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Sample records for deep impurity levels

  1. The origin of deep-level impurity transitions in hexagonal boron nitride

    SciTech Connect

    Du, X. Z.; Li, J.; Lin, J. Y.; Jiang, H. X.

    2015-01-12

    Deep ultraviolet photoluminescence (PL) emission spectroscopy has been employed to investigate the origin of the widely observed deep level impurity related donor-acceptor pair (DAP) transition with an emission peak near 4.1 eV in hexagonal boron nitride (h-BN). A set of h-BN epilayers were grown by metal-organic chemical vapor deposition (MOCVD) under different ammonia (NH{sub 3}) flow rates to explore the role of nitrogen vacancies (V{sub N}) in the deep-level transitions. The emission intensity of the DAP transition near 4.1 eV was found to decrease exponentially with an increase of the NH{sub 3} flow rate employed during the MOCVD growth, implying that impurities involved are V{sub N}. The temperature-dependent PL spectra were measured from 10 K up to 800 K, which provided activation energies of ∼0.1 eV for the shallow impurity. Based on the measured energy level of the shallow impurity (∼0.1 eV) and previously estimated bandgap value of about 6.5 eV for h-BN, we deduce a value of ∼2.3 eV for the deep impurity involved in this DAP transition. The measured energy levels together with calculation results and formation energies of the impurities and defects in h-BN suggest that V{sub N} and carbon impurities occupying the nitrogen sites, respectively, are the most probable shallow donor and deep acceptor impurities involved in this DAP transition.

  2. Shallow-deep transitions of impurities in semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Ranjan, V.; Singh, Vijay A.

    2003-03-01

    We study the hydrogenic impurity in a quantum dot (QD). We employ the effective mass theory with realistic barrier and variable effective mass. The model is simple, but it predicts features not previously observed. We observe that the shallow hydrogenic impurity becomes deeper as the dot size (R) is reduced and with further reduction of the dot size it becomes shallow and at times resonant with the conduction band. Such a shallow-deep (SHADE) transition is investigated and a critical size in terms of the impurity Bohr radius (aI*) is identified. A relevant aspect of a QD is reduction in the dielectric constant, epsilon, as its size decreases. Employing a size dependent epsilon(R), we demonstrate that the impurity level gets exceptionally deep in systems for which aI* is small. Thus, carrier "freeze out" is a distinct possibility in a wide class of materials such as ZnS, CdS, etc. The behavior of the impurity level with dot size is understood on the basis of simple scaling arguments. Calculations are presented for III-V (AlGaAs) and II-VI (ZnS, CdS) QDs. We speculate that the deepening of the impurity level is related to the high luminescence efficiency of QDs. It is suggested that quantum dots offer an opportunity for defect engineering.

  3. Shallow-deep transitions of impurities in semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Ranjan, V.; Singh, Vijay A.

    2001-06-01

    We study the hydrogenic impurity in a quantum dot (QD). We employ the effective mass theory with realistic barrier and variable effective mass. The model is simple, but it predicts features not previously observed. We observe that the shallow hydrogenic impurity becomes deeper as the dot size (R) is reduced and with further reduction of the dot size it becomes shallow and at times resonant with the conduction band. Such a shallow-deep (SHADE) transition is investigated and a critical size in terms of the impurity Bohr radius (aI*) is identified. A relevant aspect of a QD is reduction in the dielectric constant, ɛ, as its size decreases. Employing a size dependent ɛ(R), we demonstrate that the impurity level gets exceptionally deep in systems for which aI* is small. Thus, carrier "freeze out" is a distinct possibility in a wide class of materials such as ZnS, CdS, etc. The behavior of the impurity level with dot size is understood on the basis of simple scaling arguments. Calculations are presented for III-V (AlGaAs) and II-VI (ZnS, CdS) QDs. We speculate that the deepening of the impurity level is related to the high luminescence efficiency of QDs. It is suggested that quantum dots offer an opportunity for defect engineering.

  4. Energy levels of isoelectronic impurities by large scale LDA calculations

    SciTech Connect

    Li, Jingbo; Wang, Lin-Wang

    2002-11-22

    Isoelectronic impurity states are localized states induced by stoichiometric single atom substitution in bulk semiconductor. Photoluminescence spectra indicate deep impurity levels of 0.5 to 0.9eV above the top of valence band for systems like: GaN:As, GaN:P, CdS:Te, ZnS:Te. Previous calculations based on small supercells seemingly confirmed these experimental results. However, the current ab initio calculations based on thousand atom supercells indicate that the impurity levels of the above systems are actually much shallower(0.04 to 0.23 eV), and these impurity levels should be compared with photoluminescence excitation spectra, not photoluminescence spectra.

  5. Deep impurity trapping concepts for power semiconductor devices

    NASA Technical Reports Server (NTRS)

    Sundberg, G. R.

    1982-01-01

    High voltage semiconductor switches using deep impurity doped silicon now appear feasible for high voltage (1-100 kV), high power (10 Kw) switching and protection functions for future space power applications. Recent discoveries have demonstrated several practical ways of gating deep impurity doped silicon devices in planar configurations and of electrically controlling their characteristics, leading to a vast array of possible circuit applications. A new family of semiconductor switching devices and transducers are possible based on this technology. New deep impurity devices could be simpler than conventional p-n junction devices and yet use the same basic materials and processing techniques. In addition, multiple functions may be possible on a single device as well as increased ratings.

  6. Double-injection, deep-impurity switch development

    NASA Technical Reports Server (NTRS)

    Selim, F. A.; Whitson, D. W.

    1983-01-01

    The overall objective of this program is the development of device design and process techniques for the fabrication of a double-injection, deep-impurity (DI)(2) silicon switch that operates in the 1-10 kV range with conduction current of 10 and 1A, respectively. Other major specifications include a holding voltage of 0 to 5 volts at 1 A anode current, 10 microsecond switching time, and power dissipation of 50 W at 75 C. This report describes work that shows how the results obtained at the University of Cincinnati under NASA Grant NSG-3022 have been applied to larger area and higher voltage devices. The investigations include theoretical, analytical, and experimental studies of device design and processing. Methods to introduce deep levels, such as Au diffusion and electron irradiation, have been carried out to "pin down' the Fermi level and control device-switching characteristics. Different anode, cathode, and gate configurations are presented. Techniques to control the surface electric field of planar structures used for (DI)(2) switches are examined. Various sections of this report describe the device design, wafer-processing techniques, and various measurements which include ac and dc characteristics, 4-point probe, and spreading resistance.

  7. Double-injection, deep-impurity switch development

    NASA Technical Reports Server (NTRS)

    Whitson, D. W.

    1985-01-01

    The overall objective of this program was the development of device design and process techniques for the fabrication of a double-injection, deep-impurity (DI) sup 2 silicon switch that operates in the 2-10 kV range with conduction current values of 5 A at 2 kV and 1 A at 10 kV. Other major specifications include a holding voltage of 10 V with no gate current, 10 microsec switching time, and power dissipation of 50 W at 75 C. It was decided to concentrate on the lateral circular devices in order to optimize the gold diffusion. This resulted in devices that are much better switches (approx.1 micro sec switching time), and in a gold diffusion process that is much more controllable than those previously developed. Some results with injection-gated devices were also obtained. The current conduction for V less than VT was analyzed and seen to agree, for the most part, with Lampert's theory. Various sections of this report describe the device designs, wafer-processing techniques, and various measurements which include ac and dc characteristics and four-point probe.

  8. Advanced development of double-injection, deep-impurity semiconductor switches

    NASA Technical Reports Server (NTRS)

    Hanes, M. H.

    1987-01-01

    Deep-impurity, double-injection devices, commonly refered to as (DI) squared devices, represent a class of semiconductor switches possessing a very high degree of tolerance to electron and neutron irradiation and to elevated temperature operation. These properties have caused them to be considered as attractive candidates for space power applications. The design, fabrication, and testing of several varieties of (DI) squared devices intended for power switching are described. All of these designs were based upon gold-doped silicon material. Test results, along with results of computer simulations of device operation, other calculations based upon the assumed mode of operation of (DI) squared devices, and empirical information regarding power semiconductor device operation and limitations, have led to the conculsion that these devices are not well suited to high-power applications. When operated in power circuitry configurations, they exhibit high-power losses in both the off-state and on-state modes. These losses are caused by phenomena inherent to the physics and material of the devices and cannot be much reduced by device design optimizations. The (DI) squared technology may, however, find application in low-power functions such as sensing, logic, and memory, when tolerance to radiation and temperature are desirable (especially is device performance is improved by incorporation of deep-level impurities other than gold.

  9. Quantum wire hybridized with a single-level impurity.

    PubMed

    Lerner, Igor V; Yudson, Vladimir I; Yurkevich, Igor V

    2008-06-27

    We have studied low-temperature properties of interacting electrons in a one-dimensional quantum wire (Luttinger liquid) side-hybridized with a single-level impurity. The hybridization induces a backscattering of electrons in the wire which strongly affects its low-energy properties. Using a one-loop renormalization group approach valid for a weak electron-electron interaction, we have calculated a transmission coefficient through the wire, T(epsilon), and a local density of states, nu(epsilon) at low energies epsilon. In particular, we have found that the antiresonance in T(epsilon) has a generalized Breit-Wigner shape with the effective width Gamma(epsilon) which diverges at the Fermi level. PMID:18643692

  10. Impurity effects on energy levels and far-infrared spectra of nanorings

    NASA Astrophysics Data System (ADS)

    Hui, Pan; Jia-Lin, Zhu

    2003-11-01

    The effects of a positively charged impurity on the energy levels and far-infrared spectra of one and two electrons in semiconductor nanorings under magnetic fields are studied. The effects of the nanoring size and the impurity position are also discussed. It is shown that the electron-electron interaction and electron-impurity one in nanorings are strongly dependent on the nanoring size and the impurity position. Based on the studies of the impurity and field effects, the impurity-induced Aharonov-Bohm oscillations of the far-infrared spectra are found. The results predict a possibility of observing phenomena related to electron-impurity interaction in a nanoring in the future.

  11. Deep Inelastic Scattering at the Amplitude Level

    SciTech Connect

    Brodsky, Stanley J.; /SLAC

    2005-08-04

    The deep inelastic lepton scattering and deeply virtual Compton scattering cross sections can be interpreted in terms of the fundamental wavefunctions defined by the light-front Fock expansion, thus allowing tests of QCD at the amplitude level. The AdS/CFT correspondence between gauge theory and string theory provides remarkable new insights into QCD, including a model for hadronic wavefunctions which display conformal scaling at short distances and color confinement at large distances.

  12. Donor level of interstitial hydrogen in semiconductors: Deep level transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Kolkovsky, Vl.; Dobaczewski, L.; Nielsen, K. Bonde; Kolkovsky, V.; Larsen, A. Nylandsted; Weber, J.

    2009-12-01

    The behaviour of hydrogen in crystalline semiconductors has attracted considerable interest during several decades. Due to its high diffusion rate and ability to react with a wide variety of lattice imperfections such as intrinsic point defects, impurities, interfaces and surfaces, hydrogen is an impurity of fundamental importance in semiconductor materials. It has been already evidenced in previous investigations that the most fundamental hydrogen-related defects in-group IV semiconductors are interstitial hydrogen atoms occupying the bond-centre site ( BC) or the interstitial tetrahedral site ( T). Using first-principles calculations Van de Walle predicted similar properties of isolated hydrogen in other II-VI and III-V semiconductors. Another interesting prediction shown in that work was the existence of a universal alignment for the hydrogen electronic (-/+) level. Until now there is no direct experimental information regarding the individual isolated hydrogen states in compound semiconductors and most reported properties have been inferred indirectly. In the present work in-situ conventional deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques are used to analyse hydrogen-related levels after low-temperature proton implantation in different II-VI and III-V semiconductors including GaAs, ZnO and CdTe. From these experimental observations the donor level of isolated hydrogen is found to keep almost a constant value in the absolute energy scale taking into account different band-offsets calculated for the whole group of semiconductors.

  13. Cryogenic Laser Calorimetry for Impurity Analysis

    NASA Technical Reports Server (NTRS)

    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.

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

    NASA Technical Reports Server (NTRS)

    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.

  15. Impurities in silicon solar cells

    NASA Technical Reports Server (NTRS)

    Hopkins, R. H.

    1985-01-01

    Metallic impurities, both singly and in combinations, affect the performance of silicon solar cells. Czochralski silicon web crystals were grown with controlled additions of secondary impurities. The primary electrical dopants were boron and phosphorus. The silicon test ingots were grown under controlled and carefully monitored conditions from high-purity charge and dopant material to minimize unintentional contamination. Following growth, each crystal was characterized by chemical, microstructural, electrical, and solar cell tests to provide a detailed and internally consistent description of the relationships between silicon impurity concentration and solar cell performance. Deep-level spectroscopy measurements were used to measure impurity concentrations at levels below the detectability of other techniques and to study thermally-induced changes in impurity activity. For the majority of contaminants, impurity-induced performance loss is due to a reduction of the base diffusion length. From these observations, a semi-empirical model which predicts cell performance as a function of metal impurity concentration was formulated. The model was then used successfully to predict the behavior of solar cells bearing as many as 11 different impurities.

  16. Deep levels in AgGaSe{sub 2}

    SciTech Connect

    Choi, I.H.; Yu, P.Y.

    1994-08-01

    The photoluminescence spectra of AgGaSe{sub 2} obtained at 77 K is reported. Two emission peaks have been observed and their pressure dependence studied. One of these peaks has been identified with emission involving one of the two deep level peak D{sub 1} and D{sub 2} observed previously in absorption measurement [App. Phys. Lett. 64,1717 (1994)]. A simple model for the capture of carriers into these deep levels has been proposed.

  17. The effects of deep level traps on the electrical properties of semi-insulating CdZnTe

    SciTech Connect

    Zha, Gangqiang; Yang, Jian; Xu, Lingyan; Feng, Tao; Wang, Ning; Jie, Wanqi

    2014-01-28

    Deep level traps have considerable effects on the electrical properties and radiation detection performance of high resistivity CdZnTe. A deep-trap model for high resistivity CdZnTe was proposed in this paper. The high resistivity mechanism and the electrical properties were analyzed based on this model. High resistivity CdZnTe with high trap ionization energy E{sub t} can withstand high bias voltages. The leakage current is dependent on both the deep traps and the shallow impurities. The performance of a CdZnTe radiation detector will deteriorate at low temperatures, and the way in which sub-bandgap light excitation could improve the low temperature performance can be explained using the deep trap model.

  18. Electronic energy levels of nanorings with impurities and Aharonov-Bohm effects

    NASA Astrophysics Data System (ADS)

    Ramírez, S.

    2011-10-01

    By modeling impurities along a nanoring as general potential forms the Schrödinger equation for ballistic electrons is shown to separate in cylindrical coordinates. We find an analytical eigenvalue equation for N delta-function-barrier impurities in the presence of magnetic flux. Previous calculations of the electronic states of a one-dimensional (1D) and two-dimensional (2D) nanoring for only one or two impurities modeled by equal square barriers is explicitly extended to three and four different or equal impurities modeled as delta-barrier, square-barrier, or delta-well potential forms. This is shown to be generalizable to any number N. Effects on the energy spectra due to magnetic flux and different kinds and numbers of impurities are compared in 1D and 2D nanorings.

  19. Investigation of Deep Levels in GaInNas

    SciTech Connect

    Abulfotuh, F.; Balcioglu, A.; Friedman, D.; Geisz, J.; Kurtz, S.

    1998-11-12

    This paper presents and discusses the first Deep-Level transient spectroscopy (DLTS) data obtained from measurements carried out on both Schottky barriers and homojunction devices of GaInNAs. The effect of N and In doping on the electrical properties of the GaNInAs devices, which results in structural defects and interface states, has been investigated. Moreover, the location and densities of deep levels related to the presence of N, In, and N+In are identified and correlated with the device performance. The data confirmed that the presence of N alone creates a high density of shallow hole traps related to the N atom and structural defects in the device. Doping by In, if present alone, also creates low-density deep traps (related to the In atom and structural defects) and extremely deep interface states. On the other hand, the co-presence of In and N eliminates both the interface states and levels related to structural defects. However, the device still has a high density of the shallow and deep traps that are responsible for the photocurrent loss in the GaNInAs device, together with the possible short diffusion length.

  20. Deep borehole disposal of high-level radioactive waste.

    SciTech Connect

    Stein, Joshua S.; Freeze, Geoffrey A.; Brady, Patrick Vane; Swift, Peter N.; Rechard, Robert Paul; Arnold, Bill Walter; Kanney, Joseph F.; Bauer, Stephen J.

    2009-07-01

    Preliminary evaluation of deep borehole disposal of high-level radioactive waste and spent nuclear fuel indicates the potential for excellent long-term safety performance at costs competitive with mined repositories. Significant fluid flow through basement rock is prevented, in part, by low permeabilities, poorly connected transport pathways, and overburden self-sealing. Deep fluids also resist vertical movement because they are density stratified. Thermal hydrologic calculations estimate the thermal pulse from emplaced waste to be small (less than 20 C at 10 meters from the borehole, for less than a few hundred years), and to result in maximum total vertical fluid movement of {approx}100 m. Reducing conditions will sharply limit solubilities of most dose-critical radionuclides at depth, and high ionic strengths of deep fluids will prevent colloidal transport. For the bounding analysis of this report, waste is envisioned to be emplaced as fuel assemblies stacked inside drill casing that are lowered, and emplaced using off-the-shelf oilfield and geothermal drilling techniques, into the lower 1-2 km portion of a vertical borehole {approx}45 cm in diameter and 3-5 km deep, followed by borehole sealing. Deep borehole disposal of radioactive waste in the United States would require modifications to the Nuclear Waste Policy Act and to applicable regulatory standards for long-term performance set by the US Environmental Protection Agency (40 CFR part 191) and US Nuclear Regulatory Commission (10 CFR part 60). The performance analysis described here is based on the assumption that long-term standards for deep borehole disposal would be identical in the key regards to those prescribed for existing repositories (40 CFR part 197 and 10 CFR part 63).

  1. Impurity gettering

    SciTech Connect

    Picraux, S.T.

    1995-06-01

    Transition metal impurities are well known to cause detrimental effects when present in the active regions of Si devices. Their presence degrades minority carrier lifetime, provides recombination-generation centers, increases junction leakage current and reduces gate oxide integrity. Thus, gettering processes are used to reduce the available metal impurities from the active region of microelectronic circuits. Gettering processes are usually divided into intrinsic (or internal) and extrinsic (or external) categories. Intrinsic refers to processing the Si wafer in a way to make available internal gettering sites, whereas extrinsic implies externally introduced gettering sites. Special concerns have been raised for intrinsic gettering. Not only will the formation of the precipitated oxide and denuded zone be difficult to achieve with the lower thermal budgets, but another inherent limit may set in. In this or any process which relies on the precipitation of metal silicides the impurity concentration can only be reduced as low as the solid solubility limit. However, the solubilities of transition metals relative to silicide formation are typically found to be {approx_gt}10{sup 12}/cm{sup 3} at temperatures of 800 C and above, and thus inadequate to getter to the needed concentration levels. It is thus anticipated that future microelectronic device processing will require one or more of the following advances in gettering technology: (1) new and more effective gettering mechanisms; (2) quantitative models of gettering to allow process optimization at low process thermal budgets and metal impurity concentrations, and/or (3) development of front side gettering methods to allow for more efficient gettering close to device regions. These trend-driven needs provide a driving force for qualitatively new approaches to gettering and provide possible new opportunities for the use of ion implantation in microelectronics processing.

  2. Deep UV Positive Resists For Two-Level Photoresist Processes

    NASA Astrophysics Data System (ADS)

    Reichmanis, E.; Smolinsky, G.

    1984-05-01

    Interest has steadily grown during the past few years in materials that are resistant to dry etching techniques that can be used in multilevel resist processes. This is perhaps a result of the greater demands placed on resist technology by increased device complexity and resolution requirements. The most well known multilevel resist methods are the two-level PCM (portable conformable mask, first described by B. J. Lin ) and the BTL trilevel processes. In the latter, the pattern defined in the top level is transfered first to a thin silicon dioxide layer and subsequently to the substrate by dry etching. A two-level photoresist process employing 200-300 nm irradiation of the upper layer followed by transfer of the resultant image into the lower layer by dry etching, combines the attractive features of both deep UV lithography and multilevel resist 3processing. Deep UV lithography affords improved resolution due to decreased diffraction, while multilevel processing2alleviates the problems associated with substrate topography and sur-face reflectivity. An outline of this resist processing scheme is shown in Figure 1. The substrate is coated first with a thick layer of an organic polymer that effectively planarizes the wafer surface. A layer of photoresist is then applied. Deep UV exposure and routine development of the top layer generates the desired pattern which is transferred to the substrate by oxygen RIE. One means of iiproving the resistance of a material to RIE is incorporation of silicon. Taylor and Wolf have reported that the addition of silicon containing compounds to organic polymers improves their resistance to erosion by an oxygen discharge, presumably by the formation of a protective layer of SiO2. Dialkyl siloxane polymers have been Eeported to be usable as negative deep UV resists in the two-level process described above. Anotheg negative, oxygen RIE resistant, deep UV resist has been reported by MacDonald et al. This material, a copolymer of

  3. Large impurity effects in rubrene crystals: First-principles calculations

    SciTech Connect

    Tsetseris, L.; Pantelides, Sokrates T.

    2008-01-01

    Carrier mobilities of rubrene films are among the highest values reported for any organic semiconductor. Here, we probe with first-principles calculations the sensitivity of rubrene crystals on impurities. We find that isolated oxygen impurities create distinct peaks in the electronic density of states consistent with observations of defect levels in rubrene and that increased O content changes the position and shape of rubrene energy bands significantly. We also establish a dual role of hydrogen as individual H species and H impurity pairs create and annihilate deep carrier traps, respectively. The results are relevant to the performance and reliability of rubrene-based devices.

  4. Group-IV Impurity Defect Levels in beta-Gallium Oxide

    NASA Astrophysics Data System (ADS)

    Badescu, Stefan

    2015-03-01

    Beta-Gallium Oxide (β-Ga2O3) is a wide-bandgap semiconductor with a significant potential as a native substrate for electronic devices. One avenue for tuning its carrier concentration and electronic properties is doping with group-IV impurity atoms. This work presents a first-principles understanding of the effects of C, Si, Ge and Sn dopants at Ga sites. C is found to act like a bistable center whereas the other dopants preserve the symmetry of the Ga site. Hybrid functionals are used to describe accurately the effects that occur mainly in the conduction band. A Brillouin zone unfolding is used that enables a direct comparison to possible spectroscopy experiments. We delineate the effects on bandgap modulation induced by charge density on the one hand, and by conduction band resonances and effective masses on the other hand.

  5. Where is the level of neutral buoyancy for deep convection?

    NASA Astrophysics Data System (ADS)

    Takahashi, Hanii; Luo, Zhengzhao

    2012-08-01

    This study revisits an old concept in meteorology - level of neutral buoyancy (LNB). The classic definition of LNB is derived from the parcel theory and can be estimated from the ambient sounding (LNB_sounding) without having to observe any actual convective cloud development. In reality, however, convection interacts with the environment in complicated ways; it will eventually manage to find its own effective LNB and manifests it through detraining masses and developing anvils (LNB_observation). This study conducts a near-global survey of LNB_observation for tropical deep convection using CloudSat data and makes comparison with the corresponding LNB_sounding. The principal findings are as follows: First, although LNB_sounding provides a reasonable upper bound for convective development, correlation between LNB_sounding and LNB_observation is low suggesting that ambient sounding contains limited information for accurately predicting the actual LNB. Second, maximum mass outflow is located more than 3 km lower than LNB_sounding. Hence, from convective transport perspective, LNB_sounding is a significant overestimate of the “destination” height level of the detrained mass. Third, LNB_observation is consistently higher over land than over ocean, although LNB_sounding is similar between land and ocean. This difference is likely related to the contrasts in convective strength and environment between land and ocean. Finally, we estimate the bulk entrainment rates associated with the observed deep convection, which can serve as an observational basis for adjusting GCM cumulus parameterization.

  6. Human-level control through deep reinforcement learning

    NASA Astrophysics Data System (ADS)

    Mnih, Volodymyr; Kavukcuoglu, Koray; Silver, David; Rusu, Andrei A.; Veness, Joel; Bellemare, Marc G.; Graves, Alex; Riedmiller, Martin; Fidjeland, Andreas K.; Ostrovski, Georg; Petersen, Stig; Beattie, Charles; Sadik, Amir; Antonoglou, Ioannis; King, Helen; Kumaran, Dharshan; Wierstra, Daan; Legg, Shane; Hassabis, Demis

    2015-02-01

    The theory of reinforcement learning provides a normative account, deeply rooted in psychological and neuroscientific perspectives on animal behaviour, of how agents may optimize their control of an environment. To use reinforcement learning successfully in situations approaching real-world complexity, however, agents are confronted with a difficult task: they must derive efficient representations of the environment from high-dimensional sensory inputs, and use these to generalize past experience to new situations. Remarkably, humans and other animals seem to solve this problem through a harmonious combination of reinforcement learning and hierarchical sensory processing systems, the former evidenced by a wealth of neural data revealing notable parallels between the phasic signals emitted by dopaminergic neurons and temporal difference reinforcement learning algorithms. While reinforcement learning agents have achieved some successes in a variety of domains, their applicability has previously been limited to domains in which useful features can be handcrafted, or to domains with fully observed, low-dimensional state spaces. Here we use recent advances in training deep neural networks to develop a novel artificial agent, termed a deep Q-network, that can learn successful policies directly from high-dimensional sensory inputs using end-to-end reinforcement learning. We tested this agent on the challenging domain of classic Atari 2600 games. We demonstrate that the deep Q-network agent, receiving only the pixels and the game score as inputs, was able to surpass the performance of all previous algorithms and achieve a level comparable to that of a professional human games tester across a set of 49 games, using the same algorithm, network architecture and hyperparameters. This work bridges the divide between high-dimensional sensory inputs and actions, resulting in the first artificial agent that is capable of learning to excel at a diverse array of challenging tasks.

  7. Human-level control through deep reinforcement learning.

    PubMed

    Mnih, Volodymyr; Kavukcuoglu, Koray; Silver, David; Rusu, Andrei A; Veness, Joel; Bellemare, Marc G; Graves, Alex; Riedmiller, Martin; Fidjeland, Andreas K; Ostrovski, Georg; Petersen, Stig; Beattie, Charles; Sadik, Amir; Antonoglou, Ioannis; King, Helen; Kumaran, Dharshan; Wierstra, Daan; Legg, Shane; Hassabis, Demis

    2015-02-26

    The theory of reinforcement learning provides a normative account, deeply rooted in psychological and neuroscientific perspectives on animal behaviour, of how agents may optimize their control of an environment. To use reinforcement learning successfully in situations approaching real-world complexity, however, agents are confronted with a difficult task: they must derive efficient representations of the environment from high-dimensional sensory inputs, and use these to generalize past experience to new situations. Remarkably, humans and other animals seem to solve this problem through a harmonious combination of reinforcement learning and hierarchical sensory processing systems, the former evidenced by a wealth of neural data revealing notable parallels between the phasic signals emitted by dopaminergic neurons and temporal difference reinforcement learning algorithms. While reinforcement learning agents have achieved some successes in a variety of domains, their applicability has previously been limited to domains in which useful features can be handcrafted, or to domains with fully observed, low-dimensional state spaces. Here we use recent advances in training deep neural networks to develop a novel artificial agent, termed a deep Q-network, that can learn successful policies directly from high-dimensional sensory inputs using end-to-end reinforcement learning. We tested this agent on the challenging domain of classic Atari 2600 games. We demonstrate that the deep Q-network agent, receiving only the pixels and the game score as inputs, was able to surpass the performance of all previous algorithms and achieve a level comparable to that of a professional human games tester across a set of 49 games, using the same algorithm, network architecture and hyperparameters. This work bridges the divide between high-dimensional sensory inputs and actions, resulting in the first artificial agent that is capable of learning to excel at a diverse array of challenging tasks

  8. Deep levels in n-GaN Doped with Carbon Studied by Deep Level and Minority Carrier Transient Spectroscopies

    NASA Astrophysics Data System (ADS)

    Honda, Unhi; Yamada, Yujiro; Tokuda, Yutaka; Shiojima, Kenji

    2012-04-01

    Electron and hole traps in the carbon doping of n-type GaN films grown by metal-organic chemical vapor deposition were investigated by deep level and minority carrier transient spectroscopies. Four electron traps were observed in the samples. Of these traps, the electron trap concentration of E2 (Ec-0.40 eV) rose with increasing C incorporation. Two hole traps H1 (Ev + 0.86 eV) and H2 also showed the dependence of C doping concentration. According to these results, traps E2, H1, and H2 correspond to C-related defects. Moreover, the energy level of H1 was consistent with an ionization energy of 0.9 eV of CN acting as a deep acceptor, which might give rise to conventional yellow luminescence and current collapse of GaN-based high electron mobility transistors (HEMTs). This was confirmed by photoluminescence (PL) spectra that the integrated intensity of yellow luminescence (YL) band was largely dependent on C incorporation. Therefore, we speculated that hole trap H1 might be responsible for a broad YL band in the samples.

  9. Impurities in rock-salt: consequences for the temperature increases at the disposal of high-level nuclear waste. [Kainite, Kieserite

    SciTech Connect

    van den Broek, W.M.G.T.

    1982-06-01

    In part A the thermal properties of halite and the other materials occurring in rock-salt (the 'impurities') are collected. Except for sylvite (the specific heat of this salt is about 70% of the value for halite) all specific heats are larger than the specific heat of halite. The consequences for the temperature increases at the disposal of high-level nuclear waste in rock-salt are discussed for impurity concentrations of 1, 5, 10 and 15%. If the presence and distribution of the impurities are not taken into account, then - under the most unfavorable conditions - extra temperature increases of about 3% per cent impurity may occur. If, however, the geological composition and its geometry for the disposal region are known, the temperature increases can be calculated more accurately: they may or may not differ from those for pure halite. In part B the measurement of the thermal conductivity for four salts (kainite, kieserite, carnallite, and polyhalite) is described.

  10. Deep levels and radiation effects in p-InP

    NASA Technical Reports Server (NTRS)

    Anderson, W. A.; Singh, A.; Jiao, K.; Lee, B.

    1989-01-01

    A survey was conducted on past studies of hole traps in InP. An experiment was designed to evaluate hole traps in Zn-doped InP after fabrication, after electron irradiation and after annealing using deep level transient spectroscopy. Data similar to that of Yamaguchi was seen with observation of both radiation-induced hole and electron traps at E sub A=0.45 eV and 0.03 eV, respectively. Both traps are altered by annealing. It is also shown that trap parameters for surface-barrier devices are influenced by many factors such as bias voltage, which probes traps at different depths below the surface. These devices require great care in data evaluation.

  11. Deep level study of Mg-doped GaN using deep level transient spectroscopy and minority carrier transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Duc, Tran Thien; Pozina, Galia; Amano, Hiroshi; Monemar, Bo; Janzén, Erik; Hemmingsson, Carl

    2016-07-01

    Deep levels in Mg-doped GaN grown by metal organic chemical vapor deposition (MOCVD), undoped GaN grown by MOCVD, and halide vapor phase epitaxy (HVPE)-grown GaN have been studied using deep level transient spectroscopy and minority charge carrier transient spectroscopy on Schottky diodes. One hole trap, labeled HT1, was detected in the Mg-doped sample. It is observed that the hole emission rate of the trap is enhanced by increasing electric field. By fitting four different theoretical models for field-assisted carrier emission processes, the three-dimensional Coulombic Poole-Frenkel (PF) effect, three-dimensional square well PF effect, phonon-assisted tunneling, and one-dimensional Coulombic PF effect including phonon-assisted tunneling, it is found that the one-dimensional Coulombic PF model, including phonon-assisted tunneling, is consistent with the experimental data. Since the trap exhibits the PF effect, we suggest it is acceptorlike. From the theoretical model, the zero field ionization energy of the trap and an estimate of the hole capture cross section have been determined. Depending on whether the charge state is -1 or -2 after hole emission, the zero field activation energy Ei 0 is 0.57 eV or 0.60 eV, respectively, and the hole capture cross section σp is 1.3 ×10-15c m2 or 1.6 ×10-16c m2 , respectively. Since the level was not observed in undoped GaN, it is suggested that the trap is associated with an Mg related defect.

  12. Deep-level magma ascent rates at Mt. Etna (Italy)

    NASA Astrophysics Data System (ADS)

    Armienti, P.; Perinelli, C.; Putirka, K. D.

    2012-12-01

    Deep-level ascent rates are related to the triggering mechanisms of volcanic eruptions. Recent models and experimental studies have focused on the very shallow parts of magma plumbing systems, mostly the upper few km, and have thus far emphasized that volatile contents and volatile exsolution, are key to understanding eruption dynamics and its fingerprint in the rock texture. Massive volatile loss induces a dramatic change in the liquidus temperature, thus producing observable effects on the rates of nucleation and growth of minerals . Volatile saturation, however, may well occur at greater depths, which means that initial stages of magma ascent may be triggered by events taking place at much greater depths than those recorded by melt inclusions, likely captured at shallow levels. We present a method to evaluate ascent rates deep in a volcano plumbing system, discussing the implications for magma dehydration and using Mt. Etna as case a study. We investigate the deeper levels of magma transport by presenting detailed P-T paths for Etnean magmas, and combining these with Crystal Size Distribution (CSD)-derived cooling rates. The key to this analysis is the recognition that the slope of a P-T path, as determined from mineral-melt thermobarometry, is a result of magma cooling rate, which is in turn a function of magma ascent via the effect of pressure on volatile solubility. We also rely on a thermodynamic treatment of exsolution of non-ideal H2O-CO2 mixtures, based on the Kerric & Jacobs (1981) model, and the simplified solubility model of CO2 (Spera & Bergman, 1980) and H2O (Nicholls, 1980), recalibrated with experimental and melt inclusions data from Mt. Etna. Our modeling is able to decipher magma ascent velocity, v (dH/dt; H = depth, t = time), from ascent rate (dP/dt), and rate of cooling (dT/dt), where ρ is magma density, P is pressure, T is temperature and g is the acceleration of gravity. This equation for v provides a key to investigating the relationships

  13. A first-principles core-level XPS study on the boron impurities in germanium crystal

    SciTech Connect

    Yamauchi, Jun; Yoshimoto, Yoshihide; Suwa, Yuji

    2013-12-04

    We systematically investigated the x-ray photoelectron spectroscopy (XPS) core-level shifts and formation energies of boron defects in germanium crystals and compared the results to those in silicon crystals. Both for XPS core-level shifts and formation energies, relationship between defects in Si and Ge is roughly linear. From the similarity in the formation energy, it is expected that the exotic clusters like icosahedral B12 exist in Ge as well as in Si.

  14. A first-principles core-level XPS study on the boron impurities in germanium crystal

    NASA Astrophysics Data System (ADS)

    Yamauchi, Jun; Yoshimoto, Yoshihide; Suwa, Yuji

    2013-12-01

    We systematically investigated the x-ray photoelectron spectroscopy (XPS) core-level shifts and formation energies of boron defects in germanium crystals and compared the results to those in silicon crystals. Both for XPS core-level shifts and formation energies, relationship between defects in Si and Ge is roughly linear. From the similarity in the formation energy, it is expected that the exotic clusters like icosahedral B12 exist in Ge as well as in Si.

  15. Hybrid functional calculations of Copper impurities and related complexes in Silicon

    NASA Astrophysics Data System (ADS)

    Sharan, Abhishek; Gui, Zhigang; Janotti, Anderson

    Copper impurities affect electronic and optical properties of semiconductors. Cu is an ubiquitous impurity and can be introduced unintentionally during various processing step. In silicon, the fast-diffusing interstitial Cu donor often passivates shallow-acceptor dopants, affecting the electronic characteristics of devices, while deep levels associated with other forms of the Cu impurity degrade device performance. Here we revisit the problem of the Cu impurity in Si using first principles calculation based on a hybrid functional. We discuss the relative stability of the substitutional and interstitial forms, as well as the formation of complexes with hydrogen and oxygen impurities. The results of our calculations will be compared with recent experiments on the electrical activity of Cu impurities in Si.

  16. High temperature annealing effects on deep-level defects in a high purity semi-insulating 4H-SiC substrate

    SciTech Connect

    Iwamoto, Naoya Azarov, Alexander; Svensson, Bengt G.; Ohshima, Takeshi; Moe, Anne Marie M.

    2015-07-28

    Effects of high-temperature annealing on deep-level defects in a high-purity semi-insulating 4H silicon carbide substrate have been studied by employing current-voltage, capacitance-voltage, junction spectroscopy, and chemical impurity analysis measurements. Secondary ion mass spectrometry data reveal that the substrate contains boron with concentration in the mid 10{sup 15 }cm{sup −3} range, while other impurities including nitrogen, aluminum, titanium, vanadium and chromium are below their detection limits (typically ∼10{sup 14 }cm{sup −3}). Schottky barrier diodes fabricated on substrates annealed at 1400–1700 °C exhibit metal/p-type semiconductor behavior with a current rectification of up to 8 orders of magnitude at bias voltages of ±3 V. With increasing annealing temperature, the series resistance of the Schottky barrier diodes decreases, and the net acceptor concentration in the substrates increases approaching the chemical boron content. Admittance spectroscopy results unveil the presence of shallow boron acceptors and deep-level defects with levels in lower half of the bandgap. After the 1400 °C annealing, the boron acceptor still remains strongly compensated at room temperature by deep donor-like levels located close to mid-gap. However, the latter decrease in concentration with increasing annealing temperature and after 1700 °C, the boron acceptor is essentially uncompensated. Hence, the deep donors are decisive for the semi-insulating properties of the substrates, and their thermal evolution limits the thermal budget for device processing. The origin of the deep donors is not well-established, but substantial evidence supporting an assignment to carbon vacancies is presented.

  17. High temperature annealing effects on deep-level defects in a high purity semi-insulating 4H-SiC substrate

    NASA Astrophysics Data System (ADS)

    Iwamoto, Naoya; Azarov, Alexander; Ohshima, Takeshi; Moe, Anne Marie M.; Svensson, Bengt G.

    2015-07-01

    Effects of high-temperature annealing on deep-level defects in a high-purity semi-insulating 4H silicon carbide substrate have been studied by employing current-voltage, capacitance-voltage, junction spectroscopy, and chemical impurity analysis measurements. Secondary ion mass spectrometry data reveal that the substrate contains boron with concentration in the mid 1015 cm-3 range, while other impurities including nitrogen, aluminum, titanium, vanadium and chromium are below their detection limits (typically ˜1014 cm-3). Schottky barrier diodes fabricated on substrates annealed at 1400-1700 °C exhibit metal/p-type semiconductor behavior with a current rectification of up to 8 orders of magnitude at bias voltages of ±3 V. With increasing annealing temperature, the series resistance of the Schottky barrier diodes decreases, and the net acceptor concentration in the substrates increases approaching the chemical boron content. Admittance spectroscopy results unveil the presence of shallow boron acceptors and deep-level defects with levels in lower half of the bandgap. After the 1400 °C annealing, the boron acceptor still remains strongly compensated at room temperature by deep donor-like levels located close to mid-gap. However, the latter decrease in concentration with increasing annealing temperature and after 1700 °C, the boron acceptor is essentially uncompensated. Hence, the deep donors are decisive for the semi-insulating properties of the substrates, and their thermal evolution limits the thermal budget for device processing. The origin of the deep donors is not well-established, but substantial evidence supporting an assignment to carbon vacancies is presented.

  18. Acceptor levels in ZnMgO:N probed by deep level optical spectroscopy

    SciTech Connect

    Kurtz, A.; Hierro, A. Muñoz, E.

    2014-02-24

    A combination of deep level optical spectroscopy and lighted capacitance voltage profiling has been used to analyze the effect of N into the energy levels close to the valence band of Zn{sub 0.9}Mg{sub 0.1}O. Three energy levels at E{sub V} + 0.47 eV, E{sub V} + 0.35 eV, and E{sub V} + 0.16 eV are observed in all films with concentrations in the range of 10{sup 15}–10{sup 18} cm{sup −3}. The two shallowest traps at E{sub V} + 0.35 eV and E{sub V} + 0.16 eV have very large concentrations that scale with the N exposure and are thus potential acceptor levels. In order to correctly quantify the deep level concentrations, a metal-insulator-semiconductor model has been invoked, explaining well the resulting capacitance-voltage curves.

  19. A fluorescent derivatization method of proteins for the detection of low-level impurities by microchip capillary gel electrophoresis.

    PubMed

    Wenz, Christian; Marchetti-Deschmann, Martina; Herwig, Ela; Schröttner, Evita; Allmaier, Günter; Trojer, Lukas; Vollmer, Martin; Rüfer, Andreas

    2010-01-01

    A novel pre-chip fluorescent derivatization method is presented for protein sizing and quantification by microchip CGE. The derivatization reaction employed a water-soluble and stable fluorescent dye and was performed under conditions that favored the formation of homogeneous reaction products. The method delivered in terms of protein sizing similar results as microchip CGE with on-chip staining but showed an extended linear dynamic range for protein quantification encompassing four orders of magnitude. The sensitivity of the method was similar to standard silver-stained planar gels. The characterization of derivatization reaction products by MS and preparative isoelectric focusing indicated that a constant degree of dye molecule tagging was obtained over a broad range of protein/dye ratios. The method allowed detecting and quantifying an impurity spiked into an antibody preparation down to a level of 0.05%. Advantages of this method compared with CGE approaches with pre-column derivatization include a shorter analysis time and an increased robustness and ease of use. PMID:20162586

  20. Development of RP UPLC-TOF/MS, stability indicating method for omeprazole and its related substances by applying two level factorial design; and identification and synthesis of non-pharmacopoeial impurities.

    PubMed

    Jadhav, Sushant Bhimrao; Kumar, C Kiran; Bandichhor, Rakeshwar; Bhosale, P N

    2016-01-25

    A new UPLC-TOF/MS compatible, reverse phase-stability indicating method was developed for determination of Omeprazole (OMP) and its related substances in pharmaceutical dosage forms by implementing Design of Experiment (DoE) i.e. two level full factorial Design (2(3)+3 center points=11 experiments) to understand the Critical Method Parameters (CMP) and its relation with Critical Method Attribute (CMA); to ensure robustness of the method. The separation of eleven specified impurities including conversion product of OMP related compound F (13) and G (14) i.e. Impurity-I (1), OMP related compound-I (11) and OMP 4-chloro analog (12) was achieved in a single method on Acquity BEH shield RP18 100 × 2.1 mm, 1.7 μm column, with inlet filter (0.2 μm) using gradient elution and detector wavelength at 305 nm and validated in accordance with ICH guidelines and found to be accurate, precise, reproducible, robust and specific. The drug was found to degrade extensively in heat, humidity and acidic conditions and forms unknown degradation products during stability studies. The same method was used for LC-MS analysis to identify m/z and fragmentation of maximum unknown impurities (Non-Pharmacopoeial) i.e. Impurity-I (1), Impurity-III (3), Impurity-V (5) and Impurity-VIII (9) formed during stability studies. Based on the results, degradation pathway for the drug has been proposed and synthesis of identified impurities i.e. impurities (Impurity-I (1), Impurity-III (3), Impurity-V (5) and Impurity-VIII (9)) are discussed in detail to ensure in-depth understanding of OMP and its related impurities and optimum performance during lifetime of the product. PMID:26600119

  1. Low level impurities in imported wheat are a likely source of feral transgenic oilseed rape (Brassica napus L.) in Switzerland.

    PubMed

    Schulze, Juerg; Brodmann, Peter; Oehen, Bernadette; Bagutti, Claudia

    2015-11-01

    In Switzerland, the cultivation of genetically modified (GM) oilseed rape (Brassica napus L.) and the use of its seeds for food and feed are not permitted. Nevertheless, the GM oilseed rape events GT73, MS8×RF3, MS8 and RF3 have recently been found in the Rhine port of Basel, Switzerland. The sources of GM oilseed rape seeds have been unknown. The main agricultural good being imported at the Rhine port of Basel is wheat and from 2010 to 2013, 19% of all Swiss wheat imports originated from Canada. As over 90% of all oilseed rape grown in Canada is GM, we hypothesised that imports of Canadian wheat may contain low level impurities of GM oilseed rape. Therefore, waste fraction samples gathered during the mechanical cleaning of Canadian wheat from two Swiss grain mills were analysed by separating oilseed rape seeds from waste fraction samples and testing DNA of pooled seeds for the presence of transgenes by real-time PCR. Furthermore, oilseed rape seeds from each grain mill were sown in a germination experiment, and seedling DNA was tested for the presence of transgenes by real-time PCR. GT73, MS8×RF3, MS8 and RF3 oilseed rape was detected among seed samples and seedlings of both grain mills. Based on this data, we projected a mean proportion of 0.005% of oilseed rape in wheat imported from Canada. Besides Canadian wheat, the Rhine port of Basel does not import any other significant amounts of agricultural products from GM oilseed rape producing countries. We therefore conclude that Canadian wheat is the major source of unintended introduction of GM oilseed rape seeds into Switzerland. PMID:26109224

  2. Suitability of different containers for the sampling and storage of biogas and biomethane for the determination of the trace-level impurities--A review.

    PubMed

    Arrhenius, Karine; Brown, Andrew S; van der Veen, Adriaan M H

    2016-01-01

    The traceable and accurate measurement of biogas impurities is essential in order to robustly assess compliance with the specifications for biomethane being developed by CEN/TC408. An essential part of any procedure aiming to determinate the content of impurities is the sampling and the transfer of the sample to the laboratory. Key issues are the suitability of the sample container and minimising the losses of impurities during the sampling and analysis process. In this paper, we review the state-of-the-art in biogas sampling with the focus on trace impurities. Most of the vessel suitability studies reviewed focused on raw biogas. Many parameters need to be studied when assessing the suitability of vessels for sampling and storage, among them, permeation through the walls, leaks through the valves or physical leaks, sorption losses and adsorption effects to the vessel walls, chemical reactions and the expected initial concentration level. The majority of these studies looked at siloxanes, for which sampling bags, canisters, impingers and sorbents have been reported to be fit-for-purpose in most cases, albeit with some limitations. We conclude that the optimum method requires a combination of different vessels to cover the wide range of impurities commonly found in biogas, which have a wide range of boiling points, polarities, water solubilities, and reactivities. The effects from all the parts of the sampling line must be considered and precautions must be undertaken to minimize these effects. More practical suitability tests, preferably using traceable reference gas mixtures, are needed to understand the influence of the containers and the sampling line on sample properties and to reduce the uncertainty of the measurement. PMID:26703250

  3. Sea-level fluctuations and deep-sea sedimentation rates.

    PubMed

    Worsley, T R; Davies, T A

    1979-02-01

    Sediment accumulation rate curves from 95 drilled cores from the Pacific basin and sea-level curves derived from continental margin seismic stratigraphy show that high biogenous sediment accumulation rates correspond to low eustatic sea levels for at least the last 48 million years. This relationship fits a simple model of high sea levels producing lower land/sea ratios and hence slower chemical erosion of the continents, and vice versa. PMID:17734144

  4. Effect of Z1/2, EH5, and Ci1 deep defects on the performance of n-type 4H-SiC epitaxial layers Schottky detectors: Alpha spectroscopy and deep level transient spectroscopy studies

    NASA Astrophysics Data System (ADS)

    Mannan, Mohammad A.; Chaudhuri, Sandeep K.; Nguyen, Khai V.; Mandal, Krishna C.

    2014-06-01

    Spectroscopic performance of Schottky barrier alpha particle detectors fabricated on 50 μm thick n-type 4H-SiC epitaxial layers containing Z1/2, EH5, and Ci1 deep levels were investigated. The device performance was evaluated on the basis of junction current/capacitance characterization and alpha pulse-height spectroscopy. Capacitance mode deep level transient spectroscopy revealed the presence of the above-mentioned deep levels along with two shallow level defects related to titanium impurities (Ti(h) and Ti(c)) and an unidentified deep electron trap located at 2.4 eV below the conduction band minimum, which is being reported for the first time. The concentration of the lifetime killer Z1/2 defects was found to be 1.7 × 1013 cm-3. The charge transport and collection efficiency results obtained from the alpha particle pulse-height spectroscopy were interpreted using a drift-diffusion charge transport model. Based on these investigations, the physics behind the correlation of the detector properties viz., energy resolution and charge collection efficiency, the junction properties like uniformity in barrier-height, leakage current, and effective doping concentration, and the presence of defects has been discussed in details. The studies also revealed that the dominating contribution to the charge collection efficiency was due to the diffusion of charge carriers generated in the neutral region of the detector. The 10 mm2 large area detectors demonstrated an impressive energy resolution of 1.8% for 5486 keV alpha particles at an optimized operating reverse bias of 130 V.

  5. Improved Performance of the Alkaline-Side CSEX Process for Cesium Extraction from Alkaline High-Level Waste Obtained by Characterization of the Effect of Surfactant Impurities

    SciTech Connect

    Delmau, L.H.

    1999-11-04

    Improved understanding and performance of the alkaline-side CSEX process has been obtained through the characterization of impurity effects that hinder complete stripping of cesium from the solvent. It is shown in this report that tests of the alkaline-side CSEX process conducted in the summer and fall of 1998 were complicated by the presence of common surfactant anions, undecyl- and dodecylsulfonate, as trace impurities in the two simulants tested. This conclusion was drawn from the results of a series of systematic extraction tests followed by a definitive identification by electrospray mass spectrometry (ES-MS). Based on this understanding, a straightforward preventative measure involving the addition of a lipophilic tertiary amine extractant at a small concentration to the solvent is proposed and demonstrated. As part of the task ''Fission Product Solvent Extraction'' supported by the Efficient Separations and Processing Crosscutting Program within the USDOE Office of Environmental Management, the alkaline-side CSEX process has been developed for removal of radio-cesium ({sup 137}Cs) from alkaline high-level wastes stored in underground tanks at the Hanford Site and Savannah River Site (SRS). As described in a previous report, tests conducted in Fiscal Year 1998 generally demonstrated performance meeting the requirements for cesium removal from the waste to be treated at the SRS. However, discrepancies in stripping behavior were shown to arise from unidentified differences ''in the batches of waste simulant employed for testing. Various effects such as solvent impurities, kinetics, contacting method, and counting method were eliminated as possible causes of the observed discrepancies. Tests in Fiscal Year 1999 reported herein confirmed the earlier suspicion that the simulants contained lipophilic anionic impurities. Extraction tests demonstrated that the impurities could be concentrated in the solvent, and by ES-MS in the negative-ion mode it was possible to

  6. Electrical conduction and deep levels in polycrystalline diamond films

    NASA Astrophysics Data System (ADS)

    Gonon, P.; Deneuville, A.; Fontaine, F.; Gheeraert, E.

    1995-12-01

    We have studied the dark conductivity (field, temperature, and frequency dependence), and the photoconductivity in undoped polycrystalline diamond films. Detailed analysis reveals that either of two alternative models can be invoked to explain all the observed features of the dark conductivity. The first model is a Hill-type hopping conduction involving the presence of discrete acceptor states located at 0.91 eV above the valence band with a density around 1017 cm-3. The second model involves the presence of a band-tail of acceptor states extending about 1 eV above the valence band. In this case, variable range hopping conduction dominates at low fields with a density of states at the Fermi level around 5×1015 cm-3 eV-1, while space charge limited currents dominate at high fields. The states controlling the dark conductivity give rise to photoconduction with a threshold around 0.85 eV and a peak at 1.1 eV. The shape of the photoconductivity spectrum suggests that lattice relaxation (with a Franck-Condon shift around 0.08 eV) occurs at these states. Peaks in the photoconductivity at 1.4 eV and at 1.9 eV give evidence for the presence of deeper states in these films.

  7. Effect of deep breathing on extracted oxygen and cerebral hemoglobin levels.

    PubMed

    Kennedy, Patrick M; Zarbock, Christopher M; Burke, Broc A; Diamond, Solomon G

    2011-01-01

    This study examines the relationship between oxygen expired and functional near infrared spectroscopy (fNIRS) measured hemoglobin levels in the brain. Analysis of these two signals during normal versus deep breathing provides insight into the dynamics of cerebral physiology. Intersubject variation suggests the existence of two distinct groups with respect to oxygen extraction and hemoglobin levels. PMID:22254486

  8. The Impact of Glyphosate, Its Metabolites and Impurities on Viability, ATP Level and Morphological changes in Human Peripheral Blood Mononuclear Cells

    PubMed Central

    Kwiatkowska, Marta; Jarosiewicz, Paweł; Michałowicz, Jaromir; Koter-Michalak, Maria; Huras, Bogumiła; Bukowska, Bożena

    2016-01-01

    The toxicity of herbicides to animals and human is an issue of worldwide concern. The present study has been undertaken to assess toxic effect of widely used pesticide—glyphosate, its metabolites: aminomethylphosphonic acid (AMPA) and methylphosphonic acid and its impurities: N-(phosphonomethyl)iminodiacetic acid (PMIDA), N-methylglyphosate, hydroxymethylphosphonic acid and bis-(phosphonomethyl)amine on human peripheral blood mononuclear cells (PBMCs). We have evaluated the effect of those compounds on viability, ATP level, size (FSC-A parameter) and granulation (SSC-A parameter) of the cells studied. Human peripheral blood mononuclear cells were exposed to different concentrations of glyphosate, its metabolites and impurities (0.01–10 mM) for 4 and 24 h. It was found that investigated compounds caused statistically significant decrease in viability and ATP level of PBMCs. The strongest changes in cell viability and ATP level were observed after 24 h incubation of PBMCs with bis-(phosphonomethyl)amine, and particularly PMIDA. Moreover, all studied compounds changed cell granularity, while PMIDA and bis-(phosphonomethyl)amine altered PBMCs size. It may be concluded that bis-(phosphonomethyl)amine, and PMIDA caused a slightly stronger damage to PBMCs than did glyphosate. Changes in the parameters studied in PBMCs were observed only at high concentrations of the compounds examined, which clearly shows that they may occur in this cell type only as a result of acute poisoning of human organism with these substances. PMID:27280764

  9. The Impact of Glyphosate, Its Metabolites and Impurities on Viability, ATP Level and Morphological changes in Human Peripheral Blood Mononuclear Cells.

    PubMed

    Kwiatkowska, Marta; Jarosiewicz, Paweł; Michałowicz, Jaromir; Koter-Michalak, Maria; Huras, Bogumiła; Bukowska, Bożena

    2016-01-01

    The toxicity of herbicides to animals and human is an issue of worldwide concern. The present study has been undertaken to assess toxic effect of widely used pesticide-glyphosate, its metabolites: aminomethylphosphonic acid (AMPA) and methylphosphonic acid and its impurities: N-(phosphonomethyl)iminodiacetic acid (PMIDA), N-methylglyphosate, hydroxymethylphosphonic acid and bis-(phosphonomethyl)amine on human peripheral blood mononuclear cells (PBMCs). We have evaluated the effect of those compounds on viability, ATP level, size (FSC-A parameter) and granulation (SSC-A parameter) of the cells studied. Human peripheral blood mononuclear cells were exposed to different concentrations of glyphosate, its metabolites and impurities (0.01-10 mM) for 4 and 24 h. It was found that investigated compounds caused statistically significant decrease in viability and ATP level of PBMCs. The strongest changes in cell viability and ATP level were observed after 24 h incubation of PBMCs with bis-(phosphonomethyl)amine, and particularly PMIDA. Moreover, all studied compounds changed cell granularity, while PMIDA and bis-(phosphonomethyl)amine altered PBMCs size. It may be concluded that bis-(phosphonomethyl)amine, and PMIDA caused a slightly stronger damage to PBMCs than did glyphosate. Changes in the parameters studied in PBMCs were observed only at high concentrations of the compounds examined, which clearly shows that they may occur in this cell type only as a result of acute poisoning of human organism with these substances. PMID:27280764

  10. Impact of proton irradiation on deep level states in n-GaN

    SciTech Connect

    Zhang, Z.; Arehart, A. R.; Cinkilic, E.; Ringel, S. A.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; McSkimming, B.; Speck, J. S.

    2013-07-22

    Deep levels in 1.8 MeV proton irradiated n-type GaN were systematically characterized using deep level transient spectroscopies and deep level optical spectroscopies. The impacts of proton irradiation on the introduction and evolution of those deep states were revealed as a function of proton fluences up to 1.1 × 10{sup 13} cm{sup −2}. The proton irradiation introduced two traps with activation energies of E{sub C} - 0.13 eV and 0.16 eV, and a monotonic increase in the concentration for most of the pre-existing traps, though the increase rates were different for each trap, suggesting different physical sources and/or configurations for these states. Through lighted capacitance voltage measurements, the deep levels at E{sub C} - 1.25 eV, 2.50 eV, and 3.25 eV were identified as being the source of systematic carrier removal in proton-damaged n-GaN as a function of proton fluence.

  11. Comparative study of deep levels in HVPE and MOCVD GaN by combining O-DLTS and pulsed photo-ionization spectroscopy

    NASA Astrophysics Data System (ADS)

    Pavlov, J.; Čeponis, T.; Gaubas, E.; Meskauskaite, D.; Reklaitis, I.; Vaitkus, J.; Grigonis, R.; Sirutkaitis, V.

    2015-12-01

    Operational characteristics of sensors made of GaN significantly depend on technologically introduced defects acting as rapid traps of excess carriers which reduce charge collection efficiency of detectors. In order to reveal the prevailing defects in HVPE and MOCVD grown GaN, the carrier lifetime and photo-ionization spectra have been simultaneously measured by using microwave probed photo-conductivity transient technique. Several traps ascribed to impurities as well as vacancy and anti-site type defects have been identified in HVPE GaN material samples by combining photo-ionization and electron spin resonance spectroscopy. The optical deep level transient spectroscopy technique has been applied for spectroscopy of the parameters of thermal emission from the traps ascribed to technological defects in the Schottky barrier terrace structures fabricated on MOCVD GaN.

  12. Alloy Engineering of Defect Properties in Semiconductors: Suppression of Deep Levels in Transition-Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Huang, Bing; Yoon, Mina; Sumpter, Bobby G.; Wei, Su-Huai; Liu, Feng

    2015-09-01

    Developing practical approaches to effectively reduce the amount of deep defect levels in semiconductors is critical for their use in electronic and optoelectronic devices, but this still remains a very challenging task. In this Letter, we propose that specific alloying can provide an effective means to suppress the deep defect levels in semiconductors while maintaining their basic electronic properties. Specifically, we demonstrate that for transition-metal dichalcogenides, such as MoSe2 and WSe2 , where anion vacancies are the most abundant defects that can induce deep levels, the deep levels can be effectively suppressed in Mo1 -xWx Se2 alloys at low W concentrations. This surprising phenomenon is associated with the fact that the band edge energies can be substantially tuned by the global alloy concentration, whereas the defect level is controlled locally by the preferred locations of Se vacancies around W atoms. Our findings illustrate a concept of alloy engineering and provide a promising approach to control the defect properties of semiconductors.

  13. Alloy Engineering of Defect Properties in Semiconductors: Suppression of Deep Levels in Transition-Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Huang, Bing; Yoon, Mina; Sumpter, Bobby; Wei, Suhuai; Liu, Feng

    Developing practical approaches to effectively reduce the amount of deep defect levels in semiconductors is critical for their use in electronic and optoelectronic devices, but this still remains a very challenging task. In this talk, we propose that specific alloying can provide an effective means to suppress the deep defect levels in semiconductors while maintaining their basic electronic properties. Specifically, we demonstrate that for transition-metal dichalcogenides, such as MoSe2 and WSe2, where anion vacancies are the most abundant defects that can induce deep levels, the deep levels can be effectively suppressed in MoWSe2 alloys at low W concentrations. This surprising phenomenon is associated with the fact that the band edge energies can be substantially tuned by the global alloy concentration, whereas the defect level is controlled locally by the preferred locations of Se vacancies around W atoms. Our findings illustrate a concept of alloy engineering and provide a promising approach to control the defect properties of semiconductors.

  14. Correlation of a generation-recombination center with a deep level trap in GaN

    SciTech Connect

    Nguyen, X. S. E-mail: elecsj@nus.edu.sg; Lin, K.; Zhang, Z.; Arehart, A. R.; Ringel, S. A.; McSkimming, B.; Speck, J. S.; Fitzgerald, E. A.; Chua, S. J. E-mail: elecsj@nus.edu.sg

    2015-03-09

    We report on the identification of a deep level trap centre which contributes to generation-recombination noise. A n-GaN epilayer, grown by MOCVD on sapphire, was measured by deep level transient spectroscopy (DLTS) and noise spectroscopy. DLTS found 3 well documented deep levels at E{sub c} − 0.26 eV, E{sub c} − 0.59 eV, and E{sub c} − 0.71 eV. The noise spectroscopy identified a generation recombination centre at E{sub c} − 0.65 ± 0.1 eV with a recombination lifetime of 65 μs at 300 K. This level is considered to be the same as the one at E{sub c} − 0.59 eV measured from DLTS, as they have similar trap densities and capture cross section. This result shows that some deep levels contribute to noise generation in GaN materials.

  15. The effectiveness and stability of impurity/defect interactions and their impact on minority carrier lifetime. Annual subcontract report, 1 August 1990--31 July 1991

    SciTech Connect

    Rozgonyi, G.A.; Shimura, F.; Buczkowski, A.; Zhon, T.Q.

    1991-12-01

    This report covers the investigation and understanding of electrical activity of ``clean`` and metallic impurity decorated defects. A heterostructure containing a controlled number of deliberately introduced misfit dislocations is used as a model system to simulate a variety of defect/impurity interactions in photovoltaic materials. In addition, a noncontact laser/microwave deep-level transient spectroscopy technique is applied to characterize the minority carrier lifetime and determine the energy levels of defects. 59 refs.

  16. Deep levels in as-grown and electron-irradiated n-type GaN studied by deep level transient spectroscopy and minority carrier transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Duc, Tran Thien; Pozina, Galia; Son, Nguyen Tien; Kordina, Olof; Janzén, Erik; Ohshima, Takeshi; Hemmingsson, Carl

    2016-03-01

    Development of high performance GaN-based devices is strongly dependent on the possibility to control and understand defects in material. Important information about deep level defects is obtained by deep level transient spectroscopy and minority carrier transient spectroscopy on as-grown and electron irradiated n-type bulk GaN with low threading dislocation density produced by halide vapor phase epitaxy. One hole trap labelled H1 (EV + 0.34 eV) has been detected on as-grown GaN sample. After 2 MeV electron irradiation, the concentration of H1 increases and at fluences higher than 5 × 1014 cm-2, a second hole trap labelled H2 is observed. Simultaneously, the concentration of two electron traps, labelled T1 (EC - 0.12 eV) and T2 (EC - 0.23 eV), increases. By studying the increase of the defect concentration versus electron irradiation fluence, the introduction rate of T1 and T2 using 2 MeV- electrons was determined to be 7 × 10-3 cm-1 and 0.9 cm-1, respectively. Due to the low introduction rate of T1, it is suggested that the defect is associated with a complex. The high introduction rate of trap H1 and T2 suggests that the defects are associated with primary intrinsic defects or complexes. Some deep levels previously observed in irradiated GaN layers with higher threading dislocation densities are not detected in present investigation. It is therefore suggested that the absent traps may be related to primary defects segregated around dislocations.

  17. Deep-level transient spectroscopy of InAs/GaAs quantum dot superlattices

    SciTech Connect

    Sobolev, M. M.; Nevedomskii, V. N.; Zolotareva, R. V.; Vasil'ev, A. P.; Ustinov, V. M.

    2014-02-21

    Deep level transient spectroscopy (DLTS) has been applied to study the carrier emission from states of a 10-layer system of tunnel-coupled vertically correlated quantum dots (VCQDs) in p-n InAs/GaAs heterostructures with different widths of GaAs spacers under varied reverse bias (U{sub r}) and filling voltage pulse U{sub f}.

  18. Deep Intuition as a Level in the Development of the Concept Image

    ERIC Educational Resources Information Center

    Semadeni, Zbigniew

    2008-01-01

    To explicate certain phenomena, e.g., the possibility of deduction without definition, we hypothesize that an individual is able to understand and appreciate reasoning with a due feeling of its necessity when the concept image of each concept involved in the reasoning has reached a certain level of development; we then speak of "deep intuition".…

  19. Deep level defects in dilute GaAsBi alloys grown under intense UV illumination

    NASA Astrophysics Data System (ADS)

    Mooney, P. M.; Tarun, Marianne; Beaton, D. A.; Mascarenhas, A.; Alberi, K.

    2016-08-01

    Dilute GaAs1‑xBix alloys exhibiting narrow band edge photoluminescence (PL) were recently grown by molecular beam epitaxy (MBE) with the growth surface illuminated by intense UV radiation. To investigate whether the improved optical quality of these films results from a reduction in the concentration of deep level defects, p+/n and n+/p junction diodes were fabricated on both the illuminated and dark areas of several samples. Deep Level Transient Spectroscopy (DLTS) measurements show that the illuminated and dark areas of both the n- and p-type GaAs1‑xBix epi-layers have similar concentrations of near mid-gap electron and hole traps, in the 1015 cm‑3 range. Thus the improved PL spectra cannot be explained by a reduction in non-radiative recombination at deep level defects. We note that carrier freeze-out above 35 K is significantly reduced in the illuminated areas of the p-type GaAs1‑xBix layers compared to the dark areas, allowing the first DLTS measurements of defect energy levels close to the valence band edge. These defect levels may account for differences in the PL spectra from the illuminated and dark areas of un-doped layers with a similar Bi fraction.

  20. Reference design and operations for deep borehole disposal of high-level radioactive waste.

    SciTech Connect

    Herrick, Courtney Grant; Brady, Patrick Vane; Pye, Steven; Arnold, Bill Walter; Finger, John Travis; Bauer, Stephen J.

    2011-10-01

    A reference design and operational procedures for the disposal of high-level radioactive waste in deep boreholes have been developed and documented. The design and operations are feasible with currently available technology and meet existing safety and anticipated regulatory requirements. Objectives of the reference design include providing a baseline for more detailed technical analyses of system performance and serving as a basis for comparing design alternatives. Numerous factors suggest that deep borehole disposal of high-level radioactive waste is inherently safe. Several lines of evidence indicate that groundwater at depths of several kilometers in continental crystalline basement rocks has long residence times and low velocity. High salinity fluids have limited potential for vertical flow because of density stratification and prevent colloidal transport of radionuclides. Geochemically reducing conditions in the deep subsurface limit the solubility and enhance the retardation of key radionuclides. A non-technical advantage that the deep borehole concept may offer over a repository concept is that of facilitating incremental construction and loading at multiple perhaps regional locations. The disposal borehole would be drilled to a depth of 5,000 m using a telescoping design and would be logged and tested prior to waste emplacement. Waste canisters would be constructed of carbon steel, sealed by welds, and connected into canister strings with high-strength connections. Waste canister strings of about 200 m length would be emplaced in the lower 2,000 m of the fully cased borehole and be separated by bridge and cement plugs. Sealing of the upper part of the borehole would be done with a series of compacted bentonite seals, cement plugs, cement seals, cement plus crushed rock backfill, and bridge plugs. Elements of the reference design meet technical requirements defined in the study. Testing and operational safety assurance requirements are also defined. Overall

  1. Thermal quenching effect of an infrared deep level in Mg-doped p-type GaN films

    NASA Astrophysics Data System (ADS)

    Kim, Keunjoo; Chung, Sang Jo

    2002-03-01

    The thermal quenching of an infrared deep level of 1.2-1.5 eV has been investigated on Mg-doped p-type GaN films, using one- and two-step annealing processes and photocurrent measurements. The deep level appeared in the one-step annealing process at a relatively high temperature of 900 °C, but disappeared in the two-step annealing process with a low-temperature step and a subsequent high-temperature step. The persistent photocurrent was residual in the sample including the deep level, while it was terminated in the sample without the deep level. This indicates that the deep level is a neutral hole center located above a quasi-Fermi level, estimated with an energy of EpF=0.1-0.15 eV above the valence band at a hole carrier concentration of 2.0-2.5×1017/cm3.

  2. Investigation of deep level defects in CdTe thin films

    SciTech Connect

    Shankar, H.; Castaldini, A.; Dauksta, E.; Medvid, A.; Cavallini, A.

    2014-02-21

    In the past few years, a large body of work has been dedicated to CdTe thin film semiconductors, as the electronic and optical properties of CdTe nanostructures make them desirable for photovoltaic applications. The performance of semiconductor devices is greatly influenced by the deep levels. Knowledge of parameters of deep levels present in as-grown materials and the identification of their origin is the key factor in the development of photovoltaic device performance. Photo Induced Current Transient Spectroscopy technique (PICTS) has proven to be a very powerful method for the study of deep levels enabling us to identify the type of traps, their activation energy and apparent capture cross section. In the present work, we report the effect of growth parameters and LASER irradiation intensity on the photo-electric and transport properties of CdTe thin films prepared by Close-Space Sublimation method using SiC electrical heating element. CdTe thin films were grown at three different source temperatures (630, 650 and 700 °C). The grown films were irradiated with Nd:YAG LASER and characterized by Photo-Induced Current Transient Spectroscopy, Photocurrent measurementand Current Voltage measurements. The defect levels are found to be significantly influenced by the growth temperature.

  3. Interactions of structural defects with metallic impurities in multicrystalline silicon

    SciTech Connect

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

    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.

  4. Deep-level emissions influenced by O and Zn implantations in ZnO

    NASA Astrophysics Data System (ADS)

    Zhao, Q. X.; Klason, P.; Willander, M.; Zhong, H. M.; Lu, W.; Yang, J. H.

    2005-11-01

    A set of bulk ZnO samples implanted with O and Zn at various densities were investigated by photoluminescence. The implantation concentration of O and Zn is varied between 1×1017/cm3 and 5×1019/cm3. The samples were thermally treated in an oxygen gas environment after the implantation. The results clearly show the influence of O and Zn implantations on the deep-level emission. By comparing the photoluminescence spectra for the samples with different implantations, we can conclude that the VZn is responsible to the observed deep-level emission. In addition, a novel transition at the emission energy of 3.08eV at 77K appears in the O-implanted sample with 5×1019/cm3 implantation concentration. The novel emission is tentatively identified as O-antisite OZn.

  5. Deep-level emissions influenced by O and Zn implantations in ZnO

    SciTech Connect

    Zhao, Q.X.; Klason, P.; Willander, M.; Zhong, H.M.; Lu, W.; Yang, J.H.

    2005-11-21

    A set of bulk ZnO samples implanted with O and Zn at various densities were investigated by photoluminescence. The implantation concentration of O and Zn is varied between 1x10{sup 17}/cm{sup 3} and 5x10{sup 19}/cm{sup 3}. The samples were thermally treated in an oxygen gas environment after the implantation. The results clearly show the influence of O and Zn implantations on the deep-level emission. By comparing the photoluminescence spectra for the samples with different implantations, we can conclude that the V{sub Zn} is responsible to the observed deep-level emission. In addition, a novel transition at the emission energy of 3.08 eV at 77 K appears in the O-implanted sample with 5x10{sup 19}/cm{sup 3} implantation concentration. The novel emission is tentatively identified as O-antisite O{sub Zn}.

  6. Non-Contact, No Wafer Preparation Deep Level Transient Spectroscopy Based on Surface Photovoltage

    NASA Astrophysics Data System (ADS)

    Lagowski, Jacek; Morawski, Andrzej; Edelman, Piotr

    1992-08-01

    We discuss a novel approach to Deep Level Transient Spectroscopy (DLTS) in which the emission of trapped minority carriers is analyzed employing the surface photovoltage (SPV) transient as measured in a non-contact manner on the native depletion barrier on semiconductor surfaces. Optical excitation is used as the trap-filling pulse. Experiments done on n-type GaAs demonstrate that the SPV-DLTS is suitable for wafer-scale, non-contact determination of deep level defects on semiconductor surfaces. The SPV approach can monitor emission rates up to 106 s-1 which is 102 to 103 above the limit of standard capacitance DLTS. The sensitivity of the method is comparable to that of the oplical capacitance DLTS.

  7. Impure placebo is a useless concept.

    PubMed

    Louhiala, Pekka; Hemilä, Harri; Puustinen, Raimo

    2015-08-01

    Placebos are allegedly used widely in general practice. Surveys reporting high level usage, however, have combined two categories, 'pure' and 'impure' placebos. The wide use of placebos is explained by the high level usage of impure placebos. In contrast, the prevalence of the use of pure placebos has been low. Traditional pure placebos are clinically ineffective treatments, whereas impure placebos form an ambiguous group of diverse treatments that are not always ineffective. In this paper, we focus on the impure placebo concept and demonstrate problems related to it. We also show that the common examples of impure placebos are not meaningful from the point of view of clinical practice. We conclude that the impure placebo is a scientifically misleading concept and should not be used in scientific or medical literature. The issues behind the concept, however, deserve serious attention in future research. PMID:26215744

  8. Revisiting radiative deep-level transitions in CuGaSe2 by photoluminescence

    NASA Astrophysics Data System (ADS)

    Spindler, Conrad; Regesch, David; Siebentritt, Susanne

    2016-07-01

    Recent defect calculations suggest that the open circuit voltage of CuGaSe2 solar cells can be limited by deep intrinsic electron traps by GaCu antisites and their complexes with Cu-vacancies. To gain experimental evidence, two radiative defect transitions at 1.10 eV and 1.24 eV are characterized by steady-state photoluminescence on epitaxial-grown CuGaSe2 thin films. Cu-rich samples are studied, since they show highest crystal quality, exciton luminescence, and no potential fluctuations. Variations of the laser intensity and temperature dependent measurements suggest that emission occurs from two deep donor-like levels into the same shallow acceptor. At 10 K, power-law exponents of 1 (low excitation regime) and 1/2 (high excitation regime) are observed identically for both transitions. The theory and a fitting function for the double power law is derived. It is concluded that the acceptor becomes saturated by excess carriers which changes the exponent of all transitions. Activation energies determined from the temperature quenching depend on the excitation level and show unexpected values of 600 meV and higher. The thermal activation of non-radiative processes can explain the distortion of the ionization energies. Both the deep levels play a major role as radiative and non-radiative recombination centers for electrons and can be detrimental for photovoltaic applications.

  9. Deep level domain spectroscopy of low frequency oscillations in semi-insulating InP

    NASA Astrophysics Data System (ADS)

    Backhouse, C.; Young, L.

    1992-11-01

    It is known that low frequency current oscillations occur in semi-insulating GaAs due to the formation and transit of high field domains caused by enhanced trapping of hot electrons by deep levels and that power density spectra of the current show peaks whose temperature dependence gives information on deep levels. In the present work Fe-compensated InP was investigated. The peaks rose from an approximately {1}/{f}{3}/{2} background and by estimating and removing this and by averaging many spectra, no less than 14 frequency peaks were resolved which gave straight lines on an Arrhenius plot of log( {T 2}/{2f}) vs{1}/{T}. Although the amplitude of the current oscillations is not so large as to preclude multiple domain propagation, it seems more likely that the domains are caused by hot electron trapping by one level only, rather than that several traps should have the necessary characteristics to launch domains. The multiplicity of peaks could be partly due to harmonics of the basic high field domain oscillation and partly due to conductivity modulation by other levels whose occupancies are changed by the passage of the domains: the task, if so, is to determine which peaks are which. The activation energies from the Arrhenius plots fell into groups close to 0.30, 0.39, 0.41, 0.44 and 0.49 eV. The 14 peaks thus are believed to arise from 5 deep levels. Evidence was found that the 0.49 eV level is iron-related and is responsible for producing the high field domains and for drain current drift in InP metal-insulator-semiconductor field-effect transistors.

  10. Bismuth-induced deep levels and carrier compensation in CdTe

    SciTech Connect

    Du, Mao-Hua

    2008-01-01

    First-principles calculations show that Bi on Cd site in CdTe can be either a donor, Bi_Cd+, or an acceptor, Bi_Cd- , depending on the Fermi level. The can bind a substitutional O (O_Te) with large binding energy of 1.40 eV. The calculated (0/-) transition level for B_Cd- - O_Te complex is in good agreement with the observed deep hole trapping level. Bi can also substitute Te to form an acceptor. The amphoteric nature of Bi in CdTe results in the pinning of the Fermi level and the high resistivity. We also discuss the origin of p-type CdTe at high Bi doping level.

  11. Investigation of the origin of deep levels in CdTe doped with Bi

    SciTech Connect

    Saucedo, E.; Franc, J.; Elhadidy, H.; Horodysky, P.; Ruiz, C. M.; Bermudez, V.; Sochinskii, N. V.

    2008-05-01

    Combining optical (low temperature photoluminescence), electrical (thermoelectric effect spectroscopy), and structural (synchrotron X-ray powder diffraction) methods, the defect structure of CdTe doped with Bi was studied in crystals with dopant concentration in the range of 10{sup 17}-10{sup 19} at./cm{sup 3}. The semi-insulating state observed in crystals with low Bi concentration is assigned to the formation of a shallow donor level and a deep donor recombination center. Studying the evolution of lattice parameter with temperature, we postulate that the deep center is formed by a Te-Te dimer and their formation is explained by a tetrahedral to octahedral distortion, due to the introduction of Bi in the CdTe lattice. We also shows that this model agrees with the electrical, optical, and transport charge properties of the samples.

  12. Identification of process related trace level impurities in the actinide decorporation agent 3,4,3-LI(1,2-HOPO): Nozzle–skimmer fragmentation via ESI LC–QTOFMS

    SciTech Connect

    Panyala, Nagender R.; Sturzbecher-Hoehne, Manuel; Abergel, Rebecca J.

    2014-08-12

    We report that 3,4,3-LI(1,2-HOPO) is a chelating ligand and decorporation agent that can remove radioactive lanthanides and actinides from the body. Identification of trace impurities in drug samples is gaining much interest due to their significant influence on drug activity. In this study, trace impurities were detected in manufactured lots of 3,4,3-LI(1,2-HOPO) by a developed method of Liquid Chromatography coupled with photo-diode array UV detection and Electrospray Ionization-Quadrupole Time of Flight Mass spectrometry (LC-QTOFMS), via induced-in-source or collision-induced mass fragmentation (Nozzle-Skimmer Fragmentation). Molecular ions were fragmented within the nozzle-skimmer region of electrospray ionization (ESI) mass spectrometer equipped with a Time of Flight detector. Eight major (detected at levels higher than a 0.1% threshold) and seven minor trace impurities were identified. The respective structures of these impurities were elucidated via analysis of the generated fragment ions using mass fragmentation and elemental composition software. Proposed structures of impurities were further confirmed via isotopic modeling.

  13. Identification of process related trace level impurities in the actinide decorporation agent 3,4,3-LI(1,2-HOPO): Nozzle–skimmer fragmentation via ESI LC–QTOFMS

    DOE PAGESBeta

    Panyala, Nagender R.; Sturzbecher-Hoehne, Manuel; Abergel, Rebecca J.

    2014-08-12

    We report that 3,4,3-LI(1,2-HOPO) is a chelating ligand and decorporation agent that can remove radioactive lanthanides and actinides from the body. Identification of trace impurities in drug samples is gaining much interest due to their significant influence on drug activity. In this study, trace impurities were detected in manufactured lots of 3,4,3-LI(1,2-HOPO) by a developed method of Liquid Chromatography coupled with photo-diode array UV detection and Electrospray Ionization-Quadrupole Time of Flight Mass spectrometry (LC-QTOFMS), via induced-in-source or collision-induced mass fragmentation (Nozzle-Skimmer Fragmentation). Molecular ions were fragmented within the nozzle-skimmer region of electrospray ionization (ESI) mass spectrometer equipped with a Timemore » of Flight detector. Eight major (detected at levels higher than a 0.1% threshold) and seven minor trace impurities were identified. The respective structures of these impurities were elucidated via analysis of the generated fragment ions using mass fragmentation and elemental composition software. Proposed structures of impurities were further confirmed via isotopic modeling.« less

  14. Identification of process related trace level impurities in the actinide decorpration agent 3,4,3-LI(1,2-HOPO): Nozzle-Skimmer fragmentation via ESI LC-QTOFMS

    PubMed Central

    Panyala, Nagender R.; Sturzbecher-Hoehne, Manuel; Abergel, Rebecca J.

    2014-01-01

    3,4,3-LI(1,2-HOPO) is a chelating ligand and decorporation agent that can remove radioactive lanthanides and actinides from the body. Identification of trace impurities in drug samples is gaining much interest due to their significant influence on drug activity. In this study, trace impurities were detected in manufactured lots of 3,4,3-LI(1,2-HOPO) by a developed method of Liquid Chromatography coupled with photo-diode array UV detection and Electrospray Ionization-Quadrupole Time of Flight Mass spectrometry (LC-QTOFMS), via induced-in-source or collision-induced mass fragmentation (Nozzle-Skimmer Fragmentation). Molecular ions were fragmented within the nozzle-skimmer region of electrospray ionization (ESI) mass spectrometer equipped with a Time of Flight detector. Eight major (detected at levels higher than a 0.1% threshold) and seven minor trace impurities were identified. The respective structures of these impurities were elucidated via analysis of the generated fragment ions using mass fragmentation and elemental composition software. Proposed structures of impurities were further confirmed via isotopic modeling. PMID:25165012

  15. Influence of impurities on the crystallization of dextrose monohydrate

    NASA Astrophysics Data System (ADS)

    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.

  16. Influence of growth temperature and temperature ramps on deep level defect incorporation in m-plane GaN

    NASA Astrophysics Data System (ADS)

    Armstrong, A. M.; Kelchner, K.; Nakamura, S.; DenBaars, S. P.; Speck, J. S.

    2013-12-01

    The dependence of deep level defect incorporation in m-plane GaN films grown by metal-organic chemical vapor deposition on bulk m-plane GaN substrates as a function of growth temperature (Tg) and Tg ramping method was investigated using deep level optical spectroscopy. Understanding the influence of Tg on GaN deep level incorporation is important for InGaN/GaN multi-quantum well (MQW) light emitting diodes (LEDs) and laser diodes (LDs) because GaN quantum barrier (QB) layers are grown much colder than thin film GaN to accommodate InGaN QW growth. Deep level spectra of low Tg (800 °C) GaN films grown under QB conditions were compared to deep level spectra of high Tg (1150 °C) GaN. Reducing Tg, increased the defect density significantly (>50×) through introduction of emergent deep level defects at 2.09 eV and 2.9 eV below the conduction band minimum. However, optimizing growth conditions during the temperature ramp when transitioning from high to low Tg substantially reduced the density of these emergent deep levels by approximately 40%. The results suggest that it is important to consider the potential for non-radiative recombination in QBs of LED or LD active regions, and tailoring the transition from high Tg GaN growth to active layer growth can mitigate such non-radiative channels.

  17. Method for detecting trace impurities in gases

    DOEpatents

    Freund, Samuel M.; Maier, II, William B.; Holland, Redus F.; Beattie, Willard H.

    1981-01-01

    A technique for considerably improving the sensitivity and specificity of infrared spectrometry as applied to quantitative determination of trace impurities in various carrier or solvent gases is presented. A gas to be examined for impurities is liquefied and infrared absorption spectra of the liquid are obtained. Spectral simplification and number densities of impurities in the optical path are substantially higher than are obtainable in similar gas-phase analyses. Carbon dioxide impurity (.about.2 ppm) present in commercial Xe and ppm levels of Freon 12 and vinyl chloride added to liquefied air are used to illustrate the method.

  18. Method for detecting trace impurities in gases

    DOEpatents

    Freund, S.M.; Maier, W.B. II; Holland, R.F.; Beattie, W.H.

    A technique for considerably improving the sensitivity and specificity of infrared spectrometry as applied to quantitative determination of trace impurities in various carrier or solvent gases is presented. A gas to be examined for impurities is liquefied and infrared absorption spectra of the liquid are obtained. Spectral simplification and number densities of impurities in the optical path are substantially higher than are obtainable in similar gas-phase analyses. Carbon dioxide impurity (approx. 2 ppM) present in commercial Xe and ppM levels of Freon 12 and vinyl chloride added to liquefied air are used to illustrate the method.

  19. Deep-ocean contribution to sea level and energy budget not detectable over the past decade

    NASA Astrophysics Data System (ADS)

    Llovel, W.; Willis, J. K.; Landerer, F. W.; Fukumori, I.

    2014-11-01

    As the dominant reservoir of heat uptake in the climate system, the world's oceans provide a critical measure of global climate change. Here, we infer deep-ocean warming in the context of global sea-level rise and Earth's energy budget between January 2005 and December 2013. Direct measurements of ocean warming above 2,000 m depth explain about 32% of the observed annual rate of global mean sea-level rise. Over the entire water column, independent estimates of ocean warming yield a contribution of 0.77 +/- 0.28 mm yr-1 in sea-level rise and agree with the upper-ocean estimate to within the estimated uncertainties. Accounting for additional possible systematic uncertainties, the deep ocean (below 2,000 m) contributes -0.13 +/- 0.72 mm yr-1 to global sea-level rise and -0.08 +/- 0.43 W m-2 to Earth's energy balance. The net warming of the ocean implies an energy imbalance for the Earth of 0.64 +/- 0.44 W m-2 from 2005 to 2013.

  20. Deep Ocean Contribution to Sea Level and Energy Budget Not Detectable over the Past Decade

    NASA Astrophysics Data System (ADS)

    Llovel, W.; Willis, J. K.; Landerer, F. W.; Fukumori, I.

    2014-12-01

    As the dominant reservoir of heat uptake in the climate system, the world's oceans provide a critical measure of global climate change. Here, we infer deep ocean warming in the context of global sea level rise and Earth's energy budget between January 2005 and December 2013 based on satellite altimetry, GRACE and Argo floats. Direct measurements of ocean warming above 2000m depth explain 0.9 +/- 0.15 mm/yr of the observed 2.78 +/- 0.32 mm/yr rate of global mean sea level rise. Over the entire water column, independent estimates of ocean warming yield a contribution of 0.77+/-0.28 mm/yr in sea level rise and agree with the upper ocean estimate to within the estimated uncertainties. Accounting for additional possible systematic uncertainties, the deep ocean (below 2000m) contributes -0.13 +/- 0.72 mm/yr to global sea level rise and -0.08 +/- 0.43 W/m2 to Earth's energy balance. The net warming of the ocean implies an energy imbalance for the Earth of 0.64 ± 0.44 W/m2 from 2005 to 2013.

  1. Investigation of electrically-active deep levels in single-crystalline diamond by particle-induced charge transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Kada, W.; Kambayashi, Y.; Ando, Y.; Onoda, S.; Umezawa, H.; Mokuno, Y.; Shikata, S.; Makino, T.; Koka, M.; Hanaizumi, O.; Kamiya, T.; Ohshima, T.

    2016-04-01

    To investigate electrically-active deep levels in high-resistivity single-crystalline diamond, particle-induced charge transient spectroscopy (QTS) techniques were performed using 5.5 MeV alpha particles and 9 MeV carbon focused microprobes. For unintentionally-doped (UID) chemical vapor deposition (CVD) diamond, deep levels with activation energies of 0.35 eV and 0.43 eV were detected which correspond to the activation energy of boron acceptors in diamond. The results suggested that alpha particle and heavy ion induced QTS techniques are the promising candidate for in-situ investigation of deep levels in high-resistivity semiconductors.

  2. Springback assessment based on level set interpolation and shape manifolds in deep drawing

    NASA Astrophysics Data System (ADS)

    Le Quilliec, Guenhael; Raghavan, Balaji; Breitkopf, Piotr; Rassineux, Alain; Villon, Pierre; Roelandt, Jean-Marc

    2013-12-01

    In this paper, we introduce an original shape representation approach for automatic springback characterization. It is based on the generation of parameterized Level Set functions. The central idea is the concept of the shape manifold representing the design domain in the reduced-order shape-space. Performing Proper Orthogonal Decomposition on the shapes followed by using the Diffuse Approximation allows us to efficiently reduce the problem dimensionality and to interpolate uniquely between admissible input shapes, while also determining the smallest number of parameters needed to characterize the final formed shape. We apply this methodology to the problem of springback assessment for the deep drawing operation of metal sheets.

  3. Deep-level magma dehydration and ascent rates at Mt. Etna (Sicily, Italy)

    NASA Astrophysics Data System (ADS)

    Armienti, P.; Perinelli, C.; Putirka, K.

    2012-04-01

    Magma ascent velocity, v (dH/dt; H = depth, t = time),can be determined from ascent rate (dP/dt), and rate of cooling (dT/dt): v= 1/(rgpg) (dP/dT)(dT/dt) where r is magma density, P is pressure, T is temperature and g is the acceleration of gravity. This equation for v provides a key to investigating the relationships between initial ascent rate of magma and the depths of magma dehydration, and v can be calculated using pressure and temperature (P - PH2O - T) estimates from mineral-liquid thermobarometry, and cooling rates inferred from Crystal Size Distribution (CSD) theory. For recent Mt. Etna lava flows, both dP/dT and dT/dt have been well characterized based, respectively, on clinopyroxene thermobarometry, and clinopyroxene CSDs (the latter yields dT/dt = 2x10-6 °C/s). Deep-level (>20 km) magma ascent rates range from practically 0 (where clinopyroxene P - T estimates form a cluster, and so dP/dT ≈ 0), to about 10 m/hr for flows that yield very steep P - T trajectories. Many lava flows at Mt. Etna yield P - T paths that follow a hydrous (about 3% water) clinopyroxene saturation surface, which closely approximates water contents obtained from melt inclusions. Independent assessments of deep level water content yield ascent rates of ~1 m/hr, in agreement with the slowest rates derived for magma effusion or vapor-driven ascent (~0.001 to >0.2 m/s, or 3.6 to 720 m/hr). Changes in P - T slopes, as obtained by pyroxene thermobarometry, indicate an upward acceleration of magma, which may be due to the onset of deep-level magma dehydration linked to the non-ideal behavior of water and CO2 mixtures that induce a deep-level maximum of water loss at P ≈ 0.4 MPa at T ≈ 1200 ° C for a CO2 content >1000ppm. Melt inclusion data on CO2 and H2O contents are successfully reproduced and interpreted in a context of magma dehydration induced by a CO2 flux possibly deriving by decarbonation reaction of the carbonate fraction of the Capo D'Orlando flysch.

  4. Characterization of deep level defects and thermally stimulated depolarization phenomena in La-doped TlInS{sub 2} layered semiconductor

    SciTech Connect

    Seyidov, MirHasan Yu. Suleymanov, Rauf A.; Mikailzade, Faik A.; Kargın, Elif Orhan; Odrinsky, Andrei P.

    2015-06-14

    Lanthanum-doped high quality TlInS{sub 2} (TlInS{sub 2}:La) ferroelectric-semiconductor was characterized by photo-induced current transient spectroscopy (PICTS). Different impurity centers are resolved and identified. Analyses of the experimental data were performed in order to determine the characteristic parameters of the extrinsic and intrinsic defects. The energies and capturing cross section of deep traps were obtained by using the heating rate method. The observed changes in the Thermally Stimulated Depolarization Currents (TSDC) near the phase transition points in TlInS{sub 2}:La ferroelectric-semiconductor are interpreted as a result of self-polarization of the crystal due to the internal electric field caused by charged defects. The TSDC spectra show the depolarization peaks, which are attributed to defects of dipolar origin. These peaks provide important information on the defect structure and localized energy states in TlInS{sub 2}:La. Thermal treatments of TlInS{sub 2}:La under an external electric field, which was applied at different temperatures, allowed us to identify a peak in TSDC which was originated from La-dopant. It was established that deep energy level trap BTE43, which are active at low temperature (T ≤ 156 K) and have activation energy 0.29 eV and the capture cross section 2.2 × 10{sup −14} cm{sup 2}, corresponds to the La dopant. According to the PICTS results, the deep level trap center B5 is activated in the temperature region of incommensurate (IC) phases of TlInS{sub 2}:La, having the giant static dielectric constant due to the structural disorders. From the PICTS simulation results for B5, native deep level trap having an activation energy of 0.3 eV and the capture cross section of 1.8 × 10{sup −16} cm{sup 2} were established. A substantial amount of residual space charges is trapped by the deep level localized energy states of B5 in IC-phase. While the external electric field is applied, permanent dipoles

  5. Characterization of deep level defects and thermally stimulated depolarization phenomena in La-doped TlInS2 layered semiconductor

    NASA Astrophysics Data System (ADS)

    Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Mikailzade, Faik A.; Kargın, Elif Orhan; Odrinsky, Andrei P.

    2015-06-01

    Lanthanum-doped high quality TlInS2 (TlInS2:La) ferroelectric-semiconductor was characterized by photo-induced current transient spectroscopy (PICTS). Different impurity centers are resolved and identified. Analyses of the experimental data were performed in order to determine the characteristic parameters of the extrinsic and intrinsic defects. The energies and capturing cross section of deep traps were obtained by using the heating rate method. The observed changes in the Thermally Stimulated Depolarization Currents (TSDC) near the phase transition points in TlInS2:La ferroelectric-semiconductor are interpreted as a result of self-polarization of the crystal due to the internal electric field caused by charged defects. The TSDC spectra show the depolarization peaks, which are attributed to defects of dipolar origin. These peaks provide important information on the defect structure and localized energy states in TlInS2:La. Thermal treatments of TlInS2:La under an external electric field, which was applied at different temperatures, allowed us to identify a peak in TSDC which was originated from La-dopant. It was established that deep energy level trap BTE43, which are active at low temperature (T ≤ 156 K) and have activation energy 0.29 eV and the capture cross section 2.2 × 10-14 cm2, corresponds to the La dopant. According to the PICTS results, the deep level trap center B5 is activated in the temperature region of incommensurate (IC) phases of TlInS2:La, having the giant static dielectric constant due to the structural disorders. From the PICTS simulation results for B5, native deep level trap having an activation energy of 0.3 eV and the capture cross section of 1.8 × 10-16 cm2 were established. A substantial amount of residual space charges is trapped by the deep level localized energy states of B5 in IC-phase. While the external electric field is applied, permanent dipoles, which are originated from the charged B5 deep level defects, are aligned in the

  6. Halogenated persistent organic pollutants in relation to trophic level in deep sea fish.

    PubMed

    Webster, Lynda; Russell, Marie; Walsham, Pam; Hussy, Ines; Lacaze, Jean-Pierre; Phillips, Lesley; Dalgarno, Eric; Packer, Gill; Neat, Francis; Moffat, Colin F

    2014-11-15

    The bioaccumulation of persistent organic pollutants (POPs) in deep sea fish from the Rockall fishing area was investigated. Predator and prey species were analysed for stable isotopes, fatty acids, polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). δ(15)N indicated that black scabbard was at the highest trophic level and the prey the lowest. The fatty acid signatures indicated that black scabbard and black dogfish fed at a higher trophic level compared to the roundnose grenadier. PCBs and PBDEs were detected in the liver of all three predator species. PCB concentrations were significantly higher in the roundnose grenadier, possibly due to their longer life span. PCB concentrations were compared to OSPAR assessment criteria, concentrations were above background but below Environmental Assessment Criteria for all but one congener. PCB concentrations were below food safety levels in the flesh, but exceeded the limit for liver in the roundnose grenadier and black dogfish. PMID:25287221

  7. Formation of copper(I) from trace levels of copper(II) as an artifactual impurity in the HPLC analysis of olanzapine.

    PubMed

    Baertschi, Steven W; Olsen, Bernard A; Wozniak, Timothy J; Toltl, Nick; O'Shea, Colette; Jansen, Patrick J

    2016-06-01

    An analytical artifact peak appearing to be an impurity was observed intermittently among several laboratories performing HPLC analyses of olanzapine drug substance and formulation samples. The artifact peak was identified as Cu(I) that was formed from the reaction of trace amounts of Cu(II) with olanzapine in the sample solution. Unlike Cu(II), Cu(I) was retained under the ion-pairing HPLC conditions used for analysis. A reaction mechanism was postulated whereby Cu(II) present in the sample solution oxidizes olanzapine to a radical-cation, resulting in formation of Cu(I) and three oxidation products of olanzapine including a previously unknown oxidation product that was identified as hydroxy-olanzapine. Acetonitrile in the sample solution was necessary for the reaction to occur. As little as 100 ppb Cu(II) in the sample solution produced a Cu(I) peak, that by peak area, corresponded to about 0.1% relative to the olanzapine peak. The hydroxy-olanzapine oxidation product was also detectable, but the relative peak area was much smaller. To prevent formation of the Cu(I) artifact peak, EDTA was added to the sample solvent to complex any trace Cu(II) that might be present. The addition of EDTA was shown to prevent Cu(I) formation when Cu(II) was present at levels of 4ppm in the sample solution. PMID:27023131

  8. Analytical advances in pharmaceutical impurity profiling.

    PubMed

    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

  9. Milankovitch tuning of deep-sea records: Implications for maximum rates of change of sea level

    NASA Astrophysics Data System (ADS)

    Berger, Wolfgang H.

    2013-02-01

    The analysis of several stacked and tuned records from the deep-sea floor yields two rather different sets of values for rates of sea-level rise. One of these reflects "regular" growth and decay and the other represents rapid decay of polar ice. Typical rise rates during rapid decay are near 1.2 m per century; with higher values seemingly following an abundance distribution that may be described by a standard deviation of 0.4 m per century (one third of the typical value). Distributions are based on a millennium resolution, leaving room for higher values for selected centuries within any millennium. Nevertheless, rise values beyond 5 m per century seem highly unusual. The quality of the match between deep-sea record (taken as differential) and Milankovitch forcing is excellent for the last 400,000 years (that is, the time since the "mid-Brunhes Event," a period that may be referred to as the "Emiliani Chron") but is poor in certain time spans before that. Difficulties associated with precise dating and a changing level of instability of polar ice prevent identification of trigger events for deglaciation. What is observable is that during periods of rapid decay, once sea level started to rise, it kept doing so for millennia (presumably till suitable ice masses were used up). Thus, it seems that a rise of sea level is itself a positive feedback on rapid melting of ice. Negative feedback, if real (as assumed in certain hypotheses about the origin of the Younger Dryas) is an unexpected exception that presumably relies on a high threshold value of sea-level rise.

  10. Deep levels in virtually unstrained InGaAs layers deposited on GaAs

    NASA Astrophysics Data System (ADS)

    Pal, D.; Gombia, E.; Mosca, R.; Bosacchi, A.; Franchi, S.

    1998-09-01

    The dislocation-related deep levels in InxGa1-xAs layers grown by molecular beam epitaxy on GaAs substrates have been investigated. Virtually unstrained InGaAs layers with mole fraction x of 0.10, 0.20, and 0.30 have been obtained by properly designing the In composition of linearly graded InxGa1-xAs buffers. Two electron traps, labeled as E2 and E3, whose activation energy scales well with the energy gap, have been found. Unlike E2, E3 shows: (i) a logarithmic dependence of the deep level transient spectroscopy amplitude on the filling pulse width and (ii) an increase of concentration as the buffer/InGaAs interface is approached. These findings, together with the observation that, in compressively strained In0.2Ga0.8As, the E3-related concentration is definitely higher than that of virtually unstrained In0.2Ga0.8As, indicate that this trap is likely originated by extended defects like threading dislocations.

  11. Sea-level and deep-sea-temperature variability over the past 5.3 million years.

    PubMed

    Rohling, E J; Foster, G L; Grant, K M; Marino, G; Roberts, A P; Tamisiea, M E; Williams, F

    2014-04-24

    Ice volume (and hence sea level) and deep-sea temperature are key measures of global climate change. Sea level has been documented using several independent methods over the past 0.5 million years (Myr). Older periods, however, lack such independent validation; all existing records are related to deep-sea oxygen isotope (δ(18)O) data that are influenced by processes unrelated to sea level. For deep-sea temperature, only one continuous high-resolution (Mg/Ca-based) record exists, with related sea-level estimates, spanning the past 1.5 Myr. Here we present a novel sea-level reconstruction, with associated estimates of deep-sea temperature, which independently validates the previous 0-1.5 Myr reconstruction and extends it back to 5.3 Myr ago. We find that deep-sea temperature and sea level generally decreased through time, but distinctly out of synchrony, which is remarkable given the importance of ice-albedo feedbacks on the radiative forcing of climate. In particular, we observe a large temporal offset during the onset of Plio-Pleistocene ice ages, between a marked cooling step at 2.73 Myr ago and the first major glaciation at 2.15 Myr ago. Last, we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep-sea temperature. PMID:24739960

  12. Electron Traps Detected in p-type GaAsN Using Deep Level Transient Spectroscopy

    SciTech Connect

    Johnston, S.; Kurtz, S.; Friedman, D.; Ptak, A.; Ahrenkiel, R.; Crandall, R.

    2005-01-01

    The GaAsN alloy can have a band gap as small as 1.0 eV when the nitrogen composition is about 2%. Indium can also be added to the alloy to increase lattice matching to GaAs and Ge. These properties are advantageous for developing a highly-efficient, multi-junction solar cell. However, poor GaAsN cell properties, such as low open-circuit voltage, have led to inadequate performance. Deep-level transient spectroscopy of p-type GaAsN has identified an electron trap having an activation energy near 0.2 eV and a trap density of at least 1016 cm-3. This trap level appears with the addition of small amounts of nitrogen to GaAs, which also corresponds to an increased drop in open-circuit voltage.

  13. Effect of iodine impurity on relaxation of photoexcited silver chloride

    SciTech Connect

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

    2008-03-15

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

  14. Effects of Pressure on Optically Active Deep Levels in Phosphorus Doped ZnSe

    NASA Astrophysics Data System (ADS)

    Weinstein, B. A.; Iota, V.

    1998-03-01

    We report high pressure photoluminescence (PL) and PL-excitation (PLE) studies at 8K of the 'midgap' emission in P-doped ZnSe using a diamond-cell with He medium. The dominant emission at low pressure is due to donor-acceptor-pair (DAP) transitions between shallow donors and deep trigonally relaxed P_Se acceptors.(J. Davies, et al., J. Luminescence 18/19, 322 (1979)) Its PL and PLE peaks shift by 8.2meV/kbar and 5.9meV/kbar, respectively -- Stokes shift decreasing with pressure. At 35kbar a new PL band, shifting to lower energy (-5.4meV/kbar), emerges from above the absorption edge, and concurrently the original DAP PL quenches. This shows that a resonant level, a deep donor or possibly a P_Se antibonding state,(R. Watts, et al., Phys. Rev. B3), 404 (1971) crosses the conduction edge into the gap. A third PL band is seen only with internse UV excitation. It occurs initially as a high energy shoulder of the original DAP peak, but shifts more rapidly upward (9.4meV/kbar) until it crosses the edge and quenches at 40kbar. We discuss candidates for this band, including donor-P_Se complexes, and we compare our results to similar work on the Zn vacancy in ZnSe. (figures)

  15. Influence of growth temperature and temperature ramps on deep level defect incorporation in m-plane GaN

    SciTech Connect

    Armstrong, A. M.; Kelchner, K.; Nakamura, S.; DenBaars, S. P.; Speck, J. S.

    2013-12-02

    The dependence of deep level defect incorporation in m-plane GaN films grown by metal-organic chemical vapor deposition on bulk m-plane GaN substrates as a function of growth temperature (T{sub g}) and T{sub g} ramping method was investigated using deep level optical spectroscopy. Understanding the influence of T{sub g} on GaN deep level incorporation is important for InGaN/GaN multi-quantum well (MQW) light emitting diodes (LEDs) and laser diodes (LDs) because GaN quantum barrier (QB) layers are grown much colder than thin film GaN to accommodate InGaN QW growth. Deep level spectra of low T{sub g} (800 °C) GaN films grown under QB conditions were compared to deep level spectra of high T{sub g} (1150 °C) GaN. Reducing T{sub g}, increased the defect density significantly (>50×) through introduction of emergent deep level defects at 2.09 eV and 2.9 eV below the conduction band minimum. However, optimizing growth conditions during the temperature ramp when transitioning from high to low T{sub g} substantially reduced the density of these emergent deep levels by approximately 40%. The results suggest that it is important to consider the potential for non-radiative recombination in QBs of LED or LD active regions, and tailoring the transition from high T{sub g} GaN growth to active layer growth can mitigate such non-radiative channels.

  16. Intrinsic deep hole trap levels in Cu2O with self-consistent repulsive Coulomb energy

    NASA Astrophysics Data System (ADS)

    Huang, Bolong

    2016-03-01

    The large error of the DFT+U method on full-filled shell metal oxides is due to the residue of self-energy from the localized d orbitals of cations and p orbitals of the anions. U parameters are selfconsistently found to achieve the analytical self-energy cancellation. The improved band structures based on relaxed lattices of Cu2O are shown based on minimization of self-energy error. The experimentally reported intrinsic p-type trap levels are contributed by both Cu-vacancy and the O-interstitial defects in Cu2O. The latter defect has the lowest formation energy but contributes a deep hole trap level while the Cuvacancy has higher energy cost but acting as a shallow acceptor. Both present single-particle levels spread over nearby the valence band edge, consistent to the trend of defects transition levels. By this calculation approach, we also elucidated the entanglement of strong p-d orbital coupling to unravel the screened Coulomb potential of fully filled shells.

  17. Characterization of a Dominant Electron Trap in GaNAs Using Deep-Level Spectroscopy

    SciTech Connect

    Johnston, S. W.; Kurtz, S. R.

    2006-08-01

    Dilute-nitrogen GaNAs epitaxial layers grown by metal-organic chemical vapor deposition were characterized by deep-level transient spectroscopy (DLTS). For all samples, the dominant DLTS signal corresponds to an electron trap having an activation energy of about 0.25 to 0.35 eV. The minority-carrier trap density in the p-type material is quantified based on computer simulation of the devices. The simulations show that only about 2% of the traps in the depleted layer are filled during the transient. The fraction of the traps that are filled depends strongly on the depth of the trap, but only weakly on the doping of the layers and on the conduction-band offset. The simulations provide a pathway to obtain semi-quantitative data for analysis of minority-carrier traps by DLTS.

  18. Promoting and Studying Deep-Level Discourse During Large-Lecture Introductory Physics

    NASA Astrophysics Data System (ADS)

    Li, Sissi; Demaree, Dedra

    2010-10-01

    At Oregon State University, the introductory calculus-based physics sequence utilizes social engagement as a learning tool. The reformed curriculum is modeled after the Interactive Science Learning Environment from Rutgers University, and makes use of Peer Instruction as a pedagogical tool to facilitate interactions. Over the past two years we have utilized a number of techniques to understand how to facilitate activities that promote productive discussion within the large lecture classroom. We specifically seek student discussion that goes beyond agreement on conceptual questions, encouraging deeper discussions such as what assumptions are appropriate, or how different assumptions would change the chosen answer to a given question. We have quantitative analysis of engagement based on video data, qualitative analysis of dialogue from audio data, and classroom observations by an external researcher. In this paper we share a subset of what we have learned about how to engage students in deep-level discussions during lecture.

  19. Valence band offset at the Si/SiSn interface by applying deep level transient spectroscopy.

    PubMed

    Rangel-Kuoppa, Victor-Tapio; Tonkikh, Alexander; Zakharov, Nikolay; Eisenschmidt, Christian; Werner, Peter

    2016-02-19

    A set of Si1-x Sn x /Si(001) quantum wells (QWs) is grown by applying molecular beam epitaxy. The activation energies of holes in these QWs are studied by deep-level transient spectroscopy. It is observed that the holes activation energies increase monotonically with the Sn fraction (x). The valence band offset between pseudomorphic Si1-x Sn x and Si obeys the dependence ΔE(v) = 1.69x eV, while the offset between the average valence bands of unstrained Si1-x Sn x /Si heterojunction was deduced and obeys the dependence ΔE(v(av)) = 1.27x eV. PMID:26775681

  20. On the capability of deep level transient spectroscopy for characterizing multi-crystalline silicon

    SciTech Connect

    Mchedlidze, T.; Nacke, M.; Hieckmann, E.; Weber, J.

    2014-01-07

    The suitability of the deep level transient spectroscopy (DLTS) technique in exploring locations with high and degraded carrier lifetimes containing grain-boundaries (GBs) in multicrystalline silicon (mc-Si) wafers was studied. The types and locations of GBs were determined in mc-Si samples by electron backscatter diffraction. Mesa-type Schottky diodes were prepared at (along) GBs and at reference, GB-free locations. Detected DLTS signals varied strongly along the same GB. Experiments with dislocation networks, model structures for GBs, showed that GB-related traps may be explored only using special arrangement of a GB and the diode contacts. Iron-related carrier traps were detected in locations with degraded carrier lifetimes. Densities of the traps for near-GB and for GB free locations were compared to the lifetime measurement results.

  1. Behavior of the Fe impurity in Hg{sup 3}In{sup 2}Te{sup 6} crystals

    SciTech Connect

    Grushka, O. G. Savchuk, A. I.; Chupyra, S. N.; Bilichuk, S. V.

    2015-07-15

    Optical and photoelectric measurements reveal that doping with iron leads to the formation of a deep level at E{sup c}–0.69 eV in Hg{sup 3}In{sup 2}Te{sup 6} crystals. When light is absorbed by Fe{sup 2+} impurity centers, both electronic transitions of the impurity-level–conduction-band type and optical transitions between ground and excited states of the aforementioned centers (intracenter transitions) are observed. Investigations of transport phenomena point to the acceptor properties of Fe{sup 2+} centers.

  2. Silicon materials task of the low cost solar array project (Phase III). Effects of impurities and processing on silicon solar cells. Phase III summary and seventeenth quarterly report, Volume 2: analysis of impurity behavior

    SciTech Connect

    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.

    1980-01-23

    The object of this phase of the program has been to investigate the effects of various processes, metal contaminants and contaminant-process interactions on the properties of silicon and on the performance of terrestrial silicon solar cells. The study encompassed topics including thermochemical (gettering) treatments, base doping concentration, base doping type (n vs. p), grain boundary-impurity interaction, non-uniformity of impurity distribution, long term effects of impurities, as well as synergic and complexing phenomena. The program approach consists in: (1) the growth of doubly and multiply-doped silicon single crystals containing a baseline boron or phosphorus dopant and specific impurities which produce deep levels in the forbidden band gap; (2) assessment of these crystals by chemical, microstructural, electrical and solar cell tests; (3) correlation of the impurity type and concentration with crystal quality and device performance; and (4) delineation of the role of impurities and processing on subsequent silicon solar cell performance. The overall results reported are based on the assessment of nearly 200 silicon ingots. (WHK)

  3. Effect of Z{sub 1/2}, EH{sub 5}, and Ci1 deep defects on the performance of n-type 4H-SiC epitaxial layers Schottky detectors: Alpha spectroscopy and deep level transient spectroscopy studies

    SciTech Connect

    Mannan, Mohammad A.; Chaudhuri, Sandeep K.; Nguyen, Khai V.; Mandal, Krishna C.

    2014-06-14

    Spectroscopic performance of Schottky barrier alpha particle detectors fabricated on 50 μm thick n-type 4H-SiC epitaxial layers containing Z{sub 1/2}, EH{sub 5}, and Ci1 deep levels were investigated. The device performance was evaluated on the basis of junction current/capacitance characterization and alpha pulse-height spectroscopy. Capacitance mode deep level transient spectroscopy revealed the presence of the above-mentioned deep levels along with two shallow level defects related to titanium impurities (Ti(h) and Ti(c)) and an unidentified deep electron trap located at 2.4 eV below the conduction band minimum, which is being reported for the first time. The concentration of the lifetime killer Z{sub 1/2} defects was found to be 1.7 × 10{sup 13} cm{sup −3}. The charge transport and collection efficiency results obtained from the alpha particle pulse-height spectroscopy were interpreted using a drift-diffusion charge transport model. Based on these investigations, the physics behind the correlation of the detector properties viz., energy resolution and charge collection efficiency, the junction properties like uniformity in barrier-height, leakage current, and effective doping concentration, and the presence of defects has been discussed in details. The studies also revealed that the dominating contribution to the charge collection efficiency was due to the diffusion of charge carriers generated in the neutral region of the detector. The 10 mm{sup 2} large area detectors demonstrated an impressive energy resolution of 1.8% for 5486 keV alpha particles at an optimized operating reverse bias of 130 V.

  4. Impurities in snowpacks.

    PubMed

    Sommerfeld, R A

    1989-04-01

    Snow can be involved in the acquisition, transport, storage and release of atmospheric impurities. Because it can store impurities for periods of time ranging from hours to millenia, it provides a medium for monitoring atmospheric impurities for a wide range of time scales.In most climates, snow is involved in the precipitation process. It can acquire atmospheric impurities either as aerosols or as gases. The aereosols can be included in the body of the snow crystals or adhered to their surfaces. Gases may be included in bubbles, particularly in the case of rime, or adsorbed on the ice surfaces. The amount of ice surface in a small storm is about 10(10) m(2).Snow on the ground can store the impurities acquired in the precipitation process and can acquire additional impurities as dry deposition. The low temperatures and the fact that ice is a solid reduces biological activity and rates of inorganic reactions. However, the assumption that there is no activity in the winter is not well found. Exchange is possible between different layers of the snow and between the snow and the atmosphere, resulting in relocation of gases and aerosols. These processes also insure that the impurities reside on the exterior surfaces of the ice particles that form the snowpack. Biological activity is possible near the ground-snow interface in most climates.The seasonal snowpack releases its impurities when it melts. Because below freezing processes relocate any internal impurities to the ice surfaces within the snowpack, the impurities are available to the first melt water. Pulses of both acidic and alkalinic impurities have been observed with the initial snow melt water. However, the monitoring of such pulses is difficult and the measurements are inconsistent.Impurities are incorporated for longer periods of time in perennial snowpacks and finally in ice fields. These can be glaciers, or, at the largest scale, continental ice sheets. Coring such ice is expensive but provides data on

  5. Silicon materials task of the low cost solar array project (Phase III). Effect of impurities and processing on silicon solar cells. Phase III summary and seventeenth quarterly report, Volume 1: characterization methods for impurities in silicon and impurity effects data base

    SciTech Connect

    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

    The object of Phase III of the program has been to investigate the effects of various processes, metal contaminants and contaminant-process interactions on the performance of terrestrial silicon solar cells. The study encompassed a variety of tasks including: (1) a detailed examination of thermal processing effects, such as HCl and POCl/sub 3/ gettering on impurity behavior, (2) completion of the data base and modeling for impurities in n-base silicon, (3) extension of the data base on p-type material to include elements likely to be introduced during the production, refining, or crystal growth of silicon, (4) effects on cell performance on anisotropic impurity distributions in large CZ crystals and silicon webs, and (5) a preliminary assessment of the permanence of the impurity effects. Two major topics are treated: methods to measure and evaluate impurity effects in silicon and comprehensive tabulations of data derived during the study. For example, discussions of deep level spectroscopy, detailed dark I-V measurements, recombination lifetime determination, scanned laser photo-response, and conventional solar cell I-V techniques, as well as descriptions of silicon chemical analysis are included. Considerable data are tabulated on the composition, electrical, and solar cell characteristics of impurity-doped silicon.

  6. Challenges to Standardization: A Case Study Using Coastal and Deep-Ocean Water Level Data

    NASA Astrophysics Data System (ADS)

    Sweeney, A. D.; Stroker, K. J.; Mungov, G.; McLean, S. J.

    2015-12-01

    Sea levels recorded at coastal stations and inferred from deep-ocean pressure observations at the seafloor are submitted for archive in multiple data and metadata formats. These formats include two forms of schema-less XML and a custom binary format accompanied by metadata in a spreadsheet. The authors report on efforts to use existing standards to make this data more discoverable and more useful beyond their initial use in detecting tsunamis. An initial review of data formats for sea level data around the globe revealed heterogeneity in presentation and content. In the absence of a widely-used domain-specific format, we adopted the general model for structuring data and metadata expressed by the Network Common Data Form (netCDF). netCDF has been endorsed by the Open Geospatial Consortium and has the advantages of small size when compared to equivalent plain text representation and provides a standard way of embedding metadata in the same file. We followed the orthogonal time-series profile of the Climate and Forecast discrete sampling geometries as the convention for structuring the data and describing metadata relevant for use. We adhered to the Attribute Convention for Data Discovery for capturing metadata to support user search. Beyond making it possible to structure data and metadata in a standard way, netCDF is supported by multiple software tools in providing programmatic cataloging, access, subsetting, and transformation to other formats. We will describe our successes and failures in adhering to existing standards and provide requirements for either augmenting existing conventions or developing new ones. Some of these enhancements are specific to sea level data, while others are applicable to time-series data in general.

  7. Alloy Engineering of Defect Properties in Semiconductors: Suppression of Deep Levels in 2D Transition-metal Dichalcogenides

    SciTech Connect

    Huang, Bing; Yoon, Mina; Sumpter, Bobby G; Wei, Su-Huai; Liu, Feng

    2015-09-18

    Developing practical approaches to effectively reduce the deep defect levels in semiconductors is critical for their use in electronic and optoelectronic devices, but this is still a very challenging task. In this Letter, we propose that specific alloying can provide an effective means to suppress the deep defect levels in semiconductors while maintaining their basic electronic properties. Specifically, we demonstrate that for such 2D transition-metal dichalcogenides as MoSe2 and WSe2, in which the most abundant defects that can induce deep levels are anion vacancies, the deep levels can be effectively suppressed in Mo1-xWxSe2 alloys at low W concentrations. This surprising phenomenon is associated with the fact that the global alloy concentration can substantially tune the band edge energies, whereas the preferred locations of Se vacancies around W atoms control the defect level locally. Our findings illustrate a new concept of alloy engineering and provide a promising approach to control the defect properties of semiconductors.

  8. Alloy Engineering of Defect Properties in Semiconductors: Suppression of Deep Levels in 2D Transition-metal Dichalcogenides

    DOE PAGESBeta

    Huang, Bing; Yoon, Mina; Sumpter, Bobby G; Wei, Su-Huai; Liu, Feng

    2015-09-18

    Developing practical approaches to effectively reduce the deep defect levels in semiconductors is critical for their use in electronic and optoelectronic devices, but this is still a very challenging task. In this Letter, we propose that specific alloying can provide an effective means to suppress the deep defect levels in semiconductors while maintaining their basic electronic properties. Specifically, we demonstrate that for such 2D transition-metal dichalcogenides as MoSe2 and WSe2, in which the most abundant defects that can induce deep levels are anion vacancies, the deep levels can be effectively suppressed in Mo1-xWxSe2 alloys at low W concentrations. This surprisingmore » phenomenon is associated with the fact that the global alloy concentration can substantially tune the band edge energies, whereas the preferred locations of Se vacancies around W atoms control the defect level locally. Our findings illustrate a new concept of alloy engineering and provide a promising approach to control the defect properties of semiconductors.« less

  9. High levels of natural radioactivity in biota from deep-sea hydrothermal vents: a preliminary communication.

    PubMed

    Charmasson, Sabine; Sarradin, Pierre-Marie; Le Faouder, Antoine; Agarande, Michèle; Loyen, Jeanne; Desbruyères, Daniel

    2009-06-01

    Hydrothermal deep-sea vent fauna is naturally exposed to a peculiar environment enriched in potentially toxic species such as sulphides, heavy metals and natural radionuclides. It is now well established that some of the organisms present in such an environment accumulate metals during their lifespan. Though only few radionuclide measurements are available, it seems likely that hydrothermal vent communities are exposed to high natural radiation doses. Various archived biological samples collected on the East Pacific Rise and the Mid-Atlantic Ridge in 1996, 2001 and 2002 were analysed by ICP-MS in order to determine their uranium contents ((238)U, (235)U and (234)U). In addition (210)Po-Pb were determined in 2 samples collected in 2002. Vent organisms are characterized by high U, and Po-Pb levels compared to what is generally encountered in organisms from outside hydrothermal vent ecosystems. Though the number of data is low, the results reveal various trends in relation to the site, the location within the mixing zone and/or the organisms' trophic regime. PMID:19362761

  10. Thermal-mechanical modeling of deep borehole disposal of high-level radioactive waste.

    SciTech Connect

    Arnold, Bill Walter; Hadgu, Teklu

    2010-12-01

    Disposal of high-level radioactive waste, including spent nuclear fuel, in deep (3 to 5 km) boreholes is a potential option for safely isolating these wastes from the surface and near-surface environment. Existing drilling technology permits reliable and cost-effective construction of such deep boreholes. Conditions favorable for deep borehole disposal in crystalline basement rocks, including low permeability, high salinity, and geochemically reducing conditions, exist at depth in many locations, particularly in geologically stable continental regions. Isolation of waste depends, in part, on the effectiveness of borehole seals and potential alteration of permeability in the disturbed host rock surrounding the borehole. Coupled thermal-mechanical-hydrologic processes induced by heat from the radioactive waste may impact the disturbed zone near the borehole and borehole wall stability. Numerical simulations of the coupled thermal-mechanical response in the host rock surrounding the borehole were conducted with three software codes or combinations of software codes. Software codes used in the simulations were FEHM, JAS3D, Aria, and Adagio. Simulations were conducted for disposal of spent nuclear fuel assemblies and for the higher heat output of vitrified waste from the reprocessing of fuel. Simulations were also conducted for both isotropic and anisotropic ambient horizontal stress in the host rock. Physical, thermal, and mechanical properties representative of granite host rock at a depth of 4 km were used in the models. Simulation results indicate peak temperature increases at the borehole wall of about 30 C and 180 C for disposal of fuel assemblies and vitrified waste, respectively. Peak temperatures near the borehole occur within about 10 years and decline rapidly within a few hundred years and with distance. The host rock near the borehole is placed under additional compression. Peak mechanical stress is increased by about 15 MPa (above the assumed ambient

  11. Thermal-Mechanical Modeling of Deep Borehole Disposal of High-Level Radioactive Waste

    NASA Astrophysics Data System (ADS)

    Arnold, B. W.; Clayton, D. J.; Herrick, C. G.; Hadgu, T.

    2010-12-01

    Disposal of high-level radioactive waste, including spent nuclear fuel, in deep (3 to 5 km) boreholes is a potential option for safely isolating these wastes from the surface and near-surface environment. Existing drilling technology permits reliable and cost-effective construction of such deep boreholes. Conditions favorable for deep borehole disposal in crystalline basement rocks, including low permeability, high salinity, and geochemically reducing conditions, exist at depth in many locations, particularly in geologically stable continental regions. Isolation of waste depends, in part, on the effectiveness of borehole seals and potential alteration of permeability in the disturbed host rock surrounding the borehole. Coupled thermal-mechanical-hydrologic processes induced by heat from the radioactive waste may impact the disturbed zone near the borehole and borehole wall stability. Numerical simulations of the coupled thermal-mechanical response in the host rock surrounding the borehole were conducted with three software codes or combinations of software codes. Software codes used in the simulations were FEHM, JAS3D, Aria, and Adagio. Simulations were conducted for disposal of spent nuclear fuel assemblies and for the higher heat output of vitrified waste from the reprocessing of fuel. Simulations were also conducted for both isotropic and anisotropic ambient horizontal stress in the host rock. Physical, thermal, and mechanical properties representative of granite host rock at a depth of 4 km were used in the models. Simulation results indicate peak temperature increases at the borehole wall of about 30 °C and 180 °C for disposal of fuel assemblies and vitrified waste, respectively. Peak temperatures near the borehole occur within about 10 years and decline rapidly within a few hundred years and with distance. The host rock near the borehole is placed under additional compression. Peak mechanical stress is increased by about 15 MPa (above the assumed ambient

  12. Perceived Deep-Level Dissimilarity: Personality Antecedents and Impact on Overall Job Attitude, Helping, Work Withdrawal, and Turnover

    ERIC Educational Resources Information Center

    Liao, Hui; Chuang, Aichia; Joshi, Aparna

    2008-01-01

    The current research extends three research areas in relational demography: considering deep-level dissimilarity in theory building, assessing dissimilarity perceptions directly in theory testing, and examining the antecedents of dissimilarity perceptions. The results, based on two field studies using diverse samples, demonstrate the effects of…

  13. Transforming Passive Receptivity of Knowledge into Deep Learning Experiences at the Undergraduate Level: An Example from Music Theory

    ERIC Educational Resources Information Center

    Ferenc, Anna

    2015-01-01

    This article discusses transformation of passive knowledge receptivity into experiences of deep learning in a lecture-based music theory course at the second-year undergraduate level through implementation of collaborative projects that evoke natural critical learning environments. It presents an example of such a project, addresses key features…

  14. Passivation of impurities in semiconductors by hydrogen and light metal ions

    NASA Astrophysics Data System (ADS)

    Gislason, Hafliði P.

    1997-01-01

    Books as well as numerous articles have been written about hydrogen passivation in classical semiconductors such as Si and GaAs. The subject has gained a renewed interest recently since hydrogen is widely considered to saturate the hole conductivity of the wide bandgap semiconductors GaN and ZnSe which are currently most promising for blue light emitting devices. Other group-I impurities are capable of compensating the electrical conductivity of semiconductors both through directly neutralising (passivating) the impurity or providing space charge of polarity opposite to that of the dominating one. The paper reviews the similarities and differences between hydrogen and its light metallic neighbour in the periodic table, lithium. Also we provide a comparison with the heavier interstitial copper which is known for its ability to passivate shallow acceptors. Finally fundamental differences between shallow-level and deep level passivation will be addressed.

  15. Increased Levels of NF-kB-Dependent Markers in Cancer-Associated Deep Venous Thrombosis

    PubMed Central

    Bevelacqua, Valentina; Polesel, Jerry; Taborelli, Martina; Guarneri, Claudio; Fenga, Concettina; Umezawa, Kazou; Libra, Massimo

    2015-01-01

    Several studies highlight the role of inflammatory markers in thrombosis as well as in cancer. However, their combined role in cancer-associated deep vein thrombosis (DVT) and the molecular mechanisms, involved in its pathophysiology, needs further investigations. In the present study, C-reactive protein, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1β), matrix metalloproteases-9 (MMP-9), vascular endothelial growth factor (VEGF), tissue factor (TF), fibrinogen and soluble P-selectin, were analyzed in plasma and in monocyte samples from 385 cancer patients, of whom 64 were concomitantly affected by DVT (+). All these markers were higher in cancer patients DVT+ than in those DVT-. Accordingly, significantly higher NF-kB activity was observed in cancer patients DVT+ than DVT-. Significant correlation between data obtained in plasma and monocyte samples was observed. NF-kB inhibition was associated with decreased levels of all molecules in both cancer DVT+ and DVT-. To further demonstrate the involvement of NF-kB activation by the above mentioned molecules, we treated monocyte derived from healthy donors with a pool of sera from cancer patients with and without DVT. These set of experiments further suggest the significant role played by some molecules, regulated by NF-kB, and detected in cancer patients with DVT. Our data support the notion that NF-kB may be considered as a therapeutic target for cancer patients, especially those complicated by DVT. Treatment with NF-kB inhibitors may represent a possible strategy to prevent or reduce the risk of DVT in cancer patients. PMID:26192925

  16. Increased Levels of NF-kB-Dependent Markers in Cancer-Associated Deep Venous Thrombosis.

    PubMed

    Malaponte, Grazia; Signorelli, Salvatore S; Bevelacqua, Valentina; Polesel, Jerry; Taborelli, Martina; Guarneri, Claudio; Fenga, Concettina; Umezawa, Kazou; Libra, Massimo

    2015-01-01

    Several studies highlight the role of inflammatory markers in thrombosis as well as in cancer. However, their combined role in cancer-associated deep vein thrombosis (DVT) and the molecular mechanisms, involved in its pathophysiology, needs further investigations. In the present study, C-reactive protein, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1β), matrix metalloproteases-9 (MMP-9), vascular endothelial growth factor (VEGF), tissue factor (TF), fibrinogen and soluble P-selectin, were analyzed in plasma and in monocyte samples from 385 cancer patients, of whom 64 were concomitantly affected by DVT (+). All these markers were higher in cancer patients DVT+ than in those DVT-. Accordingly, significantly higher NF-kB activity was observed in cancer patients DVT+ than DVT-. Significant correlation between data obtained in plasma and monocyte samples was observed. NF-kB inhibition was associated with decreased levels of all molecules in both cancer DVT+ and DVT-. To further demonstrate the involvement of NF-kB activation by the above mentioned molecules, we treated monocyte derived from healthy donors with a pool of sera from cancer patients with and without DVT. These set of experiments further suggest the significant role played by some molecules, regulated by NF-kB, and detected in cancer patients with DVT. Our data support the notion that NF-kB may be considered as a therapeutic target for cancer patients, especially those complicated by DVT. Treatment with NF-kB inhibitors may represent a possible strategy to prevent or reduce the risk of DVT in cancer patients. PMID:26192925

  17. Trade Study of System Level Ranked Radiation Protection Concepts for Deep Space Exploration

    NASA Technical Reports Server (NTRS)

    Cerro, Jeffrey A

    2013-01-01

    A strategic focus area for NASA is to pursue the development of technologies which support exploration in space beyond the current inhabited region of low earth orbit. An unresolved issue for crewed deep space exploration involves limiting crew radiation exposure to below acceptable levels, considering both solar particle events and galactic cosmic ray contributions to dosage. Galactic cosmic ray mitigation is not addressed in this paper, but by addressing credible, easily implemented, and mass efficient solutions for the possibility of solar particle events, additional margin is provided that can be used for cosmic ray dose accumulation. As a result, NASA s Advanced Engineering Systems project office initiated this Radiation Storm Shelter design activity. This paper reports on the first year results of an expected 3 year Storm Shelter study effort which will mature concepts and operational scenarios that protect exploration astronauts from solar particle radiation events. Large trade space definition, candidate concept ranking, and a planned demonstration comprised the majority of FY12 activities. A system key performance parameter is minimization of the required increase in mass needed to provide a safe environment. Total system mass along with operational assessments and other defined protection system metrics provide the guiding metrics to proceed with concept developments. After a downselect to four primary methods, the concepts were analyzed for dosage severity and the amount of shielding mass necessary to bring dosage to acceptable values. Besides analytical assessments, subscale models of several concepts and one full scale concept demonstrator were created. FY12 work terminated with a plan to demonstrate test articles of two selected approaches. The process of arriving at these selections and their current envisioned implementation are presented in this paper.

  18. Analysis of generation and annihilation of deep level defects in a silicon-irradiated bipolar junction transistor

    NASA Astrophysics Data System (ADS)

    Madhu, K. V.; Kulkarni, S. R.; Ravindra, M.; Damle, R.

    2007-08-01

    A commercial bipolar junction transistor (2 N 2219 A, npn), irradiated with 120 MeV Si9+ ions with a fluence of the order of 1012 ions cm-2, is studied for radiation-induced gain degradation and deep level defects. I-V measurements are made to study the gain degradation as a function of ion fluence. Properties such as activation energy, trap concentration and capture cross section of deep levels are studied by deep level transient spectroscopy (DLTS). Minority carrier trap energy levels with energies ranging from EC - 0.160 eV to EC - 0.581 eV are observed in the base-collector junction of the transistor. Majority carrier trap levels are also observed with energies ranging from EV + 0.182 eV to EV + 0.401 eV. The identification of the defect type is made on the basis of its finger prints such as activation energy, annealing temperature and capture cross section by comparing with those reported in the literature. New energy levels for the defects A-center, di-vacancy and Si-interstitial are also observed. The irradiated transistor is subjected to isothermal and isochronal annealing. The defects are seen to anneal above 250 °C. The defects generated in the base region of the transistor by displacement damage appear to be responsible for transistor gain degradation.

  19. Identifying a Threshold Impurity Level for Organic Solar Cells: Enhanced First-Order Recombination Via Well-Defined PC84BM Traps in Organic Bulk Heterojunction Solar Cells

    SciTech Connect

    Cowan, Sarah R.; Leong, Wei Lin; Banerji, Natalie; Dennler, Gilles; Heeger, Alan J.

    2011-06-21

    Small amounts of impurity, even one part in one thousand, in polymer bulk heterojunction solar cells can alter the electronic properties of the device, including reducing the open circuit voltage, the short circuit current and the fill factor. Steady state studies show a dramatic increase in the trap-assisted recombination rate when [6,6]-phenyl C₈₄ butyric acid methyl ester (PC₈₄BM) is introduced as a trap site in polymer bulk heterojunction solar cells made of a blend of the copolymer poly[N-9"-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole) (PCDTBT) and the fullerene derivative [6,6]-phenyl C₆₁ butyric acid methyl ester (PC₆₀BM). The trap density dependent recombination studied here can be described as a combination of bimolecular and Shockley–Read–Hall recombination; the latter is dramatically enhanced by the addition of the PC₈₄BM traps. This study reveals the importance of impurities in limiting the efficiency of organic solar cell devices and gives insight into the mechanism of the trap-induced recombination loss.

  20. High-temperature molecular beam epitaxial growth of AlGaN/GaN on GaN templates with reduced interface impurity levels

    SciTech Connect

    Koblmueller, G.; Chu, R. M.; Raman, A.; Mishra, U. K.; Speck, J. S.

    2010-02-15

    We present combined in situ thermal cleaning and intentional doping strategies near the substrate regrowth interface to produce high-quality AlGaN/GaN high electron mobility transistors on semi-insulating (0001) GaN templates with low interfacial impurity concentrations and low buffer leakage. By exposing the GaN templates to an optimized thermal dissociation step in the plasma-assisted molecular beam epitaxy environment, oxygen, carbon, and, to lesser extent, Si impurities were effectively removed from the regrowth interface under preservation of good interface quality. Residual Si was further compensated by C-doped GaN via CBr{sub 4} to yield highly resistive GaN buffer layers. Improved N-rich growth conditions at high growth temperatures were then utilized for subsequent growth of the AlGaN/GaN device structure, yielding smooth surface morphologies and low residual oxygen concentration with large insensitivity to the (Al+Ga)N flux ratio. Room temperature electron mobilities of the two-dimensional electron gas at the AlGaN/GaN interface exceeded >1750 cm{sup 2}/V s and the dc drain current reached {approx}1.1 A/mm at a +1 V bias, demonstrating the effectiveness of the applied methods.

  1. Impurity gettering in semiconductors

    DOEpatents

    Sopori, B.L.

    1995-06-20

    A process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device is disclosed. The process comprises hydrogenating the substrate or device at the back side thereof with sufficient intensity and for a time period sufficient to produce a damaged back side. Thereafter, the substrate or device is illuminated with electromagnetic radiation at an intensity and for a time period sufficient to cause the impurities to diffuse to the back side and alloy with a metal there present to form a contact and capture the impurities. The impurity gettering process also can function to simultaneously passivate defects within the substrate or device, with the defects likewise diffusing to the back side for simultaneous passivation. Simultaneously, substantially all hydrogen-induced damage on the back side of the substrate or device is likewise annihilated. Also taught is an alternate process comprising thermal treatment after hydrogenation of the substrate or device at a temperature of from about 500 C to about 700 C for a time period sufficient to cause the impurities to diffuse to the damaged back side thereof for subsequent capture by an alloying metal. 1 fig.

  2. Impurity gettering in semiconductors

    DOEpatents

    Sopori, Bhushan L.

    1995-01-01

    A process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device. The process comprises hydrogenating the substrate or device at the back side thereof with sufficient intensity and for a time period sufficient to produce a damaged back side. Thereafter, the substrate or device is illuminated with electromagnetic radiation at an intensity and for a time period sufficient to cause the impurities to diffuse to the back side and alloy with a metal there present to form a contact and capture the impurities. The impurity gettering process also can function to simultaneously passivate defects within the substrate or device, with the defects likewise diffusing to the back side for simultaneous passivation. Simultaneously, substantially all hydrogen-induced damage on the back side of the substrate or device is likewise annihilated. Also taught is an alternate process comprising thermal treatment after hydrogenation of the substrate or device at a temperature of from about 500.degree. C. to about 700.degree. C. for a time period sufficient to cause the impurities to diffuse to the damaged back side thereof for subsequent capture by an alloying metal.

  3. Study of radiation induced deep-level defects in proton irradiated AlGaAs-GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Li, S. S.

    1980-01-01

    Radiation induced deep-level defects (both electron and hole traps) in proton irradiated AlGaAs-GaAs p-n junction solar cells are investigated along with the correlation between the measured defect parameters and the solar cell performance parameters. The range of proton energies studied was from 50 KeV to 10 MeV and the proton fluence was varied from 10 to the 10th power to 10 to the 13th power P/sq cm. Experimental tools employed include deep-level transient spectroscopy, capacitance-voltage, current voltage, and SEM-EBIC methods. Defect and recombination parameters such as defect density and energy level, capture cross section, carrier lifetimes and effective hole diffusion lengths in n-GaAs LPE layers were determined from these measurements.

  4. Characterization of deep acceptor level in as-grown ZnO thin film by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Asghar, M.; K., Mahmood; A. Hasan, M.; T. Ferguson, I.; Tsu, R.; Willander, M.

    2014-09-01

    We report deep level transient spectroscopy results from ZnO layers grown on silicon by molecular beam epitaxy (MBE). The hot probe measurements reveal mixed conductivity in the as-grown ZnO layers, and the current—voltage (I—V) measurements demonstrate a good quality p-type Schottky device. A new deep acceptor level is observed in the ZnO layer having activation energy of 0.49 ±0.03 eV and capture cross-section of 8.57 × 10-18 cm2. Based on the results from Raman spectroscopy, photoluminescence, and secondary ion mass spectroscopy (SIMS) of the ZnO layer, the observed acceptor trap level is tentatively attributed to a nitrogen-zinc vacancy complex in ZnO.

  5. Development of an LC-MS method for ultra trace-level determination of 2,2,6,6-tetramethylpiperidine-1-oxl (TEMPO), a potential genotoxic impurity within active pharmaceutical ingredients.

    PubMed

    Pennington, Justin; Cohen, Ryan D; Tian, Ye; Boulineau, Fabien

    2015-10-10

    TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) is a stable free radical which has been widely used for various research and industrial applications, including the manufacture of many active pharmaceutical ingredients. TEMPO has been identified as a potential genotoxic impurity resulting in the need for analytical methodology to accurately determine its level at several orders of magnitude less than typical impurity quantitation limits. TEMPO can undergo disproportionation to form both oxidized and reduced TEMPO, making individual determination unreliable. To overcome this challenge, all TEMPO related species were converted to the reduced form through reduction with sodium ascorbate. Given the ultra-trace (0.5 ppm) level requirements and the lack of UV response in the reduced form, a single quadrupole mass spectrometer (MS) was utilized. In order to implement a highly sensitive MS method in a GMP environment, several approaches were employed to optimize accuracy and robustness including: internal standard correction for drift elimination, six-level standard addition to reduce matrix effects, and weighted linear regression to cover a broad analytical range. The method was fully validated according to ICH guidelines. The method is specific, linear, accurate, precise, and robust within a range of 0.5-100 ppm. PMID:25921639

  6. Impurity control in TFTR

    SciTech Connect

    Cecchi, J.L.

    1980-06-01

    The control of impurities in TFTR will be a particularly difficult problem due to the large energy and particle fluxes expected in the device. As part of the TFTR Flexibility Modification (TEM) project, a program has been implemented to address this problem. Transport code simulations are used to infer an impurity limit criterion as a function of the impurity atomic number. The configurational designs of the limiters and associated protective plates are discussed along with the consideration of thermal and mechanical loads due to normal plasma operation, neutral beams, and plasma disruptions. A summary is given of the materials-related research, which has been a collaborative effort involving groups at Argonne National Laboratory, Sandia Laboratories, and Princeton Plasma Physics Laboratory. Conceptual designs are shown for getterng systems capable of regenerating absorbed tritium. Research on this topic by groups at the previously mentioned laboratories and SAES Research Laboratory is reviewed.

  7. Origin and annealing of deep-level defects in GaNAs grown by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Gelczuk, Ł.; Stokowski, H.; Dąbrowska-Szata, M.; Kudrawiec, R.

    2016-05-01

    Deep-level defects were investigated by deep level transient spectroscopy on the as-grown and annealed GaNAs layers of various nitrogen (N) contents. The unintentionally doped (uid) GaNAs layers were grown by metalorganic vapor phase epitaxy with N = 1.4%, 2.0%, 2.2%, and 2.4% on GaAs substrate. The possible origin and evolution of the deep-level defects upon annealing were analyzed with the use of the GaNAs band gap diagram concept [Kudrawiec et al., Appl. Phys. Lett. 101, 082109 (2012)], which assumes that the activation energy of donor traps decreases with N-related downward shift of the conduction band. On the basis of this diagram and in comparison with previous results, the N-related traps were associated with (N-As)As or (N-N)As split interstitials. It was also proposed that one of the electron traps and the hole trap, lying at the same level position in the bandgap of the annealed uid-GaNAs layers, can both act as one generation-recombination center partially responsible for poor optical properties of this alloy.

  8. High water level impedes the adaptation of Polygonum hydropiper to deep burial: Responses of biomass allocation and root morphology

    PubMed Central

    Pan, Ying; Xie, Yong H.; Deng, Zheng M.; Tang, Yue; Pan, Dong D.

    2014-01-01

    Many studies have investigated the individual effects of sedimentation or inundation on the performance of wetland plants, but few have examined the combined influence of these processes. Wetland plants might show greater morphological plasticity in response to inundation than to sedimentation when these processes occur simultaneously since inundation can negate the negative effects of burial on plant growth. Here, we evaluate this hypothesis by assessing growth of the emergent macrophyte Polygonum hydropiper under flooding (0 and 40 cm) and sedimentation (0, 5, and 10 cm), separately and in combination. Deep burial and high water level each led to low oxidation-reduction potential, biomass (except for 5-cm burial), and growth of thick, short roots. These characteristics were generally more significant under high water level than under deep burial conditions. More biomass was allocated to stems in the deep burial treatments, but more to leaves in the high water level treatments. Additionally, biomass accumulation was lower and leaf mass ratio was higher in the 40-cm water level + 10-cm burial depth treatment than both separate effects. Our data indicate that inundation plays a more important role than sedimentation in determining plant morphology, suggesting hierarchical effects of environmental stressors on plant growth. PMID:25002329

  9. Correlation of current-voltage-temperature analysis with deep level defects in epitaxial GaN films

    NASA Astrophysics Data System (ADS)

    Reddy, Anurag G.; Aggarwal, Neha; Krishna T. C., Shibin; Singh, Manju; Rakshit, Rajib; Gupta, Govind

    2015-06-01

    The effect of temperature on the nature of metal-semiconductor system in a Au contact deposited on c-plane and a-plane GaN film was investigated by current-voltage (I-V) measurements. The I-V measurements have been obtained systematically at different temperatures ranging from room temperature (300 K) to low temperature (78 K). Photoluminescence measurements were obtained to investigate correlation between the growth conditions, the substrate used for the growth of GaN film, and the presence of deep level defects therein by equating with the yellow band luminescence. The resistance-voltage-temperature analysis indicates that a gradual shift of the nature of contact towards Schottky behavior takes place while moving from room temperature to low temperature. Additionally, memory effect like aberration is present at low temperature, which can be attributed to the presence of deep-level defects and carrier recombination therein.

  10. Influence of EL2 deep level on photoconduction of semi-insulating GaAs under ultrashort pulse photoinjection

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Xie, Guangyong

    2016-02-01

    To investigate the influence of EL2 deep level on photoconduction of in semi-insulating GaAs (SI-GaAs), a 3 mm-electrode-gap lateral SI-GaAs photoconductive chip was manufactured and tested by using ultrashort pulse laser with 1064 nm wavelength, 10 ns pulsewidth, 3.0 mm light spot diameter and single pulse energy mean of 3.0 mJ. Based on the experimental results and the theory of trapping effect, the photon absorption process of EL2 defects in SI-GaAs is analyzed. For the influence of EL2 deep level, the lifetime of the electron gets shorter and the persistent photoconductivity (PPC) is significant. With increasing of voltage, the decay time constant of photoconduction is reduced and the decay index gets bigger for the ultrashort pulse photoinjection.

  11. Studies of deep level transient spectroscopy of DX centers in GaAlAs: Te under uniaxial stress

    SciTech Connect

    Li, Ming-Fu |; Yu, Y.P. |; Weber, E.R.; Haller, E.E. |; Hansen, W.L.; Bauser, E.

    1991-11-01

    DX centers in Al{sub 0.38}Ga{sub 0.62}As doped with Te have been studied by Deep Level Transient Spectroscopy (DLTS) as a function of uniaxial stress. No splitting nor broadening of the DLTS peaks were observed. However, the peak positions and heights depend on the stress and its directions. The results have been analyzed by comparison with existing models and hydrostatic pressure measurements.

  12. Nonradiative coherent carrier captures and defect reaction at deep-level defects via phonon-kick mechanism

    SciTech Connect

    Wakita, Masaki; Suzuki, Kei; Shinozuka, Yuzo

    2014-02-21

    We simulated the time evolution of electron-lattice coupling mode, and a series of nonradiative carrier captures by a deep-level defect in a semiconductor. For lattice relaxation energy of the order of the band gap, a series of coherent (athermal) electron and hole captures by a defect is possible for high carrier densities, which results in an inflation in the induced lattice vibration, which in turn enhances a defect reaction.

  13. Study of deep level characteristics in the neutrons irradiated Si structures by combining pulsed and steady-state spectroscopy techniques

    NASA Astrophysics Data System (ADS)

    Gaubas, E.; Kalendra, V.; Ceponis, T.; Uleckas, A.; Tekorius, A.; Vaitkus, J.; Velicka, A.

    2012-11-01

    The standard methods, such as capacitance deep level transient spectroscopy (C-DLTS) and thermally stimulated current (TSC) techniques are unsuitable for the analysis of heavily irradiated devices. In this work, therefore, several steady-state and pulsed techniques have been combined to comprehensively evaluate parameters of radiation defects and functional characteristics of the irradiated Si pin detectors. In order to understand defects created by radiation and evaluate their evolution with fluence, C-DLTS and TSC techniques have been employed to make a baseline identification of the radiation induced traps after irradiation with a rather small neutron fluence of 1012 cm-2. The steady-state photo-ionization spectroscopy (PIS) technique has been involved to correlate thermal- and photo- activation energies for definite radiation defects. A contactless technique for simultaneous measurements of the carrier lifetime and the parameters of deep levels based on microwave probed pulsed photo-conductivity (MW-PC) spectroscopy has been applied to correlate carrier capture cross-sections and densities of the identified different radiation defects. A technique for spectroscopy of deep levels in junction structures (BELIV) based on measurements of barrier capacitance charging current transient changes due to additional spectrally resolved pulsed illumination has been applied to evaluate the functional characteristics of the irradiated diodes. Pulsed spectroscopic measurements were implemented by combining the analysis of generation current and of barrier capacitance charging transients modified by a single fs pulse of illumination generated by an optical parametric oscillator of varied wavelength in the range from 0.5 to 10 μm. Several deep levels with activation energy in the range of 0.18-0.8 eV have been resolved from spectral analysis in the samples of Si grown by magnetic field applied Czochralski (MCz) technology.

  14. Impurity effects in silicon for high efficiency solar cells

    NASA Technical Reports Server (NTRS)

    Hopkins, R. H.; Rohatgi, A.

    1986-01-01

    Model analyses indicate that sophisticated solar cell designs including, e.g., back surface fields, optical reflectors, surface passivation, and double layer antireflective coatings can produce devices with conversion efficiencies above 20 percent (AM1). To realize this potential, the quality of the silicon from which the cells are made must be improved; and these excellent electrical properties must be maintained during device processing. As the cell efficiency rises, the sensitivity to trace contaminants also increases. For example, the threshold Ti impurity concentration at which cell performance degrades is more than an order of magnitude lower for an 18-percent cell. Similar behavior occurs for numerous other metal species which introduce deep level traps that stimulate the recombination of photogenerated carriers in silicon. Purification via crystal growth in conjunction with gettering steps to preserve the large diffusion length of the as-grown material can lead to the production of devices with efficiencies aboved 18 percent, as has been verified experimentally.

  15. Effects of impurities on silicon solar-cell performance

    NASA Technical Reports Server (NTRS)

    Hopkins, R. H.

    1986-01-01

    Model analyses indicate that sophisticated solar cell designs (back surface fields, optical reflectors, surface passivation, and double layer antireflective coatings) can produce devices with conversion efficiencies above 20%. To realize this potential, the quality of the silicon from which the cells are made must be improved; and these excellent electrical properties must be maintained during device processing. As the cell efficiency rises, the sensitivity to trace contaminants also increases. For example, the threshold Ti impurity concentraion at which cell performance degrades is more than an order of magnitude lower for an 18% cell than for a 16% cell. Similar behavior occurs for numerous other metal species which introduce deep level traps that stimulate the recombination of photogenerated carriers in silicon. Purification via crystal growth in conjunction with gettering steps to preserve the large diffusion length of the as grown material can lead to the production of devices with efficiencies above 18%, as verified experimentally.

  16. Dynamical impurity problems

    SciTech Connect

    Emery, V.J.; Kivelson, S.A.

    1993-12-31

    In the past few years there has been a resurgence of interest in dynamical impurity problems, as a result of developments in the theory of correlated electron systems. The general dynamical impurity problem is a set of conduction electrons interacting with an impurity which has internal degrees of freedom. The simplest and earliest example, the Kondo problem, has attracted interest since the mid-sixties not only because of its physical importance but also as an example of a model displaying logarithmic divergences order by order in perturbation theory. It provided one of the earliest applications of the renormalization group method, which is designed to deal with just such a situation. As we shall see, the antiferromagnetic Kondo model is controlled by a strong-coupling fixed point, and the essence of the renormalization group solution is to carry out the global renormalization numerically starting from the original (weak-coupling) Hamiltonian. In these lectures, we shall describe an alternative route in which we identify an exactly solvable model which renormalizes to the same fixed point as the original dynamical impurity problem. This approach is akin to determining the critical behavior at a second order phase transition point by solving any model in a given universality class.

  17. Studies of deep level centers determining the diffusion length in epitaxial layers and crystals of undoped n-GaN

    NASA Astrophysics Data System (ADS)

    Lee, In-Hwan; Polyakov, A. Y.; Smirnov, N. B.; Yakimov, E. B.; Tarelkin, S. A.; Turutin, A. V.; Shemerov, I. V.; Pearton, S. J.

    2016-05-01

    A wide variety of parameters were measured for undoped n-GaN grown by hydride vapor phase epitaxy and compared to n-GaN films grown by conventional and lateral overgrowth metalorganic chemical vapor deposition. The parameters included deep level electron and hole trap spectra, microcathodoluminescence, electron beam induced current, diffusion length, and electron capture cross section from the dependence of the low temperature persistent photocapacitance on forward bias injection pulse duration. The results show a prominent role of electron traps with levels near Ec-0.56 eV in limiting the lifetime and diffusion length values in all these materials.

  18. Dispersion retrieval from multi-level ultra-deep reactive-ion-etched microstructures for terahertz slow-wave circuits

    SciTech Connect

    Baik, Chan-Wook Young Ahn, Ho; Kim, Yongsung; Lee, Jooho; Hong, Seogwoo; Hee Choi, Jun; Kim, Sunil; Hun Lee, Sang; Min Kim, Jong; Hwang, Sungwoo; Yeon Jun, So; Yu, SeGi; Lawrence Ives, R.

    2014-01-13

    A multi-level microstructure is proposed for terahertz slow-wave circuits, with dispersion relation retrieved by scattering parameter measurements. The measured return loss shows strong resonances above the cutoff with negligible phase shifts compared with finite element analysis. Splitting the circuit into multi levels enables a low aspect ratio configuration that alleviates the loading effect of deep-reactive-ion etching on silicon wafers. This makes it easier to achieve flat-etched bottom and smooth sidewall profiles. The dispersion retrieved from the measurement, therefore, corresponds well to the theoretical estimation. The result provides a straightforward way to the precise determination of dispersions in terahertz vacuum electronics.

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

    PubMed

    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

  20. Large Deep-Ocean Impacts, Sea-Floor Hiatuses, and Apparent Short Term Sea-Level Changes

    NASA Astrophysics Data System (ADS)

    Hagstrum, J. T.

    2001-12-01

    Widespread discontinuities and unconformities in deep-sea sedimentary records (hiatuses) often correspond to rapid fluctuations in eustatic sea level. Such global paleoceanographic events have been attributed to vertical tectonic movements, to changes in ocean basin configuration and volume, and to glacial versus non-glacial climates. Alternatively, megatsunami waves generated by large deep-ocean impacts cause widespread erosion of the sea floor centered on the impact site. At the shoreline, run-up heights can exceed 1 km on a global scale. These high-energy events might be the source of some sea-floor hiatuses as well as stratigraphic intervals currently interpreted as short-term regression and transgression (r-t) pulses in sea level. A widespread hiatus, probable impact ejecta, ocean chemistry and sediment changes, and r-t pulse occurring at ~68-67 Ma indicate that a large oceanic impact might have preceded the Chicxulub impact by a few million years. The hiatus proximal to the Cretaceous-Tertiary (K-T) boundary is most pronounced in the northern Pacific basin and, because tsunami amplitude is proportional to water depth, could not have been caused by the shallow-water (<=100 m) Chicxulub impact at ~65 Ma. Thus K-T time likely experienced two large bolide impacts, one of which occurred in the deep ocean.

  1. Exploring the Deep-Level Reasoning Questions Effect during Vicarious Learning among Eighth to Eleventh Graders in the Domains of Computer Literacy and Newtonian Physics

    ERIC Educational Resources Information Center

    Gholson, Barry; Witherspoon, Amy; Morgan, Brent; Brittingham, Joshua K.; Coles, Robert; Graesser, Arthur C.; Sullins, Jeremiah; Craig, Scotty D.

    2009-01-01

    This paper tested the deep-level reasoning questions effect in the domains of computer literacy between eighth and tenth graders and Newtonian physics for ninth and eleventh graders. This effect claims that learning is facilitated when the materials are organized around questions that invite deep-reasoning. The literature indicates that vicarious…

  2. Defect levels in Cu2ZnSn(SxSe1-x)4 solar cells probed by current-mode deep level transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Das, Sandip; Chaudhuri, Sandeep K.; Bhattacharya, Raghu N.; Mandal, Krishna C.

    2014-05-01

    Defect levels in kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells have been investigated by current-mode deep level transient spectroscopy. Experiments were carried out on two CZTSSe cells with photoconversion efficiencies of 4.1% and 7.1% measured under AM 1.5 illumination. The absorber layer of the 4.1% efficiency cell was prepared by annealing evaporated ZnS/Cu/Sn stacked precursor under S/Se vapor, while the absorber of the 7.1% efficiency cell was prepared by co-evaporation of the constituent elements. The 4.1% efficiency CZTSSe cell with a S/(S + Se) ratio of 0.58 exhibited two dominant deep acceptor levels at Ev + 0.12 eV, and Ev + 0.32 eV identified as CuZn(-/0) and CuSn(2-/-) antisite defects, respectively. The 7.1% efficiency cell with purely Se composition S/(S + Se) = 0 showed only one shallow level at Ev + 0.03 eV corresponding to Cu-vacancy (VCu). Our results revealed that VCu is the primary defect center in the high-efficiency kesterite solar cell in contrast to the detrimental CuZn and CuSn antisites found in the low efficiency CZTSSe cells limiting the device performance.

  3. Evaluation of hydraulic characteristics of a deep artesian aquifer from natural water-level fluctuations, Miami, Florida

    USGS Publications Warehouse

    Meyer, Frederick W.

    1974-01-01

    Knowledge of tho hydraulic characteristics of aquifer systems is fundamental to defining the vertical and horizontal controls on fluid movement, information which is needed for assessing the environmental impact of subsurface waste storage. To meet this objective, natural water-level fluctuations in the 2,947-foot deep Peninsula Utilities disposal well near Miami, Florida were analyzed to obtain estimates of the hydraulic diffusivity, hydraulic conductivity, specific storage, transmissivity, and the storage coefficient of the Boulder Zone. The fluctuations are caused chiefly by oceanic and earth tides, and by changes in atmospheric pressure. The oceanic tidal fluctuations probably result from loading due to tides in Biscayne Bay.

  4. Deep electronic levels in high-pressure Bridgman Cd{sub 1-x}Zn{sub x}Te

    SciTech Connect

    Szeles, C.; Shan, Y.Y.; Lynn, K.G.; Eissler, E.E.

    1995-12-01

    The behavior of deep electronic levels was studied as a function of Zn concentration in CdZnTe crystals grown by the high-pressure Bridgman technique using thermoelectric effect spectroscopy. A significant increase of the thermal ionization energies of hole traps was observed with the increasing Zn content of the ternary compound. The effect explains the stronger hole trapping and the resulting much shorter hole lifetime usually observed in CdZnTe as compared to CdTe. The behavior also suggests increased carrier recombination and explains the strong deterioration of electron collection in detectors fabricated from CdZnTe of high Zn concentration.

  5. Deep level transient spectroscopy studies of n-type ZnO single crystals grown by different techniques.

    PubMed

    Scheffler, L; Kolkovsky, Vl; Lavrov, E V; Weber, J

    2011-08-24

    In the present study single-crystalline ZnO samples grown from the vapor phase, the melt, and a high-temperature aqueous solution (hydrothermal growth) are investigated before and after hydrogen plasma treatments, by means of deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS. Dominant DLTS peaks are found to appear in the range of 120-350 K for all materials. The DLTS spectra depend on the procedure of growth of the ZnO. The thermal stabilities of the defects in an oxygen atmosphere and in an oxygen-lean atmosphere are analyzed. The origin of the DLTS peaks is discussed. PMID:21813951

  6. Electronic properties of deep-level defects in proton irradiated AlGaAs-GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Li, S. S.

    1981-01-01

    Deep level transient spectroscopy and capacitance voltage techniques as well as analysis of the forward current voltage (I-V) characteristics and SEM-EIC data were carried out for proton irradiated GaAs solar cells over a wide range of proton energies and proton fluences. Defect and recombination parameters such as defect energy levels and density, carrier capture cross sections and lifetimes as well as diffusion lengths in the undoped n-GaAs LPE layers were determined. Good correlation between these defect parameters and solar cell performance parameters was obtained for GaAs solar cells irradiated by 200 and 290 KeV protons. It was found that 200 to 290 KeV protons will produce the most defects and damages to the GaAs solar cell structure used. The influence of the low temperature (200 to 400 C) periodic thermal annealing on the deep level defects and the performance of the 200 KeV proton irradiated cells is discussed.

  7. Deep-level defects and turn-on capacitance recovery characteristics in AlGaN/GaN heterostructures

    NASA Astrophysics Data System (ADS)

    Nakano, Yoshitaka; Irokawa, Yoshihiro; Sumiya, Masatomo

    2015-06-01

    We report on turn-on capacitance recovery measurements as a simple short-time method of evaluating carrier-trapping phenomena in a two-dimensional electron gas (2DEG) in the bulk region of AlGaN/GaN heterostructures, employing their Schottky barrier diodes. Using this technique, we have investigated an in-depth relation between deep-level defects and 2DEG carrier trapping in an AlGaN/GaN heterostructure with a GaN buffer layer containing a high C concentration. Steady-state photo-capacitance spectroscopy measurements revealed three C-related deep-level defects located at ~2.07, ~2.80 and ~3.23 eV below the conduction band in the GaN buffer layer. Additionally, turn-on capacitance recovery measurements showed a large decrease in recovery time under white-light optical illuminations with long-pass filters between 370 and 390 nm. It is concluded that the ~3.23 eV level is mainly responsible for the 2DEG carrier-trapping phenomena in the GaN buffer layer of the AlGaN/GaN heterostructure.

  8. Deep levels in high resistivity GaN detected by thermally stimulated luminescence and first-principles calculations

    NASA Astrophysics Data System (ADS)

    Gai, Yanqin; Li, Jingbo; Hou, Qifeng; Wang, Xiaoliang; Xiao, Hongling; Wang, Cuimei; Li, Jinmin

    2009-08-01

    Thermally stimulated luminescence spectroscopy has been applied to study the deep centres in unintentionally doped high resistivity GaN epilayers grown by the metal organic chemical vapour deposition method on c-sapphire substrates. Two trap states with activation energies of 0.12 and 0.62 eV are evaluated from two luminescence peaks at 141.9 and 294.7 K in the luminescence curve. Our spectroscopy measurement, in combination with more accurate first-principles studies, provided insights into the microscopic origin of these levels. Our investigations suggest that the lower level at 0.12 eV might originate from CN, which behaves as a hole trap state; the deeper level at 0.62 eV can be correlated with VGa that corresponds to the yellow luminescence band observed in low-temperature photoluminescence spectra.

  9. Current Collapse and Deep Levels of AlGaN/GaN Heterostructures monitored by LFN Measurements

    NASA Astrophysics Data System (ADS)

    Tacano, M.; Tanuma, N.; Yagi, S.; Okumura, H.; Matsui, T.; Sikula, J.

    2009-04-01

    The correlation between the current collapse in the IV characteristics of AlGaN/GaN HFETs and the traps monitored through the unpassivated and SiN-passivation processes of the AlGaN/GaN heterostructures by the low frequency noise measurements is reported: the noise level of E1(47 meV) trap decreased by 10 dBA/√Hz by the SiN passivation process together with the current collapse recovery in IV curves, while E2(131 meV) and E3(235 meV) levels became apparent after SiN passivation, indicating the remarkable suppression of the E1 trap by the passivation. The commercially available AlGaAs/GaAs LED heads for the page and FAX printers found several deep levels introduced during the contact formation processes, which could not be assigned by the DLTS measurements.

  10. Characterization of the deep levels responsible for non-radiative recombination in InGaN/GaN light-emitting diodes

    SciTech Connect

    Meneghini, M. La Grassa, M.; Vaccari, S.; Meneghesso, G.; Zanoni, E.

    2014-03-17

    This paper presents an extensive investigation of the deep levels related to non-radiative recombination in InGaN/GaN light-emitting diodes (LEDs). The study is based on combined optical and deep-level transient spectroscopy measurements, carried out on LEDs with identical structure and with different values of the non-radiative recombination coefficient. Experimental data lead to the following, relevant, results: (i) LEDs with a high non-radiative recombination coefficient have a higher concentration of a trap (labeled as “e{sub 2}”) with an activation energy of 0.7 eV, which is supposed to be located close to/within the active region; (ii) measurements carried out with varying filling pulse duration suggest that this deep level behaves as a point-defect/dislocation complex. The Arrhenius plot of this deep level is critically compared with the previous literature reports, to identify its physical origin.

  11. High level science products from deep ACS and WFC3/IR imaging over the CDF-S/GOODS-S region

    NASA Astrophysics Data System (ADS)

    Illingworth, Garth

    2013-10-01

    The CDF-S, with its extensive datasets that include the well-known HUDF, GOODS and CANDELS fields, is a remarkable resource for studying distant galaxies. CDF-S is a unique region in the sky. An astonishing 6 Msec of Hubble data {nearly 2600 orbits of WFC3 and ACS data alone}, 6 Msec of Spitzer IRAC images, and 4 Msec of Chandra data, plus ground-based spectra, imaging and, now, ALMA observations, make this one of Hubble's key legacy areas. Remarkably, while the major areas, HUDF, GOODS and CANDELS are available as high-level data products, over 40% { 1000 orbits} of HST data are unavailable to the community as high-level science products and catalogs in MAST. This includes several deep fields, including the parallel field HUDF09-2 which reaches as deep in ACS { 400 orbits} as the HUDF. We propose to use our extensive experience processing and delivering HST ACS and WFC3/IR datasets to STScI MAST to now deliver a complete processed and aligned dataset of all deep fields and the deeper, but as-yet-unused, SNe follow-up and parallel datasets across the CDF-S. The same will be done for the much smaller but similar dataset on the HDF-N region. These data products will add substantially to our understanding of the build up of galaxies to z 6 in the first Gyr during reionization, and their impact on reionization, the development of galaxies over the subsequent Gyr to to the peak of the star formation rate in the universe around 2-3 Gyr after the Big Bang at z 2-3, and the transition of early star-forming galaxies to the full splendor of the Hubble sequence since z 2. These Hubble Legacy Field datasets will be of great value as the Frontier Fields are used by the community.

  12. Relationship of deep defects to oxygen and hydrogen content in nanocrystalline silicon photovoltaic materials

    SciTech Connect

    Hugger, Peter G.; Cohen, J. David; Yan Baojie; Yue Guozhen; Yang, Jeffrey; Guha, Subhendu

    2010-12-20

    We report measurements of the structural and compositional properties of a range of hydrogenated nanocrystalline films. We employed Raman spectroscopy for crystallinity and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) for impurity characterizations. The crystalline volume fractions and impurity levels are correlated with the deep state densities determined by drive level capacitance profiling. Those defects were found to have a thermal emission energy of 0.65{+-}.05 eV. We found that the overall crystallinity correlated reasonably well with the density of such defect states and also found a strong correlation between the defect density and the levels of oxygen impurities. Possible origins of these defects are discussed.

  13. Influence of the Deep Water Horizon Oil Spill on Atmospheric Hydrocarbon Levels over the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Blake, N. J.; Barletta, B.; Meinardi, S.; Leifer, I.; Rowland, F. S.; Blake, D. R.

    2010-12-01

    The waters of the Gulf of Mexico recently were impacted negatively by the large oil spill that occurred after an explosion at the BP Deep Water Horizon rig on April 20, 2010. In response to this disaster, and out of concern for the multitude of chemical pollutants being emitted, we collected 96 air samples in the Gulf region aboard the 65 ft vessel “R/V Eugenie” during 20-23 May, 2010. Sample analysis was by high sensitivity gas chromatographic analysis with special attention to the presence of possible toxic components. Analysis of each canister included straight-chain saturated hydrocarbons from C1 (methane) to C12 (dodecane), aromatic hydrocarbons such as benzene and toluene, as well as higher molecular weight species. High levels of C5-C12 alkanes and cyclo-alkanes, typical of crude oil, were observed in the atmosphere downwind of the spill location. However, the most soluble components, especially methane and benzene, were largely absent from the near-surface atmosphere implying dissolution in the deep sea, where they could impact negatively oxygen levels.

  14. Quasiparticle interference from magnetic impurities

    NASA Astrophysics Data System (ADS)

    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.

  15. Growth temperature dependence of Si doping efficiency and compensating deep level defect incorporation in Al{sub 0.7}Ga{sub 0.3}N

    SciTech Connect

    Armstrong, Andrew M. Moseley, Michael W.; Allerman, Andrew A.; Crawford, Mary H.; Wierer, Jonathan J.

    2015-05-14

    The growth temperature dependence of Si doping efficiency and deep level defect formation was investigated for n-type Al{sub 0.7}Ga{sub 0.3}N. It was observed that dopant compensation was greatly reduced with reduced growth temperature. Deep level optical spectroscopy and lighted capacitance-voltage were used to understand the role of acceptor-like deep level defects on doping efficiency. Deep level defects were observed at 2.34 eV, 3.56 eV, and 4.74 eV below the conduction band minimum. The latter two deep levels were identified as the major compensators because the reduction in their concentrations at reduced growth temperature correlated closely with the concomitant increase in free electron concentration. Possible mechanisms for the strong growth temperature dependence of deep level formation are considered, including thermodynamically driven compensating defect formation that can arise for a semiconductor with very large band gap energy, such as Al{sub 0.7}Ga{sub 0.3}N.

  16. Impurity profile of rifaximin produced in China.

    PubMed

    Liuchao; Maixi; Wangchao; Wan, Chunpeng

    2012-04-01

    Impurity profiles of rifaximin produced in China were investigated systematically by LCMS methods. Eleven impurities from the raw materials of rifaximin produced in China were detected. We adopted the Diagnostic fragment-ion-based extension strategy (DFIBES) for deducing the structure of unknown impurities. Impurity 1 was the 30-hydroxylated product of rifaximin. Impurity 2 was the 25-deacetyled rifaximin. Impurity 6 was the isomeride of rifaximin. Impurity 9 was rifamycin-O. PMID:22570932

  17. Deep uncertainty about the modes and tails of sea-level projections

    NASA Astrophysics Data System (ADS)

    Ruckert, Kelsey; Guan, Yawen; Forest, Chris; Keller, Klaus

    2015-04-01

    Sea-levels are generally rising around the world, posing nontrivial risks. Managing these risks hinges on sea-level rise projections and their associated uncertainties. Deriving sea-level projections presents nontrivial methodological challenges. Previous studies projecting sea-level rise have broken new ground, but typically adopt a single calibration method. Here we use a simple sea-level rise model to analyze and quantify the structural uncertainties driven by the choice of calibration method. In particular, we analyze a frequentist bootstrap method and a Bayesian approach (one with and one without the consideration of heteroskedastic errors). We show that the Bayesian approach with a heteroskedastic likelihood function performs best in hindcast experiments with respect to producing credible intervals with appropriate coverage. The choice of calibration method has considerable impacts on the modes and tails of the projections. Specifically, the modes vary across methods by more than 0.5 meters, in the year 2100. Arguably more important, the projected sea-levels with 1 in 100 and 1 in 10,000 exceedance probabilities vary by 2.5 and 3.5 meters. This structural uncertainty introduced by the choice of the statistical method has considerable implications for the design of sea-level rise adaptation strategies.

  18. First-principles study of carbon impurities in CuInSe2 and CuGaSe2, present in non-vacuum synthesis methods

    NASA Astrophysics Data System (ADS)

    Bekaert, J.; Saniz, R.; Partoens, B.; Lamoen, D.

    2015-01-01

    A first-principles study of the structural and electronic properties of carbon impurities in CuInSe2 and CuGaSe2 is presented. Carbon is present in organic molecules in the precursor solutions used in non-vacuum growth methods for CuInSe2 and CuGaSe2 based photovoltaic cells. These growth methods make more efficient use of material, time, and energy than traditional vacuum methods. The formation energies of several carbon impurities are calculated using the hybrid HSE06 functional. CCu acts as a shallow donor, CIn and interstitial C yield deep donor levels in CuInSe2, while in CuGaSe2 CGa and interstitial C act as deep amphoteric defects. So, these defects reduce the majority carrier (hole) concentration in p-type CuInSe2 and CuGaSe2 by compensating the acceptor levels. The deep defects are likely to act as recombination centers for the photogenerated charge carriers and are thus detrimental for the performance of the photovoltaic cells. On the other hand, the formation energies of the carbon impurities are high, even under C-rich growth conditions. Thus, few C impurities will form in CuInSe2 and CuGaSe2 in thermodynamic equilibrium. However, the deposition of the precursor solution in non-vacuum growth methods presents conditions far from thermodynamic equilibrium. In this case, our calculations show that C impurities formed in non-equilibrium tend to segregate from CuInSe2 and CuGaSe2 by approaching thermodynamic equilibrium, e.g., via thorough annealing.

  19. First-principles study of carbon impurities in CuInSe{sub 2} and CuGaSe{sub 2}, present in non-vacuum synthesis methods

    SciTech Connect

    Bekaert, J. Saniz, R.; Partoens, B.; Lamoen, D.

    2015-01-07

    A first-principles study of the structural and electronic properties of carbon impurities in CuInSe{sub 2} and CuGaSe{sub 2} is presented. Carbon is present in organic molecules in the precursor solutions used in non-vacuum growth methods for CuInSe{sub 2} and CuGaSe{sub 2} based photovoltaic cells. These growth methods make more efficient use of material, time, and energy than traditional vacuum methods. The formation energies of several carbon impurities are calculated using the hybrid HSE06 functional. C{sub Cu} acts as a shallow donor, C{sub In} and interstitial C yield deep donor levels in CuInSe{sub 2}, while in CuGaSe{sub 2} C{sub Ga} and interstitial C act as deep amphoteric defects. So, these defects reduce the majority carrier (hole) concentration in p-type CuInSe{sub 2} and CuGaSe{sub 2} by compensating the acceptor levels. The deep defects are likely to act as recombination centers for the photogenerated charge carriers and are thus detrimental for the performance of the photovoltaic cells. On the other hand, the formation energies of the carbon impurities are high, even under C-rich growth conditions. Thus, few C impurities will form in CuInSe{sub 2} and CuGaSe{sub 2} in thermodynamic equilibrium. However, the deposition of the precursor solution in non-vacuum growth methods presents conditions far from thermodynamic equilibrium. In this case, our calculations show that C impurities formed in non-equilibrium tend to segregate from CuInSe{sub 2} and CuGaSe{sub 2} by approaching thermodynamic equilibrium, e.g., via thorough annealing.

  20. Effect of antimony on the deep-level traps in GaInNAsSb thin films

    SciTech Connect

    Islam, Muhammad Monirul Miyashita, Naoya; Ahsan, Nazmul; Okada, Yoshitaka; Sakurai, Takeaki; Akimoto, Katsuhiro

    2014-09-15

    Admittance spectroscopy has been performed to investigate the effect of antimony (Sb) on GaInNAs material in relation to the deep-level defects in this material. Two electron traps, E1 and E2 at an energy level 0.12 and 0.41 eV below the conduction band (E{sub C}), respectively, were found in undoped GaInNAs. Bias-voltage dependent admittance confirmed that E1 is an interface-type defect being spatially localized at the GaInNAs/GaAs interface, while E2 is a bulk-type defect located around mid-gap of GaInNAs layer. Introduction of Sb improved the material quality which was evident from the reduction of both the interface and bulk-type defects.

  1. TRANSPORT OF LOW-LEVEL RADIOACTIVE SOIL AT DEEP-OCEAN DISPOSAL SITE

    EPA Science Inventory

    Transport studies were conducted to assess ocean disposal of soil contaminated with low-level natural radioisotopes. he experimental approach involved characterization of the soil for parameters affecting transport and fate of radionuclides- Radioactivity was associated with disc...

  2. Influence of deep level defects on carrier lifetime in CdZnTe:In

    SciTech Connect

    Guo, Rongrong; Jie, Wanqi Wang, Ning; Zha, Gangqiang; Xu, Yadong; Wang, Tao; Fu, Xu

    2015-03-07

    The defect levels and carrier lifetime in CdZnTe:In crystal were characterized with photoluminescence, thermally stimulated current measurements, as well as contactless microwave photoconductivity decay (MWPCD) technique. An evaluation equation to extract the recombination lifetime and the reemission time from MWPCD signal is developed based on Hornbeck-Haynes trapping model. An excellent agreement between defect level distribution and carrier reemission time in MWPCD signal reveals the tail of the photoconductivity decay is controlled by the defect level reemission effect. Combining {sup 241}Am gamma ray radiation response measurement and laser beam induced transient current measurement, it predicted that defect level with the reemission time shorter than the collection time could lead to better charge collection efficiency of CdZnTe detector.

  3. Shear-deformation-potential constant of the conduction-band minima of Si: Experimental determination by the deep-level capacitance transient method

    NASA Astrophysics Data System (ADS)

    Li, Ming-Fu; Zhao, Xue-Shu; Gu, Zong-Quan; Chen, Jian-Xin; Li, Yan-Jin; Wang, Jian-Qing

    1991-06-01

    The shear-deformation-potential constant Ξu of the conduction-band minima of Si has been measured by a method which we called deep-level capacitance transient under uniaxial stress. The uniaxial-stress (F) dependence of the electron emission rate en from deep levels to the split conduction-band minima of Si has been analyzed. Theoretical curves are in good agreement with experimental data for the S0 and S+ deep levels in Si. The values of Ξu obtained by the method are 11.1+/-0.3 eV at 148.9 K and 11.3+/-0.3 eV at 223.6 K. The analysis and the Ξu values obtained are also valuable for symmetry determination of deep electron traps in Si.

  4. Analysis of the Effects of Impurities in Silicon. [to determine solar cell efficiency

    NASA Technical Reports Server (NTRS)

    Wohlgemuth, J. H.; Lafky, W. M.; Burkholder, J. H.

    1979-01-01

    A solar cell fabrication and analysis program to determine the effects on the resultant solar cell efficiency of impurities incorporated into silicon is conducted. Flight quality technologies and quality assurance are employed to assure that variations in cell performance are due to the impurities incorporated in the silicon. The type and level of impurity doping in each test lot is given and the mechanism responsible for the degradation of cell performance is identified and correlated to the doped impurities.

  5. The effect of secondary impurities on solar cell performance

    NASA Technical Reports Server (NTRS)

    Hill, D. E.; Gutsche, H. W.; Wang, M. S.; Gupta, K. P.; Tucker, W. F.; Dowdy, J. D.; Crepin, R. J.

    1976-01-01

    Czochralski and float zone sigle crystals of silicon were doped with the primary impurities B or P so that a resistivity of 0.5 ohm cm resulted, and in addition doped with certain secondary impurities including Al, C, Cr, Cu, Fe, Mg, Mn, Na, Ni, O, Ti, V, and Zr. The actual presence of these impurities was confirmed by analysis of the crystals. Solar cell performance was evaluated and found to be degraded most significantly by Ti, V, and Zr and to some extent by most of the secondary impurities considered. These results are of significance to the low cost silicon program, since any such process would have to yield at least tolerable levels of these impurities.

  6. Influence of surface states on deep level transient spectroscopy in AlGaN/GaN heterostructure

    NASA Astrophysics Data System (ADS)

    Qing, Zhu; Xiao-Hua, Ma; Wei-Wei, Chen; Bin, Hou; Jie-Jie, Zhu; Meng, Zhang; Li-Xiang, Chen; Yan-Rong, Cao; Yue, Hao

    2016-06-01

    Deep level transient spectroscopy (DLTS) as a method to investigate deep traps in AlGaN/GaN heterostructure or high electron mobility transistors (HEMTs) has been widely utilized. The DLTS measurements under different bias conditions are carried out in this paper. Two hole-like traps with active energies of E v + 0.47 eV, and E v + 0.10 eV are observed, which are related to surface states. The electron traps with active energies of E c ‑ 0.56 eV are located in the channel, those with E c ‑ 0.33 eV and E c ‑ 0.88 eV are located in the AlGaN layer. The presence of surface states has a strong influence on the detection of electron traps, especially when the electron traps are low in density. The DLTS signal peak height of the electron trap is reduced and even disappears due to the presence of plentiful surface state. Project supported by the National Key Basic Research Program of China (Grant No. 2011CBA00606), the Program for New Century Excellent Talents in University, China (Grant No. NCET-12-0915), and the National Natural Science Foundation of China (Grant Nos. 61334002 and 61404097).

  7. Deep-level transient spectroscopy on an amorphous InGaZnO{sub 4} Schottky diode

    SciTech Connect

    Chasin, Adrian Bhoolokam, Ajay; Nag, Manoj; Genoe, Jan; Heremans, Paul; Simoen, Eddy; Gielen, Georges

    2014-02-24

    The first direct measurement is reported of the bulk density of deep states in amorphous IGZO (indium-gallium-zinc oxide) semiconductor by means of deep-level transient spectroscopy (DLTS). The device under test is a Schottky diode of amorphous IGZO semiconductor on a palladium (Pd) Schottky-barrier electrode and with a molybdenum (Mo) Ohmic contact at the top. The DLTS technique allows to independently measure the energy and spatial distribution of subgap states in the IGZO thin film. The subgap trap concentration has a double exponential distribution as a function energy, with a value of ∼10{sup 19} cm{sup −3} eV{sup −1} at the conduction band edge and a value of ∼10{sup 17} cm{sup −3} eV{sup −1} at an energy of 0.55 eV below the conduction band. Such spectral distribution, however, is not uniform through the semiconductor film. The spatial distribution of subgap states correlates well with the background doping density distribution in the semiconductor, which increases towards the Ohmic Mo contact, suggesting that these two properties share the same physical origin.

  8. Resonance energy transfer based on shallow and deep energy levels of biotin-polyethylene glycol/polyamine stabilized CdS quantum dots

    NASA Astrophysics Data System (ADS)

    Lü, W.; Tokuhiro, Y.; Umezu, I.; Sugimura, A.; Nagasaki, Y.

    2006-10-01

    Fluorescent resonance energy transfer between the poly(ethylene glycol)-b-poly(2-(N ,N-dimethylamino)ethyl methacrylate) stabilized CdS quantum dots (QDs) and texas-red streptavidin was observed. We propose a four-state model to explain photoluminescence (PL) process of CdS QDs and suggest that there are two emission processes originated from shallow and deep trap energy levels corresponding to fast and slow components of PL decay, respectively. Energy transfer mechanism was discussed based on Dexter theory [J. Chem. Phys. 21, 863 (1953)] and the proposed four-state model. It is found that the energy transfer efficiency of deep energy level is higher than that of shallow energy level. The calculated distance between QD and texas red with the parameters of shallow energy level is the same with that of deep level, which indicates that the proposed model is reasonable for explaining the PL dynamics of CdS QDs.

  9. Isolation and structural elucidation of two impurities from a diacerein bulk drug.

    PubMed

    Ashok, Chaudhari; Golak, Maikap; Adwait, Deo; Krishna, Vivek; Himani, Agrawal; Umesh, Peshawe; Amol, Gawande; Srinivas, Sompalli; Sharad, Mane; Deepali, Jadhav; Atul, Chaudhari

    2009-02-20

    Two impurities were found in the crude sample of diacerein. The level of these impurities 1.14% and 1.24% were detected by isocratic reverse-phase high performance liquid chromatography (HPLC). The molecular weights of the impurities were determined by liquid chromatography-mass spectroscopy (LC-MS) analysis. These impurities were isolated from crude sample of diacerein by reverse-phase preparative liquid chromatography. These impurities were characterized as 5-acetoxy-4-hydroxy-9,10-dioxo-9,10-dihydroanthracene-2-carboxylic acid (Impurity-1) and 4-acetoxy-5-hydroxy-9,10-dioxo-9,10-dihydroanthracene-2-carboxylic acid (Impurity-2) respectively. Structural elucidation of both the impurities were carried out by (1)H NMR, (13)C NMR, DEPT, 1D NOESY, MS and IR spectroscopy. PMID:19131202

  10. Interactive Sea Level Rise App & Online Viewer Offers Deep Dive Into Climate

    NASA Astrophysics Data System (ADS)

    Turrin, M.; Porter, D. F.; Ryan, W. B. F.; Pfirman, S. L.

    2015-12-01

    Climate has captured the attention of the public but its complexity can cause interested individuals to turn to opinion pieces, news articles or blogs for information. These platforms often oversimplify or present heavily interpreted or personalized perspectives. Data interactives are an extremely effective way to explore complex geoscience topics like climate, opening windows of understanding for the user that have previously been closed. Layering data onto maps through programs like GeoMapApp and the Earth Observer App has allowed users to dig directly into science data, but with only limited scaffolding. The interactive 'Polar Explorer: Sea Level Explorer App' provides a richly layered introduction to a range of topics connected to sea level rise. Each map is supported with a pop up and a short audio file of supplementary material, and an information page that includes the data source and links for further reading. This type of learning platform works well for both the formal and informal learning environment. Through science data displayed as map visualizations the user is invited into topics through an introductory question, such as "Why does sea level change?" After clicking on that question the user moves to a second layer of questions exploring the role of the ocean, the atmosphere, the contribution from the world's glaciers, world's ice sheets and other less obvious considerations such as the role of post-glacial rebound, or the mining of groundwater. Each question ends in a data map, or series of maps, that offer opportunities to interact with the topic. Under the role of the ocean 'Internal Ocean Temperature' offers the user a chance to touch to see temperature values spatially over the world's ocean, or to click through a data series starting at the ocean surface and diving to 5000 meters of depth showing how temperature changes with depth. Other sections, like the role of deglaciation of North America, allow the user to click and see change through

  11. Impurity Extraction by Droplets

    NASA Technical Reports Server (NTRS)

    Morrison, G.; Kincaid, J. M.

    1985-01-01

    The goals are to model and to measure the phase equilibrium properties of a finely divided fluid containing a large number of chemically similar species. The objective is to develop an accurate, usable model for such phenomena as pollutant extraction of rain clouds, industrial separation in spray towers, and separation in emulsions. The project was designed as a hierarchy of complementary theoretical and experimental steps. A theory was developed to describe the segregation of complex impurities at the interface of a solvent. This phenomenon is important in phase behavior when a large fraction of molecules in a material are near an interface, the situation in a finely divided material. The theory will be modified to account for the effect of surface curvature on the surface tension. The study of mixtures differs from pure fluids not only because of the surface effects but also because composition differences between the droplet and the surrounding vapor can stabilize a droplet with respect to a bulk phase.

  12. The impurity of radioiodinated triolein

    PubMed Central

    Kennedy, J. A.; Kinloch, J. D.

    1964-01-01

    Commercially supplied radioiodinated triolein has been shown by thin-layer chromatography and silicic acid column chromatography to contain impurities, consisting mainly of diglycerides and monoglycerides, but also a small amount of free fatty acid. The effect of these impurities on the radioiodinated triolein absorption test requires further investigation. Images PMID:14149942

  13. Stabilization of the Particle-Hole Pfaffian Order by Landau-Level Mixing and Impurities That Break Particle-Hole Symmetry.

    PubMed

    Zucker, P T; Feldman, D E

    2016-08-26

    Numerical results suggest that the quantum Hall effect at ν=5/2 is described by the Pfaffian or anti-Pfaffian state in the absence of disorder and Landau-level mixing. Those states are incompatible with the observed transport properties of GaAs heterostructures, where disorder and Landau-level mixing are strong. We show that the recent proposal of a particle-hole (PH)-Pfaffian topological order by Son is consistent with all experiments. The absence of particle-hole symmetry at ν=5/2 is not an obstacle to the existence of the PH-Pfaffian order since the order is robust to symmetry breaking. PMID:27610872

  14. Influence of a deep-level-defect band formed in a heavily Mg-doped GaN contact layer on the Ni/Au contact to p-GaN

    NASA Astrophysics Data System (ADS)

    Li, Xiao-Jing; Zhao, De-Gang; Jiang, De-Sheng; Chen, Ping; Zhu, Jian-Jun; Liu, Zong-Shun; Le, Ling-Cong; Yang, Jing; He, Xiao-Guang; Zhang, Li-Qun; Liu, Jian-Ping; Zhang, Shu-Ming; Yang, Hui

    2015-09-01

    The influence of a deep-level-defect (DLD) band formed in a heavily Mg-doped GaN contact layer on the performance of Ni/Au contact to p-GaN is investigated. The thin heavily Mg-doped GaN (p++-GaN) contact layer with DLD band can effectively improve the performance of Ni/Au ohmic contact to p-GaN. The temperature-dependent I-V measurement shows that the variable-range hopping (VRH) transportation through the DLD band plays a dominant role in the ohmic contact. The thickness and Mg/Ga flow ratio of p++-GaN contact layer have a significant effect on ohmic contact by controlling the Mg impurity doping and the formation of a proper DLD band. When the thickness of the p++-GaN contact layer is 25 nm thick and the Mg/Ga flow rate ratio is 10.29%, an ohmic contact with low specific contact resistivity of 6.97× 10- 4 Ω·cm2 is achieved. Project supported by the National Natural Science Foundation of China (Grant Nos. 61474110, 61377020, 61376089, 61223005, and 61176126), the National Science Fund for Distinguished Young Scholars of China (Grant No. 60925017), One Hundred Person Project of the Chinese Academy of Sciences, and the Basic Research Project of Jiangsu Province, China (Grant No. BK20130362).

  15. Injection deep level transient spectroscopy: An improved method for measuring capture rates of hot carriers in semiconductors

    SciTech Connect

    Fleming, R. M.; Seager, C. H.; Lang, D. V.; Campbell, J. M.

    2015-07-02

    In this study, an improved method for measuring the cross sections for carrier trapping at defects in semiconductors is described. This method, a variation of deep level transient spectroscopy(DLTS) used with bipolar transistors, is applied to hot carrier trapping at vacancy-oxygen, carbon-oxygen, and three charge states of divacancy centers (V2) in n- and p-type silicon. Unlike standard DLTS, we fill traps by injecting carriers into the depletion region of a bipolar transistor diode using a pulse of forward bias current applied to the adjacent diode. We show that this technique is capable of accurately measuring a wide range of capture cross sections at varying electric fields due to the control of the carrier density it provides. Because this technique can be applied to a variety of carrier energy distributions, it should be valuable in modeling the effect of radiation-induced generation-recombination currents in bipolar devices.

  16. Injection deep level transient spectroscopy: An improved method for measuring capture rates of hot carriers in semiconductors

    NASA Astrophysics Data System (ADS)

    Fleming, R. M.; Seager, C. H.; Lang, D. V.; Campbell, J. M.

    2015-07-01

    An improved method for measuring the cross sections for carrier trapping at defects in semiconductors is described. This method, a variation of deep level transient spectroscopy (DLTS) used with bipolar transistors, is applied to hot carrier trapping at vacancy-oxygen, carbon-oxygen, and three charge states of divacancy centers (V2) in n- and p-type silicon. Unlike standard DLTS, we fill traps by injecting carriers into the depletion region of a bipolar transistor diode using a pulse of forward bias current applied to the adjacent diode. We show that this technique is capable of accurately measuring a wide range of capture cross sections at varying electric fields due to the control of the carrier density it provides. Because this technique can be applied to a variety of carrier energy distributions, it should be valuable in modeling the effect of radiation-induced generation-recombination currents in bipolar devices.

  17. Injection deep level transient spectroscopy: An improved method for measuring capture rates of hot carriers in semiconductors

    SciTech Connect

    Fleming, R. M.; Seager, C. H.; Lang, D. V.; Campbell, J. M.

    2015-07-07

    An improved method for measuring the cross sections for carrier trapping at defects in semiconductors is described. This method, a variation of deep level transient spectroscopy (DLTS) used with bipolar transistors, is applied to hot carrier trapping at vacancy-oxygen, carbon-oxygen, and three charge states of divacancy centers (V{sub 2}) in n- and p-type silicon. Unlike standard DLTS, we fill traps by injecting carriers into the depletion region of a bipolar transistor diode using a pulse of forward bias current applied to the adjacent diode. We show that this technique is capable of accurately measuring a wide range of capture cross sections at varying electric fields due to the control of the carrier density it provides. Because this technique can be applied to a variety of carrier energy distributions, it should be valuable in modeling the effect of radiation-induced generation-recombination currents in bipolar devices.

  18. On the behaviour and origin of the major deep level (EL2) in GaAs

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Parsey, J. M.; Kaminska, M.; Wada, K.; Gatos, H. C.

    1982-01-01

    In an extensive crystal growth and characterization study of Bridgman-grown GaAs it was established that the following factors affect the concentration of the EL2 level: (1) the As pressure during growth; (2) the partial pressure of Ga2O; (3) the concentration of shallow donors and acceptors; and (4) the post-growth cooling cycle. The role of these factors is qualitatively and quantitatively explained by attributing the 0.82 eV donor state to the antisite defect As-sub-Ga formed as a result of Ga-vacancy migration during the post-growth cooling of the crystals.

  19. Deep levels induced by reactive ion etching in n- and p-type 4H-SiC

    SciTech Connect

    Kawahara, Koutarou; Suda, Jun; Kimoto, Tsunenobu; Krieger, Michael

    2010-07-15

    In this study, the authors investigate deep levels, which are induced by reactive ion etching (RIE) of n-type/p-type 4H-SiC, by deep level transient spectroscopy (DLTS). The capacitance of a Schottky contact fabricated on as-etched p-type SiC is abnormally small due to compensation or deactivation of acceptors extending to a depth of {approx}14 {mu}m, which is nearly equal to the epilayer thickness. The value of the capacitance can recover to that of a Schottky contact on as-grown samples after annealing at 1000 deg. C. However, various kinds of defects, IN2 (E{sub C}-0.30 eV), EN (E{sub C}-1.6 eV), IP1 (E{sub V}+0.30 eV), IP2 (E{sub V}+0.39 eV), IP4 (HK0: E{sub V}+0.72 eV), IP5 (E{sub V}+0.85 eV), IP7 (E{sub V}+1.3 eV), and EP (E{sub V}+1.4 eV), remain at a high concentration (average of total defect concentration in the region ranging from 0.3 {mu}m to 1.0 {mu}m:{approx}5x10{sup 14} cm{sup -3}) even after annealing at 1000 deg. C. The concentration of all these defects generated by RIE, except for the IP4 (HK0) center, remarkably decreases by thermal oxidation. In addition, the HK0 center can also be reduced significantly by a subsequent annealing at 1400 deg. C in Ar.

  20. Identification of intrinsic deep level defects responsible for electret behavior in TlGaSe2 layered semiconductor

    NASA Astrophysics Data System (ADS)

    Seyidov, MirHasan Yu.; Mikailzade, Faik A.; Uzun, Talip; Odrinsky, Andrei P.; Yakar, Emin; Aliyeva, Vafa B.; Babayev, Sardar S.; Mammadov, Tofig G.

    2016-02-01

    Unusual behavior of pyroelectric current signal polarity near the Curie point (Tc) was observed for TlGaSe2 a ferroelectric-semiconductor. It has been revealed that the polarity of the spontaneous polarization near Tc depends on the sample poling prehistory. In particular, applying an external electric field only in the temperature range of the paraelectric state during cooling regime in darkness brought to the depolarization current at Tc with the sign opposite to the external field polarity. Otherwise, if the sample was poled in the temperature interval of the incommensurate phase, pyroelectric current exhibits a peak at Tc with the polarity that is the same as for the external poling electric field. These observations indicate that internal electric field is present in the bulk and near-surface layer regions of the electrically poled single crystal TlGaSe2. Possible mechanisms and origins responsible for the internal electric fields in TlGaSe2 are discussed. It is shown that the formation of internal electric fields in TlGaSe2 is due to charging of intrinsic native defects during the poling process. Characteristics of electrically active intrinsic defects in TlGaSe2 were investigated by using of Photo-Induced Current Transient Spectroscopy (PICTS) technique. Six deep defect levels in the band gap of TlGaSe2 were determined, which were localized both in the bulk and on the surface of the sample and could be electrically charged. The correlation between polarization effects and PICTS results has been established. It was shown that native deep defects (A3-A6) localized in the bulk of crystal are responsible for hetero-charge formation and negative sign of the pyroelectric current peak observed around the Curie temperature after poling the sample in the temperature intervals well above Tc. It was also shown that the positive sign pyrocurrent observed near the Curie point is attributed to the homo-charge formed by native A2-trapping centers which are localized near

  1. Effect of impurity doping in gapped bilayer graphene

    SciTech Connect

    Han, Qi; Yan, Baoming; Jia, Zhenzhao; Niu, Jingjing; Yu, Dapeng; Wu, Xiaosong

    2015-10-19

    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.

  2. Chronic Deep Brain Stimulation of the Hypothalamic Nucleus in Wistar Rats Alters Circulatory Levels of Corticosterone and Proinflammatory Cytokines

    PubMed Central

    Calleja-Castillo, Juan Manuel; De La Cruz-Aguilera, Dora Luz; Manjarrez, Joaquín; Velasco-Velázquez, Marco Antonio; Morales-Espinoza, Gabriel; Moreno-Aguilar, Julia; Hernández, Maria Eugenia; Aguirre-Cruz, Lucinda

    2013-01-01

    Deep brain stimulation (DBS) is a therapeutic option for several diseases, but its effects on HPA axis activity and systemic inflammation are unknown. This study aimed to detect circulatory variations of corticosterone and cytokines levels in Wistar rats, after 21 days of DBS-at the ventrolateral part of the ventromedial hypothalamic nucleus (VMHvl), unilateral cervical vagotomy (UCVgX), or UCVgX plus DBS. We included the respective control (C) and sham (S) groups (n = 6 rats per group). DBS treated rats had higher levels of TNF-α (120%; P < 0.01) and IFN-γ (305%; P < 0.001) but lower corticosterone concentration (48%; P < 0.001) than C and S. UCVgX animals showed increased corticosterone levels (154%; P < 0.001) versus C and S. UCVgX plus DBS increased IL-1β (402%; P < 0.001), IL-6 (160%; P < 0.001), and corsticosterone (178%; P < 0.001 versus 48%; P < 0.001) compared with the C and S groups. Chronic DBS at VMHvl induced a systemic inflammatory response accompanied by a decrease of HPA axis function. UCVgX rats experienced HPA axis hyperactivity as result of vagus nerve injury; however, DBS was unable to block the HPA axis hyperactivity induced by unilateral cervical vagotomy. Further studies are necessary to explore these findings and their clinical implication. PMID:24235973

  3. Distribution Coefficients of Impurities in Metals

    NASA Astrophysics Data System (ADS)

    Pearce, J. V.

    2014-04-01

    Impurities dissolved in very pure metals at the level of parts per million often cause an elevation or depression of the freezing temperature of the order of millikelvins. This represents a significant contribution to the uncertainty of standard platinum resistance thermometer calibrations. An important parameter for characterizing the behavior of impurities is the distribution coefficient , which is the ratio of the solid solubility to liquid solubility. A knowledge of for a given binary system is essential for contemporary methods of evaluating or correcting for the effect of impurities, and it is therefore of universal interest to have the most complete set of values possible. A survey of equilibrium values of (in the low concentration limit) reported in the literature for the International Temperature Scale of 1990 fixed points of Hg, Ga, In, Sn, Zn, Al, Au, Ag, and Cu is presented. In addition, thermodynamic calculations of using MTDATA are presented for 170 binary systems. In total, the combined values of from all available sources for 430 binary systems are presented. In addition, by considering all available values of for impurities in 25 different metal solvents (1300 binary systems) enough data are available to characterize patterns in the value of for a given impurity as a function of its position in the periodic table. This enables prediction of for a significant number of binary systems for which data and calculations are unavailable. By combining data from many sources, values of for solutes (atomic number from 1 to 94) in ITS-90 fixed points from Hg to Cu are suggested, together with some tentative predicted values where literature data and calculations are unavailable.

  4. Precision liquid-level measurement in deep tanks using a swept-RF resonant cavity

    NASA Astrophysics Data System (ADS)

    Piper, T. C.

    1992-03-01

    The Idaho Chemical Processing Plant (ICPP) has several large, temporary-liquid-storage tanks (50 feet diameter and 30 feet height). The tanks are located in separate underground cells. Because of the huge tank storage capacity per inch (1225 gallons), extremely accurate liquid depth measurement is required to observe normal additions (or to become aware of other than large leaks). In roughly 1970, Glenn Booman, then the header of the advanced instrumentation group of ICPP, began a program to develop what in a few years became known as 'IRF tank probes'. The initial probe was installed in tank WM-189 in 1975 and ten more were installed in other tanks in 1976. Though the RF components were fairly costly at that time, they were readily available and the system has, in general, operated without incident. Three of the most desirable features of the system not found in most other continuous reading level systems are that it exhibits no hysteresis, no creep and requires no calibration. In the years since installation the RF distribution system has been upgraded and the method of data processing has been changed somewhat. Presently, the need for more probes for more tanks has renewed interest. The original development work was never fully documented. The present talk is taken from a report being written to comprehensively describe the theory and operation of the RF probe.

  5. System-Level Analysis Modeling of Impacts of Operation Schemes of Geologic Carbon Dioxide Storage on Deep Groundwater and Carbon Dioxide Leakage Risk

    NASA Astrophysics Data System (ADS)

    Park, S.; Lee, S.; Park, J.; Kim, J.; Kihm, J.

    2013-12-01

    The objectives of this study are to predict quantitatively groundwater and carbon dioxide flow in deep saline sandstone aquifers under various carbon dioxide injection schemes (injection rate, injection period) and to analyze integratively impacts of such carbon dioxide injection schemes on deep groundwater (brine) and carbon dioxide leakage risk through abandoned wells or faults. In order to achieve the first objective, a series of process-level prediction modeling of groundwater and carbon dioxide flow in a deep saline sandstone aquifer under several carbon dioxide injection schemes was performed using a multiphase thermo-hydrological numerical model TOUGH2 (Pruess et al., 1999). The prediction modeling results show that the extent of carbon dioxide plume is significantly affected by such carbon dioxide injection schemes. In order to achieve the second objective, a series of system-level analysis modeling of deep groundwater and carbon dioxide leakage risk through an abandoned well or a fault under several carbon dioxide injection schemes was then performed using a brine and carbon dioxide leakage risk analysis model CO2-LEAK (Kim, 2012). The analysis modeling results show that the rates and amounts of deep groundwater and carbon dioxide leakage through an abandoned well or a fault increase as the carbon dioxide injection rate increases. However, the rates and amounts of deep groundwater and carbon dioxide leakage through an abandoned well or a fault decrease as the carbon dioxide injection period increases. These system-level analysis modeling results for deep groundwater and carbon dioxide leakage risk can be utilized as baseline data for establishing guidelines to mitigate anticipated environmental adverse effects on shallower groundwater systems (aquifers) when deep groundwater and carbon dioxide leakage occur. This work was supported by the Geo-Advanced Innovative Action (GAIA) Program funded by the Korea Environmental Industry and Technology Institute

  6. High-barrier Schottky contact on n-type 4H-SiC epitaxial layer and studies of defect levels by deep level transient spectroscopy (DLTS)

    NASA Astrophysics Data System (ADS)

    Nguyen, Khai V.; Pak, Rahmi O.; Oner, Cihan; Mannan, Mohammad A.; Mandal, Krishna C.

    2015-08-01

    High barrier Schottky contact has been fabricated on 50 μm n-type 4H-SiC epitaxial layers grown on 350 μm thick substrate 8° off-cut towards the [11̅20] direction. The 4H-SiC epitaxial wafer was diced into 10 x 10 mm2 samples. The metal-semiconductor junctions were fabricated by photolithography and dc sputtering with ruthenium (Ru). The junction properties were characterized through current-voltage (I-V) and capacitance-voltage (C-V) measurements. Detectors were characterized by alpha spectroscopy measurements in terms of energy resolution and charge collection efficiency using a 0.1 μCi 241Am radiation source. It was found that detectors fabricated from high work function rare transition metal Ru demonstrated very low leakage current and significant improvement of detector performance. Defect characterization of the epitaxial layers was conducted by deep level transient spectroscopy (DLTS) to thoroughly investigate the defect levels in the active region. The presence of a new defect level induced by this rare transition metal-semiconductor interface has been identified and characterized.

  7. Metallic impurities in gallium nitride grown by molecular beam epitaxy

    SciTech Connect

    McHugo, S.A.; Krueger, J.; Kisielowski, C.

    1997-04-01

    Transition metals are often encountered in trace amounts in semiconductors. They have been extensively studied in most elemental and compound systems, since they form deep donor and/or acceptor levels which usually degrade the electronic and optical material properties. Only very little is known about transition metals in recent III-V semiconducting materials, such as GaN, AlN and InN. These few studies have been done exclusively on Metal-Organic Chemical Vapor Deposition (MOCVD) or Hybrid Vapor Phase Epitaxy HVPE-grown GaN. Preliminary x-ray fluorescence studies at the Advanced Light Source, beamline 10.3.1, Lawrence Berkeley National Laboratory have revealed that GaN materials grown by Molecular Beam Epitaxy (MBE) have Fe, Ni and Cr as the dominant transition metal contaminants. This finding is commensurate with the extremely high concentrations of hydrogen, carbon and oxygen (up to 10{sup 20} cm{sup {minus}3}) measured by Secondary Ion Mass Spectroscopy (SIMS). Preliminary work using the mapping capabilities of the x-ray fluorescence microprobe revealed the metal impurities were inhomogeneously distributed over the film. Future work of this collaboration will be to find a correlation between the existence of transition metals in MBE films, as revealed by x-ray fluorescence, and Photoluminescence (PL) spectra taken in the infrared region. Also, the authors will make use of the 1 {mu}m spatial resolution of x-ray microprobe to locate the contaminants in relation to structural defects in the GaN films. Because of the large strain caused by the lattice mismatch between the GaN films and the substrates, the films grow in a columnar order with high densities of grain boundaries and dislocations. These structural defects offer preferential sites for metal precipitation or agglomeration which could degrade the optical properties of this material more so than if the impurities were left dissolved in the GaN.

  8. Negative compressibility observed in graphene containing resonant impurities

    SciTech Connect

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

    2013-05-20

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

  9. Negative compressibility observed in graphene containing resonant impurities

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

  10. Mobile impurities in ferromagnetic liquids

    NASA Astrophysics Data System (ADS)

    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.

  11. Thermal stability of deep level defects induced by high energy proton irradiation in n-type GaN

    SciTech Connect

    Zhang, Z.; Farzana, E.; Sun, W. Y.; Arehart, A. R.; Ringel, S. A.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; McSkimming, B.; Kyle, E. C. H.; Speck, J. S.

    2015-10-21

    The impact of annealing of proton irradiation-induced defects in n-type GaN devices has been systematically investigated using deep level transient and optical spectroscopies. Moderate temperature annealing (>200–250 °C) causes significant reduction in the concentration of nearly all irradiation-induced traps. While the decreased concentration of previously identified N and Ga vacancy related levels at E{sub C} − 0.13 eV, 0.16 eV, and 2.50 eV generally followed a first-order reaction model with activation energies matching theoretical values for N{sub I} and V{sub Ga} diffusion, irradiation-induced traps at E{sub C} − 0.72 eV, 1.25 eV, and 3.28 eV all decrease in concentration in a gradual manner, suggesting a more complex reduction mechanism. Slight increases in concentration are observed for the N-vacancy related levels at E{sub C} − 0.20 eV and 0.25 eV, which may be due to the reconfiguration of other N-vacancy related defects. Finally, the observed reduction in concentrations of the states at E{sub C} − 1.25 and E{sub C} − 3.28 eV as a function of annealing temperature closely tracks the detailed recovery behavior of the background carrier concentration as a function of annealing temperature. As a result, it is suggested that these two levels are likely to be responsible for the underlying carrier compensation effect that causes the observation of carrier removal in proton-irradiated n-GaN.

  12. Recent trends in the impurity profile of pharmaceuticals

    PubMed Central

    Pilaniya, Kavita; Chandrawanshi, Harish K.; Pilaniya, Urmila; Manchandani, Pooja; Jain, Pratishtha; Singh, Nitin

    2010-01-01

    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. PMID:22247862

  13. Chronological Changes of C-Reactive Protein Levels Following Uncomplicated, Two-Staged, Bilateral Deep Brain Stimulation

    PubMed Central

    Kim, Jae-hun; Ha, Sang-woo; Choi, Jin-gyu

    2015-01-01

    Objective The occurrence of acute cerebral infection following deep brain stimulation (DBS) is currently being reported with elevation of C-reactive protein (CRP) level. The aim of the present study was to establish normal range of the magnitude and time-course of CRP increases following routine DBS procedures in the absence of clinical and laboratory signs of infection. Methods A retrospective evaluation of serial changes of plasma CRP levels in 46 patients undergoing bilateral, two-staged DBS was performed. Because DBS was performed as a two-staged procedure involving; implantation of lead and internal pulse generator (IPG), CRP was measured preoperatively and postoperatively every 2 days until normalization of CRP (post-lead implantation day 2 and 4, post-IPG implantation day 2, 4, and 6). Results Compared with preoperative CRP levels (0.12±0.17 mg/dL, n=46), mean CRP levels were significantly elevated after lead insertion day 2 and 4 (1.68±1.83 mg/dL, n=46 and 0.76±0.38 mg/dL, n=16, respectively, p<0.001). The mean CRP levels at post-lead implantation day 2 were further elevated at post-IPG implantation day 2 (3.41±2.56 mg/dL, n=46, respectively, p<0.01). This elevation in post-IPG day 2 rapidly declined in day 4 (1.24±1.29 mg/dL, n=46, p<0.05) and normalized to preoperative value at day 6 (0.42±0.33 mg/dL, n=46, p>0.05). Mean CRP levels after IPG implantation were significantly higher in patients whose IPGs were implanted at post-lead day 3 than those at post-lead day 5-6 (3.99±2.80 mg/dL, n=30, and 2.31±1.56 mg/dL, n=16, respectively, p<0.05). However, there was no difference in post-IPG day 2 and 4 between them (p>0.05). Conclusion The mean postoperative CRP levels were highest on post-IPG insertion day 2 and decreased rapidly, returning to the normal range on post-IPG implantation day 6. The duration of post-lead implantation period influenced the magnitude of CRP elevation at post-IPG insertion day 2. Information about the normal response of CRP

  14. Metal impurities in food and drugs.

    PubMed

    Abernethy, Darrell R; Destefano, Anthony J; Cecil, Todd L; Zaidi, Kahkashan; Williams, Roger L

    2010-05-01

    The major metals of potential health concern found in food, drugs (medicines), and dietary supplements are lead, cadmium, mercury, and arsenic. Other metals, such as chromium, copper, manganese, molybdenum, vanadium, nickel, osmium, rhodium, ruthenium, iridium, palladium, and platinum, may be used or introduced during manufacturing and may be controlled in the final article as impurities. Screening for metals in medicines and dietary supplements rarely indicates the presence of toxic metal impurities at levels of concern. The setting of heavy metal limits is appropriate for medicines and is appropriate for supplements when heavy metals are likely or certain to contaminate a given product. Setting reasonable health-based limits for some of these metals is challenging because of their ubiquity in the environment, limitations of current analytical procedures, and other factors. Taken together, compendial tests for metals in food and drugs present an array of issues that challenge compendial scientists. PMID:20217462

  15. Extrinsic germanium Blocked Impurity Bank (BIB) detectors

    NASA Technical Reports Server (NTRS)

    Krabach, Timothy N.; Huffman, James E.; Watson, Dan M.

    1989-01-01

    Ge:Ga blocked-impurity-band (BIB) detectors with long wavelength thresholds greater than 190 microns and peak quantum efficiencies of 4 percent, at an operating temperature of 1.8 K, have been fabricated. These proof of concept devices consist of a high purity germanium blocking layer epitaxially grown on a Ga-doped Ge substrate. This demonstration of BIB behavior in germanium enables the development of far infrared detector arrays similar to the current silicon-based devices. Present efforts are focussed on improving the chemical vapor deposition process used to create the blocking layer and on the lithographic processing required to produce monolithic detector arrays in germanium. Approaches to test the impurity levels in both the blocking and active layers are considered.

  16. A New Method for Reconstructing Sea-Level and Deep-Sea-Temperature Variability over the Past 5.3 Million Years

    NASA Astrophysics Data System (ADS)

    Rohling, E. J.

    2014-12-01

    Ice volume (and hence sea level) and deep-sea temperature are key measures of global climate change. Sea level has been documented using several independent methods over the past 0.5 million years (Myr). Older periods, however, lack such independent validation; all existing records are related to deep-sea oxygen isotope (d18O) data that are influenced by processes unrelated to sea level. For deep-sea temperature, only one continuous high-resolution (Mg/Ca-based) record exists, with related sea-level estimates, spanning the past 1.5 Myr. We have recently presented a novel sea-level reconstruction, with associated estimates of deep-sea temperature, which independently validates the previous 0-1.5 Myr reconstruction and extends it back to 5.3 Myr ago. A serious of caveats applies to this new method, especially in older times of its application, as is always the case with new methods. Independent validation exercises are needed to elucidate where consistency exists, and where solutions drift away from each other. A key observation from our new method is that a large temporal offset existed during the onset of Plio-Pleistocene ice ages, between a marked cooling step at 2.73 Myr ago and the first major glaciation at 2.15 Myr ago. This observation relies on relative changes within the dataset, which are more robust than absolute values. I will discuss our method and its main caveats and avenues for improvement.

  17. Investigation of deep level defects in epitaxial semiconducting zinc sulpho-selenide. Progress report, June 15, 1980-June 14, 1981

    SciTech Connect

    Wessels, B.W.

    1981-02-15

    High conductivity ZnSe single crystalline films have been heteroepitaxially deposited on GaAs substrates using open tube chemical vapor transport. Unintentionally doped films had net donor densities of 10/sup 14/ - 10/sup 16/ cm/sup -3/ and resistivities of 1 to 10/sup 3/ ohm cm. Resistivity was found to be strongly dependent upon zinc partial pressure during deposition. Electron mobilities of the order of 50 to 200 cm/sup 2//V sec were observed which suggested that the films are highly compensated. Properties of the deep level defects in heteroepitaxially grown ZnSe have been investigated using transient capacitance spectroscopy. A series of electron traps were observed with activation energies of 0.33, 0.35, 0.42, 0.71 and 0.86 eV in Au/ZnSe Schottky diodes. Trap concentration ranged from 10/sup 12/ to 10/sup 14/ cm/sup -3/ and depended on the zinc partial pressure. A model for the defect structure of ZnSe was proposed. Growth studies of ZnS/sub x/Se/sub 1-x/ on GaAs were begun.

  18. Building a conceptual framework to culturally adapt health promotion and prevention programs at the deep structural level.

    PubMed

    Wang-Schweig, Meme; Kviz, Frederick J; Altfeld, Susan J; Miller, Arlene M; Miller, Brenda A

    2014-07-01

    The debate on the effectiveness and merit for the amount of time, effort, and resources to culturally adapt health promotion and prevention programs continues. This may be due, in large part, to the lack of theory in commonly used methods to match programmatic content and delivery to the culture of a population, particularly at the deep structural level. This paper asserts that prior to the cultural adaptation of prevention programs, it is necessary to first develop a conceptual framework. We propose a multiphase approach to address key challenges in the science of cultural adaptation by first identifying and exploring relevant cultural factors that may affect the targeted health-related behavior prior to proceeding through steps of a stage model. The first phase involves developing an underlying conceptual framework that integrates cultural factors to ground this process. The second phase employs the different steps of a stage model. For Phase I of our approach, we offer four key steps and use our research study as an example of how these steps were applied to build a framework for the cultural adaptation of a family-based intervention to prevent adolescent alcohol use, Guiding Good Choices (GGC), to Chinese American families. We then provide a summary of the preliminary evidence from a few key relationships that were tested among our sample with the greater purpose of discussing how these findings might be used to culturally adapt GGC. PMID:24396122

  19. Injection deep level transient spectroscopy: An improved method for measuring capture rates of hot carriers in semiconductors

    DOE PAGESBeta

    Fleming, R. M.; Seager, C. H.; Lang, D. V.; Campbell, J. M.

    2015-07-02

    In this study, an improved method for measuring the cross sections for carrier trapping at defects in semiconductors is described. This method, a variation of deep level transient spectroscopy(DLTS) used with bipolar transistors, is applied to hot carrier trapping at vacancy-oxygen, carbon-oxygen, and three charge states of divacancy centers (V2) in n- and p-type silicon. Unlike standard DLTS, we fill traps by injecting carriers into the depletion region of a bipolar transistor diode using a pulse of forward bias current applied to the adjacent diode. We show that this technique is capable of accurately measuring a wide range of capturemore » cross sections at varying electric fields due to the control of the carrier density it provides. Because this technique can be applied to a variety of carrier energy distributions, it should be valuable in modeling the effect of radiation-induced generation-recombination currents in bipolar devices.« less

  20. Relative contributions of ocean mass and deep steric changes to sea level rise between 1993 and 2013

    NASA Astrophysics Data System (ADS)

    Purkey, Sarah G.; Johnson, Gregory C.; Chambers, Don P.

    2014-11-01

    Regional and global trends of Sea Level Rise (SLR) owing to mass addition centered between 1996 and 2006 are assessed through a full-depth SLR budget using full-depth in situ ocean data and satellite altimetry. These rates are compared to regional and global trends in ocean mass addition estimated directly using data from the Gravity Recovery and Climate Experiment (GRACE) from 2003 to 2013. Despite the two independent methods covering different time periods with differing spatial and temporal resolution, they both capture the same large-scale mass addition trend patterns including higher rates of mass addition in the North Pacific, South Atlantic, and the Indo-Atlantic sector of the Southern Ocean, and lower mass addition trends in the Indian, North Atlantic, South Pacific, and the Pacific sector of the Southern Ocean. The global mean trend of ocean mass addition is 1.5 (±0.4) mm yr-1 for 1996-2006 from the residual method and the same for 2003-2013 from the GRACE method. Furthermore, the residual method is used to evaluate the error introduced into the mass budget if the deep steric contributions below 700, 1000, 2000, 3000, and 4000 m are neglected, revealing errors of 65%, 38%, 13%, 8%, and 4% respectively. The two methods no longer agree within error bars when only the steric contribution shallower than 1000 m is considered.

  1. Correlation of proton irradiation induced threshold voltage shifts to deep level traps in AlGaN/GaN heterostructures

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Cardwell, D.; Sasikumar, A.; Kyle, E. C. H.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; Speck, J. S.; Arehart, A. R.; Ringel, S. A.

    2016-04-01

    The impact of proton irradiation on the threshold voltage (VT) of AlGaN/GaN heterostructures is systematically investigated to enhance the understanding of a primary component of the degradation of irradiated high electron mobility transistors. The value of VT was found to increase monotonically as a function of 1.8 MeV proton fluence in a sub-linear manner reaching 0.63 V at a fluence of 1 × 1014 cm-2. Silvaco Atlas simulations of VT shifts caused by GaN buffer traps using experimentally measured introduction rates, and energy levels closely match the experimental results. Different buffer designs lead to different VT dependences on proton irradiation, confirming that deep, acceptor-like defects in the GaN buffer are primarily responsible for the observed VT shifts. The proton irradiation induced VT shifts are found to depend on the barrier thickness in a linear fashion; thus, scaling the barrier thickness could be an effective way to reduce such degradation.

  2. Three-Dimensional Geologic Modeling of a Prospective Deep Underground Laboratory Site for High-Level Radioactive Waste Disposal in Korea

    NASA Astrophysics Data System (ADS)

    Park, J. Y.; Lee, S.; Park, S. U.; Kim, J. M.; Kihm, J. H.

    2014-12-01

    A series of three-dimensional geologic modeling was performed using a geostatistical geologic model GOCAD (ASGA and Paradigm) to characterize quantitatively and to visualize realistically a prospective deep underground laboratory site for high-level radioactive waste disposal in Korea. The necessity of a deep underground laboratory arises from its in-situ conditions for related deep scientific experiments. However, the construction and operation of such a deep underground laboratory take great efforts and expenses owing to its larger depth and thus higher geologic uncertainty. For these reasons, quantitative characterization and realistic visualization of geologic formations and structures of a deep underground laboratory site is crucial before its construction and operation. The study area for the prospective deep underground laboratory site is mainly consists of Precambrian metamorphic rocks as a complex. First, various topographic and geologic data of the study area were collected from literature and boreholes and preliminarily analyzed. Based on the preliminary analysis results, a three-dimensional structural model, which consists of the boundaries between the geologic formations and structures, was established, and a three-dimensional grid model, which consists of hexahedral grid blocks, was produced. Three-dimensional geologic formation model was then established by polymerizing these two models. Finally, a series of three-dimensional lithofacies modeling was performed using the sequential indicator simulation (SIS) and truncated Gaussian simulation (TGS). The volume fractions of metamorphic rocks predicted using the TGS are more similar to the actual data observed in boreholes than those predicted using the SIS. These three-dimensional geologic modeling results can improve a quantitative and realistic understanding of geologic characteristics of the prospective deep underground laboratory site for high-level radioactive waste disposal and thus can provide

  3. Individual and Partner-Level Factors Associated with Condom Non-Use Among African American STI Clinic Attendees in the Deep South: An Event-Level Analysis.

    PubMed

    Marshall, Brandon D L; Perez-Brumer, Amaya G; MacCarthy, Sarah; Mena, Leandro; Chan, Philip A; Towey, Caitlin; Barnett, Nancy; Parker, Sharon; Barnes, Arti; Brinkley-Rubinstein, Lauren; Rose, Jennifer S; Nunn, Amy S

    2016-06-01

    The US HIV/AIDS epidemic is concentrated in the Deep South, yet factors contributing to HIV transmission are not fully understood. We examined relationships between substance use, sexual partnership characteristics, and condom non-use in an African American sample of STI clinic attendees in Jackson, Mississippi. We assessed condom non-use at last intercourse with up to three recent sexual partners reported by participants between January and June 2011. Participant- and partner-level correlates of condom non-use were examined using generalized estimating equations. The 1295 participants reported 2880 intercourse events, of which 1490 (51.7 %) involved condom non-use. Older age, lower educational attainment, reporting financial or material dependence on a sex partner, sex with a primary partner, and higher frequency of sex were associated with increased odds of condomless sex. HIV prevention efforts in the South should address underlying socioeconomic disparities and structural determinants that result in partner dependency and sexual risk behavior. PMID:26683032

  4. A biosphere modeling methodology for dose assessments of the potential Yucca Mountain deep geological high level radioactive waste repository.

    PubMed

    Watkins, B M; Smith, G M; Little, R H; Kessler, J

    1999-04-01

    Recent developments in performance standards for proposed high level radioactive waste disposal at Yucca Mountain suggest that health risk or dose rate limits will likely be part of future standards. Approaches to the development of biosphere modeling and dose assessments for Yucca Mountain have been relatively lacking in previous performance assessments due to the absence of such a requirement. This paper describes a practical methodology used to develop a biosphere model appropriate for calculating doses from use of well water by hypothetical individuals due to discharges of contaminated groundwater into a deep well. The biosphere model methodology, developed in parallel with the BIOMOVS II international study, allows a transparent recording of the decisions at each step, from the specification of the biosphere assessment context through to model development and analysis of results. A list of features, events, and processes relevant to Yucca Mountain was recorded and an interaction matrix developed to help identify relationships between them. Special consideration was given to critical/potential exposure group issues and approaches. The conceptual model of the biosphere system was then developed, based on the interaction matrix, to show how radionuclides migrate and accumulate in the biosphere media and result in potential exposure pathways. A mathematical dose assessment model was specified using the flexible AMBER software application, which allows users to construct their own compartment models. The starting point for the biosphere calculations was a unit flux of each radionuclide from the groundwater in the geosphere into the drinking water in the well. For each of the 26 radionuclides considered, the most significant exposure pathways for hypothetical individuals were identified. For 14 of the radionuclides, the primary exposure pathways were identified as consumption of various crops and animal products following assumed agricultural use of the contaminated

  5. Student Perceptions of Science Teacher Actions in Two Culturally Diverse Middle-Level Science Classrooms: A Case Study in the American Deep South.

    ERIC Educational Resources Information Center

    McGinnis, J. Randy

    The purpose of this study was to give voice to students' perceptions in two science classrooms taught by two white teachers in an urban multicultural middle-level school situated in the American Deep South. Student participants were 35 students of different ethnicities in grades 7 and 8. The theoretical reference used is social contextual, a…

  6. Revealing substructures of H4 and H5 hole traps in p-type InP using Laplace deep-level transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Darwich, R.; Mani, A. A.

    2010-08-01

    New substructures of H4 and H5 hole traps have been revealed using Laplace deep-level transient spectroscopy. Our measurements show that the hole traps H4 and H5 can have at least three components for each. Moreover, the activation energies are deduced and the microscopic nature of these substructures is discussed.

  7. Revealing substructures of H4 and H5 hole traps in p-type InP using Laplace deep-level transient spectroscopy

    SciTech Connect

    Darwich, R.; Mani, A. A.

    2010-08-15

    New substructures of H4 and H5 hole traps have been revealed using Laplace deep-level transient spectroscopy. Our measurements show that the hole traps H4 and H5 can have at least three components for each. Moreover, the activation energies are deduced and the microscopic nature of these substructures is discussed.

  8. Deep learning

    NASA Astrophysics Data System (ADS)

    Lecun, Yann; Bengio, Yoshua; Hinton, Geoffrey

    2015-05-01

    Deep learning allows computational models that are composed of multiple processing layers to learn representations of data with multiple levels of abstraction. These methods have dramatically improved the state-of-the-art in speech recognition, visual object recognition, object detection and many other domains such as drug discovery and genomics. Deep learning discovers intricate structure in large data sets by using the backpropagation algorithm to indicate how a machine should change its internal parameters that are used to compute the representation in each layer from the representation in the previous layer. Deep convolutional nets have brought about breakthroughs in processing images, video, speech and audio, whereas recurrent nets have shone light on sequential data such as text and speech.

  9. Deep learning.

    PubMed

    LeCun, Yann; Bengio, Yoshua; Hinton, Geoffrey

    2015-05-28

    Deep learning allows computational models that are composed of multiple processing layers to learn representations of data with multiple levels of abstraction. These methods have dramatically improved the state-of-the-art in speech recognition, visual object recognition, object detection and many other domains such as drug discovery and genomics. Deep learning discovers intricate structure in large data sets by using the backpropagation algorithm to indicate how a machine should change its internal parameters that are used to compute the representation in each layer from the representation in the previous layer. Deep convolutional nets have brought about breakthroughs in processing images, video, speech and audio, whereas recurrent nets have shone light on sequential data such as text and speech. PMID:26017442

  10. Impurity bubbles in a BEC

    NASA Astrophysics Data System (ADS)

    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.

  11. Isolation and characterization of a potential process related impurity of phenazopyridine HCl by preparative HPLC followed by MS-MS and 2D-NMR spectroscopy.

    PubMed

    Rao, R Nageswara; Maurya, Pawan K; Raju, A Narasa

    2009-07-12

    During the process development of phenazopyridine HCl bulk drug, a potential impurity was detected in the routine impurity profiles by HPLC. Using MS-MS and multidimensional NMR techniques, the trace level impurity was unambiguously identified to be 3-phenyl-5-phenylazo-pyridine-2,6-diamine after its isolation from phenazopyridine HCl by semi-preparative HPLC. The formation of the impurity was discussed. To our knowledge, it is a novel impurity not reported elsewhere. PMID:19376664

  12. Tuning of deep level emission in highly oriented electrodeposited ZnO nanorods by post growth annealing treatments

    NASA Astrophysics Data System (ADS)

    Simimol, A.; Manikandanath, N. T.; Anappara, Aji A.; Chowdhury, Prasanta; Barshilia, Harish C.

    2014-08-01

    Highly dense and c-axis oriented zinc oxide (ZnO) nanorods with hexagonal wurtzite facets were deposited on fluorine doped tin oxide coated glass substrates by a simple and cost-effective electrodeposition method at low bath temperature (80 °C). The as-grown samples were then annealed at various temperatures (TA = 100-500 °C) in different environments (e.g., zinc, oxygen, air, and vacuum) to understand their photoluminescence (PL) behavior in the ultra-violet (UV) and the visible regions. The PL results revealed that the as-deposited ZnO nanorods consisted of oxygen vacancy (VO), zinc interstitial (Zni), and oxygen interstitial (Oi) defects and these can be reduced significantly by annealing in different environments at optimal annealing temperatures. However, the intensity of deep level emission increased for TA greater than the optimized values for the respective environments due to the introduction of various defect centers. For example, for TA ≥ 450 °C in the oxygen and air environments, the density of Oi defects increased, whereas, the green emission associated with VO is dominant in the vacuum annealed (TA = 500 °C) ZnO nanorods. The UV peak red shifted after the post-growth annealing treatments in all the environments and the vacuum annealed sample exhibited highest UV peak intensity. The observations from the PL data are supported by the micro-Raman spectroscopy. The present study gives new insight into the origin of different defects that exist in the electrodeposited ZnO nanorods and how these defects can be precisely controlled in order to get the desired emissions for the opto-electronic applications.

  13. Tuning of deep level emission in highly oriented electrodeposited ZnO nanorods by post growth annealing treatments

    SciTech Connect

    Simimol, A.; Manikandanath, N. T.; Chowdhury, Prasanta; Barshilia, Harish C.; Anappara, Aji A.

    2014-08-21

    Highly dense and c-axis oriented zinc oxide (ZnO) nanorods with hexagonal wurtzite facets were deposited on fluorine doped tin oxide coated glass substrates by a simple and cost-effective electrodeposition method at low bath temperature (80 °C). The as-grown samples were then annealed at various temperatures (T{sub A} = 100–500 °C) in different environments (e.g., zinc, oxygen, air, and vacuum) to understand their photoluminescence (PL) behavior in the ultra-violet (UV) and the visible regions. The PL results revealed that the as-deposited ZnO nanorods consisted of oxygen vacancy (V{sub O}), zinc interstitial (Zn{sub i}), and oxygen interstitial (O{sub i}) defects and these can be reduced significantly by annealing in different environments at optimal annealing temperatures. However, the intensity of deep level emission increased for T{sub A} greater than the optimized values for the respective environments due to the introduction of various defect centers. For example, for T{sub A} ≥ 450 °C in the oxygen and air environments, the density of O{sub i} defects increased, whereas, the green emission associated with V{sub O} is dominant in the vacuum annealed (T{sub A} = 500 °C) ZnO nanorods. The UV peak red shifted after the post-growth annealing treatments in all the environments and the vacuum annealed sample exhibited highest UV peak intensity. The observations from the PL data are supported by the micro-Raman spectroscopy. The present study gives new insight into the origin of different defects that exist in the electrodeposited ZnO nanorods and how these defects can be precisely controlled in order to get the desired emissions for the opto-electronic applications.

  14. EFFECT OF FUEL IMPURITIES ON FUEL CELL PERFORMANCE AND DURABILITY

    SciTech Connect

    Colon-Mercado, H.

    2010-09-28

    A fuel cell is an electrochemical energy conversion device that produces electricity during the combination of hydrogen and oxygen to produce water. Proton exchange membranes fuel cells are favored for portable applications as well as stationary ones due to their high power density, low operating temperature, and low corrosion of components. In real life operation, the use of pure fuel and oxidant gases results in an impractical system. A more realistic and cost efficient approach is the use of air as an oxidant gas and hydrogen from hydrogen carriers (i.e., ammonia, hydrocarbons, hydrides). However, trace impurities arising from different hydrogen sources and production increases the degradation of the fuel cell. These impurities include carbon monoxide, ammonia, sulfur, hydrocarbons, and halogen compounds. The International Organization for Standardization (ISO) has set maximum limits for trace impurities in the hydrogen stream; however fuel cell data is needed to validate the assumption that at those levels the impurities will cause no degradation. This report summarizes the effect of selected contaminants tested at SRNL at ISO levels. Runs at ISO proposed concentration levels show that model hydrocarbon compound such as tetrahydrofuran can cause serious degradation. However, the degradation is only temporary as when the impurity is removed from the hydrogen stream the performance completely recovers. Other molecules at the ISO concentration levels such as ammonia don't show effects on the fuel cell performance. On the other hand carbon monoxide and perchloroethylene shows major degradation and the system can only be recovered by following recovery procedures.

  15. Endohedral impurities in carbon nanotubes.

    PubMed

    Clougherty, Dennis P

    2003-01-24

    A generalization of the Anderson model that includes pseudo-Jahn-Teller impurity coupling is proposed to describe distortions of an endohedral impurity in a carbon nanotube. Within mean-field theory, spontaneous axial symmetry breaking is found when the vibronic coupling strength g exceeds a critical value. The effective potential is found to have O(2) symmetry, in agreement with numerical calculations. For metallic zigzag nanotubes endohedrally doped with transition metals in the dilute limit, the low-energy properties of the system may display two-channel Kondo behavior; however, strong vibronic coupling is seen to exponentially suppress the Kondo energy scale. PMID:12570507

  16. Endohedral Impurities in Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Clougherty, Dennis

    2003-03-01

    A generalization of the Anderson model that includes pseudo-Jahn-Teller impurity coupling is proposed to describe distortions of an endohedral impurity in a carbon nanotube. Treating the distortion within mean-field theory, spontaneous axial symmetry breaking is found when the vibronic coupling strength g exceeds a critical value g_c. The effective potential in the symmetry-broken state is found to have O(2) symmetry, in agreement with numerical calculations. The consequences of such a distortion on electronic transport will be discussed.

  17. Endohedral Impurities in Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Clougherty, Dennis P.

    2003-01-01

    A generalization of the Anderson model that includes pseudo-Jahn-Teller impurity coupling is proposed to describe distortions of an endohedral impurity in a carbon nanotube. Within mean-field theory, spontaneous axial symmetry breaking is found when the vibronic coupling strength g exceeds a critical value. The effective potential is found to have O(2) symmetry, in agreement with numerical calculations. For metallic zigzag nanotubes endohedrally doped with transition metals in the dilute limit, the low-energy properties of the system may display two-channel Kondo behavior; however, strong vibronic coupling is seen to exponentially suppress the Kondo energy scale.

  18. ALUMINUM IMPURITY DIFFUSION IN MAGNESIUM

    SciTech Connect

    Brennan, Sarah; Warren, Andrew; Coffey, Kevin; Kulkarni, Nagraj S; Todd, Peter J; Sohn, Yong Ho; Klimov, Mikhail

    2012-01-01

    The Al impurity diffusion in polycrystalline Mg (99.9%) via depth profiling with secondary ion mass spectrometry was studied in the temperature range of 673-573K, utilizing the thin film method and thin film solution to the diffusion equation. Multiple samples were utilized and multiple profiles were obtained to determine statistically confident coefficient with maximum standard deviation of 16%. Activation energy and pre-exponential factor of Al impurity diffusion in Mg was determined as 155 kJ/mole and 3.9 x 10-3 m2/sec.

  19. Temperature Dependent Capacitance-Voltage And Deep Level Transient Spectroscopy Study Of Self-Assembled Ge Quantum Dots Embedded In P-type Silicon

    SciTech Connect

    Rangel-Kuoppa, Victor-Tapio; Chen Gang; Jantsch, Wolfgang

    2011-12-23

    Temperature dependent Capacitance-Voltage (TCV) and Deep Level Transient Spectroscopy (DLTS) techniques were used to study how Ge Quantum Dots (QDs) embedded in Silicon trap charge. Atomic Force Microscopy (AFM) is used to obtain the density of QDs, which is in the order of 3x10{sup 11} cm{sup -2}. Three shallow levels, with activation energies of 40, 65 and 90 meV, and densities around 10{sup 16} cm{sup -3}, are found and are related to Boron. Four deep levels, with activation energies of 110, 150, 330 and 380 meV, and densities between 2x10{sup 15} cm{sup -3} and 5x10{sup 15} cm{sup -3}, are also found. TCV results suggest they are related to the Ge QDs.

  20. Some logistical considerations in designing a system of deep boreholes for disposal of high-level radioactive waste.

    SciTech Connect

    Gray, Genetha Anne; Brady, Patrick Vane; Arnold, Bill Walter

    2012-09-01

    Deep boreholes could be a relatively inexpensive, safe, and rapidly deployable strategy for disposing Americas nuclear waste. To study this approach, Sandia invested in a three year LDRD project entitled %E2%80%9CRadionuclide Transport from Deep Boreholes.%E2%80%9D In the first two years, the borehole reference design and backfill analysis were completed and the supporting modeling of borehole temperature and fluid transport profiles were done. In the third year, some of the logistics of implementing a deep borehole waste disposal system were considered. This report describes what was learned in the third year of the study and draws some conclusions about the potential bottlenecks of system implementation.

  1. Ecological niches of Arctic deep-sea copepods: Vertical partitioning, dietary preferences and different trophic levels minimize inter-specific competition

    NASA Astrophysics Data System (ADS)

    Laakmann, Silke; Kochzius, Marc; Auel, Holger

    2009-05-01

    The biodiversity of pelagic deep-sea ecosystems has received growing scientific interest in the last decade, especially in the framework of international marine biodiversity initiatives, such as Census of Marine Life (CoML). While a growing number of deep-sea zooplankton species has been identified and genetically characterized, little information is available on the mechanisms minimizing inter-specific competition and thus allowing closely related species to co-occur in the deep-sea pelagic realm. Focussing on the two dominant calanoid copepod families Euchaetidae and Aetideidae in Fram Strait, Arctic Ocean, the present study strives to characterize ecological niches of co-occurring species, with regard to vertical distribution, dietary composition as derived from lipid biomarkers, and trophic level on the basis of stable isotope signatures. Closely related species were usually restricted to different depth layers, resulting in a multi-layered vertical distribution pattern. Thus, vertical partitioning was an important mechanism to avoid inter-specific competition. Species occurring in the same depth strata usually belonged to different genera. They differed in fatty acid composition and trophic level, indicating different food preferences. Herbivorous Calanus represent major prey items for many omnivorous and carnivorous species throughout the water column. The seasonal and ontogenetic vertical migration of Calanus acts as a short-cut in food supply for pelagic deep-sea ecosystems in the Arctic.

  2. Role of sea-level change in deep water deposition along a carbonate shelf margin, Early and Middle Permian, Delaware Basin: implications for reservoir characterization

    NASA Astrophysics Data System (ADS)

    Li, Shunli; Yu, Xinghe; Li, Shengli; Giles, Katherine A.

    2015-04-01

    The architecture and sedimentary characteristics of deep water deposition can reflect influences of sea-level change on depositional processes on the shelf edge, slope, and basin floor. Outcrops of the northern slope and basin floor of the Delaware Basin in west Texas are progressively exposed due to canyon incision and road cutting. The outcrops in the Delaware Basin were measured to characterize gravity flow deposits in deep water of the basin. Subsurface data from the East Ford and Red Tank fields in the central and northeastern Delaware Basin were used to study reservoir architectures and properties. Depositional models of deep water gravity flows at different stages of sea-level change were constructed on the basis of outcrop and subsurface data. In the falling-stage system tracts, sandy debris with collapses of reef carbonates are deposited on the slope, and high-density turbidites on the slope toe and basin floor. In the low-stand system tracts, deep water fans that consist of mixed sand/mud facies on the basin floor are comprised of high- to low-density turbidites. In the transgression and high-stand system tracts, channel-levee systems and elongate lobes of mud-rich calciturbidite deposits formed as a result of sea level rise and scarcity of sandy sediment supply. For the reservoir architecture, the fan-like debris and high-density turbidites show high net-to-gross ratio of 62 %, which indicates the sandiest reservoirs for hydrocarbon accumulation. Lobe-like deep water fans with net-to-gross ratio of 57 % facilitate the formation of high quality sandy reservoirs. The channel-levee systems with muddy calciturbidites have low net-to-gross ratio of 30 %.

  3. Study of the effects of impurities on the properties of silicon solar cell

    NASA Technical Reports Server (NTRS)

    Sah, C. T.

    1981-01-01

    The effect of defects across the back-surface-field junction on the performance of high efficiency and thin solar cells, using a developed-perimeter device model for the three-dimensional defects is investigated. Significant degradation of open-circuit voltage can occur even if there are only a few defects distributed in the bulk of the solar cell. Two features in the thickness dependences of the fill factor and efficiency in impurity-doped back-surface-field solar cells are discovered in the exact numerical solution which are associated with the high injection level effect in the base and not predicted by the low-level analytical theory. What are believed to be the most accurate recombination parameters at the Ti center to date are also given and a theory is developed which is capable of distinguishing an acceptor-like deep level from a donor-like deep level using the measured values of the thermal emission and capture cross sections.

  4. Al{sub x}Ga{sub 1--x}N/GaN band offsets determined by deep-level emission

    SciTech Connect

    Hang, D. R.; Chen, C. H.; Chen, Y. F.; Jiang, H. X.; Lin, J. Y.

    2001-08-15

    We present studies of the compositional dependence of the optical properties of Al{sub x}Ga{sub 1-x}N(0deep acceptor pair recombination has also been observed in Al{sub x}Ga{sub 1-x}N. As aluminum concentration increases, the color of the band changes from yellow (2.2 eV) to blue (2.6 eV). The shift was less than that of the band gap. Together with previously published studies, it implies that the deep acceptor level is pinned to a common reference level to both materials, thus the deep level responsible for the yellow emission is used as a common reference level to determine the band alignment in Al{sub x}Ga{sub 1-x}N/GaN heterojunctions. Combining with the near-band-edge modulation spectra, the estimated ratio of conduction-to-valence band discontinuity is 65:35. Our results are close to the values obtained from PL measurements on Al{sub 0.14}Ga{sub 0.86}N/GaN quantum wells and those calculated by linear muffin-tin orbital method and linearized augmented plane wave method. {copyright} 2001 American Institute of Physics.

  5. Cell-level temperature distributions in skeletal muscle post spinal cord injury as related to deep tissue injury.

    PubMed

    Ruschkewitz, Yael; Gefen, Amit

    2010-02-01

    Deep tissue injury (DTI) is a severe pressure ulcer, which initiates in skeletal muscle tissue under intact skin. Patients with spinal cord injury (SCI) are especially vulnerable to DTI, due to their impaired motosensory capacities. The underlying mechanisms that lead to DTI are, however, still poorly understood. This study focuses on cell-level temperature distributions in muscles of patients with SCI, which typically contain thinner muscle fibers and fewer capillaries. It has been shown previously by our group that ischemic muscles of rat models of DTI cool down mildly and locally, which is very likely to slow the diffusivity of metabolites in the ischemic regions. However, it is unclear how these temperature decreases affect diffusivity at the scale of individual muscle cells in the microanatomy of SCI patients. We hypothesize that a 2 degrees C drop in the temperature of inflowing capillary blood, as shown in our animal studies, has a substantial effect on lowering the diffusivity of metabolites in skeletal muscle, but the pathological microanatomy in the chronic phase of SCI is less dominant in affecting the local temperatures in and around muscle cells. In order to test this hypothesis, two-dimensional finite element (FE) models of cross sections through the microanatomy of muscle tissue were developed using COMSOL Multiphysics software for normal and SCI muscles. The models included muscle cells, extracellular matrix (ECM), and capillaries, each with its own geometrical, thermal, and heat production properties. The SCI model configuration specifically included reduced cross section of myofibrils in favor of more ECM, less capillaries, and decreased blood inflow rate. After a 20-s heat transfer simulation, it was found that temperatures around the cells of the SCI muscle were approximately 2 degrees C lower than that in the normal muscle, that is, heat production from the muscle cell metabolism did not compensate for the lower inflowing blood temperature in

  6. Control of impurities in toroidal plasma devices

    DOEpatents

    Ohkawa, Tihiro

    1980-01-01

    A method and apparatus for plasma impurity control in closed flux plasma systems such as Tokamak reactors is disclosed. Local axisymmetrical injection of hydrogen gas is employed to reverse the normally inward flow of impurities into the plasma.

  7. Deep level traps in GaN LEDs grown by metal organic vapour phase epitaxy on an 8 inch Si(111) substrate

    NASA Astrophysics Data System (ADS)

    Nguyen, Xuan Sang; Goh, Xuan Long; Zhang, Li; Zhang, Zeng; Arehart, Aaron R.; Ringel, Steven A.; Fitzgerald, Eugene A.; Chua, Soo Jin

    2016-06-01

    Deep level traps present in GaN LED grown on 8 in. Si substrate were revealed by deep level transient spectroscopy (DLTS). One electron trap located at E C ‑ 0.7 eV was revealed in the n-GaN barrier layer. Two electron traps and one hole trap were observed in the p-GaN layer. They are located at E C ‑ 0.60 eV, E C ‑ 0.79 eV and E V + 0.70 eV. The total trap density in both the n-GaN barrier layer and the p-GaN layer of the LED is in order of 1014 cm‑3, which is comparable with that found in GaN epi-layer grown on sapphire.

  8. Evidence for two distinct defects contributing to the H4 deep-level transient spectroscopy peak in electron-irradiated InP

    NASA Astrophysics Data System (ADS)

    Massarani, B.; Awad, F. G.; Kaaka, M.; Darwich, R.

    1998-12-01

    Deep-level transient spectroscopy (DLTS) has been used to study the dominant deep-level H4 produced in InP by electron irradiation. The characteristics of the H4 peak in Zn-doped InP has been studied as a function of pulse duration (tp) before and after annealing. Our results show that at least two traps contribute to the H4 peak: one is a fast trap (labeled H4F) and the other is a slow trap (labeled H4S). This is shown through several results concerning the activation energy, the capture cross section, the full width at half-maximum, and the peak temperature shift. It is shown that both traps are irradiation defects created in the P sublattice.

  9. Probing deep level centers in GaN epilayers with variable-frequency capacitance-voltage characteristics of Au /GaN Schottky contacts

    NASA Astrophysics Data System (ADS)

    Wang, R. X.; Xu, S. J.; Shi, S. L.; Beling, C. D.; Fung, S.; Zhao, D. G.; Yang, H.; Tao, X. M.

    2006-10-01

    Under identical preparation conditions, Au /GaN Schottky contacts were prepared on two kinds of GaN epilayers with significantly different background electron concentrations and mobility as well as yellow emission intensities. Current-voltage (I-V) and variable-frequency capacitance-voltage (C-V) characteristics show that the Schottky contacts on the GaN epilayer with a higher background carrier concentration and strong yellow emission exhibit anomalous reverse-bias I-V and C-V characteristics. This is attributed to the presence of deep level centers. Theoretical simulation of the low-frequency C-V curves leads to a determination of the density and energy level position of the deep centers.

  10. Impurity tolerant electrocatalysts

    SciTech Connect

    Paffett, M.T.

    1990-01-01

    This project has two central goals. The primary research effort addresses fundamental aspects of Pt electrocatalyst poisoning by CO and an understanding of practical schemes for improving the CO tolerance of electrocatalytic materials. The second mission of this work is an attempt to address, on a fundamental level, the surface chemical properties that enhance the direct electrooxidation of methanol at binary Pt alloy electrode surfaces. 8 refs., 4 figs.

  11. Impurity/defect interactions during MeV Si{sup +} ion implantation annealing

    SciTech Connect

    Agarwal, A.; Koveshnikov, S.; Christensen, K.

    1995-08-01

    Ion implantation of dopant atoms at MeV energies is currently being explored in several integrated circuit device manufacturing processes. MeV implantation offers immediate advantages such as vertical well modulation, latch-up protection, device structure isolation, and reduced temperature processing. Simultaneously, it presents an opportunity to achieve {open_quotes}proximity{close_quotes} gettering of impurities from the active device region by placing high impurity solubility and/or secondary defect gettering sites within microns of the surface. If the MeV implanted species is a dopant ion, all three gettering mechanisms, i.e, segregation, relaxation and injection, can be involved in the gettering process, complicating the analysis and optimization of the process. However, investigation of gettering using non-dopant Si{sup +} ion damage allows the relaxation component of the gettering process to be isolated and examined separately. In general, gettering is verified by a reduction in impurity concentration in the region of interest, usually the device region, and/or a build-up of concentration/precipitation in a non-device sink region. An alternate and more meaningful approach is to use simple devices as materials characterization probes via changes in the electrical activity of the gettering sites. Device space charge probes also allow the evolution of the defect sites upon contamination to be tracked. We report here results of the electrical, structural, and chemical characterization of MeV implanted Si{sup +} damage using Deep Level Transient Spectroscopy (DLTS), Transmission Electron Microscopy (TEM), and Secondary Ion Mass Spectroscopy (SIMS). The damage has been characterized both as a function of annealing from 600 to 1100{degrees}C for 1 hr, and after contamination with Fe followed by low temperature gettering annealing.

  12. Metal concentrations and metallothionein-like protein levels in deep-sea fishes captured near hydrothermal vents in the Mid-Atlantic Ridge off Azores

    NASA Astrophysics Data System (ADS)

    Company, R.; Felícia, H.; Serafim, A.; Almeida, A. J.; Biscoito, M.; Bebianno, M. J.

    2010-07-01

    The knowledge of metal contamination in deep-sea fishes living in the surroundings of hydrothermal vents is very scarce, along with the detoxification mechanisms that allow them to live near one of the most metal contaminated marine environments. Six deep-sea fish species, although not vent endemic were collected near three Mid-Atlantic Ridge (MAR) hydrothermal vents (Menez Gwen, Lucky Strike and Rainbow) and the gills, muscle and liver were selected for this study due to their importance in metal metabolism and storage. The concentrations of seven metals (Ag, Cd, Cr, Cu, Fe, Mn, and Ni) and a metal-related biomarker (metallothionein-like proteins-MTL) were assessed. Major differences in metal accumulation among fish species are related to their feeding habits and vent site of their capture. The liver and gills are in general the most important tissues for metal accumulation compared to the muscle, but tissue partitioning is very dependent on the fish species considered. Compared to other deep-sea fishes, fish capture in the vicinity of hydrothermal vents accumulates higher amounts of metals in general. However, MTL levels are not considerably different from what is found in commercial coastal fishes, and is poorly correlated with metal concentrations in the tissues. Therefore, MTL may not constitute one major detoxification system for deep-sea species living in the vicinity of three important MAR vent sites.

  13. Impurity control studies using SOL flow in DIII-D

    SciTech Connect

    Wade, M.R.; Hogan, J.T.; Isler, R.C.

    1998-11-01

    Experiments on DIII-D have demonstrated the efficacy of using induced scrape-off-layer (SOL) flow to preferentially enrich impurities in the divertor plasma. This SOL flow is produced through simultaneous deuterium gas injection at the midplane and divertor exhaust. Using this SOL flow, an improvement in enrichment (defined as the ratio of impurity fraction in the divertor to that in the plasma core) has been observed for all impurities in trace-level experiments (i.e., impurity level is non-perturbative), with the degree of improvement increasing with impurity atomic number. In the case of argon, exhaust gas enrichment using a modest SOL flow is as high as 17. Using this induced SOL flow technique and argon injection, radiative ELMing H-mode plasmas have been produced that combine high radiation losses (P{sub rad}/P{sub input} > 70%), low core fuel dilution (Z{sub eff} < 1.9), and good core confinement ({tau}{sub E} > 1.0 {tau}{sub E},ITER93H).

  14. Magnetoplasmons bound to short-range impurities in graphene: Symmetries and optics

    SciTech Connect

    Fischer, Andrea M.; Roemer, Rudolf A.; Dzyubenko, Alexander B.

    2011-10-15

    We consider a graphene sheet in the presence of a strong perpendicular magnetic field with a single short-range {delta} impurity situated at one of the carbon sites. We study the neutral inter-Landau level collective excitations, magnetoplasmons, which become localized on the impurity. Some of these excitations involve a pseudospin flip (intervalley transitions), since the impurity can scatter electrons between the two valleys. We propose a classification of states of the excitations in graphene and introduce the appropriate quantum numbers. The energies and optical strengths of collective excitations are calculated for a range of integer filling factors and impurity strengths. We establish a set of symmetries matching the energies and absorption strengths of collective excitations for different sublattice locations of the impurity, filling factors, circular light polarizations, and signs of the impurity potential.

  15. Deep-level defects introduced by 1 MeV electron radiation in AlInGaP for multijunction space solar cells

    NASA Astrophysics Data System (ADS)

    Lee, H. S.; Yamaguchi, M.; Ekins-Daukes, N. J.; Khan, A.; Takamoto, T.; Agui, T.; Kamimura, K.; Kaneiwa, M.; Imaizumi, M.; Ohshima, T.; Itoh, H.

    2005-11-01

    Presented in this paper are 1 MeV electron irradiation effects on wide-band-gap (1.97 eV) (Al0.08Ga0.92)0.52In0.48P diodes and solar cells. The carrier removal rate estimated in p-AlInGaP with electron fluence is about 1 cm-1, which is lower than that in InP and GaAs. From high-temperature deep-level transient spectroscopy measurements, a deep-level defect center such as majority-carrier (hole) trap H2 (Eν+0.90+/-0.05 eV) was observed. The changes in carrier concentrations (Δp) and trap densities as a function of electron fluence were compared, and as a result the total introduction rate, 0.39 cm-1, of majority-carrier trap centers (H1 and H2) is different from the carrier removal rate, 1 cm-1, in p-AlInGaP. From the minority-carrier injection annealing (100 mA/cm2), the annealing activation energy of H2 defect is ΔE=0.60 eV, which is likely to be associated with a vacancy-phosphorus Frenkel pair (Vp-Pi). The recovery of defect concentration and carrier concentration in the irradiated p-AlInGaP by injection relates that a deep-level defect H2 acts as a recombination center as well as compensator center.

  16. Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods

    SciTech Connect

    Alnoor, Hatim Chey, Chan Oeurn; Pozina, Galia; Willander, Magnus; Nur, Omer; Liu, Xianjie; Khranovskyy, Volodymyr

    2015-08-15

    Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 °C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (μ-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.

  17. Effects of thermal annealing on deep-level defects and minority-carrier electron diffusion length in Be-doped InGaAsN

    SciTech Connect

    Xie, S.Y.; Yoon, S.F.; Wang, S.Z.

    2005-04-01

    We report the effects of ex situ thermal annealing on the deep-level defects and the minority-carrier electron diffusion length in Be-doped, p-type In{sub 0.03}Ga{sub 0.97}As{sub 0.99}N{sub 0.01} grown by solid source molecular-beam epitaxy. Deep-level transient spectroscopy measurements reveal two majority-carrier hole traps, HT1 (0.18 eV) and HT4 (0.59 eV), and two minority-carrier electron traps, ET1 (0.09 eV) and ET3 (0.41 eV), in the as-grown sample. For the sample with postgrowth thermal annealing, the overall deep-level defect-concentration is decreased. Two hole traps, HT2 (0.39 eV) and HT3 (0.41 eV), and one electron trap, ET2 (0.19 eV), are observed. We found that the minority-carrier electron diffusion length increases by {approx}30% and the leakage current of the InGaAsN/GaAs p-n junction decreases by 2-3 orders after thermal annealing. An increase of the net acceptor concentration after annealing is also observed and can be explained by a recently proposed three-center-complex model.

  18. Detection of surface impurity phases in high T.sub.C superconductors using thermally stimulated luminescence

    DOEpatents

    Cooke, D. Wayne; Jahan, Muhammad S.

    1989-01-01

    Detection of surface impurity phases in high-temperature superconducting materials. Thermally stimulated luminescence has been found to occur in insulating impurity phases which commonly exist in high-temperature superconducting materials. The present invention is sensitive to impurity phases occurring at a level of less than 1% with a probe depth of about 1 .mu.m which is the region of interest for many superconductivity applications. Spectroscopic and spatial resolution of the emitted light from a sample permits identification and location of the impurity species. Absence of luminescence, and thus of insulating phases, can be correlated with low values of rf surface resistance.

  19. Spectroscopic studies of impurity densities and impurity transport

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

    Graff, K.

    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.

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

    SciTech Connect

    Sesnic, S.S.; Fonck, R.J.; Ida, K.; Bol, K.; Couture, P.; Gammel, G.; Kaita, R.; Kaye, S.; Kugel, H.; LeBlanc, B.

    1986-07-01

    Impurity studies in L- and H-mode discharges in PBX have shown that both types of discharges can evolve into either an impurity accumulative or nonaccumulative case. In a typical accumulative discharge, Zeff peaks in the center to values of about 5. The central metallic densities can be high, n/sub met//n/sub e/ approx. = 0.01, resulting in central radiated power densities in excess of 1 W/cm/sup 3/, consistent with bolometric estimates. The radial profiles of metals obtained independently from the line radiation in the soft x-ray and the VUV regions are very peaked. Concurrent with the peaking, an increase in the impurity influx coming from the edge of the plasma is observed. At the beginning of the accumulation phase the inward particle flux for titanium has values of 6 x 10/sup 10/ and 10 x 10/sup 10/ particles/cm/sup 2/s at minor radii of 6 and 17 cm. At the end of the accumulation phase, this particle flux is strongly increased to values of 3 x 10/sup 12/ and 1 x 10/sup 12/ particles/cm/sup 2/s. This increased flux is mainly due to influx from the edge of the plasma and to a lesser extent due to increased convective transport. Using the measured particle flux, an estimate of the diffusion coefficient D and the convective velocity v is obtained.

  2. Particle fueling and impurity control in PDX

    SciTech Connect

    Fonck, R.J.; Bell, M.; Bol, K.; Budny, R.; Couture, P.; Darrow, D.; Dylla, H.; Goldston, R.; Grek, B.; Hawryluk, R.

    1984-12-01

    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.

  3. Strain-level genomic variation in natural populations of Lebetimonas from an erupting deep-sea volcano

    PubMed Central

    Meyer, Julie L; Huber, Julie A

    2014-01-01

    Chemolithoautotrophic Epsilonproteobacteria are ubiquitous in sulfidic, oxygen-poor habitats, including hydrothermal vents, marine oxygen minimum zones, marine sediments and sulfidic caves and have a significant role in cycling carbon, hydrogen, nitrogen and sulfur in these environments. The isolation of diverse strains of Epsilonproteobacteria and the sequencing of their genomes have revealed that this group has the metabolic potential to occupy a wide range of niches, particularly at dynamic deep-sea hydrothermal vents. We expand on this body of work by examining the population genomics of six strains of Lebetimonas, a vent-endemic, thermophilic, hydrogen-oxidizing Epsilonproteobacterium, from a single seamount in the Mariana Arc. Using Lebetimonas as a model for anaerobic, moderately thermophilic organisms in the warm, anoxic subseafloor environment, we show that genomic content is highly conserved and that recombination is limited between closely related strains. The Lebetimonas genomes are shaped by mobile genetic elements and gene loss as well as the acquisition of novel functional genes by horizontal gene transfer, which provide the potential for adaptation and microbial speciation in the deep sea. In addition, these Lebetimonas genomes contain two operons of nitrogenase genes with different evolutionary origins. Lebetimonas expressed nifH during growth with nitrogen gas as the sole nitrogen source, thus providing the first evidence of nitrogen fixation in any Epsilonproteobacteria from deep-sea hydrothermal vents. In this study, we provide a comparative overview of the genomic potential within the Nautiliaceae as well as among more distantly related hydrothermal vent Epsilonproteobacteria to broaden our understanding of microbial adaptation and diversity in the deep sea. PMID:24257443

  4. A near-uniform fluctuation of ocean bottom pressure and sea level across the deep ocean basins of the Arctic Ocean and the Nordic Seas

    NASA Astrophysics Data System (ADS)

    Fukumori, Ichiro; Wang, Ou; Llovel, William; Fenty, Ian; Forget, Gael

    2015-05-01

    Across the Arctic Ocean and the Nordic Seas, a basin-wide mode of ocean bottom pressure and sea level fluctuation is identified using satellite and in situ observations in conjunction with a global ocean circulation model and its adjoint. The variation extends across the interconnected deep ocean basins of these semi-enclosed Arctic seas, collectively called the Arctic Mediterranean, with spatially near-uniform amplitude and phase. The basin-wide fluctuation is barotropic and dominates the region's large-scale variability from sub-monthly to interannual timescales. The fluctuation results from bifurcating coastally trapped waves generated by winds along the continental slopes of the Arctic Mediterranean and its neighboring seas, including the North Atlantic Ocean. The winds drive Ekman transport across the large bathymetric gradients, forcing mass divergence between the shallow coastal area and the deep ocean basins and creating ocean bottom pressure anomalies of opposite signs in the two regions. The anomalies rapidly propagate away as barotropic coastally trapped waves with the coast and continental slope as respective boundaries. The waves subsequently bifurcate at the shallow straits connecting the Arctic Mediterranean with the rest of the globe. The straits transmit the shallow anomalies but not the deep variations, thereby inhibiting the anomalies' mutual cancelation by geographically separating the two. Anomalies that enter the deep Arctic basins equilibrate uniformly across the domain characterized by a homogeneous depth-integrated planetary potential vorticity distribution. The potential vorticity's steep gradient that borders the basins shields the region from neighboring shallow variations, giving rise to the observed spatially confined fluctuation. Compensating anomalies outside the Arctic adjust similarly across the rest of the globe but are comparatively negligible in amplitude because of the global ocean's larger area relative to that of the deep

  5. Deep levels in a-plane, high Mg-content Mg{sub x}Zn{sub 1-x}O epitaxial layers grown by molecular beam epitaxy

    SciTech Connect

    Guer, Emre; Tabares, G.; Hierro, A.; Chauveau, J. M.

    2012-12-15

    Deep level defects in n-type unintentionally doped a-plane Mg{sub x}Zn{sub 1-x}O, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of Mg{sub x}Zn{sub 1-x}O were examined with x = 0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of E{sub c} - 1.4 eV, 2.1 eV, 2.6 V, and E{sub v} + 0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at E{sub c} - 2.1 eV, E{sub v} + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at E{sub v} + 0.3 eV and E{sub c} - 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the E{sub v} + 0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the E{sub c} - 1.4 eV and E{sub c} - 2.6 eV levels in Mg alloyed samples.

  6. Evolution of the Danube Deep-Sea Fan since the Last Glacial Maximum: insights into water level fluctuations in the Black Sea

    NASA Astrophysics Data System (ADS)

    Constantinescu, Adriana-Maria; Toucanne, Samuel; Dennielou, Bernanrd; Jorry, Stephan; Panin, Nicolae; Lericolais, Gilles

    2014-05-01

    cal BP). The feeding of the northern channel-levee system continued until the marine invasion ca 9,000 yr ago, while no turbidite activity in the Danube deep-sea fan and the Viteaz canyon is observed thereafter. These results are of primary importance to understand sediment transfer from source (Danube River) to sink (Danube deep-sea fan) in Central Europe since the last glacial period, and we will discuss our results in the light of recent reconstructions of past terrestrial environmental (Soulet et al., 2013) and sea-level changes in the Black Sea region (Lericolais et al., 2009).

  7. Proton irradiation effects on deep level states in Mg-doped p-type GaN grown by ammonia-based molecular beam epitaxy

    SciTech Connect

    Zhang, Z.; Arehart, A. R.; Ringel, S. A.; Kyle, E. C. H.; Speck, J. S.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.

    2015-01-12

    The impact of proton irradiation on the deep level states throughout the Mg-doped p-type GaN bandgap is investigated using deep level transient and optical spectroscopies. Exposure to 1.8 MeV protons of 1 × 10{sup 13 }cm{sup −2} and 3 × 10{sup 13 }cm{sup −2} fluences not only introduces a trap with an E{sub V} + 1.02 eV activation energy but also brings monotonic increases in concentration for as-grown deep states at E{sub V} + 0.48 eV, E{sub V} + 2.42 eV, E{sub V} + 3.00 eV, and E{sub V} + 3.28 eV. The non-uniform sensitivities for individual states suggest different physical sources and/or defect generation mechanisms. Comparing with prior theoretical calculations reveals that several traps are consistent with associations to nitrogen vacancy, nitrogen interstitial, and gallium vacancy origins, and thus are likely generated through displacing nitrogen and gallium atoms from the crystal lattice in proton irradiation environment.

  8. Volatile impurities in the ceramic form for the Plutonium Immobilization Project (PIP)

    SciTech Connect

    Cozzi, A.D.

    2000-03-02

    The primary goal for the impurity tests performed at SRS was to determine the maximum level of volatile impurities that can be accommodated into the ceramic form without significantly affecting product properties. The properties investigated in this study are the apparent porosity and the phase assemblage.

  9. Effect of hydrogenic impurity on the third-harmonic generation in a quantum well

    NASA Astrophysics Data System (ADS)

    Zhang, Zhongmin; Guo, Kangxian; Mou, Sen; Xiao, Bo; Liao, Lei

    2014-12-01

    The third-harmonic generation (THG) coefficients in a quantum well with hydrogenic impurity are theoretically investigated with the compact-density-matrix approach and iterative method. The wave functions and the energy levels can be obtained by using variational method and numerical method. Numerical results show that the THG coefficients are strongly affected by the hydrogenic impurity.

  10. Self-pumping impurity control

    DOEpatents

    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.

  11. Impurity diffusion in transition-metal oxides

    SciTech Connect

    Peterson, N.L.

    1982-06-01

    Intrinsic tracer impurity diffusion measurements in ceramic oxides have been primarily confined to CoO, NiO, and Fe/sub 3/O/sub 4/. Tracer impurity diffusion in these materials and TiO/sub 2/, together with measurements of the effect of impurities on tracer diffusion (Co in NiO and Cr in CoO), are reviewed and discussed in terms of impurity-defect interactions and mechanisms of diffusion. Divalent impurities in divalent solvents seem to have a weak interaction with vacancies whereas trivalent impurities in divalent solvents strongly influence the vacancy concentrations and significantly reduce solvent jump frequencies near a trivalent impurity. Impurities with small ionic radii diffuse more slowly with a larger activation energy than impurities with larger ionic radii for all systems considered in this review. Cobalt ions (a moderate size impurity) diffuse rapidly along the open channels parallel to the c-axis in TiO/sub 2/ whereas chromium ions (a smaller-sized impurity) do not. 60 references, 11 figures.

  12. Electrical characterization of deep levels created by bombarding nitrogen-doped 4H-SiC with alpha-particle irradiation

    NASA Astrophysics Data System (ADS)

    Omotoso, Ezekiel; Meyer, Walter E.; Auret, F. Danie; Paradzah, Alexander T.; Legodi, Matshisa J.

    2016-03-01

    Deep-level transient spectroscopy (DLTS) and Laplace-DLTS were used to investigate the effect of alpha-particle irradiation on the electrical properties of nitrogen-doped 4H-SiC. The samples were bombarded with alpha-particles at room temperature (300 K) using an americium-241 (241Am) radionuclide source. DLTS revealed the presence of four deep levels in the as-grown samples, E0.09, E0.11, E0.16 and E0.65. After irradiation with a fluence of 4.1 × 1010 alpha-particles-cm-2, DLTS measurements indicated the presence of two new deep levels, E0.39 and E0.62 with energy levels, EC - 0.39 eV and EC - 0.62 eV, with an apparent capture cross sections of 2 × 10-16 and 2 × 10-14 cm2, respectively. Furthermore, irradiation with fluence of 8.9 × 1010 alpha-particles-cm-2 resulted in the disappearance of shallow defects due to a lowering of the Fermi level. These defects re-appeared after annealing at 300 °C for 20 min. Defects, E0.39 and E0.42 with close emission rates were attributed to silicon or carbon vacancy and could only be separated by using high resolution Laplace-DLTS. The DLTS peaks at EC - (0.55-0.70) eV (known as Z1/Z2) were attributed to an isolated carbon vacancy (VC).

  13. Platinum-related deep levels in silicon and their passivation by atomic hydrogen using a home-built automated DLTS system

    NASA Astrophysics Data System (ADS)

    Reddy, B. P. N.; Reddy, P. N.; Pandu Rangaiah, S. V.

    1996-09-01

    An inexpensive automated DLTS system has been developed in modular form consisting of modules such as a capacitance meter, pulse generator, DLTS system timing controller, data acquisition system, PID temperature controller, cryostat with LN2 flow control facility, etc. These modules, except the capacitance meter and pulse generator, have been designed and fabricated in the laboratory. Further they are integrated and interfaced to PC AT/386 computer. Software has been developed to run the spectrometer, collect data and off-line data processing for the deep level parameters such as activation energy, capture cross-section and density. The system has been used to study the deep levels of platinum in n-type silicon and their passivation by atomic hydrogen. The estimated activation energy of the two acceptor levels are Ec-0.280 eV and Ec-0.522 eV and their capture cross sections are 2.2E-15 cm-2 and 4.3E-15 cm-2 respectively. These levels are found to be reactivated when the hydrogenated samples are annealed in the temperature range 350 - 500 degrees Celsius. The mechanism of passivation and reactivation of these levels are discussed.

  14. Gaseous trace impurity analyzer and method

    DOEpatents

    Edwards, Jr., David; Schneider, William

    1980-01-01

    Simple apparatus for analyzing trace impurities in a gas, such as helium or hydrogen, comprises means for drawing a measured volume of the gas as sample into a heated zone. A segregable portion of the zone is then chilled to condense trace impurities in the gas in the chilled portion. The gas sample is evacuated from the heated zone including the chilled portion. Finally, the chilled portion is warmed to vaporize the condensed impurities in the order of their boiling points. As the temperature of the chilled portion rises, pressure will develop in the evacuated, heated zone by the vaporization of an impurity. The temperature at which the pressure increase occurs identifies that impurity and the pressure increase attained until the vaporization of the next impurity causes a further pressure increase is a measure of the quantity of the preceding impurity.

  15. Molecular dynamics simulation of impurities in nanocrystalline diamond grain boundaries

    SciTech Connect

    Sternberg, M.; Zapol, P.; Frauenheim, T.; Gruen, D. M.; Curtiss, L. A.

    2000-01-12

    Nanocrystalline diamond films grown on Si substrates at 800 C from hydrogen-poor plasmas have a number of highly desirable mechanical and electronic properties. Impurities were found by SIMS measurements to be uniformly distributed throughout the thickness of the films at a level of 10{sup 17}--10{sup 18} cm{sup {minus}3}. It is likely that the impurities are located at the grain boundaries, which play a crucial role in controlling important characteristics of the films, such as electrical conductivity and electron emission. Density-functional based tight-binding (DFTB) molecular dynamics simulations were performed for diamond light-energy high-angle (100) twist grain boundaries with impurities such as N, Si and H.

  16. Deep vein thrombosis is accurately predicted by comprehensive analysis of the levels of microRNA-96 and plasma D-dimer

    PubMed Central

    Xie, Xuesheng; Liu, Changpeng; Lin, Wei; Zhan, Baoming; Dong, Changjun; Song, Zhen; Wang, Shilei; Qi, Yingguo; Wang, Jiali; Gu, Zengquan

    2016-01-01

    The aim of the present study was to investigate the association between platelet microRNA-96 (miR-96) expression levels and the occurrence of deep vein thrombosis (DVT) in orthopedic patients. A total of consecutive 69 orthopedic patients with DVT and 30 healthy individuals were enrolled. Ultrasonic color Doppler imaging was performed on lower limb veins after orthopedic surgery to determine the occurrence of DVT. An enzyme-linked fluorescent assay was performed to detect the levels of D-dimer in plasma. A quantitative polymerase chain reaction assay was performed to determine the expression levels of miR-96. Expression levels of platelet miR-96 were significantly increased in orthopedic patients after orthopedic surgery. miR-96 expression levels in orthopedic patients with DVT at days 1, 3 and 7 after orthopedic surgery were significantly increased when compared with those in the control group. The increased miR-96 expression levels were correlated with plasma D-dimer levels in orthopedic patients with DVT. However, for the orthopedic patients in the non-DVT group following surgery, miR-96 expression levels were correlated with plasma D-dimer levels. In summary, the present results suggest that the expression levels of miR-96 may be associated with the occurrence of DVT. The occurrence of DVT may be accurately predicted by comprehensive analysis of the levels of miR-96 and plasma D-dimer. PMID:27588107

  17. Messinian deep-water turbidites and glacioeustatic sea-level changes in the North Atlantic: Linkage to the Mediterranean Salinity Crisis

    NASA Astrophysics Data System (ADS)

    Zhang, Jijun; Scott, David B.

    1996-06-01

    Our benthic foraminiferal data clearly indicate eight layers of deep-water turbidites during the Messinian (MTL 1-8) and one in the early Pliocene (PTL 1) in Ocean Drilling Program Leg 105, Site 646B. These deep-water tuibidite deposits are characterized by highly concentrated agglutinated marsh benthic foraminifera (e.g., Trochammina cf. squamata, Ammotium sp. A, Miliammina fusca), rounded quartz, polished thick-walled benthic foraminifera, wood fragments, plant seeds, plant fruit, and highly concentrated mica and are interbedded with sediments containing deep-water benthic faunas. We suggest these turbidites deposited during sea-level low stands (˜80-100 m below sea level), and their ages are tentatively correlated to 6.59, 6.22, 6.01, 5.89, 5.75, 5.7, 5.65, 5.60, and 5.55 Ma, respectively, based on the Messinian oxygen isotope enrichments at Site 552A of Deep Sea Drilling Project Leg 81. The turbidites layers during the late Messinian, coeval with frequent climate changes suggested by six oxygen enrichment excursions of Site 552A, may have been in part linked to the late Messinian evaporite deposits in the Mediterranean Basin. The most profound climate changes at 5.75 and 5.55 Ma may have been related to the Lower and Upper Evaporites in the Mediterranean Basin. An electronic supplement of this material may be obtained on adiskette or Anonymous FTP from KOSMOS .AGU.ORG, (LOGIN toAGU's FTP account using ANONYMOUS as the username and GUESTas the password. Go to the right directory by typing CD APEND. TypeLS to see what files are available. Type GET and the name of the file toget it. Finally, type EXIT to leave the system. (Paper 96PA00572,Messinian deep-water turbidites and glacioeustatic sea-level changes inthe North Atlantic: Linkage to the Mediterranean Salinity Crisis, JijunZhang and David B. Scott). Diskette may be ordered from AmericanGeophysical Union, 2000 Florida Avenue, N.W., Washington, D.C.20009; $15.00. Payment must accompany order.

  18. Physical activity levels and perceived benefits and barriers to physical activity in HIV-infected women living in the deep south of the United States.

    PubMed

    Rehm, Kristina E; Konkle-Parker, Deborah

    2016-09-01

    Engaging in regular physical activity (PA) is important in maintaining health and increasing the overall quality of life of people living with HIV (PLWH). The deep south of the USA is known for its high rate of sedentary behavior although data on the activity levels and perceptions of the benefits and barriers to exercise in women living with HIV in the deep south are lacking. Understanding the perceived benefits and barriers to exercise can guide the development of PA interventions. We conducted a cross-sectional study to determine the PA levels and perceived benefits and barriers to exercise associated with both age and depression level in a group of HIV+ women living in the deep south. We recruited a total of 50 participants from a cohort site for the Women's Interagency HIV Study. Depression was assessed using the Center for Epidemiological Studies Depression Scale (CES-D) and benefits/barriers to exercise were measured using the Exercise Benefits and Barriers Scale (EBBS). We measured PA both subjectively and objectively using the International Physical Activity Questionnaire (IPAQ) and a Fitbit PA monitor, respectively. Our sample was predominantly African-American (96%) and the mean ±SD age, body mass index, and CES-D score were 42 ± 8.8 years, 36.6 ± 11.5 kg/m(2), and 15.6 ± 11.4, respectively. Both subjective and objective measures of PA indicated that our participants were sedentary. The greatest perceived benefit to exercise was physical performance and the greatest barrier to exercise was physical exertion. Higher overall perceived benefits were reported by women ≥43 years and women reporting higher levels of depression. There was no difference in overall barriers associated with age and depression level, but women with depression felt more fatigued by exercise. The results of this study can be helpful when designing and implementing PA interventions in women living with HIV in the deep south. PMID:27023306

  19. The Effect of Hydrogen Annealing on the Impurity Content of Alumina-Forming Alloys

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    2000-01-01

    Previously, the effect of hydrogen annealing on increasing the adhesion of Al2O3 scales had been related to the effective desulfurization that occurred during this process. The simultaneous reduction of other impurities has now been re-examined for up to 20 impurity elements in the case of five different alloys (NiCrAl, FeCrAl, PWA 1480, Rene'142, and Rene'N5). Hydrogen annealing produced measurable reductions in elemental concentration for B, C, Na, Mg, P, K, Sr, or Sn in varying degrees for at least one and up to three of these alloys. No single element was reduced by hydrogen annealing for all the alloys except sulfur. In many cases spalling occurred at low levels of these other impurities, while in other cases the scales were adherent at high levels of the impurities. No impurity besides sulfur was strongly correlated with adhesion.

  20. Impurity-induced divertor plasma oscillations

    NASA Astrophysics Data System (ADS)

    Smirnov, R. D.; Kukushkin, A. S.; Krasheninnikov, S. I.; Pigarov, A. Yu.; Rognlien, T. D.

    2016-01-01

    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.

  1. Impurity-induced divertor plasma oscillations

    DOE PAGESBeta

    Smirnov, R. D.; Kukushkin, A. S.; Krasheninnikov, S. I.; Pigarov, A. Yu.; Rognlien, T. D.

    2016-01-07

    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 ionmore » 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. As a result, the implications of the impurity-induced plasma oscillations for divertor operation in the next generation tokamaks are also discussed.« less

  2. First-principles electronic structure and formation energies of group V and VII impurities in the α-Fe{sub 2}O{sub 3} alloys

    SciTech Connect

    Xia, Congxin; Jia, Yu; Zhang, Qiming

    2014-09-21

    Based on density functional theory, the electronic structures, formation energy, and transition level of the selected group V and VII impurities in α-Fe{sub 2}O{sub 3} are investigated by means of first-principles methods. Numerical results show that the group V and VII atoms-doped α-Fe{sub 2}O{sub 3} can be energetically favorable under the Fe-rich condition. Group V atom substituting O atom can induce the acceptor impurity level, while the deep donor impurity states are formed inside the band gap when group VII atom substitute O atom in the α-Fe{sub 2}O{sub 3}. Moreover, our results show that halogen atom F substituting O atom should be very easy in the α-Fe{sub 2}O{sub 3}. In addition, our results also show that for both group V and VII atom-doped α-Fe{sub 2}O{sub 3}, the upper sides of valence band are modified obviously, while the conduction band edge does not change.

  3. Deep-level defects introduced by 1 MeV electron radiation in AlInGaP for multijunction space solar cells

    SciTech Connect

    Lee, H.S.; Yamaguchi, M.; Ekins-Daukes, N. J.; Khan, A.; Takamoto, T.; Agui, T.; Kamimura, K.; Kaneiwa, M.; Imaizumi, M.; Ohshima, T.; Itoh, H.

    2005-11-01

    Presented in this paper are 1 MeV electron irradiation effects on wide-band-gap (1.97 eV) (Al{sub 0.08}Ga{sub 0.92}){sub 0.52}In{sub 0.48}P diodes and solar cells. The carrier removal rate estimated in p-AlInGaP with electron fluence is about 1 cm{sup -1}, which is lower than that in InP and GaAs. From high-temperature deep-level transient spectroscopy measurements, a deep-level defect center such as majority-carrier (hole) trap H2 (E{sub {nu}}+0.90{+-}0.05 eV) was observed. The changes in carrier concentrations ({delta}p) and trap densities as a function of electron fluence were compared, and as a result the total introduction rate, 0.39 cm{sup -1}, of majority-carrier trap centers (H1 and H2) is different from the carrier removal rate, 1 cm{sup -1}, in p-AlInGaP. From the minority-carrier injection annealing (100 mA/cm{sup 2}), the annealing activation energy of H2 defect is {delta}E=0.60 eV, which is likely to be associated with a vacancy-phosphorus Frenkel pair (V{sub p}-P{sub i}). The recovery of defect concentration and carrier concentration in the irradiated p-AlInGaP by injection relates that a deep-level defect H2 acts as a recombination center as well as compensator center.

  4. Identification of nitrogen- and host-related deep-level traps in n-type GaNAs and their evolution upon annealing

    SciTech Connect

    Gelczuk, Ł.; Henini, M.

    2014-07-07

    Deep level traps in as-grown and annealed n-GaNAs layers (doped with Si) of various nitrogen concentrations (N=0.2%, 0.4%, 0.8%, and 1.2%) were investigated by deep level transient spectroscopy. In addition, optical properties of GaNAs layers were studied by photoluminescence and contactless electroreflectance. The identification of N- and host-related traps has been performed on the basis of band gap diagram [Kudrawiec, Appl. Phys. Lett. 101, 082109 (2012)], which assumes that the activation energy of electron traps of the same microscopic nature decreases with the rise of nitrogen concentration in accordance with the N-related shift of the conduction band towards trap levels. The application of this diagram has allowed to investigate the evolution of donor traps in GaNAs upon annealing. In general, it was observed that the concentration of N- and host-related traps decreases after annealing and PL improves very significantly. However, it was also observed that some traps are generated due to annealing. It explains why the annealing conditions have to be carefully optimized for this material system.

  5. Deep level defects throughout the bandgap of (010) β-Ga2O3 detected by optically and thermally stimulated defect spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Farzana, E.; Arehart, A. R.; Ringel, S. A.

    2016-02-01

    Deep level optical spectroscopy (DLOS) and deep level transient spectroscopy (DLTS) measurements performed on Ni/β-Ga2O3 Schottky diodes fabricated on unintentionally doped (010) substrates prepared by edge-defined film-fed growth revealed a rich spectrum of defect states throughout the 4.84 eV bandgap of β-Ga2O3. Five distinct defect states were detected at EC - 0.62 eV, 0.82 eV, 1.00 eV, 2.16 eV, and 4.40 eV. The EC - 0.82 eV and 4.40 eV levels are dominant, with concentrations on the order of 1016 cm-3. The three DLTS-detected traps at EC - 0.62 eV, 0.82 eV, and 1.00 eV are similar to traps reported in Czochralski-grown β-Ga2O3, [K. Irmscher et al., J. Appl. Phys. 110, 063720 (2011)], suggesting possibly common sources. The DLOS-detected states at EC - 2.16 eV and 4.40 eV exhibit significant lattice relaxation effects in their optical transitions associated with strongly bound defects. As a consequence of this study, the Ni/β-Ga2O3 (010) Schottky barrier height was determined to be 1.55 eV, with good consistency achieved between different characterization techniques.

  6. Oxidation-Induced Deep Levels in n - and p -Type 4 H - and 6 H -SiC and Their Influence on Carrier Lifetime

    NASA Astrophysics Data System (ADS)

    Booker, I. D.; Abdalla, H.; Hassan, J.; Karhu, R.; Lilja, L.; Janzén, E.; Sveinbjörnsson, E. Ö.

    2016-07-01

    We present a complete analysis of the electron- and hole-capture and -emission processes of the deep levels ON1, ON2a, and ON2b in 4 H -SiC and their 6 H -SiC counterparts OS1a and OS1b through OS3a and OS3b, which are produced by lifetime enhancement oxidation or implantation and annealing techniques. The modeling is based on a simultaneous numerical fitting of multiple high-resolution capacitance deep-level transient spectroscopy spectra measured with different filling-pulse lengths in n - and p -type material. All defects are found to be double-donor-type positive-U two-level defects with very small hole-capture cross sections, making them recombination centers of low efficiency, in accordance with minority-carrier-lifetime measurements. Their behavior as trapping and weak recombination centers, their large concentrations resulting from the lifetime enhancement oxidations, and their high thermal stability, however, make it advisable to minimize their presence in active regions of devices, for example, the base layer of bipolar junction transistors.

  7. Tunneling interstitial impurity in iron-chalcogenide-based superconductors

    NASA Astrophysics Data System (ADS)

    Huang, Huaixiang; Zhang, Degang; Gao, Yi; Ren, Wei; Ting, C. S.

    2016-02-01

    A pronounced local in-gap zero-energy bound state (ZBS) has been observed by recent scanning tunneling microscopy experiments on the interstitial Fe impurity (IFI) and its nearest-neighboring sites in an FeTe0.5Se0.5 superconducting (SC) compound. By introducing an impurity mechanism, the so-called tunneling impurity, and based on the Bogoliubov-de Gennes equations, we investigate the low-lying energy states of the IFI and the underlying Fe plane. The calculations are performed in the presence as well as in the absence of a magnetic field. We find the IFI-induced ZBS does not shift or split in a magnetic field as long as the tunneling parameter between the IFI and the Fe plane is sufficiently small and the Fe plane is deep in the SC state. Our results are in good agreement with experiments. We also show that in the underdoped cases, modulation of the spin density wave or charge density wave will suppress the intensity of the ZBS on the Fe plane in a vortex state.

  8. Impurity-induced moments in underdoped cuprates

    SciTech Connect

    Khaliullin, G. |; Kilian, R.; Krivenko, S.; Fulde, P.

    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}

  9. Trace organic impurities in gaseous helium

    NASA Technical Reports Server (NTRS)

    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.

  10. The Mg impurity in nitride alloys

    SciTech Connect

    Zvanut, M. E.; Willoughby, W. R.; Sunay, U. R.; Koleske, D. D.; Allerman, A. A.; Wang, Ke; Araki, Tsutomu; Nanishi, Yasushi

    2014-02-21

    Although several magnetic resonance studies address the Mg acceptor in GaN, there are few reports on Mg doping in the alloys, where hole production depends strongly on the Al or In content. Our electron paramagnetic resonance (EPR) measurements of the p-type alloys suggest that the Mg impurity retains the axial symmetry, characteristic of a p-type dopant in both alloys; however, In and Al produce additional, different characteristics of the acceptor. In InGaN, the behavior is consistent with a lowering of the acceptor level and increasing hole density as In concentration increases. For AlGaN, the amount of neutral Mg decreases with increasing Al content, which is attributed to different kinetics of hydrogen diffusion thought to occur in samples with higher Al mole fraction.

  11. Characterization of deep electron traps in 4H-SiC Junction Barrier Schottky rectifiers

    NASA Astrophysics Data System (ADS)

    Gelczuk, Ł.; Dąbrowska-Szata, M.; Sochacki, M.; Szmidt, J.

    2014-04-01

    Conventional deep level transient spectroscopy (DLTS) technique was used to study deep electron traps in 4H-SiC Junction Barrier Schottky (JBS) rectifiers. 4H-SiC epitaxial layers, doped with nitrogen and grown on standard n+-4H-SiC substrates were exposed to low-dose aluminum ion implantation process under the Schottky contact in order to form both JBS grid and junction termination extension (JTE), and assure good rectifying properties of the diodes. Several deep electron traps were revealed and attributed to impurities or intrinsic defects in 4H-SiC epitaxial layers, on the basis of comparison of their electrical parameters (i.e. activation energies, apparent capture cross sections and concentrations) with previously published results.

  12. Electronic structure of copper, silver, and gold impurities in silicon

    SciTech Connect

    Fazzio, A.; Caldas, M.J.; Zunger, A.

    1985-07-15

    The electronic structure of Cu, Ag, and Au impurities in silicon is studied self-consistently using the quasiband crystal-field Green's-function method. We find that a substitutional model results in a two-level (acceptor and donor), three-charge-state (A/sup +/, A/sup 0/, and A/sup -/) system, which suggests that these defects are amphoteric. Our results show that these substitutional impurities form e-type and t/sub 2/-type crystal-field resonances (CFR) near the center of the valence band and a dangling-bond hybrid (DBH) t/sub 2/ level in the gap. The e/sup CFR/ and t/sub 2//sup CFR/ states are fully occupied and represent the perturbed and hybridized impurity atomic orbitals (not simply a ''d/sup 10/'' configuration). They are magnetically and electrically inactive but are predicted to be optically active in the uv, producing both impurity-bound core excitons as well as localized-to-itinerant

  13. Defect properties of Sb- and Bi-doped CuInSe{sub 2}: The effect of the deep lone-pair s states

    SciTech Connect

    Park, Ji-Sang; Yang, Ji-Hui; Ramanathan, Kannan; Wei, Su-Huai

    2014-12-15

    Bi or Sb doping has been used to make better material properties of polycrystalline Cu{sub 2}(In,Ga)Se{sub 2} as solar cell absorbers, including the experimentally observed improved electrical properties. However, the mechanism is still not clear. Using first-principles method, we investigate the stability and electronic structure of Bi- and Sb-related defects in CuInSe{sub 2} and study their effects on the doping efficiency. Contrary to previous thinking that Bi or Sb substituted on the anion site, we find that under anion-rich conditions, the impurities can substitute on cation sites and are isovalent to In because of the formation of the impurity lone pair s states. When the impurities substitute for Cu, the defects act as shallow double donors and help remove the deep In{sub Cu} level, thus resulting in the improved carrier life time. On the other hand, under anion-poor conditions, impurities at the Se site create amphoteric deep levels that are detrimental to the device performance.

  14. Defect properties of Sb- and Bi-doped CuInSe2: The effect of the deep lone-pair s states

    NASA Astrophysics Data System (ADS)

    Park, Ji-Sang; Yang, Ji-Hui; Ramanathan, Kannan; Wei, Su-Huai

    2014-12-01

    Bi or Sb doping has been used to make better material properties of polycrystalline Cu2(In,Ga)Se2 as solar cell absorbers, including the experimentally observed improved electrical properties. However, the mechanism is still not clear. Using first-principles method, we investigate the stability and electronic structure of Bi- and Sb-related defects in CuInSe2 and study their effects on the doping efficiency. Contrary to previous thinking that Bi or Sb substituted on the anion site, we find that under anion-rich conditions, the impurities can substitute on cation sites and are isovalent to In because of the formation of the impurity lone pair s states. When the impurities substitute for Cu, the defects act as shallow double donors and help remove the deep InCu level, thus resulting in the improved carrier life time. On the other hand, under anion-poor conditions, impurities at the Se site create amphoteric deep levels that are detrimental to the device performance.

  15. On collisional impurity transport in nonaxisymmetric plasmas

    NASA Astrophysics Data System (ADS)

    Mollén, A.; Landreman, M.; Smith, H. M.

    2014-11-01

    The presence of impurity species in magnetic confinement fusion devices leads to radiation losses and plasma dilution. Thus it is important to analyze impurity dynamics, and search for means to control them. In stellarator plasmas the neoclassical ambipolar radial electric field often points radially inwards (referred to as the ion root regime), causing impurities to accumulate in the core. This can limit the performance of nonaxisymmetric devices. In the present work we analyze neoclassical impurity transport in stellarator plasmas using a recently developed continuum drift-kinetic solver, the SFINCS code (the Stellarator Fokker- Planck Iterative Neoclassical Conservative Solver). The study is performed for a case close to the edge of W7-X using the standard configuration magnetic geometry. We investigate the sensitivity of impurity transport to impurity charge, main species density and temperature gradients, as well as ion temperature. At the studied radial location we find that the neoclassical impurity peaking factor can be very large, particularly for high-Z impurities. The ambipolar radial electric field is in the ion root regime, and impurity accumulation can thus be expected. The accumulation is strengthened by the large main species density and temperature gradients. Moreover we find that the size of the bootstrap current is affected by the value of the plasma effective charge, suggesting that employing a realistic ion composition can be important when calculating the bootstrap current.

  16. In situ bacterial colonization of compacted bentonite under deep geological high-level radioactive waste repository conditions.

    PubMed

    Chi Fru, E; Athar, R

    2008-06-01

    Subsurface microorganisms are expected to invade, colonize, and influence the safety performance of deep geological spent nuclear fuel (SNF) repositories. An understanding of the interactions of subsurface dwelling microbial communities with the storage is thus essential. For this to be achieved, experiments must be conducted under in situ conditions. We investigated the presence of groundwater microorganisms in repository bentonite saturated with groundwater recovered from tests conducted at the Aspö underground Hard Rock Laboratory in Sweden. A 16S ribosomal RNA and dissimilatory bisulfite reductase gene distribution between the bentonite and groundwater samples suggested that the sulfate-reducing bacteria widespread in the aquifers were not common in the clay. Aerophilic bacteria could be cultured from samples run at or=67 degrees C. Generally, the largely gram-negative groundwater microorganisms were poorly represented in the bentonite while the gram-positive bacteria commonly found in the clay predominated. Thus, bentonite compacted to a density of approximately 2 g cm(-3) together with elevated temperatures might discourage the mass introduction of the predominantly mesophilic granitic aquifer bacteria into future SNF repositories in the long run. PMID:18379777

  17. Identification of anthropogenic and natural dust sources using Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue level 2 data

    NASA Astrophysics Data System (ADS)

    Ginoux, Paul; Garbuzov, Dmitri; Hsu, N. Christina

    2010-03-01

    Mineral dust interacts with radiation and impacts both the regional and global climate. The relative contribution of natural and anthropogenic dust sources, however, remains largely uncertain. Although human activities disturb soils and therefore enhance wind erosion, their contribution to global dust emission has never been directly evaluated because of a lack of data. The retrieval of aerosol properties over land, including deserts, using the Moderate Resolution Imaging Spectroradiometer Deep Blue algorithm makes the first direct characterization of the origin of individual sources possible. In order to separate freshly emitted dust from other aerosol types and aged dust particles, the spectral dependence of the single scattering albedo and the Angstrom wavelength exponent are used. Four years of data from the eastern part of West Africa, which includes one of the most active natural dust sources and the highest population density on the continent, are processed. Sources are identified on the basis of the persistence of significant aerosol optical depth from freshly emitted dust, and the origin is characterized as natural or anthropogenic on the basis of a land use data set. Our results indicate that although anthropogenic dust is observed less frequently and with lower optical depth than dust from natural sources in this particular region, it occupies a large area covering most of northern Nigeria and southern Chad, around Lake Chad. In addition, smaller anthropogenic sources are found as far south as 5° of latitude north, well outside the domain of most dust source inventories.

  18. Inferring a deep-crustal source terrane from a high-level granitic pluton: the Strathbogie Batholith, Australia

    NASA Astrophysics Data System (ADS)

    Clemens, J. D.; Phillips, G. N.

    2014-11-01

    The Strathbogie Igneous Complex is comprised of the ignimbritic rocks of the Violet Town Volcanics and the granitic rocks of the Strathbogie batholith. It is Late Devonian in age and postorogenic-extensional in tectonic setting. The batholith was constructed from peraluminous, metasediment-derived magmas emplaced as several internally heterogeneous plutons. Chemical variation in the magmas was largely inherited from the protolith rather than having been produced by differentiation (crystal-liquid separation) or magma mixing. The Strathbogie magmas formed during a granulite-facies metamorphic event that caused partial melting of the rocks of the Proterozoic Selwyn Block, which forms the basement in this region. The chemistry of the Strathbogie batholith, the Violet Town Volcanics and various other felsic complexes of similar age, implies that the Selwyn Block here originally consisted of andesite, dacite, greywacke and pelite, probably deposited in a back-arc extensional setting. The sedimentary components of this protolith may have been deposited in a basin that was extending and deepening with time, so that the sediments contained progressively higher ratios of clay to volcanic materials. Much later, in the Late Devonian, extensional tectonics allowed the emplacement of mantle magmas into the deep and middle crust, causing the low-pressure granulite-facies metamorphic event that was responsible for the production of the crustal components in the granitic magmas of Central Victoria.

  19. Analysis of leakage current mechanisms in Pt/Au Schottky contact on Ga-polarity GaN by Frenkel-Poole emission and deep level studies

    SciTech Connect

    Rao, Peta Koteswara; Park, Byungguon; Lee, Sang-Tae; Noh, Young-Kyun; Kim, Moon-Deock; Oh, Jae-Eung

    2011-07-01

    We report the Frenkel-Poole emission in Pt/Au Schottky contact on Ga-polarity GaN grown by molecular beam epitaxy using current-voltage-temperature (I-V-T) characteristics in the temperature ranging from 200 K to 375 K. Using thermionic emission model, the estimated Schottky barrier height is 0.49 eV at 200 K and 0.83 eV at 375 K, respectively, and it is observed that the barrier height increases with increase in temperature. The extracted emission barrier height ({phi}{sub t}) for Ga-polarity GaN Schottky diode by Frenkel-Poole theory is about 0.15 eV. Deep level transient spectroscopy study shows a deep level with activation energy of 0.44 eV, having capture cross-section 6.09 x 10{sup -14} cm{sup 2}, which is located between the metal and semiconductor interface, and trap nature is most probably associated with dislocations in Ga-polarity GaN. The analysis of I-V-T characteristics represents that the leakage current is due to effects of electrical field and temperature on the emission of electron from a trap state near the metal-semiconductor interface into continuum states associated with conductive dislocations in Ga-polarity GaN Schottky diode.

  20. Persistent photoconductivity in AlGaN/GaN heterojunction channels caused by the ionization of deep levels in the AlGaN barrier layer

    SciTech Connect

    Murayama, H.; Akiyama, Y.; Niwa, R.; Sakashita, H.; Sakaki, H.; Kachi, T.; Sugimoto, M.

    2013-12-04

    Time-dependent responses of drain current (I{sub d}) in an AlGaN/GaN HEMT under UV (3.3 eV) and red (2.0 eV) light illumination have been studied at 300 K and 250 K. UV illumination enhances I{sub d} by about 10 %, indicating that the density of two-dimensional electrons is raised by about 10{sup 12} cm{sup −2}. When UV light is turned off at 300 K, a part of increased I{sub d} decays quickly but the other part of increment is persistent, showing a slow decay. At 250 K, the majority of increment remains persistent. It is found that such a persistent increase of I{sub d} at 250 K can be partially erased by the illumination of red light. These photo-responses are explained by a simple band-bending model in which deep levels in the AlGaN barrier get positively charged by the UV light, resulting in a parabolic band bending in the AlGaN layer, while some potion of those deep levels are neutralized by the red light.

  1. Theoretical Analysis of Effects of Deep Level, Back Contact, and Absorber Thickness on Capacitance-Voltage Profiling of CdTe Thin-Film Solar Cells

    SciTech Connect

    Li, J. V.; Halverson, A. F.; Sulima, O. V.; Bansal, S.; Burst, J. M.; Barnes, T. M.; Gessert, T. A.; Levi, D. H.

    2012-05-01

    The apparent carrier density profile measured by the capacitance-voltage technique in CdTe thin-film solar cells frequently displays a distinctive U-shape. We show that, even assuming a uniform carrier density, such a U-shape may arise from deep levels, a non-ohmic back-contact, and a thin absorber, which are commonly present in practical CdTe thin-film solar cells. A thin CdTe absorber contributes to the right branch of the U-shape due to a punch-through effect at reverse or zero biases, when the CdTe absorber is nearly fully depleted. A rectifying back-contact contributes to both branches of the U-shape due to voltage sharing with the front junction under a forward bias and early punch-through under a reverse bias. Deep levels contribute to the right branch, but also raise the bottom of the U-shape, leading to an overestimate of carrier density.

  2. Nonlocal effects in double fishnet metasurfaces nanostructured at deep subwavelength level as a path toward simultaneous sensing of multiple chemical analytes

    NASA Astrophysics Data System (ADS)

    Tanasković, Dragan; Obradov, Marko; Jakšić, Olga; Jakšić, Zoran

    2016-01-01

    Nanoplasmonic devices are among the most sensitive chemical sensors, with sensitivities reaching the single-molecule level. An especially convenient class of such sensors is that based on metasurfaces with subwavelength nanoholes, examples being extraordinary optical transmission arrays and double fishnet structures. Such structures ensure operation both in transmission and reflection mode and ensure high sensitivities and excellent coupling with external readout. In this paper we consider the possibility to tailor the response of aperture-based sensor structures by modifying the geometry of nanoholes at the deep subwavelength level through ensuring controlled use of nonlocal effects. We investigate the case where nonlocality is achieved by modifying the basic metamaterial fishnet structure (a metal-dielectric-metal sandwich with rectangular openings) by superposing additional subwavelength patterns, ensuring the appearance of new optical modes. The obtained unit cell superstructure will have multiple tailorable spectral peaks that will increase the selectivity at different wavelengths. The finite elements method was used for simulations of the proposed structures. As an example, we applied our results to the case of a benzene sensor, showing that its spectral properties and selectivity can be tuned by modifying geometry at a deep subwavelength scale. The obtained custom-designed spectral selectivity is convenient for multianalyte chemical sensing using a single structure.

  3. Analysis of leakage current mechanisms in Pt/Au Schottky contact on Ga-polarity GaN by Frenkel-Poole emission and deep level studies

    NASA Astrophysics Data System (ADS)

    Rao, Peta Koteswara; Park, Byungguon; Lee, Sang-Tae; Noh, Young-Kyun; Kim, Moon-Deock; Oh, Jae-Eung

    2011-07-01

    We report the Frenkel-Poole emission in Pt/Au Schottky contact on Ga-polarity GaN grown by molecular beam epitaxy using current-voltage-temperature (I-V-T) characteristics in the temperature ranging from 200 K to 375 K. Using thermionic emission model, the estimated Schottky barrier height is 0.49 eV at 200 K and 0.83 eV at 375 K, respectively, and it is observed that the barrier height increases with increase in temperature. The extracted emission barrier height (ϕt) for Ga-polarity GaN Schottky diode by Frenkel-Poole theory is about 0.15 eV. Deep level transient spectroscopy study shows a deep level with activation energy of 0.44 eV, having capture cross-section 6.09 × 10-14 cm2, which is located between the metal and semiconductor interface, and trap nature is most probably associated with dislocations in Ga-polarity GaN. The analysis of I-V-T characteristics represents that the leakage current is due to effects of electrical field and temperature on the emission of electron from a trap state near the metal-semiconductor interface into continuum states associated with conductive dislocations in Ga-polarity GaN Schottky diode.

  4. Kinetic effects on geodesic acoustic mode from combined collisions and impurities

    SciTech Connect

    Yang, Shangchuan; Xie, Jinlin Liu, Wandong

    2015-04-15

    The dispersion relation for geodesic acoustic mode (GAM) is derived by applying a gyrokinetic model that accounts for the effects from both collisions and impurities. Based on the dispersion relation, an analysis is performed for the non-monotonic behavior of GAM damping versus the characteristic collision rate at various impurity levels. As the effective charge increases, the maximum damping rate is found to shift towards lower collision rates, nearer to the parameter range of a typical tokamak edge plasma. The relative strengths of ion-ion and impurity-induced collision effects, which are illustrated by numerical calculations, are found to be comparable. Impurity-induced collisions help decrease the frequency of GAM, while their effects on the damping rate are non-monotonic, resulting in a weaker total damping in the high collision regime. The results presented suggest considering collision effects as well as impurity effects in GAM analysis.

  5. Growth Temperature Dependence of Si Doping Efficiency and Compensating Deep Level Defect Incorporation in Al0.7Ga0.3N

    SciTech Connect

    Armstrong, Andrew; Moseley, Michael William; Allerman, Andrew A.; Crawford, Mary H.; Wierer, Jonathan

    2015-05-11

    The growth temperature dependence of Si doping efficiency and deep level defect formation was investigated for n-type Al0.7Ga0.3N. It was observed that dopant compensation was greatly reduced with reduced growth temperature. Furthermore, deep level optical spectroscopy and lighted capacitance-voltage were used to understand the role of acceptor-like deep level defects on doping efficiency. Deep level defects were observed at 2.34 eV, 3.56 eV, and 4.74 eV below the conduction band minimum. The latter two deep levels were identified as the major compensators because the reduction in their concentrations at reduced growth temperature correlated closely with the concomitant increase in free electron concentration. Possible mechanisms for the strong growth temperature dependence of deep level formation are considered, which includes thermodynamically driven compensating defect formation that can arise for a semiconductor with very large band gap energy, such as Al0.7Ga0.3N.

  6. Operation of the Oxide Washer for Water-Washing Solubles out of Impure Pu Oxide

    SciTech Connect

    Dodson, K E; Close, W L; Krikorian, O H; Summers III, H V

    2006-01-30

    An evaluation has been made for using the Oxide Washer to wash water-soluble materials out of impure Pu oxide. It is found that multiple washes are needed to reduce the water-soluble materials to very low levels in the impure Pu oxides. The removal of the wash water from the Oxide Washer is accompanied by particulates of the impure Pu oxide, which subsequently need to be filtered out. In spite of the additional filtration needed, the overall level of manpower required for processing is still only about one third of that for an all-manual operation.

  7. Identification and Characterization of Potential Impurities in Raloxifene Hydrochloride

    PubMed Central

    Reddy, Reguri Buchi; Goud, Thirumani Venkateshwar; Nagamani, Nagabushanam; Kumar, Nutakki Pavan; Alagudurai, Anandan; Murugan, Raman; Parthasarathy, Kannabiran; Karthikeyan, Vinayagam; Balaji, Perumal

    2012-01-01

    During the synthesis of the bulk drug Raloxifene hydrochloride, eight impurities were observed, four of which were found to be new. All of the impurities were detected using the gradient high performance liquid chromatographic (HPLC) method, whose area percentages ranged from 0.05 to 0.1%. LCMS was performed to identify the mass number of these impurities, and a systematic study was carried out to characterize them. These impurities were synthesized and characterized by spectral data, subjected to co-injection in HPLC, and were found to be matching with the impurities present in the sample. Based on their spectral data (IR, NMR, and Mass), these impurities were characterized as Raloxifene-N-Oxide [Impurity: 1]; EP impurity A [Impurity: 2]; EP impurity B [Impurity: 3]; Raloxifene Dimer [Impurity: 4]; HABT (6-Acetoxy-2-[4-hydroxyphenyl]-1-benzothiophene or 6-Hydroxy-2-[4-acetoxyphenyl]-1-benzothiophene) [Impurity: 5]; PEBE (Methyl[4-[2-(piperidin-1-yl)ethoxy

  8. Harnessing intrinsic localized modes to identify impurities in nonlinear periodic systems

    NASA Astrophysics Data System (ADS)

    Thota, M.; Harne, R. L.; Wang, K. W.

    2015-02-01

    Intrinsic localized modes (ILMs) are concentrations of vibrational energy in periodic systems/lattices due to the combined influences of nonlinearity and discreteness. Moreover, ILMs can move within the system and may strongly interact with an impurity, such as a stiffness change, mass variation, etc. Numerous scientific fields have uncovered examples and evidence of ILMs, motivating a multidisciplinary pursuit to rigorously understand the underlying principles. In spite of the diverse technical studies, a characterization of ILM interaction behaviors with multiple impurities in dissipative lattices remains outstanding. The insights on such behaviors may be broadly useful when dynamic measurements are the only accessible features of the periodic system. For instance, one may guide an ILM within the lattice using a deliberately applied and steered impurity and harness the observed interaction behaviors with a second, static (immovable) impurity/defect to identify how the underlying lattice is different at the second, defected site, whether or not one knew the position of the defect a priori. In this spirit, this research studies, analyzes, and characterizes the interaction types amongst an ILM and multiple impurities, and devises a method to identify a static defect impurity using quantitatively and qualitatively distinct interaction phenomena. The method is found to be robust to moderate levels of lattice stiffness heterogeneity and is applicable to monitor various property changes that represent impurities. Finally, experimental studies verify that ILMs interact with multiple impurities in unique ways such that defect features may be effectively identified.

  9. The influence of impurities on crystallization kinetics a case study on ammonium sulfate

    NASA Astrophysics Data System (ADS)

    Rauls, M.; Bartosch, K.; Kind, M.; Kuch, St.; Lacmann, R.; Mersmann, A.

    2000-05-01

    The influence of impurities on the crystallization kinetics of ammonium sulfate was investigated. MSMPR experiments were conducted with the impurities aluminum sulfate and the azo dyes amaranth and fuchsine. Nucleation and growth rates as well as mean crystal sizes were related to the supersaturation σ and-the width of the metastable zone. It was found that all impurity levels in the system reduce kinetic coefficients for crystal growth and suppress nucleation by adsorption on the crystal surfaces. An increase of supersaturation and metastable zone width compensates for this reduction at low impurity concentrations and allows the growth of larger crystals compared to the pure system. At high impurity concentrations and increasing surface coverage of the crystals, supersaturation rises faster than metastable zone width, causing an increase in nucleation rates and a higher fines content in the product compared to the pure system. A similar interdependence between impurity concentration, crystal size and supersaturation was found for other systems not reported here. The observations made can be explained in terms of adsorption equilibria of the impurities on the crystals. This seemingly general relationship allows the adjustment of crystal sizes in crystallization processes by control of impurity concentrations. A second paper will discuss the changes in crystal morphology in greater depth (Kuch et al., 2000).

  10. The correlation of a multi-level porosity system with depositional cyclicity and log signatures: Deep Cretaceous reservoirs, Lake Maracaibo, Venezuela

    SciTech Connect

    Vahrenkamp, V.C.; Franssen, R.C.M.W. ); Graaff, E.W.J.E. van de ); Munoz, P.J. )

    1991-03-01

    The correlation of a multi-level porosity system with depositional cyclicity in cores from central Lake Maracaibo (SVS-225; SVS-229) allows indirect recognition of productive intervals on logs. Deep Cretaceous reservoirs of Lake Maracaibo include Barremanian to Turonian strata (Rio negro Sandstone, Cogollo Group, and La Luna Formation). In the shallow-water carbonates of the Cogollo Group, large-scale open-marine and restricted-marine cycles (thickness; 50-200 ft) are recognized in cores as well as on logs. Organic-rich and less organic-rich limestone layers (decimeter scale) of the deep-marine La Luna source rocks probably reflect Milankovitch cyclicity. Cogollo Group/La Luna reservoirs are characterized by a dual/triple porosity system related to depositional cyclicity. Open fractures act as highly productive fluid conduits while providing little storage capacity (upper level porosity system). Open fractures occur preferentially in open-marine depositional cycles of the Cogollo Group, and fractured intervals can therefore be recognized indirectly by their log signatures. In the La Luna Formation open fractures are concentrated in less organic rich layers. The lower porosity level provides mainly storage capacity but little permeability. It consists of stylolite and patchy intervals of matrix porosity. A network of closely spaced stylolites not only provides significant storage capacity (lower level system) but also serves as an intermediate permeability system connecting matrix porosity with open fractures. Comparison with cores and logs from other wells in the Lake Maracaibo region confirms the recognized cyclicity pattern and suggests regional validity of the reservoir model.

  11. On the Diurnal Cycle of Deep Convection, High-Level Cloud, and Upper Troposphere Water Vapor in the Multiscale Modeling Framework

    SciTech Connect

    Zhang, Yunyan; Klein, Stephen A.; Liu, Chuntao; Tian, Baijun; Marchand, Roger T.; Haynes, J. M.; McCoy, Renata; Zhang, Yuying; Ackerman, Thomas P.

    2008-08-22

    The Multiscale Modeling Framework (MMF), also called ‘‘superparameterization’’, embeds a cloud-resolving model (CRM) at each grid column of a general circulation model to replace traditional parameterizations of moist convection and large-scale condensation. This study evaluates the diurnal cycle of deep convection, high-level clouds, and upper troposphere water vapor by applying an infrared (IR) brightness temperature (Tb) and a precipitation radar (PR) simulator to the CRM column data. Simulator results are then compared with IR radiances from geostationary satellites and PR reflectivities from the Tropical Rainfall Measuring Mission (TRMM). While the actual surface precipitation rate in the MMF has a reasonable diurnal phase and amplitude when compared with TRMM observations, the IR simulator results indicate an inconsistency in the diurnal anomalies of high-level clouds between the model and the geostationary satellite data. Primarily because of its excessive high-level clouds, the MMF overestimates the simulated precipitation index (PI) and fails to reproduce the observed diurnal cycle phase relationships among PI, high-level clouds, and upper troposphere relative humidity. The PR simulator results show that over the tropical oceans, the occurrence fraction of reflectivity in excess of 20 dBZ is almost 1 order of magnitude larger than the TRMM data especially at altitudes above 6 km. Both results suggest that the MMF oceanic convection is overactive and possible reasons for this bias are discussed. However, the joint distribution of simulated IR Tb and PR reflectivity indicates that the most intense deep convection is found more often over tropical land than ocean, in agreement with previous observational studies.

  12. Detection of Innate Immune Response Modulating Impurities in Therapeutic Proteins

    PubMed Central

    Haile, Lydia Asrat; Puig, Montserrat; Kelley-Baker, Logan; Verthelyi, Daniela

    2015-01-01

    Therapeutic proteins can contain multiple impurities, some of which are variants of the product, while others are derived from the cell substrate and the manufacturing process. Such impurities, even when present at trace levels, have the potential to activate innate immune cells in peripheral blood or embedded in tissues causing expression of cytokines and chemokines, increasing antigen uptake, facilitating processing and presentation by antigen presenting cells, and fostering product immunogenicity. Currently, while products are tested for host cell protein content, assays to control innate immune response modulating impurities (IIRMIs) in products are focused mainly on endotoxin and nucleic acids, however, depending on the cell substrate and the manufacturing process, numerous other IIRMI could be present. In these studies we assess two approaches that allow for the detection of a broader subset of IIRMIs. In the first, we use commercial cell lines transfected with Toll like receptors (TLR) to detect receptor-specific agonists. This method is sensitive to trace levels of IIRMI and provides information of the type of IIRMIs present but is limited by the availability of stably transfected cell lines and requires pre-existing knowledge of the IIRMIs likely to be present in the product. Alternatively, the use of a combination of macrophage cell lines of human and mouse origin allows for the detection of a broader spectrum of impurities, but does not identify the source of the activation. Importantly, for either system the lower limit of detection (LLOD) of impurities was similar to that of PBMC and it was not modified by the therapeutic protein tested, even in settings where the product had inherent immune modulatory properties. Together these data indicate that a cell-based assay approach could be used to screen products for the presence of IIRMIs and inform immunogenicity risk assessments, particularly in the context of comparability exercises. PMID:25901912

  13. Impurity accumulation in plasma regimes with high energy confinement

    NASA Astrophysics Data System (ADS)

    Ran, L. B.; Roberts, D. E.; Yang, H. R.; Dodel, G.; Gentle, K.; Von Goeler, S.; Holzhauer, E.; Hübner, K.; Keilhacker, M.; Korotkov, A.; Luce, T. C.; Miura, Y.; Tsois, N.; Würz, H.; Fussmann, G.; Hofmann, J.; Janeschitz, G.; Krieger, K.; Müller, E. R.; Nolte, R.; Röhr, H.; Steuer, K. H.; Becker, G.; Bomba, B.; Bruhns, H.; Büchl, K.; Carlson, A.; Eberhagen, A.; Fahrbach, H.-U.; Gehre, O.; Gernhardt, J.; Giannone, L.; Von Gierke, G.; Glock, E.; Gruber, O.; Haas, G.; Herrmann, H.; Kaesdorf, S.; Karger, F.; Kaufmann, M.; Klüber, O.; Kornherr, M.; Lackner, K.; Lang, R.; Lee, P.; Lisitano, G.; Mast, F.; Mayer, H. M.; McCormick, K.; Meisel, D.; Mertens, V.; Murmann, H.; Neuhauser, J.; Niedermeyer, H.; Noterdaeme, J. M.; Poschenrieder, W.; Preis, R.; Rapp, H.; Rudyj, A.; Sandmann, W.; Schneider, F.; Schnider, U.; Siller, G.; Simmet, E.; Speth, E.; Söldner, F.; Stäbler, A.; Steinmetz, K.; Stroth, U.; Vollmer, O.; Zasche, D.

    1989-04-01

    Investigations of impurity accumulation phenomena in ASDEX are reviewed. There are four different operating regimes where pronounced accumulation is observed and these regimes are also characterized by improved energy confinement. In particular, medium-Z metallic ions are involved in accumulation processes whereas low-Z ions appear almost unaffected. The rapid accumulation observed in the case of metallic ions may be explained by neoclassical inward drifts if we assume that the anomalous diffusion is sufficiently suppressed, some indication of this being found from laser blow-off studies. The present results, however, can only be partly explained by neoclassical theory, according to which accumulation of low-Z impurities should also occur. The temporal behaviour of accumulation and the retarding effect of proton dilution for collision dominated transport are also discussed. Finally, we conclude that the full benefits of improved energy confinement can be achieved only if the impurity influxes are kept to a sufficiently low level. Expressed in terms of concentrations under low confinement conditions we have to postulate, for ASDEX, concentrations ≲ 10 -4 for metals and ≲ 2% for all light impurities.

  14. Impurities in magnetic-field-induced Luttinger liquid

    NASA Astrophysics Data System (ADS)

    Tsai, Shan-Wen; Maslov, Dmitrii L.; Glazman, Leonid I.

    2001-03-01

    It has been shown recently(C. Biagini, D. L. Maslov, M. Yu. Reizer and L. I. Glazman, `` Magnetic-field-induced Luttinger liquid''), cond-mat/0006407. that a strong magnetic field applied to a bulk metal may induce a Luttinger liquid phase. This is a consequence of the reduced effective dimensionality of charge carriers from 3D to 1D, an effect which is most pronounced in the ultra-quantum limit, when only the lowest Landau level remains populated. We study the effect of impurities in this system. For the case of a point impurity, the calculation of the scattering cross section at a single impurity can be mapped exactly to a 1D problem of tunneling conductance through a barrier for interacting electrons, solved by Yue et al.(D. Yue, L. I. Glazman and K. A. Matveev, Phys. Rev. B 49) (1994) 1966.. Using this mapping, we find that the longitudinal (ɛ=+1) and transverse (ɛ=-1) Drude conductivities exhibit the scaling laws σ_ɛ∝ T^ɛα, where α=2e^2|lnκl_B|/π v_F, and vF and κ are the B-dependent Fermi velocity and screening wavevector, respectively; lB is the magnetic length. The physical reason for such a behavior of the conductivity is the almost 1D form of the Friedel oscillation around a single point impurity in the strong magnetic field.

  15. Substitutional 4d and 5d impurities in graphene.

    PubMed

    Alonso-Lanza, Tomás; Ayuela, Andrés; Aguilera-Granja, Faustino

    2016-08-21

    We describe the structural and electronic properties of graphene doped with substitutional impurities of 4d and 5d transition metals. The adsorption energies and distances for 4d and 5d metals in graphene show similar trends for the later groups in the periodic table, which are also well-known characteristics of 3d elements. However, along earlier groups the 4d impurities in graphene show very similar adsorption energies, distances and magnetic moments to the 5d ones, which can be related to the influence of the 4d and 5d lanthanide contraction. Surprisingly, within the manganese group, the total magnetic moment of 3 μB for manganese is reduced to 1 μB for technetium and rhenium. We find that compared with 3d elements, the larger size of the 4d and 5d elements causes a high degree of hybridization with the neighbouring carbon atoms, reducing spin splitting in the d levels. It seems that the magnetic adjustment of graphene could be significantly different if 4d or 5d impurities are used instead of 3d impurities. PMID:27439363

  16. Imaging the Impact of Impurities on Topological Surface States

    NASA Astrophysics Data System (ADS)

    Hoffman, Jennifer

    2013-03-01

    Harnessing the technological potential of the spin-polarized surface states on topological insulators requires a detailed understanding of the impact of nanoscale disorder on those surface states. We employ spectroscopic scanning tunneling microscopy (STM) in the presence of a magnetic field to visualize the impact of intrinsic impurities on topological surface states in Sb and Bi2Se3. We find a variety of impurities with different energy profiles that elastically scatter surface states through dispersive quasiparticle interference (QPI), that inelastically scatter surface states into the bulk, that locally destroy the extended surface state Landau level wavefunctions, or that form local resonant states interacting with the Dirac quasiparticles. By identifying impurities that strongly interact with and limit the mobility of the topological surface states, our impurity studies can directly advise the growth and development of future topological materials. Measurements carried out by Anjan Soumyanarayanan, Michael Yee, Yang He. Samples grown by Dillon Gardner & Young Lee; Zahir Salman & Amit Kanigel; Zhi Ren & Kouji Segawa & Yoichi Ando.

  17. Controlled samples for silicon defect and impurity studies

    SciTech Connect

    Ciszek, T.F.

    1995-08-01

    Because of the diverse defects and impurities that are present in any given sample of silicon material, it can be extremely difficult to conduct a controlled experiment to study the influence of any particular defect or impurity on photovoltaic properties such as minority charge carrier lifetime {tau} or solar cell efficiency q. For example, the influence of iron may be different if boron is present, or the influence of silicon self interstitial clusters may be different if oxygen is present. It thus becomes important to conduct such studies on controlled samples where the influence of secondary effects is minimized. At NREL, over the past several years, we have focused on using the high-purity float-zone (FZ) growth method to obtain controlled samples. Because the silicon melt is not in contact with a container, and no heated components are in the growth region, very high purities and low defect levels can be achieved in baseline material. The baseline can be controllably perturbed by introduction of specific defects or impurities. The chart shown below lists some of the types of defect and impurity. combinations that can be studied in this way. The boxes marked with an {open_quotes}x{close_quotes} represent combinations we have studied to some extent.

  18. Local moment formation and Kondo screening in impurity trimers.

    PubMed

    Mitchell, Andrew K; Jarrold, Thomas F; Galpin, Martin R; Logan, David E

    2013-10-24

    We study theoretically a triangular cluster of three magnetic impurities, hybridizing locally with conduction electrons of a metallic host. Such a cluster is the simplest to exhibit frustration, an important generic feature of many complex molecular systems in which different interactions compete. Here, low-energy doublet states of the trimer are favored by effective exchange interactions produced by strong electronic repulsion in localized impurity orbitals. Parity symmetry protects a level crossing of such states on tuning microscopic parameters, while an avoided crossing arises in the general distorted case. Upon coupling to a metallic host, the behavior is shown to be immensely rich because collective quantum many-body effects now also compete. In particular, impurity degrees of freedom are totally screened at low temperatures in a Kondo-screened Fermi liquid phase, while degenerate ground states persist in a local moment phase. Local frustration drives the quantum phase transition between the two, which may be first order or of Kosterlitz-Thouless type, depending on symmetries. Unusual mechanisms for local moment formation and Kondo screening are found due to the orbital structure of the impurity trimer. Our results are of relevance for triple quantum dot devices. The problem is studied by a combination of analytical arguments and the numerical renormalization group. PMID:23527540

  19. Groundwater level changes in a deep well in response to a magma intrusion event on Kilauea Volcano, Hawai'i

    USGS Publications Warehouse

    Hurwitz, S.; Johnston, M.J.S.

    2003-01-01

    On May 21, 2001, an abrupt inflation of Kilauea Volcano's summit induced a rapid and large increase in compressional strain, with a maximum of 2 ??strain recorded by a borehole dilatometer. Water level (pressure) simultaneously dropped by 6 cm. This mode of water level change (drop) is in contrast to that expected for compressional strain from poroelastic theory, and therefore it is proposed that the stress applied by the intrusion has caused opening of fractures or interflows that drained water out of the well. Upon relaxation of the stress recorded by the dilatometer, water levels have recovered at a similar rate. The proposed model has implications for the analysis of ground surface deformation and for mechanisms that trigger phreatomagmatic eruptions.

  20. Eliminating Impurity Traps in the Silane Process

    NASA Technical Reports Server (NTRS)

    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.

  1. Subthalamic Nucleus Deep Brain Stimulation Modulate Catecholamine Levels with Significant Relations to Clinical Outcome after Surgery in Patients with Parkinson’s Disease

    PubMed Central

    Yamamoto, Tatsuya; Uchiyama, Tomoyuki; Higuchi, Yoshinori; Asahina, Masato; Hirano, Shigeki; Yamanaka, Yoshitaka; Kuwabara, Satoshi

    2015-01-01

    Aims Although subthalamic nucleus deep brain stimulation (STN-DBS) is effective in patients with advanced Parkinson’s disease (PD), its physiological mechanisms remain unclear. Because STN-DBS is effective in patients with PD whose motor symptoms are dramatically alleviated by L-3,4-dihydroxyphenylalanine (L-DOPA) treatment, the higher preoperative catecholamine levels might be related to the better clinical outcome after surgery. We aimed to examine the correlation between the preoperative catecholamine levels and postoperative clinical outcome after subthalamic nucleus deep brain stimulation. The effectiveness of STN-DBS in the patient who responded well to dopaminergic medication suggest the causal link between the dopaminergic system and STN-DBS. We also examined how catecholamine levels were modulated after subthalamic stimulation. Methods In total 25 patients with PD were enrolled (Mean age 66.2 ± 6.7 years, mean disease duration 11.6 ± 3.7 years). Mean levodopa equivalent doses were 1032 ± 34.6 mg before surgery. Cerebrospinal fluid and plasma catecholamine levels were measured an hour after oral administration of antiparkinsonian drugs before surgery. The mean Unified Parkinson’s Disease Rating Scale scores (UPDRS) and the Parkinson’s disease Questionnaire-39 (PDQ-39) were obtained before and after surgery. Of the 25 patients, postoperative cerebrospinal fluid and plasma were collected an hour after oral administration of antiparkinsonian drugs during on stimulation at follow up in 11 patients. Results Mean levodopa equivalent doses significantly decreased after surgery with improvement in motor functions and quality of life. The preoperative catecholamine levels had basically negative correlations with postoperative motor scores and quality of life, suggesting that higher preoperative catecholamine levels were related to better outcome after STN-DBS. The preoperative plasma levels of L-DOPA had significantly negative correlations with

  2. Arthropod Phylogenetics in Light of Three Novel Millipede (Myriapoda: Diplopoda) Mitochondrial Genomes with Comments on the Appropriateness of Mitochondrial Genome Sequence Data for Inferring Deep Level Relationships

    PubMed Central

    Brewer, Michael S.; Swafford, Lynn; Spruill, Chad L.; Bond, Jason E.

    2013-01-01

    Background Arthropods are the most diverse group of eukaryotic organisms, but their phylogenetic relationships are poorly understood. Herein, we describe three mitochondrial genomes representing orders of millipedes for which complete genomes had not been characterized. Newly sequenced genomes are combined with existing data to characterize the protein coding regions of myriapods and to attempt to reconstruct the evolutionary relationships within the Myriapoda and Arthropoda. Results The newly sequenced genomes are similar to previously characterized millipede sequences in terms of synteny and length. Unique translocations occurred within the newly sequenced taxa, including one half of the Appalachioria falcifera genome, which is inverted with respect to other millipede genomes. Across myriapods, amino acid conservation levels are highly dependent on the gene region. Additionally, individual loci varied in the level of amino acid conservation. Overall, most gene regions showed low levels of conservation at many sites. Attempts to reconstruct the evolutionary relationships suffered from questionable relationships and low support values. Analyses of phylogenetic informativeness show the lack of signal deep in the trees (i.e., genes evolve too quickly). As a result, the myriapod tree resembles previously published results but lacks convincing support, and, within the arthropod tree, well established groups were recovered as polyphyletic. Conclusions The novel genome sequences described herein provide useful genomic information concerning millipede groups that had not been investigated. Taken together with existing sequences, the variety of compositions and evolution of myriapod mitochondrial genomes are shown to be more complex than previously thought. Unfortunately, the use of mitochondrial protein-coding regions in deep arthropod phylogenetics appears problematic, a result consistent with previously published studies. Lack of phylogenetic signal renders the

  3. The Waste Isolation Pilot Plant Deep Geological Repository: A Domestic and Global Blueprint for Safe Disposal of High-Level Radioactive Waste - 12081

    SciTech Connect

    Eriksson, Leif G.; Dials, George E.

    2012-07-01

    At the end of 2011, the world's first used/spent nuclear fuel and other long-lived high-level radioactive waste (HLW) repository is projected to open in 2020, followed by two more in 2025. The related pre-opening periods will be at least 40 years, as it also would be if USA's candidate HLW-repository is resurrected by 2013. If abandoned, a new HLW-repository site would be needed. On 26 March 1999, USA began disposing long-lived radioactive waste in a deep geological repository in salt at the Waste Isolation Pilot Plant (WIPP) site. The related pre-opening period was less than 30 years. WIPP has since been re-certified twice. It thus stands to reason the WIPP repository is the global proof of principle for safe deep geological disposal of long-lived radioactive waste. It also stands to reason that the lessons learned since 1971 at the WIPP site provide a unique, continually-updated, blueprint for how the pre-opening period for a new HLW repository could be shortened both in the USA and abroad. (authors)

  4. Donor and double-donor transitions of the carbon vacancy related EH6/7 deep level in 4H-SiC

    NASA Astrophysics Data System (ADS)

    Booker, I. D.; Janzén, E.; Son, N. T.; Hassan, J.; Stenberg, P.; Sveinbjörnsson, E. Ö.

    2016-06-01

    Using medium- and high-resolution multi-spectra fitting of deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy (MCTS), optical O-DLTS and optical-electrical (OE)-MCTS measurements, we show that the EH6/7 deep level in 4H-SiC is composed of two strongly overlapping, two electron emission processes with thermal activation energies of 1.49 eV and 1.58 eV for EH6 and 1.48 eV and 1.66 eV for EH7. The electron emission peaks of EH7 completely overlap while the emission peaks of EH6 occur offset at slightly different temperatures in the spectra. OE-MCTS measurements of the hole capture cross section σp0(T) in p-type samples reveal a trap-Auger process, whereby hole capture into the defect occupied by two electrons leads to a recombination event and the ejection of the second electron into the conduction band. Values of the hole and electron capture cross sections σn(T) and σp(T) differ strongly due to the donor like nature of the deep levels and while all σn(T) have a negative temperature dependence, the σp(T) appear to be temperature independent. Average values at the DLTS measurement temperature (˜600 K) are σn2+(T) ≈ 1 × 10-14 cm2, σn+(T) ≈ 1 × 10-14 cm2, and σp0(T) ≈ 9 × 10-18 cm2 for EH6 and σn2+(T) ≈ 2 × 10-14 cm2, σn+(T) ≈ 2 × 10-14 cm2, σp0(T) ≈ 1 × 10-20 cm2 for EH7. Since EH7 has already been identified as a donor transition of the carbon vacancy, we propose that the EH6/7 center in total represents the overlapping first and second donor transitions of the carbon vacancy defects on both inequivalent lattice sites.

  5. EFFECT OF IMPURITIES ON THE PERFORMANCE OF A Pd-Ag DIFFUSER

    SciTech Connect

    Morgan, G.

    2010-12-16

    A commercially fabricated diffuser purchased from Johnson-Matthey, Inc. was evaluated for performance characterization testing at the Savannah River National Laboratory (SRNL). Different impurities are often present in the feed streams of the process diffusers, but the effect of these impurities on the diffuser performance is currently unknown. Various impurities were introduced into the feed stream of the diffuser at various levels ranging from 0.5% to 10% of the total flow in order to determine the effect that these impurities have on the permeation of hydrogen through the palladium-silver membrane. The introduction of various impurities into the feed stream of the diffuser had a minimal effect on the overall permeation of hydrogen through the Pd-Ag membrane. Of the four impurities introduced into the feed stream, carbon monoxide (CO) was the only impurity that showed any evidence of causing a reduction in the amount of hydrogen permeating through the Pd-Ag membrane. The hydrogen permeation returned to its baseline level after the CO was removed from the feed stream. There were no lasting effects of the CO exposure on the ability of the membrane to effectively separate hydrogen from the non-hydrogen species in the gas stream under the conditions tested.

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

    SciTech Connect

    Savinov, S. V.; Oreshkin, A. I. E-mail: oreshkin@spmlab.ru; Oreshkin, S. I.; Haesendonck, C. van

    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.

  7. Diagnostic accuracy of deep vein thrombosis is increased by analysis using combined optimal cut-off values of postoperative plasma D-dimer levels

    PubMed Central

    JIANG, YONG; LI, JIE; LIU, YANG; ZHANG, WEIGUO

    2016-01-01

    The present study aimed to evaluate the accuracy of analysis using optimal cut-off values of plasma D-dimer levels in the diagnosis of deep vein thrombosis (DVT). A total of 175 orthopedic patients with DVT and 162 patients without DVT were included in the study. Ultrasonic color Doppler imaging was performed on lower limb veins prior to and following orthopedic surgery in order to determine the types of orthopedic conditions that were present. An enzyme-linked fluorescent assay was performed to detect the expression levels of D-dimer in plasma, and receiver operating characteristic analysis was performed to predict the occurrence of DVT on the basis of the expression levels of D-dimer. After surgery, the expression levels of D-dimer in the plasma of DVT patients were significantly higher in comparison with those in orthopedic patients without DVT (P<0.05). When the patients were divided into subgroups according to the underlying orthopedic condition, the expression levels of D-dimer in the plasma of each subgroup were higher 1 day after orthopedic surgery in comparison to those prior to surgery (P<0.05). The diagnostic accuracy achieved using combined optimal cut-off values at 1 and 3 days post-surgery was significantly higher than the accuracy when using a single optimal cut-off value (P<0.05). In conclusion, detection of D-dimer expression levels at 1 day post-orthopedic surgery may be important in predicting DVT. In addition, the diagnostic accuracy of DVT is significantly increased by analysis using combined optimal cut-off values of D-dimer plasma expression levels. PMID:27168793

  8. Segregation Coefficients of Impurities in Selenium by Zone Refining

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Sha, Yi-Gao

    1998-01-01

    The purification of Se by zone refining process was studied. The impurity solute levels along the length of a zone-refined Se sample were measured by spark source mass spectrographic analysis. By comparing the experimental concentration levels with theoretical curves the segregation coefficient, defined as the ratio of equilibrium concentration of a given solute in the solid to that in the liquid, k = x(sub s)/x(sub l) for most of the impurities in Se are found to be close to unity, i.e., between 0.85 and 1.15, with the k value for Si, Zn, Fe, Na and Al greater than 1 and that for S, Cl, Ca, P, As, Mn and Cr less than 1. This implies that a large number of passes is needed for the successful implementation of zone refining in the purification of Se.

  9. Deep XMM observations of Draco rule out at the 99 per cent confidence level a dark matter decay origin for the 3.5 keV line

    NASA Astrophysics Data System (ADS)

    Jeltema, Tesla; Profumo, Stefano

    2016-06-01

    We searched for an X-ray line at energies around 3.5 keV in deep, ˜1.6 Ms XMM-Newton observations of the dwarf spheroidal galaxy Draco. No line was found in either the Metal Oxide Semi-conductor (MOS) or the p-type/n-type semiconductor (PN) detectors. The data in this energy range are completely consistent with a single, unfolded power-law modelling the particle background, which dominates at these energies, plus instrumental lines; the addition of a ˜3.5 keV line feature gives no improvement to the fit. The corresponding upper limit on the line flux rules out a dark matter decay origin for the 3.5 keV line found in observations of clusters of galaxies and in the Galactic Centre at greater than 99 per cent confidence level.

  10. Deep level defect correlated emission and Si diffusion in ZnO:Tb(3+) thin films prepared by pulsed laser deposition.

    PubMed

    Kumar, Vinod; Ntwaeaborwa, Odireleng M; Swart, Hendrik C

    2016-03-01

    Terbium (Tb(3+)) doped zinc oxide (ZnO) or (ZnO:Tb(3+)) thin films were grown on silicon substrates by the pulsed laser deposition technique at different growth temperatures that were varied from room temperature (RT) to 400°C. The effects of substrate temperature on the structural and optical properties of the ZnO:Tb(3+) films were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and RT photoluminescence spectroscopy. The band to band and deep level defect emissions were observed for all substrate temperatures. The silicon that has diffused from the substrate has occupied the position of the Zn vacancies in the ZnO:Tb(3+) thin films at the higher substrate temperatures (400°C). A blue emission was observed for all the ZnO:Tb(3+) thin films deposited at the different substrate temperatures. PMID:26688121

  11. Investigation of buffer traps in an AlGaN/GaN/Si high electron mobility transistor by backgating current deep level transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Marso, M.; Wolter, M.; Javorka, P.; Kordoš, P.; Lüth, H.

    2003-01-01

    The influence of a substrate voltage on the dc characteristics of an AlGaN/GaN high electron mobility transistor (HEMT) on silicon (111) substrate is profited to investigate traps that are located between the substrate and the two-dimensional electron gas channel. The transient of the drain current after applying a negative substrate voltage is evaluated in the temperature range from 30 to 100 °C. With this method, known as backgating current deep level transient spectroscopy, majority carrier traps with activation energy of 200 meV as well as minority carrier traps at 370 meV are identified. The experiments are performed on completed HEMTs, allowing the investigation of the influence of device fabrication technology.

  12. Effect of fill-pulse parameters on deep-level transient spectroscopy peaks in highly doped p-type InP

    NASA Astrophysics Data System (ADS)

    Darwich, R.; Massarani, B.

    2000-07-01

    The effect of different fill-pulse parameters on the characteristics of deep-level transient spectroscopy (DLTS) peaks has been studied in the example of the hole traps H4F and H5 in electron-irradiated highly doped p-type InP. It is shown that the saturation peak height, the temperature of the peak maximum and its full width at half maximum depend on the applied reverse bias, the pulse amplitude, its frequency and duration. Our results show that the origin of this dependence is the electric field present in the space charge region (SCR). The experimental results are analyzed in terms of the effect of the electric field on the refilled traps in the SCR. The appropriate experimental conditions for the correct extraction of information from the DLTS spectrum are defined.

  13. Single scan defect identification by deep level transient spectroscopy using a two-phase lock-in amplifier (IQ-DLTS)

    NASA Astrophysics Data System (ADS)

    Auret, F. D.; Nel, M.

    1988-02-01

    A simple method of analyzing the deep level transient spectroscopy (DLTS) transient signal by recording its in-phase (I) and quadrature (Q) DLTS spectra using a two-phase lock-in amplifier with a sine wave mixing function, IQ-DLTS, is presented. Measurement of the peak positions on the I and Q spectra, which are simultaneously recorded during a single temperature scan, facilitates the calculation of the defect's activation energy Et, and capture cross section σt, which are required for its identification. It was found that the Et values obtained when analyzing proton implantation-induced defects in GaAs were within 5% of those determined from the conventional DLTS Arrhenius plots.

  14. Impurity effects on reduced-activation ferritic steels developed for fusion applications

    NASA Astrophysics Data System (ADS)

    Klueh, R. L.; Cheng, E. T.; Grossbeck, M. L.; Bloom, E. E.

    2000-08-01

    Reduced-activation steels are being developed for fusion applications by restricting alloying elements that produce long-lived radioactive isotopes when irradiated in the fusion neutron environment. Another source of long-lived isotopes is the impurities in the steel. To examine this, three heats of reduced-activation martensitic steel were analyzed by inductively coupled plasma mass spectrometry for low-level impurities that compromise the reduced-activation characteristics: a 5-ton heat of modified F82H (F82H-Mod) for which an effort was made during production to reduce detrimental impurities, a 1-ton heat of JLF-1, and an 18-kg heat of ORNL 9Cr-2WVTa. Specimens from commercial heats of modified 9Cr-1Mo and Sandvik HT9 were also analyzed. The objective was to determine the difference in the impurity levels in the F82H-Mod and steels for which less effort was used to ensure purity. Silver, molybdenum, and niobium were found to be the tramp impurities of most importance. The F82H-Mod had the lowest levels, but in some cases the levels were not much different from the other heats. The impurity levels in the F82H-Mod produced with present technology did not achieve the low-activation limits for either shallow land burial or recycling. The results indicate the progress that has been made and what still must be done before the reduced-activation criteria can be achieved.

  15. The beauty of impurities: Two revivals of Friedel's virtual bound-state concept

    NASA Astrophysics Data System (ADS)

    Georges, Antoine

    2016-03-01

    Jacques Friedel pioneered the theoretical study of impurities and magnetic impurities in metals. He discovered Friedel oscillations, introduced the concept of virtual bound-state, and demonstrated that the charge on the impurity is related to the scattering phase-shift at the Fermi level (Friedel sum-rule). After a brief review of some of these concepts, I describe how they proved useful in two new contexts. The first one concerns the Coulomb blockade in quantum dots, and its suppression by the Kondo effect. The second one is the dynamical mean-field theory of strong electronic correlations. xml:lang="fr"

  16. Method and apparatus for detecting and measuring trace impurities in flowing gases

    DOEpatents

    Taylor, Gene W.; Dowdy, Edward J.

    1979-01-01

    Trace impurities in flowing gases may be detected and measured by a dynamic atomic molecular emission spectrograph utilizing as its energy source the energy transfer reactions of metastable species, atomic or molecular, with the impurities in the flowing gas. An electronically metastable species which maintains a stable afterglow is formed and mixed with the flowing gas in a region downstream from and separate from the region in which the metastable species is formed. Impurity levels are determined quantitatively by the measurement of line and/or band intensity as a function of concentration employing emission spectroscopic techniques.

  17. MOS Capacitance—Voltage Characteristics: IV. Trapping Capacitance from 3-Charge-State Impurities

    NASA Astrophysics Data System (ADS)

    Binbin, Jie; Chihtang, Sah

    2012-01-01

    Metal—Oxide—Semiconductor Capacitance—Voltage (MOSCV) characteristics containing giant carrier trapping capacitances from 3-charge-state or 2-energy-level impurities are presented for not-doped, n-doped, p-doped and compensated silicon containing the double-donor sulfur and iron, the double-acceptor zinc, and the amphoteric or one-donor and one-acceptor gold and silver impurities. These impurities provide giant trapping capacitances at trapping energies from 200 to 800 meV (50 to 200 THz and 6 to 1.5 μm), which suggest potential sub-millimeter, far-infrared and spin electronics applications.

  18. Revised shallow and deep water-level and storage-volume changes in the Equus Beds Aquifer near Wichita, Kansas, predevelopment to 1993

    USGS Publications Warehouse

    Hansen, Cristi V.; Lanning-Rush, Jennifer L.; Ziegler, Andrew C.

    2013-01-01

    credits from the Equus Beds aquifer by the city of Wichita. The 1993 water levels correspond to the lowest recorded levels and largest storage declines since 1940. Revised and new water-level maps of shallow and deep layers were developed to better represent the general condition of the aquifer. Only static water levels were used to better represent the general condition of the aquifer and comply with Wichita’s ASR permits. To ensure adequate data density, the January 1993 period was expanded to October 1992 through February 1993. Static 1993 water levels from the deep aquifer layer of the Equus Beds aquifer possibly could be used as the lower baseline for regulatory purposes. Previously, maps of water-level changes used to estimate the storage-volume changes included a combination of static (unaffected by pumping or nearby pumping) and stressed (affected by pumping or nearby pumping) water levels from wells. Some of these wells were open to the shallow aquifer layer and some were open to the deep aquifer layer of the Equus Beds aquifer. In this report, only static water levels in the shallow aquifer layer were used to determine storage-volume changes. The effects on average water-level and storage-volume change from the use of mixed, stressed water levels and a specific yield of 0.20 were compared to the use of static water levels in the shallow aquifer and a specific yield of 0.15. This comparison indicates that the change in specific yield causes storage-volume changes to decrease about 25 percent, whereas the use of static water levels in the shallow aquifer layer causes an increase of less than 4 percent. Use of a specific yield of 0.15 will result in substantial decreases in the amount of storage-volume change compared to those reported previously that were calculated using a specific yield of 0.20. Based on these revised water-level maps and computations, the overall decline and change in storage from predevelopment to 1993 represented a loss in storage of about

  19. Paramagnetic Attraction of Impurity-Helium Solids

    NASA Technical Reports Server (NTRS)

    Bernard, E. P.; Boltnev, R. E.; Khmelenko, V. V.; Lee, D. M.

    2003-01-01

    Impurity-helium solids are formed when a mixture of impurity and helium gases enters a volume of superfluid helium. Typical choices of impurity gas are hydrogen deuteride, deuterium, nitrogen, neon and argon, or a mixture of these. These solids consist of individual impurity atoms and molecules as well as clusters of impurity atoms and molecules covered with layers of solidified helium. The clusters have an imperfect crystalline structure and diameters ranging up to 90 angstroms, depending somewhat on the choice of impurity. Immediately following formation the clusters aggregate into loosely connected porous solids that are submerged in and completely permeated by the liquid helium. Im-He solids are extremely effective at stabilizing high concentrations of free radicals, which can be introduced by applying a high power RF dis- charge to the impurity gas mixture just before it strikes the super fluid helium. Average concentrations of 10(exp 19) nitrogen atoms/cc and 5 x 10(exp 18) deuterium atoms/cc can be achieved this way. It shows a typical sample formed from a mixture of atomic and molecular hydrogen and deuterium. It shows typical sample formed from atomic and molecular nitrogen. Much of the stability of Im-He solids is attributed to their very large surface area to volume ratio and their permeation by super fluid helium. Heat resulting from a chance meeting and recombination of free radicals is quickly dissipated by the super fluid helium instead of thermally promoting the diffusion of other nearby free radicals.

  20. Direct Visualization of an Impurity Depletion Zone

    NASA Technical Reports Server (NTRS)

    Chernov, Alex A.; Garcia-Ruiz, Juan Ma; Thomas, Bill R.

    2000-01-01

    When a crystal incorporates more impurity per unit of its volume than the impurity concentration in solution, the solution in vicinity of the growing crystal is depleted with respect to the impurity I,2. With a stagnant solution, e. g. in microgravity or gels, an impurity depletion zone expands as the crystal grows and results in greater purity in most of the outer portion of the crystal than in the core. Crystallization in gel provides an opportunity to mimic microgravity conditions and visualize the impurity depletion zone. Colorless, transparent apoferritin (M congruent to 450 KDa) crystals were grown in the presence of red holoferritin dimer as a microheterogeneous impurity (M congruent to 900 KDa) within agarose gel by counterdiffusion with Cd(2+) precipitant. Preferential trapping of dimers, (distribution coefficient K = 4 (exp 1,2)) results in weaker red color around the crystals grown in the left tube in the figure as compared to the control middle tube without crystals. The left and the middle tubes contain colored ferritin dimers, the right tube contains colored trimers. The meniscus in the left tube separate gel (below) and liquid solution containing Cd(2+) (above). Similar solutions, though without precipitants, were present on top of the middle and right tube allowing diffusion of dimers and trimers. The area of weaker color intensity around crystals directly demonstrates overlapped impurity depletion zones.

  1. A Rydberg impurity in a dense background gas (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Liebisch, Tara; Schlagmüller, Michael; Engel, Felix; Westphal, Karl; Kleinbach, Kathrin; Böttcher, Fabian; Loew, Robert; Hofferberth, Sebastian; Pfau, Tilman; Perez-Rios, Jesus; Greene, Chris

    2016-04-01

    A single Rydberg atom impurity excited in a BEC is a system that can be utilized to measure the quantum mechanical properties of electron - neutral scattering andthe electron probability density of a Rydberg atom. The Rydberg electron - neutral atom scattering process, is a fundamental scattering process, which can be described via Fermi's pseudopotential as V{ěc{r},ěc{R} )=2pi {a}[k(R)]&delta^{(3)}(ěc{r}-ěc{R}). The scattering length is dependent on the momentum of the Rydberg electron, and therefore is dependent on the separation of the Rydberg electron from the ion core. At the classical outermost turning point of the electron, it has the slowest momentum leading to s-wave dominated scattering potentials 10's of MHz in depth for n<40 (Greene et al. PRL 85 2458 (2000), Bendkowsky et al. PRL 105 163201 (2010)). In alkali atoms there is a shape resonance for p-wave scattering, which becomes relevant at ion-neutral separations of 75nm (I.I. Fabrikant J.Phys B 19, 1527 (1985)). This shape resonance potential is several GHz deep, spanning the energy level spacing between n and n-1 principal quantum numbers. At high BEC densities of 5x10^14cm-3 the nearest neighbor spacing is less than 70nm. A Rydberg atom excited within a BEC, is an excitation of the Rydberg atom and all N neutral atoms located within the Rydberg orbit, described as nS+N x 5S. The nS+N x 5S state is density shifted from the Rydberg resonance. Not only does the distribution of atoms within the Rydberg orbit lead to a density shift, but, at these high densities, atoms excited in the nS+N x 5S state near the shape resonance potential cause large perturbations to the density shift, leading to a line broadening. Therefore the spectroscopic line shape of a Rydberg atom in a BEC allows us to probe the theoretically calculated p-wave shape resonance potential. Furthermore, we can observe and measure the dynamics of neutrals excited in the nS+N x 5S state. In the ultracold regime of a BEC, the background

  2. Impurity Particle Transport in High Confinement Regimes Without ELMs on DIII-D

    NASA Astrophysics Data System (ADS)

    Grierson, B. A.

    2014-10-01

    Recent experiments on DIII-D using trace levels of fluorine gas injection have shown that high confinement regimes without ELMs can achieve rapid transport of impurity ions. Much attention has recently been given to regimes with H-mode energy confinement without edge-localized modes (ELMs), accessed either through Resonant Magnetic Perturbations (RMPs) or MHD such as edge harmonic oscillations or quasi-coherent edge oscillations. Experiments on DIII-D have used gas puffing of trace levels of fluorine to introduce this fully-stripped, non-intrinsic and non-recycling impurity that can be easily measured with charge-exchange recombination spectroscopy. Trace fluorine is used because the time-history of the fluorine density profile permits direct extraction of the confinement time, particle diffusivity and convective velocity without relying on atomic modeling or assumptions about the source recycling. Results indicate impurity accumulation is more pronounced in RMP ELM suppressed plasmas with a pure n = 3 spectrum compared with mixed n = 1 and n = 3 RMP fields with reduced number of control coils. In cases where strong central carbon impurity accumulation occurs, trace fluorine analysis reveals a strong inward impurity pinch. Conversely, in plasmas with weak central carbon accumulation, the fluorine pinch is significantly lower. These measurements of impurity influx are consistent with TGLF modeling of the ELM-suppressed phase of the discharge revealing that strong impurity influx occurs when the ratio V/D is between -1 to -3. In this work, the dependencies of impurity transport on local driving gradients will be presented, and the means of increasing the impurity diffusion to recover high purity plasmas will be discussed providing a basis for achieving low-dilution, stationary ELM-free operation in ITER and future devices. Supported by the US DOE under DE-AC0-09CH11466 and DE-FC02-05ER54698.

  3. An introduction to blocked impurity band detectors

    NASA Technical Reports Server (NTRS)

    Geist, Jon

    1988-01-01

    Blocked impurity band detectors fabricated using standard silicon technologies offer the possibility of combining high sensitivity and high accuracy in a single detector operating in a low background environment. The solid state photomultiplier described by Petroff et al., which is a new type of blocked impurity band detector, offers even higher sensitivity as well as operation in the visible spectral region. The principle of operation and possible application of blocked impurity band detectors for stellar seismology and the search for extra-solar planets are described.

  4. Mitigation of Effects of Occlusion on Object Recognition with Deep Neural Networks through Low-Level Image Completion.

    PubMed

    Chandler, Benjamin; Mingolla, Ennio

    2016-01-01

    Heavily occluded objects are more difficult for classification algorithms to identify correctly than unoccluded objects. This effect is rare and thus hard to measure with datasets like ImageNet and PASCAL VOC, however, owing to biases in human-generated image pose selection. We introduce a dataset that emphasizes occlusion and additions to a standard convolutional neural network aimed at increasing invariance to occlusion. An unmodified convolutional neural network trained and tested on the new dataset rapidly degrades to chance-level accuracy as occlusion increases. Training with occluded data slows this decline but still yields poor performance with high occlusion. Integrating novel preprocessing stages to segment the input and inpaint occlusions is an effective mitigation. A convolutional network so modified is nearly as effective with more than 81% of pixels occluded as it is with no occlusion. Such a network is also more accurate on unoccluded images than an otherwise identical network that has been trained with only unoccluded images. These results depend on successful segmentation. The occlusions in our dataset are deliberately easy to segment from the figure and background. Achieving similar results on a more challenging dataset would require finding a method to split figure, background, and occluding pixels in the input. PMID:27340396

  5. Mitigation of Effects of Occlusion on Object Recognition with Deep Neural Networks through Low-Level Image Completion

    PubMed Central

    Mingolla, Ennio

    2016-01-01

    Heavily occluded objects are more difficult for classification algorithms to identify correctly than unoccluded objects. This effect is rare and thus hard to measure with datasets like ImageNet and PASCAL VOC, however, owing to biases in human-generated image pose selection. We introduce a dataset that emphasizes occlusion and additions to a standard convolutional neural network aimed at increasing invariance to occlusion. An unmodified convolutional neural network trained and tested on the new dataset rapidly degrades to chance-level accuracy as occlusion increases. Training with occluded data slows this decline but still yields poor performance with high occlusion. Integrating novel preprocessing stages to segment the input and inpaint occlusions is an effective mitigation. A convolutional network so modified is nearly as effective with more than 81% of pixels occluded as it is with no occlusion. Such a network is also more accurate on unoccluded images than an otherwise identical network that has been trained with only unoccluded images. These results depend on successful segmentation. The occlusions in our dataset are deliberately easy to segment from the figure and background. Achieving similar results on a more challenging dataset would require finding a method to split figure, background, and occluding pixels in the input. PMID:27340396

  6. Multiple magnetic impurities on surfaces: Scattering and quasiparticle interference

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    We study systems of multiple interacting quantum impurities deposited on a metallic surface in a three-dimensional host. For the real-space two-impurity problem, using numerical renormalization group calculations, a rich range of behavior is shown to arise due to the interplay between Kondo physics and effective Ruderman-Kittel-Kasuya-Yosida interactions—provided the impurity separation is small. Such calculations allow identification of the minimum impurity separation required for a description in terms of independent impurities, and thereby the onset of the "dilute-impurity limit" in many-impurity systems. A "dilute-cluster" limit is also identified in systems with higher impurity density, where interimpurity interactions are important only within independent clusters. We calculate the quasiparticle interference due to two and many impurities, and explore the consequences of the independent impurity and cluster paradigms. Our results provide a framework to investigate the effects of disorder due to interacting impurities at experimentally relevant surface coverages.

  7. Influence of impurities on the solid-solid phase transitions in zirconium

    SciTech Connect

    Rigg, Paulo A; Greeff, Carl W; Gray, George T., III; Knudson, Marcus D

    2009-08-04

    In an effort to better understand the influence of impurities on the solid-solid phase transitions in Group IVb metals, experiments have been carried out on polycrystalline zirconium samples using plate impact and isentropic loading techniques. Samples with three levels of impurities were shock-loaded using both gas and powder-driven guns and isentropically loaded using magnetic drive (Sandia's Z-Machine) to determine the properties and characteristics of both the {alpha} {yields} {omega} and {omega} {yields} {beta} transitions.

  8. Effect of impurity doping concentration on solar cell output

    NASA Technical Reports Server (NTRS)

    Iles, P. A.; Soclof, S. I.

    1975-01-01

    Experimental measurements were made of solar cell and related photovoltaic parameters for silicon with high concentrations of dopant impurities. The cell output peaked for doping levels around 10 to the 17th power per cu cm. Independent measurements of diffusion length and open circuit voltage at high doping levels showed severe reductions at concentrations above 10 to the 18th power per cu cm. Theoretical reasons are given to explain these reductions. Indication is given of the problems requiring solution before increased cell output can be achieved at high doping levels.

  9. Influence of magnetic shear on impurity transport

    SciTech Connect

    Nordman, H.; Fueloep, T.; Candy, J.; Strand, P.; Weiland, J.

    2007-05-15

    The magnetic shear dependence of impurity transport in tokamaks is studied using a quasilinear fluid model for ion temperature gradient (ITG) and trapped electron (TE) mode driven turbulence in the collisionless limit and the results are compared with nonlinear gyrokinetic results using GYRO [J. Candy and R. E. Waltz, J. Comput. Phys 186, 545 (2003)]. It is shown that the impurity transport is sensitive to the magnetic shear, in particular for weak, negative, and large positive shear where a strong reduction of the effective impurity diffusivity is obtained. The fluid and gyrokinetic results are in qualitative agreement, with the gyrokinetic diffusivities typically a factor 2 larger than the fluid diffusivities. The steady state impurity profiles in source-free plasmas are found to be considerably less peaked than the electron density profiles for moderate shear. Comparisons between anomalous and neoclassical transport predictions are performed for ITER-like profiles [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)].

  10. DIVIMP Modeling of Impurity Transport in EAST

    NASA Astrophysics Data System (ADS)

    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.

  11. Numerical Studies of Impurities in Fusion Plasmas

    DOE R&D Accomplishments Database

    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.

  12. Impurity induced resistivity upturns in underdoped cuprates

    NASA Astrophysics Data System (ADS)

    Das, Nabyendu; Singh, Navinder

    2016-01-01

    Impurity induced low temperature upturns in both the ab-plane and the c-axis dc-resistivities of cuprates in the pseudogap state have been observed in experiments. We provide an explanation of this phenomenon by incorporating impurity scattering of the charge carriers within a phenomenological model proposed by Yang, Rice and Zhang. The scattering between charge carriers and the impurity atom is considered within the lowest order Born approximation. Resistivity is calculated within Kubo formula using the impurity renormalized spectral functions. Using physical parameters for cuprates, we describe qualitative features of the upturn phenomena and its doping evolution that coincides with the experimental findings. We stress that this effect is largely due to the strong electronic correlations.

  13. Single impurity in ultracold Fermi superfluids

    SciTech Connect

    Jiang Lei; Baksmaty, Leslie O.; Pu, Han; Hu Hui; Chen Yan

    2011-06-15

    The role of impurities as experimental probes in the detection of quantum material properties is well appreciated. Here we study the effect of a single classical magnetic impurity in trapped ultracold Fermi superfluids. Depending on its shape and strength, a magnetic impurity can induce single or multiple midgap bound states in a superfluid Fermi gas. The multiple midgap states could coincide with the development of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase within the superfluid. As an analog of the scanning tunneling microsope, we propose a modified rf spectroscopic method to measure the local density of states which can be employed to detect these states and other quantum phases of cold atoms. A key result of our self-consistent Bogoliubov-de Gennes calculations is that a magnetic impurity can controllably induce an FFLO state at currently accessible experimental parameters.

  14. Elemental impurity analysis of mercuric iodide by ICP/MS

    SciTech Connect

    Cross, E.S.; Mroz, E.; Olivares, J.A.

    1994-06-01

    A method has been developed to analyze mercuric iodide (HgI{sub 2}) for elemental contamination using Inductively Coupled Plasma/Mass Spectroscopy (ICP/MS). This paper discusses the ICP/MS method, the effectiveness of purification schemes for removing impurities from HgI{sub 2}, as well as preliminary correlations between HgI{sub 2} detector performance and elemental contamination levels. The purified HgI{sub 2} is grown into a single crystal by physical vapor transport. The crystal are cut into slices and they are fabricated into room temperature radiation detectors and photocells. Crystals that produce good resolution gamma detector do not necessarily make good resolution photocells or x-ray detectors. Many factors other than elemental impurities may contribute to these differences in performance.

  15. Effects of Impurities on Alumina-Niobium InterfacialMicrostructures

    SciTech Connect

    McKeown, Joseph T.; Sugar, Joshua D.; Gronsky, Ronald; Glaeser,Andreas M.

    2005-06-20

    Optical microscopy, scanning electron microscopy, and transmission electron microscopy were employed to examine the interfacial microstructural effects of impurities in alumina substrates used to fabricate alumina-niobium interfaces via liquid-film-assisted joining. Three types of alumina were used: undoped high-purity single-crystal sapphire; a high-purity, high-strength polycrystalline alumina; and a lower-purity, lower-strength polycrystalline alumina. Interfaces formed between niobium and both the sapphire and high-purity polycrystalline alumina were free of detectable levels of impurities. In the lower-purity alumina, niobium silicides were observed at the alumina-niobium interface and on alumina grain boundaries near the interface. These silicides formed in small-grained regions of the alumina and were found to grow from the interface into the alumina along grain boundaries. Smaller silicide precipitates found on grain boundaries are believed to form upon cooling from the bonding temperature.

  16. Precipitating Chromium Impurities in Silicon Wafers

    NASA Technical Reports Server (NTRS)

    Salama, A. M.

    1982-01-01

    Two new treatments for silicon wafers improve solar-cell conversion efficiency by precipitating electrically-active chromium impurities. One method is simple heat treatment. Other involves laser-induced damage followed by similar heat treatment. Chromium is one impurity of concern in metallurgical-grade silicon for solar cells. In new treatment, chromium active centers are made electrically inactive by precipitating chromium from solid solution, enabling use of lower grade, lower cost silicon in cell manufacture.

  17. Role of impurities in fusion plasmas

    SciTech Connect

    Tokar, M. Z.

    2008-10-15

    The role of impurity at the plasma edge of fusion devices is considered by analysing the influence on radiation losses and anomalous transport of particle and energy. The conditions critical for the development of radiative instabilities leading to the formation of detachment and MARFE and those necessary for the creation of a stable radiating edge, protecting the wall elements from intensive heat loads, are analyzed. Mechanisms responsible for anomalous transport suppression with impurity seeding are elucidated.

  18. Ultrashort pulses in graphene with Coulomb impurities

    NASA Astrophysics Data System (ADS)

    Konobeeva, N. N.; Belonenko, M. B.

    2016-06-01

    We have investigated the propagation of an electromagnetic field in graphene with impurities, including the two-dimensional case. The spectrum of electrons for the graphene subsystem is taken from a model that takes into account Coulomb impurities. Based on Maxwell's equations, we have obtained an effective equation for the vector potential of the electromagnetic field. It has been revealed that the pulse shape depends on free parameters.

  19. Method of removing phosphorus impurities from yellowcake

    SciTech Connect

    Brown, R.A.; Winkley, D.C.

    1983-04-05

    PhospHorus impurities are removed from yellowcake by dissolving it in hydrochloric or sulfuric acid to a U/sub 3/O/sub 88/ assay of at least 150 g/l at a pH of 2; precipitating uranium peroxide W hydrogen peroxide while keeping the pH between 2.2 and 2.6 and recovering the uranium peroxide from the phosphorus impurities remaining in solution.

  20. Deep-level transient spectroscopy of low-free-carrier-concentration n-GaN layers grown on freestanding GaN substrates: Dependence on carbon compensation ratio

    NASA Astrophysics Data System (ADS)

    Tanaka, Takeshi; Shiojima, Kenji; Mishima, Tomoyoshi; Tokuda, Yutaka

    2016-06-01

    Electron traps in n-GaN layers with a relatively low-free-carrier-concentration of approximately 1 × 1016 cm‑3 were characterized by deep-level transient spectroscopy. Sample layers were grown by metal organic chemical vapor deposition with a thickness of 12 µm on freestanding GaN substrates, and were doped with both silicon and carbon. The measurement results showed a reduction in the density of carbon-related electron traps at an energy level of E C ‑0.40 eV in GaN on GaN samples, compared with GaN on SiC samples. It was also observed that the doping of carbon significantly suppressed electron traps at E C ‑0.61 eV, which was associated with the nitrogen antisite. Consequently, the possibility of minimizing all of the electron traps located between E C ‑0.19 and ‑0.89 eV in n-GaN was demonstrated by controlling the carbon doping in the nitrogen site.

  1. Deep-level Transient Spectroscopy of GaAs/AlGaAs Multi-Quantum Wells Grown on (100) and (311)B GaAs Substrates

    PubMed Central

    2010-01-01

    Si-doped GaAs/AlGaAs multi-quantum wells structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates have been studied by using conventional deep-level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques. One dominant electron-emitting level is observed in the quantum wells structure grown on (100) plane whose activation energy varies from 0.47 to 1.3 eV as junction electric field varies from zero field (edge of the depletion region) to 4.7 × 106 V/m. Two defect states with activation energies of 0.24 and 0.80 eV are detected in the structures grown on (311)B plane. The Ec-0.24 eV trap shows that its capture cross-section is strongly temperature dependent, whilst the other two traps show no such dependence. The value of the capture barrier energy of the trap at Ec-0.24 eV is 0.39 eV. PMID:21170404

  2. Transport of Impurity Ions in the Wendelstein 7-AS Stellarator Plasma

    SciTech Connect

    Burhenn, Rainer; Baldzuhn, Juergen; Beidler, Craig; Brakel, Rudolf; Ehmler, Hartmut; Giannone, Louis; Grigull, Peter; Hirsch, Matthias; Knauer, Jens; Krychowiak, Maciej; Maassberg, Henning; McCormick, Kent; Pasch, Ekkehard; Weller, Arthur; Ida, Katsumi

    2006-01-15

    The impact of global plasma parameters on impurity transport in the stellarator W7-AS was investigated by laser blow-off technique. Both, density and heating power were identified to have a strong influence on impurity confinement {tau}{sub I} {approx} n{sub e}{sup 1.2}/P{sub ECRH}{sup 0.8}. In spite of stationary conditions at lower densities, an increasing trend for accumulation was observed at plasma densities beyond 5{center_dot}1019 m-3 due to reduction of the diffusion coefficients. Up to densities of at least 9{center_dot}1019 m-3, launching of electron cyclotron resonance heating (ECRH) power of 1.2 MW is able to counteract the impurity accumulation by deterioration of the impurity confinement with heating power according to the scaling law as given above. In neutral beam injection (NBI) heated plasmas at densities higher than 1{center_dot}1020m-3, long confinement times were observed, often accompanied by loss of density control and degradation of plasma energy due to increasing radiation losses. The installation of island divertor allowed a general extension of the range of accessible densities up to 4{center_dot}1020m-3: beyond a certain power-dependent threshold density (1.5-2.1{center_dot}1020m-3), the plasma enters the High Density H-mode (HDH) regime and the impurity confinement time drops to values comparable to the energy confinement time. High density plasmas could be sustained quasi-stationary with a low level of impurity radiation. The favourable impurity behavior goes along with a reduction of the inward impurity convection in the core plasma and possible changes in the edge transport. For the characterization of the general impurity behavior in W7-AS plasmas the usual transport models for axisymmetric devices are not sufficient and additional stellarator specific processes have to be considered.

  3. Mechanisms of impurity diffusion in rutile

    SciTech Connect

    Peterson, N.L.; Sasaki, J.

    1984-01-01

    Tracer diffusion of /sup 46/Sc, /sup 51/Cr, /sup 54/Mn, /sup 59/Fe, /sup 60/Co, /sup 63/Ni, and /sup 95/Zr, was measured as functions of crystal orientation, temperature, and oxygen partial pressure in rutile single crystals using the radioactive tracer sectioning technique. Compared to cation self-diffusion, divalent impurities (e.g., Co and Ni) diffuse extremely rapidly in TiO/sub 2/ and exhibit a large anisotropy in the diffusion behavior; divalent-impurity diffusion parallel to the c-axis is much larger than it is perpendicular to the c-axis. The diffusion of trivalent impurity ions (Sc and Cr) and tetravalent impurity ions (Zr) is similar to cation self-diffusion, as a function of temperature and of oxygen partial pressure. The divalent impurity ions Co and Ni apparently diffuse as interstitial ions along open channels parallel to the c-axis. The results suggest that Sc, Cr, and Zr ions diffuse by an interstitialcy mechanism involving the simultaneous and cooperative migration of tetravalent interstitial titanium ions and the tracer-impurity ions. Iron ions diffused both as divalent and as trivalent ions. 8 figures.

  4. Improved analysis of impurity transport coefficient profiles

    NASA Astrophysics Data System (ADS)

    Chilenski, M. A.; Greenwald, M.; Marzouk, Y.; Howard, N. T.; Rice, J.; White, A. E.

    2015-11-01

    Work is underway on the development of a novel technique to estimate impurity transport coefficient profiles and their uncertainties. Inference of impurity transport coefficient profiles using x-ray imaging crystal spectroscopy measurements of laser blow-off impurity injections has played a key role in the validation of gyrokinetic simulations of impurity transport in L-mode (Howard et al. 2012, Nucl. Fusion 52, 063002). Recent attempts to apply the existing methodology for interpreting such measurements to H-mode have failed to yield reliable estimates, however. This failure exposes key issues regarding the uniqueness of the solution and the rigorous estimation of the uncertainty. A new approach is under development which uses a combination of Markov chain Monte Carlo (MCMC) and global optimization techniques to estimate impurity transport coefficient profiles even when there are multiple possible solutions. This poster will present the new methodology in detail and will show preliminary results from applying it to Alcator C-Mod data. This new approach will enable us to test the existing understanding of L-mode impurity transport and to move towards multichannel validation of gyrokinetic simulations of H-modes. Supported by USDOE award DE-FC02-99ER54512.

  5. The effect of elemental and hydrocarbon impurities on mercuric iodide gamma ray detector performance

    NASA Astrophysics Data System (ADS)

    Cross, Eilene S.; Buffleben, George; Soria, Ed; James, Ralph; Schieber, Michael; Natarajan, Raj; Gerrish, Vern

    Mercuric iodide is a room temperature semiconductor material that is used for gamma ray and x-ray radiation detection. Mercuric iodide is synthesized from mercuric chloride and potassium iodide and is then purified by a series of melts and sublimation steps and by zone refining. The mercuric iodide is grown into crystals and platelets and then fabricated into detectors. Elemental contamination may be a determining factor in the performance of these detectors. These contaminates may be present in the starting material or may be introduced during, or be unaffected by, the purification, growth or fabrication steps. Methods have been developed for the analysis of trace levels of elemental contamination. Inductively Coupled Plasma/Mass Spectroscopy (ICP/MS), Inductively Coupled Plasma/Optical Emission Spectroscopy (ICP/OES) and Gas Chromatography/Mass Spectroscopy (GC/MS) are used to determine sub ppm levels of many trace elemental impurities. Trace levels of many elemental impurities in the raw mercuric iodide are significantly reduced during the purification and zone refining processes. Though the levels of impurities are reduced, poor performing mercuric iodide detectors have contamination levels remaining or reintroduced which are higher for Ag, Al, Ca, Cu, Mg, Mn, Na, Pb and Zn than detectors with good gamma ray response. This paper will discuss the analytical methodology, the effects of purification on impurity levels, and the correlation between detector performance and impurity levels.

  6. Intrinsic point defects and their interaction with impurities in mono-crystalline zinc oxide

    NASA Astrophysics Data System (ADS)

    Svensson, Bengt G.

    2015-03-01

    Zinc oxide (ZnO) is a direct and wide band-gap semiconductor with several attractive features, like an exciton binding energy of ~ 60 meV, for light emitting devices, photovoltaics and spintronics. In the past decade, ZnO has received tremendous attention by the semiconductor physics community and many challenging issues have been addressed, especially the ``native'' n-type conductivity, the role of intrinsic point defects, and the realization of reproducible p-type doping. The latter is, indeed, decisive for a true breakthrough of ZnO-based optoelectronics. In this contribution, recent progress in our understanding of the interaction between intrinsic point defects and impurities in ZnO will be discussed. Aluminum (Al) is often introduced intentionally to accomplish high n-type conductivity since Al on Zn-site (AlZn) acts as a shallow donor. However, AlZn was recently found to react strongly with Zn vacancies (VZn) and the resulting complex (AlZn-VZn) is energetically favorable. The AlZn-VZn complex is a deep acceptor limiting the n-type doping efficiency and this finding is expected to hold in general for complexes between VZn and group-III elements. Further, implantation of self-ions (Zn and O) has been demonstrated to affect radically the balance of intrinsic point defects where an excess of Zn interstitials gives rise to a dramatic depletion of residual Li impurities on Zn-site (LiZn) whilst the opposite holds for an excess of O interstitials. In fact, this behavior appears to be of general validity and Li depletion occurs for a wide variety of implanted elements incorporated into the Zn sub-lattice while Li pile-up occurs for elements residing on O-site. Finally, the most prominent deep-level defect in ZnO, labelled E3, will be shown to involve hydrogen. E3 exists in most ZnO materials, irrespective of the growth method used, and evidence for a center formed by reaction between interstitial hydrogen and primary defects on the Zn sub-lattice will be given.

  7. Coseismic and aseismic deformations of the rock mass around deep level mining in South Africa - Joint South African and Japanese study

    NASA Astrophysics Data System (ADS)

    Milev, A. M.; Yabe, Y.; Naoi, M. M.; Nakatani, M.; Durrheim, R. J.; Ogasawara, H.; Scholz, C. H.

    2010-12-01

    Two underground sites in a deep level gold mine in South Africa were instrumented by the Council for Scientific and Industrial Research (CSIR) with tilt meters and seismic monitors. One of the sites was also instrumented by JApanese-German Underground Acoustic emission Research in South Africa (JAGUARS) with a small network, approx. 40 m span, of eight Acoustic Emission (AE) sensors. The rate of tilt, defined as quasi-static deformations, and the seismic ground motion, defined as dynamic deformations, were analysed in order to understand the rock mass behavior around deep level mining. In addition the high frequency AE events recorded at hypocentral distances of about 50m were analysed. This was the first implementation of high frequency AE events at such a great depth (3300m below the surface). A good correspondence between the dynamic and quasi-static deformations was found. The rate of coseismic and aseismic tilt, as well as seismicity recorded by the mine seismic network, are approximately constant until the daily blasting time, which takes place from about 19:30 until shortly before 21:00. During the blasting time and the subsequent seismic events the coseismic and aseismic tilt shows a rapid increase indicated by a rapid change of the tilt during the seismic event. Much of the quasi-static deformation, however, occurs independently of the seismic events and was described as ‘slow’ or aseismic events. During the monitoring period a seismic event with MW 1.9 (2.1) occurred in the vicinity of the instrumented site. This event was recorded by both the CSIR integrated monitoring system and JAGUARS acoustic emotion network. The tilt changes associated with this event showed a well pronounced after-tilt. More than 21,000 AE aftershocks were located in the first 150 hours after the main event. Using the distribution of the AE events the position of the fault in the source area was successfully delineated. The distribution of the AE events following the main shock

  8. Turbulent and neoclassical impurity transport in tokamak plasmas

    SciTech Connect

    Fueloep, T.; Nordman, H.

    2009-03-15

    Impurity particle transport in tokamaks is studied using an electrostatic fluid model for main ion and impurity temperature gradient (ITG) mode and trapped electron (TE) mode turbulence in the collisionless limit and neoclassical theory. The impurity flux and impurity density peaking factor obtained from a self-consistent treatment of impurity transport are compared and contrasted with the results of the often used trace impurity approximation. Comparisons between trace and self-consistent turbulent impurity transport are performed for ITER-like profiles. It is shown that for small impurity concentrations the trace impurity limit is adequate if the plasma is dominated by ITG turbulence. However, in case of TE mode dominated plasmas the contribution from impurity modes may be significant, and therefore a self-consistent treatment may be needed.

  9. Cr impurity-induced electronic states in ZnTe(110) surface

    NASA Astrophysics Data System (ADS)

    Kanazawa, Ken; Nishimura, Taku; Yoshida, Shoji; Shigekawa, Hidemi; Kuroda, Shinji

    2015-08-01

    The impurity states of Cr atoms, which substituted Zn sites in the topmost layer of a p-type ZnTe(110) surface, were investigated by scanning tunneling microscopy/spectroscopy (STM/STS) and we firstly observed Cr-induced impurity states in the energy gap region of the host ZnTe including the unoccupied states by STS. Furthermore, we compared the observed energy levels and spatial distributions of the local density of states with those in the previous theoretical study [Katayama-Yoshida et al., Phys. Status Solidi A 204, 15 (2007)] and successfully identified the impurity states as the respective spin-polarized impurity states predicted by the theoretical study.

  10. Impurity segregation in zone-refined precursors for crystalline halide scintillators

    NASA Astrophysics Data System (ADS)

    Swider, S.; Lam, S.; Motakef, S.; Donohoe, E.; Coers, L.; Taylor, S.; Spencer, S.

    2015-06-01

    Successful growth of halide scintillator crystals depends on a supply of ultra-high purity (UHP) precursor materials. Metallic interstitials and substitutions may provide traps that quench luminescence. Oxygen impurities can create competing compounds within a matrix, such as oxyhalides, that disrupt crystallinity and nucleate cracks. Using mass spectroscopy and oxygen combustion analysis, we analyzed impurities in SrI2, EuI2, and YCl3 precursors before and after zone refining. The data show most alkali and alkali earth impurities segregated easily. However, with the exception of iron, many transition metals were incorporated into the solid. Reliable oxygen measurements proved difficult to achieve. Additional oxygen was measured in nitrates and sulfates, via ion chromatography. Zone refining reduced the overall impurity content, but levels remained above a 10 ppm target.

  11. Human adipocytes from the subcutaneous superficial layer have greater adipogenic potential and lower PPAR-γ DNA methylation levels than deep layer adipocytes.

    PubMed

    Kosaka, Kentaro; Kubota, Yoshitaka; Adachi, Naoki; Akita, Shinsuke; Sasahara, Yoshitaro; Kira, Tomoe; Kuroda, Masayuki; Mitsukawa, Nobuyuki; Bujo, Hideaki; Satoh, Kaneshige

    2016-08-01

    Human subcutaneous fat tissue consists of two layers, superficial adipose tissue (SAT) and deep adipose tissue (DAT). Some recent reports suggest that a disproportionate accumulation of DAT is related to obesity-associated metabolic complications. However, the differences in adipocyte function between SAT and DAT are unclear. To clarify the differences in human adipocyte characteristics between SAT and DAT, human ceiling culture-derived proliferative adipocytes (ccdPAs) were primary cultured from SAT and DAT of three lean female patients. Differences in adipogenic differentiation potential and sensitivity to exogenous adipogenic factors were examined. Epigenetic modification of the CpG island DNA methylation levels of genes related to adipogenesis was measured. In histological analyses, the mean adipocyte size in SAT was significantly larger than that in DAT (8,741 ± 416 vs. 7,732 ± 213 μm(2), P < 0.05). Primary cultured adipocytes from SAT showed significantly greater adipogenesis than did those of DAT. Sensitivity to partial adipogenic stimulation was significantly different between ccdPAs of SAT and DAT. Peroxisome proliferator-activated receptor-γ (PPAR-γ) protein expression and leptin protein secretion from ccdPAs were significantly higher in SAT than DAT. DNA methylation levels of PPAR-γ were significantly lower in ccdPAs of SAT than DAT. Adipocyte size was larger in SAT than DAT in vivo. This is consistent with the findings of an in vitro study that, compared with ccdPAs in DAT, ccdPAs in SAT have higher adipogenic potential and lower DNA methylation levels of PPAR-γ. PMID:27251439

  12. Nitrogen Impurity Gettering in Oxide Dispersion Ductilized Chromium

    SciTech Connect

    Brady, Michael P; Anderson, Ian M; Weaver, Mark; Meyer III, Harry M; Walker, Larry R; Miller, Michael K; Larson, David James; Wright, Ian G; Sikka, Vinod K; Rar, Andrei; Pharr, George Mathews; Keiser, James R; Walls, Claudia Alexandra

    2003-01-01

    Work by Scruggs in the 1960s demonstrated that tensile ductility could be achieved at room temperature in powder metallurgically-produced Cr alloyed with MgO. During consolidation, much of the MgO converted to the MgCr{sub 2}O{sub 4} spinel phase, which was hypothesized to getter nitrogen from the Cr, rendering it ductile. We have duplicated this effect, achieving room temperature tensile elongations of 4% for hot-pressed Cr-6MgO-(0-1)Ti (wt.%) and 10% for hot-pressed and extruded Cr-6MgO-0.75Ti. Direct incorporation of nitrogen into the MgCr{sub 2}O{sub 4} phase was not detected; however, impurities, particularly nitrogen and sulfur, were observed to segregate to and/or precipitate at interfaces between the MgO/MgCr{sub 2}O{sub 4} phases and the Cr matrix. Exploratory studies of other non-spinel forming oxide dispersions (La{sub 2}O{sub 3}, TiO{sub 2} and Y{sub 2}O{sub 3}) showed a similar pattern of impurity segregation/precipitation, suggesting that there is nothing unique about spinel dispersions in Cr with regards to impurities. However, none of these other dispersions resulted in similar levels of tensile elongation.

  13. Impurity effects on polarized magnetoexcitons with ring-like confinement.

    NASA Astrophysics Data System (ADS)

    Dias da Silva, Luis G.; Ulloa, Sergio E.; Govorov, Alexander O.

    2004-03-01

    We study the role of impurity scattering on the photoluminescence(PL) emission of polarized magnetoexcitons. We consider the case where both the electron and hole are confined on a ring structure(Quantum Rings) and also type-II Quantum Dot excitons, where the electron is spatially separated from the hole. Despite their neutral character, excitons exhibit strong modulation effects on the energy and oscillator strength in the presence of magnetic fields [1]. The presence of scattering impurities enhances the PL intensity on otherwise "dark" magnetic field windows and non-zero PL emission appears for a wide magnetic field range even at zero temperature. For higher temperatures, impurity-induced anticrossings on the excitonic energy levels lead to peaks and valleys on the PL intensity as function of magnetic field. Such behavior is absent on clean systems and could account for some unexpected features on recent experimental results [2]. Supported by the US DOE and FAPESP [1] A.O. Govorov et al. Phys. Rev. B 66 081309 (2002); A.O. Govorov et al. Physica E 13, 297 (2002). [2] E. Ribeiro, G. Medeiros-Ribeiro, W. Carvalho Jr., cond-mat 0304092

  14. Petrology and Sm-Nd dating of the Genina Gharbia Alaskan-type complex (Egypt): Insights into deep levels of Neoproterozoic island arcs

    NASA Astrophysics Data System (ADS)

    Helmy, Hassan M.; Abd El-Rahman, Yasser M.; Yoshikawa, Masako; Shibata, Tomoyuki; Arai, Shoji; Tamura, Akihiro; Kagami, Hiroo

    2014-06-01

    The deep levels of Neoproterozoic island arcs are poorly known due to limited accessibility. The Genina Gharbia Alaskan-type complex (south Eastern Desert, Egypt) is the remains of a magma chamber that crystallized at the base (crust-mantle boundary) of a mature Neoproterozoic island arc. The rock assemblage comprises hornblende-bearing harzburgite, lherzolite, pyroxenite, norite and gabbro. All lithologies show cumulus texture with evidence of extensive cumulus mineral-melt interactions. Clinopyroxenes from all lithologies have similar rare earth element (REE) patterns with slight medium-rare earth element (MREE) enrichment. Hornblendes are slightly enriched in MREE and light rare earth elements (LREE). Island arc signatures are indicated by high contents of large ion-lithophile elements and low concentration of high field-strength elements. Positive initial εNd (+ 5.7 to + 7.0) and Nd model ages (963 ± 81 Ma) are consistent with the Genina Gharbia magma being extracted from a depleted mantle source. Modeling of estimated parental magma indicates 10% partial melting of a 90% depleted mantle source with a 10% (MORB + sediments)-derived fluid, commencing in the spinel stability field (< 85 km). Relative to Phanerozoic arcs, the Neoproterozoic arcs were more hydrous, had low oxidation states and probably lasted shorter time to build-up. The hydrous nature of the sub-Arabian-Nubian Shield mantle and the long-life of the arcs are among reasons responsible for the vast crustal growth during the Pan-African Orogeny throughout the Gondwana.

  15. Potential interactions between different levels of cosmic radiation and their influence on the assessment of radiation risk during a manned deep space mission

    NASA Astrophysics Data System (ADS)

    Mortazavi, S.

    Despite the fact that galactic cosmic rays is believed to be isotropic throughout interstellar space, solar flares and coronal mass ejections can produce sudden and dramatic increase in flux of particles and expose the astronauts to transient high levels of ionizing radiation Furthermore, astronauts receive extra doses in the course of their extravehicular activities. It has been estimated that exposure to unpredictable extremely large solar particle events would kill the astronauts without massive shielding in interplanetary space. It is also generally believed that the biological effects of small doses of ionizing radiation may lie below the detection limits. However, potential interactions between a small dose and a subsequent high dose are still a black box that its output may be much different from the effect of a high dose alone. Potential interactions from low and high doses can either be a simple additivity, adaptive responses or synergistic effects. Significant adaptive response has been demonstrated in humans after exposure to high levels of natural radiation. Furthermore, non-linear behavior has been observed for cosmic radiation. Recent long-term follow-up studies as well as studies performed on twins show that in contrast to early reports, the type of interaction is determined by intrinsic factors such as genetic constitution of each individual. Despite that these responses for low- LET radiations (mainly photons and beta particles) are documented to some extent, there are no data on possible interactions of high-energy protons or high-LET heavy ions. The assessment of potential interactions between chronic low doses and acute high doses of high energy protons and heavy ions will be of importance in practical radiation protection of cosmonauts during a deep space mission.

  16. Methylenetetrahydrofolate reductase (MTHFR-677 and MTHFR-1298) genotypes and haplotypes and plasma homocysteine levels in patients with occlusive artery disease and deep venous thrombosis.

    PubMed

    Spiroski, Igor; Kedev, Sashko; Antov, Slobodan; Arsov, Todor; Krstevska, Marija; Dzhekova-Stojkova, Sloboda; Bosilkova, Gordana; Kostovska, Stojanka; Trajkov, Dejan; Petlichkovski, Aleksandar; Strezova, Ana; Efinska-Mladenovska, Olivija; Spiroski, Mirko

    2008-01-01

    The aim was to investigate different genotypes and haplotypes of methylenetetrahydrofolate reductase (MTHFR-677, -1298) and plasma concentration of total homocysteine (tHcy) in Macedonian patients with occlusive artery disease (OAD) and deep venous thrombosis (DVT). Investigated groups consists of 80 healthy, 74 patients with OAD, and 63 patients with DVT. Plasma tHcy was measured with Microplate Enzyme Immunoassay. Identification of MTHFR genotypes and haplotypes was done with CVD StripAssay. The probability level (P-value) was evaluated by the Student's t-test. Plasma concentration of tHcy in CC and CT genotypes of MTHFR C677T was significantly increased in patients with OAD and in patients with DVT. Plasma concentration of tHcy in AC genotype of MTHFR A1298C was increased in patients with OAD and in patients with DVT. Plasma concentration of tHcy was significantly increased in AA genotype of patients with OAD, but not in patients with DVT. We found a significant increase of plasma tHcy in patients with OAD in comparison with healthy respondents for normal:heterozygote (CC:AC), heterozygote:normal (CT:AA), and heterozygote:heterozygote (CT:AC) haplotypes. Plasma concentration of tHcy in patients with DVT in comparison with healthy respondents was significantly increased for normal:normal (CC:AA), normal heterozygote (CC:AC), and heterozygote:heterozygote (CT:AC) haplotypes. We conclude that MTHFR C677T and MTHFR A1289C genotypes and haplotypes are connected with tHcy plasma levels in Macedonian patients with OAD and DVT. PMID:18800176

  17. The Bremen ocean bottom tiltmeter (OBT) - a technical article on a new instrument to monitor deep sea floor deformation and seismicity level

    NASA Astrophysics Data System (ADS)

    Fabian, Marcus; Villinger, Heinrich

    2007-03-01

    The Bremen ocean bottom tiltmeter is a new 6000 m-depth deep sea instrument for autonomous observation of sea floor tilt with signal periods longer than 7.5 s. The instrument also records vertical acceleration in the frequency range from DC to 1 Hz. The tiltmeter has an Applied Geomechanics Inc. 756 wide angle biaxial bubble tilt sensor with a resolution of 1.0μ rad (0.2 arc second). A Kistler Corp. MEMS accelerometer of type Servo K-Beam 8330A2.5 with about 10-5m/s2 resolution is used for the acceleration measurements. An Oceanographic Embedded Systems AD24 24 bit Sigma-Delta converter, which is controlled by a low-power Persistor Inc. embedded computer system of type CF 2, samples the data. The duration of tiltmeter operation is more than one year, which is controlled by the battery life. In our design the tiltmeter does not need active leveling devices, i.e., servo motors or other moving components to adjust sensors or frame. We designed the instrument for deployments by means of a remote operated vehicle. Since May 2005 the Bremen ocean bottom tiltmeter has recorded sea floor deformation and seismicity level in the Logatchev hydrothermal vent field, Mid-Atlantic Ridge. The tiltmeter is a part of the monitoring system of project ‘Logatchev Long-Term Environmental Monitoring,’ called LOLEM, of the German research program with the name ‘Schwerpunktprogramm 1144: Vom Mantel zum Ozean.’

  18. Rydberg Impurity Probes in Ultracold Gases

    NASA Astrophysics Data System (ADS)

    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.

  19. Modeling of Carbon Impurity Anomalous Transport

    NASA Astrophysics Data System (ADS)

    Stamm, Roland; Voitsekhovitch, Irina; Benkadda, Sadri; Beyer, Peter; Koubiti, Mohamed; Marandet, Yannick; Godbert-Mouret, Laurence; Bateman, Glenn; Kritz, Arnold; Pankin, Andre

    2001-10-01

    An improvement of plasma confinement by impurity seeding has been observed on different Tokamak. The understanding of the physics of the impurity transport is an important step towards the control of the plasma confinement in such regimes. Different physical mechanisms of the anomalous transport of carbon impurity and their impact on the evolution of the scenario of a tokamak discharge are analyzed in this work. This is done by using a self-consistent modeling of thermal electron and ion energy, and main ion and carbon impurity content with the multi-mode model taking into account the contributions from different types of plasma instabilities [1]. This study has been performed for the medium size tokamak with a central heating of the electron and ion species, and with both central (NBI) and wall particle source. The L-mode scenario and the scenario with an improved particle and energy confinement due to the reversed q-profile has been analyzed and the influence of the carbon impurity on the plasma evolution has been investigated by varying the starting time and the magnitude of the carbon influx. The effect of the main ion dilution on the growth rate as well as the effect of radiative cooling at the plasma edge on the power balance are analyzed under different conditions. 1. Bateman G., et al., Phys. Plasmas, 5 (1998) 1793

  20. Impurities in the Lithium Tokamak Experiment

    NASA Astrophysics Data System (ADS)

    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.

  1. Gettering of metal impurities in silicon

    SciTech Connect

    Schroeter, W.; Spiecker, E.; Apel, M.

    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.

  2. Deep Earthquakes.

    ERIC Educational Resources Information Center

    Frohlich, Cliff

    1989-01-01

    Summarizes research to find the nature of deep earthquakes occurring hundreds of kilometers down in the earth's mantle. Describes further research problems in this area. Presents several illustrations and four references. (YP)

  3. An investigation of impurity centers in semiconductors of variable composition. Part 1: General theory and some applications

    NASA Technical Reports Server (NTRS)

    Vonroos, O. H.

    1982-01-01

    A theory of deep point defects imbedded in otherwise perfect semiconductor crystals is developed with the aid of pseudopotentials. The dominant short-range forces engendered by the impurity are sufficiently weakened in all cases where the cancellation theorem of the pseudopotential formalism is operative. Thus, effective-mass-like equations exhibiting local effective potentials derived from nonlocal pseudopotentials are shown to be valid for a large class of defects. A two-band secular determinant for the energy eigenvalues of deep defects is also derived from the set of integral equations which corresponds to the set of differential equations of the effective-mass type. Subsequently, the theory in its simplest form, is applied to the system Al(x)Ga(1-x)As:Se. It is shown that the one-electron donor level of Se within the forbidden gap of Al(x)Ga(1-x)As as a function of the AlAs mole fraction x reaches its maximum of about 300 meV (as measured from the conduction band edge) at the cross-over from the direct to the indirect band-gap at x = 0.44 in agreement with experiments.

  4. Estimated Tissue and Blood N2 Levels and Risk of Decompression Sickness in Deep-, Intermediate-, and Shallow-Diving Toothed Whales during Exposure to Naval Sonar

    PubMed Central

    Kvadsheim, P. H.; Miller, P. J. O.; Tyack, P. L.; Sivle, L. D.; Lam, F. P. A.; Fahlman, A.

    2012-01-01

    Naval sonar has been accused of causing whale stranding by a mechanism which increases formation of tissue N2 gas bubbles. Increased tissue and blood N2 levels, and thereby increased risk of decompression sickness (DCS), is thought to result from changes in behavior or physiological responses during diving. Previous theoretical studies have used hypothetical sonar-induced changes in both behavior and physiology to model blood and tissue N2 tension PN2, but this is the first attempt to estimate the changes during actual behavioral responses to sonar. We used an existing mathematical model to estimate blood and tissue N2 tension PN2 from dive data recorded from sperm, killer, long-finned pilot, Blainville’s beaked, and Cuvier’s beaked whales before and during exposure to Low- (1–2 kHz) and Mid- (2–7 kHz) frequency active sonar. Our objectives were: (1) to determine if differences in dive behavior affects risk of bubble formation, and if (2) behavioral- or (3) physiological responses to sonar are plausible risk factors. Our results suggest that all species have natural high N2 levels, with deep diving generally resulting in higher end-dive PN2 as compared with shallow diving. Sonar exposure caused some changes in dive behavior in both killer whales, pilot whales and beaked whales, but this did not lead to any increased risk of DCS. However, in three of eight exposure session with sperm whales, the animal changed to shallower diving, and in all these cases this seem to result in an increased risk of DCS, although risk was still within the normal risk range of this species. When a hypothetical removal of the normal dive response (bradycardia and peripheral vasoconstriction), was added to the behavioral response during model simulations, this led to an increased variance in the estimated end-dive N2 levels, but no consistent change of risk. In conclusion, we cannot rule out the possibility that a combination of behavioral and physiological responses to sonar

  5. The excited state dynamics of KLa(MoO{sub 4}){sub 2}:Pr{sup 3+}: From a case study to the determination of the energy levels of rare earth impurities relative to the bandgap in oxidising host lattices

    SciTech Connect

    Cavalli, Enrico Boutinaud, Philippe; Bettinelli, Marco; Dorenbos, Pieter

    2008-05-15

    The luminescence properties of KLa(MoO{sub 4}){sub 2} (KLM) single crystals doped with Pr{sup 3+} have been measured in the 10-600 K temperature range in order to investigate the mechanisms involved in the radiationless processes. At variance with previously studied scheelite-like molybdates activated with Pr{sup 3+}, no effects attributed to the formation of intervalence charge transfer states have been observed. The model proposed in order to account for this behaviour allows the determination of the energy of the Pr{sup 3+} levels relative to the valence and conduction bands of the host. This model has firstly been confirmed for Tb{sup 3+}-doped KLM, for which suitable experimental data are available, and then extended to the other rare earth ions on the basis of the systematic nature of the lanthanide energy levels properties. The obtained conclusions are finally supported in the light of the comparison with some other representative cases. - Graphical abstract: The study of the excited state dynamics of KLa(MoO{sub 4}){sub 2} single crystals doped with Pr{sup 3+} allows to determine the energies of the levels of the active ion relative to the valence and conduction bands of the host. This model has then been extended to the other rare earth ions on the basis of the systematic nature of the lanthanide energy levels properties.

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

    PubMed Central

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

    2013-01-01

    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. PMID:24192986

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

    NASA Astrophysics Data System (ADS)

    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.

  8. Identification, Characterization, Synthesis and Quantification of Related Impurities of Liguzinediol.

    PubMed

    Cheng, Dong; Zhou, Ying; Li, Wei; Shan, Chen-Xiao; Chai, Chuan; Cui, Xiao-Bing; Kang, Bi; Wang, Tian-Lin; Wen, Hong-Mei

    2015-09-01

    An HPLC method was employed to create an impurity profile for liguzinediol as an active pharmaceutical ingredient (API), which resulted in the identification of two related impurities. Therefore, in order to improve the quality control of the liguzinediol-API, we identified and then developed a method for quantifying the two impurities (impurity-1 and impurity-2) by LC-TOF-MS-MS and then chemically synthesized them for further studies. Based on spectral data from IR, MS, (1)H and (13)C NMR, the structures of impurity-1 and impurity-2 were characterized as 2-hydroxymethyl-3,6-dimethylpyrazine and 2-hydroxymethyl-3,5,6-trimethylpyrazine, respectively. We further validated the method according to the International Conference on Harmonization guidelines to demonstrate the sensitivity, precision, linearity, accuracy and stability of the method described. In addition, the potential mechanisms underlying formation of impurity-1 and impurity-2 in the liguzinediol-API are discussed in detail. PMID:25680683

  9. Impurity and particle control for INTOR

    SciTech Connect

    Post, D.

    1985-02-01

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

  10. On charged impurity structures in liquid helium

    NASA Astrophysics Data System (ADS)

    Pelmenev, A. A.; Krushinskaya, I. N.; Bykhalo, I. B.; Boltnev, R. E.

    2016-03-01

    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.

  11. Characteristics of impurity-induced pseudogap

    NASA Astrophysics Data System (ADS)

    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.

  12. Quantitative assessment of cumulative carcinogenic risk for multiple genotoxic impurities in a new drug substance.

    PubMed

    Bercu, Joel P; Hoffman, Wherly P; Lee, Cindy; Ness, Daniel K

    2008-08-01

    In pharmaceutical development, significant effort is made to minimize the carcinogenic potential of new drug substances (NDS). This involves appropriate genotoxicity and carcinogenicity testing of the NDS, and understanding the genotoxic potential of its impurities. Current available guidance recommends the use of the threshold of toxicological concern (TTC) for a single impurity where mutagenicity but no carcinogenicity information exists. Despite best efforts, the presence of more than one genotoxic impurity in an NDS may occur at trace levels. This paper repeats the analysis performed by others for a single genotoxic compound, but also uses statistical simulations to assess the impact on cancer risk for a mixture of genotoxic compounds. In summary, with the addition of multiple impurities all controlled to the TTC, an increase in cancer risk was observed. This increase is relatively small when considering the conservative assumptions of the TTC. If structurally similar compounds had an assumed strong correlation (+/-10-fold from the first randomly selected impurity) in cancer potency, the resulting cancer risk was not negatively impacted. Findings based on probabilistic analysis here can be very useful in making appropriate decisions about risk management of multiple genotoxic impurities measured in the final drug substance. PMID:18550240

  13. Theory of the electronic states and absorption spectrum of the LiCl:Ag+ impurity system

    NASA Astrophysics Data System (ADS)

    Jackson, Koblar A.; Lin, Chun C.

    1990-01-01

    The impurity absorption spectra of Ag+ and Cu+ impurities in alkali halide hosts show characteristically different features, despite the similar nature of the corresponding free ions. We use the self-interaction-corrected local-spin-density (SIC-LSD) theory to calculate the electronic structure of the ground state (4d) and the 5s and 5p excited states of the LiCl:Ag+ impurity ion. The method of linear combinations of atomic orbitals is used to determine the wave functions and energy levels. By comparing with previous calculations for LiCl:Cu+, we are able to attribute the differences in the d-->s and d-->p transitions in the ultraviolet spectra of these systems to the increased bonding between host crystal and impurity orbitals in LiCl:Ag+, due to the more extensive nature of the Ag+ 4d orbitals. A modification of the earlier SIC-LSD impurity-crystal procedure is introduced to treat the strongly mixed impurity states.

  14. Some aspects of selection of impurities improving photoelectric characteristics of chalcogenide vitreous semiconductors

    SciTech Connect

    Burdiyan, I. I.; Cosiuc, V. V. Pynzar', R. A.

    2008-02-15

    The effect of low concentrations of two groups of doping impurities (one group includes Sn, Pb, Dy, Ho, Y and the other group includes In, Cs, and Al) on photoelectric properties of As{sub 2}Se{sub 3} and (As{sub 2}S{sub 3}){sub 0.3}(As{sub 2}Se{sub 3}){sub 0.7} was investigated. Studies of spectral distributions of photoconductivity and optical absorption showed that there is a distinct increase in photoconductivity if the level of doping with elements of the first group is as high as 0.015%. Elements of the second group of impurities did not exert any significant effect on photoconductivity. The effect of impurities of the first group is attributed to occupation of vacant sites (formed as a result of removal of highly volatile Se and S atoms) by low concentrations of impurity atoms. The observed effect is related to the fact that substitutional atoms can preserve covalent bonds and to the small difference between atomic sizes and electron affinity for doping impurities and S and Se. Atoms of the second group of impurities lack these features.

  15. The physics of Kondo impurities in graphene.

    PubMed

    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

  16. The physics of Kondo impurities in graphene

    NASA Astrophysics Data System (ADS)

    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.

  17. Two-impurity helical Majorana problem

    NASA Astrophysics Data System (ADS)

    Eriksson, Erik; Zazunov, Alex; Sodano, Pasquale; Egger, Reinhold

    2015-02-01

    We predict experimentally accessible signatures for helical Majorana fermions in a topological superconductor by coupling to two quantum dots in the local moment regime (corresponding to spin-1 /2 impurities). Taking into account Ruderman-Kittel-Kasuya-Yosida interactions mediated by bulk and edge modes, where the latter cause a long-range antiferromagnetic Ising coupling, we formulate and solve the low-energy theory for this two-impurity helical Majorana problem. In particular, we show that the long-time spin dynamics after a magnetic field quench displays weakly damped oscillations with universal quality factor.

  18. Mapping itinerant electrons around Kondo impurities.

    PubMed

    Prüser, H; Wenderoth, M; Weismann, A; Ulbrich, R G

    2012-04-20

    We investigate single Fe and Co atoms buried below a Cu(100) surface using low temperature scanning tunneling spectroscopy. By mapping the local density of states of the itinerant electrons at the surface, the Kondo resonance near the Fermi energy is analyzed. Probing bulk impurities in this well-defined scattering geometry allows separating the physics of the Kondo system and the measuring process. The line shape of the Kondo signature shows an oscillatory behavior as a function of depth of the impurity as well as a function of lateral distance. The oscillation period along the different directions reveals that the spectral function of the itinerant electrons is anisotropic. PMID:22680744

  19. Observational study of rock mass response to mining induced seismic events and controlled blasting experiments at deep level gold mines in South Africa

    NASA Astrophysics Data System (ADS)

    Milev, A.; Durrheim, R. J.; Nakatani, M.; Yabe, Y.; Naoi, M. M.; Ogasawara, H.

    2012-12-01

    The strong ground motion generated by mining induced seismic events was studied to characterize the rock mass response and to estimate the site effect on the surface of the underground excavations. A stand-alone instruments, especially designed for recording strong ground motions, were installed underground at a number of deep level gold mines in South Africa. The instruments were recording data at the surface of the stope hangingwalls. A maximum value of 3 m/s was measured. Therefore data were compared to the data recorded in the solid rock by the mine seismic networks to determine the site response. The site response was defined as the ratio of the peak ground velocity measured at the surface of the excavations to the peak ground velocity inferred from the mine seismic data measured in the solid rocks. The site response measured at all mines studied was found to be 9 ± 3 times larger on average. In addition a number of simulated rockbursts were conducted underground in order to estimate the rock mass response when subjected to strong ground motion. The rockbursts were simulated by means of large blasts detonated in solid rock close to the sidewall of a tunnel. The numerical models used in the design of the simulated rockbursts were calibrated by small blasts taking place at each experimental site. A dense array of shock type accelerometers was installed along the blasting wall to monitor the attenuation of the strong ground motion as a function of the distance from the source. The attenuation of peak particle velocity was found to be proportional to R-1.7. In order to improve the understanding of the rock mass behaviour around deep level mining the rate of tilt was monitor and then compare to the seismic ground motion. A good correspondence between the rate of tilt and seismic ground motion was found. The rate of coseismic and aseismic tilt, as well as seismicity recorded by the mine seismic network, are approximately constant until the daily blasting time

  20. Seismic risk mitigation in deep level South African mines by state of the art underground monitoring - Joint South African and Japanese study

    NASA Astrophysics Data System (ADS)

    Milev, A.; Durrheim, R.; Nakatani, M.; Yabe, Y.; Ogasawara, H.; Naoi, M.

    2012-04-01

    Two underground sites in a deep level gold mine in South Africa were instrumented by the Council for Scientific and Industrial Research (CSIR) with tilt meters and seismic monitors. One of the sites was also instrumented by JApanese-German Underground Acoustic emission Research in South Africa (JAGUARS) with a small network, approximately 40m span, of eight Acoustic Emission (AE) sensors. The rate of tilt, defined as quasi-static deformations, and the seismic ground motion, defined as dynamic deformations, were analysed in order to understand the rock mass behavior around deep level mining. In addition the high frequency AE events recorded at hypocentral distances of about 50m located at 3300m below the surface were analysed. A good correspondence between the dynamic and quasi-static deformations was found. The rate of coseismic and aseismic tilt, as well as seismicity recorded by the mine seismic network, are approximately constant until the daily blasting time, which takes place from about 19:30 until shortly before 21:00. During the blasting time and the subsequent seismic events the coseismic and aseismic tilt shows a rapid increase.Much of the quasi-static deformation, however, occurs independently of the seismic events and was described as 'slow' or aseismic events. During the monitoring period a seismic event with MW 2.2 occurred in the vicinity of the instrumented site. This event was recorded by both the CSIR integrated monitoring system and JAGUARS acoustic emotion network. The tilt changes associated with this event showed a well pronounced after-tilt. The aftershock activities were also well recorded by the acoustic emission and the mine seismic networks. More than 21,000 AE aftershocks were located in the first 150 hours after the main event. Using the distribution of the AE events the position of the fault in the source area was successfully delineated. The distribution of the AE events following the main shock was related to after tilt in order to

  1. Impurity Crystal in a Bose-Einstein Condensate

    SciTech Connect

    Roberts, David C.; Rica, Sergio

    2009-01-16

    We investigate the behavior of impurity fields immersed in a larger condensate field in various dimensions. We discuss the localization of a single impurity field within a condensate and note the effects of surface energy. We derive the functional form of the attractive condensate-mediated interaction between two impurities. Generalizing the analysis to N impurity fields, we show that within various parameter regimes a crystal of impurity fields can form spontaneously in the condensate. Finally, the system of condensate and crystallized impurity structure is shown to have nonclassical rotational inertia, which is characteristic of superfluidity; i.e., the system can be seen to exhibit supersolid behavior.

  2. New impurity profiles of recent Australian imported 'ice': methamphetamine impurity profiling and the identification of (pseudo)ephedrine and Leuckart specific marker compounds.

    PubMed

    Qi, Ying; Evans, Ian; McCluskey, Adam

    2007-07-01

    Determination of the synthetic route in methamphetamine profiling relies on the identification of key, route specific marker impurity compounds. Impurity profiling of recent crystalline methamphetamine ('ice'), seized by the Australian Federal Police at the Australian border in 2003-2004, identified route specific marker compounds normally associated with two different synthetic approaches in the same samples. Impurities consistent with the ephedrine route included 1,2-dimethyl-3-phenyl aziridine (I), 1,3-dimethyl-2-phenylnaphthalene (VIII) and 1-benzyl-3-methylnaphthalene (IX), alongside N-formylmethamphetamine (V), N,N-di-(beta-phenylisopropyl)amine (XII) and N,N-di-(beta-phenylisopropyl)methylamine (XIII), N-benzoylamphetamine (XIV) and N,N-di-(beta-phenylisopropyl)formamide (XV) commonly associated with the Leuckart route and/or reductive amination. A non-synthetic process related origin of low-level N-formylmethamphetamine is proposed. PMID:17145150

  3. Impurity content of reduced-activation ferritic steels and a vanadium alloy

    SciTech Connect

    Klueh, R.L.; Grossbeck, M.L.; Bloom, E.E.

    1997-04-01

    Inductively coupled plasma mass spectrometry was used to analyze a reduced-activation ferritic/martensitic steel and a vanadium alloy for low-level impurities that would compromise the reduced-activation characteristics of these materials. The ferritic steel was from the 5-ton IEA heat of modified F82H, and the vanadium alloy was from a 500-kg heat of V-4Cr-4Ti. To compare techniques for analysis of low concentrations of impurities, the vanadium alloy was also examined by glow discharge mass spectrometry. Two other reduced-activation steels and two commercial ferritic steels were also analyzed to determine the difference in the level of the detrimental impurities in the IEA heat and steels for which no extra effort was made to restrict some of the tramp impurities. Silver, cobalt, molybdenum, and niobium proved to be the tramp impurities of most importance. The levels observed in these two materials produced with present technology exceeded the limits for low activation for either shallow land burial or recycling. The chemical analyses provide a benchmark for the improvement in production technology required to achieve reduced activation; they also provide a set of concentrations for calculating decay characteristics for reduced-activation materials. The results indicate the progress that has been made and give an indication of what must still be done before the reduced-activation criteria can be achieved.

  4. IDENTIFYING IMPURITIES IN SURPLUS NON PIT PLUTONIUM FEEDS FOR MOX OR ALTERNATIVE DISPOSITION

    SciTech Connect

    Allender, J; Moore, E

    2010-07-14

    This report provides a technical basis for estimating the level of corrosion products in materials stored in DOE-STD-3013 containers based on extrapolating available chemical sample results. The primary focus is to estimate the levels of nickel, iron, and chromium impurities in plutonium-bearing materials identified for disposition in the United States Mixed Oxide fuel process.

  5. The role of deep convection and nocturnal low-level jets for dust emission in summertime West Africa: Estimates from convection-permitting simulations

    PubMed Central

    Heinold, B; Knippertz, P; Marsham, JH; Fiedler, S; Dixon, NS; Schepanski, K; Laurent, B; Tegen, I

    2013-01-01

    [1] Convective cold pools and the breakdown of nocturnal low-level jets (NLLJs) are key meteorological drivers of dust emission over summertime West Africa, the world’s largest dust source. This study is the first to quantify their relative contributions and physical interrelations using objective detection algorithms and an off-line dust emission model applied to convection-permitting simulations from the Met Office Unified Model. The study period covers 25 July to 02 September 2006. All estimates may therefore vary on an interannual basis. The main conclusions are as follows: (a) approximately 40% of the dust emissions are from NLLJs, 40% from cold pools, and 20% from unidentified processes (dry convection, land-sea and mountain circulations); (b) more than half of the cold-pool emissions are linked to a newly identified mechanism where aged cold pools form a jet above the nocturnal stable layer; (c) 50% of the dust emissions occur from 1500 to 0200 LT with a minimum around sunrise and after midday, and 60% of the morning-to-noon emissions occur under clear skies, but only 10% of the afternoon-to-nighttime emissions, suggesting large biases in satellite retrievals; (d) considering precipitation and soil moisture effects, cold-pool emissions are reduced by 15%; and (e) models with parameterized convection show substantially less cold-pool emissions but have larger NLLJ contributions. The results are much more sensitive to whether convection is parameterized or explicit than to the choice of the land-surface characterization, which generally is a large source of uncertainty. This study demonstrates the need of realistically representing moist convection and stable nighttime conditions for dust modeling. Citation: Heinold, B., P. Knippertz, J. H. Marsham, S. Fiedler, N. S. Dixon, K. Schepanski, B. Laurent, and I. Tegen (2013), The role of deep convection and nocturnal low-level jets for dust emission in summertime West Africa: Estimates from convection

  6. Cardiac dosimetric evaluation of deep inspiration breath-hold level variances using computed tomography scans generated from deformable image registration displacement vectors.

    PubMed

    Harry, Taylor; Rahn, Doug; Semenov, Denis; Gu, Xuejun; Yashar, Catheryn; Einck, John; Jiang, Steve; Cerviño, Laura

    2016-01-01

    There is a reduction in cardiac dose for left-sided breast radiotherapy during treatment with deep inspiration breath-hold (DIBH) when compared with treatment with free breathing (FB). Various levels of DIBH may occur for different treatment fractions. Dosimetric effects due to this and other motions are a major component of uncertainty in radiotherapy in this setting. Recent developments in deformable registration techniques allow displacement vectors between various temporal and spatial patient representations to be digitally quantified. We propose a method to evaluate the dosimetric effect to the heart from variable reproducibility of DIBH by using deformable registration to create new anatomical computed tomography (CT) scans. From deformable registration, 3-dimensional deformation vectors are generated with FB and DIBH. The obtained deformation vectors are scaled to 75%, 90%, and 110% and are applied to the reference image to create new CT scans at these inspirational levels. The scans are then imported into the treatment planning system and dose calculations are performed. The average mean dose to the heart was 2.5Gy (0.7 to 9.6Gy) at FB, 1.2Gy (0.6 to 3.8Gy, p < 0.001) at 75% inspiration, 1.1Gy (0.6 to 3.1Gy, p = 0.004) at 90% inspiration, 1.0Gy (0.6 to 3.0Gy) at 100% inspiration or DIBH, and 1.0Gy (0.6 to 2.8Gy, p = 0.019) at 110% inspiration. The average mean dose to the left anterior descending artery (LAD) was 19.9Gy (2.4 to 46.4Gy), 8.6Gy (2.0 to 43.8Gy, p < 0.001), 7.2Gy (1.9 to 40.1Gy, p = 0.035), 6.5Gy (1.8 to 34.7Gy), and 5.3Gy (1.5 to 31.5Gy, p < 0.001), correspondingly. This novel method enables numerous anatomical situations to be mimicked and quantifies the dosimetric effect they have on a treatment plan. PMID:26206154

  7. Discriminating assimilants and decoupling deep- vs. shallow-level crystal records at Mount Adams using 238U-230Th disequilibria and Os isotopes

    USGS Publications Warehouse

    Jicha, B.R.; Johnson, C.M.; Hildreth, W.; Beard, B.L.; Hart, G.L.; Shirey, S.B.; Singer, B.S.

    2009-01-01

    A suite of 23 basaltic to dacitic lavas erupted over the last 350??kyr from the Mount Adams volcanic field has been analyzed for U-Th isotope compositions to evaluate the roles of mantle versus crustal components during magma genesis. All of the lavas have (230Th/238U) > 1 and span a large range in (230Th/232Th) ratios, and most basalts have higher (230Th/232Th) ratios than andesites and dacites. Several of the lavas contain antecrysts (crystals of pre-existing material), yet internal U-Th mineral isochrons from six of seven lavas are indistinguishable from their eruption ages. This indicates a relatively brief period of time between crystal growth and eruption for most of the phenocrysts (olivine, clinopyroxene, plagioclase, magnetite) prior to eruption. One isochron gave a crystallization age that is ~ 20-25??ka older than its corresponding eruptive age, and is interpreted to reflect mixing of older and juvenile crystals or a protracted period of magma storage in the crust. Much of the eruptive volume since 350??ka consists of lavas that have small to moderate 230Th excesses (2-16%), which are likely inherited from melting of a garnet-bearing intraplate ("OIB-like") mantle source. Following melt generation and subsequent migration through the upper mantle, most Mt. Adams magmas interacted with young, mafic lower crust, as indicated by 187Os/188Os ratios that are substantially more radiogenic than the mantle or those expected via mixing of subducted material and the mantle wedge. Moreover, Os-Th isotope variations suggest that unusually large 230Th excesses (25-48%) and high 187Os/188Os ratios in some peripheral lavas reflect assimilation of small degree partial melts of pre-Quaternary basement that had residual garnet or Al-rich clinopyroxene. Despite the isotopic evidence for lower crustal assimilation, these processes are not generally recorded in the erupted phenocrysts, indicating that the crystal record of the deep-level 'cryptic' processes has been

  8. The Effect of Impurities on Firn Layering

    NASA Astrophysics Data System (ADS)

    Keegan, K. M.; Baker, I.; Albert, M. R.

    2013-12-01

    Recently, there has been increased interest in incorporating firn layering into firn densification models, and a correlation between impurities and density differences in firn layering has been described. Measuring the stratigraphy from firn cores is a tedious process, but a chemical proxy for firn layering would be an easy way to incorporate layering into the existing firn models. To explore the correlation of chemical impurities in firn, we collected Raman spectra from samples of a NEEM 2009 firn core using a confocal scanning optical microscope with a Raman spectrometer. We found sulfuric acid (H2SO4), calcium carbonate (CaCO3), gypsum (CaSO4*2H2O), hydroxyl herderite (CaBePO4(OH)), and sodium chloride (NaCl) in the firn with a greater concentration of these impurities at the grain boundaries and triple junctions. We will discuss the effects of these impurities on the firn densification processes, as well as the potential for a proxy of layering in firn densification models.

  9. Pharmaceutical impurities and degradation products: uses and applications of NMR techniques.

    PubMed

    Maggio, Rubén M; Calvo, Natalia L; Vignaduzzo, Silvana E; Kaufman, Teodoro S

    2014-12-01

    Current standards and regulations demand the pharmaceutical industry not only to produce highly pure drug substances, but to achieve a thorough understanding of the impurities accompanying their manufactured drug substances and products. These challenges have become important goals of process chemistry and have steadily stimulated the search of impurities after accelerated or forced degradation procedures. As a result, impurity profiling is one of the most attractive, active and relevant fields of modern pharmaceutical analysis. This activity includes the identification, structural elucidation and quantitative determination of impurities and degradation products in bulk drugs and their pharmaceutical formulations. Nuclear magnetic resonance (NMR) spectroscopy has evolved into an irreplaceable approach for pharmaceutical quality assessment, currently playing a critical role in unequivocal structure identification as well as structural confirmation (qualitative detection), enabling the understanding of the underlying mechanisms of the formation of process and/or degradation impurities. NMR is able to provide qualitative information without the need of standards of the unknown compounds and multiple components can be quantified in a complex sample without previous separation. When coupled to separative techniques, the resulting hyphenated methodologies enhance the analytical power of this spectroscopy to previously unknown levels. As a result, and by enabling the implementation of rational decisions regarding the identity and level of impurities, NMR contributes to the goal of making better and safer medicines. Herein are discussed the applications of NMR spectroscopy and its hyphenated derivate techniques to the study of a wide range pharmaceutical impurities. Details on the advantages and disadvantages of the methodology and well as specific challenges with regards to the different analytical problems are also presented. PMID:24853620

  10. Impurity transport in trapped electron mode driven turbulence

    SciTech Connect

    Mollen, A.; Fueloep, T.; Moradi, S.; Pusztai, I.

    2013-03-15

    Trapped electron mode turbulence is studied by gyrokinetic simulations with the GYRO code and an analytical model including the effect of a poloidally varying electrostatic potential. Its impact on radial transport of high-Z trace impurities close to the core is thoroughly investigated, and the dependence of the zero-flux impurity density gradient (peaking factor) on local plasma parameters is presented. Parameters such as ion-to-electron temperature ratio, electron temperature gradient, and main species density gradient mainly affect the impurity peaking through their impact on mode characteristics. The poloidal asymmetry, the safety factor, and magnetic shear have the strongest effect on impurity peaking, and it is shown that under certain scenarios where trapped electron modes are dominant, core accumulation of high-Z impurities can be avoided. We demonstrate that accounting for the momentum conservation property of the impurity-impurity collision operator can be important for an accurate evaluation of the impurity peaking factor.

  11. Process and system for removing impurities from a gas

    SciTech Connect

    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.

  12. Fluorine plasma treatment induced deep level traps and their effect on current transportation in Al0.83In0.17N/AlN/GaN Schottky barrier diodes

    NASA Astrophysics Data System (ADS)

    Xiang, Yong; Yu, Tongjun; Ji, Cheng; Cheng, Yutian; Yang, Xuelin; Kang, Xiangning; Shen, Bo; Zhang, Guoyi

    2016-08-01

    The deep level traps and the electrical properties of fluorine plasma treated (F-treated) and non-treated Al0.83In0.17N/AlN/GaN Schottky barrier diodes (SBDs) were investigated by the temperature-dependent current–voltage (I–V) and deep level transient spectroscopy (DLTS) measurements. Three deep level traps were detected in the SBD after F-treatment at ~E c  ‑  0.17 eV, ~E c  ‑  0.27 eV and ~E c  ‑  1.14 eV. One of the deep level traps at ~E c  ‑  1.14 eV is mainly located in the Al0.83In0.17N barrier layer with a captured cross section (σ) of ~6.50  ×  10‑18 cm2. This F-related deep level trap has 3–4 orders of magnitude of the larger σ and ~0.46 eV greater active energy than that of the dislocation-related one at ~E c  ‑  0.68 eV with σ of ~1.92  ×  10‑21 cm2. Meanwhile, the leakage current of F-treated SBD at  ‑5 V is reduced by ~2 orders of magnitude compared with that of the non-treated one. This leakage current reduction is mainly attributed to the increase of the Poole–Frenkel emission barrier height from ~0.09 eV in non-treated SBD to ~0.46 eV in the F-treated one. It is believed that the main reverse current transportation is the Poole–Frenkel emission from the F-related deep level trap states into the continuum states of the dislocations in F-treated Al0.83In0.17N/AlN/GaN SBD.

  13. Study of impurity distribution in mechanically polished, chemically treated and high vacuum degassed pure niobium samples using the TOFSIMS technique

    NASA Astrophysics Data System (ADS)

    Bose, A.; Joshi, S. C.

    2015-07-01

    The performance of superconducting radio frequency (SRF) cavities is strongly influenced by various impurities within the penetration depth (∼50 nm) of niobium (Nb), which in turn depends on the applied surface treatments. The effect of these surface treatments on the impurities of Nb has been explored using various surface analytical techniques. However, the results are still inadequate in many aspects and the effect of sequential SRF treatments on the impurity distribution has not been explored. The present study analyzes various impurities within the penetration depth of Nb samples, treated by SRF cavity processing techniques such as colloidal silica polishing (simulating centrifugal barrel polishing), buffer chemical polishing (BCP), high pressure rinsing (HPR) and degassing under a high vacuum (HV) condition at 600 °C for 10 h. Static, dynamic and slow sputtering modes of the time of flight secondary ion mass spectrometry (TOFSIMS) technique were employed to study the effect of the above treatments on interstitial impurities, hydrocarbons, oxides, acidic residues, reaction products and metallic contaminations. The study confirms that the impurity distribution in Nb is not only sensitive to the surface treatments, but also to their sequence. Varying the treatment sequence prior to HV degassing treatments affected the final impurity levels in HV degassed bulk Nb samples. The HV degassing treatment was capable of reducing hydrogen contamination, but oxygen, carbon and metallic impurities were introduced into bulk Nb due to poor isolation from furnace contamination. On the other hand, BCP treated samples exhibited minimum hydrocarbon and metallic contamination along with the thinnest oxide layer at ∼2.8 nm, but led to extensive contamination of the oxide layer with residuals and reaction products of acids used in the BCP solution. HPR treatment, on the other hand, was effective in reducing the acidic impurities on the top surface. Variability of the

  14. Deep Lysimeter

    DOEpatents

    Hubbell, Joel M.; Sisson, James B.

    2004-06-01

    A deep lysimeter including a hollow vessel having a chamber, a fill conduit extending into the chamber through apertures, a semi-permeable member mounted on the vessel and in fluid communication with the fill conduit, and a line connection for retrieving the lysimeter.

  15. The Potts model on a Bethe lattice with nonmagnetic impurities

    SciTech Connect

    Semkin, S. V. Smagin, V. P.

    2015-10-15

    We have obtained a solution for the Potts model on a Bethe lattice with mobile nonmagnetic impurities. A method is proposed for constructing a “pseudochaotic” impurity distribution by a vanishing correlation in the arrangement of impurity atoms for the nearest sites. For a pseudochaotic impurity distribution, we obtained the phase-transition temperature, magnetization, and spontaneous magnetization jumps at the phase-transition temperature.

  16. Impact of Pharmaceutical Impurities in Ecstasy Tablets: Gas Chromatography-Mass Spectrometry Study.

    PubMed

    Jalali, Amir; Hatamie, Amir; Saferpour, Tahere; Khajeamiri, Alireza; Safa, Tahere; Buazar, Foad

    2016-01-01

    In this study, a simple and reliable method by gas chromatograph-mass spectrometry (GC-MS) was developed for the fast and regular identification of 3, 4-MDMA impurities in ecstasy tablets. In so doing, 8 samples of impurities were extracted by diethyl ether under alkaline condition and then analyzed by GC-MS. The results revealed high MDMA levels ranging from 37.6% to 57.7%. The GC-MS method showed that unambiguous identification can be achieved for MDMA from 3, 4-methylenedioxyamphetamine (MDA), Amphetamine (AM), methamphetamine (MA) and ketamine (Keta) compounds, respectively. The experimental results indicated the acceptable time window without interfering peaks. It is found that GC-MS was provided a suitable and rapid identification approach for MDMA (Ecstacy) tablets, particularly in the Forensic labs. Consequently, the intense MDMA levels would support the police to develop a simple quantification of impurity in Ecstasy tablets. PMID:27610162

  17. Impact of Pharmaceutical Impurities in Ecstasy Tablets: Gas Chromatography-Mass Spectrometry Study

    PubMed Central

    Jalali, Amir; Hatamie, Amir; Saferpour, Tahere; Khajeamiri, Alireza; Safa, Tahere; Buazar, Foad

    2016-01-01

    In this study, a simple and reliable method by gas chromatograph–mass spectrometry (GC–MS) was developed for the fast and regular identification of 3, 4-MDMA impurities in ecstasy tablets. In so doing, 8 samples of impurities were extracted by diethyl ether under alkaline condition and then analyzed by GC–MS. The results revealed high MDMA levels ranging from 37.6% to 57.7%. The GC-MS method showed that unambiguous identification can be achieved for MDMA from 3, 4-methylenedioxyamphetamine (MDA), Amphetamine (AM), methamphetamine (MA) and ketamine (Keta) compounds, respectively. The experimental results indicated the acceptable time window without interfering peaks. It is found that GC-MS was provided a suitable and rapid identification approach for MDMA (Ecstacy) tablets, particularly in the Forensic labs. Consequently, the intense MDMA levels would support the police to develop a simple quantification of impurity in Ecstasy tablets. PMID:27610162

  18. Impurity enrichment and radiative enhancement using induced SOL flow in DIII-D

    SciTech Connect

    Wade, M.R.; West, W.P.; Wood, R.D.

    1998-07-01

    Experiments on DIII-D have demonstrated the efficacy of using induced scrap-off-layer (SOL) flow to preferentially enrich impurities in the divertor plasma. This SOL floe is produced through simultaneous deuterium gas injection at the midplane and divertor exhaust. Using this SOL flow, an improvement in enrichment (defined as the ratio of impurity fraction in the divertor to that in the plasma core) has been observed for all impurities in trace-level experiments (i.e., impurity level is non-perturbative), with the degree of improvement increasing with impurity atomic number. In the case of argon, exhaust gas enrichment using modest SOL flow is as high as 17. Using this induced SOL flow technique and argon injection, radiative plasmas have been produced that combine high radiation losses (P{sub rad}/P{sub input} > 70%), low core fuel dilution (Z{sub eff} < 1.9), and good core confinement ({tau}{sub E} > 1.0 {tau}{sub E,ITER93H}).

  19. Iron impurities on Sb (111) surface and their effects on topological surface state

    NASA Astrophysics Data System (ADS)

    Han, Jinhee; Lee, Hyungjun; Choi, Hyoung Joon

    2012-02-01

    We study iron impurities on Sb (111) surface and their effects on topological surface state by using an ab-initio pseudopotential density-functional method. We implemented the spin-orbit interaction into the SIESTA in a form of additional fully non-local projectors. To calculate electronic structure of topological surface states, we consider a slab of Sb using a supercell containing 20 atomic layers with experimental bulk Sb lattice parameters. We determine atomic positions of Fe impurities on Sb (111) surface by minimizing the total energy, and calculate surface band structures near the Fermi level. To find effects of the impurity on the surface states of Sb (111) surface, we simulate ARPES spectra as a function of impurity density on the surface. From the results, we find that Fe impurity states are present near Fermi level and they strongly interact with the surface states. This work was supported by the NRF of Korea (Grant Nos. 2009-0081204 and 2011-0018306) and KISTI Supercomputing Center (Project No. KSC-2011-C2-04).

  20. Regional and Site-Scale Hydrogeologic Analyses of a Proposed Canadian Deep Geologic Repository for Low and Intermediate Level Radioactive Waste

    NASA Astrophysics Data System (ADS)

    Sykes, J. F.; Normani, S. D.; Yin, Y.; Sykes, E. A.

    2009-05-01

    A Deep Geologic Repository (DGR) for Low and Intermediate Level radioactive waste has been proposed by Ontario Power Generation for the eastern edge of the Michigan Basin at the Bruce site, near Tiverton, Ontario, Canada. The DGR is to be constructed within the argillaceous Ordovician limestone of the Cobourg Formation at a depth of about 680 m below ground surface. This paper describes a regional-scale and linked site-scale geologic conceptual model for the DGR site and analyzes flow system evolution using the FRAC3DVS-OPG flow and transport model. The work illustrates the factors that influence the predicted long-term performance of the geosphere barrier and provides a framework for the assembly and integration of site-specific geoscientific data. The structural contours at the regional and site scale of the 31 sedimentary strata that may be present above the Precambrian crystalline basement rock were defined by the Ontario Petroleum Institute's Oil, Gas and Salt Resources Library borehole logs covering Southern Ontario and by site-specific data. The regional- scale domain encompasses an 18,500 km2 region extending from Lake Huron to Georgian Bay. The site- scale spatial domain encompasses an area of approximately 361 km2 with the repository at its centre. Its boundary conditions are determined using both the nested model approach and an embedment approach. The groundwater zone below the Devonian is characterized by units containing pore fluids with high concentrations of total dissolved solids that can exceed 300 g/l. Site-specific data indicate that the Ordovician is under-pressured relative to the surface elevation while the Cambrian is over-pressured. The computational sequence for the analyses involves the calculation of steady-state density independent flow that is used as the initial condition for the determination of pseudo-equilibrium for a density-dependent flow system that has an initial TDS distribution developed from observed data. Sensitivity

  1. Strong ground motion generated by controlled blasting experiments and mining induced seismic events recorded underground at deep level mines in South Africa

    NASA Astrophysics Data System (ADS)

    Milev, A.; Selllers, E.; Skorpen, L.; Scheepers, L.; Murphy, S.; Spottiswoode, S. M.

    2011-12-01

    A number of simulated rockbursts were conducted underground at deep level gold mines in South Africa in order to estimate the rock mass response when subjected to strong ground motion. The rockbursts were simulated by means of large blasts detonated in solid rock close to the sidewall of a tunnel. The simulated rockbursts involved the design of the seismic source, seismic observations in the near and far field, high-speed video filming, a study of rock mass conditions such as fractures, joints, rock strength etc. Knowledge of the site conditions before and after the simulated rockbursts was also gained. The numerical models used in the design of the simulated rockbursts were calibrated by small blasts taking place at each experimental site. A dense array of shock type accelerometers was installed along the blasting wall to monitor the attenuation of the strong ground motion as a function of the distance from the source. The attenuation of peak particle velocities, was found to be proportional to R^-1.7. Special investigations were carried out to evaluate the mechanism and the magnitude of damage, as well as the support behaviour under excessive dynamic loading. The strong ground motion generated by mining induced seismic events was studied, as part of this work, not only to characterize the rock mass response, but also to estimate the site effect on the surface of the underground excavations. A stand-alone instrument especially designed for recording strong ground motions was used to create a large database of peak particle velocities measured on stope hangingwalls. A total number of 58 sites located in stopes where the Carbon Leader Reef, Ventersdorp Contact Reef, Vaal Reef and Basal Reef are mined, were monitored. The peak particle velocities were measured at the surface of the excavations to identify the effect of the free surface and the fractures surrounding the underground mining. Based on these measurements the generally accepted velocity criterion of 3 m

  2. Major deep levels with the same microstructures observed in n-type 4H-SiC and 6H-SiC

    SciTech Connect

    Sasaki, S.; Kawahara, K.; Feng, G.; Alfieri, G.; Kimoto, T.

    2011-01-01

    Major deep levels observed in as-grown and irradiated n-type 4H-SiC and 6H-SiC epilayers have been investigated. After low-energy electron irradiation, by which only carbon atoms are displaced, five traps, EH1 (E{sub C}-0.36 eV), Z{sub 1}/Z{sub 2} (E{sub C}-0.65 eV), EH3 (E{sub C}-0.79 eV), EH5 (E{sub C}-1.0 eV), and EH6/7 (E{sub C}-1.48 eV), were detected in 4H-SiC and four traps, E{sub 1}/E{sub 2} (E{sub C}-0.45 eV), RD{sub 5} (E{sub C}-0.57 eV), ES (E{sub C}-0.80 eV), and R (E{sub C}-1.25 eV), were detected in 6H-SiC. The Z{sub 1}/Z{sub 2}, EH6/7 centers in 4H-SiC and the E{sub 1}/E{sub 2}, R centers in 6H-SiC exhibit common features as follows: their generation rates by the e{sup -}-irradiation were almost the same each other, their concentrations were not changed by heat treatments up to 1500 deg. C, and they showed very similar annealing behaviors at elevated temperatures. Furthermore, these defect centers were almost eliminated by thermal oxidation. Taking account of the observed results and the energy positions, the authors suggest that the Z{sub 1}/Z{sub 2} center in 4H-SiC corresponds to the E{sub 1}/E{sub 2} center in 6H-SiC, and the EH6/7 center in 4H-SiC to the R center in 6H-SiC, respectively. Since the concentrations of these four centers are almost the same for as-grown, electron-irradiated, annealed, and oxidized samples, these centers will contain a common intrinsic defect, most likely carbon vacancy. The authors also observed similar correspondence for other thermally unstable traps in 4H-SiC and 6H-SiC.

  3. The development of a potassium-sulfide glass fiber cell and studies on impurities in alkali metal-sulfur cells

    NASA Technical Reports Server (NTRS)

    Tsang, F. Y.

    1977-01-01

    Potassium sulfur rechargeable cells, having as the electrolyte the thin walls of hollow glass fibers made from permeable glass, were developed. The cells had short lives, probably due to the construction materials and impurities in the potassium. The effect of the impurities in the analogous NA-S system was studied. Calcium, potassium, and NaOH/oxide impurities caused increased resistance or corrosion of the glass fibers. For long lived cell operation, the Na must contain less than 1 ppm Ca and less than a few ppm of hydroxide/oxide. Up to 150 ppm K can be tolerated. After purification of the Na anolyte, cell lifetimes in excess of 1000 deep charge-discharge cycles or over 8 months on continuous cycling at 10-30 percent depth of discharge were obtained.

  4. Quantification of active pharmaceutical ingredient and impurities in sildenafil citrate obtained from the Internet

    PubMed Central

    Nutan, Mohammad T.; Dodla, Uday Krishna Reddy

    2014-01-01

    Background: The accessibility of prescription drugs produced outside of the United States, most notably sildenafil citrate (innovator product, Viagra®), has been made much easier by the Internet. Of greatest concern to clinicians and policymakers is product quality and patient safety. The US Food and Drug Administration (FDA) has issued warnings to potential buyers that the safety of drugs purchased from the Internet cannot be guaranteed, and may present a health risk to consumers from substandard products. Objective: The objective of this study was to determine whether generic sildenafil citrate tablets from international markets obtained via the Internet are equivalent to the US innovator product regarding major aspects of pharmaceutical quality: potency, accuracy of labeling, and presence and level of impurities. This will help identify aspects of drug quality that may impact public health risks. Methods: A total of 15 sildenafil citrate tablets were obtained for pharmaceutical analysis: 14 generic samples from international Internet pharmacy websites and the US innovator product. According to US Pharmacopeial guidelines, tablet samples were tested using high-performance liquid chromatography for potency of active pharmaceutical ingredient (API) and levels of impurities (impurities A, B, C, and D). Impurity levels were compared with International Conference on Harmonisation (ICH) limits. Results: Among the 15 samples, 4 samples possessed higher impurity B levels than the ICH qualification threshold, 8 samples possessed higher impurity C levels than the ICH qualification threshold, and 4 samples possessed more than 1% impurity quantity of maximum daily dose (MDD). For API, 6 of the samples failed to fall within the 5% assay limit. Conclusions: Quality assurance tests are often used to detect formulation defects of drug products during the manufacturing and/or storage process. Results suggest that manufacturing standards for sildenafil citrate generic drug

  5. Recent advances in trace analysis of pharmaceutical genotoxic impurities.

    PubMed

    Liu, David Q; Sun, Mingjiang; Kord, Alireza S

    2010-04-01

    Genotoxic impurities (GTIs) in pharmaceuticals at trace levels are of increasing concerns to both pharmaceutical industries and regulatory agencies due to their potentials for human carcinogenesis. Determination of these impurities at ppm levels requires highly sensitive analytical methodologies, which poses tremendous challenges on analytical communities in pharmaceutical R&D. Practical guidance with respect to the analytical determination of diverse classes of GTIs is currently lacking in the literature. This article provides an industrial perspective with regard to the analysis of various structural classes of GTIs that are commonly encountered during chemical development. The recent literatures will be reviewed, and several practical approaches for enhancing analyte detectability developed in recent years will be highlighted. As such, this article is organized into the following main sections: (1) trace analysis toolbox including sample introduction, separation, and detection techniques, as well as several 'general' approaches for enhancing detectability; (2) method development: chemical structure and property-based approaches; (3) method validation considerations; and (4) testing and control strategies in process chemistry. The general approaches for enhancing detection sensitivity to be discussed include chemical derivatization, 'matrix deactivation', and 'coordination ion spray-mass spectrometry'. Leveraging the use of these general approaches in method development greatly facilitates the analysis of poorly detectable or unstable/reactive GTIs. It is the authors' intent to provide a contemporary perspective on method development and validation that can guide analytical scientists in the pharmaceutical industries. PMID:20022442

  6. When small is big: the role of impurities in electrocatalysis.

    SciTech Connect

    Strmcnik, Dusan; Li, Dongguo; Lopes, Pietro P.; Tripkovic, Dusan; Kodama, Kensaku; Stamenkovic, Vojislav R.; Markovic, Nenad M.

    2015-11-01

    Improvements in the fundamental understanding of electrocatalysis have started to revolutionize the development of electrochemical interfaces for the efficient conversion of chemical energy into electricity, as well as for the utilization of electrons to produce new chemicals that then can be re-used in energy conversion systems. Here, some facets of the role of trace level of impurities (from 10-7 to 10-6 M) in electrocatalysis of the oxygen reduction reaction, hydrogen oxidation and evolution reactions, and CO oxidation reactions are explored on well-characterized platinum single crystal surfaces and high surface area materials in alkaline and acidic environments. Of particular interest is the effect of anions (e.g., Cl-, NO3-) and cations (i.e., Cu2+) present in the supporting electrolytes as well as surface defects (i.e., ad-islands) that are present on metal surfaces. The examples presented are chosen to demonstrate that a small level of impurities may play a crucial role in governing the reactivity of electrochemical interfaces.

  7. Deep level transient spectroscopy in plasma-assisted molecular beam epitaxy grown Al{sub 0.2}Ga{sub 0.8}N/GaN interface and the rapid thermal annealing effect

    SciTech Connect

    Park, Young S.; Lee, Minyoung; Jeon, Kiyoung; Im, Hyunsik; Yoon, Im T.; Shon, Yoon; Park, C. J.; Cho, Hoon Y.; Han, Myung-Soo

    2010-09-13

    We investigated deep-level traps formed in Al{sub 0.2}Ga{sub 0.8}N/GaN heterostructures grown using plasma-assisted molecular beam epitaxy and by performing deep level transient spectroscopy (DLTS). Two electron traps with activation energies of E{sub c}-150 meV and E{sub c}-250 meV were observed, and their capture cross-sections ({sigma}{sub T}) were estimated to be 2.0x10{sup -18} cm{sup 2} and 1.1x10{sup -17} cm{sup 2}, respectively. Different behaviors in the dependence of DLTS on filling pulse length confirm that the traps originated from N vacancies and dislocations. The amplitude of the dislocation-induced DLTS signal was reduced significantly by high-temperature rapid thermal annealing under N{sub 2} ambient after hydrogen treatment due to the reduction in dislocation density.

  8. Deep-level-driven anomalous temperature dependence of lattice constants and energy gaps in MgxZn1-xSe and MgxZn1-xSe:Co2+ single crystals

    NASA Astrophysics Data System (ADS)

    Kim, Wha-Tek

    1999-02-01

    Pure MgxZn1-xSe (type C) single crystals were grown by the closed-tube sublimation method. MgxZn1-xSe (type D) and MgxZn1-xSe:Co2+ single crystals in which deep levels exist were grown by the chemical transport reaction method. The temperature dependence of the optical energy gaps of the MgxZn1-xSe (type C) single crystals fitted well with the Manoogian-Leclerc equation. However, the temperature dependence of the optical energy gaps of the MgxZn1-xSe (type D) and MgxZn1-xSe:Co2+ single crystals was anomalous in the temperature range of 10-70 K. This anomalous temperature dependence was analyzed as originating from a volume dilation effect due to deep-level defects.

  9. Theoretical analysis of impurity precipitation in nanopores in crystals. II: Kinetics of impurity cluster growth in pores

    NASA Astrophysics Data System (ADS)

    Lubov, M. N.; Kulikov, D. V.; Trushin, Yu. V.; Kurnosikov, O.

    2013-03-01

    The kinetics of the formation of impurity clusters in subsurface nanopores in crystals is studied theoretically. A physical model of precipitation of the impurity phase in nanopores in a sample with sinks of various types is developed. This model forms the basis for the calculation of the annealing kinetics of copper containing subsurface pores and cobalt impurity atoms. The optimal annealing conditions are determined in which cobalt atoms diffuse predominantly into pores and form impurity clusters in them.

  10. Protein Crystal Growth Dynamics and Impurity Incorporation

    NASA Technical Reports Server (NTRS)

    Chernov, Alex A.; Thomas, Bill

    2000-01-01

    The general concepts and theories of crystal growth are proven to work for biomolecular crystallization. This allowed us to extract basic parameters controlling growth kinetics - free surface energy, alpha, and kinetic coefficient, beta, for steps. Surface energy per molecular site in thermal units, alpha(omega)(sup 2/3)/kT approx. = 1, is close to the one for inorganic crystals in solution (omega is the specific molecular volume, T is the temperature). Entropic restrictions on incorporation of biomolecules into the lattice reduce the incorporation rate, beta, by a factor of 10(exp 2) - 10(exp 3) relative to inorganic crystals. A dehydration barrier of approx. 18kcal/mol may explain approx. 10(exp -6) times difference between frequencies of adding a molecule to the lattice and Brownian attempts to do so. The latter was obtained from AFM measurements of step and kink growth rates on orthorhombic lysozyme. Protein and many inorganic crystals typically do not belong to the Kossel type, thus requiring a theory to account for inequivalent molecular positions within its unit cell. Orthorhombic lysozyme will serve as an example of how to develop such a theory. Factors deteriorating crystal quality - stress and strain, mosaicity, molecular disorder - will be reviewed with emphasis on impurities. Dimers in ferritin and lysozyme and acetylated lysozyme, are microheterogeneous i.e. nearly isomorphic impurities that are shown to be preferentially trapped by tetragonal lysozyme and ferritin crystals, respectively. The distribution coefficient, K defined as a ratio of the (impurity/protein) ratios in crystal and in solution is a measure of trapping. For acetylated lysoyzme, K = 2.15 or, 3.42 for differently acetylated forms, is independent of both the impurity and the crystallizing protein concentration. The reason is that impurity flux to the surface is constant while the growth rate rises with supersaturation. About 3 times lower dimer concentration in space grown ferritin and

  11. An Experimental Design Approach for Impurity Profiling of Valacyclovir-Related Products by RP-HPLC.

    PubMed

    Katakam, Prakash; Dey, Baishakhi; Hwisa, Nagiat T; Assaleh, Fathi H; Chandu, Babu R; Singla, Rajeev K; Mitra, Analava

    2014-09-01

    Impurity profiling has become an important phase of pharmaceutical research where both spectroscopic and chromatographic methods find applications. The analytical methodology needs to be very sensitive, specific, and precise which will separate and determine the impurity of interest at the 0.1% level. Current research reports a validated RP-HPLC method to detect and separate valacyclovir-related impurities (Imp-E and Imp-G) using the Box-Behnken design approach of response surface methodology. A gradient mobile phase (buffer: acetonitrile as mobile phase A and acetonitrile: methanol as mobile phase B) was used. Linearity was found in the concentration range of 50-150 μg/mL. The mean recovery of impurities was 99.9% and 103.2%, respectively. The %RSD for the peak areas of Imp-E and Imp-G were 0.9 and 0.1, respectively. No blank interferences at the retention times of the impurities suggest the specificity of the method. The LOD values were 0.0024 μg/mL for Imp-E and 0.04 μg/mL for Imp-G and the LOQ values were obtained as 0.0082 μg/mL and 0.136 μg/mL, respectively, for the impurities. The S/N ratios in both cases were within the specification limits. Proper peak shapes and satisfactory resolution with good retention times suggested the suitability of the method for impurity profiling of valacyclovir-related drug substances. PMID:25853072

  12. An Experimental Design Approach for Impurity Profiling of Valacyclovir-Related Products by RP-HPLC

    PubMed Central

    Katakam, Prakash; Dey, Baishakhi; Hwisa, Nagiat T; Assaleh, Fathi H; Chandu, Babu R; Singla, Rajeev K; Mitra, Analava

    2014-01-01

    Abstract Impurity profiling has become an important phase of pharmaceutical research where both spectroscopic and chromatographic methods find applications. The analytical methodology needs to be very sensitive, specific, and precise which will separate and determine the impurity of interest at the 0.1% level. Current research reports a validated RP-HPLC method to detect and separate valacyclovir-related impurities (Imp-E and Imp-G) using the Box-Behnken design approach of response surface methodology. A gradient mobile phase (buffer: acetonitrile as mobile phase A and acetonitrile: methanol as mobile phase B) was used. Linearity was found in the concentration range of 50–150 μg/mL. The mean recovery of impurities was 99.9% and 103.2%, respectively. The %RSD for the peak areas of Imp-E and Imp-G were 0.9 and 0.1, respectively. No blank interferences at the retention times of the impurities suggest the specificity of the method. The LOD values were 0.0024 μg/mL for Imp-E and 0.04 μg/mL for Imp-G and the LOQ values were obtained as 0.0082 μg/mL and 0.136 μg/mL, respectively, for the impurities. The S/N ratios in both cases were within the specification limits. Proper peak shapes and satisfactory resolution with good retention times suggested the suitability of the method for impurity profiling of valacyclovir-related drug substances. PMID:25853072

  13. EVALUATION OF IMPURITY EXTREMES IN A PLUTONIUM-LOADED BOROSILICATE GLASS

    SciTech Connect

    Marra, J; Kevin Fox, K; Charles Crawford, C; Ned Bibler, N; Elizabeth Hoffman, E; Tommy Edwards, T

    2007-11-12

    A vitrification technology utilizing a lanthanide borosilicate (LaBS) glass appears to be a viable option for the disposition of excess weapons-useable plutonium that is not suitable for processing into mixed oxide (MOX) fuel. A significant effort to develop a glass formulation and vitrification process to immobilize plutonium was completed in the mid-1990s. The LaBS glass formulation was found to be capable of immobilizing in excess of 10 wt % Pu and to be tolerant of a range of impurities. To confirm the results of previous testing with surrogate Pu feeds containing impurities, four glass compositions were selected for fabrication with actual plutonium oxide and impurities. The four compositions represented extremes in impurity type and concentration. The homogeneity and durability of these four compositions were measured. The homogeneity of the glasses was evaluated using x-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS). The XRD results indicated that the glasses were amorphous with no evidence of crystalline species in the glass. The SEM/EDS analyses did show the presence of some undissolved PuO{sub 2} material. The EDS spectra indicated that some of the PuO{sub 2} crystals also contained hafnium oxide. The SEM/EDS analyses showed that there were no heterogeneities in the glass due to the feed impurities. The durability of the glasses was measured using the Product Consistency Test (PCT). The PCT results indicated that the durability of Pu impurity glasses was comparable with Pu glasses without impurities and significantly more durable than the Environmental Assessment (EA) glass used as the benchmark for repository disposition of high-level waste (HLW) glasses.

  14. Power Radiated from ITER and CIT by Impurities

    DOE R&D Accomplishments Database

    Cummings, J.; Cohen, S. A.; Hulse, R.; Post, D. E.; Redi, M. H.; Perkins, J.

    1990-07-01

    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 Z{sub eff}, 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.

  15. Interaction of two substitutional impurity atoms in an hcp crystal

    NASA Astrophysics Data System (ADS)

    Belan, V. I.; Landau, A. I.

    2010-04-01

    Molecular dynamics computer simulation with a Lennard-Jones potential is used to investigate the interaction of two identical substitutional impurity atoms in an hcp crystal lattice. Different atomic radii of the impurities atoms, interaction energy of the atoms and the lattice atoms, and initial distances between the impurity atoms at zero temperature and pressure. It is found that in a number of cases for small distances between the impurity atoms not exceeding five interatomic distances these atoms attract one another contrary to the well-known laws of the continuum theory of elasticity. Good agreement between the computational results and the theory of elasticity obtains for short distances between impurity atoms.

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

    PubMed

    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

  17. Physicochemical characterization of ezetimibe and its impurities

    NASA Astrophysics Data System (ADS)

    Filip, Katarzyna; Bańkowski, Krzysztof; Sidoryk, Katarzyna; Zagrodzka, Joanna; Łaszcz, Marta; Trzcińska, Kinga; Szyprowska, Anna; Cmoch, Piotr; Maruszak, Wioleta

    2011-04-01

    The physicochemical characterization of major degradation and process-related impurities associated with the synthesis of ezetimibe was performed. The possibility of forming the undesirable ( R, R, S) stereoisomer of ezetimibe has been mentioned in literature (Vinod KK, Suhail A, Bhupendra T, Nitin G US 2010/0010212 A1, Ind-Swift Laboratories Limited WO 2008/096372), but no study of its structure determination has been published yet. This paper discusses the structure elucidation of the ( R, R, S) stereoisomer as well as ezetimibe degradation product on the bases of NMR, IR and MS data. Other potential impurities of ezetimibe are also described. A selective and stability-indicating high-performance liquid chromatography method with dual UV detection was developed for the determination of chemical and stereochemical purity of ezetimibe. The characterization of particle size and shape for ezetimibe and its stereoisomer is also described.

  18. Bound States in Boson Impurity Models

    NASA Astrophysics Data System (ADS)

    Shi, Tao; Wu, Ying-Hai; González-Tudela, A.; Cirac, J. I.

    2016-04-01

    The formation of bound states involving multiple particles underlies many interesting quantum physical phenomena, such as Efimov physics or superconductivity. In this work, we show the existence of an infinite number of such states for some boson impurity models. They describe free bosons coupled to an impurity and include some of the most representative models in quantum optics. We also propose a family of wave functions to describe the bound states and verify that it accurately characterizes all parameter regimes by comparing its predictions with exact numerical calculations for a one-dimensional tight-binding Hamiltonian. For that model, we also analyze the nature of the bound states by studying the scaling relations of physical quantities, such as the ground-state energy and localization length, and find a nonanalytical behavior as a function of the coupling strength. Finally, we discuss how to test our theoretical predictions in experimental platforms, such as photonic crystal structures and cold atoms in optical lattices.

  19. Tin impurity centers in glassy germanium chalcogenides

    SciTech Connect

    Bordovsky, G. A.; Gladkikh, P. V.; Kozhokar, M. Yu.; Marchenko, A. V.; Seregin, P. P.; Terukov, E. I.

    2011-10-15

    Tin atoms produced by radioactive decay of {sup 119mm}Sn and {sup 119}Sn impurity atoms in the structure of Ge{sub x}S{sub 1-x} and Ge{sub x}Se{sub 1-x} glasses are stabilized in the form of Sn{sup 2+} and Sn{sup 4+} ions and correspond to ionized states of the amphoteric two-electron center with negative correlation energy (Sn{sup 2+} is an ionized acceptor, and Sn{sup 4+} is an ionized donor), whereas the neutral state of the Sn{sup 3+} center appears to be unstable. {sup 119}Sn atoms produced by radioactive decay of {sup 119m}Te impurity atoms in the structure of Ge{sub x}S{sub 1-x} and Ge{sub x}Se{sub 1-x} glasses are stabilized at both chalcogen sites (they are electrically inactive) and germanium sites.

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

    SciTech Connect

    Czarnecka, A.; Bobkov, V.; Maggi, C.; Pütterich, T.; Coffey, I. H.; Colas, L.; Jacquet, P.; Lawson, K. D.; Mayoral, M.-L. [Euratom Collaboration: JET-EFDA Contributors

    2014-02-12

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

  1. Impurity transport and retention in a gas target divertor: simulation experiments in PISCES-A and modeling results

    NASA Astrophysics Data System (ADS)

    Schmitz, L.; Blush, L.; Chevalier, G.; Lehmer, R.; Hirooka, Y.; Chia, P.; Tynan, G.; Conn, R. W.

    1992-12-01

    Impurity retention in the gaseous divertor regime is investigated in the PISCES-A facility at UCLA. We report measurements and 1 1/2D fluid modeling results of impurity transport for typical tokamak divertor plasma parameters (10 18≤ ne≤3×10 19m -3, kTe≤20 eV). The neutral hydrogen density close to the (simulated) divertor target is 10 20≤ n0≤3×10 21 m -3. Gaseous trace impurities (argon, neon) as well as low- Z and high- Z materials sputtering carbon, tungsten) are studied. It is observed that the impurity retention in a gaseous divertor is substantially improved as compared to conventional divertor operating regimes. The modeling results suggest that the retention of neutral and ionized impurities is mainly due to collisions with hydrogen (deuterium) neutrals and ions streaming towards the divertor target a a velocity of 0.25-0.5 cs. A low level of residual impurity transport, observed at high neutral density, is attributed to a plasma flow reversal close to the radial boundary. Sputtering of a tungsten sample by intrinsic impurities has been shown to decrease substantially for target electron temperatures kTe<5 eV.

  2. Impurities: Curse and blessing for crystal growers

    NASA Astrophysics Data System (ADS)

    Fox, Donald K.; Mazelsky, R.

    1990-11-01

    The indespensability of high-quality source materials research and development has been established for many years. However, because contributors to this field are diverse and communication of research results is often fragmented, transfer of the new knowledge is very slow. This paper describes how increasing source purity has improved the quality of several crystals, and how the addition of controlled impurities has decreased the defect density in these crystals. Experimental evidence is presented in this paper.

  3. Heat of segregation of single substitutional impurities

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Good, Brian; Ferrante, John

    1993-01-01

    The method of Bozzolo, Ferrante and Smith (BFS) is applied for the calculation of the heat of segregation of single substitutional impurities in fcc metals. A simple equation for predicting the heat of segregation is derived for the rigid case (no atomic relaxations). The results of including atomic relaxation using a Monte Carlo method are also presented and the results compared with a number of experimental and theoretical results.

  4. Thermalization and dynamics in the single-impurity Anderson model

    NASA Astrophysics Data System (ADS)

    Weymann, Ireneusz; von Delft, Jan; Weichselbaum, Andreas

    2015-10-01

    We analyze the process of thermalization, dynamics, and the eigenstate thermalization hypothesis (ETH) for the single-impurity Anderson model, focusing on the Kondo regime. For this we construct the complete eigenbasis of the Hamiltonian using the numerical renormalization group (NRG) method in the language of the matrix product states. It is a peculiarity of the NRG that while the Wilson chain is supposed to describe a macroscopic bath, very few single-particle excitations already suffice to essentially thermalize the impurity system at finite temperature, which amounts to having added a macroscopic amount of energy. Thus, given an initial state of the system such as the ground state together with microscopic excitations, we calculate the spectral function of the quantum impurity using the microcanonical and diagonal ensembles. These spectral functions are compared to the time-averaged spectral function obtained by time evolving the initial state according to the full Hamiltonian, and to the spectral function calculated using the thermal density matrix. By adding or removing particles at a certain Wilson energy shell on top of the ground state, we find qualitative agreement between the resulting spectral functions calculated for different ensembles. This indicates that the system thermalizes in the long-time limit, and can be described by an appropriate statistical-mechanical ensemble. Moreover, by calculating static quantities such as the impurity spectral density at the Fermi level as well as the dot occupancy for energy eigenstates relevant for microcanonical ensemble, we find good support for the ETH. The ultimate mechanism responsible for this effective thermalization within the NRG can be identified as Anderson orthogonality: the more charge that needs to flow to or from infinity after applying a local excitation within the Wilson chain, the more the system looks thermal afterwards at an increased temperature. For the same reason, however, thermalization

  5. Phase growth in bistable systems with impurities.

    PubMed

    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

  6. Inhomogeneous CDMFT and nonmagnetic impurities in graphene

    NASA Astrophysics Data System (ADS)

    Charlebois, M.; Sénéchal, D.; Gagnon, A.-M.; Tremblay, A.-M. S.

    In cluster dynamical mean-field theory (CDMFT), we usually apply the self-consistency condition on an infinite super-lattice of identical clusters. However, in some problems a large unit cell is required, for instance in the presence of a periodically repeated impurity. Since the impurity solver (exact diagonalization) can only treat small clusters, we break the unit cell into multiple small clusters that can be solved individually. This new technique is called inhomogeneous CDMFT (1) and is analogous to inhomogeneous DMFT (2). In this presentation, we will explain both the CDMFT and inhomogeneous CDMFT self-consistency loops within a unified, simple picture. We then apply this technique to a nonmagnetic impurity in graphene and study the emerging magnetism. Our results take into account dynamical correlations; nevertheless they qualitatively agree with previous mean-field and density functional theory studies. (1) Charlebois, M. et al., Phys. Rev. B 91, 035132 (2015). (2) Snoek, M. et al., New J. Phys. 10, 093008 (2008). Supported by NSERC, CIFAR and the Tier I Canada Research Chair Program.

  7. Effect of hydrogenic impurity on linear and nonlinear optical absorption coefficients and refractive index changes in a quantum dot

    NASA Astrophysics Data System (ADS)

    Guo, Kangxian; Zhang, Zhongmin; Mou, Sen; Xiao, Bo

    2015-05-01

    The analytical expressions of linear and nonlinear optical absorption coefficients and refractive index changes in a quantum dot with a hydrogenic impurity are obtained by using the compact-density-matrix approach and iterative method. The wave functions and the energy levels are obtained by using the variational method. Numerical results show that the optical absorption coefficients and refractive index changes are strongly affected by the hydrogenic impurity.

  8. Impure CO2 geological storage: Preliminary laboratory experiments at ambient conditions

    NASA Astrophysics Data System (ADS)

    Oostrom, M.; Wei, N.; Wang, Y.; Zhang, C.; Bonneville, A.

    2011-12-01

    The cost of carbon capture is related to the purity of the CO2 and subsequent removal of the impurities may be costly. For several sites, it is likely to be more cost effective if impure CO2 is injected, although non-condensable impurities may reduce storage capacity and increase the injection pressure. The feasibility of co-sequestration of CO2 with a certain level of impurity has not been experimentally studied in much detail due to severe limitations associated with visualization and sampling at high pressure and temperature conditions. A series of intermediate-scale experiments has been conducted in a 100-cm-long, 20-cm-high, and 5-cm-wide intermediate-scale flow cell studying the effects of N2 and H2S impurities on CO2 transport in initially brine-saturated porous media. Homogeneous and simple layered heterogeneous systems were used to evaluate pH behavior, measure water and gas pressures, and analyze the gas composition at several locations. A multiphase code was used to compare simulation results for equilibrium dissolution conditions with experimental results. Although these preliminary analogue experiments were conducted at ambient pressure and temperature, the provide insight in the behavior of injected multi-component gas in initially saturated porous media.

  9. Chiral phase transition in QED3 at finite temperature and impurity potential

    NASA Astrophysics Data System (ADS)

    Yin, Pei-Lin; Wei, Wei; Xiao, Hai-Xiao; Feng, Hong-Tao; Liu, Xiao-Jun; Zong, Hong-Shi

    2016-01-01

    In a realistic interacting system described by (2 +1 )-dimensional quantum electrodynamics (QED3 ), there is always a certain number of impurities by which fermions are scattered. In general, impurity scattering can generate a finite density of states at the Fermi level, which screens the temporal component of the gauge field. This effect is expected to weaken dynamical fermion mass generation. Within the Born approximation, by introducing a damping term in the energy component of the fermion propagator, the influences of finite temperature and impurity scattering on the chiral phase transition in QED3 are investigated. Pursuing this aim, we solve the Dyson-Schwinger equations for the fermion and boson propagators to the leading order in 1 /Nf expansion at zero frequency and then calculate the chiral condensate, the chiral susceptibility, and the thermal susceptibility within a range of the impurity scattering rates Γ and the numbers of fermion flavors Nf. It is found that impurity scattering leads to an obvious suppression of the dynamical fermion mass generation and critical temperature Tc.

  10. Non-intrusive, on-line, simultaneous multi-species impurity monitoring in hydrogen using LIBS

    NASA Astrophysics Data System (ADS)

    Eseller, K. E.; Yueh, F.-Y.; Singh, J. P.

    2011-03-01

    Laser-induced breakdown spectroscopy (LIBS) has been evaluated for on-line, simultaneous multi-species impurity monitoring in hydrogen. A miniature spectrometer with spectral coverage of 620-800 nm and a gated detection system with spectral coverage of 40 nm were both used to record LIBS spectra from the spark produced in sample gas by a frequency-doubled Nd YAG laser. The effect of pressure on detecting the impurity (e.g., nitrogen, argon, and oxygen) in hydrogen was studied. LIBS spectra with different impurity levels of nitrogen, argon, and oxygen were recorded, and the intensity of the spectral lines of Ar, O, N, and H observed were used to form calibration plots for impurity measurement. The limits of detection (LODs) for oxygen, argon, and nitrogen in hydrogen were estimated from the calibration obtained with both the gated and ungated detection. The hydrogen impurity measurements based on the ungated miniature system show reliable and reproductive results. But the LODs with this system are about four times higher than the LODs obtained with a gated detection system in this work.

  11. Impurity scattering and Friedel oscillations in monolayer black phosphorus

    NASA Astrophysics Data System (ADS)

    Zou, Yong-Lian; Song, Juntao; Bai, Chunxu; Chang, Kai

    2016-07-01

    We study the impurity scattering effect in black phosphorene (BP) in this work. For a single impurity, we calculate the impurity-induced local density of states (LDOS) in momentum space numerically based on a tight-binding Hamiltonian. In real space, we calculate the LDOS and Friedel oscillation analytically. The LDOS shows strong anisotropy in BP. Many impurities in BP are investigated using the T -matrix approximation when the density is low. Midgap states appear in the band gap with peaks in the DOS. The peaks of midgap states are dependent on the impurity potential. For finite positive potential, the impurity tends to bind negative charge carriers and vice versa. The infinite-impurity-potential problem is related to chiral symmetry in BP.

  12. EFFECTS OF FUEL IMPURITIES ON PEM FUEL CELL PERFORMANCE.

    SciTech Connect

    Uribe, F. A.; Zawodzinski, T. A. , Jr.

    2001-01-01

    the membrane, is the primary reason for cell current losses. H{sub 2}S also adversely affects FC performance. Figure 1 depicts the current density changes in a FC exposed to both 1 and 3 ppm H{sub 2}S while operating at a constant voltage of 0.5 V. As expected, the greater the contamination level the faster the current density drops. Eventually in each case the cell becomes totally disabled. The effect H{sub 2}S appears to be cumulative, because even sub-ppm H{sub 2}S levels will decrease the FC performance if the exposure is long enough. We have recorded slow current droppings to about 20% of the initial value after exposure to concentrations of H{sub 2}S of 200 parts per billion (10{sup 9}) for 650 hours. Exposure to higher concentrations of H{sub 2}S may bring catastrophic consequences. We have exposed cell anodes to H{sub 2}S burps of the order of 8 ppm, and observed that the current at 0.5 V dropped from 1.1 to 0.3 A cm{sup -2} in just few minutes. Figure 2 shows the effect of H{sub 2}S on cell polarization. Curves b and c in this figure were recorded after 4 and 21 hours of exposure to 1 ppm H{sub 2}S, respectively, while keeping the cell at a constant voltage of 0.5 V. Regardless impurity concentration and running time, replacing the contaminated fuel stream with pure H{sub 2} does not allow any recovery as observed with CO poisoning. Cyclic voltammmetry (CV) indicates that H{sub 2}S chemisorbs very strongly onto Pt catalyst surface and high voltages are required for full cleansing of the H{sub 2}S-poisoned active sites. After full anode poisoning with H{sub 2}S (curve c), the electrode was subjected to CV (up to 1.4 V) and then the polarization curve d (with neat H{sub 2}) was recorded. The complete cell performance recovery is apparent from this curve. A more extended discussion on H{sub 2}S catalyst poisoning and cleaning will be presented. We also tested methane (0.5 % by vol.) and ethylene (50 ppm) as potential fuel impurities and we found no effects on

  13. Lanthanide impurities in wide bandgap semiconductors: A possible roadmap for spintronic devices

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

    The electronic properties of lanthanide (from Eu to Tm) impurities in wurtzite gallium nitride and zinc oxide were investigated by first principles calculations, using an all electron methodology plus a Hubbard potential correction. The results indicated that the 4f-related energy levels remain outside the bandgap in both materials, in good agreement with a recent phenomenological model, based on experimental data. Additionally, zinc oxide doped with lanthanide impurities became an n-type material, showing a coupling between the 4f-related spin polarized states and the carriers. This coupling may generate spin polarized currents, which could lead to applications in spintronic devices.

  14. Devolution and grant-in-aid design for the provision of impure public goods.

    PubMed

    Levaggi, Laura; Levaggi, Rosella

    2016-01-01

    Traditional fiscal federalism theory postulates that devolution for the provision of local public goods increases welfare. However, most of the services offered at local level are local impure public goods whose characteristics may prevent devolution from being efficient. Our paper shows that devolution is the optimal choice only for local impure public goods. For an environment characterised by coordination and asymmetry of information problems, we propose the optimal grants-in-aid formula that Central Government should use to reduce welfare losses and we compare it with what suggested by the mainstream literature. Finally, we show under which conditions devolution should be preferred to a centralised solution. From a policy point of view, our paper may explain the heterogeneity in the choices made by countries in terms of devolution in the provision of merit and impure public goods. PMID:27047708

  15. Quantum correlations of magnetic impurities by a multiple electron scattering in carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Gamboa Angulo, Didier; Cordourier Maruri, Guillermo; de Coss Gómez, Romeo

    In this work we analyze the quantum correlations and polarizations states of magnetic impurities spins, when a multiple electron scattering was taken place. A sequence of non-correlated electrons interacts through scattering producing quantum correlation which will have an impact on the electronic transmission. We consider a short range Heisenberg interaction between ballistic electron and static impurities. We analyze the cases when the electron scattering is produce by one and two impurities, obtaining the electronic transmission rates. Concurrence and fidelity calculations are performed to obtain the level of quantum entanglement and polarization correlations. We also discuss the possible application of this model to metallic and semiconductor carbon nanotubes, which could have important implications on spintronics and quantum information devices.

  16. Effect of weak impurities on electronic properties of graphene: Functional renormalization-group analysis

    NASA Astrophysics Data System (ADS)

    Katanin, A.

    2013-12-01

    We consider an effect of weak impurities on the electronic properties of graphene within the functional renormalization-group approach. The energy dependences of the electronic self-energy and density of states near the neutrality point are discussed. Depending on the symmetry of the impurities, the electronic damping Γ and density of states ρ can deviate substantially from those given by the self-consistent Born approximation. We investigate the crossover from the results of the self-consistent Born approximation, which are valid far from the neutrality point to the strong-coupling (diffusive) regime near the neutrality point. For impurities, which are diagonal in both valley and sublattice indices, we obtain a finite density of states at the Fermi level with values which are much bigger than the result of the self-consistent Born approximation.

  17. Detection of subsurface trace impurity in polished fused silica with biological method.

    PubMed

    Wang, Zhuo; Wang, Lin; Yang, Junhong; Peng, Wenqiang; Hu, Hao

    2014-09-01

    Subsurface damage (SSD), especially photoactive impurities, degrades the performance of high energy optics by reduction in the laser induced damage threshold. As the polishing defects are trace content and lie beneath the surface, they are difficult to detect. We herein present a biological method to measure impurities on polished fused silica, based on the intense inhibiting ability about trace level of ceria on enzyme activity. And the enzyme activity is measured in the individual etching solutions of a sequential etching process. Results show that detectability of the biological method satisfies the needs of trace impurity detection with low cost and simple apparatus. Furthermore ceria can be used to tag SSD in lapped and polished optics. PMID:25321508

  18. Joint interpretation of high-precision tilt data and mining induced seismic events recorded underground in deep level gold mine in South Africa

    NASA Astrophysics Data System (ADS)

    Milev, Alexander; Share, Pieter; Durrheim, Ray; Naoi, Makoto; Nakatani, Masao; Yabe, Yasuo; Ogasawara, Hiroshi

    2013-04-01

    Seismicity associated with deep-level mining has for long been a problem, leading to rockburst and other similar hazards. Several studies have been completed in an attempt to minimize the total amount of seismicity. In this study high resolution measurements of ground tilting in combination with seismic monitoring is used to observe how the rock mass responds to mining. A good correspondence between the coseismic and the aseismic tilt was found. The rate of coseismic and aseismic tilt, as well as seismicity recorded by the mine seismic network, are approximately constant until the daily blasting time, which takes place from about 19:30 until shortly before 21:00. During the blasting time and the subsequent seismic events, the coseismic and aseismic tilt shows a rapid increase. In an attempt to distinguish between the different mechanisms of tilting two types of events were recognized. The "fast" seismic events characterized with sharp increase of the tilt during the seismic rupture and "slow" seismic events characterized by creep type post seismic deformations. Tilt behaviour before and after a seismic event was also analysed. The fact that no recognizable aftertilt was observed for more of the "fast" seismic events means that there is no gradual release of stress and an associated continuous strain rate change afterwards. It can therefore be concluded that a large seismic event causes a rapid change in the state of stress rather than a gradual change in the strain rate. The mechanism of the observed "slow" seismic events is more complicated. Although several explanations have been proposed, a suggestion for further work could be to investigate the presence of "slow" events in or after blasting time more closely. During the monitoring period a seismic event with MW 2.2 occurred in the vicinity of the instrumented site. This event was recorded by both the CSIR integrated monitoring system and JAGUARS acoustic emission network. More than 21,000 AE aftershocks were

  19. Laser-induced fluorescence of metal-atom impurities in a neutral beam

    SciTech Connect

    Burrell, C.F.; Pyle, R.V.; Sabetimani, Z.; Schlachter, A.S.

    1984-10-01

    The need to limit impurities in fusion devices to low levels is well known. We have investigated, by the technique of laser-induced fluorescence, the concentration of heavy-metal atoms in a neutral beam caused by their evaporation from the hot filaments in a conventional high-current multifilament hydrogen-ion source.

  20. A mechanistic study of impurity segregation at silicon grain boundaries

    SciTech Connect

    Käshammer, Peter; Sinno, Talid

    2015-09-07

    The segregation behavior of carbon and oxygen atoms at various silicon grain boundaries was studied using a combination of atomistic simulation and analytical modeling. First, quasi-lattice Grand Canonical Monte Carlo simulations were used to compute segregation isotherms as a function of grain boundary type, impurity atom loading level, and temperature. Next, the atomistic results were employed to regress different analytical segregation models and extract thermodynamic and structural properties. The multilayer Brunauer–Emmett–Teller (BET) isotherm was found to quantitatively capture all the simulation conditions probed in this work, while simpler, single layer models such as the Langmuir-McLean model did not. Some of the BET parameters, namely, the binding free energy of the first adsorption layer and the impurity holding capacity of each layer, were tested for correlation with various measures of grain boundary structure and/or mechanical properties. It was found that certain measures of the atomistic stress distribution correlate strongly with the first-layer binding free energy for substitutional carbon atoms, while common grain boundary identifiers such as sigma value and energy density are not useful in this regard. Preliminary analysis of the more complex case of interstitial oxygen segregation showed that similar measures based on atomistic stress also may be useful here, but more systematic correlative studies are needed to develop a comprehensive picture.

  1. A mechanistic study of impurity segregation at silicon grain boundaries

    NASA Astrophysics Data System (ADS)

    Käshammer, Peter; Sinno, Talid

    2015-09-01

    The segregation behavior of carbon and oxygen atoms at various silicon grain boundaries was studied using a combination of atomistic simulation and analytical modeling. First, quasi-lattice Grand Canonical Monte Carlo simulations were used to compute segregation isotherms as a function of grain boundary type, impurity atom loading level, and temperature. Next, the atomistic results were employed to regress different analytical segregation models and extract thermodynamic and structural properties. The multilayer Brunauer-Emmett-Teller (BET) isotherm was found to quantitatively capture all the simulation conditions probed in this work, while simpler, single layer models such as the Langmuir-McLean model did not. Some of the BET parameters, namely, the binding free energy of the first adsorption layer and the impurity holding capacity of each layer, were tested for correlation with various measures of grain boundary structure and/or mechanical properties. It was found that certain measures of the atomistic stress distribution correlate strongly with the first-layer binding free energy for substitutional carbon atoms, while common grain boundary identifiers such as sigma value and energy density are not useful in this regard. Preliminary analysis of the more complex case of interstitial oxygen segregation showed that similar measures based on atomistic stress also may be useful here, but more systematic correlative studies are needed to develop a comprehensive picture.

  2. Valency configuration of transition metal impurities in ZnO

    SciTech Connect

    Petit, Leon; Schulthess, Thomas C; Svane, Axel; Temmerman, Walter M; Szotek, Zdzislawa; Janotti, Anderson

    2006-01-01

    We use the self-interaction corrected local spin-density approximation to investigate the ground state valency configuration of transition metal (TM=Mn, Co) impurities in n- and p-type ZnO. We find that in pure Zn{sub 1-x}TM{sub x}O, the localized TM{sup 2+} configuration is energetically favored over the itinerant d-electron configuration of the local spin density (LSD) picture. Our calculations indicate furthermore that the (+/0) donor level is situated in the ZnO gap. Consequently, for n-type conditions, with the Fermi energy {epsilon}F close to the conduction band minimum, TM remains in the 2+ charge state, while for p-type conditions, with {epsilon}F close to the valence band maximum, the 3+ charge state is energetically preferred. In the latter scenario, modeled here by co-doping with N, the additional delocalized d-electron charge transfers into the entire states at the top of the valence band, and hole carriers will only exist, if the N concentration exceeds the TM impurity concentration.

  3. Oxygen and carbon impurities and related defects in silicon

    NASA Technical Reports Server (NTRS)

    Pearce, C. W.

    1985-01-01

    Oxygen and carbon are the predominant impurities in Czochralski-grown silicon. The incorporation of oxygen and carbon during crystal growth is reviewed and device effects are discussed. Methods for controlling oxygen and carbon incorporation during crystal growth are discussed and results supporting a segregation coefficient of k=0.5 for oxygen are presented. The nucleation and precipitation behavior of oxygen is complex. Temperature and doping level effects which add insight into the role of point defects in the nucleation process are highlighted. In general, precipitation is found to be retarded in N+ and P+ silicon. The types and quantities of defects resulting from the oxygen precipitates is of interest as they are technologically useful in the process called intrinsic gettering. A comparison is made between the available defect sites and the quantities of metallic impurities present in a typical wafer which need to be gettered. Finally, a discussion of the denuded-zone, intrinsic-gettered (DZ-IG) structure on device properties is presented.

  4. Characterization and validation of an in silico toxicology model to predict the mutagenic potential of drug impurities*

    SciTech Connect

    Valerio, Luis G.; Cross, Kevin P.

    2012-05-01

    Control and minimization of human exposure to potential genotoxic impurities found in drug substances and products is an important part of preclinical safety assessments of new drug products. The FDA's 2008 draft guidance on genotoxic and carcinogenic impurities in drug substances and products allows use of computational quantitative structure–activity relationships (QSAR) to identify structural alerts for known and expected impurities present at levels below qualified thresholds. This study provides the information necessary to establish the practical use of a new in silico toxicology model for predicting Salmonella t. mutagenicity (Ames assay outcome) of drug impurities and other chemicals. We describe the model's chemical content and toxicity fingerprint in terms of compound space, molecular and structural toxicophores, and have rigorously tested its predictive power using both cross-validation and external validation experiments, as well as case studies. Consistent with desired regulatory use, the model performs with high sensitivity (81%) and high negative predictivity (81%) based on external validation with 2368 compounds foreign to the model and having known mutagenicity. A database of drug impurities was created from proprietary FDA submissions and the public literature which found significant overlap between the structural features of drug impurities and training set chemicals in the QSAR model. Overall, the model's predictive performance was found to be acceptable for screening drug impurities for Salmonella mutagenicity. -- Highlights: ► We characterize a new in silico model to predict mutagenicity of drug impurities. ► The model predicts Salmonella mutagenicity and will be useful for safety assessment. ► We examine toxicity fingerprints and toxicophores of this Ames assay model. ► We compare these attributes to those found in drug impurities known to FDA/CDER. ► We validate the model and find it has a desired predictive performance.

  5. Theoretical Study of Radiation from a Broad Range of Impurity Ions for Magnetic Fusion Diagnostics

    SciTech Connect

    Safronova, Alla

    2014-03-14

    Spectroscopy of radiation emitted by impurities plays an important role in the study of magnetically confined fusion plasmas. The measurements of these impurities are crucial for the control of the general machine conditions, for the monitoring of the impurity levels, and for the detection of various possible fault conditions. Low-Z impurities, typically present in concentrations of 1%, are lithium, beryllium, boron, carbon, and oxygen. Some of the common medium-Z impurities are metals such as iron, nickel, and copper, and high-Z impurities, such as tungsten, are present in smaller concentrations of 0.1% or less. Despite the relatively small concentration numbers, the aforementioned impurities might make a substantial contribution to radiated power, and also influence both plasma conditions and instruments. A detailed theoretical study of line radiation from impurities that covers a very broad spectral range from less than 1 Å to more than 1000 Å has been accomplished and the results were applied to the LLNL Electron Beam Ion Trap (EBIT) and the Sustained Spheromak Physics Experiment (SSPX) and to the National Spherical Torus Experiment (NSTX) at Princeton. Though low- and medium-Z impurities were also studied, the main emphasis was made on the comprehensive theoretical study of radiation from tungsten using different state-of-the-art atomic structure codes such as Relativistic Many-Body Perturbation Theory (RMBPT). The important component of this research was a comparison of the results from the RMBPT code with other codes such as the Multiconfigurational Hartree–Fock developed by Cowan (COWAN code) and the Multiconfiguration Relativistic Hebrew University Lawrence Atomic Code (HULLAC code), and estimation of accuracy of calculations. We also have studied dielectronic recombination, an important recombination process for fusion plasma, for variety of highly and low charged tungsten ions using COWAN and HULLAC codes. Accurate DR rate coefficients are needed for

  6. A charge-based deep level transient spectroscopy measurement system and characterization of a ZnO-based varistor and a Fe-doped SrTiO3 dielectric

    NASA Astrophysics Data System (ADS)

    Okamoto, Takafumi; Long, Jeffrey; Wilke, Rudeger H. T.; Stitt, Joseph; Maier, Russell; Randall, Clive A.

    2016-02-01

    A charge-based deep level transient spectroscopy (Q-DLTS) method is applied to provide insights into the electronic behavior near grain boundaries and may provide new insights into mechanisms such as fatigue, degradation, dielectric aging, and dielectric breakdown. Here, we tested the Q-DLTS in both a ZnO varistor material and Fe-doped SrTiO3 materials. Comparisons are made to other data on ZnO varistors, and we obtain very good agreement for the energy levels. The status of deep traps in Fe-doped SrTiO3 dielectrics has been investigated where the relaxation was contrasted in a single crystal and polycrystalline ceramic materials. The relaxation is only observable in the polycrystalline materials, and was absent in single crystal Fe-doped crystals indicating that the deep traps originating from the Schottky barriers at the grain boundaries provide the DLTS signals. The energy associated with this grain boundary trap was found to be 1.26 eV.

  7. Wafer-level fabrication of a high-silica v-groove for fiber-optic packaging using deep dry-etching with a dual-frequency high-density plasma

    NASA Astrophysics Data System (ADS)

    Ha, Tae-Won; Heo, Gi-Seok; Choi, Bum-Ho; Kim, Young-Baek; Oh, Jin-Kyoung; Lee, Hyung-Jong

    2015-10-01

    We developed a procedure for fabricating deep silica v-grooves of about 70 μm for fiber-optic applications by using a deep dry-etching with a dual-frequency high-density plasma source. This procedure has the advantages of sub-micron precision with wafer-level productivity and a high etching speed of 0.7 μm/sec. An electro-plated hard mask as thick as 8 μm that can endure the deep dry-etch was also developed. In particular, the angular inclination of the etched groove was controllable by using the flow of C4F8 gas. A fiber array block was assembled by using a v-groove chip. The location error of the fiber cores in the block was measured to be less than 0.3 μm. This confirms that the dry-etched silica v-grooves can be applied to the packaging of optical devices with wafer-level productivity and high precision.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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. PMID:27104716

  10. Motion of a distinguishable Impurity in the Bose gas: Arrested expansion without a lattice and impurity snaking

    DOE PAGESBeta

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

    2016-04-07

    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. In conclusion, when the impurity is injected with a finite center-of-mass momentum,more » 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.« less

  11. Deep smarts.

    PubMed

    Leonard, Dorothy; Swap, Walter

    2004-09-01

    When a person sizes up a complex situation and rapidly comes to a decision that proves to be not just good but brilliant, you think, "That was smart." After you watch him do this a few times, you realize you're in the presence of something special. It's not raw brainpower, though that helps. It's not emotional intelligence, either, though that, too, is often involved. It's deep smarts. Deep smarts are not philosophical--they're not"wisdom" in that sense, but they're as close to wisdom as business gets. You see them in the manager who understands when and how to move into a new international market, in the executive who knows just what kind of talk to give when her organization is in crisis, in the technician who can track a product failure back to an interaction between independently produced elements. These are people whose knowledge would be hard to purchase on the open market. Their insight is based on know-how more than on know-what; it comprises a system view as well as expertise in individual areas. Because deep smarts are experienced based and often context specific, they can't be produced overnight or readily imported into an organization. It takes years for an individual to develop them--and no time at all for an organization to lose them when a valued veteran walks out the door. They can be taught, however, with the right techniques. Drawing on their forthcoming book Deep Smarts, Dorothy Leonard and Walter Swap say the best way to transfer such expertise to novices--and, on a larger scale, to make individual knowledge institutional--isn't through PowerPoint slides, a Web site of best practices, online training, project reports, or lectures. Rather, the sage needs to teach the neophyte individually how to draw wisdom from experience. Companies have to be willing to dedicate time and effort to such extensive training, but the investment more than pays for itself. PMID:15449858

  12. Deep Level Defect Studies in MOCVD-Grown In(x)Ga(1-x)As(1-y)N(y) Films Lattice-Matched to GaAs

    SciTech Connect

    Allerman, A.A.; Boeckl, J.J.; Jones, E.D.; Kaplar, R.J.; Kurtz, S.R.; Kwon, D.; Ringel, S.A.

    1999-03-04

    Deep level defects in MOCVD-grown, unintentionally doped p-type InGaAsN films lattice matched to GaAs were investigated using deep level transient spectroscopy (DLTS) measurements. As-grown p-InGaAsN showed broad DLTS spectra suggesting that there exists a broad distribution of defect states within the band-gap. Moreover, the trap densities exceeded 10{sup 15} cm{sup {minus}3}. Cross sectional transmission electron microscopy (TEM) measurements showed no evidence for threading dislocations within the TEM resolution limit of 10{sup 7} cm{sup {minus}2}. A set of samples was annealed after growth for 1800 seconds at 650 C to investigate the thermal stability of the traps. The DLTS spectra of the annealed samples simplified considerably, revealing three distinct hole trap levels with energy levels of 0.10 eV, 0.23 eV, and 0.48 eV above the valence band edge with trap concentrations of 3.5 x 10{sup 14} cm{sup {minus}3}, 3.8 x 10{sup 14} cm {sup {minus}3}, and 8.2 x 10{sup 14} cm{sup {minus}3}, respectively. Comparison of as-grown and annealed DLTS spectra showed that post-growth annealing effectively reduced the total trap concentration by an order of magnitude across the bandgap. However, the concentration of a trap with an energy level of 0.48 eV was not affected by annealing indicating a higher thermal stability for this trap as compared with the overall distribution of shallow and deep traps.

  13. Deep traps in nonpolar m-plane GaN grown by ammonia-based molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Hurni, C. A.; Arehart, A. R.; Yang, J.; Myers, R. C.; Speck, J. S.; Ringel, S. A.

    2012-01-01

    Deep level defects in nonpolar m-plane GaN grown by ammonia-based molecular beam epitaxy were characterized using deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) and compared with polar c-plane GaN that was grown simultaneously in the same growth run. Significant differences in both the levels present and their concentrations were observed upon comparison of both growth orientations. DLTS revealed electron traps with activation energies of 0.14 eV, 0.20 eV, and 0.66 eV in the m-plane material, with concentrations that were ˜10-50 × higher than traps of similar activation energies in the c-plane material. Likewise, DLOS measurements showed ˜20 × higher concentrations of both a CN acceptor-like state at EC - 3.26 eV, which correlates with a high background carbon concentration observed by secondary ion mass spectroscopy for the m-plane material [A. Armstrong, A. R. Arehart, B. Moran, S. P. DenBaars, U. K. Mishra, J. S. Speck, and S. A. Ringel, Appl. Phys. Lett. 84, 374 (2004)], and the VGa-related state level at EC - 2.49 eV, which is consistent with an enhanced yellow luminescence observed by photoluminescence. The findings suggest a strong impact of growth dynamics on the incorporation of impurities and electrically active native point defects as a function of GaN growth plane polarity.

  14. A review of impurity transport characteristics in the LHD

    NASA Astrophysics Data System (ADS)

    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.

  15. Density matrix renormalization group study in energy space for a single-impurity Anderson model and an impurity quantum phase transition

    NASA Astrophysics Data System (ADS)

    Shirakawa, Tomonori; Yunoki, Seiji

    2016-05-01

    The density matrix renormalization group method is introduced in energy space to study Anderson impurity models. The method allows for calculations in the thermodynamic limit and is advantageous for studying not only the dynamical properties, but also the quantum entanglement of the ground state at the vicinity of an impurity quantum phase transition. This method is applied to obtain numerically exactly the ground-state phase diagram of the single-impurity Anderson model on the honeycomb lattice at half-filling. The calculation of local static quantities shows that the phase diagram contains two distinct phases, the local moment (LM) phase and the asymmetric strong coupling (ASC) phase, but no Kondo screening phase. These results are supported by the local spin and charge excitation spectra, which exhibit qualitatively different behavior in these two phases and also reveal the existence of the valence fluctuating point at the phase boundary. For comparison, we also study the low-energy effective pseudogap Anderson model using the method introduced here. Although the high-energy excitations are obviously different, we find that the ground-state phase diagram and the asymptotically low-energy excitations are in good quantitative agreement with those for the single-impurity Anderson model on the honeycomb lattice, thus providing a quantitative justification for the previous studies based on low-energy approximate approaches. Furthermore, we find that the lowest entanglement level is doubly degenerate for the LM phase, whereas it is singlet for the ASC phase and is accidentally threefold degenerate at the valence fluctuating point. This should be contrasted with the degeneracy of the energy spectrum because the ground state is found to be always singlet. Our results therefore clearly demonstrate that the low-lying entanglement spectrum can be used to determine with high accuracy the phase boundary of the impurity quantum phase transition.

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

    PubMed

    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. Electronic structure of magnetic impurities in copper

    SciTech Connect

    Vvedensky, D.D.; Eberhart, M.E.; McHenry, M.E.

    1987-02-01

    We show that the anomalously small impurity exchange splittings obtained from previously reported multiple-scattering X..cap alpha.. cluster calculations for the dilute alloys CuM (M represents a 3d transition metal) were due to incomplete convergence to self-consistency. Proper self-consistent calculations produce exchange splittings that are in excellent agreement with other calculations, which we illustrate with CuMn. We compare in detail the results of our calculations with those obtained with other approaches and discuss briefly the role of many-body effects in the CuM alloy series.

  18. Enhanced ionized impurity scattering in nanowires

    NASA Astrophysics Data System (ADS)

    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)].

  19. Impurities Formed in Artificially Aged Methylhydrazine

    NASA Technical Reports Server (NTRS)

    McClure, Mark B.; Dee, Louis A.; Johnson, Harry T.; Fries, Joseph (Technical Monitor)

    2000-01-01

    A sample of monomethylhydrazine (MMH) meeting MIL-PRF-27404C requirements was split into two portions. One portion was periodically exposed to atmospheric contaminants while stored in clear glass, and the other portion, held as a reference sample, was stored under nitrogen in amber glass. Impurities in both samples were periodically characterized by Gas Chromatograph-Mass Spectrometer (GC-MS) to determine what changes might occur in MMH when it is stored in less than ideal conditions. The qualitative and semi-quantitative results of this study are reported herein.

  20. Integrable Two-Impurity Kondo Model

    SciTech Connect

    Schlottmann, P.

    1998-06-01

    The exact solution by means of Bethe{close_quote}s {ital Ansatz} of a variant of the two-impurity Kondo problem is presented. The occupation of the singlet and triplet states, the expectation value {l_angle}{rvec S}{sub 1}{center_dot} {cflx S}{sub 2}{r_angle} , the homogeneous and staggered magnetic field susceptibilities, and the specific heat {gamma} coefficient are studied for the ground state as a function of the Ruderman-Kittel-Kasuya-Yosida{endash}coupling strength. {copyright} {ital 1998} {ital The American Physical Society}

  1. Evaluating additives and impurities in zinc electrowinning

    NASA Astrophysics Data System (ADS)

    Gonzalez-Dominguez, J. A.; Lew, R. W.

    1995-01-01

    The zinc electrowinning (EW) process is very sensitive to the presence of impurities. There is only one EW plant in the world that we know of that operates at moderate current efficiency and deposition times without using any additives. All the others must use them continuously. Additives allow zinc EW to occur at high current efficiencies while suppressing excessive acid mist formation. The study of the electrochemical effects of additives in zinc EW is not straightforward. This article presents a review of the experimental techniques currently used at Cominco Research: Cyclic voltammetry, Hull cells, laboratory and mini-cell electrowinning techniques are all described and their relationship to the industrial operation is discussed.

  2. Polar clusters in impurity-doped quantum paraelectric K1-xLixTaO3

    NASA Astrophysics Data System (ADS)

    Geneste, Grégory; Kiat, Jean-Michel; Yokota, Hiroko; Uesu, Yoshiaki; Porcher, Florence

    2010-04-01

    From density-functional calculations, we show that large off-center motions (≈1.0Å) of Li impurities in the KTaO3 matrix (studied at 3.7% concentration) create very anisotropic polar clusters oriented along the Li off-center dipole. The polarization induced by Li in the matrix decreases very sharply in the lateral directions so that polar clusters are only ≈ two lattice constants thick (one-dimensional or needlelike clusters). The polarization in such polar regions is mainly constituted by the displacements in the (highly polarizable) matrix rather than by the impurity itself. These results suggest that Li-doped potassium tantalate (3.7% concentration) is not ferroelectric at low temperature and rather behaves as a relaxor. These small polar zones around Li correlate at TB to form larger polar nanoregions, in which the matrix remains however nonpolar. This is confirmed by a low temperature neutron-diffraction analysis showing that the KTaO3 matrix remains paraelectric. Li-doped KTaO3 is an order-disorder system with a very deep local potential felt by the Li impurities (≈-200meV) . The energy barrier for Li hopping is estimated at 80-90 meV. An analytic expression for this local potential is provided, as well as a simple model describing the energetics of K1-xLixTaO3 .

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

    NASA Astrophysics Data System (ADS)

    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.

  4. Impurity confinement and transport in high confinement regimes without edge localized modes on DIII-D

    SciTech Connect

    Grierson, B. A. Nazikian, R. M.; Solomon, W. M.; Burrell, K. H.; Garofalo, A. M.; Belli, E. A.; Staebler, G. M.; Evans, T. E.; Smith, S. P.; Chrobak, C.; Fenstermacher, M. E.; McKee, G. R.; Orlov, D. M.; Chrystal, C.

    2015-05-15

    Impurity transport in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] is investigated in stationary high confinement (H-mode) regimes without edge localized modes (ELMs). In plasmas maintained by resonant magnetic perturbation (RMP), ELM-suppression, and QH-mode, the confinement time of fluorine (Z = 9) is equivalent to that in ELMing discharges with 40 Hz ELMs. For selected discharges with impurity injection, the impurity particle confinement time compared to the energy confinement time is in the range of τ{sub p}/τ{sub e}≈2−3. In QH-mode operation, the impurity confinement time is shown to be smaller for intense, coherent magnetic, and density fluctuations of the edge harmonic oscillation than weaker fluctuations. Transport coefficients are derived from the time evolution of the impurity density profile and compared to neoclassical and turbulent transport models NEO and TGLF. Neoclassical transport of fluorine is found to be small compared to the experimental values. In the ELMing and RMP ELM-suppressed plasma, the impurity transport is affected by the presence of tearing modes. For radii larger than the mode radius, the TGLF diffusion coefficient is smaller than the experimental value by a factor of 2–3, while the convective velocity is within error estimates. Low levels of diffusion are observed for radii smaller than the tearing mode radius. In the QH-mode plasma investigated, the TGLF diffusion coefficient is higher inside of ρ=0.4 and lower outside of 0.4 than the experiment, and the TGLF convective velocity is more negative by a factor of approximately 1.7.

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

    NASA Astrophysics Data System (ADS)

    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.

  6. Macromolecule Crystal Quality Improvement in Microgravity: The Role of Impurities

    NASA Technical Reports Server (NTRS)

    Judge, Russell A.; Snell, Edward H.; Pusey, Marc L.; Sportiello, Michael G.; Todd, Paul; Bellamy, Henry; Borgstahl, Gloria E.; Pokros, Matt; Cassanto, John M.

    2000-01-01

    While macromolecule impurities may affect crystal size and morphology the over-riding question is; "How do macromolecule impurities effect crystal X-ray quality and diffraction resolution?" In the case of chicken egg white lysozyme, crystals can be grown in the presence of a number of impurities without affecting diffraction resolution. One impurity however, the lysozyme dimer, does negatively impact the X-ray crystal properties. Crystal quality improvement as a result of better partitioning of this impurity during crystallization in microgravity has been reported'. In our recent experimental work dimer partitioning was found to be not significantly different between the two environments. Mosaicity analysis of pure crystals showed a reduced mosaicity and increased signal to noise for the microgravity grown crystals. Dimer incorporation however, did greatly reduce the resolution limit in both ground and microgravity grown crystals. These results indicate that impurity effects in microgravity are complex and may rely on the conditions or techniques employed.

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

    PubMed

    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

  8. Combining impurity X-ray and impurity density measurements to determine Zeff

    NASA Astrophysics Data System (ADS)

    Nornberg, M. D.; Galante, M. E.; Reusch, L. M.; den Hartog, D. J.; Franz, P.; Stephens, H. D.

    2015-11-01

    Determining the resistive dissipation of hot plasmas requires knowledge of the effective charge Zeff. Typically Zeff is determined from visible bremsstrahlung emission. In limiter plasmas with relatively high core and edge neutral density, the neutrals likely contribute as much emission to the visible spectrum as do the impurities. By using sufficiently thick Be filters, detected soft x-ray emission can be limited to a region of the spectrum dominated by bremsstrahlung and impurity recombination. Modeling this emission requires good constraints on the impurity density profiles and charge state balance. This information can be supplied by charge exchange recombination measurements (CHERS). Combining these two different diagnostic measurements within a Bayesian framework enables the self-consistent determination of Zeff = 1 . 9 +/- 0 . 1 in the core of MST RFP plasmas with tearing mode suppression. This integrated data analysis (IDA) has the additional benefit of helping identify systematic uncertainties in the individual measurements and facilitates constraining the densities of other impurities for which there are no CHERS measurements. This work is supported by the US DOE.

  9. Structural elucation of a novel impurity in rifaximin.

    PubMed

    Liuchao; Maixi; Wangchao; Wan, Chunpeng

    2012-05-01

    Rifaximin is a semi-synthetic rifamycin derivate. It acts on RNA polymerase of the subunit of DNA beta-2 in bacteria to restrain synthesis of RNA leading to antibacterial activity. The purpose of this study was to analyse the structure of the prepared impurity a. We found that the impurity a is the isomeride of impurity G defined in the European Pharmacopoeia. PMID:22764576

  10. Photocurrent in a quantum channel with an impurity

    SciTech Connect

    Margulis, V. A. Pyataev, M. A. Ulyanov, S. N.

    2013-09-15

    The influence of electromagnetic radiation on electron transport in a quantum channel with a single short-range impurity is studied using the generalization of the Landauer-Buettiker method. It is shown that a direct photocurrent is induced in the system in the case of asymmetric impurity location. The dependence of the photocurrent on the electron chemical potential, impurity location, and radiation frequency is studied.

  11. Stark effect of hydrogenic impurities in a quantum box

    NASA Astrophysics Data System (ADS)

    del Castillo-Mussot, Marcelo; Vazquez, Gerardo J.; Mendoza, Carlos I.; Spector, Harold N.

    2004-03-01

    We extend the model of a cubic quantum box proposed by Ribeiro and Latge to carry out a variational calculation of the bindingenergy of impurities in such a structure as function of anelectric field.The binding energy of the impurities increases with the electric field. In addition, the electric field splits the energy of impurities on the faces of the box which are equivalent in the absence of the electric field.

  12. The numerical renormalization group and multi-orbital impurity models

    NASA Astrophysics Data System (ADS)

    Weichselbaum, Andreas; Stadler, K. M.; von Delft, J.; Yin, Z. P.; Kotliar, G.; Mitchell, Andrew

    The numerical renormalization group (NRG) is a highly versatile and accurate method for the simulation of (effective) fermionic impurity models. Despite that the cost of NRG is exponential in the number of orbitals, by now, symmetric three-band calculations have become available on a routine level. Here we present a recent detailed study on the spin-orbital separation in a three-band Hund metal with relevance for iron-pnictides via the dynamical mean field theory (DMFT). In cases, finally, where the orbital symmetry is broken, we demonstrate that interleaved NRG still offers an accurate alternative approach within the NRG with dramatically improved numerical efficiency at comparable accuracy relative to conventional NRG.

  13. The effect of working gas impurities on plasma jets

    SciTech Connect

    Liu, X. Y.; He, M. B.; Liu, D. W.

    2015-04-15

    Air intrusion reduced the purity of working gas inside the tube for plasma jet, and thereby, affected the discharge dynamics. In this paper, the effect of using working gas with different purity level (helium purity 99.99999%, 99.99%, 99.9%, and 99%) on photoionization and the chemical reactivity of plasma jet were studied using a 2 dimensional plasma jet model. Photoionization of air species acted as a source of pre-ionization in front of the ionization region, which facilitated the transition from localized discharge to streamers inside the tube. The density of reactive species inside the tube was found to increase with the concentration of working gas impurities. For the highest purity helium (99.99999%), despite a low photoionization rate and the distance between the photoionization region and ionization region inside the tube, by increasing the applied voltage and decreasing the distance between the electrode and nozzle, plasma jets were formed.

  14. Two-impurity Anderson model: A variational study

    SciTech Connect

    Andreani, L.C. , PHB-Ecublens, CH-1015 Lausanne Dipartimento di Fisica A. Volta,'' Universita di Pavia, via Bassi 6, I-27100 Pavia ); Beck, H. )

    1993-09-01

    A comprehensive variational study of the two-impurity Anderson model is presented. First a lowest-order basis is introduced, which does not contain electronic excitations above the Fermi level: in this basis, the indirect [ital f]-[ital f] interaction of the form [minus][ital J][bold S][sub 1][center dot][bold S][sub 2] is not generated but is added by hand. The effect of electron-hole (EH) excitations is also studied. A suitable discretization of the continuous band spectrum allows us to obtain all eigenvalues and eigenvectors and to calculate finite-temperature magnetic properties. For a distance [ital R][gt][ital R][sub [ital c

  15. Characterization of potential impurities and degradation products in electronic cigarette formulations and aerosols.

    PubMed

    Flora, Jason W; Meruva, Naren; Huang, Chorng B; Wilkinson, Celeste T; Ballentine, Regina; Smith, Donna C; Werley, Michael S; McKinney, Willie J

    2016-02-01

    E-cigarettes are gaining popularity in the U.S. as well as in other global markets. Currently, limited published analytical data characterizing e-cigarette formulations (e-liquids) and aerosols exist. While FDA has not published a harmful and potentially harmful constituent (HPHC) list for e-cigarettes, the HPHC list for currently regulated tobacco products may be useful to analytically characterize e-cigarette aerosols. For example, most e-cigarette formulations contain propylene glycol and glycerin, which may produce aldehydes when heated. In addition, nicotine-related chemicals have been previously reported as potential e-cigarette formulation impurities. This study determined e-liquid formulation impurities and potentially harmful chemicals in aerosols of select commercial MarkTen(®) e-cigarettes manufactured by NuMark LLC. The potential hazard of the identified formulation impurities and aerosol chemicals was also estimated. E-cigarettes were machine puffed (4-s duration, 55-mL volume, 30-s intervals) to battery exhaustion to maximize aerosol collection. Aerosols analyzed for carbonyls were collected in 20-puff increments to account for analyte instability. Tobacco specific nitrosamines were measured at levels observed in pharmaceutical grade nicotine. Nicotine-related impurities in the e-cigarette formulations were below the identification and qualification thresholds proposed in ICH Guideline Q3B(R2). Levels of potentially harmful chemicals detected in the aerosols were determined to be below published occupational exposure limits. PMID:26617410

  16. Unsteady-state transfer of impurities during crystal growth of sucrose in sugarcane solutions

    NASA Astrophysics Data System (ADS)

    Martins, P. M.; Ferreira, A.; Polanco, S.; Rocha, F.; Damas, A. M.; Rein, P.

    2009-07-01

    In this work, we present growth rate data of sucrose crystals in the presence of impurities that can be used by both sugar technologists and crystal growth scientists. Growth rate curves measured in a pilot-scale evaporative crystallizer suggest a period of slow growth that follows the seeding of crystals into supersaturated technical solutions. The observed trend was enhanced by adding typical sugarcane impurities such as starch, fructose or dextran to the industrial syrups. Maximum growth rates of sucrose resulted at intermediate rather than high supersaturation levels in the presence of the additives. The effects of the additives on the sucrose solubility and sucrose mass transfer in solution were taken into account to explain the observed crystal growth kinetics. A novel mechanism was identified of unsteady-state adsorption of impurities at the crystal surface and their gradual replacement by the crystallizing solute towards the equilibrium occupation of the active sites for growth. Specifically designed crystallization experiments at controlled supersaturation confirmed this mechanism by showing increasing crystal growth rates with time until reaching a steady-state value for a given supersaturation level and impurity content.

  17. Neutron scattering from coupled phonon-impurity modes in KCl1-c(KCN)c

    NASA Astrophysics Data System (ADS)

    Nicklow, R. M.; Crummett, W. P.; Mostoller, M.; Wood, R. F.

    1980-09-01

    The hybridization of host-lattice phonons with the internal-energy states of CN- impurities in KCl has been studied by inelastic neutron scattering as a function of temperature between 10 and 100 K for samples with impurity concentrations in the range c=0.4 to 6 at.%. A temperature- and concentration-dependent coupling between phonons with Eg symmetry and the Eg transitions of CN- ions is observed near a frequency of 0.5 THz, a value which is consistent with the energy-level spacings for CN- in KCl as deduced by Beyeler. However, an expected coupling of phonons and CN- transitions with T2g symmetry near the same frequency was not detected. A simple two-level model for the CN- impurity provides a rather good description of the data for the Eg coupled modes for c<2 at.%, but it deviates significantly for larger concentrations. Quasielastic scattering, which has a strong dependence on impurity concentration, temperature, and phonon wave vector, is also observed.

  18. Numerical Simulation of mobile BEC-impurity interaction

    NASA Astrophysics Data System (ADS)

    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.

  19. HPLC-MS Examination of Impurities in Pentaerythritol Tetranitrate

    NASA Astrophysics Data System (ADS)

    Brown, Geoffrey W.; Giambra, Anna M.

    2014-04-01

    Pentaerythritol tetranitrate (PETN) has trace homolog impurities that can be detected by high-performance liquid chromatography-mass spectrometry. Consideration of observed impurity masses and candidate structures based on known pentaerythritol impurities allows identification of 22 compounds in the data. These are all consistent with either fully nitrated homologs or derivatives substituted with methyl, methoxy, or hydroxyl groups in place of a nitric ester. Examining relative impurity concentrations in three starting batches of PETN and six subsequently processed batches shows that it is possible to use relative concentration profiles as a fingerprint to differentiate batches and follow them through recrystallization steps.

  20. Oxygen impurity radiation from Tokamak-like plasmas

    NASA Technical Reports Server (NTRS)

    Rogerson, J. E.; Davis, J.; Jacobs, V. L.

    1977-01-01

    We have constructed a nonhydrodynamic coronal model for calculating radiation from impurity atoms in a heated plasma. Some recent developments in the calculation of dielectronic recombination rate coefficients and collisional excitation rate coefficients are included. The model is applied to oxygen impurity radiation during the first few milliseconds of a TFR Tokamak plasma discharge, and good agreement with experimental results is obtained. Estimates of total line and continuum radiation from the oxygen impurity are given. It is shown that impurity radiation represents a considerable energy loss.

  1. Interaction of infrared light with impurity gels in superfluid helium

    NASA Astrophysics Data System (ADS)

    Izotov, A. N.; Efimov, V. B.

    2011-05-01

    Rapid cooling of an impurity-helium mixture into superfluid helium produces a distinctive soft matter—impurity-helium gel, clusters of which coagulate into nanoparticles. The sizes of the particles and their mutual interaction depend on the nature of the impurity atoms and the impurity-helium coupling. Here we describe the setup of and preliminary results from an experiment to study infrared absorption by a water-helium gel. Comparisons of the infrared absorption spectra of the gel and of water and ice suggests a peculiar interaction among water molecules in a water-helium gel.

  2. Quantum impurities: from mobile Josephson junctions to depletons

    NASA Astrophysics Data System (ADS)

    Schecter, Michael; Gangardt, Dimitri M.; Kamenev, Alex

    2016-06-01

    We overview the main features of mobile impurities moving in one-dimensional superfluid backgrounds by modeling it as a mobile Josephson junction, which leads naturally to the periodic dispersion of the impurity. The dissipation processes, such as radiative friction and quantum viscosity, are shown to result from the interaction of the collective phase difference with the background phonons. We develop a more realistic depleton model of an impurity-hole bound state that provides a number of exact results interpolating between the semiclassical weakly interacting picture and the strongly interacting Tonks–Girardeau regime. We also discuss the physics of a trapped impurity, relevant to current experiments with ultra cold atoms.

  3. Topological state engineering by potential impurities on chiral superconductors

    NASA Astrophysics Data System (ADS)

    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. Tuning emergent magnetism in a Hund's impurity.

    PubMed

    Khajetoorians, A A; Valentyuk, M; Steinbrecher, M; Schlenk, T; Shick, A; Kolorenc, J; Lichtenstein, A I; Wehling, T O; Wiesendanger, R; Wiebe, J

    2015-11-01

    The recently proposed concept of a Hund's metal--a metal in which electron correlations are driven by Hund's rule coupling-can be used to explain the exotic magnetic and electronic behaviour of strongly correlated electron systems of multi-orbital metallic materials. Tuning the abundance of parameters that determine these materials is, however, experimentally challenging. Here, we show that the basic constituent of a Hund's metal--a Hund's impurity--can be realized using a single iron atom adsorbed on a platinum surface, a system that comprises a magnetic moment in the presence of strong charge fluctuations. The magnetic properties can be controlled by using the tip of a scanning tunnelling microscope to change the binding site and degree of hydrogenation of the 3d transition-metal atom. We are able to experimentally explore a regime of four almost degenerate energy scales (Zeeman energy, temperature, Kondo temperature and magnetic anisotropy) and probe the magnetic excitations with the microscope tip. The regime of our Hund's impurity can be tuned from an emergent magnetic moment to a multi-orbital Kondo state, and the system could be used to test predictions of advanced many-body theories for non-Fermi liquids in quantum magnets or unconventional superconductors. PMID:26344182

  5. Deuterium permeation through copper with trapping impurities

    NASA Astrophysics Data System (ADS)

    Mitchell, D. J.; Harris, J. M.; Patrick, R. C.; Boespflug, E. P.; Beavis, L. C.

    1982-02-01

    The time dependence of the deuterium permeation rate through impurity-doped copper membranes was measured in the temperature range 300-700 °C. Copper membranes that were doped with Er, Zr, and Ti all exhibited permeabilities that were nearly equal to pure copper, but the apparent diffusivities were smaller than those for pure copper by factors of 10-100 over the experimental temperature range. The permeation characteristics of these alloys appear to be altered from those for pure copper due to trapping of deuterium at sites that are associated with the impurity atoms. It is shown that the deuterium permeation rate through the copper alloys can be expressed in an analytical form that is analogous to that for pure copper, except that the apparent diffusivity takes on a value which depends on the trap concentration and binding energy for deuterium. The binding energies that are calculated for the alloys are used to determine the lag time which is required for deuterium or hydrogen to permeate through initially evacuated membranes. The lag times for copper alloys containing about 1% Er, Zr, or Ti are many orders of magnitude longer than for pure copper at room temperature. Copper alloys containing Cr do not appear to exhibit deuterium trapping. Nuclear reaction and backscattering analyses were used to help determine the effect or surface oxides on the permeation measurements.

  6. Effect of surface passivation by SiN/SiO{sub 2} of AlGaN/GaN high-electron mobility transistors on Si substrate by deep level transient spectroscopy method

    SciTech Connect

    Gassoumi, Malek Mosbahi, Hana; Zaidi, Mohamed Ali; Gaquiere, Christophe; Maaref, Hassen

    2013-07-15

    Device performance and defects in AlGaN/GaN high-electron mobility transistors have been correlated. The effect of SiN/SiO{sub 2} passivation of the surface of AlGaN/GaN high-electron mobility transistors on Si substrates is reported on DC characteristics. Deep level transient spectroscopy (DLTS) measurements were performed on the device after the passivation by a (50/100 nm) SiN/SiO{sub 2} film. The DLTS spectra from these measurements showed the existence of the same electron trap on the surface of the device.

  7. Assessment of Embrittlement of VHTR Structural Alloys in Impure Helium Environments

    SciTech Connect

    Crone, Wendy; Cao, Guoping; Sridhara, Kumar

    2013-05-31

    The helium coolant in high-temperature reactors inevitably contains low levels of impurities during steady-state operation, primarily consisting of small amounts of H{sub 2}, H{sub 2}O, CH{sub 4}, CO, CO{sub 2}, and N{sub 2} from a variety of sources in the reactor circuit. These impurities are problematic because they can cause significant long-term corrosion in the structural alloys used in the heat exchangers at elevated temperatures. Currently, the primary candidate materials for intermediate heat exchangers are Alloy 617, Haynes 230, Alloy 800H, and Hastelloy X. This project will evaluate the role of impurities in helium coolant on the stress-assisted grain boundary oxidation and creep crack growth in candidate alloys at elevated temperatures. The project team will: • Evaluate stress-assisted grain boundary oxidation and creep crack initiation and crack growth in the temperature range of 500-850°C in a prototypical helium environment. • Evaluate the effects of oxygen partial pressure on stress-assisted grain boundary oxidation and creep crack growth in impure helium at 500°C, 700°C, and 850°C respectively. • Characterize the microstructure of candidate alloys after long-term exposure to an impure helium environment in order to understand the correlation between stress-assisted grain boundary oxidation, creep crack growth, material composition, and impurities in the helium coolant. • Evaluate grain boundary engineering as a method to mitigate stress-assisted grain boundary oxidation and creep crack growth of candidate alloys in impure helium. The maximum primary helium coolant temperature in the high-temperature reactor is expected to be 850-1,000°C.Corrosion may involve oxidation, carburization, or decarburization mechanisms depending on the temperature, oxygen partial pressure, carbon activity, and alloy composition. These corrosion reactions can substantially affect long-term mechanical properties such as crack- growth rate and fracture

  8. Deep pockets for deep seas

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    Peter Auster, a fisheries ecologist with the National Undersea Research Center in Connecticut, plans to assess degradation of the deep-shelf seafloor from bottom trawling. Magnus Ngoile, an official with Tanzania's National Environmental Management Council, will work on building capacity of poor villagers to protect their coastline. And Alison Rieser, a lawyer with the University of Maine School of Law, will produce a textbook to educate scientists on how to apply the law for marine conservation.These individuals are among 11 recipients of the Pew Charitable Trust's 10th annual marine conservation fellowships, announced on July 12. With each recipient receiving an award of $150,000, the program is the world's largest award for marine conservationists. Other 1999 recipients will be involved with areas including investigating marine pollution in the Arctic region, examining economic incentives for conservation in Baja, Mexico, and establishing a marine conservation biology training program for minority students.

  9. Effect of single interstitial impurity in iron-based superconductors with sign-changed s-wave pairing symmetry

    NASA Astrophysics Data System (ADS)

    Yu, Xiang-Long; Liu, Da-Yong; Quan, Ya-Min; Zheng, Xiao-Jun; Zou, Liang-Jian

    2015-12-01

    We employ the self-consistent Bogoliubov-de Gennes (BdG) formulation to investigate the effect of single interstitial nonmagnetic/magnetic impurity in iron-based superconductors with s ± -wave pairing symmetry. We find that both the nonmagnetic and magnetic impurities can induce bound states within the superconducting (SC) gap and a π phase shift of SC order parameter at the impurity site. However, different from the interstitial-nonmagnetic-impurity case characterized by two symmetric peaks with respect to zero energy, the interstitial magnetic one only induces single bound-state peak. In the strong scattering regime this peak can appear at the Fermi level, which has been observed in the recent scanning tunneling microscope (STM) experiment of Fe(Te,Se) superconductor with interstitial Fe impurities (Yin et al. 2015 [44]). This novel single in-gap peak feature also distinguishes the interstitial case from the substitutional one with two peaks. These results provide important information for comparing the different impurity effects in the iron-based superconductors.

  10. Parallel transport studies of high-Z impurities in the core of Alcator C-Mod plasmasa)

    NASA Astrophysics Data System (ADS)

    Reinke, M. L.; Hutchinson, I. H.; Rice, J. E.; Greenwald, M.; Howard, N. T.; Hubbard, A.; Hughes, J. W.; Terry, J. L.; Wolfe, S. M.

    2013-05-01

    Measurements of poloidal variation, ñz/⟨nz⟩, in high-Z impurity density have been made using photodiode arrays sensitive to vacuum ultraviolet and soft x-ray emission in Alcator C-Mod plasmas. In/out asymmetries in the range of -0.20, of a flux surface is found to be well described by a combination of centrifugal, poloidal electric field, and ion-impurity friction effects. Up/down asymmetries, -0.050 corresponding to accumulation opposite the ion ∇B drift direction. Measurements of the up/down asymmetry of molybdenum are found to disagree with predictions from recent neoclassical theory in the trace limit, nzZ2/ni≪1. Non-trace levels of impurities are expected to modify the main-ion poloidal flow and thus change friction-driven impurity density asymmetries and impurity poloidal rotation, vθ ,z. Artificially modifying main-ion flow in parallel transport simulations is shown to impact both n˜z/⟨nz⟩ and vθ ,z, but simultaneous agreement between measured and predicted up/down and in/out asymmetry as well as impurity poloidal rotation is not possible for these C-Mod data. This link between poloidal flow and poloidal impurity density variation outlines a more stringent test for parallel neoclassical transport theory than has previously been performed. Measurement and computational techniques specific to the study of poloidal impurity asymmetry physics are discussed as well.

  11. Spatial variability of nutrients (N, P) in a deep, temperate lake with a low trophic level supported by global navigation satellite systems, geographic information system and geostatistics.

    PubMed

    Łopata, Michał; Popielarczyk, Dariusz; Templin, Tomasz; Dunalska, Julita; Wiśniewski, Grzegorz; Bigaj, Izabela; Szymański, Daniel

    2014-01-01

    We investigated changes in the spatial distribution of phosphorus (P) and nitrogen (N) in the deep, mesotrophic Lake Hańcza. The raw data collection, supported by global navigation satellite system (GNSS) positioning, was conducted on 79 sampling points. A geostatistical method (kriging) was applied in spatial interpolation. Despite the relatively small area of the lake (3.04 km(2)), compact shape (shore development index of 2.04) and low horizontal exchange of water (retention time 11.4 years), chemical gradients in the surface waters were found. The largest variation concerns the main biogenic element - phosphorus. The average value was 0.032 at the extreme values of 0.019 to 0.265 mg L(-1) (coefficient of variation 87%). Smaller differences are related to nitrogen compounds (0.452-1.424 mg L(-1) with an average value of 0.583 mg L(-1), the coefficient of variation 20%). The parts of the lake which are fed with tributaries are the richest in phosphorus. The water quality of the oligo-mesotrophic Lake Hańcza has been deteriorating in recent years. Our results indicate that inferences about trends in the evolution of examined lake trophic status should be based on an analysis of the data, taking into account the local variation in water chemistry. PMID:24804657

  12. First insights into genus level diversity and biogeography of deep sea benthopelagic calanoid copepods in the South Atlantic and Southern Ocean

    NASA Astrophysics Data System (ADS)

    Renz, Jasmin; Markhaseva, Elena L.

    2015-11-01

    Calanoid copepods constitute the most numerous organisms not only in the pelagic realm, but also in the benthic boundary layer, which gives them an important role in the turnover of organic matter in the benthopelagic habitat. During seven expeditions to the South Atlantic and Southern Ocean, the diversity and biogeography of deep-sea benthopelagic calanoid copepods were studied. The communities of calanoids living in the vicinity of the seabed were characterized by high diversity comparable to many pelagic habitats, but low abundance of individuals. Members of the taxon Clausocalanoidea dominated the communities, and within this taxon most individuals belonged to detritivore calanoids characterized by sensory setae on the second maxillae or aetideid copepods. 73% of all genera classified as obligate or predominantly benthopelagic copepods detected during these expeditions were new to science and a vast number of genera and species have been described since then. Comparing the communities of calanoid genera between different regions, the assemblages in the Southern Ocean differed significantly from the Southeast and Southwest Atlantic. A latitudinal diversity gradient could be observed, with highest numbers of genera in the Southwest Atlantic and low numbers at stations in the Southern Ocean. Reviewing the literature, endemism for benthopelagic calanoids appeared to be low on a latitudinal range caused by connectivity in benthopelagic habitats through spreading water masses. However, considering the habitats structuring the water column vertically, a high number of genera are endemic in the benthopelagial and specialized to living within the vicinity of the seabed.

  13. Finite size effect and Friedel oscillations for a Friedel-Anderson impurity by FAIR method

    NASA Astrophysics Data System (ADS)

    Tao, Yaqi

    A compact solution consisting of 4-8 Slater states (FAIR solution) is introduced to treat the Friedel Anderson and Kondo impurity problem. The ground state energy is obtained with impressively high accuracy. Net integrated polarization density is calculated and it confirms the existence of Kondo cloud. Finite size effect in the impurity problem is studied using FAIR method. It is shown that the formation of a Kondo ground state requires a minimum sample size and is accompanied by the presence of Kondo cloud. The Friedel Oscillations in the vicinity of a Friedel-Anderson impurity are investigated by FAIR method. The development of Friedel oscillation with a phase shift of pi/2 outside the Kondo radius is confirmed. And the amplitude A(xi) of the Friedel oscillations show a very similar behavior to that of a simple non-interacting Friedel impurity with a narrow resonance at the Fermi level. This similarity supports the concept of a "Kondo" resonance. And the Kondo resonance half width GammaFA is suggested to be GammaFA ≈ Echi/2.4, where Echi is the Kondo energy calculated from susceptibility.

  14. Mesoscopic Impurities Expose a Nucleation-Limited Regime of Crystal Growth

    NASA Astrophysics Data System (ADS)

    Sleutel, Mike; Lutsko, James F.; Maes, Dominique; Van Driessche, Alexander E. S.

    2015-06-01

    Nanoscale self-assembly is naturally subject to impediments at the nanoscale. The recently developed ability to follow processes at the molecular level forces us to resolve older, coarse-grained concepts in terms of their molecular mechanisms. In this Letter, we highlight one such example. We present evidence based on experimental and simulation data that one of the cornerstones of crystal growth theory, the Cabrera-Vermilyea model of step advancement in the presence of impurities, is based on incomplete physics. We demonstrate that the piercing of an impurity fence by elementary steps is not solely determined by the Gibbs-Thomson effect, as assumed by Cabrera-Vermilyea. Our data show that for conditions leading up to growth cessation, step retardation is dominated by the formation of critically sized fluctuations. The growth recovery of steps is counter to what is typically assumed, not instantaneous. Our observations on mesoscopic impurities for lysozyme expose a nucleation-dominated regime of growth that has not been hitherto considered, where the system alternates between zero and near-pure velocity. The time spent by the system in arrest is the nucleation induction time required for the step to amass a supercritical fluctuation that pierces the impurity fence.

  15. Impurity Effects on Caroli-de Gennes-Matricon Mode in Vortex Core in Superconductors

    NASA Astrophysics Data System (ADS)

    Masaki, Yusuke; Kato, Yusuke

    2016-01-01

    We have developed a scheme of Gor'kov Green's functions to treat the impurity effects on the Caroli-de Gennes-Matricon (CdGM) mode in superconductors (SCs) by improving the Kopnin-Kravtsov scheme with respect to the coherence factors and applicability to various SCs. We can study the impurity effects while keeping the discreteness of the energy spectrum, in contrast to the quasiclassical theory. We can thus apply this scheme to SCs with a small quasiclassical parameter kFξ0 (which is the product of the Fermi wavenumber kF and the coherence length ξ0 in a pure SC at zero temperature) and/or in the superclean regime Δ miniτ ≫ 1 (Δmini and τ denote, respectively, the level spacing of the CdGM mode called the minigap and the relaxation time for the CdGM mode and we take ħ = 1). We investigate the impurity effects as a white noise for a vortex in an s-wave SC and two types of vortex in a chiral p-wave SC for various values of the quasiclassical parameter and impurity strength (from the moderately clean regime to the superclean regime) and confirm the validity of this scheme.

  16. Revealing the Degree of Magnetic Frustration by Non-Magnetic Impurities

    SciTech Connect

    Not Available

    2011-08-12

    Imaging the magnetic fields around a non-magnetic impurity can provide a clear benchmark for quantifying the degree of magnetic frustration. Focusing on the strongly frustrated J{sub 1}-J{sub 2} model and the spatially anisotropic J{sub 1a}-J{sub 1b}-J{sub 2} model, very distinct low energy behaviors reflect different levels of magnetic frustration. In the J{sub 1}-J{sub 2} model, bound magnons appear trapped near the impurity in the ground state and strongly reduce the ordered moments for sites proximal to the impurity. In contrast, local moments in the J{sub 1a}-J{sub 1b}-J{sub 2} model are enhanced on the impurity neighboring sites. These theoretical predictions can be probed by experiments such as nuclear magnetic resonance and scanning tunneling microscopy, and the results can elucidate the role of frustration in antiferromagnets and help narrow the possible models to understand magnetism in the iron pnictdies.

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

    PubMed

    Tsetseris, Leonidas

    2016-07-27

    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. PMID:27248787

  18. Electrically Driven Spin Dynamics of Paramagnetic Impurities

    NASA Astrophysics Data System (ADS)

    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.

  19. Electrically driven spin dynamics of paramagnetic impurities.

    PubMed

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

    2008-05-16

    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. PMID:18518470

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

    NASA Astrophysics Data System (ADS)

    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.