluminescence intensity decreases with temperature, but 90% of the 77 K emission integrated intensity remains at room temperature. Moreover, from lifetime results we estimate that Co2+ emission quantum efficiency is about 1.0 at room temperature. We also observe that between 0.1 and 1.0% of Co2+ the luminescence intensity decreases. For 1.0% of Co2+ the luminescence intensity is 37% of the obtained for 0.1%. This fact is attributed to non-radiative transfer processes of impurity ion relaxation that become competitive at 1.0% of Co2+ and show that there is a strongly impurity-concentration luminescence dependence. We also observed that for the higher

  17. Temperature and impurity concentration effects on Mg(1-x)CoxGa2O4 photoluminescence

    Science.gov (United States)

    Sosman, L. P.; Tavares, A. Dias; da Fonseca, R. J. M.; Papa, A. R. R.

    2008-04-01

    Ceramic materials doped with magnetic ions that present emission in the visible and near-infrared spectral regions are very attractive due to their inherent tunability. Possible applications include their utilization as optoelectronic and display devices, as spintronic material, in signal transmission and information storage, in the fabrication of special papers, as dosimetric materials and room temperature solid state lasers. Materials doped with tetrahedrally coordinated Co2+ present wide bands originated from electronic transitions in the ionic unfilled 3d electronic shell. The Co2+ 3d electrons are outside of the ion core and therefore their optical properties are directly affected by static and dynamic properties of ligand anions. The magnesium gallate MgGa2O4 is a partially inverted spinel described as a AB2O4 material with two possible positions for A2+ and B3+ cations. Polycrystalline MgGa2O4 : Co2+ samples were produced by solid-state reactions between ultra-pure raw oxides MgO, β-Ga2O3 and the desired CoCO3 quantities. Photoluminescence data at room temperature and 77 K of MgGa2O4 polycrystalline samples doped with 0.1 and 1.0% of Co2+ are presented. The visible emission observed is attributed to the 4T1(4P) →4A2(4F) spin-allowed transition of Co2+ ions tetrahedrally coordinated by O2- ions. The photoluminescence intensity decreases with temperature, but 90% of the 77 K emission integrated intensity remains at room temperature. Moreover, from lifetime results we estimate that Co2+ emission quantum efficiency is about 1.0 at room temperature. We also observe that between 0.1 and 1.0% of Co2+ the luminescence intensity decreases. For 1.0% of Co2+ the luminescence intensity is 37% of the obtained for 0.1%. This fact is attributed to non-radiative transfer processes of impurity ion relaxation that become competitive at 1.0% of Co2+ and show that there is a strongly impurity-concentration luminescence dependence. We also observed that for the higher

  18. Demographic Data - MDC_Block

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — A polygon feature class of Miami-Dade Census 2000 Blocks. Census blocks are areas bounded on all sides by visible and/or invisible features shown on a map prepared...

  19. Ear - blocked at high altitudes

    Science.gov (United States)

    High altitudes and blocked ears; Flying and blocked ears; Eustachian tube dysfunction - high altitude ... you are going up or coming down from high altitudes. Chewing gum the entire time you are changing ...

  20. Compressible impurity flow in the TJ-II stellarator

    CERN Document Server

    Arévalo, J; McCarthy, K J; Velasco, J L; García-Regaña, J M; Landreman, M

    2013-01-01

    Fully-ionised carbon impurity flow is studied in ion-root, neutral beam heated plasmas by means of Charge Exchange Recombination Spectroscopy (CXRS) in the TJ-II stellarator. Perpendicular flows are found to be in reasonable agreement with neoclassical calculations of the radial electric field. The parallel flow of the impurity is obtained at two locations of the same flux surface after subtraction of the calculated Pfirsch-Schl\\"uter parallel velocity. For the medium density plasmas studied, $\\bar{n}_{\\rm e}\\in(1.2-2.4)\\times 10^{19}$ m$^{-3}$, the measured impurity flow is found to be inconsistent with a total incompressible flow, i.e. $\

  1. Effect of donor impurity dislocation in elliptical quantum rings

    International Nuclear Information System (INIS)

    We investigate the effect of an off-center donor impurity on the electronic properties of a two-dimensional quantum ring with a deformed geometrical structure in the form of an ellipse. It is shown that the dislocation of impurity from the center of elliptical quantum ring opens sizable gaps in the energy spectrum and largely deforms the eigenenergies near the ground state. As a result, the Aharonov–Bohm oscillations are quenched and the persistent electron current decreases intensely. Moreover, we show that the ground state energy exhibits a local extremum when the donor impurity is located on semi-minor (or -major) axis of the elliptic ring. The effects of the eccentricity of elliptical ring on the energy spectra and persistent current are also studied

  2. Detection and identification of light impurities by electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Idrobo Tapia, Juan C [ORNL; Oxley, Mark P [ORNL; Walkosz, Weronika [University of Illinois, Chicago; Klie, Robert F [University of Illinois, Chicago; Ogut, Serdar [University of Illinois, Chicago; Mikijelj, B [Ceradyne Inc., Costa Mesa, CA; Pennycook, Stephen J [ORNL; Pantelides, Sokrates T. [Vanderbilt University

    2009-01-01

    For over 40 years impurities have been believed to stabilize the ceramic {alpha}-Si{sub 3}N{sub 4} but there is no direct evidence for their identity or lattice location. In bulk materials electron microscopy can generally image heavy impurities. Here we report direct imaging of N columns in {alpha}-Si{sub 3}N{sub 4} that suggests the presence of excess light elements in specific N columns. First-principles calculations rule out Si or N interstitials and suggest O impurities, which are then confirmed by atomically resolved electron-energy-loss spectroscopy. The result provides a possible explanation for the stability of {alpha}-Si{sub 3}N{sub 4} with implications for the design of next-generation structural ceramics.

  3. The measurement of impurities in silicon for solar cell production

    International Nuclear Information System (INIS)

    The power conversion efficiency of solar cells is largely dependent on impurity levels in silicon. In the current investigations two sample preparation methods of silicon had been used before analysis - acid dissolution at atmospheric pressure and pressured microwave assisted technique. Quantification of impurities in solar silicon was done by inductively coupled plasma mass spectrometry and electrothermal atomic spectrometry. Microwave assisted dissolution of solar silicon was more effective compared to the traditional dissolution method on the hot plate, but complete dissolution of impurities and silicon matrix was achieved with a nitric and hydrofluoric acid mixture. The mass of solar silicon for the microwave dissolution is about 0.5 g and optimal ratio of HF and HNO3 acids mixture is 3 to 5.

  4. Power balance and characterization of impurities in the Maryland Spheromak

    Energy Technology Data Exchange (ETDEWEB)

    Cote, C.

    1993-12-31

    The Maryland Spheromak is a medium size magnetically confined plasma of toroidal shape. Low T{sub e} and higher n{sub 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.

  5. Fuel retention in impurity seeded long discharges in Tore Supra

    Energy Technology Data Exchange (ETDEWEB)

    Tsitrone, E., E-mail: emmanuelle.tsitrone@cea.f [Association Euratom CEA, CEA/DSM/IRFM, Cadarache, Bat. 513, 13108 Saint-Paul-lez-Durance (France); Bucalossi, J. [Association Euratom CEA, CEA/DSM/IRFM, Cadarache, Bat. 513, 13108 Saint-Paul-lez-Durance (France); Brezinsek, S. [Institut fuer Plasma Physik, FZ Juelich, Euratom Association, Juelich (Germany); Brosset, C.; Carpentier, S.; Corre, Y.; Delchambre, E.; Devynck, P.; Grosman, A.; Gunn, J.; Kocan, M.; Loarer, T. [Association Euratom CEA, CEA/DSM/IRFM, Cadarache, Bat. 513, 13108 Saint-Paul-lez-Durance (France); Marandet, Y. [PIIM, Universite de Provence, Centre Saint Jerome, F13397 Marseille (France); Meyer, O.; Monier-Garbet, P.; Pegourie, B. [Association Euratom CEA, CEA/DSM/IRFM, Cadarache, Bat. 513, 13108 Saint-Paul-lez-Durance (France); Roubin, P. [PIIM, Universite de Provence, Centre Saint Jerome, F13397 Marseille (France); Vallet, J.C.; Balorin, C. [Association Euratom CEA, CEA/DSM/IRFM, Cadarache, Bat. 513, 13108 Saint-Paul-lez-Durance (France)

    2009-06-15

    In next step machines, tritium retention in the carbon walls is a major concern. In Tore Supra, long pulses with impurity seeding were developed to study deuterium retention in stationary conditions at low edge temperatures. A double feedback was implemented, with deuterium injection set on plasma density and impurity injection set on the radiated fraction. Long discharges (approx1 min) were obtained with radiated fractions in the range 60-80%. Neon and argon seeding were tested. In both cases, a small fraction of the injected impurity is transiently trapped in the wall, and released at the end of the shot. The deuterium retention rate decreases significantly with increasing radiated fraction, both for Ne and Ar seeding, in absolute and relative value (when related to D{sub 2} injection rate, or Dalpha recycling on the limiter). Interpretation is still an open question, as different retention mechanisms could be affected (implantation, codeposition, bulk diffusion).

  6. Impurity formation energies and effective interactions in DMS

    International Nuclear Information System (INIS)

    We use a recently developed method (Phil. Mag. 88 (2008), 2777) based on the TB-LMTO scheme to calculate the electronic structure of atomic clusters embedded in an ideal crystal or in an effective medium that represents a random alloy. We determine from the first principles impurity formation energies and effective interatomic interactions (i.e. the parameters of the alloy Ising Hamiltonian that governs structural stability of materials) and exchange interactions (i.e. parameters of the Heisenberg Hamiltonian that determines the magnetic structure). We present the results for impurities in (Ga,Mn)As alloys and for vacancies and alkali metal impurities in zirconia that can induce the the so-called d0-magnetism.

  7. Effect of impurities on kinetic transport processes in fusion plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Braun, Stefanie

    2010-12-10

    Within the framework of this thesis, different problems arising in connection with impurities have been investigated. Collisional damping of zonal flows in tokamaks: Since the Coulomb collision frequency increases with increasing ion charge, heavy, highly charged impurities play an important role in this process. The effect of such impurities on the linear response of the plasma to an external potential perturbation, as caused by zonal flows, is calculated with analytical methods. In comparison with a pure plasma, the damping of the flows occurs, as expected, considerably faster; for experimentally relevant parameters, the enhancement exceeds the effective charge Z{sub eff} of the plasma. Impurity transport driven by microturbulence in tokamaks: With regard to impurities, it is especially important whether the resulting flows are directed inwards or outwards, since they are deleterious for core energy confinement on the one hand, but on the other hand help protecting plasma-facing components from too high energy fluxes in the edge region. A semi-analytical model is presented describing the resulting impurity fluxes and the stability boundary of the underlying mode. The main goal is to bridge the gap between, on the one hand, costly numerical simulations, which are applicable to a broad range of problems but yield scarcely traceable results, and, on the other hand, analytical theory, which might ease the interpretation of the results but is so far rather rudimentary. The model is based on analytical formulae whenever possible but resorts to a numerical treatment when the approximations necessary for an analytical solution would lead to a substantial distortion of the results. Both the direction of the impurity flux and the stability boundary are found to depend sensitively on the plasma parameters such as the impurity density and the temperature gradient. Pfirsch-Schlueter transport in stellarators: Due to geometry effects, collisional transport plays a much more

  8. Effect of donor impurity dislocation in elliptical quantum rings

    Energy Technology Data Exchange (ETDEWEB)

    Khajeh Salehani, Hojjatollah, E-mail: hksalehani@damavandiau.ac.ir [Department of Physics, Damavand Branch, Islamic Azad University, Damavand 39718-78911 (Iran, Islamic Republic of); Shakouri, Khosrow [Young Researchers and Elites Club, Damavand Branch, Islamic Azad University, Damavand 39718-78911 (Iran, Islamic Republic of); Department of Physics, Iran University of Science and Technology, Narmak, Tehran 16846 (Iran, Islamic Republic of); Esmaeilzadeh, Mahdi [Department of Physics, Iran University of Science and Technology, Narmak, Tehran 16846 (Iran, Islamic Republic of)

    2015-02-15

    We investigate the effect of an off-center donor impurity on the electronic properties of a two-dimensional quantum ring with a deformed geometrical structure in the form of an ellipse. It is shown that the dislocation of impurity from the center of elliptical quantum ring opens sizable gaps in the energy spectrum and largely deforms the eigenenergies near the ground state. As a result, the Aharonov–Bohm oscillations are quenched and the persistent electron current decreases intensely. Moreover, we show that the ground state energy exhibits a local extremum when the donor impurity is located on semi-minor (or -major) axis of the elliptic ring. The effects of the eccentricity of elliptical ring on the energy spectra and persistent current are also studied.

  9. Giant g-factors of natural impurities in synthetic quartz

    Energy Technology Data Exchange (ETDEWEB)

    Goryachev, Maxim; Farr, Warrick G.; Tobar, Michael E., E-mail: michael.tobar@uwa.edu.au [ARC Centre of Excellence for Engineered Quantum Systems, University of Western Australia, 35 Stirling Highway, Crawley WA 6009 (Australia)

    2013-12-23

    We report the observation of g-factors of natural paramagnetic impurities in a pure synthetic quartz crystal at milli-Kelvin temperatures. Measurements are made by performing spectroscopy using multiple high-Q whispering gallery modes sustained in the crystal. Extreme sensitivity of the method at low temperatures allows the determination of natural residual impurities introduced during the crystal growth. We observe g-factors that significantly differ from integer multiples of the electron g-factor in vacuum, and with values of up to 7.6, which reveals much stronger coupling between impurities and the crystal lattice than in previous studies. Both substitutional and interstitial ions are proposed as candidates for the observed interactions.

  10. Polymeric efficiency in remove impurities during cottonseed biodiesel production

    Science.gov (United States)

    Lin, H. L.; Liang, Y. H.; Yan, J.; Lin, H. D.; Espinosa, A. R.

    2016-07-01

    This paper describes a new process for developing biodiesel by polymer from crude cottonseed oil. The study was conducted to examine the effectiveness of the alkali transesterification-flocculation-sedimentation process on fast glycerol and other impurities in the separation from biodiesel by using quaternary polyamine-based cationic polymers SL2700 and polyacylamide cationic polymer SAL1100. The settling velocity of glycerol and other impurities in biodiesel was investigated through settling test experiments; the quality of the biodiesel was investigated by evaluating the viscosity and density. The results revealed that SL2700, SAL1100 and their combination dramatically improved the settling velocity of glycerol and other impurities materials than traditional method. SL 2700 with molecular weight of 0.2 million Da and charge density of 50% then plus SAL1100 with molecular weight of 11 million Da and charge density of 10% induced observable particle aggregation with the best settling performance.

  11. Power balance and characterization of impurities in the Maryland Spheromak

    International Nuclear Information System (INIS)

    The Maryland Spheromak is a medium size magnetically confined plasma of toroidal shape. Low Te and higher ne 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

  12. Effect of impurities on kinetic transport processes in fusion plasmas

    International Nuclear Information System (INIS)

    Within the framework of this thesis, different problems arising in connection with impurities have been investigated. Collisional damping of zonal flows in tokamaks: Since the Coulomb collision frequency increases with increasing ion charge, heavy, highly charged impurities play an important role in this process. The effect of such impurities on the linear response of the plasma to an external potential perturbation, as caused by zonal flows, is calculated with analytical methods. In comparison with a pure plasma, the damping of the flows occurs, as expected, considerably faster; for experimentally relevant parameters, the enhancement exceeds the effective charge Zeff of the plasma. Impurity transport driven by microturbulence in tokamaks: With regard to impurities, it is especially important whether the resulting flows are directed inwards or outwards, since they are deleterious for core energy confinement on the one hand, but on the other hand help protecting plasma-facing components from too high energy fluxes in the edge region. A semi-analytical model is presented describing the resulting impurity fluxes and the stability boundary of the underlying mode. The main goal is to bridge the gap between, on the one hand, costly numerical simulations, which are applicable to a broad range of problems but yield scarcely traceable results, and, on the other hand, analytical theory, which might ease the interpretation of the results but is so far rather rudimentary. The model is based on analytical formulae whenever possible but resorts to a numerical treatment when the approximations necessary for an analytical solution would lead to a substantial distortion of the results. Both the direction of the impurity flux and the stability boundary are found to depend sensitively on the plasma parameters such as the impurity density and the temperature gradient. Pfirsch-Schlueter transport in stellarators: Due to geometry effects, collisional transport plays a much more

  13. The effects of ambient impurities on the surface tension

    Directory of Open Access Journals (Sweden)

    Ponce-Torres A.

    2016-01-01

    Full Text Available A liquid bridge is a liquid column held captive between two coaxial and parallel solid disks. It is an excellent test bench where measuring the surface tension. In this paper, we used this fluid configuration to examine experimentally the effects of ambient impurities on the surface tension over time. For this purpose, the liquid bridge equilibrium shape was analyzed when the liquid bridge was surrounded by three environments: the uncontrolled ambient, and both air and argon encapsulated in a small glass cover. Ambient contamination produced a sharp decrease of the surface tension of ultra-pure water. The presence of an anionic surfactant in the free surface of an aqueous solution did not inhibit the action of impurities coming from the ambient. Impurities can influence the dynamical behavior of the free surface in flows dominated by the surface tension. Therefore, a careful control of that influence can be crucial in many applications of fluid mechanics.

  14. The effects of ambient impurities on the surface tension

    Science.gov (United States)

    Ponce-Torres, A.; Vega, E. J.

    2016-03-01

    A liquid bridge is a liquid column held captive between two coaxial and parallel solid disks. It is an excellent test bench where measuring the surface tension. In this paper, we used this fluid configuration to examine experimentally the effects of ambient impurities on the surface tension over time. For this purpose, the liquid bridge equilibrium shape was analyzed when the liquid bridge was surrounded by three environments: the uncontrolled ambient, and both air and argon encapsulated in a small glass cover. Ambient contamination produced a sharp decrease of the surface tension of ultra-pure water. The presence of an anionic surfactant in the free surface of an aqueous solution did not inhibit the action of impurities coming from the ambient. Impurities can influence the dynamical behavior of the free surface in flows dominated by the surface tension. Therefore, a careful control of that influence can be crucial in many applications of fluid mechanics.

  15. Pairwise entanglement in the XX model with a magnetic impurity

    International Nuclear Information System (INIS)

    For a three-qubit Heisenberg model in a uniform magnetic field, the pairwise thermal entanglement of any two sites is identical due to the exchange symmetry of sites. In this paper we consider the effect of a non-uniform magnetic field on the Heisenberg model, modelling a magnetic impurity on one site. Since pairwise entanglement is calculated by tracing out one of the three sites, the entanglement clearly depends on which site the impurity is located. When the impurity is located on the site which is traced out, that is, when it acts as an external field of the pair, the entanglement can be enhanced to the maximal value 1; while when the field acts on a site of the pair the corresponding concurrence can only be increased from 1/3 to 2/3. (author)

  16. Radiated power distributions in impurity-seeded plasmas in LHD

    Energy Technology Data Exchange (ETDEWEB)

    Morisaki, T., E-mail: morisaki@nifs.ac.jp [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292 (Japan); Nagoya University, Nagoya 464-8602 (Japan); Oyama, K. [Nagoya University, Nagoya 464-8602 (Japan); Tamura, N.; Masuzaki, S.; Akiyama, T.; Motojima, G.; Miyazawa, J.; Peterson, B.J. [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292 (Japan); Ohno, N. [Nagoya University, Nagoya 464-8602 (Japan); Yamada, H. [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292 (Japan)

    2015-08-15

    In LHD, impurity seeding has been performed to enhance the radiative cooling in the edge region. Neon, nitrogen and argon were seeded by gas puffing, and the behaviour of those impurities in the plasma was investigated with the innovative diagnostic method. Two bolometer arrays were used to measure the two-dimensional radiated power distribution. Using the tomographic technique, radiated power distributions on a poloidal plane can be obtained with the high time resolution. During the discharge with neon puff, considerable radiation from the core region was observed, in addition to the strong edge radiation. In spite of the highly radiated power, plasma did not result in the radiation collapse. On the other hand, in the nitrogen-seeded discharge, the strong radiation only from the peripheral region was observed. Different time evolutions of the total radiated power between neon and nitrogen seeded discharges were observed after stopping each impurity puff.

  17. Long time impurity confinement as a precursor to disruptions

    International Nuclear Information System (INIS)

    The confinement time of laser-ablated test impurities in tokamaks lengthens considerably as operation approaches the density-limit boundary. Observations on the TEXT takamak indicate that a sharp change in the balance of diffusion and inward convection mechanisms governing impurity transport, at least in the interior of plasmas, occurs as a precursor of both partial and major disruptions in Ohmically heated discharges. Similar phenomena have been observed on other tokamaks, albeit with certain chartacteristics peculiar to each individual machine. These transitions can induce partial disruptions through impurity accumulation. Further study is required to ascertain whether they are a contributing factor major disruptions. Corresponding changes in the transport of the working gas ions have also been documented in TEXT. 11 refs., 9 figs

  18. Excitations in doped quantum dot driven by discontinuously and randomly reversing electric field: Influence of impurity

    International Nuclear Information System (INIS)

    Graphical abstract: We explore the excitation profile of a repulsive impurity doped quantum dot. The dopant impurity potential chosen assumes Gaussian form. The quantum dot is subject to a discontinuously and randomly reversing static electric field. The investigation reveals how impurity strength, impurity location, and impurity domain can influence the excitation rate when the maximum value of randomly varying field reversal time is kept above a threshold value. Time-dependent Hellman-Feynman theorem has been invoked to understand the extent of external field-to-dot energy transfer. Research Highlights: RHtriangle The excitation profile of quantum dot subject to discontinuously and randomly reversing static electric field has been investigated. RHtriangle The quantum dot is doped with a repulsive Gaussian Impurity. RHtriangle The impurity strength, impurity domain, and impurity location delicately modulate the excitation profile when the field reversal time is kept above a threshold value. RHtriangle The findings could have important engineering applications. - Abstract: We explore the excitation profile of a repulsive impurity doped quantum dot. The dopant impurity potential chosen assumes Gaussian form. The quantum dot is subject to a discontinuously and randomly reversing static electric field. The investigation reveals how impurity strength, impurity location, and impurity domain can influence the excitation rate when the maximum value of randomly varying field reversal time is kept above a threshold value. Time-dependent Hellman-Feynman theorem has been invoked to understand the extent of external field-to-dot energy transfer.

  19. When Repetition Isn't the Best Practice Strategy: Effects of Blocked and Random Practice Schedules

    Science.gov (United States)

    Stambaugh, Laura A.

    2011-01-01

    The purpose of this study was to investigate the effects of blocked and random practice schedules on the performance accuracy, speed, temporal evenness, and attitude of beginning band students in a group instructional setting. The research assumptions were based on the contextual interference hypothesis, which predicts that a blocked practice…

  20. Porous block nanofiber composite filters

    Energy Technology Data Exchange (ETDEWEB)

    Ginley, David S.; Curtis, Calvin J.; Miedaner, Alexander; Weiss, Alan J.; Paddock, Arnold

    2016-08-09

    Porous block nano-fiber composite (110), a filtration system (10) and methods of using the same are disclosed. An exemplary porous block nano-fiber composite (110) includes a porous block (100) having one or more pores (200). The porous block nano-fiber composite (110) also includes a plurality of inorganic nano-fibers (211) formed within at least one of the pores (200).

  1. Interactions of structural defects with metallic impurities in multicrystalline silicon

    Energy Technology Data Exchange (ETDEWEB)

    McHugo, S.A.; Thompson, A.C. [Lawrence Berkeley National Lab., CA (United States); Hieslmair, H. [Univ. of California, Berkeley, CA (United States)] [and others

    1997-04-01

    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{sub 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.

  2. Interactions of structural defects with metallic impurities in multicrystalline silicon

    International Nuclear Information System (INIS)

    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 Ln 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

  3. Selective Absorption Mechanism for the Maintenance of Blocking

    Science.gov (United States)

    Yamazaki, Akira; Itoh, Hisanori

    2010-05-01

    Atmospheric blocking is one of the most influential phenomena in global atmospheric environments. The understanding of its dynamical processes is important to clarify weather extremes and the stratosphere-troposphere coupling and to extend forecast periods. In the dynamics of blocking, especially, its maintenance mechanism has been a stimulating topic for many meteorologists. About the maintenance mechanism of blocking, Shutts (1983) evaluated the effect of synoptic eddies in his numerical model and proposed the Eddy Straining Mechanism (hereafter, referred to as ESM). Using simple numerical models, he demonstrated that synoptic eddies strained in the north-south direction by blocking provide negative/positive vorticity to a blocking high/low and this vorticity forcing, i.e., the second-order flow maintains the blocking dipole structure against dissipation. Some pieces of evidence, however have shown that the ESM does not work well in several real cases of the block maintenance. For example, Arai and Mukougawa (2002) performed a similar experiment to Shutts (1983) and indicated the strong sensitivity of the ESM against a small meridional shift of the stormtrack (strictly speaking, wavemaker), or a small change of the size of high-frequency eddies. This is a very adverse constraint in the real atmosphere because the relative positions of blocking to the stormtrack tend to fluctuate from case to case so that they do not necessarily exist in the same latitude band. Thus, we propose a more realistic mechanism of the block maintenance named as the Selective Absorption Mechanism (hereafter referred to as SAM), in which a blocking anticyclone selectively and exclusively absorbs synoptic anticyclones. This mechanism is essentially the same mechanism as the Fujiwhara effect, which qualitatively explains that binary eddies with the same polarity merge and eddies with the opposite polarity separate. In this study, we verify the effectiveness of the SAM by observational

  4. Transport of molecular impurities at the edge of tokamaks

    International Nuclear Information System (INIS)

    The transport of molecules at the plasma edge in tokamaks is discussed in order to compare how light impurities enter the plasma if they are released either in atomic or molecular forms. Differences in their transport arise because of the dissimilarities between the atomic and molecular reactions with the bulk of the plasma. It is found that recycling to the walls is more efficient for the light impurities released in molecular form, but, also, that a substantial fraction of those atoms which originate from molecules may penetrate further into the plasma

  5. Impurity transport in a collision-dominated rotating tokamak plasma

    International Nuclear Information System (INIS)

    The flux of heavy impurities is an axisymmetric, toroidal plasma with all particles in the collision-dominated regime is considered. Plasma rotation and charge-exchange with neutrals are taken into account. A hydrodynamic model employing Braginskii's transport equations is used. The theorry is extended to higher collision freqencies as compared to previous treatments. It is found that the Pfirsch-Schlueter flux is significantly reduced as compared to the value given by Rutherford and that it is of the same order of magnitude, or less, than the classical flux in all regimes considered. It is also shown that the impurity flux can be influenced by charge-exchange with neutrals. (author)

  6. Magnetic Vortex Induced by Nonmagnetic Impurity in Frustrated Magnets.

    Science.gov (United States)

    Lin, Shi-Zeng; Hayami, Satoru; Batista, Cristian D

    2016-05-01

    We study the effect of a nonmagnetic impurity inserted in a two-dimensional frustrated ferromagnet above its saturation magnetic field H_{sat} for arbitrary spin S. We demonstrate that the ground state includes a magnetic vortex that is nucleated around the impurity over a finite range of magnetic field H_{sat}≤H≤H_{sat}^{I}. Upon approaching the quantum critical point at H=H_{sat}, the radius of the magnetic vortex diverges as the magnetic correlation length: ξ∝1/sqrt[H-H_{sat}]. These results are derived both for the lattice and in the continuum limit. PMID:27203342

  7. Effects of surface impurities on epitaxial graphene growth

    Science.gov (United States)

    del Campo, Valeria; Henríquez, Ricardo; Häberle, Patricio

    2013-01-01

    The focus of this report is to explore the large scale growth of graphene on Ru(0 0 0 1) and verify the possible effects of crystallographic defects and impurities in the quality of the synthesized material. After a Low Pressure Chemical Vapor Deposition (LP-CVD) process we obtained a graphene film accompanied by other types of graphitic structures. Impurities on the ruthenium surface behaved as nucleation sites in the formation of carbon islands several micrometers wide. The morphological structure of these islands is constituted by carbon discs with diameters in the range of few to several hundred nanometers and thicknesses always below 1 nm.

  8. Flat panel display - Impurity doping technology for flat panel displays

    International Nuclear Information System (INIS)

    Features of the flat panel displays (FPDs) such as liquid crystal display (LCD) and organic light emitting diode (OLED) display, etc. using low temperature poly-Si (LTPS) thin film transistors (TFTs) are briefly reviewed comparing with other FPDs. The requirements for fabricating TFTs used for high performance FPDs and system on glass (SoG) are addressed. This paper focuses on the impurity doping technology, which is one of the key technologies together with crystallization by laser annealing, formation of high quality gate insulator and gate-insulator/poly-Si interface. The issues to be solved in impurity doping technology for state of the art and future TFTs are clarified

  9. Flat panel display - Impurity doping technology for flat panel displays

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, Toshiharu [Advanced Technology Planning, Sumitomo Eaton Nova Corporation, SBS Tower 9F, 10-1, Yoga 4-chome, Setagaya-ku, 158-0097 Tokyo (Japan)]. E-mail: suzuki_tsh@senova.co.jp

    2005-08-01

    Features of the flat panel displays (FPDs) such as liquid crystal display (LCD) and organic light emitting diode (OLED) display, etc. using low temperature poly-Si (LTPS) thin film transistors (TFTs) are briefly reviewed comparing with other FPDs. The requirements for fabricating TFTs used for high performance FPDs and system on glass (SoG) are addressed. This paper focuses on the impurity doping technology, which is one of the key technologies together with crystallization by laser annealing, formation of high quality gate insulator and gate-insulator/poly-Si interface. The issues to be solved in impurity doping technology for state of the art and future TFTs are clarified.

  10. A nonmagnetic impurity in a 2D quantum critical antiferromagnet

    Science.gov (United States)

    Troyer, Matthias

    2003-03-01

    We compute the properties of a mobile hole and a static impurity injected into a two-dimensional antiferromagnet or superconductor in the vicinity of a magnetic quantum critical point. A static S=1/2 impurity doped into a quantum-disordered spin gap system induces a local moment with spin S=1/2 and a corresponding Curie-like impurity susceptibility, while the same impurity in a Néel ordered state only gives a finite impurity susceptibility. For the quantum critical system however an interesting field-theoretical prediction has been made that there the impurity spin susceptibility still has a Curie-like divergence, but with a universal effective spin that is neither an integer nor a half-odd integer [1]. In large-scale quantum Monte Carlo (QMC) simulations using the loop algorithm we calculate the impurity susceptibility and find that, unfortunately, this effect is not observable since the renormalization of the effective spin away from S=1/2 is minimal. Other predictions of the field theory, such as a new critical exponent η' describing the time-dependent impurity spin correlations can however be confirmed [2]. Next we compute the spectral function of a hole injected into a 2D antiferromagnet or superconductor in the vicinity of a magnetic quantum critical point [3]. We show that, near van Hove singularities, the problem maps onto that of a static vacancy. This allows the calculation of the spectral function in a QMC simulation without encountering the negative sign problem. We find a vanishing quasiparticle residue at the critical point, a new exponent η_h0.080.04 describing the frequency dependence of the spectral function G_h(ω)(ɛ_0-ω)-1+ηh and discuss possible relevance to photoemission spectra of cuprate superconductors near the antinodal points. ^1 S. Sachdev, C. Buragohain and M. Vojta, Science 286, 2479 (1999). ^2 M. Troyer, in Prog. Theor. Phys. Suppl. 145 (2002); M. Körner and M. Troyer, ibid. ^3 S. Sachdev, M. Troyer, and M. Vojta, Phys. Rev

  11. Impurities in the heavy-Fermion superconductor UBe13

    International Nuclear Information System (INIS)

    Small amounts of Sc, Lu, Gd, Np, Ce, Th, La, and Ba have been substituted for uranium in UBe13 to observe their effects. 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 tat heavy Fermion behavior is only a necessary condition for heavy Fermion superconductivity. All of the impurities tested resulted in a transition temperature depression

  12. Numerical study of impurity distribution in ultrasonic heat meter body

    Institute of Scientific and Technical Information of China (English)

    石硕; 孙建亭; 杜广生; 张敏

    2015-01-01

    Based on a discrete phase model, the numerical simulation is carried out for the flow fields of different size calcium carbo- nate suspensions in the ultrasonic heat meter body. The flow characteristics and the impurity distribution in the ultrasonic heat meter body are analyzed. The errors of the ultrasonic heat meter in measuring calcium carbonate suspensions of particles of 10 micrometers and the causes are analyzed by simulation and experiment. Results show the effects of the impurities on the value of the k coeffi- cient and the sound attenuation on the reflection path due to the particle distribution are the two main factors that influence the mea- surement accuracy.

  13. Magnetic impurities on the surface of a topological insulator

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Qin; /Fudan U.; Liu, Chao-Xing; /Tsinghua U. /Stanford U., Phys. Dept.; Xu, Cenke; /Harvard U., Phys. Dept.; Qi, Xiao-Liang; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-03-25

    The surface states of a topological insulator are described by an emergent relativistic massless Dirac equation in 2+1 dimensions. In contrast to graphene, there is an odd number of Dirac points, and the electron spin is directly coupled to the momentum. We show that a magnetic impurity opens up a local gap and suppresses the local density of states. Furthermore, the Dirac electronic states mediate an RKKY interaction among the magnetic impurities which is always ferromagnetic, whenever the chemical potential lies near the Dirac point. These effects can be directly measured in STM experiments. We also study the case of quenched disorder through a renormalization group analysis.

  14. Multi-photon Rabi oscillations in high spin paramagnetic impurity

    International Nuclear Information System (INIS)

    We report on multiple photon monochromatic quantum oscillations (Rabi oscillations) observed by pulsed EPR (Electron Paramagnetic Resonance) of Mn2+ (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.

  15. Strongly reduced band gap in NiMn2O4 due to cation exchange

    International Nuclear Information System (INIS)

    NiMn2O4 is extensively used as a basis material for temperature sensors due to its negative temperature coefficient of resistance (NTCR), which is commonly attributed to the hopping mechanism involving coexisting octahedral-site Mn4+ and Mn3+. Using density-functional theory + Hubbard U calculations, we identify a ferrimagnetic inverse spinel phase as the collinear ground state of NiMn2O4. By a 12.5% cation exchange, a mixed phase with slightly higher energy can be constructed, accompanied by the formation of an impurity-like band in the original 1 eV band gap. This impurity-like band reduces the gap to 0.35 eV, suggesting a possible source of NTCR. - Highlights: • Density functional based calculations were used to study collinear phase of NiMn2O4. • The ground-state structure is a ferrimagnetic inverse spinel phase. • The tetrahedral and octahedral Mn cations have ferromagnetic interactions. • A 12.5% cation exchange introduces an impurity-like band in the original 1 eV gap. • The 0.35 eV gap suggests a source of negative temperature coefficient of resistance

  16. Teletraffic performance Analysis of Multi-band Overlaid WCDMA Systems

    DEFF Research Database (Denmark)

    Wang, Hua; Iversen, Villy Bæk

    2007-01-01

    services. In this paper, we present a novel approach for evaluating the teletraffic performance of multi-band overlaid WCDMA systems in terms of time, call, and traffic blocking probabilities of each service class. We convert the radio model into a circuit switched network by introducing the concept of...

  17. Effect of a localized impurity on soliton dynamics in the Bose-Einstein condensates

    Institute of Scientific and Technical Information of China (English)

    Yang Ru-Shu; Yao Chun-Mei; Wu Zong-Fu

    2011-01-01

    By using a multiple-scale method, we analytically study the effect of a localized impurity on the soliton dynamics in the Bose-Einstein condensates. It is shown that a dark soliton can be transmitted through a repulsive (or attractive) impurity, while at the position of the localized impurity the soliton can be quasitrapped by the impurity. Additionally, we find that the strength of the localized impurity has an important effect on the dark soliton dynamics. With increasing strength of the localized impurity, the amplitude of the dark soliton becomes bigger, while its width is narrower, and the soliton propagates slower.

  18. Investigation of the impurity transport in the ASDEX tokamak by spectroscopical methods

    International Nuclear Information System (INIS)

    Plasma impurities: a central problem of controlled thermonuclear fusion; magnetic plasma confinement in a Tokamak; methods to the determination of plasma impurity transport coefficients - by temporally modulated gas admission; the transport equation for impurities; neoclassical and anomalous transport; harmonic analysis of time-dependent signals; solutions of the transport equation; experimental equipment and measurements; measuring results - consistency of simple transport models with radial phase measurements; linearity of the transport processes; plasma disturbance by impurity injection; determination of the diffusion coefficient by simplified transport models; comparison of transport models for impurities and background plasma; measurements of the impurity transport at the plasma edge by high modulation frequencies. (AH)

  19. Zeroth order phase transition in a holographic superconductor with single impurity

    Directory of Open Access Journals (Sweden)

    Hua Bi Zeng

    2015-08-01

    Full Text Available We investigate the single normal impurity effect in a superconductor by the holographic method. When the size of impurity is much smaller than the host superconductor, we can reproduce the Anderson theorem, which states that a conventional s-wave superconductor is robust to a normal (non-magnetic impurity with small impurity strength. However, by increasing the size of the impurity in a fixed-size host superconductor, we find a decreasing critical temperature Tc of the host superconductor, which agrees with the results in condensed matter literatures. More importantly, the phase transition at the critical impurity strength (or the critical temperature is of zeroth order.

  20. Ground state normalized binding energy of impurity in asymmetric quantum wells under hydrostatic pressure

    Science.gov (United States)

    Akbas, H.; Sucu, S.; Minez, S.; Dane, C.; Akankan, O.; Erdogan, I.

    2016-06-01

    We have studied and computed variationally the impurity energy, impurity energy turning points, and ground state normalized binding energy as functions of the impurity position for shallow impurity in asymmetric quantum wells under hydrostatic pressure. We found that the normalized binding energy significantly depends on the asymmetry of the well, besides depending on the impurity position and hydrostatic pressure. Also, the dependence of the positive normalized binding energy on the pressure can be used to find out the degree of the asymmetry of the well or the impurity position in the well.