Journal articles: 'Impurity models'

1

Weston, Robert. "Impurity operators in RSOS models." Journal of Physics A: Mathematical and General 33, no. 48 (November 24, 2000): 8981–9001. http://dx.doi.org/10.1088/0305-4470/33/48/326.

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2

Hewson, A. C., A. Oguri, and D. Meyer. "Renormalized parameters for impurity models." European Physical Journal B 40, no. 2 (August 2004): 177–89. http://dx.doi.org/10.1140/epjb/e2004-00256-0.

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3

Qiu, Huanhuan, Jianing Zhuang, Li Huang, Jianzhou Zhao, and Liang Du. "Improved Hubbard-I approximation impurity solver for quantum impurity models." Journal of Physics: Condensed Matter 31, no. 2 (December 7, 2018): 025601. http://dx.doi.org/10.1088/1361-648x/aaee95.

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4

Hafermann, H., C. Jung, S. Brener, M. I. Katsnelson, A. N. Rubtsov, and A. I. Lichtenstein. "Superperturbation solver for quantum impurity models." EPL (Europhysics Letters) 85, no. 2 (January 2009): 27007. http://dx.doi.org/10.1209/0295-5075/85/27007.

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5

Bracken, Anthony J., Xiang-Yu Ge, Mark D. Gould, and Huan-Qiang Zhou. "Integrable extended Hubbard models with boundary Kondo impurities." Bulletin of the Australian Mathematical Society 64, no. 3 (December 2001): 445–67. http://dx.doi.org/10.1017/s0004972700019912.

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Three kinds of integrable Kondo impurity additions to one-dimensional q-deformed extended Hubbard models are studied by means of the boundary Z2-graded quantum inverse scattering method. The boundary K matrices depending on the local magnetic moments of the impurities are presented as nontrivial realisations of the reflection equation algebras in an impurity Hilbert space. The models are solved by using the algebraic Bethe ansatz method, and the Bethe ansatz equations are obtained.

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6

Jin-Jun, Liang, Clive Emary, and Tobias Brandes. "Quantum Impurity Models with Coupled Cluster Method." Communications in Theoretical Physics 54, no. 3 (September 2010): 509–17. http://dx.doi.org/10.1088/0253-6102/54/3/26.

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7

Morozov, D. Kh. "Reduced Models of Impurity Seeded Edge Plasmas." Contributions to Plasma Physics 48, no. 1-3 (March 2008): 234–42. http://dx.doi.org/10.1002/ctpp.200810041.

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8

Salleh, Faiz, and Hiroya Ikeda. "Influence of Impurity Band on Seebeck Coefficient in Heavily-Doped Si." Advanced Materials Research 222 (April 2011): 197–200. http://dx.doi.org/10.4028/www.scientific.net/amr.222.197.

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We calculated the Seebeck coefficient of heavily-doped Si based on theoretical models of impurity-band formation, ionization-energy shift and conduction-band tailing. The impurity band was described by using two kinds of band-width definitions and it was found that the calculated Seebeck coefficient strongly depended on the impurity-band definition. In the high impurity-concentration region, the Seebeck coefficient decreased with increasing impurity concentration, and with a peak around 1×1019 cm-3. This result was qualitatively in good agreement with the experimental result, while there was quantitative disagreement between them.

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9

Petrenko, T. L., V. V. Teslenko, and E. N. Mokhov. "Models of Impurity Boron in Various SiC Polytypes." Defect and Diffusion Forum 103-105 (January 1993): 667–72. http://dx.doi.org/10.4028/www.scientific.net/ddf.103-105.667.

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10

Mochizuki, Kazuhiro, Fumimasa Horikiri, Hiroshi Ohta, and Tomoyoshi Mishima. "Models for Impurity Incorporation during Vapor-Phase Epitaxy." Materials Science Forum 1062 (May 31, 2022): 3–7. http://dx.doi.org/10.4028/p-9bg88x.

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Impurity incorporation during vapor-phase epitaxy on stepped surfaces was modeled by classifying rate-limiting processes into i) surface diffusion, ii) step kinetics, and iii) segregation. Examples were shown for i) desorption-limited Al incorporation during chemical vapor deposition (CVD) of (0001) SiC, ii) preferential desorption of C atoms from kinks during CVD of Al-doped (000-1) SiC, and iii) segregation-limited C incorporation during metalorganic vapor-phase epitaxy of (0001), (000-1), and (10-10) GaN.

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11

Stangeby, P. C., and J. D. Elder. "Impurity retention by divertors. I. One dimensional models." Nuclear Fusion 35, no. 11 (November 1995): 1391–412. http://dx.doi.org/10.1088/0029-5515/35/11/i06.

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12

Sorensen, E. S., S. Eggert, and I. Affleck. "Integrable versus non-integrable spin chain impurity models." Journal of Physics A: Mathematical and General 26, no. 23 (December 7, 1993): 6757–76. http://dx.doi.org/10.1088/0305-4470/26/23/023.

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13

Gruneberg, J., and H. Keiter. "Single impurity models in the strong-coupling regime." Physica B: Condensed Matter 199-200 (April 1994): 195–96. http://dx.doi.org/10.1016/0921-4526(94)91780-9.

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14

Jin, Zuxin, Wenjie Dou, and Joseph E. Subotnik. "Configuration interaction approaches for solving quantum impurity models." Journal of Chemical Physics 152, no. 6 (February 14, 2020): 064105. http://dx.doi.org/10.1063/1.5131624.

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15

Maki, Kazumi, and Xiaozhou Huang. "Models of heavy fermion superconductors; impurity scattering effect." Journal of Magnetism and Magnetic Materials 76-77 (December 1988): 499–503. http://dx.doi.org/10.1016/0304-8853(88)90466-0.

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16

Krippl, Maximilian, Ignasi Bofarull-Manzano, Mark Duerkop, and Astrid Dürauer. "Hybrid Modeling for Simultaneous Prediction of Flux, Rejection Factor and Concentration in Two-Component Crossflow Ultrafiltration." Processes 8, no. 12 (December 9, 2020): 1625. http://dx.doi.org/10.3390/pr8121625.

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Ultrafiltration is a powerful method used in virtually every pharmaceutical bioprocess. Depending on the process stage, the product-to-impurity ratio differs. The impact of impurities on the process depends on various factors. Solely mechanistic models are currently not sufficient to entirely describe these complex interactions. We have established two hybrid models for predicting the flux evolution, the protein rejection factor and two components’ concentration during crossflow ultrafiltration. The hybrid models were compared to the standard mechanistic modeling approach based on the stagnant film theory. The hybrid models accurately predicted the flux and concentration over a wide range of process parameters and product-to-impurity ratios based on a minimum set of training experiments. Incorporating both components into the modeling approach was essential to yielding precise results. The stagnant film model exhibited larger errors and no predictions regarding the impurity could be made, since it is based on the main product only. Further, the developed hybrid models exhibit excellent interpolation properties and enable both multi-step ahead flux predictions as well as time-resolved impurity forecasts, which is considered to be a critical quality attribute in many bioprocesses. Therefore, the developed hybrid models present the basis for next generation bioprocessing when implemented as soft sensors for real-time monitoring of processes.

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17

Morozova, Ekaterina, and Vladimir Panov. "Extreme Value Analysis for Mixture Models with Heavy-Tailed Impurity." Mathematics 9, no. 18 (September 9, 2021): 2208. http://dx.doi.org/10.3390/math9182208.

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This paper deals with the extreme value analysis for the triangular arrays which appear when some parameters of the mixture model vary as the number of observations grows. When the mixing parameter is small, it is natural to associate one of the components with “an impurity” (in the case of regularly varying distribution, “heavy-tailed impurity”), which “pollutes” another component. We show that the set of possible limit distributions is much more diverse than in the classical Fisher–Tippett–Gnedenko theorem, and provide the numerical examples showing the efficiency of the proposed model for studying the maximal values of the stock returns.

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18

Georges, Antoine, Gabriel Kotliar, and Qimiao Si. "Strongly Correlated Systems in Infinite Dimensions and Their Zero Dimensional Counterparts." International Journal of Modern Physics B 06, no. 05n06 (March 1992): 705–30. http://dx.doi.org/10.1142/s0217979292000426.

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We extend a mapping from infinite dimensional to zero dimensional (impurity) models to derive mean field equations of several strongly correlated systems which become exact in infinite dimensions. We discuss various magnetic phases of the Hubbard model, the periodic Anderson model the Kondo lattice and the Falicov Kimball model and we relate them to different impurity models. Qualitative insights into these models is gained from the exact results obtained for their zero dimensional counterparts.

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19

HEWSON, A. C., S. C. BRADLEY, R. BULLA, and Y. ŌNO. "RENORMALIZATION GROUP APPROACHES TO STRONGLY CORRELATED ELECTRON SYSTEMS." International Journal of Modern Physics B 15, no. 19n20 (August 10, 2001): 2549–67. http://dx.doi.org/10.1142/s0217979201006367.

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In recent years the numerical renormalization group (NRG) method has been extended to the calculation of dynamic response functions and transport properties of magnetic impurity models. The approach can now be applied more widely to lattice models of strongly correlated electron systems by the use of dynamical mean field theory (DMFT), in which the lattice problem is transformed into one for an effective impurity with an additional self-consistency constraint. We review these developments and assess the potential for further applications of this approach. We also discuss an alternative approach to renormalization, renormalized perturbation theory, in which the leading asymptotically exact results for the low temperature regime for a number of magnetic impurity models can be obtained within finite order perturbation theory.

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20

Skrobian, Milan, and Rudolf Pernis. "MATHEMATICAL EQUATION FOR IMPURITY DISTRIBUTION AFTER SECOND PASS OF ZONE REFINING." Acta Metallurgica Slovaca 27, no. 1 (February 25, 2021): 32–35. http://dx.doi.org/10.36547/ams.27.1.808.

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A mathematical equation has been derived that describes impurity distribution in ingot after second pass of zone refining. While an exponential impurity distribution is calculated by a simplified model after first pass, second pass is described by mixed linear - exponential model. Relationship of transformed impurity concentration is constant over whole length of semi-infinite ingot for first pass. However, it has linear trend for second pass. Last part of molten zone at infinity solidifies differently and can be described mathematically as directional crystallization. A mathematical tool devised for second pass of zone refining can be tried to be used for derivation of functions of more complex models that would describe impurity distribution in more realistic way compared to simplified approach. Such models could include non-constant distribution coefficient and/or shrinking or widening molten zone over a length of ingot.

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21

Gull, Emanuel, Andrew J. Millis, Alexander I. Lichtenstein, Alexey N. Rubtsov, Matthias Troyer, and Philipp Werner. "Continuous-time Monte Carlo methods for quantum impurity models." Reviews of Modern Physics 83, no. 2 (May 5, 2011): 349–404. http://dx.doi.org/10.1103/revmodphys.83.349.

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22

Gervids, V. I., V. I. Kogan, and D. Kh Morozov. "Reduced models of the dynamics of light impurity stripping." Plasma Physics Reports 27, no. 11 (November 2001): 938–46. http://dx.doi.org/10.1134/1.1416205.

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23

Vojta, M., R. Bulla, and P. Wölfle. "Critical quasiparticles in single-impurity and lattice Kondo models." European Physical Journal Special Topics 224, no. 6 (July 2015): 1127–46. http://dx.doi.org/10.1140/epjst/e2015-02449-0.

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24

Schmitteckert, Peter, Michael Dzierzawa, and Peter Schwab. "Exact time-dependent density functional theory for impurity models." Physical Chemistry Chemical Physics 15, no. 15 (2013): 5477. http://dx.doi.org/10.1039/c3cp44639e.

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25

Žitko, Rok. "Quantum impurity models for magnetic adsorbates on superconductor surfaces." Physica B: Condensed Matter 536 (May 2018): 230–34. http://dx.doi.org/10.1016/j.physb.2017.08.019.

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26

Oliveira, L. N., V. L. Líbero, H. O. Frota, and M. Yoshida. "Renormalization-group calculation of dynamical properties for impurity models." Physica B: Condensed Matter 171, no. 1-4 (May 1991): 61–68. http://dx.doi.org/10.1016/0921-4526(91)90491-v.

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27

GRUNEBERG, J., and H. KEITER. "SELF-CONSISTENT PERTURBATION EXPANSIONS FOR SINGLE-IMPURITY-EXCHANGE-MODELS." International Journal of Modern Physics B 09, no. 26 (November 30, 1995): 3429–87. http://dx.doi.org/10.1142/s0217979295001361.

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Combining self-consistent perturbation theory with conventional renormalization group equations, a new systematic approach to Kondo-type models is developed, which yields analytical expressions for universal quantities like pseudofermion exponents and large effective couplings, usually out of reach from perturbative calculations. The new approach is related to the parquet-treatment of the x-ray-edge-singularity by Noziéres and coworkers in the late sixties and makes no use of a linearization of the band-electron-dispersion-relation, which is crucial for the Bethe Ansatz, conformal field theory, or numerical renormalization group treatment of the models. In addition it covers 1/N2-corrections to the well-known Non-Crossing-Approximation.

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28

Futatani, S., W. Horton, S. Benkadda, I. O. Bespamyatnov, and W. L. Rowan. "Fluid models of impurity transport via drift wave turbulence." Physics of Plasmas 17, no. 7 (July 2010): 072512. http://dx.doi.org/10.1063/1.3459062.

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29

Yoshida, M., M. A. Whitaker, and L. N. Oliveira. "Renormalization-group calculation of excitation properties for impurity models." Physical Review B 41, no. 13 (May 1, 1990): 9403–14. http://dx.doi.org/10.1103/physrevb.41.9403.

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30

Bi, Sheng, Li Huang, and Ning-Hua Tong. "Natural orbital-based Lanczos method for Anderson impurity models." Computer Physics Communications 235 (February 2019): 196–209. http://dx.doi.org/10.1016/j.cpc.2018.09.002.

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31

TAKESHIMA, MASUMI. "NON-BORN CALCULATION OF ZERO TEMPERATURE CONDUCTIVITY OF A DOPED SEMICONDUCTOR UNDER VARIOUS SCREENING MODELS." International Journal of Modern Physics B 06, no. 13 (July 10, 1992): 2423–38. http://dx.doi.org/10.1142/s0217979292001225.

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The zero temperature conductivity of a doped semiconductor is calculated by numerically solving the integral equation which is given as a formal solution of the impurity scattering problem. Here the free-carrier screening of the impurity potential is also discussed, giving a tentative model of the screening. Then the critical exponent for the relation between conductivity and carrier concentration is found to be 0.8 for uncompensated Si:P. The critical carrier concentration for the metal-insulator transition is also calculated for the model of Mott localization as compared with that of Anderson localization, showing largely different results.

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32

Biliaiev, M. M., A. S. Kovalenko, R. P. Pobiedonnyi, and M. V. Chyrva. "MODELLING OF MASS TRANSFER IN WASTEWATER FACILITIES." Ukrainian Journal of Civil Engineering and Architecture, no. 1 (019) (April 20, 2024): 62–68. http://dx.doi.org/10.30838/j.bpsacea.2312.270224.62.1024.

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Problem statement. The design of wastewater treatment systems is a complex process and requires the use of special mathematical models. As a rule, empirical models are used at the stage of designing structures of water drainage systems, which allow obtaining only an “integral” characteristic of the efficiency of wastewater treatment. But in a number of cases, it is important to have information about the spatial distribution of the impurity concentration in the structure. To solve this problem, you need to have three-dimensional mathematical models. In the future, there is a shortage of such models, so the creation of three-dimensional multifactorial models for the analysis of the efficiency of drainage system structures is an urgent task. The purpose of the article. Development of a three-dimensional numerical model for the analysis of the mass transfer process to determine the impurity concentration in the clarifier. Methodology. The analysis of impurity concentration fields in the clarifier is carried out by numerical integration of the three-dimensional equation for the velocity potential and the three-dimensional equation of the convective-diffusion transport of the impurity. For the numerical integration of the Laplace equation for the velocity potential, the variable-triangular method and the Liebmann method are used. Finite-difference splitting schemes are used for numerical integration of the three-dimensional equation of convective-diffusion transport of impurities. Scientific novelty. A dynamic multifactorial numerical model was created for the analysis of the process of mass transfer of impurities in a settling tank by conducting a computational experiment. Practical value. The built multifactorial numerical model makes it possible to analyze the efficiency of wastewater treatment in clarifiers that have a complex geometric shape and cannot be calculated on the basis of existing engineering methods. Conclusions. On the basis of the developed three-dimensional numerical model, a computer code was created, which allows you to quickly obtain information about the distribution of the impurity concentration in the settling tank.

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33

Ronowicz, Joanna, Bogumiła Kupcewicz, Joanna Mydłowska, and Elżbieta Budzisz. "Impurity profile analysis of drug products containing acetylsalicylic acid: a chemometric approach." Open Chemistry 11, no. 7 (July 1, 2013): 1091–100. http://dx.doi.org/10.2478/s11532-013-0243-2.

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AbstractIn this work attention is focused on impurity profile analysis in combination with infrared spectroscopy and chemometric methods. This approach is considered as an alternative to generally complex and time-consuming classic analytical techniques such as liquid chromatography. Various strategies for constructing descriptive models able to identify relations among drug impurity profiles hidden in multivariate chromatographic data sets are also presented and discussed. The hierarchical (cluster analysis) and non-hierarchical segmentation algorithms (k-means method) and principal component analysis are applied to gain an overview of the similarities and dissimilarities among impurity profiles of acetylsalicylic acid formulations. A tree regression algorithm based on infrared spectra is used to predict the relative content of impurities in the drug products investigated. Satisfactory predictive abilities of the models derived indicate the possibility of implementing them in the quality control of drug products.

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34

BACHMANN, P., and D. SÜNDER. "One-dimensional multifluid plasma models. Part 1. Fundamentals." Journal of Plasma Physics 61, no. 4 (May 1999): 645–67. http://dx.doi.org/10.1017/s002237789900762x.

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This paper is concerned with one-dimensional and time-dependent multifluid plasma models derived from multifluid MHD equations. In order to reduce the number of equations to be solved, the impurities are described in the framework of the average ion approach without restricting the impurity densities to be small compared with the hydrogen plasma density. Equalizing the plasma temperatures and adopting the condition of quasineutrality, we arrive at a three-fluid description of a current-carrying plasma, and analyse the ability of the self-consistent system of model equations thus obtained to support stationary solutions in a moving frame. This system is reduced to a currentless plasma description assuming at first different flow velocities of the particles and then a currentless, streaming plasma where all particles move with the same velocity. Introducing Lagrangian coordinates and adopting an equation of state, a single reaction–diffusion equation (RDE) for the temperature is obtained. The impurity density, which affects the radiation loss term and the heat conduction coefficient of the RDE, has to be calculated as a function of the temperature by solving additionally a first-order differential equation. This is demonstrated for carbon and high-Z impurities.

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35

Kazen, Thomas. "Levels of Explanation for Ideas of Impurity." Journal of Ancient Judaism 9, no. 1 (May 19, 2018): 75–100. http://dx.doi.org/10.30965/21967954-00901005.

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When trying to understand purity practices and conceptions of impurity, which often seem enigmatic, scholars construe “explanations” on very different levels and frequently do not distinguish clearly between cause and effect. In the present article, I seek to disentangle various levels or types of explanation, ranging from evolutionary and historical, through cognitive and social, to structuralist and symbolic. While many attempts to explain impurity look for origins, reasons, or at least backgrounds, others rather aim at the results, or functions, of various ideas and practices of purity. Some explanations focus on analogies and correspondences, even treating purity codes as object lessons or illustrations of beliefs. Several explanatory models are frequently used for claims at levels to which they do not belong. Special critique is directed against the misuse of functionalist, structuralist, and symbolic models beyond their validity at a certain level of reception, for arguing or implying more than they can actually accommodate. The usefulness and integration of biopsychological and cognitive linguistic models for solving certain key questions without imposing ideological superstructures is argued.

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36

Arabei, S. M., I. V, Stanishevsky, T. A. Pavich, and S. V. Slonskaya. "Evolution of the Impurity Sites and Electronic Spectra of Aluminum Phthalocyanine in a Silicate Nanoreactor." Журнал физической химии 97, no. 6 (June 1, 2023): 843–49. http://dx.doi.org/10.31857/s004445372306002x.

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The evolution of the electronic absorption spectra of substituted aluminum phthalocyanine incorporated into a nanoporous silicate gel matrix has been studied. The decomposition of the contour of the long-wavelength Q-absorption band of molecules into Voigt components reveals the dependence of the formation of various types of impurity sites in the matrix nanopores, which act as a solid-state nanoreactor, on the drying time of the matrix. Possible mechanisms of the effect of the internal structure of the synthesized silicate material during the transition from a sol state to a dried xerogel state on the spectral properties of phthalocyanine impurity molecules are discussed. Models of the interaction of the impurity molecules with the surface of the matrix nanopores during drying are considered; the features of the evolution of the resulting impurity sites are elucidated.

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37

Segal, Dvira, Andrew J. Millis, and David R. Reichman. "Nonequilibrium transport in quantum impurity models: exact path integral simulations." Physical Chemistry Chemical Physics 13, no. 32 (2011): 14378. http://dx.doi.org/10.1039/c1cp20702d.

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38

Joussaume, Sylvie. "Simulation of Airborne Impurity Cycles Using Atmospheric General Circulation Models." Annals of Glaciology 7 (1985): 131–37. http://dx.doi.org/10.3189/s0260305500006042.

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Atmospheric general circulation models are believed to be appropriate tools for studying airborne impurity cycles in order to supplement observations and to improve our knowledge of gaseous and particulate pollutant cycles in the atmosphere. The main aspects of the modelling of tracer cycles are reviewed and illustrated by two particular examples: desert dust particles in the 1 μm range and water isotope species HDO and H218O. Some results from a first simulation including desert dust and water isotope cycles using the model developed at the Laboratoire de Météorologie Dynamique (LMD) are presented and compared to observations, with particular emphasis on ice-sheet data. The relatively good agreement with observations obtained so far is encouraging and should stimulate further applications to other types of tracers.

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39

Gull, E., P. Werner, O. Parcollet, and M. Troyer. "Continuous-time auxiliary-field Monte Carlo for quantum impurity models." EPL (Europhysics Letters) 82, no. 5 (May 27, 2008): 57003. http://dx.doi.org/10.1209/0295-5075/82/57003.

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40

Schiro, Marco, and Orazio Scarlatella. "Quantum impurity models coupled to Markovian and non-Markovian baths." Journal of Chemical Physics 151, no. 4 (July 28, 2019): 044102. http://dx.doi.org/10.1063/1.5100157.

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41

Yu, Yue, and Wan-Peng Tan. "Phase structures of magnetic impurity models with two-body hybridization." Physical Review B 57, no. 10 (March 1, 1998): 5879–90. http://dx.doi.org/10.1103/physrevb.57.5879.

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42

Joussaume, Sylvie. "Simulation of Airborne Impurity Cycles Using Atmospheric General Circulation Models." Annals of Glaciology 7 (1985): 131–37. http://dx.doi.org/10.1017/s0260305500006042.

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Atmospheric general circulation models are believed to be appropriate tools for studying airborne impurity cycles in order to supplement observations and to improve our knowledge of gaseous and particulate pollutant cycles in the atmosphere. The main aspects of the modelling of tracer cycles are reviewed and illustrated by two particular examples: desert dust particles in the 1 μm range and water isotope species HDO and H2 18O. Some results from a first simulation including desert dust and water isotope cycles using the model developed at the Laboratoire de Météorologie Dynamique (LMD) are presented and compared to observations, with particular emphasis on ice-sheet data. The relatively good agreement with observations obtained so far is encouraging and should stimulate further applications to other types of tracers.

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43

Eckle, Hans-Peter. "Exact results for two integrable models of quantum impurity physics." Reports on Mathematical Physics 61, no. 2 (April 2008): 221–28. http://dx.doi.org/10.1016/s0034-4877(08)80010-9.

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44

Kroha, J., and P. Wölfle. "Conserving Diagrammatic Approximations for Quantum Impurity Models: NCA and CTMA." Journal of the Physical Society of Japan 74, no. 1 (January 2005): 16–26. http://dx.doi.org/10.1143/jpsj.74.16.

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45

Ellis, Donald E., Jun Guo, and Daniel J. Lam. "Cluster Models of Bulk, Surface, and Impurity Structure.in alpha-Alumina." Journal of the American Ceramic Society 77, no. 2 (February 1994): 398–403. http://dx.doi.org/10.1111/j.1151-2916.1994.tb07007.x.

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46

Krlín, L., R. Pánek, P. Pavlo, V. Petrzílka, J. Stöckel, V. Svoboda, S. Kuhn, D. Tskhakaya, and M. Tendler. "Anomalous impurity diffusion in models of tokamak edge plasma turbulence." Czechoslovak Journal of Physics 54, S3 (March 2004): C157—C163. http://dx.doi.org/10.1007/bf03166395.

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47

Freitag, Johannes, Sepp Kipfstuhl, Thomas Laepple, and Frank Wilhelms. "Impurity-controlled densification: a new model for stratified polar firn." Journal of Glaciology 59, no. 218 (2013): 1163–69. http://dx.doi.org/10.3189/2013jog13j042.

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AbstractA new densification model, which simulates the effect of impurities on the densification of polar firn, is presented. The classical densification models of Herron and Langway (1980) and Pimienta and Barnola (Barnola and others, 1991) are modified by assuming that the activation energy for deformation is reduced by the impurities. Motivated by recent observations, the impurity effect is formulated on an empirical basis using the seasonally varying Ca2+ ion concentration. Excellent agreement between simulated and measured high-resolution density profiles confirms the new approach. The same parameterization applies for Greenland and Antarctica despite the one order of magnitude difference in impurity concentration. The new models allow us, for the first time, to simulate the density layering in firn down to the firn–ice transition. Our results emphasize the importance of impurities and density layering for the air entrapment and for dating gas records of deep ice cores, in particular for glacial climate conditions where the impurity concentrations are 10–100-fold higher than in modern firn.

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48

BILIAIEV, M. M., V. A. KOZACHYNA, P. B. MASHYKHINA, and V. V. TSURKAN. "MATHEMATICAL MODELING IN WATER TREATMENT PROBLEMS." Ukrainian Journal of Civil Engineering and Architecture, no. 4 (October 22, 2022): 13–19. http://dx.doi.org/10.30838/j.bpsacea.2312.250822.13.872.

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Problem statement. Analysis of the treatment facilities efficiency in sewerage at the stage of their design is great importance. Also, at the stage of structures’ reconstruction or their operation adjustment under different load conditions, it is necessary to know the efficiency of water treatment in different areas of treatment facilities. Such information makes it possible to rationally operate facilities. For solving problems of this class, the most effective tool is the use of the numerical modeling method. The work considers development of numerical models set for solving problems of this class. Methodology. Two fundamental models are used to solve the velocity field determination of the wastewater flow in the sewage treatment plant. The first is a model of the vortex-free motion for an incompressible fluid. The second model is the Navier-Stokes equations written in Helmholtz variables. The mass transfer equation is used to determine impurity concentration fields in sewage treatment plants, which takes into account flow velocity, diffusion and the presence of impurity emission sources. Material balance equations for the substrate and activated sludge are used to calculate the process of biological wastewater treatment. Finite-difference schemes are used to build numerical models that allow calculating the hydrodynamics of the flow and the distribution of the impurity concentration in the facility. The Euler method is used for the numerical solution of the material balance equations. Results. Numerical models were built, which were used to develop a complex of computer programs. These computer programs allow real-time analysis of the water treatment efficiency in the facility. Scientific novelty. Numerical models have been developed that allow investigating the process of water treatment in facilities of the «settler» type and in aeration tanks, that is, for a significant class of treatment facilities used in practice. Practical value. The calculation time of the velocity field and the impurity concentration field in a water treatment plant with a complex geometric shape is few seconds. This allows usinge the developed numerical models for serial calculations in project organizations in daily work.

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Matsui, Chihiro, and Naoto Tsuji. "Exact steady states of the impurity-doped XXZ spin chain coupled to dissipators." Journal of Statistical Mechanics: Theory and Experiment 2024, no. 3 (March 18, 2024): 033105. http://dx.doi.org/10.1088/1742-5468/ad2b5c.

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Abstract We give an exact matrix product steady state and matrix product forms of local observables for the bulk impurity-doped XXZ spin model coupled to dissipators at both ends, whose dynamics is described by the Lindblad quantum master equation. We find that local magnetization is induced at the impurity site when the spin current flows, which is contrary to the usual situation where the current suppresses magnetization due to heating. It is proved that this current-induced magnetization survives in the thermodynamic limit, and the spin current does not depend on the impurity strength. We discuss the role of bulk integrability by comparing the results with those of non-integrable models solved numerically by the quantum trajectory method.

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Jain, Sandeep Kumar, and Pankaj Srivastava. "Effect of Nitrogen Impurity on Electronic Properties of Boron Nanotubes." Advances in Condensed Matter Physics 2014 (2014): 1–8. http://dx.doi.org/10.1155/2014/706218.

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

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Journal articles on the topic 'Impurity models'

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