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Sample records for impurity-bound small polarons

  1. Study of strong-coupling impurity bound polaron in a quantum pseudodot

    NASA Astrophysics Data System (ADS)

    Khordad, R.

    2015-01-01

    In the present work, we have studied the first internal excited state energy and transition frequency of strong-coupling impurity bound polaron in a quantum pseudodot using the well-known Lee-Low-Pines (LLP) unitary transformation method. We show the effect of Coulomb bound potential, electron-phonon (e-p) coupling strength, the quantum dot radius and potential height on first internal excited state energy and the transition frequency of the impurity bound polaron. According to the results, it is found that the first internal excited state energy is decreased with increasing quantum dot radius. Also, this energy is increased with enhancing potential height. The transition frequency is increased with increasing the e-p coupling strength. Also, the first internal excited state energy is increased with decreasing the e-p coupling strength. The transition frequency is enhanced with increasing the Coulomb bound potential.

  2. Electric field and image charge effects on impurity-bound polarons in a CdS colloidal quantum dot embedded in organic matrices

    NASA Astrophysics Data System (ADS)

    Asatryan, A. L.; Vartanian, A. L.; Kirakosyan, A. A.; Vardanyan, L. A.

    2016-12-01

    An adiabatic variational approach is used to study the ground and first excited states of a hydrogen-like impurity bound polaron in a colloidal quantum dot (QD) under an external electric field, including image charge effect (ICE). The binding energy (BE) of donor impurity is calculated by taking into account the interaction of an electron with both bulk-type longitudinal optical (LO) phonons and interface optical phonons. Calculations have been carried out for CdS colloidal quantum dots embedded in thiophenol and oleic acid. Both parabolic confinement and electric field effects on the binding energy and its polaronic shift for 1s and 2s hydrogen-like states with and without ICE are investigated in detail.

  3. Image Charge and Electric Field Effects on Hydrogen-like Impurity-bound Polaron Energies and Oscillator Strengths in a Quantum Dot

    NASA Astrophysics Data System (ADS)

    Vardanyan, L. A.; Vartanian, A. L.; Asatryan, A. L.; Kirakosyan, A. A.

    2016-11-01

    By using Landau-Pekar variational method, the ground and the first excited state energies and the transition frequencies between the ground and the first excited states of a hydrogen-like impurity-bound polaron in a spherical quantum dot (QD) have been studied by taking into account the image charge effect (ICE). We employ the dielectric continuum model to describe the phonon confinement effects. The oscillator strengths (OSs) of transitions from the 1 s-like state to excited states of 2 s, 2 p x , and 2 p z symmetries are calculated as functions of the applied electric field and strength of the confinement potential. We have shown that with and without image charge effect, the increase of the strength of the parabolic confinement potential leads to the increase of the oscillator strengths of 1 s - 2 p x and 1 s - 2 p z transitions. This indicates that the energy differences between 1 s- and 2 p x - as well as 1 s- and 2 p z -like states have a dominant role determining the oscillator strength. Although there is almost no difference in the oscillator strengths for transitions 1 s - 2 p x and 1 s -2 p z when the image charge effect is not taken into account, it becomes significant with the image charge effect.

  4. Small polarons in dry DNA

    NASA Astrophysics Data System (ADS)

    Chacham, Helio; Alexandre, Simone S.; Soler, Jose M.; Artacho, Emilio

    2004-03-01

    The phenomenon of charge transport in DNA has been attracting attention of both biologists and physicists. From the biology side, there are evidences that charge injection can be associated to damage, mutation, and repair processes in DNA. From the physical sciences side, recent developments in nanotechnology now allow the measurement of currents through single DNA molecules in dried samples, which depict semiconductor behavior. Several mechanisms have been proposed for charge migration and transport in DNA. In that respect, detailed electrical transport measurements through DNA molecules containing identical base pairs (poly(dA)-poly(dT) and poly(dG)-poly(dC)) have been recently reported by Yoo et al [1]. These results fit extremely well a model in which the conduction is due to small polaron motion. In particular, these results indicate that the I-V characteristic of poly(dG)-poly(dC) DNA above 200 K is consistent with a small polaron hopping regime with an activation energy of 0.12 eV. In this work [2] we investigate the polaron formation in dry DNA by applying ab initio calculations to both neutral and charged fragments of dry poly(dG)-poly(dC). Our calculations show that the hole polaron in dry poly(dG)-poly(dC) DNA is a clear case of small polaron. This is verified by four basic properties: (i) the small variation of the polaron binding energy as a function of the DNA fragment size, for small fragment sizes, which is an indication of polaron localization; (ii) the fact that the width of the uppermost valence band is an order of magnitude smaller than the polaron binding energy; (iii) the explicit localization of the hole wavefunction for the largest considered fragment (four base pairs), indicated by the fact that about half of the norm of the hole is localized on a single guanine site; (iv) the localization of structural deformations at the nucleotides where the hole is concentrated. Our calculations also give a polaron binding energy of 0.30 eV. This allows

  5. Small-polaron theory of doped antiferromagnets

    NASA Astrophysics Data System (ADS)

    Auerbach, Assa; Larson, Brond E.

    1991-04-01

    The spin-hole coherent-state path integral is used to generate a systematic large-spin expansion of the t-J model on the square lattice. The single hole's classical energy is minimized by small polarons with short-ranged interactions. Intersublattice hopping of polarons is forbidden by a tunneling selection rule. We derive the low-energy Lagrangian which reduces to the model of Wiegmann, Wen, Shankar, and Lee of Néel-gauge-field induced superconductivity.

  6. Optical nonlinearities of small polarons in lithium niobate

    NASA Astrophysics Data System (ADS)

    Imlau, Mirco; Badorreck, Holger; Merschjann, Christoph

    2015-12-01

    An overview of optical nonlinearities of small bound polarons is given, which can occur in the congruently melting composition of LiNbO3. Such polarons decisively influence the linear and nonlinear optical performance of this material that is important for the field of optics and photonics. On the basis of an elementary phenomenological approach, the localization of carriers in a periodic lattice with intrinsic defects is introduced. It is applied to describe the binding energies of four electron and hole small polarons in LiNbO3: small free NbNb4 + polarons, small bound NbLi4 + polarons, small bound NbLi4 +:NbNb4 + bipolarons, and small bound O- hole polarons. For the understanding of their linear interaction with light, an optically induced transfer between nearest-neighboring polaronic sites is assumed. It reveals spectrally well separated optical absorption features in the visible and near-infrared spectral range, their small polaron peak energies and lineshapes. Nonlinear interaction of light is assigned to the optical formation of short-lived small polarons as a result of carrier excitation by means of band-to-band transitions. It is accompanied by the appearance of a transient absorption being spectrally constituted by the individual fingerprints of the small polarons involved. The relaxation dynamics of the transients is thermally activated and characterized phenomenologically by a stretched exponential behavior, according to incoherent 3D small polaron hopping between regular and defect sites of the crystal lattice. It is shown that the analysis of the dynamics is a useful tool for revealing the recombination processes between small polarons of different charge. Nonlinear interaction of small polarons with light furthermore results in changes of the index of refraction. Besides its causal relation to the transients via Kramers-Kronig relation, pronounced index changes may occur due to optically generated electric fields modulating the index of refraction

  7. Small hole polarons in rare-earth titanates

    SciTech Connect

    Bjaalie, L.; Moetakef, P.; Cain, T. A.; Janotti, A.; Himmetoglu, B.; Stemmer, S.; Van de Walle, C. G.; Ouellette, D. G.; Allen, S. J.

    2015-06-08

    We investigate the behavior of hole polarons in rare-earth titanates by combining optical conductivity measurements with first-principles hybrid density functional calculations. Sr-doped GdTiO{sub 3} (Gd{sub 1−x}Sr{sub x}TiO{sub 3}) was grown by molecular beam epitaxy. We show that a feature in the optical conductivity that was previously identified with the Mott-Hubbard gap is actually associated with the excitation of a small polaron. The assignment is based on an excellent match between the experimental spectra and first-principles calculations for polaron excitation mechanisms.

  8. Small polaron formation in porous WO3-x nanoparticle films

    NASA Astrophysics Data System (ADS)

    Ederth, J.; Hoel, A.; Niklasson, G. A.; Granqvist, C. G.

    2004-11-01

    Porous tungsten oxide nanoparticle films were prepared by reactive gas evaporation. The structure was studied by x-ray diffraction and scanning electron microscopy, and the oxygen nonstoichiometry was inferred by x-ray photoelectron spectroscopy, elastic recoil detection analysis, and neutron scattering. Specifically, the films consisted of WO3-x with 0.25small polarons having a radius of 5-6Å. The infrared optical data, used to extract information on phonon energies, were instrumental to reach this conclusion. The polaron hopping energy was about half the polaron binding energy, as expected from the theory.

  9. TOPICAL REVIEW: O- bound small polarons in oxide materials

    NASA Astrophysics Data System (ADS)

    Schirmer, O. F.

    2006-11-01

    Holes bound to acceptor defects in oxide crystals are often localized by lattice distortion at just one of the equivalent oxygen ligands of the defect. Such holes thus form small polarons in symmetric clusters of a few oxygen ions. An overview on mainly the optical manifestations of those clusters is given. The article is essentially divided into two parts: the first one covers the basic features of the phenomena and their explanations, exemplified by several paradigmatic defects; in the second part numerous oxide materials are presented which exhibit bound small polaron optical properties. The first part starts with summaries on the production of bound hole polarons and the identification of their structure. It is demonstrated why they show strong, wide absorption bands, usually visible, based on polaron stabilization energies of typically 1 eV. The basic absorption process is detailed with a fictitious two-well system. Clusters with four, six and twelve equivalent ions are realized in various oxide compounds. In these cases several degenerate optically excited polaron states occur, leading to characteristic final state resonance splittings. The peak energies of the absorption bands as well as the sign of the transfer energy depend on the topology of the clusters. A special section is devoted to the distinction between interpolaron and intrapolaron optical transitions. The latter are usually comparatively weak. The oxide compounds exhibiting bound hole small polaron absorptions include the alkaline earth oxides (e.g. MgO), BeO and ZnO, the perovskites BaTiO3 and KTaO3, quartz, the sillenites (e.g. Bi12TiO20), Al2O3, LiNbO3, topaz and various other materials. There are indications that the magnetic crystals NiO, doped with Li, and LaMnO3, doped with Sr, also show optical features caused by bound hole polarons. Beyond being elementary paradigms for the properties of small polarons in general, the defect species treated can be used to explain radiation and light

  10. Unravelling Small-Polaron Transport in Metal Oxide Photoelectrodes.

    PubMed

    Rettie, Alexander J E; Chemelewski, William D; Emin, David; Mullins, C Buddie

    2016-02-04

    Transition-metal oxides are a promising class of semiconductors for the oxidation of water, a process that underpins both photoelectrochemical water splitting and carbon dioxide reduction. However, these materials are limited by very slow charge transport. This is because, unlike conventional semiconductors, material aspects of metal oxides favor the formation of slow-moving, self-trapped charge carriers: small polarons. In this Perspective, we seek to highlight the salient features of small-polaron transport in metal oxides, offer guidelines for their experimental characterization, and examine recent transport studies of two prototypical oxide photoanodes: tungsten-doped monoclinic bismuth vanadate (W:BiVO4) and titanium-doped hematite (Ti:α-Fe2O3). Analysis shows that conduction in both materials is well-described by the adiabatic small-polaron model, with electron drift mobility (distinct from the Hall mobility) values on the order of 10(-4) and 10(-2) cm(2) V(-1) s(-1), respectively. Future directions to build a full picture of charge transport in this family of materials are discussed.

  11. Spectroscopic Evidence of Formation of Small Polarons in Doped Manganites

    NASA Astrophysics Data System (ADS)

    Moritomo, Yutaka; Machida, Akihiko; Nakamura, Arao

    1998-03-01

    Temperature dependence of absorption spectra for thin films of doped manganites R_0.6Sr_0.4MnO_3, where R is rare-earth atom, has been investigated systematically changing averaged ionic radius < rA > of perovskite A-site. We have observed a specific absorption band at ~1.5eV due to optical excitations from small polarons (SP)(Machida et al.), submitted.. Spectral weight of the SP band increases with decreasing temperature and eventually disappears at the insulator-metal (IM) transition, indicating that SP in the paramagnetic state (T >= T_C) changes into bare electrons (or large polarons) in the ferromagnetic state due to the enhanced one-electron bandwidth W. We further derived important physical quantities, i.e., W, on-site exchange interaction J and binding energy Ep of SP, and discuss material dependence of stability of SP. This work was supported by a Grant-In-Aid for Scientific Research from the Ministry of Education, Science, Sport and Culture and from PRESTO, Japan Scienece and Technology Corporation (JST), Japan.

  12. Infrared absorption spectra of molecular crystals: Possible evidence for small-polaron formation?

    NASA Astrophysics Data System (ADS)

    Pržulj, Željko; Čevizović, Dalibor; Zeković, Slobodan; Ivić, Zoran

    2008-09-01

    The temperature dependence of the position of the so-called anomalous band peaked at 1650cm in the IR-absorption spectrum of crystalline acetanilide (ACN) is theoretically investigated within the small-polaron theory. Its pronounced shift towards the position of the normal band is predicted with the rise of temperature. Interpretation of the IR-absorption spectra in terms of small-polaron model has been critically assessed on the basis of these results.

  13. Inapplicability of small-polaron model for the explanation of infrared absorption spectrum in acetanilide.

    PubMed

    Zeković, Slobodan; Ivić, Zoran

    2009-01-01

    The applicability of small-polaron model for the interpretation of infrared absorption spectrum in acetanilide has been critically reexamined. It is shown that the energy difference between the normal and anomalous peak, calculated by means of small-polaron theory, displays pronounced temperature dependence which is in drastic contradiction with experiment. It is demonstrated that self-trapped states, which are recently suggested to explain theoretically the experimental absorption spectrum in protein, cannot cause the appearance of the peaks in absorption spectrum for acetanilide.

  14. Electron small polarons and their transport in bismuth vanadate: a first principles study.

    PubMed

    Kweon, Kyoung E; Hwang, Gyeong S; Kim, Jinhan; Kim, Sungjin; Kim, SeongMin

    2015-01-07

    Relatively low electron mobility has been thought to be a key factor that limits the overall photocatalytic performance of BiVO4, but the behavior of electrons has not been fully elucidated. We examine electron localization and transport in BiVO4 using hybrid density functional theory calculations. An excess electron is found to remain largely localized on one V atom. The predicted hopping barrier for the small polaron is 0.35 eV (with inclusion of 15% Hartree-Fock exchange), and tends to increase almost linearly with lattice constant associated with pressure and/or temperature changes. We also examine the interaction between polarons, and discuss the possible concentration-dependence of electron mobility in BiVO4.

  15. Small polaron characteristics of the OH center in TiO2

    NASA Astrophysics Data System (ADS)

    Fowler, W. Beall

    2013-03-01

    Most insulating crystals have nearly-free-electron conduction bands and corresponding conduction properties, with the effective mass increased slightly by large-polaron effects. In TiO2, the lowest conduction bands contain considerable admixture of Ti 3d states. In this case the conduction electrons become localized, or self-trapped, into small-polaron states, and their conduction properties differ considerably from the usual case. EPR experiments by Halliburton et al. have shown that this self-trapping is also present in association with point defects, namely substitutional F and interstitial H (which forms a bond with a lattice O). In each case the spin of the unpaired electron is localized on a nearest neighbor Ti. Infrared absorption experiments as a function of temperature on the OH center by Bekisli et al. have resolved apparent inconsistencies in the model used to fit earlier IR data. Through detailed analysis they have interpreted their results in terms of a small polaron model which involves several configurations corresponding to the localization of the OH electron on different Ti sites, each of which yields an IR line of slightly different frequency. These conclusions are supported by theoretical results in the literature and by our calculations using the CRYSTAL06 code with a hybridized DFT Hamiltonian. This work was done in collaboration with Figen Bekisli and Michael Stavola, and was supported by NSF Grant No. DMR 1160756.

  16. High-density two-dimensional small polaron gas in a delta-doped Mott insulator.

    PubMed

    Ouellette, Daniel G; Moetakef, Pouya; Cain, Tyler A; Zhang, Jack Y; Stemmer, Susanne; Emin, David; Allen, S James

    2013-11-21

    Heterointerfaces in complex oxide systems open new arenas in which to test models of strongly correlated material, explore the role of dimensionality in metal-insulator-transitions (MITs) and small polaron formation. Close to the quantum critical point Mott MITs depend on band filling controlled by random disordered substitutional doping. Delta-doped Mott insulators are potentially free of random disorder and introduce a new arena in which to explore the effect of electron correlations and dimensionality. Epitaxial films of the prototypical Mott insulator GdTiO3 are delta-doped by substituting a single (GdO)(+1) plane with a monolayer of charge neutral SrO to produce a two-dimensional system with high planar doping density. Unlike metallic SrTiO3 quantum wells in GdTiO3 the single SrO delta-doped layer exhibits thermally activated DC and optical conductivity that agree in a quantitative manner with predictions of small polaron transport but with an extremely high two-dimensional density of polarons, ~7 × 10(14) cm(-2).

  17. High-density Two-Dimensional Small Polaron Gas in a Delta-Doped Mott Insulator

    PubMed Central

    Ouellette, Daniel G.; Moetakef, Pouya; Cain, Tyler A.; Zhang, Jack Y.; Stemmer, Susanne; Emin, David; Allen, S. James

    2013-01-01

    Heterointerfaces in complex oxide systems open new arenas in which to test models of strongly correlated material, explore the role of dimensionality in metal-insulator-transitions (MITs) and small polaron formation. Close to the quantum critical point Mott MITs depend on band filling controlled by random disordered substitutional doping. Delta-doped Mott insulators are potentially free of random disorder and introduce a new arena in which to explore the effect of electron correlations and dimensionality. Epitaxial films of the prototypical Mott insulator GdTiO3 are delta-doped by substituting a single (GdO)+1 plane with a monolayer of charge neutral SrO to produce a two-dimensional system with high planar doping density. Unlike metallic SrTiO3 quantum wells in GdTiO3 the single SrO delta-doped layer exhibits thermally activated DC and optical conductivity that agree in a quantitative manner with predictions of small polaron transport but with an extremely high two-dimensional density of polarons, ~7 × 1014 cm−2. PMID:24257578

  18. Density of states and extent of wave function: two crucial factors for small polaron hopping conductivity in 1D

    NASA Astrophysics Data System (ADS)

    Dimakogianni, M.; Simserides, C.; Triberis, G. P.

    2013-07-01

    We introduce a theoretical model to scrutinize the conductivity of small polarons in 1D disordered systems, focusing on two crucial - as will be demonstrated - factors: the density of states and the spatial extent of the electronic wave function. The investigation is performed for any temperature up to 300 K and under electric field of arbitrary strength up to the polaron dissociation limit. To accomplish this task, we combine analytical work with numerical calculations.

  19. Analog of small Holstein polaron in hydrogen-bonded amide systems

    NASA Astrophysics Data System (ADS)

    Alexander, D. M.

    1985-01-01

    A class of amide-I (C = O stretch) related excitations and their contribution to the spectral function for infrared absorption is determined by use of the Davydov Hamiltonian. The treatment is a fully quantum, finite-temperature one. A consistent picture and a quantitative fit to the absorption data for crystalline acetanilide confirms that the model adequately explains the anomalous behavior cited by Careri et al. The localized excitation responsible for this behavior is the vibronic analog of the small Holstein polaron. The possible extension to other modes and biological relevance is examined.

  20. Anisotropic small-polaron hopping in W:BiVO{sub 4} single crystals

    SciTech Connect

    Rettie, Alexander J. E.; Chemelewski, William D.; Zhou, Jianshi; Lindemuth, Jeffrey; McCloy, John S.; Marshall, Luke G.; Emin, David; Mullins, C. Buddie

    2015-01-12

    DC electrical conductivity, Seebeck and Hall coefficients are measured between 300 and 450 K on single crystals of monoclinic bismuth vanadate that are doped n-type with 0.3% tungsten donors (W:BiVO{sub 4}). Strongly activated small-polaron hopping is implied by the activation energies of the Arrhenius conductivities (about 300 meV) greatly exceeding the energies characterizing the falls of the Seebeck coefficients' magnitudes with increasing temperature (about 50 meV). Small-polaron hopping is further evidenced by the measured Hall mobility in the ab-plane (10{sup −1 }cm{sup 2 }V{sup −1 }s{sup −1} at 300 K) being larger and much less strongly activated than the deduced drift mobility (about 5 × 10{sup −5 }cm{sup 2 }V{sup −1 }s{sup −1} at 300 K). The conductivity and n-type Seebeck coefficient is found to be anisotropic with the conductivity larger and the Seebeck coefficient's magnitude smaller and less temperature dependent for motion within the ab-plane than that in the c-direction. These anisotropies are addressed by considering highly anisotropic next-nearest-neighbor (≈5 Å) transfers in addition to the somewhat shorter (≈4 Å), nearly isotropic nearest-neighbor transfers.

  1. Anisotropic small-polaron hopping in W:BiVO4 single crystals

    NASA Astrophysics Data System (ADS)

    Rettie, Alexander J. E.; Chemelewski, William D.; Lindemuth, Jeffrey; McCloy, John S.; Marshall, Luke G.; Zhou, Jianshi; Emin, David; Mullins, C. Buddie

    2015-01-01

    DC electrical conductivity, Seebeck and Hall coefficients are measured between 300 and 450 K on single crystals of monoclinic bismuth vanadate that are doped n-type with 0.3% tungsten donors (W:BiVO4). Strongly activated small-polaron hopping is implied by the activation energies of the Arrhenius conductivities (about 300 meV) greatly exceeding the energies characterizing the falls of the Seebeck coefficients' magnitudes with increasing temperature (about 50 meV). Small-polaron hopping is further evidenced by the measured Hall mobility in the ab-plane (10-1 cm2 V-1 s-1 at 300 K) being larger and much less strongly activated than the deduced drift mobility (about 5 × 10-5 cm2 V-1 s-1 at 300 K). The conductivity and n-type Seebeck coefficient is found to be anisotropic with the conductivity larger and the Seebeck coefficient's magnitude smaller and less temperature dependent for motion within the ab-plane than that in the c-direction. These anisotropies are addressed by considering highly anisotropic next-nearest-neighbor (≈5 Å) transfers in addition to the somewhat shorter (≈4 Å), nearly isotropic nearest-neighbor transfers.

  2. Appearance of small polaron hopping conduction in iron modified cobalt lithium bismuth borate glasses

    NASA Astrophysics Data System (ADS)

    Dahiya, M. S.; Khasa, S.; Yadav, Arti; Agarwal, A.

    2016-05-01

    Lithium bismuth borate glasses containing different amounts of cobalt and iron oxides having chemical composition xFe2O3•(20-x)CoO•30Li2O•10Bi2O3•40B2O3 (x = 0, 5, 10, 15 and 20 mol% abbreviated as CFLBB1-5 respectively) prepared via melt quench technique have been investigated for their dc electrical conductivity. The amorphous nature of prepared glasses has been confirmed through X-ray diffraction measurements. The dc electrical conductivity has been analyzed by applying Mott's small polaron hopping model. Activation energies corresponding to lower and higher temperature region have been evaluated. The iron ion concentration (N), mean spacing between iron ions (R) and polaron radius (Rp) has been evaluated using the values of phonon radius (Rph) and Debye temperature (θD). The glass sample without iron (CFLBB1) shows ionic conductivity but the incorporation of iron in the glass matrix results in the appearance of electronic conductivity.

  3. Optical Conductivity of Small Polarons in Sm1-xSrxTiO3 Epitaxial Films

    NASA Astrophysics Data System (ADS)

    Flaherty, William; Hauser, Adam; Law, Strange; Jackson, Clayton; Raghavan, Santosh; Isaac, Brandon; Freeze, Chris; Allen, S. James; Stemmer, Susanne

    2015-03-01

    We present our findings in the optical conductivity in a doping-controlled metal-to-Mott-insulator transition. These samples, grown using hybrid MBE, span the transition from the Mott insulator SmTiO3 to metallic, lightly-doped SrTiO3. Zhou and Goodenough have studied a wide range of rare earth titanates and found that SmTiO3 has thermally activated transport. We measure the optical conductivity to determine the conduction mechanism. Using FTIR spectroscopy, we extract the optical conductivity in the 0.06-2.5 eV range. If conduction in Sm1-xSrxTiO3 is due to small polarons, it will have a distinct Gaussian optical conductivity feature, related to the DC transport, as described by David Emin. Alternatively, conduction could be due to variable-range hopping between defects. Furthermore, the combination of DC and optical conductivity can test the prediction of Yee and Balents that the metal-to-insulator transition is first-order with percolative phase separation between metallic and localized regions. Such a sample would have a distinct Drude tail plus polaron contributions to its conductivity. Extreme Electron Concentration Oxide Devices, Supported by ONR N00014-12-0976.

  4. Cadmium and indium defects in ceria and their interaction with oxygen vacancies and small polarons

    SciTech Connect

    Pryde, A.K.A.; Vyas, S.; Grimes, R.W.; Gardner, J.A.; Wang, R.

    1995-11-01

    Atomistic simulation calculations have been used to investigate the energetics of defect clustering and migration in ceria. The defects considered are In{sup 3+}, Cd{sup 2+}, their associated oxygen vacancies, and small polarons modeled as Ce{sup 3+} ions. Thus a range of complex defect clusters is considered. The overall aim of the study is to generate a better understanding of these defects as they relate to recent experimental results obtained using perturbed-angular-correlation spectroscopy. The calculations are successful in this regard, correctly predicting both binding energies and an oxygen migration activation energy. More importantly, the calculations provide an atomistic explanation for certain of the experimental observations. As such, the synergy between calculations and experiment is an important feature of this paper.

  5. Small polaronic hole hopping mechanism and Maxwell-Wagner relaxation in NdFeO3

    NASA Astrophysics Data System (ADS)

    Ahmad, I.; Akhtar, M. J.; Younas, M.; Siddique, M.; Hasan, M. M.

    2012-10-01

    In the modern micro-electronics, transition metal oxides due to their colossal values of dielectric permittivity possess huge potential for the development of capacitive energy storage devices. In the present work, the dielectric permittivity and the effects of temperature and frequency on the electrical transport properties of polycrystalline NdFeO3, prepared by solid state reaction method, are discussed. Room temperature Mossbauer spectrum confirms the phase purity, octahedral environment for Fe ion, and high spin state of Fe3+ ion. From the impedance spectroscopic measurements, three relaxation processes are observed, which are related to grains, grain boundaries (gbs), and electrode-semiconductor contact in the measured temperature and frequency ranges. Decrease in resistances and relaxation times of the grains and grain boundaries with temperature confirms the involvement of thermally activated conduction mechanisms. Same type of charge carriers (i.e., small polaron hole hopping) have been found responsible for conduction and relaxation processes through the grain and grain boundaries. The huge value of the dielectric constant (˜8 × 103) at high temperature and low frequency is correlated to the Maxwell-Wagner relaxation due to electrode-sample contact.

  6. Holes bound as small polarons to acceptor defects in oxide materials: why are their thermal ionization energies so high?

    NASA Astrophysics Data System (ADS)

    Schirmer, O. F.

    2011-08-01

    Holes bound to acceptor defects in oxide materials usually need comparatively high energies, of the order of 0.5-1.0 eV, to be ionized thermally to the valence band maximum. It is discussed that this has to be attributed to the stabilization of such holes by mainly short range interactions with the surrounding lattice, leading to the formation of small O - polarons. This is tantamount to the localization of the hole at only one of several equivalent oxygen ions next to the defect. The hole stabilizing energies can be determined experimentally from the related intense optical absorption bands. This paper exploits previous phenomenological studies of bound-hole small polarons in order to account for the large hole stabilization energies on this basis. A compilation demonstrates that bound-hole small polarons occur rather often in oxides and also in some related materials. The identification of such systems is based on EPR and optical studies and also on recent advanced electronic structure calculations.

  7. Small polaron hopping conduction mechanism in LiFePO4 glass and crystal

    NASA Astrophysics Data System (ADS)

    Banday, Azeem; Murugavel, Sevi

    2017-01-01

    The optimization of a cathode material is the most important criterion of lithium ion battery technology, which decides the power density. In order to improve the rate capability, a cathode material must possess high electronic and ionic conductivities. Therefore, it is important to understand the charge transport mechanism in such an advanced cathode material in its intrinsic state before modifying it by various means. In this work, we report the thermal, structural, and electrical conductivity studies on lithium iron phosphate, LiFePO4, both in its polycrystalline (LFPC) and glassy (LFPG) counterpart states. The vibrational spectroscopic measurements reveal the characteristic vibrational modes, which are the intrinsic part of LFPC, whereas in LFPG, the phonon modes become broader and overlap with each other due to the lattice disorder. The electrical conductivity measurements reveal that LFPG exhibits a higher polaronic conductivity of 1.6 orders than the LFPC sample. The temperature dependent dc conductivity has been analyzed with the Mott model of polarons and reveals the origin of enhanced polaronic conductivity in LFPG. Based on the analysis, the enhanced polaronic conductivity in LFPG has been attributed to the combined effect of reduced hopping length, decreased activation energy, and enhanced polaron concentration.

  8. Optically generated small electron and hole polarons in nominally undoped and Fe-doped KNbO3 investigated by transient absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Torbrügge, S.; Imlau, M.; Schoke, B.; Merschjann, C.; Schirmer, O. F.; Vernay, S.; Gross, A.; Wesemann, V.; Rytz, D.

    2008-09-01

    Transient light-induced absorption in nominally undoped and Fe-doped KNbO3 crystals is observed in the visible and infrared spectral ranges after single pulse illumination with λ=532nm . For nominally undoped KNbO3 the decay of the light-induced absorption in a single step can be explained by incoherent hopping transport of optically generated small bound O- hole and small free Nb4+ electron polarons and their mutual recombination. Iron doping causes an additional slow decay component and, remarkably, accelerates the initial decay process. A consistent model for the formation, hopping, and recombination paths of hole and electron polarons is deduced from the experimental data set for both nominally undoped and Fe-doped KNbO3 . The decrease in the polaron hopping-transport length in Fe-doped samples is attributed to the increased number densities of optically generated hole polarons by additional one-quantum excitations.

  9. Magnetic, optical, and electron transport properties of n -type CeO2: Small polarons versus Anderson localization

    NASA Astrophysics Data System (ADS)

    Kolodiazhnyi, Taras; Charoonsuk, Thitirat; Seo, Yu-Seong; Chang, Suyong; Vittayakorn, Naratip; Hwang, Jungseek

    2017-01-01

    We report magnetic susceptibility, electrical conductivity and optical absorption of Ce1 -xMxO2 where M = Nb,Ta and 0 ≤x ≤0.03 . The dc conductivity follows a simple thermally activated Arrhenius-type behavior in the T =70 -700 K range with a change in slope at T*≈155 K. The high-temperature activation energy shows gradual increase from ≈170 to 220 meV as the dopant concentration increases. The activation energy of the low-temperature conductivity shows a broad minimum of ≈77 meV at x ≈0.01 . Electron transport and localization mechanisms are analyzed in the framework of the Holstein small polaron, Anderson localization, and Jahn-Teller distortion models. The fit to the small polaron mobility is dramatically improved when, instead of the longitudinal phonons, the transverse optical phonons are considered in the phonon-assisted electron transport. This serves as an indirect evidence of a strong 4 f1 orbital interaction with the oxygen ligands, similar to the case of PrO2. Based on comparison of the experimental data to the models, it is proposed that the defect-induced random electric fields make the dominant contribution to the electron localization in donor-doped ceria.

  10. Light-induced polaronic absorption at low temperature in pure and (Fe, Ce, Cr) doped SrxBa1-xNb2O6 or Ba1-yCayTiO3 crystals and photodissociation of VIS centers into small polarons

    NASA Astrophysics Data System (ADS)

    Kapphan, S. E.; Kislova, I.; Wierschem, M.; Lindemann, T.; Gao, M.; Pankrath, R.; Vikhnin, V. S.; Kutsenko, A. B.

    2003-01-01

    Congruent SBN and BCT crystals doped with Fe, Cr, Ce to enhance photorefractive properties, are investigated at low temperature (T>1 K) under illumination with Ar+- and Kr+-laser light. Light-induced absorption changes in a wide spectral range from UV to IR indicate photoinduced charge transfer processes from impurities to polaronic centers. Broad NIR absorptions (at about 0,7 eV) associated with Ti3+ polarons in BCT or with Nb4+ polarons in SBN are observed and their non-linear behaviour with illumination intensity, polarization and temperature is described on the basis of the simple model for the photo charge transport (in SBN: Ce3+ +Nb5+ <----> Ce4++ Nb4+). A broad visible absorption VIS (at about 2 eV) appearing together with the NIR polarons, is shown by photodissociation (with a Kr+-laser) to consist at least partly of small polarons (in BCT and SBN).

  11. Hole polaron of small radius in assemblies of hydrated mono-protonated meso-tetraphenylporphine dimers at 77 K

    NASA Astrophysics Data System (ADS)

    Udal'tsov, Alexander V.

    2015-11-01

    Polaron theory is often used for the study of electrons and holes mobility in semiconductors when longitudinal optical (LO) phonons are generated upon the charge carriers moving. The polaron theory was applied to explain long-wavelength absorptions observed nearby Soret band in the electronic spectra of assemblies of mono-protonated meso-tetraphenylporphine dimer (TPP2H+) that are interpreted as LO-phonons originated due to proton movement. The energy of hole polaron is found to be 1.50 eV at 77 K. Energy of Franck-Condon transitions of LO-phonons generated by hole polaron moving through water confined in the assemblies with distortions of O-H bonds is 0.2653 eV (2138 cm-1). A broad band around 2127 cm-1 corresponding the same energy of O-H bonds vibrations is observed in IR spectra of the assemblies consisting of water and mainly of TPP2H+ species in the solid state indicating the presence of similar distortions of the hydrogen bonds. The radius of protonic sphere of 0.202 Å, which was estimated as a polaron quasiparticle moving through the confined water at 77 K, is found in agreement with earlier evaluated one of 0.265 Å that was obtained for proton diffusion at 298 K in similar assemblies.

  12. Infrared optical properties of α-alumina with the approach to melting: γ-like tetrahedral structure and small polaron conduction

    SciTech Connect

    Brun, J. F.; Campo, L. del; De Sousa Meneses, D.; Echegut, P.

    2013-12-14

    The normal spectral emittance of α-Al{sub 2}O{sub 3} single crystal has been measured from room temperature up to the liquid state and from 20 cm{sup −1} up to 10 000 cm{sup −1}, in two polarization configurations. The spectra were fitted with a semi-quantum dielectric function model. AlO{sub 4} structure units are revealed within the phonon spectral range more than a hundred degrees below the melting point when heating from the solid state. In parallel, the anomalous increase of emittance observed within the transparency spectral range with the approach to melting appears strongly correlated. Implications on the electronic structure are discussed: the existence of small polaron conduction is suggested which has never been mentioned before.

  13. High temperature transport properties of thermoelectric CaMnO{sub 3−δ} — Indication of strongly interacting small polarons

    SciTech Connect

    Schrade, M. Finstad, T. G.; Kabir, R.; Li, S.; Norby, T.

    2014-03-14

    The conductivity and Seebeck coefficient of CaMnO{sub 3−δ} have been studied at temperatures up to 1000 °C and in atmospheres with controlled oxygen partial pressure. Both transport coefficients were varied in situ by the reversible formation of oxygen vacancies up to δ = 0.15. The charge carrier concentration was calculated using a defect chemical model. The Seebeck coefficient could be approximated by Heikes' formula, while the conductivity shows a maximum at a molar charge carrier concentration of 0.25. These results were interpreted as a signature of strong electronic correlation effects, and it was concluded that charge transport in CaMnO{sub 3−δ} occurs via strongly interacting small polarons. General prospects for strongly correlated materials as potential candidates for high temperature thermoelectric power generation were discussed.

  14. Small polarons and magnetic antiphase boundaries in Ca2-xNaxCuO2Cl2 (x=0.06,0.12) : Origin of striped phases in cuprates

    NASA Astrophysics Data System (ADS)

    Patterson, C. H.

    2008-03-01

    We report hybrid density functional theory calculations on hole doped Ca2-xNaxCuO2Cl2 performed in 4×4 , 42×42 , and 8×2 supercells with hole concentrations x=0.0625 and x=0.125 . Holes at the lower concentration form small polarons, in which the hole is mainly localized on four oxygen ions surrounding one copper ion. The polaron is a spin one-half ferromagnetic polaron (Cu5O4) , in which the moment on the central copper ion is parallel to those on the four neighboring copper ions and the moment on the oxygen ions is opposed to that on the copper ions. This is therefore an Emery-Reiter spin polaron rather than a Zhang-Rice singlet. At the higher hole concentration (x=0.125) , many cuprates form stripes. Hybrid density functional theory calculations on linear chains of spin polarons separated by 4a0 show a group of bands localized mainly on the stripe. Spins on neighboring copper ions in the stripe are parallel and so the stripe forms a magnetic antiphase boundary between antiferromagnetically ordered blocks of copper spins. Stripes of this kind, which run in one direction only, may explain recent scanning tunneling microscopy data from Ca2-xNaxCuO2Cl2 by Kohsaka [Science 315, 1380 (2007)]. We also consider an ordered spin polaron phase where magnetic antiphase boundaries intersect at right angles. In this case, sets of four copper ions in squares at stripe intersections have parallel spins. This phase may be the 4×4 checkerboard pattern reported by Hanaguri [Nature (London) 430, 1001 (2004)].

  15. Polarons in acetanilide

    NASA Astrophysics Data System (ADS)

    Scott, Alwyn C.; Bigio, Irving J.; Johnston, Clifford T.

    1989-06-01

    The best available data are presented of the integrated intensity of the 1650-cm-1 band in crystalline acetanilide as a function of temperature. A concise theory of polaron states is presented and used to interpret the data.

  16. Polarons in acetanilide

    SciTech Connect

    Scott, A. C.; Bigio, I. J.; Johnston, C. T.

    1989-06-15

    The best available data are presented of the integrated intensity of the1650-cm/sup /minus/1/ band in crystalline acetanilide as a function oftemperature. A concise theory of polaron states is presented and used tointerpret the data.

  17. Engineering Polarons at a Metal Oxide Surface

    NASA Astrophysics Data System (ADS)

    Yim, C. M.; Watkins, M. B.; Wolf, M. J.; Pang, C. L.; Hermansson, K.; Thornton, G.

    2016-09-01

    Polarons in metal oxides are important in processes such as catalysis, high temperature superconductivity, and dielectric breakdown in nanoscale electronics. Here, we study the behavior of electron small polarons associated with oxygen vacancies at rutile TiO2(110 ) , using a combination of low temperature scanning tunneling microscopy (STM), density functional theory, and classical molecular dynamics calculations. We find that the electrons are symmetrically distributed around isolated vacancies at 78 K, but as the temperature is reduced, their distributions become increasingly asymmetric, confirming their polaronic nature. By manipulating isolated vacancies with the STM tip, we show that particular configurations of polarons are preferred for given locations of the vacancies, which we ascribe to small residual electric fields in the surface. We also form a series of vacancy complexes and manipulate the Ti ions surrounding them, both of which change the associated electronic distributions. Thus, we demonstrate that the configurations of polarons can be engineered, paving the way for the construction of conductive pathways relevant to resistive switching devices.

  18. Effect of epitaxial strain on small-polaron hopping conduction in Pr{sub 0.7}(Ca{sub 0.6}Sr{sub 0.4}){sub 0.3}MnO{sub 3} thin films

    SciTech Connect

    Wang, Jing Hu, Feng-xia; Zhao, Ying-ying; Liu, Yao; Wu, Rong-rong; Sun, Ji-rong; Shen, Bao-gen

    2015-03-09

    We investigated the epitaxial strain effect on the small-polaron hopping conduction properties in Pr{sub 0.7}(Ca,Sr){sub 0.3}MnO{sub 3} (PCSMO) films. An increase in the carrier localization, as evidenced by the enhancement of the small-polaron activation energy E{sub A} in the high temperature region, was obtained by increasing the epitaxial lattice strain in either the tensile or compressive strained film. Furthermore, it was found that the magnitude of E{sub A}, and thus the carrier localization, strongly depends on the sign of the lattice strain, which explains the diverse percolative transport behaviors in PCSMO films with different types of strains. Meanwhile, similar dependencies on the strain of the films were also obtained for the electron-phonon interaction, characterized by the calculated small-polaron coupling constant. Our results reveal that the type of lattice strain plays a crucial role in determining the degree of localization of charge carriers and the electron-phonon coupling strength, which is important for understanding the lattice strain-induced various novel properties related to phase separation and percolation behaviors.

  19. Photoinduced giant magnetic polarons in EuTe

    NASA Astrophysics Data System (ADS)

    Henriques, A. B.; Naupa, A. R.; Usachev, P. A.; Pavlov, V. V.; Rappl, P. H. O.; Abramof, E.

    2017-01-01

    Photoinduced magnetic polarons in EuTe, with a magnetic moment of several hundred Bohr magnetons, were investigated as a function of pump intensity and temperature by pump-probe Faraday rotation. The quantum efficiency for optical generation of magnetic polarons is found to be 0.09. The pump-intensity dependence of the photoinduced Faraday rotation shows a sublinear increase, from which we deduce that the population of photoexcited polarons is limited by a maximum value of 4.5 ×1015cm-3 . This is four orders of magnitude less than the concentration of polarons that would completely fill the crystal, which suggests that the photoexcited polarons are anchored by defects. In addition to the generation of polarons, at high pump densities the modulated pump light also causes a small alternating heating of the illuminated region. The temperature dependence of the polaron magnetic moment is well described by the Curie-Weiss law. Above 100 K, polarons are thermally quenched with an activation energy of 11 meV.

  20. Dielectric properties and study of AC electrical conduction mechanisms by non-overlapping small polaron tunneling model in Bis(4-acetylanilinium) tetrachlorocuprate(II) compound

    NASA Astrophysics Data System (ADS)

    Abkari, A.; Chaabane, I.; Guidara, K.

    2016-09-01

    In the present work, the synthesis and characterization of the Bis(4-acetylanilinium) tetrachlorocuprate(II) compound are presented. The structure of this compound is analyzed by X-ray diffraction which confirms the formation of single phase and is in good agreement the literature. Indeed, the Thermo gravimetric Analysis (TGA) shows that the decomposition of the compound is observed in the range of 420-520 K. However, the differential thermal analysis (DTA) indicates the presence of a phase transition at T=363 k. Furthermore, the dielectric properties and AC conductivity were studied over a temperature range (338-413 K) and frequency range (200 Hz-5 MHz) using complex impedance spectroscopy. Dielectric measurements confirmed such thermal analyses by exhibiting the presence of an anomaly in the temperature range of 358-373 K. The complex impedance plots are analyzed by an electrical equivalent circuit consisting of resistance, constant phase element (CPE) and capacitance. The activation energy values of two distinct regions are obtained from log σT vs 1000/T plot and are found to be E=1.27 eV (T<363 K) and E=1.09 eV (363 Ksmall polaron tunneling (NSPT) model is the most applicable conduction mechanism in the title compound. Complex impedance spectra of [C8H10NO]2CuCl4 at different temperatures.

  1. Two-Dimensional Polaronic Behavior in the Binary Oxides m-HfO2 and m-ZrO2

    SciTech Connect

    Mckenna, Keith P.; Wolf, Matthew J.; Shluger, Alexander L.; Lany, Stephan; Zunger, Alex

    2012-03-14

    We demonstrate that the three-dimensional (3D) binary monoclinic oxides HfO2 and ZrO2 exhibit quasi-2D polaron localization and conductivity, which results from a small difference in the coordination of two oxygen sublattices in these materials. The transition between a 2D large polaron into a zerodimensional small polaron state requires overcoming a small energetic barrier. These results demonstrate how a small asymmetry in the lattice structure can determine the qualitative character of polaron localization and significantly broaden the realm of quasi-2D polaron systems.

  2. Extreme electron polaron spatial delocalization in π-conjugated materials

    PubMed Central

    Rawson, Jeff; Angiolillo, Paul J.; Therien, Michael J.

    2015-01-01

    The electron polaron, a spin-1/2 excitation, is the fundamental negative charge carrier in π-conjugated organic materials. Large polaron spatial dimensions result from weak electron-lattice coupling and thus identify materials with unusually low barriers for the charge transfer reactions that are central to electronic device applications. Here we demonstrate electron polarons in π-conjugated multiporphyrin arrays that feature vast areal delocalization. This finding is evidenced by concurrent optical and electron spin resonance measurements, coupled with electronic structure calculations that suggest atypically small reorganization energies for one-electron reduction of these materials. Because the electron polaron dimension can be linked to key performance metrics in organic photovoltaics, light-emitting diodes, and a host of other devices, these findings identify conjugated materials with exceptional optical, electronic, and spintronic properties. PMID:26512097

  3. Polaron stability in oligoacene crystals.

    PubMed

    Pereira Junior, Marcelo Lopes; Ribeiro Junior, Luiz Antonio

    2017-03-01

    The polaron stability in organic molecular crystals is theoretically investigated in the scope of a two-dimensional Holstein-Peierls model that includes lattice relaxation. Particularly, the investigation is focused on designing a model Hamiltonian that can address properly the polaron properties in different model oligoacene crystals. The findings showed that a suitable choice for a set of parameters can play the role of distinguishing the model crystals and, consequently, different properties related to the polaron stability in these systems are observed. Importantly, the usefulness of this model is stressed by investigating the electronic localization of the polaron, which provides a deeper understanding into the properties associated with the polaron stability in oligoacene crystals.

  4. Some approaches to polaron theory

    NASA Astrophysics Data System (ADS)

    Bogolubov, N. N.; Bogolubov, N. N.

    1985-11-01

    Here, in our approximation of polaron theory, we examine the importance of introducing the T product, which turn out to be a very convenient theoretical approach for the calculation of thermodynamical averages. We focus attention on the investigation of the so-called linear polaron Hamiltonian and present in detail the calculation of the correlation function, spectral function, and Green function for such a linear system. It is shown that the linear polaron Hamiltonian provides an exactly solvable model of our system, and the result obtained with this approach holds true for an arbitrary coupling constant which describes the strength of interaction between the electron and the lattice vibrations. Then, with the help of a variational technique, we show the possibility of reducing the real polaron Hamiltonian to a socalled trial or approximate linear model Hamiltonian. We also consider the exact calculation of free energy with a special technique that reduces calculations with the help of the T product, which, in our opinion, works much better and is easier than other analogous considerations, for example, the path-integral or Feynman-integral method.(1,2) Here we furthermore recall our own work,(4) where it was shown that the results of Refs. 7 and 8 concerning the impedance calculation in the polaron model may be obtained directly without the use of the path-integral method. The study of the polaron system's thermodynamics is carried out by us in the framework of the functional method. A calculation of the free energy and the momentum distribution function is proposed. Note also that the polaron systems with strong coupling(9) proved to be useful in different quantum field models in connection with the construction of dynamical models of composite particles. A rigorous solution of the special strong-coupling polaron problem, describing the interaction of a nonrelativistic particle with a quantum field, was given by Bogolubov.(3) The works of Tavkhelidze, Fedyanin

  5. Polaron in a Quasi 0D Nanocrystal

    NASA Astrophysics Data System (ADS)

    Fai, L. C.; Fotue, A. J.; Mborong, V. B.; Domngang, S.; Issofa, N.; Tchassem, D.

    2005-01-01

    Polaron states in a spherical quantum dot with a spherical symmetric parabolic confinement potential are investigated applying the Feynman variational principle. Effects of the dot radius on the polaron ground state energy level, the self-action potential energy, the mass and the Fröhlich electron phonon-coupling constant are obtained for a spherical quantum dot. The electron phonon-coupling amplitude derived from the Maxwell equation in a material medium is used. This yields a better upper bound for strong coupling polaron energy in a spherical quantum dot. The polaron mass, energy and self-action potential energy are found to have a monotonous decrease as the structures' radius increases. As the spherical quantum dot radius is reduced the regimes of weak and intermediate coupling polaron shorten and the strong coupling polaron region broadens and extends into weak and intermediate ones. The main contribution to polaron energy and mass comes from the self-action potential.

  6. Polaron effects in asymmetric semiconductor quantum-well structures

    NASA Astrophysics Data System (ADS)

    Shi, Jun-Jie; Zhu, Xiu-Qin; Liu, Zi-Xin; Pan, Shao-Hua; Li, Xing-Yi

    1997-02-01

    In this paper, polaron effects in asymmetric quantum-well structures (QW's) are investigated by using second-order perturbation theory and the modified Lee-Low-Pines (LLP) variational method. By applying the Green"s-function method, explicit analytical expressions for the electron extended-state wave functions and the density of states in a general step QW's are given. Within the framework of second-order perturbation theory, the ground-state polaron binding energy and effective mass in step and asymmetric single QW"s are studied as due to the interface optical phonons, confined bulklike LO and half-space LO phonons. The full energy spectrum is included in our calculations. The effects of the finite electronic confinement potential and the subband nonparabolicity are also considered. The relative importance of the different phonon modes is analyzed. By means of the modified LLP variational method, the binding energy of a polaron confined to asymmetric single QW's is also investigated. Our results show that in ordinary asymmetric QW"s, the asymmetry of the QW's has a significant influence on the polaron effect, which has a close relationship to the interface phonon dispersion. When the well width and one side barrier height of asymmetric single QW"s are fixed and identical with those of symmetric QW's, the polaron binding energy in asymmetric QW"s is always smaller than that in symmetric QW's. We have also found that it is necessary to include the continuum energy spectrum as intermediate states in the perturbation calculations in order to obtain the correct results; the subband nonparabolicity has a small influence on the polaron effect. Comparing our results obtained by using two different methods, good agreement is found.

  7. Doping dependent evolution of the polaron metal

    NASA Astrophysics Data System (ADS)

    Mannella, N.; Tanaka, K.; Mo, S.-K.; Yang, W.; Zheng, H.; Mitchell, J.; Zaanen, J.; Deveraux, T. P.; Nagaosa, N.; Hussain, Z.; Shen, Z.-X.

    2009-03-01

    Experimental and theoretical evidence has already suggested that the ferromagnetic metallic (FM) phase in colossal magnetoresistive manganites is not a conventional metal but rather a polaronic conductor. In the bilayer manganites La2-2xSr1+2xMn2O7 (LSMO), Angle Resolved Photoemission (ARPES) experiment revealed that the FM phase is a polaronic metal with a strong anisotropic character of the electronic excitations [1,2]. A small but well-defined quasiparticle (QP) with heavy mass along the [110] or ``nodal'' direction is found to account for the metallic properties and their temperature dependent evolution [2]. In this talk, we will discuss recent ARPES results on the x = 0.60 composition and contrast them to the x = 0.40 results. Recent work has shown that the region in proximity of x = 0.60 constitute the most metallic bilayer manganite with DC conductivity about one order of magnitude higher than that corresponding to the region 0.30 < x < 0.40. Much as in the x = 0.40 composition, for x = 0.60 along the nodal direction we observe a peak-dip-hump structure with QP of heavy effective mass. Quantitative differences in the electron-phonon coupling constant λ, the QP spectral weight and the hump energy are fully consistent with the doping evolution of the transport properties. [1] Nature 438, 474 (2005), [2] Phys. Rev. B 76, 233102 (2007).

  8. Band Structures of Plasmonic Polarons

    NASA Astrophysics Data System (ADS)

    Caruso, Fabio; Lambert, Henry; Giustino, Feliciano

    2015-03-01

    In angle-resolved photoemission spectroscopy (ARPES), the acceleration of a photo-electron upon photon absorption may trigger shake-up excitations in the sample, leading to the emission of phonons, electron-hole pairs, and plasmons, the latter being collective charge-density fluctuations. Using state-of-the-art many-body calculations based on the `GW plus cumulant' approach, we show that electron-plasmon interactions induce plasmonic polaron bands in group IV transition metal dichalcogenide monolayers (MoS2, MoSe2, WS2, WSe2). We find that the energy vs. momentum dispersion relations of these plasmonic structures closely follow the standard valence bands, although they appear broadened and blueshifted by the plasmon energy. Based on our results we identify general criteria for observing plasmonic polaron bands in the angle-resolved photoelectron spectra of solids.

  9. Hole polaron formation and migration in olivine phosphate materials

    NASA Astrophysics Data System (ADS)

    Johannes, M. D.; Hoang, Khang; Allen, J. L.; Gaskell, K.

    2012-03-01

    By combining first-principles calculations and experimental x-ray photoemission (XPS) spectroscopy measurements, we investigate the electronic structure of potential Li-ion battery cathode materials LiMPO4 (M=Mn, Fe, Co, Ni) to uncover the underlying mechanisms that determine small hole polaron formation and migration. We show that small hole polaron formation depends on features in the electronic structure near the valence-band maximum and that, calculationally, these features depend on the methodology chosen for dealing with the correlated nature of the transition-metal d-derived states in these systems. Comparison with experiment reveals that a hybrid functional approach is superior to GGA+U in correctly reproducing the XPS spectra. Using this approach, we find that LiNiPO4 cannot support small hole polarons, but that the other three compounds can. The migration barrier is determined mainly by the strong- or weak-bonding nature of the states at the top of the valence band, resulting in a substantially higher barrier for LiMnPO4 than for LiCoPO4 or LiFePO4.

  10. Polaronic trapping in magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Raebiger, Hannes

    2012-02-01

    GaN doped with iron is an interesting candidate material for magnetic semiconductors, as p-d coupling between the localized Fe-d and extended N-p hole states is expected to facilitate long-range ferromagnetic alignment of the Fe spins [1]. This picture of extended states in GaN:Fe, however, falls apart due to a polaronic localization of the hole carriers nearby the Fe impurities. To elucidate the carrier localization in GaN:Fe and related iron doped III-V semiconductors, I present a systematic study using self-interaction corrected density-functional calculations [2]. These calculations predict three distinct scenarios. (i) Some systems do sustain extended host-like hole states, (ii) some exhibit polaronic trapping, (iii) and some exhibit carrier trapping at Fe-d orbitals. These behaviors are described in detail to give an insight as to how to distinguish them experimentally. I thank T. Fujita, C. Echeverria-Arrondo, and A. Ayuela for their collaboration.[4pt] [1] T. Dietl et al, Science, 287, 1019 (2000).[0pt] [2] S. Lany and A. Zunger, Phys. Rev. B, 80, 085202 (2009).

  11. Bose Polarons in the Strongly Interacting Regime

    NASA Astrophysics Data System (ADS)

    Hu, Ming-Guang; Van de Graaff, Michael J.; Kedar, Dhruv; Corson, John P.; Cornell, Eric A.; Jin, Deborah S.

    2016-07-01

    When an impurity is immersed in a Bose-Einstein condensate, impurity-boson interactions are expected to dress the impurity into a quasiparticle, the Bose polaron. We superimpose an ultracold atomic gas of 87Rb with a much lower density gas of fermionic 40 impurities. Through the use of a Feshbach resonance and radio-frequency spectroscopy, we characterize the energy, spectral width, and lifetime of the resultant polaron on both the attractive and the repulsive branches in the strongly interacting regime. The width of the polaron in the attractive branch is narrow compared to its binding energy, even as the two-body scattering length diverges.

  12. Path-integral approach to lattice polarons

    NASA Astrophysics Data System (ADS)

    Kornilovitch, P. E.

    2007-06-01

    The basic principles behind a path integral approach to the lattice polaron are reviewed. Analytical integration of phonons reduces the problem to one self-interacting imaginary-time path, which is then simulated by Metropolis Monte Carlo. Projection operators separate states of different symmetry, which provides access to various excited states. Shifted boundary conditions in imaginary time enable calculation of the polaron mass, spectrum and density of states. Other polaron characteristics accessible by the method include the polaron energy, number of excited phonons and isotope exponent on mass. Monte Carlo updates are formulated in continuous imaginary time on infinite lattices and as such provide statistically unbiased results without finite-size and finite time-step errors. Numerical data are presented for models with short-range and long-range electron-phonon interactions.

  13. Polaron action for multimode dispersive phonon systems

    NASA Astrophysics Data System (ADS)

    Kornilovitch, P. E.

    2006-03-01

    The path-integral approach to the tight-binding polaron is extended to multiple optical phonon modes of arbitrary dispersion and polarization. The nonlinear lattice effects are neglected. Only one electron band is considered. The electron-phonon interaction is of the density-displacement type, but can be of arbitrary spatial range and shape. Feynman’s analytical integration of ion trajectories is performed by transforming the electron-ion forces to the basis in which the phonon dynamical matrix is diagonal. The resulting polaron action is derived for the periodic and shifted boundary conditions in imaginary time. The former can be used for calculating polaron thermodynamics while the latter for the polaron mass and spectrum. The developed formalism is the analytical basis for numerical analysis of such models by path-integral Monte Carlo methods.

  14. Bose polarons in the strongly interacting regime

    NASA Astrophysics Data System (ADS)

    Kedar, Dhruv; Hu, Ming-Guang; van de Graaff, Michael; Corson, John; Cornell, Eric; Jin, Deborah

    2016-05-01

    Impurities immersed in and interacting with a Bose-Einstein condensate (BEC) are predicted to form quasiparticle excitations called Bose polarons. I will present experimental evidence of Bose polarons in cold atoms obtained using radio-frequency spectroscopy to measure the excitation spectrum of fermionic K-40 impurities interacting with a BEC of Rb-87 atoms. We use an interspecies Feshbach resonance to tune the interactions between the impurities and the bosons, and we take data in the strongly interacting regime.

  15. Determining a hopping polaron's bandwidth from its Seebeck coefficient: Measuring the disorder energy of a non-crystalline semiconductor

    SciTech Connect

    Emin, David

    2016-01-28

    Charge carriers that execute multi-phonon hopping generally interact strongly enough with phonons to form polarons. A polaron's sluggish motion is linked to slowly shifting atomic displacements that severely reduce the intrinsic width of its transport band. Here a means to estimate hopping polarons' bandwidths from Seebeck-coefficient measurements is described. The magnitudes of semiconductors' Seebeck coefficients are usually quite large (>k/|q| = 86 μV/K) near room temperature. However, in accord with the third law of thermodynamics, Seebeck coefficients must vanish at absolute zero. Here, the transition of the Seebeck coefficient of hopping polarons to its low-temperature regime is investigated. The temperature and sharpness of this transition depend on the concentration of carriers and on the width of their transport band. This feature provides a means of estimating the width of a polaron's transport band. Since the intrinsic broadening of polaron bands is very small, less than the characteristic phonon energy, the net widths of polaron transport bands in disordered semiconductors approach the energetic disorder experienced by their hopping carriers, their disorder energy.

  16. Giant Optical Polarization Rotation Induced by Spin-Orbit Coupling in Polarons

    NASA Astrophysics Data System (ADS)

    Casals, Blai; Cichelero, Rafael; García Fernández, Pablo; Junquera, Javier; Pesquera, David; Campoy-Quiles, Mariano; Infante, Ingrid C.; Sánchez, Florencio; Fontcuberta, Josep; Herranz, Gervasi

    2016-07-01

    We have uncovered a giant gyrotropic magneto-optical response for doped ferromagnetic manganite La2 /3Ca1 /3MnO3 around the near room-temperature paramagnetic-to-ferromagnetic transition. At odds with current wisdom, where this response is usually assumed to be fundamentally fixed by the electronic band structure, we point to the presence of small polarons as the driving force for this unexpected phenomenon. We explain the observed properties by the intricate interplay of mobility, Jahn-Teller effect, and spin-orbit coupling of small polarons. As magnetic polarons are ubiquitously inherent to many strongly correlated systems, our results provide an original, general pathway towards the generation of magnetic-responsive gigantic gyrotropic responses that may open novel avenues for magnetoelectric coupling beyond the conventional modulation of magnetization.

  17. Photophysics of the geminate polaron-pair state in copper phthalocyanine organic photovoltaic blends: evidence for enhanced intersystem crossing.

    PubMed

    Snedden, Edward W; Monkman, Andrew P; Dias, Fernando B

    2013-04-04

    Geminate polaron-pair recombination directly to the triplet state of the small dye molecule copper(II) 1,4,8,11,15,18,22,25-octabutoxy-29H,31H- phthalocyanine (CuPC) and exciton trapping in CuPC domains, combine to reduce the internal quantum efficiency of free polaron formation in the bulk-heterojunction blends of CuPC doped with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the electron acceptor.

  18. The Holstein polaron problem revisited

    NASA Astrophysics Data System (ADS)

    Tayebi, Amin; Zelevinsky, Vladimir

    2016-06-01

    The Holstein Hamiltonian was proposed half a century ago; since then, decades of research have come up empty handed in the pursuit of a closed-form solution. An exact solution to the two-site Holstein model is presented in this paper. The obtained results provide a clear image of the Hamiltonian structure and allow for the investigation of the symmetry, energy level crossings and polaronic characteristics of the system. The main mathematical tool is a three-term recurrence relation between the wave function amplitudes, which was obtained using the properties of a family of orthogonal functions, namely the Poisson-Charlier polynomials. It is shown that, with the appropriate choice of basis, the eigenfunctions of the problem naturally fall into two families (parities) associated with the discrete {{{Z}}}2 symmetry of the Hamiltonian. The asymptotic solution to the recurrence relation is found by using the Birkhoff expansion. The asymptotic sets the truncation criterion for the wave function, which ensures the accurate calculation of the energy levels for any strength of electron-phonon interaction. The level crossing of states with different parities is discussed and the exact points of broken symmetry are found analytically. The results are used as the building blocks for studying a four-site system. The inherited symmetries lead to the formation of a sparse matrix that is convenient for numerical calculations.

  19. Evidence for Light-Induced Hole Polarons in LiNbO3

    NASA Astrophysics Data System (ADS)

    Herth, P.; Granzow, T.; Schaniel, D.; Woike, Th.; Imlau, M.; Krätzig, E.

    2005-08-01

    Transient light-induced absorption in LiNbO3 is observed in the blue-green spectral range after pulsed illumination with 532 nm. Its buildup and decay in Fe-doped LiNbO3 is satisfactorily described by a sum of two stretched exponential functions. For undoped LiNbO3, however, only one stretched exponential decay is observed. These experimental results are explained by the formation of both small Nb4+Li electron polarons and O- hole polarons. The mechanism is discussed on the basis of a proposed band scheme.

  20. Stationary Phonon Squeezing by Optical Polaron Excitation

    NASA Astrophysics Data System (ADS)

    Papenkort, T.; Axt, V. M.; Kuhn, T.

    2017-03-01

    We demonstrate that a stationary squeezed phonon state can be prepared by a pulsed optical excitation of a semiconductor quantum well. Unlike previously discussed scenarios for generating squeezed phonons, the corresponding uncertainties become stationary after the excitation and do not oscillate in time. The effect is caused by two-phonon correlations within the excited polaron. We demonstrate by quantum kinetic simulations and by a perturbation analysis that the energetically lowest polaron state comprises two-phonon correlations which, after the pulse, result in an uncertainty of the lattice momentum that is continuously lower than in the ground state of the semiconductor. The simulations show the dynamics of the polaron formation process and the resulting time-dependent lattice uncertainties.

  1. POLARON DYNAMICS. Long-lived photoinduced polaron formation in conjugated polyelectrolyte-fullerene assemblies.

    PubMed

    Huber, Rachel C; Ferreira, Amy S; Thompson, Robert; Kilbride, Daniel; Knutson, Nicholas S; Devi, Lekshmi Sudha; Toso, Daniel B; Challa, J Reddy; Zhou, Z Hong; Rubin, Yves; Schwartz, Benjamin J; Tolbert, Sarah H

    2015-06-19

    The efficiency of biological photosynthesis results from the exquisite organization of photoactive elements that promote rapid movement of charge carriers out of a critical recombination range. If synthetic organic photovoltaic materials could mimic this assembly, charge separation and collection could be markedly enhanced. We show that micelle-forming cationic semiconducting polymers can coassemble in water with cationic fullerene derivatives to create photoinduced electron-transfer cascades that lead to exceptionally long-lived polarons. The stability of the polarons depends on the organization of the polymer-fullerene assembly. Properly designed assemblies can produce separated polaronic charges that are stable for days or weeks in aqueous solution.

  2. The asymmetric quantum Rabi model in the polaron picture

    NASA Astrophysics Data System (ADS)

    Liu, Maoxin; Ying, Zu-Jian; An, Jun-Hong; Luo, Hong-Gang; Lin, Hai-Qin

    2017-02-01

    The concept of the polaron in condensed matter physics has been extended to the Rabi model, where polarons resulting from the coupling between a two-level system and single-mode photons represent two oppositely displaced oscillators. Interestingly, tunneling between these two displaced oscillators can induce an anti-polaron, which has not been systematically explored in the literature, especially in the presence of an asymmetric term. In this paper, we present a systematic analysis of the competition between the polaron and anti-polaron under the interplay of the coupling strength and the asymmetric term. While intuitively the anti-polaron should be secondary owing to its higher potential energy, we find that, under certain conditions, the minor anti-polaron may gain a reversal in the weight over the major polaron. If the asymmetric amplitude ɛ is smaller than the harmonic frequency ω, such an overweighted anti-polaron can occur beyond a critical value of the coupling strength g; if ɛ is larger, the anti-polaron can even be always overweighted at any g. We propose that the explicit occurrence of the overweighted anti-polaron can be monitored by a displacement transition from negative to positive values. This displacement is an experimentally accessible observable, which can be measured by quantum optical methods, such as balanced Homodyne detection.

  3. Electrons on helium — The ``polaron'' transition

    NASA Astrophysics Data System (ADS)

    Andrei, E. Y.; Grimes, C. C.; Adams, G.

    1984-07-01

    We describe the observation of the polaronic transition of a system of electrons supported above a helium film. The electron mobility drops sharply by more than four orders of magnitude as the film thickness is reduced below ≈ 1000 Å. The transition was observed in the temperature range 0.4 ⩽ T ⩽ 1 K.

  4. Coherent state polarons in quantum wells

    NASA Astrophysics Data System (ADS)

    Thilagam, A.; Lohe, M. A.

    2005-01-01

    We investigate the polaronic effects of an electron confined in a quantum well, which we describe through its algebraic properties using su (1 , 1), taking into account the electron-bulk longitudinal-optical phonon interaction. We construct the variational wave function as the direct product of an electronic part and a part describing coherent phonons generated by the Low-Lee-Pines transformation from the vacuum state. We use two explicit forms of coherent states, Perelomov and Barut-Girardello states, to represent the electronic part in the quantum well spectrum. Our results show that in a coherent state basis for electrons the basic polaron parameters such as the energy gap shift and effective mass are further enhanced compared to those obtained with the conventional sinusoidal form of the basis. The difference between the two types of quantum well coherent states appears in polaronic interactions in quantum wells. We extend the calculations in order to estimate polaron lifetimes for a variety of different material systems.

  5. Quantum vibrational polarons: Crystalline acetanilide revisited

    NASA Astrophysics Data System (ADS)

    Hamm, Peter; Edler, Julian

    2006-03-01

    We discuss a refined theoretical description of the peculiar spectroscopy of crystalline acetanilide (ACN). Acetanilide is a molecular crystal with quasi-one-dimensional chains of hydrogen-bonded units, which is often regarded as a model system for the vibrational spectroscopy of proteins. In linear spectroscopy, the CO stretching (amide I) band of ACN features a double-peak structure, the lower of which shows a pronounced temperature dependence which has been discussed in the context of polaron theory. In nonlinear spectroscopy, both of these peaks respond distinctly differently. The lower-frequency band exhibits the anharmonicity expected from polaron theory, while the higher-frequency band responds as if it were quasiharmonic. We have recently related the response of the higher-frequency band to that of a free exciton [J. Edler and P. Hamm, J. Chem. Phys. 117, 2415 (2002)]. However, as discussed in the present paper, the free exciton is not an eigenstate of the full quantum version of the Holstein polaron Hamiltonian, which is commonly used to describe these phenomena. In order to resolve this issue, we present a numerically exact solution of the Holstein polaron Hamiltonian in one dimension (1D) and 3D. In 1D, we find that the commonly used displaced oscillator picture remains qualitatively correct, even for relatively large exciton coupling. However, the result is not in agreement with the experiment, as it fails to explain the free-exciton band. In contrast, when taking into account the 3D nature of crystalline acetanilide, certain parameter regimes exist where the displaced oscillator picture breaks down and states appear in the spectrum that indeed exhibit the characteristics of a free exciton. The appearance of these states is a speciality of vibrational polarons, whose source of exciton coupling is transition dipole coupling which is expected to have opposite signs of interchain and intrachain coupling.

  6. Polarons and bipolarons in cis-polyacetylene

    NASA Astrophysics Data System (ADS)

    Utz, Wolfram; Förner, Wolfgang

    1998-05-01

    We present a parametrization for the Pariser-Parr-Pople Hamiltonian for the description of cis-polyacetylene (cPA). In contrast to trans-polyacetylene, we have to include symmetry breaking between neighboring sites into the Su-Schrieffer-Heeger-type one-electron part of the Hamiltonian. Our parametrization is based on correlated ab initio calculations on cis-hexatriene and on the results of independent calculations found in the literature. For open-shell systems (singly charged polarons) we use the annihilated unrestricted Hartree-Fock method to avoid the artificial spin contaminations inherent in UHF (unrestricted HF) calculations, which lead to the inclusion of fractions of the correlation energy in UHF total energies which cannot be controlled and are different for different systems and even for different geometries of the same system. Thus UHF is useless for the calculation of potential hypersurfaces and thus in turn for dynamical simulations. We find that in cPA singly-charged polarons are formed, while in doubly-charged chains stable bipolarons are found, although of a quite large width. This is in contrast to recent results reported by Shimoi and Abe [Y. Shimoi and S. Abe, Synth. Met. 69, 687 (1995) and Phys. Rev. B 50, 14 781 (1994)] who found that two singly-charged polarons are more stable for realistic parameter values than a doubly-charged bipolaron. We further find that the charged polarons are mobile in the chain and thus we conclude that polarons and bipolarons can serve as charge carriers (the latter ones spinless) in doped cPA.

  7. Optical dynamics of exciton and polaron formation in molecular aggregates

    NASA Astrophysics Data System (ADS)

    de Boer, Steven; Wiersma, Douwe A.

    1989-03-01

    Results of femtosecond accumulated photon echo, picosecond pump-probe and fluorescence lifetime measurements are reported on aggregates of the dyes pseudoisocyanine (PIC) and substituted thiapyrylium (TPY), embedded in a polycarbonate matrix. It is concluded that in the PIC aggregate, delocalized excitations (excitons) are formed, which are weakly coupled to the aggregate's nuclear frame. In the TPY aggregate, excitons are also initially formed, but through strong local electron-phonon coupling these excitons are not stable and decay into polarons, which become trapped. It is suggested that the nature of the excitations in aggregates crucially depends on the change of electron density distribution upon optical excitation. When this change is large, as revealed by a large change of dipole moment, polarons will be formed. In the other limit of a small change of dipole moment on optical excitation, excitons with an enhanced radiative lifetime are formed, which coherently propagate over that part of the aggregate where the molecules are electronically strongly coupled. The relevance of these findings towards energy transport in photo-biological systems is also discussed.

  8. Modeling of magnetic polaron properties in (Zn,Mn)Te quantum dots

    NASA Astrophysics Data System (ADS)

    Pientka, James; Barman, B.; Schweidenback, L.; Russ, A. H.; Tsai, Y.; Murphy, J. R.; Cartwright, A. N.; Zutic, I.; McCombe, B. D.; Petrou, A.; Chou, W.-C.; Fan, W. C.; Sellers, I. R.; Petukhov, A. G.; Oszwaldowski, R.

    Magnetic polarons in (Zn,Mn)Te quantum dots (QD) show unconventional behavior. These structures exhibit a small red shift of the photoluminescence peak energy in the presence of a magnetic field B and they also have a weak dependence of the polaron energy EMP on temperature T and B. We attribute these properties to a large molecular field Bm that is proportional to the heavy holes spin density. We have calculated Bm using the QD diameter and height as adjustable parameters. Assuming hole localization, this calculation yields values of Bm >20 T. The assumption that the hole localization diameter can be smaller than the QD diameter is justified due to alloy and spin disorder scattering. Using the magnetic polaron free energy, we calculate EMP as function of T and B for a variety of Bm values. To get a weak dependence of EMP on T and Bwe must assume that the polaron temperature is higher than T. This work was supported by U.S. DOE BES, Award DE-SC0004890, NSF DMR-1305770 and U.S. ONR N000141310754.

  9. Bose polarons: Dynamical decay and RF signatures

    NASA Astrophysics Data System (ADS)

    Corson, John; Bohn, John

    2016-05-01

    Interactions of a single impurity with a quantum many-body environment are known to alter the character of the impurity, thereby forming a ``quasiparticle''. The condensed matter tradition often identifies quasiparticles as poles of a Green function in the complex plane, a notion whose sophistication sometimes obscures the underlying physics. The problem of a single quantum impurity in a Bose condensate, or Bose polaron, is an illustrative example where the meaning of the impurity Green function, and hence the quasiparticle itself, becomes especially transparent. Using direct diagonalization in a truncated Hilbert space, we examine the dynamical evolution and quasiparticle decay of the repulsive Bose polaron. This approach also allows us to simulate RF spectroscopy across a Feshbach resonance and outside the linear regime, as well as account for motional and thermal effects in a harmonic trap.

  10. Magnon Polarons in the Spin Seebeck Effect.

    PubMed

    Kikkawa, Takashi; Shen, Ka; Flebus, Benedetta; Duine, Rembert A; Uchida, Ken-Ichi; Qiu, Zhiyong; Bauer, Gerrit E W; Saitoh, Eiji

    2016-11-11

    Sharp structures in the magnetic field-dependent spin Seebeck effect (SSE) voltages of Pt/Y_{3}Fe_{5}O_{12} at low temperatures are attributed to the magnon-phonon interaction. Experimental results are well reproduced by a Boltzmann theory that includes magnetoelastic coupling. The SSE anomalies coincide with magnetic fields tuned to the threshold of magnon-polaron formation. The effect gives insight into the relative quality of the lattice and magnetization dynamics.

  11. Magnon Polarons in the Spin Seebeck Effect

    NASA Astrophysics Data System (ADS)

    Kikkawa, Takashi; Shen, Ka; Flebus, Benedetta; Duine, Rembert A.; Uchida, Ken-ichi; Qiu, Zhiyong; Bauer, Gerrit E. W.; Saitoh, Eiji

    2016-11-01

    Sharp structures in the magnetic field-dependent spin Seebeck effect (SSE) voltages of Pt /Y3Fe5 O12 at low temperatures are attributed to the magnon-phonon interaction. Experimental results are well reproduced by a Boltzmann theory that includes magnetoelastic coupling. The SSE anomalies coincide with magnetic fields tuned to the threshold of magnon-polaron formation. The effect gives insight into the relative quality of the lattice and magnetization dynamics.

  12. Possible formation of chiral polarons in graphene.

    PubMed

    Kandemir, B S

    2013-01-16

    A theoretical investigation of the possible existence of chiral polaron formation in graphene is reported. We present an analytical method to calculate the ground-state of the electron-phonon system within the framework of the Lee-Low-Pines theory. On the basis of our model, the influence of electron-optical phonon interaction on the graphene electronic spectrum is investigated. We considered only the doubly degenerate optical phonon modes of E(2g) symmetry near the zone center Γ. It is analytically shown that the energy dispersions of both valence and conduction bands of the pristine graphene differ significantly from those obtained through the standard electron self-energy calculations arising from the electron-optical phonon interactions. In this paper, we also show for the first time that the degenerate band structure of the graphene promotes the chiral polaron formation. Furthermore, due to the k-dependent nature of the polaronic self-energy, in analogy with quantum chromodynamics, we also propose a running electron-phonon coupling constant as a function of energy.

  13. Polaron dynamics in anisotropic Holstein-Peierls systems.

    PubMed

    Ribeiro Junior, Luiz Antonio; Stafström, Sven

    2017-02-01

    Polaron dynamics in anisotropic organic molecular semiconductors is theoretically investigated and simulated in the framework of a semi-classical Holstein-Peierls model. Our computational protocol is presented and applied to studies of a two-dimensional molecular crystal. The intermolecular (Peierls) parameters for a particular crystal direction are systematically changed in order to study the effect of anisotropy in the system. The usefulness of this methodology is highlighted by studying the polaron dynamics on a picosecond timescale, which provides a microscopic insight into the influence of the interplay between different intramolecular parameters on the charge transport mechanism. Our results show that the polaron mobility is substantially reduced in going from an anisotropic to an isotropic relationship between the Peierls parameters for different directions in the crystal. Interestingly, the molecular charge distribution presents three different signatures corresponding to a one-dimensional polaron, a two-dimensional polaron, and an intermediate state for which the polaron localization depends on the degree of anisotropy. Importantly, the two-dimensional polaron, which is present in the essentially isotropic system, is immobile whereas the other two types of polarons are mobile. This, in order for polaron transport to occur in a two-dimensional molecular based system, this system has to be anisotropic.

  14. Polarons in π-Conjugated Polymers: Anderson or Landau?

    PubMed

    Barford, William; Marcus, Max; Tozer, Oliver Robert

    2016-02-04

    Using both analytical expressions and the density matrix renormalization group method, we study the fully quantized disordered Holstein model to investigate the localization of charges and excitons by vibrational or torsional modes-i.e., the formation of polarons-in conformationally disordered π-conjugated polymers. We identify two distinct mechanisms for polaron formation, namely Anderson localization via disorder (causing the formation of Anderson polarons) and self-localization by self-trapping via normal modes (causing the formation of Landau polarons). We identify the regimes where either description is more valid. The key distinction between Anderson and Landau polarons is that for the latter the particle wave function is a strong function of the normal coordinates, and hence the "vertical" and "relaxed" wave functions are different. This has theoretical and experimental consequences for Landau polarons. Theoretically, it means that the Condon approximation is not valid, and so care needs to be taken when evaluating transition rates. Experimentally, it means that the self-localization of the particle as a consequence of its coupling to the normal coordinates may lead to experimental observables, e.g., ultrafast fluorescence depolarization. We apply these ideas to poly(p-phenylenevinylene). We show that the high frequency C-C bond oscillation only causes Landau polarons for a very narrow parameter regime; generally we expect disorder to dominate and Anderson polarons to be a more applicable description. Similarly, for the low frequency torsional fluctuations we show that Anderson polarons are expected for realistic parameters.

  15. Polaron transport in TiO{sub 2} thin films

    SciTech Connect

    Yildiz, Abdullah; Iacomi, Felicia; Mardare, Diana

    2010-10-15

    Undoped and Fe-doped TiO{sub 2} thin films were obtained by rf-sputtering technique onto heated glass substrates (250 deg. C) covered with indium tin oxide. The temperature dependence of the electrical conductivity was investigated in the temperature range 13-320 K, and it shows that the conduction mechanism in the studied samples is described by small-polaron hopping (SPH) at temperatures higher than half of the Debye temperature ({theta}{sub D}). It was found that the magnitude of the SPH coupling increases by Fe doping in TiO{sub 2} thin films. With decreasing temperature, the conduction behavior transited from SPH conduction to variable-range hopping (VRH) conduction. In the intermediate temperature domain (200 K

  16. Jahn-Teller assisted polaronic hole hopping as a charge transport mechanism in CuO nanograins

    NASA Astrophysics Data System (ADS)

    Younas, M.; Nadeem, M.; Idrees, M.; Akhtar, M. J.

    2012-04-01

    Impedance spectroscopy has been employed to investigate the dielectric and electric transport phenomena in sol-gel synthesized CuO nanograins. Semiconducting features of the grains and grain boundaries have been endorsed to the thermal activation of the localized charge carriers. On cooling below 303 K, a transition from Jahn-Teller polaron hopping mechanism to the Mott's variable range hopping mechanism has been observed owing to random potential fluctuations among localized sites. Activation energies for conduction and relaxation processes at grain boundaries provide strong signatures for the involvement of Jahn-Teller adiabatic small polarons as a charge transport mechanism in CuO nanograins.

  17. Spectrally resolved hyperfine interactions between polaron and nuclear spins in organic light emitting diodes: Magneto-electroluminescence studies

    SciTech Connect

    Crooker, S. A.; Kelley, M. R.; Martinez, N. J. D.; Nie, W.; Mohite, A.; Nayyar, I. H.; Tretiak, S.; Smith, D. L.; Liu, F.; Ruden, P. P.

    2014-10-13

    We use spectrally resolved magneto-electroluminescence (EL) measurements to study the energy dependence of hyperfine interactions between polaron and nuclear spins in organic light-emitting diodes. Using layered devices that generate bright exciplex emission, we show that the increase in EL emission intensity I due to small applied magnetic fields of order 100 mT is markedly larger at the high-energy blue end of the EL spectrum (ΔI/I ∼ 11%) than at the low-energy red end (∼4%). Concurrently, the widths of the magneto-EL curves increase monotonically from blue to red, revealing an increasing hyperfine coupling between polarons and nuclei and directly providing insight into the energy-dependent spatial extent and localization of polarons.

  18. Dual coupling effective band model for polarons

    NASA Astrophysics Data System (ADS)

    Marchand, Dominic J. J.; Stamp, Philip C. E.; Berciu, Mona

    2017-01-01

    Nondiagonal couplings to a bosonic bath completely change polaronic dynamics, from the usual diagonally coupled paradigm of smoothly varying properties. We study, using analytic and numerical methods, a model having both diagonal Holstein and nondiagonal Su-Schrieffer-Heeger (SSH) couplings. The critical coupling found previously in the pure SSH model, at which the k =0 effective mass diverges, now becomes a transition line in the coupling constant plane—the form of the line depends on the adiabaticity parameter. Detailed results are given for the quasiparticle and ground-state properties, over a wide range of couplings and adiabaticity ratios. The new paradigm involves a destabilization, at the transition line, of the simple Holstein polaron to one with a finite ground-state momentum, but with everywhere a continuously evolving band shape. No "self-trapping transition" exists in any of these models. The physics may be understood entirely in terms of competition between different hopping terms in a simple renormalized effective band theory. The possibility of further transitions is suggested by the results.

  19. Polaron Stabilization by Cooperative Lattice Distortion and Cation Rotations in Hybrid Perovskite Materials

    DOE PAGES

    Neukirch, Amanda J.; Nie, Wanyi; Blancon, Jean-Christophe; ...

    2016-05-25

    Solution-processed organometallic perovskites have rapidly developed into a top candidate for the active layer of photovoltaic devices. In spite of the remarkable progress associated with perovskite materials, many questions about the fundamental photophysical processes taking place in these devices, remain open. High on the list of unexplained phenomena are very modest mobilities despite low charge carrier effective masses. Moreover, experiments elucidate unique degradation of photocurrent affecting stable operation of perovskite solar cells. These puzzles suggest that, while ionic hybrid perovskite devices may have efficiencies on par with conventional Si and GaAs devices, they exhibit more complicated charge transport phenomena. Wemore » report the results from an in-depth computational study of small polaron formation, electronic structure, charge density, and reorganization energies using both periodic boundary conditions and isolated structures. Using the hybrid density functional theory, we found that volumetric strain in a CsPbI3 cluster creates a polaron with binding energy of around 300 and 900 meV for holes and electrons, respectively. In the MAPbI3 (MA = CH3NH3) cluster, both volumetric strain and MA reorientation effects lead to larger binding energies at around 600 and 1300 meV for holes and electrons, respectively. Such large reorganization energies suggest appearance of small polarons in organometallic perovskite materials. Furthermore, the fact that both volumetric lattice strain and MA molecular rotational degrees of freedom can cooperate to create and stabilize polarons indicates that in order to mitigate this problem, formamidinium (FA = HC(NH2)2) and cesium (Cs) based crystals and alloys, are potentially better materials for solar cell and other optoelectronic applications.« less

  20. Polaron Stabilization by Cooperative Lattice Distortion and Cation Rotations in Hybrid Perovskite Materials

    SciTech Connect

    Neukirch, Amanda J.; Nie, Wanyi; Blancon, Jean-Christophe; Appavoo, Kannatassen; Tsai, Hsinhan; Sfeir, Matthew Y.; Katan, Claudine; Pedesseau, Laurent; Even, Jacky; Crochet, Jared J.; Gupta, Gautam; Mohite, Aditya D.; Tretiak, Sergei

    2016-05-25

    Solution-processed organometallic perovskites have rapidly developed into a top candidate for the active layer of photovoltaic devices. In spite of the remarkable progress associated with perovskite materials, many questions about the fundamental photophysical processes taking place in these devices, remain open. High on the list of unexplained phenomena are very modest mobilities despite low charge carrier effective masses. Moreover, experiments elucidate unique degradation of photocurrent affecting stable operation of perovskite solar cells. These puzzles suggest that, while ionic hybrid perovskite devices may have efficiencies on par with conventional Si and GaAs devices, they exhibit more complicated charge transport phenomena. We report the results from an in-depth computational study of small polaron formation, electronic structure, charge density, and reorganization energies using both periodic boundary conditions and isolated structures. Using the hybrid density functional theory, we found that volumetric strain in a CsPbI3 cluster creates a polaron with binding energy of around 300 and 900 meV for holes and electrons, respectively. In the MAPbI3 (MA = CH3NH3) cluster, both volumetric strain and MA reorientation effects lead to larger binding energies at around 600 and 1300 meV for holes and electrons, respectively. Such large reorganization energies suggest appearance of small polarons in organometallic perovskite materials. Furthermore, the fact that both volumetric lattice strain and MA molecular rotational degrees of freedom can cooperate to create and stabilize polarons indicates that in order to mitigate this problem, formamidinium (FA = HC(NH2)2) and cesium (Cs) based crystals and alloys, are potentially better materials for solar cell and other optoelectronic applications.

  1. Method of time-ordered products in polaron theory

    SciTech Connect

    Bogolyupov, N.N.; Kireev, A.N.; Kurbatov, A.M.

    1986-10-01

    The method of time-ordered products is used to investigate the equilibrium thermodynamic properties of the Frolich model in polaron theory. The polaron free energy at finite temperatures is calculated on the basis of Bogolyubov's variational principle. The trial functional is chosen in the most general form corresponding to an arbitrary number of harmonic oscillators interacting with the electron. An upper bound for the polaron ground-state energy is obtained and studied in the case of weak coupling and low temperatures. It is shown that the accuracy of the bound increases with increasing number of oscillators.

  2. Semiclassical and quantum polarons in crystalline acetanilide

    NASA Astrophysics Data System (ADS)

    Hamm, P.; Tsironis, G. P.

    2007-08-01

    Crystalline acetanilide is a an organic solid with peptide bond structure similar to that of proteins. Two states appear in the amide I spectral region having drastically different properties: one is strongly temperature dependent and disappears at high temperatures while the other is stable at all temperatures. Experimental and theoretical work over the past twenty five years has assigned the former to a selftrapped state while the latter to an extended free exciton state. In this article we review the experimental and theoretical developments on acetanilide paying particular attention to issues that are still pending. Although the interpretation of the states is experimentally sound, we find that specific theoretical comprehension is still lacking. Among the issues that that appear not well understood is the effective dimensionality of the selftrapped polaron and free exciton states.

  3. Quantum Dynamics of Ultracold Bose Polarons

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    We analyze the dynamics of Bose polarons in the vicinity of a Feshbach resonance between the impurity and host atoms. We compute the radio-frequency absorption spectra for the case when the initial state of the impurity is noninteracting and the final state is strongly interacting with the host atoms. We compare results of different theoretical approaches including a single excitation expansion, a self-consistent T -matrix method, and a time-dependent coherent state approach. Our analysis reveals sharp spectral features arising from metastable states with several Bogoliubov excitations bound to the impurity atom. This surprising result of the interplay of many-body and few-body Efimov type bound state physics can only be obtained by going beyond the commonly used Fröhlich model and including quasiparticle scattering processes. Close to the resonance we find that strong fluctuations lead to a broad, incoherent absorption spectrum where no quasiparticle peak can be assigned.

  4. Mapping polaronic states and lithiation gradients in individual V2O5 nanowires

    NASA Astrophysics Data System (ADS)

    de Jesus, Luis R.; Horrocks, Gregory A.; Liang, Yufeng; Parija, Abhishek; Jaye, Cherno; Wangoh, Linda; Wang, Jian; Fischer, Daniel A.; Piper, Louis F. J.; Prendergast, David; Banerjee, Sarbajit

    2016-06-01

    The rapid insertion and extraction of Li ions from a cathode material is imperative for the functioning of a Li-ion battery. In many cathode materials such as LiCoO2, lithiation proceeds through solid-solution formation, whereas in other materials such as LiFePO4 lithiation/delithiation is accompanied by a phase transition between Li-rich and Li-poor phases. We demonstrate using scanning transmission X-ray microscopy (STXM) that in individual nanowires of layered V2O5, lithiation gradients observed on Li-ion intercalation arise from electron localization and local structural polarization. Electrons localized on the V2O5 framework couple to local structural distortions, giving rise to small polarons that serves as a bottleneck for further Li-ion insertion. The stabilization of this polaron impedes equilibration of charge density across the nanowire and gives rise to distinctive domains. The enhancement in charge/discharge rates for this material on nanostructuring can be attributed to circumventing challenges with charge transport from polaron formation.

  5. Polaronic contributions to oxidation and hole conductivity in acceptor-doped BaZrO3

    NASA Astrophysics Data System (ADS)

    Lindman, Anders; Erhart, Paul; Wahnström, Göran

    2016-08-01

    Acceptor-doped perovskite oxides like BaZrO3 are showing great potential as materials for renewable energy technologies where hydrogen acts an energy carrier, such as solid oxide fuel cells and hydrogen separation membranes. While ionic transport in these materials has been investigated intensively, the electronic counterpart has received much less attention and further exploration in this field is required. Here, we use density functional theory (DFT) to study hole polarons and their impact on hole conductivity in Y-doped BaZrO3. Three different approaches have been used to remedy the self-interaction error of local and semilocal exchange-correlation functionals: DFT +U , pSIC-DFT, and hybrid functionals. Self-trapped holes are found to be energetically favorable by about -0.1 eV and the presence of yttrium results in further stabilization. Polaron migration is predicted to occur through intraoctahedral transfer and polaron rotational processes, which are associated with adiabatic barriers of about 0.1 eV. However, the rather small energies associated with polaron formation and migration suggest that the hole becomes delocalized and bandlike at elevated temperatures. These results together with an endothermic oxidation reaction [A. Lindman, P. Erhart, and G. Wahnström, Phys. Rev. B 91, 245114 (2015), 10.1103/PhysRevB.91.245114] yield a picture that is consistent with experimental data for the hole conductivity. The results we present here provide new insight into hole transport in acceptor-doped BaZrO3 and similar materials, which will be of value in the future development of sustainable technologies.

  6. Polaronic interactions between oxygen vacancies in rutile Ti O2

    NASA Astrophysics Data System (ADS)

    Zhao, Liang; Magyari-Köpe, Blanka; Nishi, Yoshio

    2017-02-01

    Oxygen vacancy-vacancy interactions in rutile Ti O2 are studied in conjunction with polaron formation trends using density functional theory calculations. It is found that polarons strongly enhance the formation of oxygen vacancies in this material and also mediate the interactions between existing vacancies. At distances below 1 nm, two isolated and charge-neutral vacancies exhibit attractive interactions with an equilibrium distance of about 4 Å. The attractive forces between vacancies partly arise from the polaronic transfer of excess electrons to reduce the potential energy. These discoveries provide microscopic explanations to the vacancy clustering phenomena, as well as a practical approach to stabilize the polarons at arbitrary Ti atoms in Ti O2 .

  7. Tracking the coherent generation of polaron pairs in conjugated polymers

    NASA Astrophysics Data System (ADS)

    de Sio, Antonietta; Troiani, Filippo; Maiuri, Margherita; Réhault, Julien; Sommer, Ephraim; Lim, James; Huelga, Susana F.; Plenio, Martin B.; Rozzi, Carlo Andrea; Cerullo, Giulio; Molinari, Elisa; Lienau, Christoph

    2016-12-01

    The optical excitation of organic semiconductors not only generates charge-neutral electron-hole pairs (excitons), but also charge-separated polaron pairs with high yield. The microscopic mechanisms underlying this charge separation have been debated for many years. Here we use ultrafast two-dimensional electronic spectroscopy to study the dynamics of polaron pair formation in a prototypical polymer thin film on a sub-20-fs time scale. We observe multi-period peak oscillations persisting for up to about 1 ps as distinct signatures of vibronic quantum coherence at room temperature. The measured two-dimensional spectra show pronounced peak splittings revealing that the elementary optical excitations of this polymer are hybridized exciton-polaron-pairs, strongly coupled to a dominant underdamped vibrational mode. Coherent vibronic coupling induces ultrafast polaron pair formation, accelerates the charge separation dynamics and makes it insensitive to disorder. These findings open up new perspectives for tailoring light-to-current conversion in organic materials.

  8. Tunable Polaronic Conduction in Anatase TiO2

    NASA Astrophysics Data System (ADS)

    Moser, S.; Moreschini, L.; Jaćimović, J.; Barišić, O. S.; Berger, H.; Magrez, A.; Chang, Y. J.; Kim, K. S.; Bostwick, A.; Rotenberg, E.; Forró, L.; Grioni, M.

    2013-05-01

    Oxygen vacancies created in anatase TiO2 by UV photons (80-130 eV) provide an effective electron-doping mechanism and induce a hitherto unobserved dispersive metallic state. Angle resolved photoemission reveals that the quasiparticles are large polarons. These results indicate that anatase can be tuned from an insulator to a polaron gas to a weakly correlated metal as a function of doping and clarify the nature of conductivity in this material.

  9. Polaron formation and transport in olivine cathode materials

    NASA Astrophysics Data System (ADS)

    Johannes, Michelle; Hoang, Khang

    2011-03-01

    One of the critical factors limiting Li ion battery performance is electronic conduction through the cathode material. In the olivine structure type materials, such as LiFe PO4 , the parent materials are insulators with a gap of approximately 4 (or more) eV. The withdrawal of an electron results not in a band-type hole state, but rather a localized polaronic state. Transport then occurs via hopping of the polaron through the crystal. The measured electronic conduction in olivine materials depends on the transition metal cation type. In this study, we use density functional theory to compare formation of polarons in olivine materials with different transition metal cations: Mn, Fe, Co, and Ni. We show that the underlying electronic structure of the fully lithiated material (or fully delithiated material) essentially determines whether or not polaron formation is possible in localized d -states or whether the holes that result from adding or removing an electron reside in oxygen-derived states. We also investigate the facility of polaronic hopping by calculating the barrier between adjacent polaron sites in each of the four materials.

  10. Spin dynamics of polarons and polaron pairs in a random hyperfine field

    NASA Astrophysics Data System (ADS)

    Roundy, Robert C.

    Spin-dependent recombination of polaron pairs and spin relaxation of a single polaron are the most fundamental processes are responsible for the performance of organic spintronics-based devices such as light-emitting diodes and organic spin valves. In organic materials, with no spin-orbit coupling, both processes are due to random hyperfine fields created by protons neighboring the polaron sites. The essence of spin-dependent recombination is that in order to recombine the pair must be in the singlet state. Hyperfine fields acting on the electron and hole govern the spin-dynamics of localized pairs during the waiting time for recombination. We demonstrate that for certain domain of trapping configurations of hyperfine fields, crossover to the singlet state is quenched. This leads to the blocking of current. The phenomenon of organic magnetoresistance (OMAR) is described by counting the weights of trapping configurations as a function of magnetic field. This explains the universality of the lineshapes of the OMAR curves. In finite samples incomplete averaging over the hyperfine fields gives rise to mesoscopic fluctuations of the current response. We also demonstrate that under the condition of magnetic resonance, new trapping configurations emerge. This leads to nontrivial evolution of current through the sample with microwave power. When discussing spin-relaxation two questions can be asked: (a) How does the local spin polarization decay as a function of distance from the spin-polarized injector? (b) How does the injected spin decay as a function of time after spatial averaging? With regard to (a), we demonstrate that, while decaying exponentially on average, local spin-polarization exhibits giant fluctuations from point to point. Concerning (b), we find that for a spin-carrier which moves diffusively in low dimensions the decay is faster than a simple exponent. The underlying physics for both findings is that in describing spin evolution it is necessary to add up

  11. Use of site symmetry in supercell models of defective crystals: polarons in CeO2.

    PubMed

    Evarestov, R A; Gryaznov, D; Arrigoni, M; Kotomin, E A; Chesnokov, A; Maier, J

    2017-03-22

    In supercell calculations of defective crystals, it is common to place a point defect or vacancy in the atomic position with the highest possible point symmetry. Then, the initial atomic structure is often arbitrary distorted before its optimization, which searches for the total energy minimum. In this paper, we suggest an alternative approach to the application of supercell models and show that it is necessary to preliminarily analyze the site symmetry of the split Wyckoff positions of the perfect crystal supercell atoms (which will be substituted or removed in defective crystals) and then perform supercell calculations with point defects for different possible site symmetries, to find the energetically most favorable defect configuration, which does not necessarily correspond to the highest site symmetry. Using CeO2 as an example, it is demonstrated that this use of the site symmetry of the removed oxygen atoms in the supercells with vacancies allows us to obtain all the possible atomic and magnetic polaron configurations, and predict which vacancy positions correspond to the lowest formation energies associated with small polarons. We give a simple symmetry based explanation for the existence of controversies in the literature on the nature of the oxygen vacancies in CeO2. In particular, the experimentally observed small polaron formation could arise for oxygen vacancies with the lowest Cs site symmetry, which exist in 3 × 3 × 3 and larger supercells. The results of first principles calculations using a linear combination of atomic orbitals and hybrid exchange-correlation functionals are compared with those from previous studies, obtained using a widely used DFT+U approach.

  12. Tunable potentials and decoherence effect on polaron in nanostructures

    NASA Astrophysics Data System (ADS)

    Fotue, A. J.; Fobasso, M. F. C.; Kenfack, S. C.; Tiotsop, M.; Djomou, J.-R. D.; Ekosso, C. M.; Nguimeya, G.-P.; Danga, J. E.; Keumo Tsiaze, R. M.; Fai, L. C.

    2016-06-01

    We studied the effect of the tunable potential and decoherence of polaron in nanostructures. We have arbitrarily chosen eight potentials: the elliptical potential, square potential, triangular potential, the quadratic potential, the delta potential, the Gaussian potential, the pseudo-harmonic potential and Coulombic potential. In order to evaluate different polaronic parameters, we used the unitary transformation of LLP and the Pekar-type variational method (PTVM). This system can be considered as a two-level quantum system. We demonstrate in this work that the elliptical potential best confines the polaron and provides interesting information transfer, whereas, Gaussian, pseudo-harmonic and Coulombic potentials transfer information slowly. It is also found in this work that the Coulomb potential seems to be the most chaotic compared to the seven other used. This work confirms that the choice of a potential is crucial for the study of decoherence in nanostructures.

  13. Two-dimensional polaron in a magnetic field

    NASA Astrophysics Data System (ADS)

    Xiaoguang, Wu; Peeters, F. M.; Devreese, J. T.

    1985-12-01

    The ground-state energy of a Fröhlich optical polaron confined to two dimensions, placed in a perpendicular magnetic field is calculated within the Feynman path-integral approach. The Feynman-model mass, the magnetization and the susceptibility are calculated as a function of the magnetic field strength for different values of the electron-phonon coupling. We find that within the generalized Feynman approximation the polaron exhibits a discontinuous transition from a dressed state to a stripped state if the electron-phonon constant α is larger than 1.60. For α<1.60, the transition occurs continuously with increasing magnetic field.

  14. Numerical simulation of photoexcited polaron states in water

    SciTech Connect

    Zemlyanaya, E. V. Volokhova, A. V.; Amirkhanov, I. V.; Puzynin, I. V.; Puzynina, T. P.; Rikhvitskiy, V. S.; Lakhno, V. D.; Atanasova, P. Kh.

    2015-10-28

    We consider the dynamic polaron model of the hydrated electron state on the basis of a system of three nonlinear partial differential equations with appropriate initial and boundary conditions. A parallel numerical algorithm for the numerical solution of this system has been developed. Its effectiveness has been tested on a few multi-processor systems. A numerical simulation of the polaron states formation in water under the action of the ultraviolet range laser irradiation has been performed. The numerical results are shown to be in a reasonable agreement with experimental data and theoretical predictions.

  15. Superexchange coupling and electron transfer in globular proteins via polaron excitations.

    PubMed

    Chuev, G N; Lakhno, V D; Ustitnin, M N

    2000-06-01

    The polaron approach is used to treat long-range electron transfersbetween globular proteins. A rate expression for the polaron transfer model is given along with a description of appropriate conditions forits use. Assuming that electrons transfer via a superexchange couplingdue to a polaron excitation, we have estimated the distance dependenceof the rate constant for the self-exchange reactions between globularproteins in solutions. The distance dependence of the polaron coupling andsolvent reorganization energy are provided as a basis forunderstanding and interpreting a long-range electron transfer experiment.The difficulties and problems of the polaron treatment of long-rangeelectron transfers are discussed, and suggestions for new experimentsare made.

  16. Polaronic transport and current blockades in epitaxial silicide nanowires and nanowire arrays.

    PubMed

    Iancu, Violeta; Zhang, X-G; Kim, Tae-Hwan; Menard, Laurent D; Kent, P R C; Woodson, Michael E; Ramsey, J Michael; Li, An-Ping; Weitering, Hanno H

    2013-08-14

    Crystalline micrometer-long YSi2 nanowires with cross sections as small as 1 × 0.5 nm(2) can be grown on the Si(001) surface. Their extreme aspect ratios make electron conduction within these nanowires almost ideally one-dimensional, while their compatibility with the silicon platform suggests application as metallic interconnect in Si-based nanoelectronic devices. Here we combine bottom-up epitaxial wire synthesis in ultrahigh vacuum with top-down miniaturization of the electrical measurement probes to elucidate the electronic conduction mechanism of both individual wires and arrays of nanowires. Temperature-dependent transport through individual nanowires is indicative of thermally assisted tunneling of small polarons between atomic-scale defect centers. In-depth analysis of complex wire networks emphasize significant electronic crosstalk between the nanowires due to the long-range Coulomb fields associated with polaronic charge fluctuations. This work establishes a semiquantitative correlation between the density and distributions of atomic-scale defects and resulting current-voltage characteristics of nanoscale network devices.

  17. Tracking the coherent generation of polaron pairs in conjugated polymers

    PubMed Central

    De Sio, Antonietta; Troiani, Filippo; Maiuri, Margherita; Réhault, Julien; Sommer, Ephraim; Lim, James; Huelga, Susana F.; Plenio, Martin B.; Rozzi, Carlo Andrea; Cerullo, Giulio; Molinari, Elisa; Lienau, Christoph

    2016-01-01

    The optical excitation of organic semiconductors not only generates charge-neutral electron-hole pairs (excitons), but also charge-separated polaron pairs with high yield. The microscopic mechanisms underlying this charge separation have been debated for many years. Here we use ultrafast two-dimensional electronic spectroscopy to study the dynamics of polaron pair formation in a prototypical polymer thin film on a sub-20-fs time scale. We observe multi-period peak oscillations persisting for up to about 1 ps as distinct signatures of vibronic quantum coherence at room temperature. The measured two-dimensional spectra show pronounced peak splittings revealing that the elementary optical excitations of this polymer are hybridized exciton-polaron-pairs, strongly coupled to a dominant underdamped vibrational mode. Coherent vibronic coupling induces ultrafast polaron pair formation, accelerates the charge separation dynamics and makes it insensitive to disorder. These findings open up new perspectives for tailoring light-to-current conversion in organic materials. PMID:27929115

  18. The strong-coupling polaron in reduced dimensionality

    NASA Astrophysics Data System (ADS)

    Sahoo, Satyabrata

    1998-03-01

    Based on the LLP-H approach, a detailed study of the electron confinement in a polar semiconductor heterostructure has been made to derive analytically the ground state energy and the effective mass of the Fröhlich polaron in quasi-two-dimensional (Q2D) and quasi-one-dimensional (Q1D) systems.

  19. Polaron mass of charge carriers in semiconductor quantum wells

    SciTech Connect

    Maslov, A. Yu. Proshina, O. V.

    2015-10-15

    A theory of the interaction of charge carriers with optical phonons in a quantum well is developed with consideration for interface optical phonons. The dependence of the polaron effective mass on the quantum-well dimensions and dielectric characteristics of barriers is analyzed in detail. It is shown that, in narrow quantum wells, a quasi-two-dimensional polaron can be formed. In this case, however, the interaction parameters are defined by the charge-carrier effective mass in the quantum well and by the frequencies of interface optical phonons. If barriers are made of a nonpolar material, the polaron effective mass depends on the quantum-well width. As the quantum-well width is increased, a new mechanism of enhancement of the electron–phonon interaction develops. The mechanism is implemented, if the optical phonon energy is equal to the energy of one of the electronic transitions. This condition yields an unsteady dependence of the polaron effective mass on the quantum-well width.

  20. A Nonempirical Comparison of the Polaron and Mowat Sensor.

    ERIC Educational Resources Information Center

    Moore, Karyl A.

    1995-01-01

    This article compares two electronic aids that send out an elliptical cone of ultrasonic sound that bounces back as a usable information signal for individuals with blindness. The Polaron is better for people who are predominantly route travelers or with limited hand use. The Mowat Sensor is better for travelers in a variety of environments. (JDD)

  1. Tracking the coherent generation of polaron pairs in conjugated polymers.

    PubMed

    De Sio, Antonietta; Troiani, Filippo; Maiuri, Margherita; Réhault, Julien; Sommer, Ephraim; Lim, James; Huelga, Susana F; Plenio, Martin B; Rozzi, Carlo Andrea; Cerullo, Giulio; Molinari, Elisa; Lienau, Christoph

    2016-12-08

    The optical excitation of organic semiconductors not only generates charge-neutral electron-hole pairs (excitons), but also charge-separated polaron pairs with high yield. The microscopic mechanisms underlying this charge separation have been debated for many years. Here we use ultrafast two-dimensional electronic spectroscopy to study the dynamics of polaron pair formation in a prototypical polymer thin film on a sub-20-fs time scale. We observe multi-period peak oscillations persisting for up to about 1 ps as distinct signatures of vibronic quantum coherence at room temperature. The measured two-dimensional spectra show pronounced peak splittings revealing that the elementary optical excitations of this polymer are hybridized exciton-polaron-pairs, strongly coupled to a dominant underdamped vibrational mode. Coherent vibronic coupling induces ultrafast polaron pair formation, accelerates the charge separation dynamics and makes it insensitive to disorder. These findings open up new perspectives for tailoring light-to-current conversion in organic materials.

  2. The structure of nanoscale polaron correlations in the layered manganites

    NASA Astrophysics Data System (ADS)

    Campbell, Branton

    2002-03-01

    Recent x-ray and neutron scattering experiments have uncovered nanoscale polaron correlations that play an essential role in the colossal magnetoresistive (CMR) behavior of the perovskite manganites. Short-range polaronic order decreases the charge-carrier mobility of the high-temperature paramagnetic state, and subsequently becomes unstable at the ferromagnetic transition, contributing to a pronounced resistivity decrease at T_C. In the bilayered perovskite system La_2-2xSr_1+2xMn_2O7 (0.3 < x < 0.5), weak x-ray diffuse scattering maxima reveal a one-dimensional incommensurate structural modulation with wavevector q = (0.3, 0, ± 1) and a correlation length of 10 to 30 Angstroms. A crystallographic analysis of the diffuse satellite intensities yields a longitudinal Jahn-Teller stretch mode suggestive of charge-density-wave fluctuations. Within the correlated regions, polaronic eg electrons form a striped pattern of occupied d(3x^2-r^2) orbitals. Dynamic polaron correlations of the zig-zag orbital type are also observed above TC and exhibit distinctly glassy behavior. These structures provide unique insights into the nature of strongly correlated polaronic systems. Collaborators: R. Osborn, D.N. Argyriou, S. Rosenkranz, L. Vasiliu-Doloc, J.F. Mitchell, S.K. Sinha, J.W. Lynn, C.D. Ling, Z. Islam, U. Ruett, and A. Berger. This work was supported by the U.S. DOE Office of Science contract No. W-31-109-ENG-38.

  3. Ab initio study of the Zener polaron spectrum of half-doped manganites: Comparison of several model Hamiltonians

    NASA Astrophysics Data System (ADS)

    Bastardis, Roland; Guihéry, Nathalie; de Graaf, Coen

    2006-07-01

    The low-energy spectrum of the Zener polaron in half-doped manganite is studied by means of correlated ab initio calculations. It is shown that the electronic structure of the low-energy states results from a subtle interplay between double-exchange configurations and O 2pσ to Mn 3d charge-transfer configurations that obey a Heisenberg logic. The comparison of the calculated spectrum to those predicted by the Zener Hamiltonian reveals that this simple description does not correctly reproduces the Zener polaron physics. A better reproduction of the calculated spectrum is obtained with either a Heisenberg model that considers a purely magnetic oxygen or the Girerd-Papaefthymiou double-exchange model. An additional significant improvement is obtained when different antiferromagnetic contributions are combined with the double-exchange model, showing that the Zener polaron spectrum is actually ruled by a refined double-exchange mechanism where non-Hund atomic states play a non-negligible role. Finally, eight states of a different nature have been found to be intercalated in the double-exchange spectrum. These states exhibit an O to Mn charge transfer, implying a second O 2p orbital of approximate π character instead of the usual σ symmetry. A small mixing of the two families of states occurs, accounting for the final ordering of the states.

  4. Polarons and Mobile Impurities Near a Quantum Phase Transition

    NASA Astrophysics Data System (ADS)

    Shadkhoo, Shahriar

    This dissertation aims at improving the current understanding of the physics of mobile impurities in highly correlated liquid-like phases of matter. Impurity problems pose challenging and intricate questions in different realms of many-body physics. For instance, the problem of ''solvation'' of charged solutes in polar solvents, has been the subject of longstanding debates among chemical physicists. The significant role of quantum fluctuations of the solvent, as well as the break down of linear response theory, render the ordinary treatments intractable. Inspired by this complicated problem, we first attempt to understand the role of non-specific quantum fluctuations in the solvation process. To this end, we calculate the dynamic structure factor of a model polar liquid, using the classical Molecular Dynamics (MD) simulations. We verify the failure of linear response approximation in the vicinity of a hydrated electron, by comparing the outcomes of MD simulations with the predictions of linear response theory. This nonlinear behavior is associated with the pronounced peaks of the structure factor, which reflect the strong fluctuations of the local modes. A cavity picture is constructed based on heuristic arguments, which suggests that the electron, along with the surrounding polarization cloud, behave like a frozen sphere, for which the linear response theory is broken inside and valid outside. The inverse radius of the spherical region serves as a UV momentum cutoff for the linear response approximation to be applicable. The problem of mobile impurities in polar liquids can be also addressed in the framework of the ''polaron'' problem. Polaron is a quasiparticle that typically acquires an extended state at weak couplings, and crossovers to a self-trapped state at strong couplings. Using the analytical fits to the numerically obtained charge-charge structure factor, a phenomenological approach is proposed within the Leggett's influence functional formalism, which

  5. A polaron model for electron transfer in globular proteins.

    PubMed

    Chuev, G N; Lakhno, V D

    1993-07-07

    Polaron models have been considered for the electron states in protein globules existing in a solvent. These models account for two fundamental effects, viz, polarization interaction of an electron with the conformational vibrations and the heterogeneity of the medium. Equations have been derived to determine the electron state in a protein globule. The parameters of this state show that it is an extended state with an energy of 2 eV. The electron transfer rate for cyt C self-exchange reaction has been calculated in the polaron model. Reorganization energy, tunneling matrix element and the rate constant have also been estimated. The results are compared with experimental data. The influence of model parameters on the significance of the data obtained has been studied. The potentialities of the model are discussed.

  6. Polaron theory of electrons solvated in molten salts

    NASA Astrophysics Data System (ADS)

    Malescio, G.; Parrinello, M.

    1987-01-01

    A suitably modified version of the polaron theory of Chandler et al. [J. Chem. Phys. 81, 1975 (1984)] is applied to the study of the solvation of electrons in molten salts. The results obtained compare favorably with recent numerical simulations and confirm the picture of the formation in the melt of an F-center analog. A novel expression for the explicit evaluation of the electron kinetic energy is given.

  7. Rotational polarons and transport in short molecular devices

    NASA Astrophysics Data System (ADS)

    Ulloa, Sergio E.; Sierra-Ortega, J.; Zhang, Wei

    2003-03-01

    In many organic materials and/or complex molecular structures, there are twist/rotational modes that appear at low temperature and are easily excitable. The interaction between these rotational phonon modes and electrons generates a new quasiparticle, the rotational polaron. We study here a two-site rotational Holstein polaron. Our model gives nontrivial polaron physics due to anharmonic oscillations and nonlinear electron-phonon interactions. The results are relevant for molecular electronic devices composed of two molecular units with excitable intra-molecular rotations. Analytical and numerical calculations allow a full quantum mechanical description. We study all frequency and coupling regimes, paying special attention to the transition/crossover between different coupling ratios. We find that under resonant conditions between the electron level splitting and the phonon frequency, complex level crossings and anticrossings occur, indicating mixing of excited states with different characters, which depend on underlying symmetries of the system. The mixing is accompanied by charge and phonon amplitude transfer which yields observable signatures in electronic transport through this system. Supported by NSF-NIRT, US-DOE, and OU-CMSS.

  8. Novel, discontinuous polaron transition in a two-band model

    NASA Astrophysics Data System (ADS)

    Moeller, Mirko M.; Sawatzky, George A.; Berciu, Mona

    The coupling of charge carriers (electrons or holes) to phonons leads to the formation of a polaron, a coherent quasi-particle consisting of the charge carrier and the cloud of phonons surrounding it and moving coherently with it. Here we present exact diagonalization and momentum average approximation results for the single polaron properties of a two-band model with phonon modulated hopping, inspired by the perovskite BaBiO3. For large coupling we find that the ground state momentum changes discontinuously from k = π to k = 0 . Such sharp transitions of the polaron's ground state properties cannot occur in the well-studied models of the Holstein or Fröhlich type in which the carrier-phonon coupling modulates the on-site energies. However, they can occur in models where the carrier-phonon coupling modulates the hopping integrals such as the SSH model for which a similar yet smooth transition of the ground state momentum was recently shown to exist. We compare our findings to the SSH model and point out qualitative differences which we believe to be due to the two band nature of our model versus the single band SSH model. This work was supported by NSERC, QMI and the UBC 4YF.

  9. Effect of interchain coupling on the excited polaron in conjugated polymers

    NASA Astrophysics Data System (ADS)

    Li, Xiao-xue; Chen, Gang

    2017-02-01

    Based on the one-dimensional extended Su-Schrieffer-Heeger model, we theoretically investigate the effect of interchain coupling on the formation and polarization of the single-excited state of polaron in conjugated polymers. It is found that there exists a turnover value of the coupling strength, over which the excited polaron could not be formed in either of the two coupled chains. Instead, a polaron-like particle is localized at the center of each chain. In addition, we also find that the reverse polarization of the excited polaron could be enhanced for some cases in polymer when the interchain coupling becomes strong until it exceeds the critical value.

  10. Polaron conductivity mechanism in potassium acid phthalate crystal: AC-conductivity investigation

    NASA Astrophysics Data System (ADS)

    Filipič, Cene; Levstik, Iva; Levstik, Adrijan; Hadži, Dušan

    2016-08-01

    The complex dielectric constant, \\varepsilon *(ν ,T), of potassium acid phthalate monocrystal (KAP) was investigated over the broad frequency and temperature range. While the imaginary part of dielectric constant ε‧‧(ν) increases rapidly with increasing temperature in the studied temperature range, the real part of dielectric constant ε‧(ν) increases only at high temperatures; there is almost no change of ε‧(ν) below 200 K. Both values of ε‧ and ε‧‧ are frequency dependent; the values increase with decreasing frequencies. At temperatures below 450 K the ac electrical conductivity and dielectric constant follow simultaneously the universal dielectric response (UDR). The analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for small polarons revealed that this mechanism governs the charge transport in KAP crystal in the studied temperature range.

  11. Light-induced charge transfer and kinetics of the NIR absorption of Nb4+ polarons in SBN crystals at low temperatures

    NASA Astrophysics Data System (ADS)

    Gao, M.; Pankrath, R.; Kapphan, S.; Vikhnin, V.

    Sr1-xBaxNb2O6 (SBN) crystals with open tungsten-bronze structure show enhanced photorefractive properties with doping of impurities such as Ce, Cr, Rh etc. Under illumination with Kr+ laser (647 nm) or Ar+ laser light (488 nm or 514 nm) or UV light at low temperature, pure and doped SBN crystals show a broad polaron absorption band around 0.7 eV (6000 cm-1). The first step of a theoretical model involves the excitation of electrons by illumination from Cr3+/Ce3+ to higher excited states or the conduction band. The excited electrons can then be trapped by Nb5+ to form Nb4+ polarons and further on can directly tunnel through or hop over the potential barrier (with a value Δ 0.15+/-0.02 eV) to recombine with Cr4+/Ce4+ ions. The experimental intensity dependence, temperature dependence, and decay process of the light-induced Nb4+ polarons can be fitted with the help of this model. Small, but systematic, differences lead to the additional assumption of different recombination rates of polarons at distinct distances from the Cr4+/Ce4+ recombination centers and therefore many parallel decay channels are active where each decay channel obeys a monoexponential decay law. A stretched exponential decay function is employed to fit in this case the decay process of the Nb4+ polarons at different temperatures and under illumination with different intensities. Due to the high dielectric constant value (ɛ33 and ɛ11 have values in the 102-103 range) at low temperature, the long range Coulomb attraction (to Ce3+Sr/Ba) or repulsion (from Cr3+Nb) of the electronic polaron is suppressed. The leading role in the attraction and the following trapping of the electronic Jahn-Teller polaron, both on Cr3+Nb and Ce3+Sr/Ba centers, is played by the indirect dipole-dipole interaction via the soft TO-mode.

  12. The Influence of Surface Phonons on Polaron States in Quantum Dots

    NASA Astrophysics Data System (ADS)

    Maslov, A. Yu.; Proshina, O. V.; Rusina, A. N.

    2007-04-01

    The influence of the surface phonons on the polaron effect in a quantum dot is investigated. We consider the polar quantum dot embedded into the polar matrix. The polaron energy shift for the electron and hole ground states is calculated. It is shown that the contribution of the surface phonons may exceed the bulk phonon contribution.

  13. A New Insight into the Polaron-Li Complex Diffusion in Cathode Material LiFe1-yMnyPO4 for Li Ion Batteries

    NASA Astrophysics Data System (ADS)

    Dinh, Van An; Nara, Jun; Ohno, Takahisa

    2012-04-01

    Based on the Heyd-Scuseria-Ernzerhof hybrid density functionals study, we proposed a new insight into the diffusion of polaron-Li vacancy complexes in LiFe1-yMnyPO4 (y=0,1/2,1). It is found that the polaron migrates along a crossing or a parallel path relative to the Li moving direction. In LiFePO4, the complex diffusion along the zigzag pathway is favorable and has a barrier of 600 meV, while the diffusion along the parallel pathway with a barrier of 623 meV is favorable in LiMnPO4. For LiFe1/2Mn1/2PO4, since the polaron is formed within a single Fe layer, the diffusion proceeds along the parallel pathway with a barrier of 635 meV.

  14. Superexchange coupling and electron transfer in globular proteins via polaron excitations.

    PubMed

    Chuev, G N; Lakhno, V D; Ustitnin, M N

    1999-06-01

    The polaron approach is used to treat long-range electron transfers between globular proteins. A rate expression for the polaron transfer model is given along with a description of appropriate conditions for its use. Assuming that electrons transfer via a superexchange coupling due to a polaron excitation, we have estimated the distance dependence of the rate constant for the self-exchange reactions between globular proteins in solutions. The distance dependence of the polaron coupling and solvent reorganization energy are provided as a basis for understanding and interpreting a long-range electron transfer experiment. The difficulties and problems of the polaron treatment of long-range electron transfers are discussed, and suggestions for new experiments are made.

  15. Bilayer manganites: polarons in the midst of a metallic breakdown

    NASA Astrophysics Data System (ADS)

    Golden, Mark; Massee, Freek; de Jong, Sanne; Huang, Yingkai; Boothroyd, Andrew; Prabhakaran, D.; Follath, Rolf; Varykhalov, Andrei; Patthey, Luc; Shi, Ming; Goedkoop, Jeroen

    2011-03-01

    The exact nature of the low temperature electronic phase of the manganite materials family, and hence the origin of their colossal magnetoresistive (CMR) transition is still a flagship issue in emergent correlated matter research. By combining new photoemission and tunneling data, we show that in the bilayer (N = 2) manganite La 2-2x Sr 1+2x Mn 2 O7 the lattice/spin/orbital polaronic degrees of freedom win out, all across the CMR region of the phase diagram. This means that the generic ground state is that of a system in which strong interactions result in vanishing coherent quasi--particle spectral weight at the Fermi level for all locations in k --space. The incoherence of the charge carriers offers a unifying explanation for the anomalous charge-carrier dynamics seen in transport, optics and electron spectroscopic data. The stacking number N is the key factor for true metallic behavior, as an intergrowth-driven breakdown of the polaronic domination to give a robust metal possessing a traditional Fermi surface is seen in the bilayer system.

  16. Polaron assisted charge transfer in model biological systems

    NASA Astrophysics Data System (ADS)

    Li, Guangqi; Movaghar, Bijan

    2016-11-01

    We use a tight binding Hamiltonian to simulate the electron transfer from an initial charge-separating exciton to a final target state through a two-arm transfer model. The structure is copied from the model frequently used to describe electron harvesting in photosynthesis (photosystems I). We use this network to provide proof of principle for dynamics, in quantum system/bath networks, especially those involving interference pathways, and use these results to make predictions on artificially realizable systems. Each site is coupled to the phonon bath via several electron-phonon couplings. The assumed large energy gaps and weak tunneling integrals linking the last 3 sites give rise to"Stark Wannier like" quantum localization; electron transfer to the target cluster becomes impossible without bath coupling. As a result of the electron-phonon coupling, local electronic energies relax when the site is occupied, and transient polaronic states are formed as photo-generated electrons traverse the system. For a symmetric constructively interfering two pathway network, the population is shared equally between two sets of equivalent sites and therefore the polaron energy shift is smaller. The smaller energy shift however makes the tunnel transfer to the last site slower or blocks it altogether. Slight disorder (or thermal noise) can break the symmetry, permitting essentially a "one path", and correspondingly more efficient transfer.

  17. Influence of lithium vacancies on the polaronic transport in olivine phosphate structure

    SciTech Connect

    Murugavel, Sevi Sharma, Monika; Shahid, Raza

    2016-01-28

    Intercalation and deintercalation of lithium ions in cathode materials are of principal to the operation of current rechargeable lithium ion batteries. The performance of lithium ion batteries highly relies on the active cathode material which includes cell potential, power/energy density, capacity, etc. An important issue in this class of material is to resolve the factors governing the electron and ion transport in olivine phosphate structure. In this class of material, there is still an open debate on the mechanism of charge transport including both polarons and lithium ions. On the one hand, this is due to the large disparity between the experimental results and the theoretical model predictions. On the other hand, this is also due to the lack of precise experimental measurement without any parasitic phases in a given cathode material. Here, we present the polaronic conduction in lithiated triphylite LiFePO{sub 4} (LFP) and delithiated heterosite FePO{sub 4} (FP) by means of broadband ac impedance spectroscopy over wide range temperatures and frequency. It is found that the LFP phase possess two orders of higher polaronic conductivity than FP phase despite having similar mobility of polarons in both phases. We show that the differences in the polaronic conductivity of two phases are due to the significant differences in concentration of polarons. It is found that the formation energy of polarons in individual phases is mainly determined by the corresponding defect state associated with it. The temperature dependent dc conductivity has been analyzed within the framework of Mott model of polaronic conduction and explored the origin of polaronic conduction mechanism in this class of material.

  18. Magnetic-polaron-induced colossal magnetocapacitance in CdCr2S4

    NASA Astrophysics Data System (ADS)

    Xie, Y. M.; Yang, Z. R.; Zhang, Z. T.; Yin, L. H.; Chen, X. L.; Song, W. H.; Sun, Y. P.; Zhou, S. Q.; Tong, W.; Zhang, Y. H.

    2013-10-01

    The origin of colossal magnetoresistance and colossal magnetocapacitance in a CdCr2S4 system was investigated. Thermoelectric-power and electronic spin resonance spectra reveal that the magnetic polaron is responsible for the colossal magnetoresistance in the n-type sample. The existence of magnetic polarons in the paramagnetic insulting matrix forms an intrinsic Maxwell-Wagner system, leading to the appearance of colossal magnetocapacitance. Being consistent with the evolution of magnetic polarons upon cooling, the Maxwell-Wagner system is valid around insulator-metal transition, where the resistance derived from impedance spectroscopy matches perfectly with DC resistance.

  19. Bose polaron problem: Effect of mass imbalance on binding energy

    NASA Astrophysics Data System (ADS)

    Ardila, L. A. Peña; Giorgini, S.

    2016-12-01

    By means of quantum Monte Carlo methods we calculate the binding energy of an impurity immersed in a Bose-Einstein condensate at T =0 . The focus is on the attractive branch of the Bose polaron and on the role played by the mass imbalance between the impurity and the surrounding particles. For an impurity resonantly coupled to the bath, we investigate the dependence of the binding energy on the mass ratio and on the interaction strength within the medium. In particular, we determine the equation of state in the case of a static (infinite mass) impurity, where three-body correlations are irrelevant and the result is expected to be a universal function of the gas parameter. For the mass ratio corresponding to 40K impurities in a gas of 87Rb atoms, we provide an explicit comparison with the experimental findings of a recent study carried out at JILA.

  20. Polaron-electron assisted giant dielectric dispersion in SrZrO3 high-k dielectric

    NASA Astrophysics Data System (ADS)

    Borkar, Hitesh; Barvat, Arun; Pal, Prabir; Shukla, A. K.; Pulikkotil, J. J.; Kumar, Ashok

    2016-06-01

    The SrZrO3 is a well known high-k dielectric constant (˜22) and high optical bandgap (˜5.8 eV) material and one of the potential candidates for future generation nanoelectronic logic elements (8 nm node technology) beyond silicon. Its dielectric behavior is fairly robust and frequency independent till 470 K; however, it suffers a strong small-polaron based electronic phase transition (Te) linking 650 to 750 K. The impedance spectroscopy measurements revealed the presence of conducting grains and grain boundaries at elevated temperature which provide energetic mobile charge carriers with activation energy in the range of 0.7 to 1.2 eV supporting the oxygen ions and proton conduction. X-ray photoemission spectroscopy measurements suggest the presence of weak non-stoichiometric O2- anions and hydroxyl species bound to different sites at the surface and bulk. These thermally activated charge carriers at elevated temperature significantly contribute to the polaronic based dielectric anomaly and conductivity. Our dielectric anomaly supports pseudo phase transition due to high degree of change in ZrO6 octahedral angle in the temperature range of 650-750 K, where electron density and phonon vibration affect the dielectric and conductivity properties.

  1. Hybrid functional studies of defects and hole polarons in oxides

    NASA Astrophysics Data System (ADS)

    Varley, Joel

    Transparent conducting oxides (TCOs) are ubiquitous, appearing in windows, flat-panel displays, solar cells, solid-state lighting, and transistors that all exploit TCOs' combination of high electrical conductivity and optical transparency. Thanks to this large and growing list of applications, there has been a surge of interest in the science of these materials, focusing on the fundamental properties and doping opportunities in traditional TCOs as well as the exploration of promising new candidate materials. Hybrid density functional theory has proven instrumental in elucidating the physics of TCOs. One example is the study of dopants and defects that determine the conductivity. Accurate formation energies and charge-state transition levels can now be obtained thanks to the accurate electronic structure provided by a hybrid functional. This allows us to address the origins of unintentional conductivity: for SnO2, In2O3, and Ga2O3, we demonstrate that this is not due to native defects such as oxygen vacancies, but must be attributed to unintentional incorporation of impurities. We can also provide guidelines for achieving higher doping levels, suggesting several impurities as candidate donors with high solubility. Limitations on doping due to the formation or incorporation of compensating centers are addressed as well. Hybrid functional calculations also overcome the shortcomings associated with traditional local or semi-local functionals, which do not properly describe charge localization. Hybrid functionals accurately describe polaron formation, i.e., the self-trapping of holes when p - type doping of the oxide materials is attempted. Consequences of polaron formation for optical characterization of the material will be discussed. This work was performed in collaboration with Anderson Janotti and Chris G. Van de Walle, and was in part under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  2. Dynamics of light-induced NIR-absorption of Nb4 polarons in SBN

    NASA Astrophysics Data System (ADS)

    Gao, Ming; Vikhnin, V.; Kapphan, S.

    The dynamics of light-induced (Kr+-, Ar+-laser) electronic polarons (Nb4+ centers with broad absorption band around 0.8 eV) and light-induced centers of other types were investigated in SrxBa1-xNb2O6: Cr (SBN:Cr) and in SBN: Ce using FTIR absorption measurements at low temperature. A theoretical model involving Cr3+/Cr4+, Ce3+/Ce4+, Nb4+ electronic polarons and trapping X-centers is proposed. The trapping of polarons at Cr4+/Ce4+ centers with subsequent recharging is shown to play an important role in the polaron dynamics. The predictions of the model are in very good agreement with the experimental results.

  3. Formation and local symmetry of the Holstein polaron in the t-J model

    NASA Astrophysics Data System (ADS)

    Ma, Han; Lee, T. K.; Chen, Yan

    2013-04-01

    The formation and local symmetry of a spin-lattice polaron has been investigated semiclassically in planar Holstein t-J-like models within the exact diagonalization method. Due to the interplay of strong correlations and electron-lattice interaction, the doped hole may either move freely or lead to the localized spin-lattice distortion and form a Holstein polaron. The formation of a polaron breaks the translational symmetry by suppression of antiferromagnetic correlations and inducement of ferromagnetic correlations locally. Moreover, the breaking of local rotational symmetry around the polaron has been shown. The ground state is generically a parity singlet and the first excited state may be a parity doublet. Further consequences of the density of states spectra for comparison with scanning tunneling microscopy experiments are discussed.

  4. [Long-range electron transfer in globular proteins by polaron excitation].

    PubMed

    Lakhno, V L; Chuev, G N

    1997-01-01

    Considering polaron model, we have calculated an electron state localized in the protein heme. Using these calculations: the electron density and electron energy, we estimated the self-exchange rate constant for cyt c (horse heart), its reorganization energy, matrix element, and dependence of this rate on the distance between hemes. The results are compared with the experimental data and other theoretical estimations. We discuss the role of polaron excitations in the long-range electron transfer in globular proteins.

  5. Diagrammatic Monte Carlo study of mass-imbalanced Fermi-polaron system

    NASA Astrophysics Data System (ADS)

    Pollet, Lode

    After a brief introduction and review of diagrammatic Monte Carlo, I present our results for the three-dimensional Fermi-polaron system with mass-imbalance, where an impurity interacts resonantly with a noninteracting Fermi sea whose atoms have a different mass. This method allows to go beyond frequently used variational techniques by stochastically summing all relevant impurity Feynman diagrams up to a maximum expansion order limited by the sign problem. The polaron energy and quasiparticle residue can be accurately determined over a broad range of impurity masses. Furthermore, the spectral function of an imbalanced polaron demonstrates the stability of the quasiparticle and allows to locate in addition also the repulsive polaron as an excited state. The quantitative exactness of two-particle-hole wave-functions is investigated, resulting in a relative lowering of polaronic energies in the mass-imbalance phase diagram. Tan's contact coefficient for the mass-balanced polaron system is found in good agreement with variational methods. Mass-imbalanced systems can be studied experimentally by ultracold atom mixtures like 6Li-40K. I will discuss some open questions and links with recent experiments.

  6. Diagrammatic Monte Carlo study of a mass-imbalanced Fermi-polaron system

    NASA Astrophysics Data System (ADS)

    Kroiss, Peter; Pollet, Lode

    2015-04-01

    We apply the diagrammatic Monte Carlo approach to three-dimensional Fermi-polaron systems with mass imbalance, where an impurity interacts resonantly with a noninteracting Fermi sea whose atoms have a different mass. This method allows us to go beyond frequently used variational techniques by stochastically summing all relevant impurity Feynman diagrams up to a maximum expansion order limited by the sign problem. Polaron energy and quasiparticle residue can be accurately determined over a broad range of impurity masses. Furthermore, the spectral function of an imbalanced polaron demonstrates the stability of the quasiparticle and allows us to locate in addition also the repulsive polaron as an excited state. The quantitative exactness of two-particle-hole wave functions is investigated, resulting in a relative lowering of polaronic energies in the mass-imbalance phase diagram. Tan's contact coefficient for the mass-balanced polaron system is found in good agreement with variational methods. Mass-imbalanced systems can be studied experimentally by ultracold atom mixtures such as 6Li-40K.

  7. A magnetic polaron model for the enhanced Curie temperature of EuO(1-x).

    PubMed

    Liu, Pan; Tang, Jinke

    2013-03-27

    The investigation of a series of oxygen-deficient EuO thin films provided strong evidence that the doped electrons form magnetic polarons with the nearby Eu2+ 4f spins; this is responsible for the enhanced Curie temperature observed near 140 K. Unlike in the previous magnetic polaron models proposed for the metal-to-insulator transition in EuO, the exchange coupling J between the doped electron and its neighboring 4f spins is antiferromagnetic. The model explains satisfactorily the fact that the ordering temperature of the magnetic polarons occurs at ~140 K, independently of the oxygen vacancy concentration, and the contradiction that electron doping increases T(c) and yet reduces the red shift in the optical absorption. The magnetic polarons are coupled antiferromagnetically to the Eu2+ local moments that are ordered in the Heisenberg ferromagnet below 69 K. This coupling was observable in the vicinity of 69 K. We discuss how, with increasing concentration of the oxygen vacancies, their behaviors evolve from those of isolated superparamagnetic polarons to those of percolating magnetic polarons with a finite coercivity.

  8. Fermi polaron-polaritons in charge-tunable atomically thin semiconductors

    NASA Astrophysics Data System (ADS)

    Sidler, Meinrad; Back, Patrick; Cotlet, Ovidiu; Srivastava, Ajit; Fink, Thomas; Kroner, Martin; Demler, Eugene; Imamoglu, Atac

    2016-10-01

    The dynamics of a mobile quantum impurity in a degenerate Fermi system is a fundamental problem in many-body physics. The interest in this field has been renewed due to recent ground-breaking experiments with ultracold Fermi gases. Optical creation of an exciton or a polariton in a two-dimensional electron system embedded in a microcavity constitutes a new frontier for this field due to an interplay between cavity coupling favouring ultralow-mass polariton formation and exciton-electron interactions leading to polaron or trion formation. Here, we present cavity spectroscopy of gate-tunable monolayer MoSe2 (ref. ) exhibiting strongly bound trion and polaron resonances, as well as non-perturbative coupling to a single microcavity mode. As the electron density is increased, the oscillator strength determined from the polariton splitting is gradually transferred from the higher-energy repulsive exciton-polaron resonance to the lower-energy attractive exciton-polaron state. Simultaneous observation of polariton formation in both attractive and repulsive branches indicates a new regime of polaron physics where the polariton impurity mass can be much smaller than that of the electrons. Our findings shed new light on optical response of semiconductors in the presence of free carriers by identifying the Fermi polaron nature of excitonic resonances and constitute a first step in investigation of a new class of degenerate Bose-Fermi mixtures.

  9. A correlated-polaron electronic propagator: Open electronic dynamics beyond the Born-Oppenheimer approximation

    NASA Astrophysics Data System (ADS)

    Parkhill, John A.; Markovich, Thomas; Tempel, David G.; Aspuru-Guzik, Alan

    2012-12-01

    In this work, we develop an approach to treat correlated many-electron dynamics, dressed by the presence of a finite-temperature harmonic bath. Our theory combines a small polaron transformation with the second-order time-convolutionless master equation and includes both electronic and system-bath correlations on equal footing. Our theory is based on the ab initio Hamiltonian, and is thus well-defined apart from any phenomenological choice of basis states or electronic system-bath coupling model. The equation-of-motion for the density matrix we derive includes non-Markovian and non-perturbative bath effects and can be used to simulate environmentally broadened electronic spectra and dissipative dynamics, which are subjects of recent interest. The theory also goes beyond the adiabatic Born-Oppenheimer approximation, but with computational cost scaling such as the Born-Oppenheimer approach. Example propagations with a developmental code are performed, demonstrating the treatment of electron-correlation in absorption spectra, vibronic structure, and decay in an open system. An untransformed version of the theory is also presented to treat more general baths and larger systems.

  10. A correlated-polaron electronic propagator: open electronic dynamics beyond the Born-Oppenheimer approximation.

    PubMed

    Parkhill, John A; Markovich, Thomas; Tempel, David G; Aspuru-Guzik, Alan

    2012-12-14

    In this work, we develop an approach to treat correlated many-electron dynamics, dressed by the presence of a finite-temperature harmonic bath. Our theory combines a small polaron transformation with the second-order time-convolutionless master equation and includes both electronic and system-bath correlations on equal footing. Our theory is based on the ab initio Hamiltonian, and is thus well-defined apart from any phenomenological choice of basis states or electronic system-bath coupling model. The equation-of-motion for the density matrix we derive includes non-markovian and non-perturbative bath effects and can be used to simulate environmentally broadened electronic spectra and dissipative dynamics, which are subjects of recent interest. The theory also goes beyond the adiabatic Born-Oppenheimer approximation, but with computational cost scaling such as the Born-Oppenheimer approach. Example propagations with a developmental code are performed, demonstrating the treatment of electron-correlation in absorption spectra, vibronic structure, and decay in an open system. An untransformed version of the theory is also presented to treat more general baths and larger systems.

  11. Dielectric relaxation and polaronic conduction in epitaxial BaFe12O19 hexaferrite thin film

    NASA Astrophysics Data System (ADS)

    Tang, Rujun; Zhou, Hao; Zhao, Run; Jian, Jie; Wang, Han; Huang, Jijie; Fan, Meng; Zhang, Wei; Wang, Haiyan; Yang, Hao

    2016-03-01

    The dielectric properties of epitaxial BaFe12O19 hexaferrite thin film have been investigated as a function of frequency (50 Hz  -  2 MHz) and temperature (100-375 K). The frequency dependent permittivity, impedance ({{Z}\\prime \\prime} ) and modulus ({{M}\\prime \\prime} ) spectra show that the dielectric responses of BaFe12O19 thin film are thermally activated. The activation energy of BaFe12O19 film (E a) is much smaller than that of the polycrystalline bulk BaFe12O19. In addition, E a increases with increasing temperature and there is a distribution of relaxation time in the sample. The scaling behavior of {{Z}\\prime \\prime} and {{M}\\prime \\prime} spectra of the sample further suggest that the distribution of relaxation time is temperature independent at low temperatures (<250 K) and temperature dependent at high temperatures. The temperature dependent dc conductivity shows that small polaron hopping is the most probable conduction mechanism for BaFe12O19 film.

  12. Magnetic-Polaron-Induced Enhancement of Surface Raman Scattering

    PubMed Central

    Shao, Qi; Liao, Fan; Ruotolo, Antonio

    2016-01-01

    The studies of the effects of magnetic field on surface enhanced Raman scattering (SERS) have been so far limited to the case of ferromagnetic/noble-metal, core/shell nano-particles, where the influence was always found to be negative. In this work, we investigate the influence of magnetic field on a diluted magnetic semiconductor/metal SERS system. Guided by three dimensional finite-difference time-domain simulations, a high efficient SERS substrate was obtained by diluting Mn into Au-capped ZnO, which results in an increase of the dielectric constant and, therefore, an enhancement of Raman signals. More remarkably, an increase of intensities as well as a reduction of the relative standard deviation (RSD) of Raman signals have been observed as a function of the external magnetic strength. We ascribe these positive influences to magnetic-field induced nucleation of bound magnetic polarons in the Mn doped ZnO. The combination of diluted magnetic semiconductors and SERS may open a new avenue for future magneto-optical applications. PMID:26754049

  13. Light induced polaron formation in perovskite solar cell devices

    NASA Astrophysics Data System (ADS)

    Neukirch, Amanda; Nie, Wanyi; Blancon, Jean-Christophe; Appavoo, Kannatassen; Tsai, Hsinhan; Chhowalla, Manish; Alam, Muhammad; Sfeir, Matthew; Katan, Claudine; Even, Jacky; Crochet, Jared; Gupta, Gautum; Mohite, Aditya; Tretiak, Sergei

    The need for a low-cost, clean, and abundant source of energy has generated large amounts of research in solution processed solar cell materials. The lead halide perovskite has rapidly developed as a serious candidate for the active layer of photovoltaic devices. The efficiencies of devices made with this material have increased from 3.5% to over 20% in around 5 years. Despite the remarkable progress associated with perovskite materials, there are still fundamental questions regarding their lack of photo-stability over prolonged solar irradiation that need to be addressed. Recent experiments on photo-degradation under constant illumination have found fast self-healing by resting the device in the dark for less than 1 minute. Density functional theory and symmetry analysis show that localized charge states couple to local structural lattice distortions and methyl ammonium quasistatic configurations. Once translational symmetry is lost, additional bonding configurations become symmetry allowed, triggering localized charges in the vicinity over time under constant illumination, thus seeding the formation of macroscopic charged domains and preventing efficient charge extraction. Here we present an in-depth study of polaron formation and binding energy at the atomistic level.

  14. Fragility, Intermediate Phase and Polaronic conductivity in heavy metal oxides

    NASA Astrophysics Data System (ADS)

    Chakraborty, Shibalik; Gunasekera, Kapila; Boolchand, Punit; Malki, Mohammed; Micoulaut, Matthieu

    2013-03-01

    The (B2O3)5 (TeO2)95-x (V2O5)x ternary forms bulk glasses over a wide range of compositions, 18% < x < 35%. Complex Cp(x) measurements as a function of modulation frequency reveal that melt fragility (m) show a global minimum (m = 52(2)) in the 23% < x < 26% range with m > 65 outside that window. These results suggest more stable network structure in the window than outside it. The fragility window coincides with a global minimum of the non-reversing enthalpy of relaxation at Tg, the reversibility window (23% < x < 27%), a behavior also found in chalcogenide glasses. Conductivity (σ) data show three regimes of variation; a low σ at x < 23%, a plateau in 23% < x < 27%, and an exponential increase at x > 27%. The reduced activation energy for conductivity at x > 27% is consistent with increased polaronic mobility as the network becomes flexible. These findings show glasses at x < 23% are stressed-rigid, in 23% < x < 27% range in the Intermediate Phase, and at x > 27% to be flexible. Supported by NSF grant DMR 08-53957.

  15. Liquid-state polaron theory of the hydrated electron revisited

    NASA Astrophysics Data System (ADS)

    Donley, James P.; Heine, David R.; Tormey, Caleb A.; Wu, David T.

    2014-07-01

    The quantum path integral/classical liquid-state theory of Chandler and co-workers, created to describe an excess electron in solvent, is re-examined for the hydrated electron. The portion that models electron-water density correlations is replaced by two equations: the range optimized random phase approximation (RO-RPA), and the Donley, Rajasekaran, and Liu (DRL) approximation to the "two-chain" equation, both shown previously to describe accurately the static structure and thermodynamics of strongly charged polyelectrolyte solutions. The static equilibrium properties of the hydrated electron are analyzed using five different electron-water pseudopotentials. The theory is then compared with data from mixed quantum/classical Monte Carlo and molecular dynamics simulations using these same pseudopotentials. It is found that the predictions of the RO-RPA and DRL-based polaron theories are similar and improve upon previous theory, with values for almost all properties analyzed in reasonable quantitative agreement with the available simulation data. Also, it is found using the Larsen, Glover, and Schwartz pseudopotential that the theories give values for the solvation free energy that are at least three times larger than that from experiment.

  16. Liquid-state polaron theory of the hydrated electron revisited

    SciTech Connect

    Donley, James P.; Heine, David R.; Tormey, Caleb A.; Wu, David T.

    2014-07-14

    The quantum path integral/classical liquid-state theory of Chandler and co-workers, created to describe an excess electron in solvent, is re-examined for the hydrated electron. The portion that models electron-water density correlations is replaced by two equations: the range optimized random phase approximation (RO-RPA), and the Donley, Rajasekaran, and Liu (DRL) approximation to the “two-chain” equation, both shown previously to describe accurately the static structure and thermodynamics of strongly charged polyelectrolyte solutions. The static equilibrium properties of the hydrated electron are analyzed using five different electron-water pseudopotentials. The theory is then compared with data from mixed quantum/classical Monte Carlo and molecular dynamics simulations using these same pseudopotentials. It is found that the predictions of the RO-RPA and DRL-based polaron theories are similar and improve upon previous theory, with values for almost all properties analyzed in reasonable quantitative agreement with the available simulation data. Also, it is found using the Larsen, Glover, and Schwartz pseudopotential that the theories give values for the solvation free energy that are at least three times larger than that from experiment.

  17. Thermodynamics of the polaron master equation at finite bias

    SciTech Connect

    Krause, Thilo Brandes, Tobias; Schaller, Gernot; Esposito, Massimiliano

    2015-04-07

    We study coherent transport through a double quantum dot. Its two electronic leads induce electronic matter and energy transport and a phonon reservoir contributes further energy exchanges. By treating the system-lead couplings perturbatively, whereas the coupling to vibrations is treated non-perturbatively in a polaron-transformed frame, we derive a thermodynamic consistent low-dimensional master equation. When the number of phonon modes is finite, a Markovian description is only possible when these couple symmetrically to both quantum dots. For a continuum of phonon modes however, also asymmetric couplings can be described with a Markovian master equation. We compute the electronic current and dephasing rate. The electronic current enables transport spectroscopy of the phonon frequency and displays signatures of Franck-Condon blockade. For infinite external bias but finite tunneling bandwidths, we find oscillations in the current as a function of the internal bias due to the electron-phonon coupling. Furthermore, we derive the full fluctuation theorem and show its identity to the entropy production in the system.

  18. All-coupling polaron optical response: Analytic approaches beyond the adiabatic approximation

    NASA Astrophysics Data System (ADS)

    Klimin, S. N.; Tempere, J.; Devreese, J. T.

    2016-09-01

    In the present work, the problem of an all-coupling analytic description for the optical conductivity of the Fröhlich polaron is treated, with the goal being to bridge the gap in the validity range that exists between two complementary methods: on the one hand, the memory-function formalism and, on the other hand, the strong-coupling expansion based on the Franck-Condon picture for the polaron response. At intermediate coupling, both methods were found to fail as they do not reproduce diagrammatic quantum Monte Carlo results. To resolve this, we modify the memory-function formalism with respect to the Feynman-Hellwarth-Iddings-Platzman approach in order to take into account a nonquadratic interaction in a model system for the polaron. The strong-coupling expansion is extended beyond the adiabatic approximation by including in the treatment nonadiabatic transitions between excited polaron states. The polaron optical conductivity that we obtain at T =0 by combining the two extended methods agrees well, both qualitatively and quantitatively, with the diagrammatic quantum Monte Carlo results in the whole available range of the electron-phonon coupling strength.

  19. First-principles study of hole polaron formation and migration in SrI2

    NASA Astrophysics Data System (ADS)

    Zhou, Fei; Sadigh, Babak; Aberg, Daniel

    2015-03-01

    We investigate the formation of self-trapped holes (STH) in the high performance scintillator material SrI2 using a recently developed first principles method, polaron self-interaction correction (pSIC). pSIC removes the significant spurious self-interaction of localized polaron states. It is capable of accurately reproduce the configurational energy landscape of polaronic states from optimized hybrid functionals at the computational cost of the local density approximation. We searched for and identified all symmetrically distinct STH states localized on neighboring I-I dimers, i.e. Vk centers, and found non-trivial relation between the STH formation energies and dimer separation. All possible polaron hopping paths of the type IAIB -->IBIC are investigated systematically with pSIC and the elastic band method, and paths with low migration barrier energy of about 0.2 eV were identified, suggesting high mobility in SrI2. We expect that the present approach can be applied to study polaron formation and migration in other materials. Support from the National Nuclear Security Administration Office of Nonproliferation Research and Development (NA-22) is acknowledged. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore N We acknowledge funding from the NA-22 agency.

  20. Tunable Polarons of Slow-Light Polaritons in a Two-Dimensional Bose-Einstein Condensate

    NASA Astrophysics Data System (ADS)

    Grusdt, Fabian; Fleischhauer, Michael

    2016-02-01

    When an impurity interacts with a bath of phonons it forms a polaron. For increasing interaction strengths the mass of the polaron increases and it can become self-trapped. For impurity atoms inside an atomic Bose-Einstein condensate (BEC) the nature of this transition is not understood. While Feynman's variational approach to the Fröhlich model predicts a sharp transition for light impurities, renormalization group studies always predict an extended intermediate-coupling region characterized by large phonon correlations. To investigate this intricate regime and to test polaron physics beyond the validity of the Fröhlich model we suggest a versatile experimental setup that allows us to tune both the mass of the impurity and its interactions with the BEC. The impurity is realized as a dark-state polariton (DSP) inside a quasi-two-dimensional BEC. We show that its interactions with the Bogoliubov phonons lead to photonic polarons, described by the Bogoliubov-Fröhlich Hamiltonian, and make theoretical predictions using an extension of a recently introduced renormalization group approach to Fröhlich polarons.

  1. Possibility of observation of polaron normal modes at the far-infrared spectrum of acetanilide and related organics

    NASA Astrophysics Data System (ADS)

    Kalosakas, G.; Aubry, S.; Tsironis, G. P.

    1998-10-01

    We use a stationary and normal mode analysis of the semiclassical Holstein model in order to connect the low-frequency linear polaron modes to low-lying far-infrared lines of the acetanilide spectrum and through parameter fitting we comment on the validity of the polaron results in this system.

  2. Ab initio prediction of fast non-equilibrium transport of nascent polarons in SrI2: a key to high-performance scintillation [First-principles study of hole polaron formation and migration in strontium iodide

    DOE PAGES

    Zhou, Fei; Sadigh, Babak; Aberg, Daniel; ...

    2016-08-12

    The excellent light yield proportionality of europium-doped strontium iodide (SrI2:Eu) has resulted in state-of-the-art γ-ray detectors with remarkably high-energy resolution, far exceeding that of most halide compounds. In this class of materials, the formation of self-trapped hole polarons is very common. However, polaron formation is usually expected to limit carrier mobilities and has been associated with poor scintillator light-yield proportionality and resolution. Here using a recently developed first-principles method, we perform an unprecedented study of polaron transport in SrI2, both for equilibrium polarons, as well as nascent polarons immediately following a self-trapping event. We propose a rationale for the unexpectedmore » high-energy resolution of SrI2. We identify nine stable hole polaron configurations, which consist of dimerised iodine pairs with polaron-binding energies of up to 0.5 eV. They are connected by a complex potential energy landscape that comprises 66 unique nearest-neighbour migration paths. Ab initio molecular dynamics simulations reveal that a large fraction of polarons is born into configurations that migrate practically barrier free at room temperature. Consequently, carriers created during γ-irradiation can quickly diffuse away reducing the chance for nonlinear recombination, the primary culprit for non-proportionality and resolution reduction. We conclude that the flat, albeit complex, landscape for polaron migration in SrI2 is a key for understanding its outstanding performance. This insight provides important guidance not only for the future development of high-performance scintillators but also of other materials, for which large polaron mobilities are crucial such as batteries and solid-state ionic conductors.« less

  3. Ab initio prediction of fast non-equilibrium transport of nascent polarons in SrI2: a key to high-performance scintillation [First-principles study of hole polaron formation and migration in strontium iodide

    SciTech Connect

    Zhou, Fei; Sadigh, Babak; Aberg, Daniel; Erhart, Paul

    2016-08-12

    The excellent light yield proportionality of europium-doped strontium iodide (SrI2:Eu) has resulted in state-of-the-art γ-ray detectors with remarkably high-energy resolution, far exceeding that of most halide compounds. In this class of materials, the formation of self-trapped hole polarons is very common. However, polaron formation is usually expected to limit carrier mobilities and has been associated with poor scintillator light-yield proportionality and resolution. Here using a recently developed first-principles method, we perform an unprecedented study of polaron transport in SrI2, both for equilibrium polarons, as well as nascent polarons immediately following a self-trapping event. We propose a rationale for the unexpected high-energy resolution of SrI2. We identify nine stable hole polaron configurations, which consist of dimerised iodine pairs with polaron-binding energies of up to 0.5 eV. They are connected by a complex potential energy landscape that comprises 66 unique nearest-neighbour migration paths. Ab initio molecular dynamics simulations reveal that a large fraction of polarons is born into configurations that migrate practically barrier free at room temperature. Consequently, carriers created during γ-irradiation can quickly diffuse away reducing the chance for nonlinear recombination, the primary culprit for non-proportionality and resolution reduction. We conclude that the flat, albeit complex, landscape for polaron migration in SrI2 is a key for understanding its outstanding performance. This insight provides important guidance not only for the future development of high-performance scintillators but also of other materials, for which large polaron mobilities are crucial such as batteries and solid-state ionic conductors.

  4. Bloch oscillations as generators of polarons in a 1D crystal

    NASA Astrophysics Data System (ADS)

    Nazareno, H. N.; Brito, P. E. de

    2016-08-01

    The main purpose of this work is to characterize the kind of propagation/localization of carriers in a one-dimensional crystalline structure along the tight-binding model while the electron-phonon interaction is taken into account through a deformation potential and the system is under the action of a dc electric field. The lattice was treated in the classical formalism of harmonic vibrations. A remarkable effect is obtained due to the presence of the electric field. On one side the particle performs Bloch oscillations and at the same time it interacts with the lattice and as a result at each turning point of its trajectory phonons are generated that carry with them a fraction of the electronic wave packet, it is the polaron formation. This way the Bloch oscillations pump polarons into the system. We explain why the polaron is formed at returning points of the oscillations.

  5. Polaronic approach to strongly correlated electron systems with strong electron-phonon interaction

    NASA Astrophysics Data System (ADS)

    Makarov, I. A.; Shneyder, E. I.; Kozlov, P. A.; Ovchinnikov, S. G.

    2015-10-01

    The three-band p -d model of strongly correlated electrons interacting with optical phonons via diagonal and off-diagonal electron-phonon interactions is considered within the cluster perturbation theory. In the beginning, the exact diagonalization of the Hamiltonian of a CuO4 cluster results in the construction of local polaronic eigenstates |p > with hole numbers nh=0 ,1 ,2 per unit cell. The intercluster hoppings and interactions are exactly written in terms of Hubbard operators Xfp q=|p >polaronic eigenstates |p > at site f . The Fermi-type single-electron quasiparticle dispersion and spectral weight are calculated for the undoped antiferromagnetic parent insulator like La2CuO4 . The quasiparticle dispersion of Hubbard polarons is determined by a hybridization of the Hubbard fermion subbands with local Franck-Condon resonances so the main polaronic effect of the quasiparticle band structure is a splitting of the Hubbard bands on the number of Hubbard polaron subbands. Increasing of the EPI constant results in an increase of splitting, decrease of the subband width, transfer of the spectral weight to high-energy multiphonon excitations, and subsequent localization of the charge carriers. Herewith, the effect of such renormalization for the conduction band and the valence one differs depending on the ratio of the diagonal and off-diagonal EPI. In the framework of the GTB method, the Franck-Condon broadening of the spectral function of polaronic excitations is also reproduced for strongly correlated systems with strong electron-phonon interaction.

  6. Complex magneto-polaron spectrum of the layer compound InSe

    NASA Astrophysics Data System (ADS)

    Brancus, D. E. N.; Stan, G.; Dafinei, A.

    2005-06-01

    We analyse the energy magneto-polaron spectrum of the polar uniaxial layer compound InSe in a magnetic field directed along the optical axis. A quasi-bidimensional behaviour of the electron gas in this particular structure was considered. In the framework of the Wigner-Brillouin perturbational theory we systematically take into account all the sources of anisotropy. We found that the implied anisotropy brings distinctive contributions to the complex energy magneto-polaron spectrum of polar uniaxial crystals. The theory is used to examine the experimental results obtained from cyclotron resonance frequency measurements in InSe at low temperature.

  7. Q1D-Polarons in Rigid Boundary Cylindrical Wires: "Mixed-Coupling Approximation"

    NASA Astrophysics Data System (ADS)

    Senger, R. T.; Erçelebý, A.

    1998-02-01

    We consider the interaction of a confined electron with bulk polar-optical phonons in a cylindrical quantum well wire with infinite boundary potential. Expressions for the polaron self energy and mass are derived within a composite variational scheme consisting of a strong-coupling characterization imposed in the lateral directions and a weak-coupling LLP-counterpart structured along the length of the wire. The formulation is seen to be rather commendable and yields a sensible description of the Q1D-polaron in thin wires of weak or intermediate electron-phonon coupling strengths.

  8. Effects of Shannon entropy and electric field on polaron in RbCl triangular quantum dot

    NASA Astrophysics Data System (ADS)

    M, Tiotsop; A, J. Fotue; S, C. Kenfack; N, Issofa; H, Fotsin; L, C. Fai

    2016-04-01

    In this paper, the time evolution of the quantum mechanical state of a polaron is examined using the Pekar type variational method on the condition of the electric-LO-phonon strong-coupling and polar angle in RbCl triangular quantum dot. We obtain the eigenenergies, and the eigenfunctions of the ground state, and the first excited state respectively. This system in a quantum dot can be treated as a two-level quantum system qubit and the numerical calculations are performed. The effects of Shannon entropy and electric field on the polaron in the RbCl triangular quantum dot are also studied.

  9. Influence of molecular designs on polaronic and vibrational transitions in a conjugated push-pull copolymer

    PubMed Central

    Cobet, Christoph; Gasiorowski, Jacek; Menon, Reghu; Hingerl, Kurt; Schlager, Stefanie; White, Matthew S.; Neugebauer, Helmut; Sariciftci, N. Serdar; Stadler, Philipp

    2016-01-01

    Electron-phonon interactions of free charge-carriers in doped pi-conjugated polymers are conceptually described by 1-dimensional (1D) delocalization. Thereby, polaronic transitions fit the 1D-Froehlich model in quasi-confined chains. However, recent developments in conjugated polymers have diversified the backbones to become elaborate heterocylcic macromolecules. Their complexity makes it difficult to investigate the electron-phonon coupling. In this work we resolve the electron-phonon interactions in the ground and doped state in a complex push-pull polymer. We focus on the polaronic transitions using in-situ spectroscopy to work out the differences between single-unit and push-pull systems to obtain the desired structural- electronic correlations in the doped state. We apply the classic 1D-Froehlich model to generate optical model fits. Interestingly, we find the 1D-approach in push-pull polarons in agreement to the model, pointing at the strong 1D-character and plain electronic structure of the push-pull structure. In contrast, polarons in the single-unit polymer emerge to a multi- dimensional problem difficult to resolve due to their anisotropy. Thus, we report an enhancement of the 1D-character by the push-pull concept in the doped state - an important view in light of the main purpose of push-pull polymers for photovoltaic devices. PMID:27731421

  10. Polaron effect on the optical rectification in spherical quantum dots with electric field

    NASA Astrophysics Data System (ADS)

    Feng, Zhen-Yu; Yan, Zu-Wei

    2016-10-01

    The polaron effect on the optical rectification in spherical quantum dots with a shallow hydrogenic impurity in the presence of electric field is theoretically investigated by taking into account the interactions of the electrons with both confined and surface optical phonons. Besides, the interaction between impurity and phonons is also considered. Numerical calculations are presented for typical Zn1-x Cd x Se/ZnSe material. It is found that the polaronic effect or electric field leads to the redshifted resonant peaks of the optical rectification coefficients. It is also found that the peak values of the optical rectification coefficients with the polaronic effect are larger than without the polaronic effect, especially for smaller Cd concentrations or stronger electric field. Project supported by the National Natural Science Foundation of China (Grant No. 11364028), the Major Projects of the Natural Science Foundation of Inner Mongolia Autonomous Region, China (Grant No. 2013ZD02), and the Project of “Prairie Excellent” Engineering in Inner Mongolia Autonomous Region, China.

  11. Unified analysis of transient and steady-state electrophosphorescence using exciton and polaron dynamics modeling

    NASA Astrophysics Data System (ADS)

    Hershey, Kyle W.; Holmes, Russell J.

    2016-11-01

    Phosphorescent organic light-emitting devices (OLEDs) can suffer a significant reduction in device efficiency under high current density excitation. This steady-state efficiency roll-off is frequently modeled by including losses from exciton-exciton and exciton-polaron quenching. Despite success in modeling the steady-state efficiency roll-off, the corresponding transient electroluminescence behavior has not been modeled as effectively using the same quenching processes. In this work, both the steady-state and transient electroluminescence behavior of phosphorescent OLEDs based on tris[2-phenylpyridinato-C2,N]Iridium(III) (Ir(ppy)3) are successfully reproduced by considering a dynamic polaron population. Within this model, polarons are able to either form excitons or leak through the device emissive layer, reducing the overall efficiency. This formalism permits a natural and rigorous connection between exciton and polaron dynamics and device charge balance, with the charge balance cast as the efficiency of exciton formation. The full dynamics model reproduces both the rise and decay of transient electroluminescence, as well as the full dependence of the external quantum efficiency on current density. Fit parameters are independently verified using separate studies of transient and steady-state photoluminescence. The model provides a complete picture for the dynamics present during the electrical operation of phosphorescent OLEDs, while also offering a direct route to elucidate exciton formation.

  12. Optical polaron effect on the electronic states of a heterojunction potential

    NASA Astrophysics Data System (ADS)

    Ban, S. L.; Hasbun, J. E.

    1997-11-01

    The polaron effect contribution to the electronic ground state in a heterojunction potential is investigated by considering the bulk and the interface phonons influence. A self-consistent heterojunction potential is used and an LLP-like method is used to obtain the polaron effect. The GaAs/Al_xGa_1-xAs (0.3polaron parallel to the interface. The bulk longitudinal optical phonons (BP) are the main contribution and force the electrons to shift into the channel layer(GaAs)slightly, however the influence from the two branches of interface phonons (IP), which attract the electron toward the interface, compete against the bulk phonons. The IP contribution is about 20 % of the BP. The penetration of the electron wave function into the barrier layer due to the polaron effect is not significant. The results are in qualitative agreement with a previous work (S. L. Ban and X. X. Liang, Phys. Rev. B, (1997), submitted) using an infinite barrier.

  13. Influence of molecular designs on polaronic and vibrational transitions in a conjugated push-pull copolymer

    NASA Astrophysics Data System (ADS)

    Cobet, Christoph; Gasiorowski, Jacek; Menon, Reghu; Hingerl, Kurt; Schlager, Stefanie; White, Matthew S.; Neugebauer, Helmut; Sariciftci, N. Serdar; Stadler, Philipp

    2016-10-01

    Electron-phonon interactions of free charge-carriers in doped pi-conjugated polymers are conceptually described by 1-dimensional (1D) delocalization. Thereby, polaronic transitions fit the 1D-Froehlich model in quasi-confined chains. However, recent developments in conjugated polymers have diversified the backbones to become elaborate heterocylcic macromolecules. Their complexity makes it difficult to investigate the electron-phonon coupling. In this work we resolve the electron-phonon interactions in the ground and doped state in a complex push-pull polymer. We focus on the polaronic transitions using in-situ spectroscopy to work out the differences between single-unit and push-pull systems to obtain the desired structural- electronic correlations in the doped state. We apply the classic 1D-Froehlich model to generate optical model fits. Interestingly, we find the 1D-approach in push-pull polarons in agreement to the model, pointing at the strong 1D-character and plain electronic structure of the push-pull structure. In contrast, polarons in the single-unit polymer emerge to a multi- dimensional problem difficult to resolve due to their anisotropy. Thus, we report an enhancement of the 1D-character by the push-pull concept in the doped state - an important view in light of the main purpose of push-pull polymers for photovoltaic devices.

  14. Generalized Hartree-Fock-Bogoliubov description of the Fröhlich polaron

    NASA Astrophysics Data System (ADS)

    Kain, Ben; Ling, Hong Y.

    2016-07-01

    We adapt the generalized Hartree-Fock-Bogoliubov (HFB) method to an interacting many-phonon system free of impurities. The many-phonon system is obtained from applying the Lee-Low-Pine (LLP) transformation to the Fröhlich model which describes a mobile impurity coupled to noninteracting phonons. We specialize our general HFB description of the Fröhlich polaron to Bose polarons in quasi-one-dimensional cold-atom mixtures. The LLP-transformed many-phonon system distinguishes itself with an artificial phonon-phonon interaction which is very different from the usual two-body interaction. We use the quasi-one-dimensional model, which is free of an ultraviolet divergence that exists in higher dimensions, to better understand how this unique interaction affects polaron states and how the density and pair correlations inherent to the HFB method conspire to create a polaron ground state with an energy in good agreement with and far closer to the prediction from Feynman's variational path integral approach than mean-field theory where HFB correlations are absent.

  15. Polaronic exciton in self-organized assemblies of protonated meso-tetraphenylporphine dimers and water at room temperature

    NASA Astrophysics Data System (ADS)

    Udal'tsov, Alexander V.

    2016-12-01

    Assemblies consisting of protonated meso-tetraphenylporphine (TPP) dimers and water have been investigated by UV-vis and infrared (IR) spectroscopy and by atomic force microscopy (AFM) in thin layers. Features of electronic absorption spectra of the assemblies are interpreted in terms of hole polaron combined with exciton theory using quantum well with parameters obtained from the dimer structure. It appears to be hole polaron moving defines kinetic energy of polaronic exciton confined in a quantum well when the electron absorbs photon. Hole polaron characteristics such as polaron self-energy, energy of Frank-Condon transitions, and radius of hole polaron moving through water are found to be 1.38 eV, 0.2445 eV, and 0.246 Å, respectively. A doublet at 1944, 1960 cm-1 (0.2412, 0.2432 eV) observed in IR spectra matches the energy of Frank-Condon transitions. Excitation energies estimated using molecular parameters for polaronic excitons in pure water and in the TPP dimers are found in a good agreement with the experimental data.

  16. Polaron dynamics in two types of long oligothiophenes revealed by Q - and X -band ESR measurements

    NASA Astrophysics Data System (ADS)

    Kanemoto, Katsuichi; Furukawa, Ko; Negishi, Nobukazu; Aso, Yoshio; Otsubo, Tetsuo

    2007-10-01

    The polaron dynamics has been investigated through the X - and Q -band ESR measurements for two types of iodine-doped long oligothiophenes, the 20-mer with octyl substituents (o-20T) and the 16-mer with hexyl substituents (h-16T) . o-20T , used as a model compound of conjugated polymers with crystalline grains, gives anisotropic ESR spectra attributed to g anisotropy at low temperatures. The anisotropic spectra are found to be brought by polarons moving within the crystalline grains consisting of parallel chains. The anisotropy is shown to decrease with increasing temperature. This provides definite evidence that the polarons transfer among some grains by the assist of temperature. In contrast, h-16T , used as a model of the polymers with amorphous morphology, gives almost isotropic ESR spectra even in the Q -band measurement. This feature of h-16T is explained to be caused by a rapid interchain transfer of polarons. Spectral simulations performed for obtained spectra reveal that the ESR linewidth in the Q -band measurement is larger than that in the X band for both oligothiophenes. The difference of the linewidth is analyzed by a simplified motional narrowing model in order to draw the information of polaron dynamics. Analyses for o-20T show that the intergrain motion almost follows the variable range hopping model. The interchain motion in h-16T is found to have a much weaker temperature dependence than the intergrain motion in o-20T . This result suggests that the interchain dynamics of h-16T revealed by the ESR technique includes a variety of processes of motion.

  17. Polaronic Transport in Phosphate Glasses Containing Transition Metal Ions

    NASA Astrophysics Data System (ADS)

    Henderson, Mark

    The goal of this dissertation is to characterize the basic transport properties of phosphate glasses containing various amounts of TIs and to identify and explain any electronic phase transitions which may occur. The P2 O5-V2O5-WO3 (PVW) glass system will be analyzed to find the effect of TI concentration on conduction. In addition, the effect of the relative concentrations of network forming ions (SiO2 and P2O5) on transport will be studied in the P2O5-SiO2-Fe2O 3 (PSF) system. Also presented is a numerical study on a tight-binding model adapted for the purposes of modelling Gaussian traps, mimicking TI's, which are arranged in an extended network. The results of this project will contribute to the development of fundamental theories on the electronic transport in glasses containing mixtures of transition oxides as well as those containing multiple network formers without discernible phase separation. The present study on the PVW follows up on previous investigation into the effect on mixed transition ions in oxide glasses. Past research has focused on glasses containing transition metal ions from the 3d row. The inclusion of tungsten, a 5d transition metal, adds a layer of complexity through the mismatch of the energies of the orbitals contributing to localized states. The data have indicated that a transition reminiscent of a metal-insulator transition (MIT) occurs in this system as the concentration of tungsten increases. As opposed to some other MIT-like transitions found in phosphate glass systems, there seems to be no polaron to bipolaron conversion. Instead, the individual localization parameter for tungsten noticeably decreases dramatically at the transition point as well as the adiabaticity. Another distinctive feature of this project is the study of the PSF system, which contains two true network formers, phosphorous pentoxide (P2O 5) and silicon dioxide (SiO2). It is not usually possible to do a reliable investigation of the conduction properties of

  18. Temperature effects on interface polarons in a strained (111)-oriented zinc-blende GaN/AlGaN heterojunction under pressure

    NASA Astrophysics Data System (ADS)

    Min, Zhang; Shiliang, Ban

    2009-03-01

    The properties of interface polarons in a strained (111)-oriented zinc-blende GaN/AlxGa1-xN heterojunction at finite temperature under hydrostatic pressure are investigated by adopting a modified LLP variational method and a simplified coherent potential approximation. Considering the effect of hydrostatic pressure on the bulk longitudinal optical phonon mode, two branches interface-optical phonon modes and strain, respectively, we calculated the polaronic self-trapping energy and effective mass as functions of temperature, pressure and areal electron density. The numerical result shows that both of them near linearly increase with pressure but the self-trapping energies are nonlinear monotone increasing with increasing of the areal electron density. They are near constants below a range of temperature whereas decrease dramatically with increasing temperature beyond the range. The contributions from the bulk longitudinal optical phonon mode and one branch of interface optical phonon mode with higher frequency are important whereas the contribution from another branch of interface optical phonon mode with lower frequency is extremely small so that it can be neglected in the further discussion.

  19. Property comparison of polarons in zinc-blende and wurtzite GaN/AlN quantum wells

    NASA Astrophysics Data System (ADS)

    Jun, Zhu; Shiliang, Ban; Sihua, Ha

    2011-11-01

    The properties of polarons in zinc-blende and wurtzite GaN/AlN quantum wells with Fröhlich interaction Hamiltonians are compared in detail. The energy shifts of polarons at ground state due to the interface (IF), confined (CO) and half-space phonon modes are calculated by a finite-difference computation combined with a modified LLP variational method. It is found that the two Fröhlich interaction Hamiltonians are consistent with each other when the anisotropic effect from the z-direction and the x-y plane is neglected. The influence of the anisotropy on the polaron energy shifts due to the IF phonon modes for a smaller well width or due to the CO phonon modes for a moderate well width is obvious. In addition, the built-in electric field has a remarkable effect on the polaron energy shifts contributed by the various phonon modes.

  20. Decoherence time, hydrogenic-like impurity effect and Shannon entropy on polaron in RbCl triangular quantum dot qubit

    NASA Astrophysics Data System (ADS)

    Tiotsop, M.; Fotue, A. J.; Fautso, G. K.; Kenfack, C. S.; Fotsin, H. B.; Fai, L. C.

    2017-03-01

    Using Pekar variational method, Eigen energies of the ground and first excited states of the polaron in triangular bound and Coulomb potential quantum dot are derived in view of investigating the density of probability, the decoherence time and the Shannon entropy. Numerical analysis show that the decoherence time is decreasing function of polaron radius and the strength of the Coulombic impurity and the increase function of dispersion coefficient. These results suggest that the decrease of polaron radius and Coulombic impurity lead to the increase of coherence time. Also the entropy shows the oscillatory periodic evolution as function of the time due to the triangular form of the confinement. It's also seen that entropy is periodic for the lower value of Coulomb impurity parameter and for the higher value of the polaronic radius.

  1. Effectis of Lattice Distortion, Polaron Sonduction and Double-Exchange Interaction on the Physical Properties of Magnetoresistive Manganites and Cobaltites

    NASA Technical Reports Server (NTRS)

    Yeh, N. C.; Vasquez, R. P.; Wei, J. Y. T.; Fu, C. C.; Beach, G.; Huynh, J.; Samoilov, A. V.; Boris, A. V.; Kovaleva, N. N.; Bazhenov, A. V.

    1997-01-01

    The relevance of lattice distortion, polaron conduction, and double-exchange interaction to the occurrence of colossal magnetoresistance (SMR) is investigated by comparing the physical properties of magnetoresistive manganites and cobaltites.

  2. Non-canonical distribution and non-equilibrium transport beyond weak system-bath coupling regime: A polaron transformation approach

    NASA Astrophysics Data System (ADS)

    Xu, Dazhi; Cao, Jianshu

    2016-08-01

    The concept of polaron, emerged from condense matter physics, describes the dynamical interaction of moving particle with its surrounding bosonic modes. This concept has been developed into a useful method to treat open quantum systems with a complete range of system-bath coupling strength. Especially, the polaron transformation approach shows its validity in the intermediate coupling regime, in which the Redfield equation or Fermi's golden rule will fail. In the polaron frame, the equilibrium distribution carried out by perturbative expansion presents a deviation from the canonical distribution, which is beyond the usual weak coupling assumption in thermodynamics. A polaron transformed Redfield equation (PTRE) not only reproduces the dissipative quantum dynamics but also provides an accurate and efficient way to calculate the non-equilibrium steady states. Applications of the PTRE approach to problems such as exciton diffusion, heat transport and light-harvesting energy transfer are presented.

  3. Renormalization group approach to the Fröhlich polaron model: application to impurity-BEC problem

    PubMed Central

    Grusdt, F.; Shchadilova, Y. E.; Rubtsov, A. N.; Demler, E.

    2015-01-01

    When a mobile impurity interacts with a many-body system, such as a phonon bath, a polaron is formed. Despite the importance of the polaron problem for a wide range of physical systems, a unified theoretical description valid for arbitrary coupling strengths is still lacking. Here we develop a renormalization group approach for analyzing a paradigmatic model of polarons, the so-called Fröhlich model, and apply it to a problem of impurity atoms immersed in a Bose-Einstein condensate of ultra cold atoms. Polaron energies obtained by our method are in excellent agreement with recent diagrammatic Monte Carlo calculations for a wide range of interaction strengths. They are found to be logarithmically divergent with the ultra-violet cut-off, but physically meaningful regularized polaron energies are also presented. Moreover, we calculate the effective mass of polarons and find a smooth crossover from weak to strong coupling regimes. Possible experimental tests of our results in current experiments with ultra cold atoms are discussed. PMID:26183614

  4. Experimental study of NIR absorption due to Nb4+ polarons in pure and Cr- or Ce-doped SBN crystals

    NASA Astrophysics Data System (ADS)

    Gao, Ming; Kapphan, S.; Porcher, S.; Pankrath, R.

    1999-06-01

    A broad absorption band around 0.72 eV, assigned to the absorption of Nb4+ polarons, is observed in strontium barium niobate (SBN) crystals (nominally pure or Cr- or Ce-doped) either under illumination at low temperature or after a previous reduction treatment. The absorption spectra of Nb4+ polarons at low temperature show considerable dichroism, which in reduced SBN crystals exists even far above room temperature. The peak position of the Nb4+ polaron absorption in reduced SBN crystals shifts to higher energies with decreasing temperature. The dependence on light intensity and temperature of the Nb4+ polaron absorption during the build-up process under illumination and the decay process after the illumination is switched off are investigated in detail. Compared with pure SBN, doping with Ce or Cr creates additional absorption bands in the visible (2.6 eV) and red (1.9 eV for Cr doping) spectral regions. Illumination in these absorption bands at low temperature gives rise to strong Nb4+ polaron absorption in the NIR (0.72 eV), giving evidence of the enhanced sensitivity even in the red spectral region for SBN:Cr. The light-induced charge transfer process and formation of Nb4+ polarons in SBN are briefly discussed.

  5. Magnetic hard gap due to bound magnetic polarons in the localized regime

    NASA Astrophysics Data System (ADS)

    Rimal, Gaurab; Tang, Jinke

    2017-02-01

    We investigate the low temperature electron transport properties of manganese doped lead sulfide films. The system shows variable range hopping at low temperatures that crosses over into an activation regime at even lower temperatures. This crossover is destroyed by an applied magnetic field which suggests a magnetic origin of the hard gap, associated with bound magnetic polarons. Even though the gap forms around the superconducting transition temperature of lead, we do not find evidence of this being due to insulator-superconductor transition. Comparison with undoped PbS films, which do not show the activated transport behavior, suggests that bound magnetic polarons create the hard gap in the system that can be closed by magnetic fields.

  6. Rashba Effect on the Bound Polaron in an Asymmetric Quantum Dot

    NASA Astrophysics Data System (ADS)

    Shan, Shu-Ping; Chen, Shi-Hua; Xiao, Jing-Lin

    2014-07-01

    By using LLP variational method, the Rashba effect on the bound polaron in an asymmetric quantum dot is investigated and the expression of the bound polaron ground state energy is derived. Considering different Coulomb bound potentials, we discuss the relations between the ground state energy and the electron-phonon coupling strength, the wave vector, the transverse effective confinement length and the longitudsinal effective confinement length, respectively. The results show that the ground state energy is a decreasing function of the Coulomb bound potential, the electron-phonon coupling strength, the transverse effective confinement length and the longitudinal effective confinement length. On the contrary, it is an increasing function of the wave vector. Due to the Rashba effect, the ground state energy splits into two branches.

  7. Chain Length Dependence of Energies of Electron and Triplet Polarons in Oligofluorenes

    DOE PAGES

    Chen, Hung Cheng; Sreearunothai, Paiboon; Cook, Andrew R.; ...

    2017-03-01

    Bimolecular equilibria measured the one-electron reduction potentials and triplet free energies (ΔG°T) of oligo(9,9-dihexyl)fluorenes and a polymer with lengths of n = 1–10 and 57 repeat units. We can accurately measure one-electron potentials electrochemically only for the shorter oligomers. Starting at n = 1 the free energies change rapidly with increasing length and become constant for lengths longer than the delocalization length. Both the reduction potentials and triplet energies can be understood as the sum of a free energy for a fixed polaron and a positional entropy. Furthermore, the positional entropy increases gradually with length beyond the delocalization length duemore » to the possible occupation sites of the charge or the triplet exciton. Our results reinforce the view that charges and triplet excitons in conjugated chains exist as polarons and find that positional entropy can replace a popular empirical model of the energetics.« less

  8. Fermi polaron in two dimensions: Importance of the two-body bound state

    SciTech Connect

    Klawunn, Michael; Recati, Alessio

    2011-09-15

    We investigate a single impurity interacting with a free two-dimensional atomic Fermi gas. The interaction between the impurity and the gas is characterized by an arbitrary attractive short-range potential, which, in two dimensions, always admits a two-particle bound state. We provide analytical expressions for the energy and the effective mass of the dressed impurity by including the two-body bound state, which is crucial for strong interactions, in the integral equation for the effective interaction. Using the same method, we also give the results for the polaron parameters in one and three dimensions and find good agreement with previous results. Thus, our relations can be used as a simple way to estimate the polaron parameters once the two-body bound state of the interaction potential is known.

  9. Magnetic polaron on dangling-bond spins in CdSe colloidal nanocrystals.

    PubMed

    Biadala, Louis; Shornikova, Elena V; Rodina, Anna V; Yakovlev, Dmitri R; Siebers, Benjamin; Aubert, Tangi; Nasilowski, Michel; Hens, Zeger; Dubertret, Benoit; Efros, Alexander L; Bayer, Manfred

    2017-03-13

    Non-magnetic colloidal nanostructures can demonstrate magnetic properties typical for diluted magnetic semiconductors because the spins of dangling bonds at their surface can act as the localized spins of magnetic ions. Here we report the observation of dangling-bond magnetic polarons (DBMPs) in 2.8-nm diameter CdSe colloidal nanocrystals (NCs). The DBMP binding energy of 7 meV is measured from the spectral shift of the emission lines under selective laser excitation. The polaron formation at low temperatures occurs by optical orientation of the dangling-bond spins (DBSs) that result from dangling-bond-assisted radiative recombination of spin-forbidden dark excitons. Modelling of the temperature dependence of the DBMP-binding energy and emission intensity shows that the DBMP is composed of a dark exciton and about 60 DBSs. The exchange integral of one DBS with the electron confined in the NC is ∼0.12 meV.

  10. Magnetic hard gap due to bound magnetic polarons in the localized regime

    PubMed Central

    Rimal, Gaurab; Tang, Jinke

    2017-01-01

    We investigate the low temperature electron transport properties of manganese doped lead sulfide films. The system shows variable range hopping at low temperatures that crosses over into an activation regime at even lower temperatures. This crossover is destroyed by an applied magnetic field which suggests a magnetic origin of the hard gap, associated with bound magnetic polarons. Even though the gap forms around the superconducting transition temperature of lead, we do not find evidence of this being due to insulator-superconductor transition. Comparison with undoped PbS films, which do not show the activated transport behavior, suggests that bound magnetic polarons create the hard gap in the system that can be closed by magnetic fields. PMID:28176857

  11. Spin-polaron nature of fermion quasiparticles and their d-wave pairing in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Val'kov, V. V.; Dzebisashvili, D. M.; Barabanov, A. F.

    2016-11-01

    In the framework of the spin-fermion model, to which the Emery model is reduced in the limit of strong electron correlations, it is shown that the fermion quasiparticles in cuprate high- T c superconductors (HTSCs) arise under a strong effect of exchange coupling between oxygen holes and spins of copper ions. This underlies the spin-polaron nature of fermion quasiparticles in cuprate HTSCs. The Cooper instability with respect to the d-wave symmetry of the order parameter is revealed for an ensemble of such quasiparticles. For the normal phase, the spin-polaron concept allows us to reproduce the fine details in the evolution of the Fermi surface with the changes in the doping level x observed in experiment for La2-xSrxCuO4. The calculated T-x phase diagram correlates well with the available experimental data for cuprate HTSCs.

  12. Tunable breakdown of the polaron picture for mobile impurities in a topological semimetal

    NASA Astrophysics Data System (ADS)

    Caracanhas, M. A.; Pereira, R. G.

    2016-12-01

    Mobile impurities in cold atomic gases constitute a new platform for investigating polaron physics. Here we show that when impurity atoms interact with a two-dimensional Fermi gas with quadratic band touching, the polaron picture may either hold or break down depending on the particle-hole asymmetry of the band structure. If the hole band has a smaller effective mass than the particle band, the quasiparticle is stable and its diffusion coefficient varies with temperature as D (T ) ∝ln2T . If the hole band has larger mass, the quasiparticle weight vanishes at low energies due to an emergent orthogonality catastrophe. In this case we map the problem onto a set of one-dimensional channels and use conformal field theory techniques to obtain D (T ) ∝Tν with an interaction-dependent exponent ν . The different regimes can be detected in the nonequilibrium expansion dynamics of an initially confined impurity.

  13. Polaron Coherence Condensation As the Mechanism for Colossal Magnetoresistance in Layered Manganites

    SciTech Connect

    Mannella, N.; Yang, W.L.; Tanaka, K.; Zhou, X.J.; Zheng, H.; Mitchell, J.F.; Zaanen, J.; Devereaux, T.P.; Nagaosa, N.; Hussain, Z.; Shen, Z.-X.; /SLAC

    2007-11-20

    Angle-resolved photoemission spectroscopy data for the bilayer manganite La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} show that, upon lowering the temperature below the Curie point, a coherent polaronic metallic groundstate emerges very rapidly with well defined quasiparticles which track remarkably well the electrical conductivity, consistent with macroscopic transport properties. Our data suggest that the mechanism leading to the insulator-to-metal transition in La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} can be regarded as a polaron coherence condensation process acting in concert with the Double Exchange interaction.

  14. Electric and magnetic optical polaron in quantum dot—Part 1: strong coupling

    NASA Astrophysics Data System (ADS)

    Fotue, A. J.; Issofa, N.; Tiotsop, M.; Kenfack, S. C.; Tabue Djemmo, M. P.; Fotsin, H.; Fai, L. C.

    2015-07-01

    We investigated the influence of electric field and magnetic field on the ground state energy of polaron in spherical semiconductor quantum dot (QD) using a modified Lee Low Pines (LLP) method. The numerical results show the increase of the ground state energy with the increase of the electric field and the decreasing with the magnetic field. The modulation of the electric field, magnetic field and the confinement lengths lead to the control of the decoherence of the system.

  15. Polaronic atom-trimer continuity in three-component Fermi gases.

    PubMed

    Nishida, Yusuke

    2015-03-20

    Recently it has been proposed that three-component Fermi gases may exhibit a new type of crossover physics in which an unpaired Fermi sea of atoms smoothly evolves into that of trimers in addition to the ordinary BCS-BEC crossover of condensed pairs. Here we study its corresponding polaron problem in which a single impurity atom of one component interacts with condensed pairs of the other two components with equal populations. By developing a variational approach in the vicinity of a narrow Feshbach resonance, we show that the impurity atom smoothly changes its character from atom to trimer with increasing the attraction and eventually there is a sharp transition to dimer. The emergent polaronic atom-trimer continuity can be probed in ultracold atoms experiments by measuring the impurity spectral function. Our novel crossover wave function properly incorporating the polaronic atom-trimer continuity will provide a useful basis to further investigate the phase diagram of three-component Fermi gases in more general situations.

  16. Mapping polarons in polymer FETs by charge modulation microscopy in the mid-infrared

    PubMed Central

    Chin, Xin Yu; Yin, Jun; Wang, Zilong; Caironi, Mario; Soci, Cesare

    2014-01-01

    We implemented spatial mapping of charge carrier density in the channel of a conventional polymer Field-Effect Transistor (FET) by mid-infrared Charge Modulation Spectroscopy (CMS). CMS spectra are recorded with a high sensitivity confocal Fourier Transform Infra-Red (FTIR) microscope by probing electroinduced Infra-Red Active Vibrational (IRAV) modes and low-energy polaron bands in the spectral region 680–4000 cm−1. Thanks to the high specificity and strong oscillator strength of these modes, charge-induced reflectance measurements allow quantitative estimation of charge carrier densities within the FET channel, without the need for amplitude or phase modulation. This is illustrated by identifying the contribution of intrinsic and electrostatically induced polarons to conduction, and by mapping the polaron spatial distribution in a P3HT (Poly(3-hexylthiophene-2,5-diyl)) FET channel under different drain-source bias conditions. This work demonstrates the potential of mid-infrared charge modulation microscopy to characterize carrier injection and transport in semiconducting polymer materials. PMID:24406635

  17. DFT +U Modeling of Hole Polarons in Organic Lead Halide Perovskites

    NASA Astrophysics Data System (ADS)

    Welch, Eric; Erhart, Paul; Scolfaro, Luisa; Zakhidov, Alex

    Due to the ever present drive towards improved efficiencies in solar cell technology, new and improved materials are emerging rapidly. Organic halide perovskites are a promising prospect, yet a fundamental understanding of the organic perovskite structure and electronic properties is missing. Particularly, explanations of certain physical phenomena, specifically a low recombination rate and high mobility of charge carriers still remain controversial. We theoretically investigate possible formation of hole polarons adopting methodology used for oxide perovskites. The perovskite studied here is the ABX3structure, with A being an organic cation, B lead and C a halogen; the combinations studied allow for A1,xA2 , 1 - xBX1,xX2 , 3 - xwhere the alloy convention is used to show mixtures of the organic cations and/or the halogens. Two organic cations, methylammonium and formamidinium, and three halogens, iodine, chlorine and bromine are studied. Electronic structures and polaron behavior is studied through first principle density functional theory (DFT) calculations using the Vienna Ab Initio Simulation Package (VASP). Local density approximation (LDA) pseudopotentials are used and a +U Hubbard correction of 8 eV is added; this method was shown to work with oxide perovskites. It is shown that a localized state is realized with the Hubbard correction in systems with an electron removed, residing in the band gap of each different structure. Thus, hole polarons are expected to be seen in these perovskites.

  18. Magnetic polarons in type-II (Zn,Mn)Se/ZnTe quantum dots

    NASA Astrophysics Data System (ADS)

    Murphy, J. R.; Barman, B.; Tsai, Y.; Scrace, T.; Pientka, J. M.; Zutic, I.; McCombe, B. D.; Petrou, A.; Cartwright, A. N.; Chou, W. C.; Tsou, M. H.; Yang, C. S.; Sellers, I. R.; Oszwaldowski, R.; Petukhov, A. G.

    2014-03-01

    We have studied magnetic polaron formation dynamics in (Zn,Mn)Se/ZnTe quantum dots2 (QDs) using time-resolved photoluminescence (TRPL) spectroscopy. The emitted light was spectrally and temporally analyzed; the emission spectra were recorded as function of time delay (Δt) from the exciting laser pulse. The recombination time at T = 10 K in our samples is 2.3 ns. The peak energy of the emission red shifts with increasing Δt due to the lowering of the hole-Mn spin complex (magnetic polaron) energy. From this shift we determined the magnetic polaron formation energy (EMP) at T = 10 K to be 20 meV, which is half the value observed in the ZnSe/(Zn,Mn)Te system studied previously.3EMP decreases with increasing temperature, in contrast to the behavior of the ZnSe/(Zn,Mn)Te system3 in which EMP is temperature independent. These results are discussed in terms of a theoretical model. This work is supported by DOE-BES, ONR and NSF.

  19. Energy Migration in Organic Thin Films--From Excitons to Polarons

    NASA Astrophysics Data System (ADS)

    Mullenbach, Tyler K.

    The rise of organic photovoltaic devices (OPVs) and organic light-emitting devices has generated interest in the physics governing exciton and polaron dynamics in thin films. Energy transfer has been well studied in dilute solutions, but there are emergent properties in thin films and greater complications due to complex morphologies which must be better understood. Despite the intense interest in energy transport in thin films, experimental limitations have slowed discoveries. Here, a new perspective of OPV operation is presented where photovoltage, instead of photocurrent, plays the fundamental role. By exploiting this new vantage point the first method of measuring the diffusion length (LD) of dark (non-luminescent) excitons is developed, a novel photodetector is invented, and the ability to watch exciton arrival, in real-time, at the donor-acceptor heterojunction is presented. Using an enhanced understanding of exciton migration in thin films, paradigms for enhancing LD by molecular modifications are discovered, and the first exciton gate is experimentally and theoretically demonstrated. Generation of polarons from exciton dissociation represents a second phase of energy migration in OPVs that remains understudied. Current approaches are capable of measuring the rate of charge carrier recombination only at open-circuit. To enable a better understanding of polaron dynamics in thin films, two new approaches are presented which are capable of measuring both the charge carrier recombination and transit rates at any OPV operating voltage. These techniques pave the way for a more complete understanding of charge carrier kinetics in molecular thin films.

  20. Small polaron dynamics: A self-consistent nonlinear spin-field model

    NASA Astrophysics Data System (ADS)

    Feinberg, D.; Ranninger, J.

    1984-12-01

    The motion of an electron strongly and locally coupled to the lattice deformation is considered as a dynamical system. Our study is based on a model where the electron remains to two adjacent diatomic molecules vibrating around positions which evolve in time as the charge distribution of the electron gradually shifts from one of the molecules to the other one. This model is cast into an intuitively more accesible model of spin {1}/{2} in an external field plus a reaction field. Within a semiclassical approach this is a Hamiltonian system expressed with two sets of action-angle variables. We show how the regular trajectories (describing the cooperative mechanism between the charge transfer and rearrangement of the molecular positions) in this phase space gradually disappear and global stochasticity sets in as either the ratio of the electron hopping rate over the electron-lattice coupling constant or the total energy is varied.

  1. Detailed Relationship Between Local Structure Polarons and Magnetization for La1-xCaxMnO3 (0.21 lt x lt 0.45)

    SciTech Connect

    F Bridges; L Downward; J Neumeier; T Tyson

    2011-12-31

    We present detailed local structure measurements (using the extended x-ray absorption fine structure technique) for the colossal magnetoresistive material La{sub 1-x}Ca{sub x}MnO{sub 3} (0.21 < x < 0.45) as a function of temperature and magnetic field. The local distortions of the Mn-O bonds are parameterized using {sigma}, the width of the Mn-O pair-distribution function (PDF). After subtracting thermal phonon contributions, we show that the contributions to {sigma}{sup 2} from polaron and Jahn-Teller (JT) distortions, {sigma}{sub JT/polaron}{sup 2}, are a universal function of the magnetization, independent of how the magnetization is achieved via changes in temperature or magnetic field. However this universal behavior is only observed for B fields {ge} 2 T, likely as a result of domain canting in low B fields. The resulting curve is well described by two straight lines with significantly different slopes. These regimes represent two distinctly differ distortions of the oxygen octahedra about the Mn. For low magnetizations up to {approx}65% of the theoretical maximum magnetization, M{sub T}, the slope is low and the distortion removed as the sample becomes magnetized is small - we argue this arises from polarons which have a low distortion around two (or possibly three) Mn sites. At high magnetizations large distortions per Mn site are removed as these sites become magnetized. The data are also analyzed in terms of a two Mn-O peak distribution using experimental standards for Mn-O. The results agree well with recent neutron PDF results but not with some earlier results. We discuss the limitations of assuming a two peak distribution in view of the two distortions needed to describe the Mn-O distortions as a function of T and B for B {ge} 2 T. It is likely that there is a distribution of longer bonds. Finally we show that with increasing B field, the Mn-Mn peak also has a small B-field-induced change - a measure at the unit cell level of magnetostriction but find

  2. Acceptor and Excitation Density Dependence of the Ultrafast Polaron Absorption Signal in Donor-Acceptor Organic Solar Cell Blends.

    PubMed

    Zarrabi, Nasim; Burn, Paul L; Meredith, Paul; Shaw, Paul E

    2016-07-21

    Transient absorption spectroscopy on organic semiconductor blends for solar cells typically shows efficient charge generation within ∼100 fs, accounting for the majority of the charge carriers. In this Letter, we show using transient absorption spectroscopy on blends containing a broad range of acceptor content (0.01-50% by weight) that the rise of the polaron signal is dependent on the acceptor concentration. For low acceptor content (<10% by weight), the polaron signal rises gradually over ∼1 ps with most polarons generated after 200 fs, while for higher acceptor concentrations (>10%) most polarons are generated within 200 fs. The rise time in blends with low acceptor content was also found to be sensitive to the pump fluence, decreasing with increasing excitation density. These results indicate that the sub-100 fs rise of the polaron signal is a natural consequence of both the high acceptor concentrations in many donor-acceptor blends and the high excitation densities needed for transient absorption spectroscopy, which results in a short average distance between the exciton and the donor-acceptor interface.

  3. Effects of Lattice Vibration on the Properties of the Strong-Coupling Polaron in a Quantum Well

    NASA Astrophysics Data System (ADS)

    Eerdunchaol; Xiao, J. L.

    2007-04-01

    In this paper, the effects of lattice vibration on the properties of the polaron, which is weakly coupled with bulk longitudinal optical (LO) phonons and strongly coupled with interface optical (IO) phonons, in an infinite quantum well are studied by means of Huybrechts’ linear-combination operator and the modified Lee-Low-Pines (LLP) variational method. The expressions for the self-trapping energy of the polaron in a quantum well as a function of the well width and temperature were derived. In particular, the law governing the change of the vibration frequency of the polaron with changing well width and temperature is obtained for the first time. Numerical results of the polaron self-trapping energy and the vibration frequency for KI/AgCl/KI QW show that the vibration frequency and the self-trapping energy of the polaron decrease with increasing well width and temperature, but the contributions of the interaction between the electron and the different branches of phonons to the self-trapping energy, the vibration frequency and the change of their variation with well width and temperature differ markedly.

  4. Polaron effects on the optical rectification and the second harmonic generation in cylindrical quantum dots with magnetic field

    NASA Astrophysics Data System (ADS)

    Liu, Guanghui; Guo, Kangxian; Wu, Qingjie; Wu, Jing-He

    2013-01-01

    Polaron effects on the optical rectification (OR) and the second harmonic generation (SHG) in cylindrical quantum dots (CQDs) with the radial parabolic potential and the z-direction linear potential in the presence of the magnetic field are theoretically investigated. The expressions for both the OR and the SHG are obtained within the framework of the compact-density-matrix approach and the iterative method. After considering the electron-LO-phonon interaction (ELOPI) as perturbation, the energy levels and the wave functions of an electron confined in CQD are obtained by perturbation theory. Numerical calculations are presented for GaAs/AlGaAs. It is found that when we consider the ELOPI, the resonant peak of the OR χ0(2) is enhanced, whereas the magnitude of the SHG χ2ω(2) is greatly enhanced. It is also found that when we ignore the ELOPI, with the increase of the radial confinement frequency ωρ and the magnetic field B, respectively, the resonant peak of the OR χ0(2) remains constant, whereas the magnitude of the SHG χ2ω(2) becomes small. However, when we consider the ELOPI, with the increase of ωρ,B and V respectively, both the resonant peak of the OR χ0(2) and the magnitude of the SHG χ2ω(2) become small. Our results also find that whether the ELOPI is considered or not, with the increase of ωρ, B and V, respectively, both χ0(2) and χ2ω(2) exhibit a blue shift.

  5. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Spin Polaron in a Diluted Parabolic Magnetic Quantum Well

    NASA Astrophysics Data System (ADS)

    Peter, A. John; Zheng, Jin-Liang

    2010-04-01

    Theoretical investigations of spin polaron in a quantum well in the spin doping superlattice systems Cd1 - xin Mn1 - xout Te/Cd1 - xout Mnxout Te are presented in this paper. A variational procedure within the effective mass approximation is employed in the presence of magnetic held to calculate the donor ionization energy. Spin polaronic shifts are estimated using a mean held theory. The results show that the donor binding energy (i) Increases with the reduction in well sizes (ii) Decreases with the magnetic held is increased for a given well width (iii) Increases to a maximum value at 90 Å and then decreases as the size of the well increases beyond 90 Å and (iv) Spin polaronic shifts to the donor binding energy not only decrease in a magnetic held but also with the well width. The results are compared with the existing available literature.

  6. Temperature Dependence of the Properties of the Strong-Coupling Polaron in a Slab of Polar Crystal

    NASA Astrophysics Data System (ADS)

    Bao, Eerdunchaolu; Xiao, J. L.

    2003-03-01

    In this paper, the temperature dependence of the properties of polaron, which is weakly coupled with bulk LO phonons and strongly coupled with SO phonons, in a slab of polar crystal is studied by means of a modified second LLP transformation for the first time. An expressions for the self-trapping energy and the effective mass of the polaron in a slab of polar crystal as a function of the temperature and slab thickness are derived by using a linear combination operator and two modified LLP variational method. Our numerical results of the self-trapping energy and the effective mass for KCl show that the polaron self-trapping energy and effective mass in a polar crystal are strongly related to the slab thickness and the temperature. The self-trapping energy and the effective mass will decrease with increasing slab thickness and temperature.

  7. Signature of polaron formation in Na0.025WO3: Photoemission and X-ray diffraction investigations

    NASA Astrophysics Data System (ADS)

    Paul, Sanhita; Ghosh, Anirudha; Raj, Satyabrata

    2013-06-01

    We have carried out temperature dependent high-resolution angle-resolved photoemission spectroscopy and x-ray diffraction studies on non-stoichiometric sodium tungsten bronzes (NaxWO3 for x=0.025). Our photoemission investigation shows evidence for polaron formation at the valence band edge and the photoemission spectra collected in different modes of the electron analyzer suggest that the density of states at valence band edge gradually moves to other k-points in the Brillouin zone with increasing temperature and explain the dynamics of polaron formation in Na0.025WO3. Infact our x-ray diffraction measurements reveal a structural modification of Na0.025WO3 around 230K. The corner sharing WO6 octadedra gets sufficiently distorted at low temperature due to displacement of tugsten and oxygen atoms from their mean position. This structural modification induces polaron formation in Na0.025WO3 below 230K.

  8. Repulsive Fermi Polarons in a Resonant Mixture of Ultracold ^{6}Li Atoms.

    PubMed

    Scazza, F; Valtolina, G; Massignan, P; Recati, A; Amico, A; Burchianti, A; Fort, C; Inguscio, M; Zaccanti, M; Roati, G

    2017-02-24

    We employ radio-frequency spectroscopy to investigate a polarized spin mixture of ultracold ^{6}Li atoms close to a broad Feshbach scattering resonance. Focusing on the regime of strong repulsive interactions, we observe well-defined coherent quasiparticles even for unitarity-limited interactions. We characterize the many-body system by extracting the key properties of repulsive Fermi polarons: the energy E_{+}, the effective mass m^{*}, the residue Z, and the decay rate Γ. Above a critical interaction, E_{+} is found to exceed the Fermi energy of the bath, while m^{*} diverges and even turns negative, thereby indicating that the repulsive Fermi liquid state becomes energetically and thermodynamically unstable.

  9. Repulsive Fermi Polarons in a Resonant Mixture of Ultracold 6Li Atoms

    NASA Astrophysics Data System (ADS)

    Scazza, F.; Valtolina, G.; Massignan, P.; Recati, A.; Amico, A.; Burchianti, A.; Fort, C.; Inguscio, M.; Zaccanti, M.; Roati, G.

    2017-02-01

    We employ radio-frequency spectroscopy to investigate a polarized spin mixture of ultracold 6Li atoms close to a broad Feshbach scattering resonance. Focusing on the regime of strong repulsive interactions, we observe well-defined coherent quasiparticles even for unitarity-limited interactions. We characterize the many-body system by extracting the key properties of repulsive Fermi polarons: the energy E+, the effective mass m*, the residue Z , and the decay rate Γ . Above a critical interaction, E+ is found to exceed the Fermi energy of the bath, while m* diverges and even turns negative, thereby indicating that the repulsive Fermi liquid state becomes energetically and thermodynamically unstable.

  10. Energy levels of magneto-optical polaron in spherical quantum dot — Part 1: Strong coupling

    NASA Astrophysics Data System (ADS)

    Fotue, A. J.; Kenfack, S. C.; Issofa, N.; Tiotsop, M.; Fotsin, H.; Mainimo, E.; Fai, L. C.

    2015-09-01

    We investigate the influence of a magnetic field on the ground state energy of a polaron in a spherical semiconductor quantum dot (QD) using the modified LLP method. The ground state energy is split into sub-energy levels and there is a degeneracy of energy levels. It is also observed that the degenerate energy increase with the electron-phonon coupling constant and decrease with the magnetic field. The numerical results show that, under the influence of magnetic field and the interaction with the total momentum along the z-direction, the split energy increases and decreases with the longitudinal and the transverse confinement length, respectively.

  11. Ab initio prediction of fast non-equilibrium transport of nascent polarons in SrI2: a key to high-performance scintillation

    NASA Astrophysics Data System (ADS)

    Zhou, Fei; Sadigh, Babak; Erhart, Paul; Åberg, Daniel

    2016-08-01

    The excellent light yield proportionality of europium-doped strontium iodide (SrI2:Eu) has resulted in state-of-the-art γ-ray detectors with remarkably high-energy resolution, far exceeding that of most halide compounds. In this class of materials, the formation of self-trapped hole polarons is very common. However, polaron formation is usually expected to limit carrier mobilities and has been associated with poor scintillator light-yield proportionality and resolution. Here using a recently developed first-principles method, we perform an unprecedented study of polaron transport in SrI2, both for equilibrium polarons, as well as nascent polarons immediately following a self-trapping event. We propose a rationale for the unexpected high-energy resolution of SrI2. We identify nine stable hole polaron configurations, which consist of dimerised iodine pairs with polaron-binding energies of up to 0.5 eV. They are connected by a complex potential energy landscape that comprises 66 unique nearest-neighbour migration paths. Ab initio molecular dynamics simulations reveal that a large fraction of polarons is born into configurations that migrate practically barrier free at room temperature. Consequently, carriers created during γ-irradiation can quickly diffuse away reducing the chance for non-linear recombination, the primary culprit for non-proportionality and resolution reduction. We conclude that the flat, albeit complex, landscape for polaron migration in SrI2 is a key for understanding its outstanding performance. This insight provides important guidance not only for the future development of high-performance scintillators but also of other materials, for which large polaron mobilities are crucial such as batteries and solid-state ionic conductors.

  12. Hybrid em wave - polar semiconductor interaction: A polaronic study

    SciTech Connect

    Paliwal, Ayushi Dubey, Swati; Ghosh, S.

    2015-07-31

    Present paper considers incidence of a most realistic hybrid pump wave on a weakly polar semiconductor having a very small coupling constant. Possibility of optical parametric interaction has been explored in the presence of an external transverse magnetic field. The effect of doping concentrations and transverse magnetostatic field on threshold characteristics of optical parametric interaction in polar semiconductor plasma has been studied, using hydrodynamic model of semiconductors, in the far infrared regime. Numerical estimations have been carried out by using data of weakly polar III-V GaAs semiconductor and influence of control parameters on electron-LO phonon interaction has been analyzed. A particular range of physical parameters is found to be suitable for minimum threshold. The choice of nonlinear medium and favorable range of operating parameters are crucial aspects in design and fabrication of parametric amplifiers and oscillators. The hybrid mode of the pump is found to be favorable for the onset of the said process and realization of a low cost amplifier.

  13. Polaron effects on the dc- and ac-tunneling characteristics of molecular Josephson junctions

    NASA Astrophysics Data System (ADS)

    Wu, B. H.; Cao, J. C.; Timm, C.

    2012-07-01

    We study the interplay of polaronic effect and superconductivity in transport through molecular Josephson junctions. The tunneling rates of electrons are dominated by vibronic replicas of the superconducting gap, which show up as prominent features in the differential conductance for the dc and ac current. For relatively large molecule-lead coupling, a features that appears when the Josephson frequency matches the vibron frequency can be identified with an over-the-gap structure observed by Marchenkov [Nat. Nanotech. 1748-338710.1038/nnano.2007.2182, 481 (2007)]. However, we are more concerned with the weak-coupling limit, where resonant tunneling through the molecular level dominates. We find that certain features involving both Andreev reflection and vibron emission show an unusual shift of the bias voltage V at their maximum with the gate voltage Vg as V˜(2/3)Vg. Moreover, due to the polaronic effect, the ac Josephson current shows a phase shift of π when the bias eV is increased by one vibronic energy quantum ℏωv. This distinctive even-odd effect is explained in terms of the different sign of the coupling to vibrons of electrons and of Andreev-reflected holes.

  14. Density functional theory + U modeling of polarons in organohalide lead perovskites

    NASA Astrophysics Data System (ADS)

    Welch, Eric; Scolfaro, Luisa; Zakhidov, Alex

    2016-12-01

    We investigate the possible formation of polarons in four organic perovskites (CH3NH3PbI3, CH3NH3PbBr3, CH3NH3PbCl3, and CH3NH3PbI2Cl1) using a density functional theory (DFT) calculations with local potentials and hybrid functionals. We show that DFT+U method with U = 8 eV predicts a correct band-gap and matches the forces on ions from hybrid calculations. We then use the DFT + U approach to study the effect of polarons, i.e. to search the configuration space and locate the lowest energy localized band gap state self-trapped hole (STH). STH configurations were found for three pure halides and one mixed halide system. Spin orbit coupling (SOC) was also taken into account and the results may be found in the supplementary material. This study focuses on the +U method; however, SOC corrections added to the DFT+U calculations also resulted in STH states in all four systems.

  15. Madelung and Hubbard interactions in polaron band model of doped organic semiconductors

    PubMed Central

    Png, Rui-Qi; Ang, Mervin C.Y.; Teo, Meng-How; Choo, Kim-Kian; Tang, Cindy Guanyu; Belaineh, Dagmawi; Chua, Lay-Lay; Ho, Peter K.H.

    2016-01-01

    The standard polaron band model of doped organic semiconductors predicts that density-of-states shift into the π–π* gap to give a partially filled polaron band that pins the Fermi level. This picture neglects both Madelung and Hubbard interactions. Here we show using ultrahigh workfunction hole-doped model triarylamine–fluorene copolymers that Hubbard interaction strongly splits the singly-occupied molecular orbital from its empty counterpart, while Madelung (Coulomb) interactions with counter-anions and other carriers markedly shift energies of the frontier orbitals. These interactions lower the singly-occupied molecular orbital band below the valence band edge and give rise to an empty low-lying counterpart band. The Fermi level, and hence workfunction, is determined by conjunction of the bottom edge of this empty band and the top edge of the valence band. Calculations are consistent with the observed Fermi-level downshift with counter-anion size and the observed dependence of workfunction on doping level in the strongly doped regime. PMID:27582355

  16. Excitonic-type polaron states: photoluminescence in SBN and in other ferroelectric oxides

    NASA Astrophysics Data System (ADS)

    Vikhnin, V. S.; Kislova, I.; Kutsenko, A. B.; Kapphan, S. E.

    2002-07-01

    A theoretical model for two characteristic photoluminescence (PL) bands in SBN, 'green luminescence' and 'red luminescence' is proposed on the basis of the extended photoluminescence experiments in SBN:Cr, and also in SBN:Ce and in nominally pure SBN systems under different conditions. While the RL-band is suggested to be connected with charge transfer vibronic exciton (CTVE) clusters induced by Cr3+ impurities in the Nb-sites, the GL- band is connected with Nb4+ electronic polarons in a new, charge transfer excited states. Here Nb4+ centers are the cores of the CTVE clusters induced by these charged scores. The PL mechanism is the in-cluster CTVE recombination for both bands under discussion. But the CTVE states are quasi-resonantly mixed here with 4T2 states of the Cr3+ core in the RL-band case, and with 5s-states of the Nb4+ core in the GL-band case. The role of excitonic polarons of CTVE nature is also discussed in connection with 'green' luminescence origin in KTaO3 and KNbO3 crystals.

  17. Photochromism and polaronic photocharge localization in diluted KTa1-xNbxO3

    NASA Astrophysics Data System (ADS)

    Gubaev, A. I.; Kapphan, S. E.; Jastrabik, L.; Trepakov, V. A.; Syrnikov, P. P.

    2006-07-01

    Ultraviolet (UV)-light-induced optical absorption in the near infrared (NIR) region was observed in diluted KTa1-xNbxO3 single crystals (x =0,0.004,0.007,0.012,0.07) at low temperatures. Illumination by wideband light (3.10-4.13eV, 300-400nm) is accompanied by the appearance of a broad NIR absorption band with the position of the maxima varying in the 0.69-0.8eV (1.54-1.79μ, T =1.3K) region for different Nb concentrations. This UV-light-induced absorption is absent in nominally pure KTaO3, as well as in all Nb diluted specimens at elevated temperatures. The centers responsible for the photochromic NIR absorption bands are tied to interband optical transitions of pair Nb4+ electronic polarons. The photochromic experimental data, supplemented by luminescence studies in the visible range, evidence the strong localization of the photocharge carriers by pair Nb4+ polarons at low temperatures. It is suggested that namely the strong localization of the photocarriers plays a crucial role in photoinduced gigantic dielectric effects and possible phase transitions, which have been recognized recently in incipient ferroelectrics at low temperatures.

  18. Doping-Induced Absorption Bands in P3HT: Polarons and Bipolarons.

    PubMed

    Enengl, Christina; Enengl, Sandra; Pluczyk, Sandra; Havlicek, Marek; Lapkowski, Mieczyslaw; Neugebauer, Helmut; Ehrenfreund, Eitan

    2016-12-05

    In this work, we focus on the formation of different kinds of charge carriers such as polarons and bipolarons upon p-type doping (oxidation) of the organic semiconductor poly(3- hexylthiophene-2,5-diyl) (P3HT). We elucidate the cyclic voltammogram during oxidation of this polymer and present spectroscopic changes upon doping in the UV/Vis/near-IR range as well as in the mid-IR range. In the low-oxidation regime, two absorption bands related to sub-gap transitions appear, one in the UV/Vis range and another one in the mid-IR range. The UV/Vis absorption gradually decreases upon further doping while the mid-IR absorption shifts to lower energy. Additionally, electron paramagnetic resonance (EPR) measurements are performed, showing an increase of the EPR signal up to a certain doping level, which significantly decreases upon further doping. Furthermore, the absorption spectra in the UV/Vis range are analyzed in relation to the morphology (crystalline vs. amorphous) by using theoretical models. Finally, the calculated charge carriers from cyclic voltammogram are linked together with optical transitions as well as with the EPR signals upon p-type doping. We stress that our results indicate the formation of polarons at low doping levels and the existence of bipolarons at high doping levels. The presented spectroscopic data are an experimental evidence of the formation of bipolarons in P3HT.

  19. The influence of built-in electric field on binding energy of bound polaron and polaron effects in wurtzite ZnO/MgxZn1-xO quantum well

    NASA Astrophysics Data System (ADS)

    Zhao, Feng-qi; Guo, Zi-Zheng; Zhu, Jun

    2016-10-01

    The influence of the built-in electric field on the binding energy of a bound polaron and the polaron effect in a wurtzite ZnO/MgxZn1-xO quantum well are studied using the improved Lee-Low-Pines intermediate coupling method. The ground-state binding energy, the contributions from different branches of optical phonons to the energy and the binding energy are presented as the functions of well width, impurity position and composition. In the numerical calculations, the anisotropic properties of the frequencies of the different branches of optical phonons, electron effective mass, dielectric constant, the electron-optical phonon interaction and the impurity center-optical phonon interaction are considered. The results show that the built-in electric field has obvious influence on the energy, the binding energy and the polaron effect, and it affects the contributions of different phonon modes to the energy and the binding energy with different degrees. The built-in electric field significantly increases the total phonon contribution to the energy, but it reduces the total phonon contribution to the binding energy. The binding energy of the bound polaron with the built-in electric field is less than that without the built-in electric field, and it declines rapidly with increasing well width. Because of the built-in electric field effects, the contributions from different branches of phonons to the energy and the binding energy and the functions of binding energy with well width and impurity center position are different from the cases without the built-in electric field. The built-in electric field in the wurtzite ZnO/MgxZn1-xO quantum wells has a great impact on the binding energy and polaron effect, and the polaron effect in the wurtzite ZnO/MgxZn1-xO quantum wells is significantly greater than that in the zinc blende GaAs/AlxGa1-xAs QWs, hence, it is necessary to discuss the built-in electric field and polaron effect when considering the problem of electronic state

  20. Fermi polaron in a one-dimensional quasiperiodic optical lattice: The simplest many-body localization challenge

    NASA Astrophysics Data System (ADS)

    Hu, Hui; Wang, An-Bang; Yi, Su; Liu, Xia-Ji

    2016-05-01

    We theoretically investigate the behavior of a moving impurity immersed in a sea of fermionic atoms that are confined in a quasiperiodic (bichromatic) optical lattice within a standard variational approach. We consider both repulsive and attractive contact interactions for such a simple many-body localization problem of Fermi polarons. The variational approach enables us to access relatively large systems and therefore may be used to understand many-body localization in the thermodynamic limit. The energy and wave function of the polaron states are found to be strongly affected by the quasirandom lattice potential and their experimental measurements (i.e., via radio-frequency spectroscopy or quantum gas microscope) therefore provide a sensitive way to underpin the localization transition. We determine a phase diagram by calculating two critical quasirandom disorder strengths, which correspond to the onset of the localization of the ground-state polaron state and the many-body localization of all polaron states, respectively. Our predicted phase diagram could be straightforwardly examined in current cold-atom experiments.

  1. Kinetics of light-induced polaron- and VIS-centers in SBN:Ce single crystals at low temperature

    NASA Astrophysics Data System (ADS)

    Gubaev, A.; Kapphan, S.; Kislova, I.; Kutsenko, A.; Pankrath, R.; Vikhnin, V.

    2005-01-01

    The promising photorefractive crystal SrxBa1-xNb2O6 (SBN, congruent composition x = 0.61) can be doped with polyvalent ions like Ce to enhance photorefractive properties. Illumination with blue Ar+-laser light at low temperature creates light-induced NIR and VIS absorption bands. The NIR absorption has been identified as being due to Nb4+ electron polarons and their properties have been investigated in some detail. The VIS-Centers are less well understood and their nature is still under discussion. It has been shown by our previous measurements that illumination with red Kr+-laser light (647 nm) or red laser diodes (673 nm) leads to a dissociation of the VIS-Centers and a simultaneous build-up of a transient NIR-polaron absorption. We report here some new facts important for the simplified charge transfer model needed to describe quantitatively the equilibrium values and the dynamics of the NIR-polaron and VIS-center absorption. These features give new insight into the dynamic nature of these VIS-centers, which are currently being discussed as either bipolarons (in analogy to LiNbO3) or polarons trapped at charged centers, or charge transfer vibronic exitons (CTVEs) being trapped at charged centers.

  2. Binding Energy of a Bound Polaron in the Finite Parabolic Quantum Well

    NASA Astrophysics Data System (ADS)

    Zhao, Feng-Qi; Liang, Xi Xia

    We have studied the effect of the electron-phonon interaction on the energy levels of the bound polaron and calculated the ground-state energy, the binding energy of the ground state, and the 1s-->2p+/- transition energy in the GaAs/AlxGa1-xAs parabolic quantum well (PQW) structure by using a modified Lee-Low-Pines (LLP) variational method. The numerical results are given and discussed. It is found that the contribution of electron-phonon interaction to the ground-state energy and the binding energy is obvious, especially in large well-width PQWs. The electron-phonon interaction should not be neglected.

  3. Electro-magnetic weak coupling optical polaron and temperature effect in quantum dot

    NASA Astrophysics Data System (ADS)

    Tiotsop, M.; Fotue, A. J.; Kenfack, S. C.; Issofa, N.; Wirngo, A. V.; Tabue Djemmo, M. P.; Fotsin, H.; Fai, L. C.

    2015-10-01

    We investigate the influence of the electric field and magnetic fields on the ground state energy of a polaron in a spherical semiconductor quantum dot (QD) using the modified Lee Low Pines (LLP) method. The numerical results show the increase of the ground state energy with the increase of the electric field and the electron-phonon coupling constant, and the decrease with the magnetic field and the longitudinal confinement length. It is also seen that the temperature is an increasing function of the cyclotron frequency and the coupling constant whereas it decreases with the electric field strength. The modulation of the electric field, the magnetic field and the confinement length leads to the control of decoherence in the system.

  4. Phonon-mediated interactions and polaron formation of slow-light polaritons in a BEC

    NASA Astrophysics Data System (ADS)

    Haug, Hanna-Lena; Fleischhauer, Michael

    2014-05-01

    We study the motion of dark-state polaritons (DSP) in a Bose-Einstein condensate. DSPs are formed in an atomic ensemble interacting in a Λ-type configuration with two light fields under conditions of electromagnetically induced transparency. In particular, we consider the ground-state atoms to form a BEC which can be well described by a macroscopic Gross-Pitaevskii wavefunction. Taking into account the interaction of pairs of ground-state atoms and between ground and spin-state atoms leads to the formation of polaronic quasi-particles consisting of DSPs and Bogoliubov phonons. In additon, the coupling to phonons results into a coupling between dark and bright-state polaritons as well as into phonon-mediated interactions between DSPs.

  5. Polaron physics and crossover transition in magnetite probed by pressure-dependent infrared spectroscopy.

    PubMed

    Ebad-Allah, J; Baldassarre, L; Sing, M; Claessen, R; Brabers, V A M; Kuntscher, C A

    2013-01-23

    The optical properties of magnetite at room temperature were studied by infrared reflectivity measurements as a function of pressure up to 8 GPa. The optical conductivity spectrum consists of a Drude term, two sharp phonon modes, a far-infrared band at around 600 cm(-1) and a pronounced mid-infrared absorption band. With increasing pressure both absorption bands shift to lower frequencies and the phonon modes harden in a linear fashion. Based on the shape of the MIR band, the temperature dependence of the dc transport data, and the occurrence of the far-infrared band in the optical conductivity spectrum, the polaronic coupling strength in magnetite at room temperature should be classified as intermediate. For the lower energy phonon mode an abrupt increase of the linear pressure coefficient occurs at around 6 GPa, which could be attributed to minor alterations of the charge distribution among the different Fe sites.

  6. LETTER TO THE EDITOR: Quantum chemical modelling of electron polarons and excitons in ABO3 perovskites

    NASA Astrophysics Data System (ADS)

    Kotomin, E. A.; Eglitis, R. I.; Borstel, G.

    2000-09-01

    Quantum chemical calculations using the intermediate neglect of the differential overlap (INDO) method, combined with the large unit cell periodic model argue for an existence of the self-trapped electrons in KNbO3 and KTaO3 perovskite crystals. An electron in the ground state occupies predominantly t2g orbital of a Nb4+ ion. Its orbital degeneracy is lifted by a combination of the breathing and Jahn-Teller modes where four nearest equatorial O atoms are displaced outwards and two oxygens shift inwards along the z axis. Triplet exciton is shown to be in a good approximation of a pair of nearest Jahn-Teller electron and hole polarons (a bipolaron) which is very likely responsible for the `green' luminescence observed in these crystals.

  7. Inter-subband structure factor for a quasi-one-dimensional polaron gas

    NASA Astrophysics Data System (ADS)

    Machado, Paulo César Miranda; Osório, Francisco Aparecido Pinto; Borges, Antônio Newton

    2016-08-01

    In this work, the collective excitation spectra of quasi-one-dimensional plasmon in a rectangular GaAs quantum wire is investigated. Our calculations are performed within the Singwi, Tosi, Land and Sjölander (STLS) self-consistent theory taking into account the plasmon-longitudinal optical (LO) phonon coupling effects. We have employed a three subband model with only the first subband occupied by electrons and we have considered intra-subband and inter-subband transitions. We show that the polaronic effects cause the appearance of dips and oscillations in the static structure factor dispersion relation, which are directly related with the oscillator strength transfer between the collective excitation energy branches. We have also observed oscillations in the pair-correlation function that are characteristic of inter-subband transitions and it denotes partial localization of the particle.

  8. Nonadiabatic effects in a generalized Jahn-Teller lattice model: Heavy and light polarons, pairing, and the metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Majerníková, Eva; Riedel, J.; Shpyrko, S.

    2002-05-01

    The self-consistent ground state polaron potential of one-dimensional lattice of two-level molecules with spinless electrons and two dispersionless phonon modes with linear coupling and quantum phonon-assisted (nonadiabatic) transitions between the levels is found anharmonic in phonon displacements. As a function of these, the potential shows a crossover from two nonequivalent broad minima to a single narrow minimum which correspond to the positions of the levels in the ground state. Generalized variational approach respecting the mixing of levels (reflection) via a variational parameter implies prominent nonadiabatic effects: (i) In the limit of the symmetric E⊗e Jahn-Teller situation they cause transition between the regime of the predominantly one-level ``heavy'' polaron and a ``light'' polaron oscillating between the levels due to phonon assistance with almost vanishing polaron displacement. Vanishing polaron selflocalization implies enhancement of the electron transfer due to decrease of the ``heavy'' polaron mass (undressing) at the point of the transition. There can occur pairing of ``light'' polarons due to exchange of virtual phonons. Continuous transition to new energy ground state close to the transition from ``heavy'' polaron phase to ``light'' (bi)polaron phase occurs. In the ``heavy'' phase, we have found anomalous (anharmonic) enhancements of quantum fluctuations of the phonon coordinate, conjugated momentum and their product in the ground state as functions of the effective coupling which reach their maxima at E⊗e JT symmetry. They decrease rapidly to their harmonic values as soon as the ``light'' phase is stabilized. (ii) Nonadiabatic dependence of the polaron mass (Debye-Waller screening) on the optical phonon frequency appears. (iii) The contribution of Rabi oscillations to the transfer enhances significantly quantum shift of the insulator-metal transition line to higher values of the critical effective electron-phonon coupling supporting so

  9. Impurity bound states in fully gapped d-wave superconductors with subdominant order parameters.

    PubMed

    Mashkoori, Mahdi; Björnson, Kristofer; Black-Schaffer, Annica M

    2017-03-10

    Impurities in superconductors and their induced bound states are important both for engineering novel states such as Majorana zero-energy modes and for probing bulk properties of the superconducting state. The high-temperature cuprates offer a clear advantage in a much larger superconducting order parameter, but the nodal energy spectrum of a pure d-wave superconductor only allows virtual bound states. Fully gapped d-wave superconducting states have, however, been proposed in several cuprate systems thanks to subdominant order parameters producing d + is- or d + id'-wave superconducting states. Here we study both magnetic and potential impurities in these fully gapped d-wave superconductors. Using analytical T-matrix and complementary numerical tight-binding lattice calculations, we show that magnetic and potential impurities behave fundamentally different in d + is- and d + id'-wave superconductors. In a d + is-wave superconductor, there are no bound states for potential impurities, while a magnetic impurity produces one pair of bound states, with a zero-energy level crossing at a finite scattering strength. On the other hand, a d + id'-wave symmetry always gives rise to two pairs of bound states and only produce a reachable zero-energy level crossing if the normal state has a strong particle-hole asymmetry.

  10. Impurity bound states in fully gapped d-wave superconductors with subdominant order parameters

    PubMed Central

    Mashkoori, Mahdi; Björnson, Kristofer; Black-Schaffer, Annica M.

    2017-01-01

    Impurities in superconductors and their induced bound states are important both for engineering novel states such as Majorana zero-energy modes and for probing bulk properties of the superconducting state. The high-temperature cuprates offer a clear advantage in a much larger superconducting order parameter, but the nodal energy spectrum of a pure d-wave superconductor only allows virtual bound states. Fully gapped d-wave superconducting states have, however, been proposed in several cuprate systems thanks to subdominant order parameters producing d + is- or d + id′-wave superconducting states. Here we study both magnetic and potential impurities in these fully gapped d-wave superconductors. Using analytical T-matrix and complementary numerical tight-binding lattice calculations, we show that magnetic and potential impurities behave fundamentally different in d + is- and d + id′-wave superconductors. In a d + is-wave superconductor, there are no bound states for potential impurities, while a magnetic impurity produces one pair of bound states, with a zero-energy level crossing at a finite scattering strength. On the other hand, a d + id′-wave symmetry always gives rise to two pairs of bound states and only produce a reachable zero-energy level crossing if the normal state has a strong particle-hole asymmetry. PMID:28281570

  11. Impurity bound states in fully gapped d-wave superconductors with subdominant order parameters

    NASA Astrophysics Data System (ADS)

    Mashkoori, Mahdi; Björnson, Kristofer; Black-Schaffer, Annica M.

    2017-03-01

    Impurities in superconductors and their induced bound states are important both for engineering novel states such as Majorana zero-energy modes and for probing bulk properties of the superconducting state. The high-temperature cuprates offer a clear advantage in a much larger superconducting order parameter, but the nodal energy spectrum of a pure d-wave superconductor only allows virtual bound states. Fully gapped d-wave superconducting states have, however, been proposed in several cuprate systems thanks to subdominant order parameters producing d + is- or d + id‧-wave superconducting states. Here we study both magnetic and potential impurities in these fully gapped d-wave superconductors. Using analytical T-matrix and complementary numerical tight-binding lattice calculations, we show that magnetic and potential impurities behave fundamentally different in d + is- and d + id‧-wave superconductors. In a d + is-wave superconductor, there are no bound states for potential impurities, while a magnetic impurity produces one pair of bound states, with a zero-energy level crossing at a finite scattering strength. On the other hand, a d + id‧-wave symmetry always gives rise to two pairs of bound states and only produce a reachable zero-energy level crossing if the normal state has a strong particle-hole asymmetry.

  12. SEMICONDUCTOR PHYSICS: Pressure influence on bound polarons in a strained wurtzite GaN/AlxGa1-xN heterojunction under an electric field

    NASA Astrophysics Data System (ADS)

    Min, Zhang; Shiliang, Ban

    2010-05-01

    The binding energies of bound polarons near the interface of a strained wurtzite GaN/AlxGa1-xN heterojunction are studied by using a modified LLP variational method and a simplified coherent potential approximation under hydrostatic pressure and an external electric field. Considering the biaxial strain due to lattice mismatch or epitaxial growth, the uniaxial strain effects and the influences of the electron-phonon interaction as well as impurity-phonon interaction including the effects of interface-optical phonon modes and half-space phonon modes, the binding energies as functions of pressure, the impurity position, areal electron density and the phonon effect on the Stark energy shift are investigated. The numerical result shows that the contributions from the interface optical phonon mode with higher frequency and the LO-like half space mode to the binding energy and the Stark energy shift are important and obviously increase with increasing hydrostatic pressure, whereas the interface optical phonon mode with lower frequency and the TO-like half space mode are extremely small and are insensitive to the impurity position and hydrostatic pressure. It is also shown that the conductive band bending should not be neglected.

  13. Polaron effects on the performance of light-harvesting systems: a quantum heat engine perspective

    NASA Astrophysics Data System (ADS)

    Xu, Dazhi; Wang, Chen; Zhao, Yang; Cao, Jianshu

    2016-02-01

    We explore energy transfer in a generic three-level system, which is coupled to three non-equilibrium baths. Built on the concept of quantum heat engine, our three-level model describes non-equilibrium quantum processes including light-harvesting energy transfer, nano-scale heat transfer, photo-induced isomerization, and photovoltaics in double quantum-dots. In the context of light-harvesting, the excitation energy is first pumped up by sunlight, then is transferred via two excited states which are coupled to a phonon bath, and finally decays to the reaction center. The efficiency of this process is evaluated by steady state analysis via a polaron-transformed master equation; thus the entire range of the system-phonon coupling strength can be covered. We show that the coupling with the phonon bath not only modifies the steady state, resulting in population inversion, but also introduces a finite steady state coherence which optimizes the energy transfer flux and efficiency. In the strong coupling limit, the steady state coherence disappears and the efficiency recovers the heat engine limit given by Scovil and Schultz-Dubois (1959 Phys. Rev. Lett. 2 262).

  14. Energy levels of an anisotropic three-dimensional polaron in a magnetic field

    NASA Astrophysics Data System (ADS)

    Brancus, D. E.; Stan, G.

    2001-06-01

    In the context of the improved Wigner-Brillouin theory, the energy levels are found of a Fröhlich polaron in a uniaxial anisotropic polar semiconductor with complex structure, placed in a magnetic field directed either along the optical axis or orthogonal to it. All sources of anisotropy that are contained in the shape of constant-energy surfaces of the bare electron, the electron-optical-phonon interaction, and the frequency spectrum of the extraordinary phonon modes are considered. Analytical results for the electron-phonon interaction correction to the Landau levels below the optical-phonon continuum are given and, numerical results for the magnetic-field dependence of the cyclotron resonance frequency at low temperature are presented for the particular case of the layered semiconductors InSe and GaSe. Although the interaction between the bare electron and quasitransverse optical-phonon modes is weak, these modes play an important role in the pinning of Landau levels. The results given by Das Sarma for a two-dimensional isotropic magnetopolaron are generalized to the anisotropic uniaxial case by taking formally m∥-->∞ in the expression of the perturbed Landau levels found when the magnetic field is directed along the optical axis, m∥ being the component of the bare-electron effective-mass tensor along the optical axis.

  15. Polaronic metal state at the LaAlO3/SrTiO3 interface

    PubMed Central

    Cancellieri, C.; Mishchenko, A. S.; Aschauer, U.; Filippetti, A.; Faber, C.; Barišić, O. S.; Rogalev, V. A.; Schmitt, T.; Nagaosa, N.; Strocov, V. N.

    2016-01-01

    Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 that hosts a two-dimensional electron system. Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LaAlO3 overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally limits the carrier mobility and explains its puzzling drop at high temperatures. PMID:26813124

  16. Charge ordering and magneto-polarons in NaxCoO2

    NASA Astrophysics Data System (ADS)

    Bernhard, Christian

    2005-03-01

    Using spectral ellipsometry, we measured the dielectric function of a NaxCoO2 single crystals. In particular, we investigated samples with x>0.75 that exhibit bulk AF with TN=20K. We identify two prominent transitions in the optical response as a function of temperature. The first one at 260-280 K involves marked changes of the electronic and lattice responses that are indicative of charge ordering. Besides the formation of a very narrow Drude-peak we observe a strong collective mode and the formation of a pseudogap with a large energy scale of about 0.5 eV. The second transition occurs at TN, it also involves a surprisingly large energy scale of about 0.4 eV and gives clear evidence for a strong spin-charge coupling. The data are discussed in terms of charge ordering and formation of magneto-polarons due to a charge-induced spin-state transition of adjacent Co^+3 ions. C.Bernhard et al., PRL 93, 167003 (2004)

  17. Time-resolved polaron dynamics in molten solutions of cesium-doped cesium iodide.

    PubMed

    Chandrasekhar, N; Unterreiner, A-N

    2007-11-14

    Temperature-dependent investigations of excess electrons in molten solutions of cesium-doped cesium iodide (Cs-CsI) (mole fraction of Cs approximately 0.003) were performed applying femtosecond pump-probe absorption spectroscopy. The pulse-limited induced bleach observed at probe wavelengths from 600 to 1240 nm was attributed to the excitation of equilibrated excess electrons which were initially formed by melting a Cs-CsI mixture. The interpretation of the relaxation process is based on strongly localized polarons that constitute the majority of defect states in this melt. As expected, the bipolaron contribution was insignificant. The time constants (tau1) were found to be temperature dependent confirming our earlier findings in Na-NaI melts that ionic diffusion almost exclusively controls the dynamics of excess electrons in high temperature ionic liquids. Apart from this temperature dependence, the relaxation dynamics of excess electrons do not differ irrespective of the excitation regime (blue or red part of the respective stationary spectra).

  18. Polaronic metal state at the LaAlO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Cancellieri, C.; Mishchenko, A. S.; Aschauer, U.; Filippetti, A.; Faber, C.; Barišić, O. S.; Rogalev, V. A.; Schmitt, T.; Nagaosa, N.; Strocov, V. N.

    2016-01-01

    Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 that hosts a two-dimensional electron system. Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LaAlO3 overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally limits the carrier mobility and explains its puzzling drop at high temperatures.

  19. Zener Polarons Ordering Variants Induced by A-Site Ordering in Half-Doped Manganites

    NASA Astrophysics Data System (ADS)

    Daoud-Aladine, Aziz

    2006-03-01

    Zener Polaron (ZP) ordering [1] provides a still polemic [2] and elusive interpretation of the charge ordering (CO) phenomenon in A site disordered half doped (A1/2Ca1/2) MnO3, which is classically pictured by the Goodenough model (GM) of Mn^3+ and Mn^4+ CO [3,4]. ZP ordering considers instead the ordering of pre-formed ferromagnetic Mn pairs sharing an charge and keeping Mn in a Mn^+3.5 valence state. The recently synthesized A site cation ordered ABaMn2O6 were shown to not present the generic magnetic CE state found of (A1/2Ca1/2)MnO3 [5]. We present our magnetic structure determination of YBaMn2O6: the non- collinear magnetic order obtained unexpectedly reveals ferromagnetic plaquettes of four Mn attributable to larger 4-Mn ZPs, whose presence additionally fits very well the effective paramagnetic moments inferred from susceptibility measurements. The results unambiguously reveal the possible existence of ZP ordering variant in charge ordered manganites. [1] A. Daoud-Aladine et al., Phys. Rev. Lett. 89, 097205 (2002) [2] S. Grenier et al., Phys. Rev. B 69, 134419 (2004) [3] J. B. Goodenough, Phys. Rev. 100, 564 (1955) [4] P.G. Radaelli et al., Phys. Rev. B, 55, 3015 (1997) [5] T. Arima et al., Phys. Rev. B 66, 140408 (2002)

  20. Polaronic metal state at the LaAlO3/SrTiO3 interface.

    PubMed

    Cancellieri, C; Mishchenko, A S; Aschauer, U; Filippetti, A; Faber, C; Barišić, O S; Rogalev, V A; Schmitt, T; Nagaosa, N; Strocov, V N

    2016-01-27

    Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 that hosts a two-dimensional electron system. Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LaAlO3 overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally limits the carrier mobility and explains its puzzling drop at high temperatures.

  1. Dynamics of carrier populations and localized spins during magnetic-polaron formation in quantum dots

    NASA Astrophysics Data System (ADS)

    Barman, Biplob; Oszwaldowski, Rafal; Schweidenback, Lars; Russ, Andreas; Murphy, Joseph; Cartwright, Alexander; Zutic, Igor; McCombe, Bruce; Petrou, Athos; Chou, Wu-Ching; Chung Fan, Wen; Sellers, Ian; Petukhov, Andre

    2013-03-01

    We have extended our previous investigation of time evolution of PL from (Zn,Mn)Te/ZnSe quantum dots in a magnetic field B. PL studies at T = 5 K in these type-II dots reveal formation of magnetic polarons (MP). We find their formation time τMP to be 0.5 ns, which varies little with B. The circular polarization P of the emission shows a surprising behavior. For all fields, the characteristic time τP is longer than τMP. Furthermore, τP decreases from 10 ns to 1.9 ns as B increases from 1 to 4 tesla. We attribute this effect to a low- B bottleneck in the σ+ recombination channel, due to the almost equal populations of the spin +/- 1 / 2 electrons participating in the interband transitions. In contrast, the +/- 3 / 2 holes in the (Zn,Mn)Te QDs, are affected mostly by the effective field due to exchange interaction between hole and Mn spins around it. This effective field is much larger than B. Work supported by DOE-BES, ONR and NSF.

  2. Singlet and triplet excitons and charge polarons in cycloparaphenylenes. A density functional theory study

    SciTech Connect

    Liu, Jin; Adamska, Lyudmyla; Doorn, Stephen K.; Tretiak, Sergei

    2015-05-14

    Conformational structure and the electronic properties of various electronic excitations in cycloparaphenylenes (CPPs) are calculated using hybrid Density Functional Theory (DFT). The results demonstrate that wavefunctions of singlet and triplet excitons as well as the positive and negative polarons remain fully delocalized in CPPs. In contrast, these excitations in larger CPP molecules become localized on several phenyl rings, which are locally planarized, while the undeformed ground state geometry is preserved on the rest of the hoop. As evidenced by the measurements of bond-length alternation and dihedral angles, localized regions show stronger hybridization between neighboring bonds and thus enhanced electronic communication. This effect is even more significant in the smaller hoops, where phenyl rings have strong quinoid character in the ground state. Thus, upon excitation, electron–phonon coupling leads to the self-trapping of the electronic wavefunction and release of energy from fractions of an eV up to two eVs, depending on the type of excitation and the size of the hoop. The impact of such localization on electronic and optical properties of CPPs is systematically investigated and compared with the available experimental measurements.

  3. Singlet and triplet excitons and charge polarons in cycloparaphenylenes. A density functional theory study

    DOE PAGES

    Liu, Jin; Adamska, Lyudmyla; Doorn, Stephen K.; ...

    2015-05-14

    Conformational structure and the electronic properties of various electronic excitations in cycloparaphenylenes (CPPs) are calculated using hybrid Density Functional Theory (DFT). The results demonstrate that wavefunctions of singlet and triplet excitons as well as the positive and negative polarons remain fully delocalized in CPPs. In contrast, these excitations in larger CPP molecules become localized on several phenyl rings, which are locally planarized, while the undeformed ground state geometry is preserved on the rest of the hoop. As evidenced by the measurements of bond-length alternation and dihedral angles, localized regions show stronger hybridization between neighboring bonds and thus enhanced electronic communication.more » This effect is even more significant in the smaller hoops, where phenyl rings have strong quinoid character in the ground state. Thus, upon excitation, electron–phonon coupling leads to the self-trapping of the electronic wavefunction and release of energy from fractions of an eV up to two eVs, depending on the type of excitation and the size of the hoop. The impact of such localization on electronic and optical properties of CPPs is systematically investigated and compared with the available experimental measurements.« less

  4. Observation of a two-dimensional liquid of Fröhlich polarons at the bare SrTiO3 surface

    PubMed Central

    Chen, Chaoyu; Avila, José; Frantzeskakis, Emmanouil; Levy, Anna; Asensio, Maria C.

    2015-01-01

    The polaron is a quasi-particle formed by a conduction electron (or hole) together with its self-induced polarization in a polar semiconductor or an ionic crystal. Among various polarizable examples of complex oxides, strontium titanate (SrTiO3) is one of the most studied. Here we examine the carrier type and the interplay of inner degrees of freedom (for example, charge, lattice, orbital) in SrTiO3. We report the experimental observation of Fröhlich polarons, or large polarons, at the bare SrTiO3 surface prepared by vacuum annealing. Systematic analyses of angle-resolved photoemission spectroscopy and X-ray absorption spectra show that these Fröhlich polarons are two-dimensional and only exist with inversion symmetry breaking by two-dimensional oxygen vacancies. Our discovery provides a rare solvable field theoretical model, and suggests the relevance of large (bi)polarons for superconductivity in perovskite oxides, as well as in high-temperature superconductors. PMID:26489376

  5. Observation of a two-dimensional liquid of Fröhlich polarons at the bare SrTiO3 surface.

    PubMed

    Chen, Chaoyu; Avila, José; Frantzeskakis, Emmanouil; Levy, Anna; Asensio, Maria C

    2015-10-22

    The polaron is a quasi-particle formed by a conduction electron (or hole) together with its self-induced polarization in a polar semiconductor or an ionic crystal. Among various polarizable examples of complex oxides, strontium titanate (SrTiO3) is one of the most studied. Here we examine the carrier type and the interplay of inner degrees of freedom (for example, charge, lattice, orbital) in SrTiO3. We report the experimental observation of Fröhlich polarons, or large polarons, at the bare SrTiO3 surface prepared by vacuum annealing. Systematic analyses of angle-resolved photoemission spectroscopy and X-ray absorption spectra show that these Fröhlich polarons are two-dimensional and only exist with inversion symmetry breaking by two-dimensional oxygen vacancies. Our discovery provides a rare solvable field theoretical model, and suggests the relevance of large (bi)polarons for superconductivity in perovskite oxides, as well as in high-temperature superconductors.

  6. Polaronic quasiparticle picture for generation dynamics of coherent phonons in semiconductors: Transient and nonlinear Fano resonance

    NASA Astrophysics Data System (ADS)

    Watanabe, Yohei; Hino, Ken-ichi; Hase, Muneaki; Maeshima, Nobuya

    2017-01-01

    We examine generation dynamics of coherent phonons in both polar and nonpolar semiconductors, such as GaAs and Si, based on a polaronic-quasiparticle (PQ) model. In this model, the PQ operator is composed of two kinds of operators: one is a quasiboson operator, defined as a linear combination of a set of pairs of electron operators, and the other is a longitudinal optical (LO) phonon operator. In particular, the problem of transient and nonlinear Fano resonance (FR) is tackled, where the vestige of this quantum interference effect was observed exclusively in lightly n -doped Si immediately after carriers were excited by an ultrashort pulse laser [M. Hase et al., Nature (London) 426, 51 (2003), 10.1038/nature02044], although not observed yet in GaAs. The PQ model enables us to show straightforwardly that the phonon energy state is embedded in continuum states formed by a set of adiabatic eigenstates of the quasiboson; this energy configuration is a necessary condition of the manifestation of the transient FR in the present optically nonlinear system. Numerical calculations are done for photoemission spectra relevant to the retarded longitudinal dielectric function of transient photoexcited states and for power spectra relevant to the LO-phonon displacement function of time. The photoemission spectra show that in undoped Si, an asymmetric spectral profile characteristic of FR comes into existence immediately after the instantaneous carrier excitation to fade out gradually, whereas in undoped GaAs, no asymmetry in spectra appears in the whole temporal region. The similar results are also obtained in the power spectra. These results are in harmony with the reported experimental results. It is found that the obtained difference in spectral profile between undoped Si and GaAs is attributed to a phase factor of an effective interaction between the LO phonon and the quasiboson. More detailed discussion of the FR dynamics is made in the text.

  7. The structure of nanoscale polaron correlations in La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7}.

    SciTech Connect

    Campbell, B. J.; Osborn, R.; Argyriou, D. N.; Vasiliu-Doloc, L.; Mitchell, J. F.; Sinha, S. K.; Ruett, U.; Ling, C. D.; Islam, Z.; Lynn, J. W.; Northern Illinois Univ.; NIST

    2002-01-01

    A system of strongly interacting electron-lattice polarons can exhibit charge and orbital order at sufficiently high polaron concentrations. In this study, the structure of short-range polaron correlations in the layered colossal magnetoresistive perovskite manganite La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} has been determined by a crystallographic analysis of broad satellite maxima observed in diffuse x-ray and neutron-scattering data. The resulting q{approx}(0.3,0,{+-}1) modulation is a longitudinal octahedral-stretch mode, consistent with incommensurate Jahn-Teller-coupled charge-density-wave fluctuations, that implies an unusual orbital-stripe pattern parallel to the {l_angle}100{r_angle} directions.

  8. Exploring the impact of semicore level electronic relaxation on polaron dynamics: An adiabatic ab initio study of FePO4

    NASA Astrophysics Data System (ADS)

    Wang, Zi; Bevan, Kirk H.

    2016-01-01

    In the present work, we study the effects of the electronic relaxation of semicore levels on polaron activation energies and dynamics. Within the framework of adiabatic ab initio theory, we utilize both static transition state theory and molecular dynamics methods for an in-depth study of polaronic hopping in delithiated LiFePO4 (FePO4). Our results show that electronic relaxation of semicore states is significant in FePO4, resulting in a lower activation barrier and kinetics that is one to two orders faster compared to the result of calculations that do not incorporate semicore states. In general, the results suggest that the relaxation of states far below the Fermi energy could dramatically impact the ab initio polaronic barrier estimates for many transition metal oxides and phosphates.

  9. Bi-stability in single impurity Anderson model with strong electron-phonon interaction(polaron regime)

    NASA Astrophysics Data System (ADS)

    Eskandari-asl, Amir

    2016-09-01

    We consider a single impurity Anderson model (SIAM) in which the quantum dot(QD) is strongly coupled to a phonon bath in polaron regime. This coupling results in an effective e-e attraction. By computing the self energies using a current conserving approximation which is up to second order in this effective attraction, we show that if the interaction is strong enough, in non particle-hole (PH) symmetric case, the system would be bi-stable and we have hysteresis loop in the I-V characteristic. Moreover, the system shows negative differential conductance in some bias voltage intervals.

  10. Angle-resolved photoemission spectroscopy of the insulating NaxWO3: Anderson localization, polaron formation, and remnant Fermi surface.

    PubMed

    Raj, S; Hashimoto, D; Matsui, H; Souma, S; Sato, T; Takahashi, T; Sarma, D D; Mahadevan, Priya; Oishi, S

    2006-04-14

    The electronic structure of the insulating sodium tungsten bronze, Na(0.025)WO(3), is investigated by high-resolution angle-resolved photoemission spectroscopy. We find that near-E(F) states are localized due to the strong disorder arising from random distribution of Na+ ions in the WO(3) lattice, which makes the system insulating. The temperature dependence of photoemission spectra provides direct evidence for polaron formation. The remnant Fermi surface of the insulator is found to be the replica of the real Fermi surface in the metallic system.

  11. Effective Landé factor in a GaMnAs quantum dot; with the effects of sp-d exchange on a bound polaron

    SciTech Connect

    Lalitha, D. Peter, A. John

    2014-04-24

    The effective g-factor of conduction (valence) band electron (hole) is obtained in the GaMnAs quantum dot. Magneto bound polaron in a GaMnAs/Ga{sub 0.6}Al{sub 0.4}As quantum dot is investigated with the inclusion of exchange interaction effects due to Mn alloy content and the geometrical confinement. The spin polaronic energy of the heavy hole exciton is studied with the spatial confinement using a mean field theory in the presence of magnetic field strength.

  12. Temperature Effects of Electric Field on the First Excited State of Strong Coupling Polaron in a CsI Quantum Pseudodot

    NASA Astrophysics Data System (ADS)

    Sun, Yong; Ding, Zhao-Hua; Xiao, Jing-Lin

    2017-03-01

    Employing variational method of Pekar type (VMPT), this paper investigates the first-excited state energy (FESE), excitation energy and transition frequency of the strongly-coupled polaron in the CsI quantum pseudodot (QPD) with electric field. The temperature effects on the strong-coupling polaron in electric field are calculated by using the quantum statistical theory (QST). The results from the present investigation show that the FESE, excitation energy and transition frequency increase (decrease) firstly and then at lower (higher) temperature regions. They are decreasing functions of the electric field strength. Supported by the National Natural Science Foundation of China under Grant No. 11464033

  13. Coherent quantum transport in disordered systems: A unified polaron treatment of hopping and band-like transport.

    PubMed

    Lee, Chee Kong; Moix, Jeremy; Cao, Jianshu

    2015-04-28

    Quantum transport in disordered systems is studied using a polaron-based master equation. The polaron approach is capable of bridging the results from the coherent band-like transport regime governed by the Redfield equation to incoherent hopping transport in the classical regime. A non-monotonic dependence of the diffusion coefficient is observed both as a function of temperature and system-phonon coupling strength. In the band-like transport regime, the diffusion coefficient is shown to be linearly proportional to the system-phonon coupling strength and vanishes at zero coupling due to Anderson localization. In the opposite classical hopping regime, we correctly recover the dynamics described by the Fermi's Golden Rule and establish that the scaling of the diffusion coefficient depends on the phonon bath relaxation time. In both the hopping and band-like transport regimes, it is demonstrated that at low temperature, the zero-point fluctuations of the bath lead to non-zero transport rates and hence a finite diffusion constant. Application to rubrene and other organic semiconductor materials shows a good agreement with experimental mobility data.

  14. Loosening quantum confinement: observation of real conductivity caused by hole polarons in semiconductor nanocrystals smaller than the Bohr radius.

    PubMed

    Ulbricht, Ronald; Pijpers, Joep J H; Groeneveld, Esther; Koole, Rolf; Donega, Celso de Mello; Vanmaekelbergh, Daniel; Delerue, Christophe; Allan, Guy; Bonn, Mischa

    2012-09-12

    We report on the gradual evolution of the conductivity of spherical CdTe nanocrystals of increasing size from the regime of strong quantum confinement with truly discrete energy levels to the regime of weak confinement with closely spaced hole states. We use the high-frequency (terahertz) real and imaginary conductivities of optically injected carriers in the nanocrystals to report on the degree of quantum confinement. For the smaller CdTe nanocrystals (3 nm < radius < 5 nm), the complex terahertz conductivity is purely imaginary. For nanocrystals with radii exceeding 5 nm, we observe the onset of real conductivity, which is attributed to the increasingly smaller separation between the hole states. Remarkably, this onset occurs for a nanocrystal radius significantly smaller than the bulk exciton Bohr radius a(B) ∼ 7 nm and cannot be explained by purely electronic transitions between hole states, as evidenced by tight-binding calculations. The real-valued conductivity observed in the larger nanocrystals can be explained by the emergence of mixed carrier-phonon, that is, polaron, states due to hole transitions that become resonant with, and couple strongly to, optical phonon modes for larger QDs. These polaron states possess larger oscillator strengths and broader absorption, and thereby give rise to enhanced real conductivity within the nanocrystals despite the confinement.

  15. Anomalous dispersion and band gap reduction in UO2+x and its possible coupling to the coherent polaronic quantum state

    NASA Astrophysics Data System (ADS)

    Conradson, Steven D.; Andersson, David A.; Bagus, Paul S.; Boland, Kevin S.; Bradley, Joseph A.; Byler, Darrin D.; Clark, David L.; Conradson, Dylan R.; Espinosa-Faller, Francisco J.; Lezama Pacheco, Juan S.; Martucci, Mary B.; Nordlund, Dennis; Seidler, Gerald T.; Valdez, James A.

    2016-05-01

    Hypervalent UO2, UO2(+x) formed by both addition of excess O and photoexcitation, exhibits a number of unusual or often unique properties that point to it hosting a polaronic Bose-Einstein(-Mott) condensate. A more thorough analysis of the O X-ray absorption spectra of UO2, U4O9, and U3O7 shows that the anomalous increase in the width of the spectral features assigned to predominantly U 5f and 6d final states that points to increased dispersion of these bands occurs on the low energy side corresponding to the upper edge of the gap bordered by the conduction or upper Hubbard band. The closing of the gap by 1.5 eV is more than twice as much as predicted by calculations, consistent with the dynamical polaron found by structural measurements. In addition to fostering the excitation that is the proposed mechanism for the coherence, the likely mirroring of this effect on the occupied, valence side of the gap below the Fermi level points to increased complexity of the electronic structure that could be associated with the Fermi topology of BEC-BCS crossover and two band superconductivity.

  16. Quantum Monte Carlo study of the Bose-polaron problem in a one-dimensional gas with contact interactions

    NASA Astrophysics Data System (ADS)

    Parisi, L.; Giorgini, S.

    2017-02-01

    We present a theoretical study based upon quantum Monte Carlo methods of the Bose polaron in one-dimensional systems with contact interactions. In this instance of the problem of a single impurity immersed in a quantum bath, the medium is a Lieb-Liniger gas of bosons ranging from the weakly interacting to the Tonks-Girardeau regime, whereas the impurity is coupled to the bath via a different contact potential, producing both repulsive and attractive interactions. Both the case of a mobile impurity, having the same mass as the particles in the medium, and the case of a static impurity with infinite mass are considered. We make use of numerical techniques that allow us to calculate the ground-state energy of the impurity, its effective mass, and the contact parameter between the impurity and the bath. These quantities are investigated as a function of the strength of interactions between the impurity and the bath and within the bath. In particular, we find that the effective mass rapidly increases to very large values when the impurity gets strongly coupled to an otherwise weakly repulsive bath. This heavy impurity hardly moves within the medium, thereby realizing the "self-localization" regime of the Landau-Pekar polaron. Furthermore, we compare our results with predictions of perturbation theory valid for weak interactions and with exact solutions available when the bosons in the medium behave as impenetrable particles.

  17. Influences of RSO interaction and LO phonon effect on the spin polarization state energy of polaron in a quantum rod

    NASA Astrophysics Data System (ADS)

    Li, Zhi-xin; Wang, Xiao-yu

    2016-12-01

    On the basis of Lee-Low-Pines unitary transformation, the influences of Rashba spin-orbit (RSO) coupling energy and Zeeman splitting energy on the ground-state energy of polaron in a quantum rod (QRD) have been studied by using a variational method of Pekar type. Taking the RSO interaction and the Zeeman splitting into account, we derive the variational relations of the absolute ratios ζ1 and ζ2 of the RSO coupling energy and the Zeeman splitting energy to the ground-state energy of polaron with the transverse confinement radius (TCR) and the longitudinal confinement length (LCL) of QRD, as well as and the magnetic field adjusting length (MFAL). The results show that the absolute ratios ζ1 and ζ2 will increase when the TCR and the LCL become larger, but will slowly decrease while the MFAL and the aspect ratio of the ellipsoid δ increase, respectively. The above results can be attributed to the spin effects and interesting quantum size confining.

  18. Coherent quantum transport in disordered systems: A unified polaron treatment of hopping and band-like transport

    SciTech Connect

    Lee, Chee Kong; Moix, Jeremy; Cao, Jianshu

    2015-04-28

    Quantum transport in disordered systems is studied using a polaron-based master equation. The polaron approach is capable of bridging the results from the coherent band-like transport regime governed by the Redfield equation to incoherent hopping transport in the classical regime. A non-monotonic dependence of the diffusion coefficient is observed both as a function of temperature and system-phonon coupling strength. In the band-like transport regime, the diffusion coefficient is shown to be linearly proportional to the system-phonon coupling strength and vanishes at zero coupling due to Anderson localization. In the opposite classical hopping regime, we correctly recover the dynamics described by the Fermi’s Golden Rule and establish that the scaling of the diffusion coefficient depends on the phonon bath relaxation time. In both the hopping and band-like transport regimes, it is demonstrated that at low temperature, the zero-point fluctuations of the bath lead to non-zero transport rates and hence a finite diffusion constant. Application to rubrene and other organic semiconductor materials shows a good agreement with experimental mobility data.

  19. Ultrafast Dynamics of Localized and Delocalized Polaron Transitions in P3HT/PCBM Blend Materials: The Effects of PCBM Concentration

    NASA Astrophysics Data System (ADS)

    Lioudakis, Emmanouil; Alexandrou, Ioannis; Othonos, Andreas

    2009-12-01

    Nowadays, organic solar cells have the interest of engineers for manufacturing flexible and low cost devices. The considerable progress of this nanotechnology area presents the possibility of investigating new effects from a fundamental science point of view. In this letter we highlight the influence of the concentration of fullerene molecules on the ultrafast transport properties of charged electrons and polarons in P3HT/PCBM blended materials which are crucial for the development of organic solar cells. Especially, we report on the femtosecond dynamics of localized (P2 at 1.45 eV) and delocalized (DP2 at 1.76 eV) polaron states of P3HT matrix with the addition of fullerene molecules as well as the free-electron relaxation dynamics of PCBM-related states. Our study shows that as PCBM concentration increases, the amplified exciton dissociation at bulk heterojunctions leads to increased polaron lifetimes. However, the increase in PCBM concentration can be directly related to the localization of polarons, creating thus two competing trends within the material. Our methodology shows that the effect of changes in structure and/or composition can be monitored at the fundamental level toward optimization of device efficiency.

  20. Charge Transport in 4 nm Molecular Wires with Interrupted Conjugation: Combined Experimental and Computational Evidence for Thermally Assisted Polaron Tunneling.

    PubMed

    Taherinia, Davood; Smith, Christopher E; Ghosh, Soumen; Odoh, Samuel O; Balhorn, Luke; Gagliardi, Laura; Cramer, Christopher J; Frisbie, C Daniel

    2016-04-26

    We report the synthesis, transport measurements, and electronic structure of conjugation-broken oligophenyleneimine (CB-OPI 6) molecular wires with lengths of ∼4 nm. The wires were grown from Au surfaces using stepwise aryl imine condensation reactions between 1,4-diaminobenzene and terephthalaldehyde (1,4-benzenedicarbaldehyde). Saturated spacers (conjugation breakers) were introduced into the molecular backbone by replacing the aromatic diamine with trans-1,4-diaminocyclohexane at specific steps during the growth processes. FT-IR and ellipsometry were used to follow the imination reactions on Au surfaces. Surface coverages (∼4 molecules/nm(2)) and electronic structures of the wires were determined by cyclic voltammetry and UV-vis spectroscopy, respectively. The current-voltage (I-V) characteristics of the wires were acquired using conducting probe atomic force microscopy (CP-AFM) in which an Au-coated AFM probe was brought into contact with the wires to form metal-molecule-metal junctions with contact areas of ∼50 nm(2). The low bias resistance increased with the number of saturated spacers, but was not sensitive to the position of the spacer within the wire. Temperature dependent measurements of resistance were consistent with a localized charge (polaron) hopping mechanism in all of the wires. Activation energies were in the range of 0.18-0.26 eV (4.2-6.0 kcal/mol) with the highest belonging to the fully conjugated OPI 6 wire and the lowest to the CB3,5-OPI 6 wire (the wire with two saturated spacers). For the two other wires with a single conjugation breaker, CB3-OPI 6 and CB5-OPI 6, activation energies of 0.20 eV (4.6 kcal/mol) and 0.21 eV (4.8 kcal/mol) were found, respectively. Computational studies using density functional theory confirmed the polaronic nature of charge carriers but predicted that the semiclassical activation energy of hopping should be higher for CB-OPI molecular wires than for the OPI 6 wire. To reconcile the experimental and

  1. Angle-resolved photoemission studies of lattice polaron formation in the cuprate Ca2CuO2Cl2

    SciTech Connect

    Shen, K.M.

    2010-05-03

    To elucidate the nature of the single-particle excitations in the undoped parent cuprates, we have performed a detailed study of Ca{sub 2}CuO{sub 2}Cl{sub 2} using photoemission spectroscopy. The photoemission lineshapes of the lower Hubbard band are found to be well-described by a polaron model. By comparing the lineshape and temperature dependence of the lower Hubbard band with additional O 2p and Ca 3p states, we conclude that the dominant broadening mechanism arises from the interaction between the photohole and the lattice. The strength of this interaction was observed to be strongly anisotropic and may have important implications for the momentum dependence of the first doped hole states.

  2. Experimental manifestations of the Nb4+-O- polaronic excitons in KTa0.988Nb0.012O3

    NASA Astrophysics Data System (ADS)

    Yusupov, R. V.; Gracheva, I. N.; Rodionov, A. A.; Syrnikov, P. P.; Gubaev, A. I.; Dejneka, A.; Jastrabik, L.; Trepakov, V. A.; Salakhov, M. Kh.

    2011-11-01

    The formation of the photopolaronic excitons in ABO3 perovskite-type oxides has been detected experimentally by means of the photoinduced electron paramagnetic resonance (EPR) studies of KTa0.988Nb0.012O3 crystals. The corresponding microwave x-band spectrum at T< 10 K consists of a narrow, nearly isotropic signal located at g ˜ 2 and a strongly anisotropic component. The first signal, which has a rich structure due to hyperfine interactions with the lattice nuclei, is attributed to the single trapped charge carriers: the electrons and/or the holes. The anisotropic spectrum is caused by the axial centers oriented along the C4 pseudocubic principal crystalline axes. The spectrum angular dependence can be described well by an axial center with S = 1, g∥ = 0.82, g⊥ = 0.52, and D = 0.44 cm-1. The anisotropic spectrum is attributed to the Nb4+-O- polaronic excitons. The temperature dependence of the anisotropic component is characterized by two activation energies: the internal dynamics activation Ea1 = 3.7 ± 0.5 meV, which makes the EPR spectrum unobservable above 10 K, and the destruction energy Ea2 = 52 ± 4 meV. By comparing the anisotropic photo-EPR spectrum and the photoinduced optical absorption temperature dependencies, we found that the Nb4+-O- polaronic excitons also manifested themselves via the wide absorption band at ˜0.7 eV arising under ultraviolet light excitation in the weakly concentrated KTaO3:Nb crystals.

  3. BEC-polaron gas in a boson-fermion mixture: A many-body extension of Lee-Low-Pines theory

    NASA Astrophysics Data System (ADS)

    Nakano, Eiji; Yabu, Hiroyuki

    2016-05-01

    We investigate the ground state properties of the gaseous mixture of a single species of bosons and fermions at zero temperature, where bosons are major in population over fermions, and form the Bose-Einstein condensate (BEC). The boson-boson and boson-fermion interactions are assumed to be weakly repulsive and attractive, respectively, while the fermion-fermion interaction is absent due to the Pauli exclusion for the low energy s -wave scattering. We treat fermions as a gas of polarons dressed with Bogoliubov phonons, which is an elementary excitation of the BEC, and evaluate the ground state properties with the method developed by Lemmens, Devreese, and Brosens (LDB) originally for the electron polaron gas, and also with a general extension of the Lee-Low-Pines theory for many-body systems (eLLP), which incorporates the phonon drag effects as in the original LLP theory. The formulation of eLLP is developed and discussed in the present paper. The binding (interaction) energy of the polaron gas is calculated in these methods and shown to be finite (negative) for the dilute gas of heavy fermions with attractive boson-fermion interactions, though the suppression by the many-body effects exists.

  4. Effect of carrier doping on the formation and collapse of magnetic polarons in lightly hole-doped La1-xSrxCoO3

    SciTech Connect

    Podlesnyak, Andrey A; Ehlers, Georg; Frontzek, Matthias D; Sefat, A. S.; Furrer, Albert; Straessle, Thierry; Pomjakushina, Ekaterina; Conder, Kazimierz; Demmel, F.; Khomskii, D. I.

    2011-01-01

    We investigate the doping dependence of the nanoscale electronic and magnetic inhomogeneities in the hole-doping range 0.002 < x < 0.1 of cobalt based perovskites, La{sub 1-x}Sr{sub x}CoO{sub 3}. Using single-crystal inelastic neutron scattering and magnetization measurements we show that the lightly doped system exhibits magnetoelectronic phase separation in the form of spin-state polarons. Higher hole doping leads to a decay of spin-state polarons in favor of larger scale magnetic clusters, due to competing ferromagnetic correlations of Co{sup 3+} ions which are formed by neighboring polarons. The present data give evidence for two regimes of magnetoelectronic phase separation in this system: (i) x {approx}< 0.05, dominated by ferromagnetic intrapolaron interactions, and (ii) x {approx}> 0.05, dominated by Co{sup 3+}-Co{sup 3+} intracluster interactions. Our conclusions are in good agreement with a recently proposed model of the phase separation in cobalt perovskites.

  5. Probing electrons in TiO2 polaronic trap states by IR-absorption: Evidence for the existence of hydrogenic states

    PubMed Central

    Sezen, Hikmet; Buchholz, Maria; Nefedov, Alexei; Natzeck, Carsten; Heissler, Stefan; Di Valentin, Cristiana; Wöll, Christof

    2014-01-01

    An important step in oxide photochemistry, the loading of electrons into shallow trap states, was studied using infrared (IR) spectroscopy on both, rutile TiO2 powders and single-crystal, r-TiO2(110) oriented samples. After UV-irradiation or n-doping by exposure to H-atoms broad IR absorption lines are observed for the powders at around 940 cm−1. For the single crystal substrates, the IR absorption bands arising from an excitation of the trapped electrons into higher-lying final states show additional features not observed in previous work. On the basis of our new, high-resolution data and theoretical studies on the polaron binding energy in rutile we propose that the trap states correspond to polarons and are thus intrinsic in nature. We assign the final states probed by the IR-experiments to hydrogenic states within the polaron potential. Implications of these observations for photochemistry on oxides will be briefly discussed. PMID:24448350

  6. THz conductivity of semi-insulating and magnetic CoFe2O4 nano-hollow structures through thermally activated polaron

    NASA Astrophysics Data System (ADS)

    Rakshit, Rupali; Serita, Kazunori; Tonouchi, Masayoshi; Mandal, Kalyan

    2016-11-01

    Herein, terahertz (THz) time domain spectroscopy is used to measure the complex conductivity of semi-insulating CoFe2O4 nanoparticles (NPs) and nano-hollow spheres (NHSs) with different diameters ranging from 100 to 350 nm having a nanocrystalline shell thickness of 19 to 90 nm, respectively. Interestingly, the magnitude of conductivity for CoFe2O4 NPs and NHSs of same average diameter (˜100 nm) for a given frequency of 0.3 THz is found to be 0.33 S/m and 9.08 S/m, respectively, indicating that the hollow structure exhibits greater THz conduction in comparison to its solid counterpart. Moreover, THz conductivity can be tailored by varying the nano-shell thickness of NHSs, and a maximum conductivity of 15.61 S/m is observed at 0.3 THz for NHSs of average diameter 250 nm. A detailed study reveals that thermally activated polaronic hopping plays the key role in determining the electrical transport property of CoFe2O4 nanostructures, which is found to solely depend on their magnitude of THz absorptivity. The non-Drude conductivity of all CoFe2O4 nanostructures is well described by the Polaron model instead of the Drude-Smith model, which is relevant for backscattering of free electrons in a nanostructured material. The Polaron model includes intra-particle and interparticle polaronic conductivities for closely spaced magnetic nanostructures and provides a mean free path of 29 nm for CoFe2O4 NPs of diameter 100 nm, which is comparable with its average crystallite size, indicating the applicability of the developed model for nanomaterials where charge transport is determined by polaronic hopping. Finally, we have demonstrated the morphology and size dependent magnetic measurements of ferrimagnetically aligned CoFe2O4 nanostructures through a vibrating sample magnetometer in the temperature range of 80-250 K, revealing that the disordered surface spin layer of nanostructures significantly controls their magnetism.

  7. A huge renormalization of transport effective mass in the magnetic-polaronic state of EuB 6

    NASA Astrophysics Data System (ADS)

    Glushkov, V.; Bogach, A.; Demishev, S.; Gon'kov, K.; Ignatov, M.; Khayrullin, Eu.; Samarin, N.; Shubin, A.; Shitsevalova, N.; Flachbart, K.; Sluchanko, N.

    2008-04-01

    The comprehensive study of galvanomagnetic, thermoelectric and magnetic properties was carried out on the single crystals of low carrier density ferromagnetic metal EuB 6 ( TC≈13.9 K, Tm=15.8 K) in a wide range of temperatures (1.8-300 K) and magnetic fields (up to 80 kOe). The analysis of the microscopic characteristics estimated from the data revealed a giant renormalization of the charge carriers’ effective mass meff, which is observed in the paramagnetic state of this compound with strong electron correlations. The gradual decrease of meff from the maximum of meff∼30 meff detected at T*≈80 K to the low temperature values of meff ( T⩽ TC)∼0.2-1 m0 is discussed in terms of the phase separation with the formation of low resistive ferromagnetic nano-sized regions (ferrons) in the dielectric magnetic polaronic state ( T> Tm). The observed unusual behavior of meff favors recent explanation of the genesis of the metal-insulator transition scenario proposed for La-doped EuB 6 systems [U. Yu, B.I. Min, Phys. Rev. Lett. 94 (2005) 117202.].

  8. Enhanced surface losses of organic solar cells induced by efficient polaron pair dissociation at the metal/organic interface

    NASA Astrophysics Data System (ADS)

    Yang, Wenchao; Li, De-Li; Yao, Yao; Hou, Xiaoyuan; Wu, Chang-Qin

    2012-08-01

    As a growing importance is placed on developing more efficient organic solar cells, understanding the behavior of free charge carriers at the metal/organic (M/O) interface is critical. One of the current challenges is understanding surface losses, essentially the loss of free charge carriers at the electrode/organic interface. In this paper, we use device model simulations to study such phenomena and we pay particular attention to the role of polaron pair (PP) M/O interfacial dissociation. The origin of surface losses is through the extraction of free charge carriers from the wrong electrodes, or direct surface recombination of PPs. Through simulation, we find that a high injection barrier leads to a large surface loss. In addition, surface loss increases with both the interfacial dissociation rate and PP diffusivity. Efficient interfacial dissociation can significantly enhance surface losses if the PP diffusivity is relatively large. Furthermore, current voltage characteristics reveal that surface losses undermine the device operating parameters and efficiency. Interlayers inserted at the M/O interface could block wrong electrode carriers, suppress the interfacial dissociation and reduce surface losses.

  9. Hubbard Model for Atomic Impurities Bound by the Vortex Lattice of a Rotating Bose-Einstein Condensate

    NASA Astrophysics Data System (ADS)

    Johnson, T. H.; Yuan, Y.; Bao, W.; Clark, S. R.; Foot, C.; Jaksch, D.

    2016-06-01

    We investigate cold bosonic impurity atoms trapped in a vortex lattice formed by condensed bosons of another species. We describe the dynamics of the impurities by a bosonic Hubbard model containing occupation-dependent parameters to capture the effects of strong impurity-impurity interactions. These include both a repulsive direct interaction and an attractive effective interaction mediated by the Bose-Einstein condensate. The occupation dependence of these two competing interactions drastically affects the Hubbard model phase diagram, including causing the disappearance of some Mott lobes.

  10. Hubbard Model for Atomic Impurities Bound by the Vortex Lattice of a Rotating Bose-Einstein Condensate.

    PubMed

    Johnson, T H; Yuan, Y; Bao, W; Clark, S R; Foot, C; Jaksch, D

    2016-06-17

    We investigate cold bosonic impurity atoms trapped in a vortex lattice formed by condensed bosons of another species. We describe the dynamics of the impurities by a bosonic Hubbard model containing occupation-dependent parameters to capture the effects of strong impurity-impurity interactions. These include both a repulsive direct interaction and an attractive effective interaction mediated by the Bose-Einstein condensate. The occupation dependence of these two competing interactions drastically affects the Hubbard model phase diagram, including causing the disappearance of some Mott lobes.

  11. Interfacial and bulk polaron masses in Zn{sub 1−x}Mg{sub x}O/ZnO heterostructures examined by terahertz time-domain cyclotron spectroscopy

    SciTech Connect

    Lloyd-Hughes, J. Failla, M.; Ye, J.; Jones, S. P. P.; Teo, K. L.; Jagadish, C.

    2015-05-18

    The cyclotron resonance of polarons in Zn{sub 1−x}Mg{sub x}O/ZnO heterostructures (with 0.15polaron density, mass, and scattering rate. The cyclotron mass of 2D polarons was found to increase significantly with magnetic field B from 0.24 m{sub e} at B = 2 T to 0.37 m{sub e} at B = 7.5 T. A nonlinear cyclotron frequency with B was also observed for 3D polarons in ZnO. The findings are discussed in the context of polaron mass renormalization driven by the electron-LO-phonon and electron-acoustic phonon interactions.

  12. Picosecond Dynamics of Excitonic Magnetic Polarons in Colloidal Diffusion-Doped Cd(1-x)Mn(x)Se Quantum Dots.

    PubMed

    Nelson, Heidi D; Bradshaw, Liam R; Barrows, Charles J; Vlaskin, Vladimir A; Gamelin, Daniel R

    2015-11-24

    Spontaneous magnetization is observed at zero magnetic field in photoexcited colloidal Cd(1-x)Mn(x)Se (x = 0.13) quantum dots (QDs) prepared by diffusion doping, reflecting strong Mn(2+)-exciton exchange coupling. The picosecond dynamics of this phenomenon, known as an excitonic magnetic polaron (EMP), are examined using a combination of time-resolved photoluminescence, magneto-photoluminescence, and Faraday rotation (TRFR) spectroscopies, in conjunction with continuous-wave absorption, magnetic circular dichroism (MCD), and magnetic circularly polarized photoluminescence (MCPL) spectroscopies. The data indicate that EMPs form with random magnetization orientations at zero external field, but their formation can be directed by an external magnetic field. After formation, however, external magnetic fields are unable to reorient the EMPs within the luminescence lifetime, implicating anisotropy in the EMP potential-energy surfaces. TRFR measurements in a transverse magnetic field reveal rapid (<5 ps) spin transfer from excitons to Mn(2+) followed by coherent EMP precession at the Mn(2+) Larmor frequency for over a nanosecond. A dynamical TRFR phase inversion is observed during EMP formation attributed to the large shifts in excitonic absorption energies during spontaneous magnetization. Partial optical orientation of the EMPs by resonant circularly polarized photoexcitation is also demonstrated. Collectively, these results highlight the extraordinary physical properties of colloidal diffusion-doped Cd(1-x)Mn(x)Se QDs that result from their unique combination of strong quantum confinement, large Mn(2+) concentrations, and relatively narrow size distributions. The insights gained from these measurements advance our understanding of spin dynamics and magnetic exchange in colloidal doped semiconductor nanostructures, with potential ramifications for future spin-based information technologies.

  13. New concept of energy migration and trapping in purple bacteria. Charge transfer-polaron model.

    PubMed

    Borisov AYu

    1995-04-01

    A new hypothetical concept of the reaction center (RC) and the core BChl antenna is developed which claims to fit all up to date experimental data. In particular, the concept accounts for a number of findings still waiting for an explanation: a) the "red" shifts of the core BChl absorption peaks relative to those in their corresponding core BChls; b) the reason why in purple bacteria the second P2-P800-BPH-Q brunch of RC is inactive c) recent data parallel 1,2 on a small excitation portion which escapes from the excited RC special pair back to antenna BChls; d) why the primary electron donor is not monomer but a pair of parallel B Chls; e) the reason why the fluorescence spectra of the RC special pairs are enormously red-shifted relative to their absorption spectra.

  14. Highly-Efficient Charge Separation and Polaron Delocalization in Polymer-Fullerene Bulk-Heterojunctions: A Comparative Multi-Frequency EPR & DFT Study

    PubMed Central

    Niklas, Jens; Mardis, Kristy L.; Banks, Brian P.; Grooms, Gregory M.; Sperlich, Andreas; Dyakonov, Vladimir; Beaupré, Serge; Leclerc, Mario; Xu, Tao; Yu, Luping; Poluektov, Oleg G.

    2016-01-01

    The ongoing depletion of fossil fuels has led to an intensive search for additional renewable energy sources. Solar-based technologies could provide sufficient energy to satisfy the global economic demands in the near future. Photovoltaic (PV) cells are the most promising man-made devices for direct solar energy utilization. Understanding the charge separation and charge transport in PV materials at a molecular level is crucial for improving the efficiency of the solar cells. Here, we use light-induced EPR spectroscopy combined with DFT calculations to study the electronic structure of charge separated states in blends of polymers (P3HT, PCDTBT, and PTB7) and fullerene derivatives (C60-PCBM and C70-PCBM). Solar cells made with the same composites as active layers show power conversion efficiencies of 3.3% (P3HT), 6.1% (PCDTBT), and 7.3% (PTB7), respectively. Under illumination of these composites, two paramagnetic species are formed due to photo-induced electron transfer between the conjugated polymer and the fullerene. They are the positive, P+, and negative, P-, polarons on the polymer backbone and fullerene cage, respectively, and correspond to radical cations and radical anions. Using the high spectral resolution of high-frequency EPR (130 GHz), the EPR spectra of these species were resolved and principal components of the g-tensors were assigned. Light-induced pulsed ENDOR spectroscopy allowed the determination of 1H hyperfine coupling constants of photogenerated positive and negative polarons. The experimental results obtained for the different polymer-fullerene composites have been compared with DFT calculations, revealing that in all three systems the positive polaron is distributed over distances of 40 - 60 Å on the polymer chain. This corresponds to about 15 thiophene units for P3HT, approximately three units PCDTBT, and about three to four units for PTB7. No spin density delocalization between neighboring fullerene molecules was detected by EPR. Strong

  15. Highly-efficient charge separation and polaron delocalization in polymer-fullerene bulk-heterojunctions: a comparative multi-frequency EPR and DFT study.

    PubMed

    Niklas, Jens; Mardis, Kristy L; Banks, Brian P; Grooms, Gregory M; Sperlich, Andreas; Dyakonov, Vladimir; Beaupré, Serge; Leclerc, Mario; Xu, Tao; Yu, Luping; Poluektov, Oleg G

    2013-06-28

    The ongoing depletion of fossil fuels has led to an intensive search for additional renewable energy sources. Solar-based technologies could provide sufficient energy to satisfy the global economic demands in the near future. Photovoltaic (PV) cells are the most promising man-made devices for direct solar energy utilization. Understanding the charge separation and charge transport in PV materials at a molecular level is crucial for improving the efficiency of the solar cells. Here, we use light-induced EPR spectroscopy combined with DFT calculations to study the electronic structure of charge separated states in blends of polymers (P3HT, PCDTBT, and PTB7) and fullerene derivatives (C60-PCBM and C70-PCBM). Solar cells made with the same composites as active layers show power conversion efficiencies of 3.3% (P3HT), 6.1% (PCDTBT), and 7.3% (PTB7), respectively. Upon illumination of these composites, two paramagnetic species are formed due to photo-induced electron transfer between the conjugated polymer and the fullerene. They are the positive, P(+), and negative, P(-), polarons on the polymer backbone and fullerene cage, respectively, and correspond to radical cations and radical anions. Using the high spectral resolution of high-frequency EPR (130 GHz), the EPR spectra of these species were resolved and principal components of the g-tensors were assigned. Light-induced pulsed ENDOR spectroscopy allowed the determination of (1)H hyperfine coupling constants of photogenerated positive and negative polarons. The experimental results obtained for the different polymer-fullerene composites have been compared with DFT calculations, revealing that in all three systems the positive polaron is distributed over distances of 40-60 Å on the polymer chain. This corresponds to about 15 thiophene units for P3HT, approximately three units for PCDTBT, and about three to four units for PTB7. No spin density delocalization between neighboring fullerene molecules was detected by EPR

  16. Generalized polaron ansatz for the ground state of the sub-Ohmic spin-boson model: an analytic theory of the localization transition.

    PubMed

    Chin, Alex W; Prior, Javier; Huelga, Susana F; Plenio, Martin B

    2011-10-14

    The sub-Ohmic spin-boson model possesses a quantum phase transition at zero temperature between a localized and a delocalized phase, whose properties have so far only been extracted by numerical approaches. Here we present an extension of the Silbey-Harris variational polaron ansatz which allows us to develop an analytical theory which correctly describes a continuous transition with mean-field exponents for 0

  17. Photoionization absorption and zero-field spin splitting of acceptor-bound magnetic polaron in p-type Hg1-xMnxTe single crystals

    NASA Astrophysics Data System (ADS)

    Zhu, Liangqing; Shao, Jun; Lin, Tie; Lü, Xiang; Zhu, Junyu; Tang, Xiaodong; Chu, Junhao

    2012-04-01

    Temperature-dependent magnetic (2-300 K), DC Hall (10-300 K), and infrared transmission (11.5-300 K) measurements are performed on a series of p-type Hg1-xMnxTe (0.12 ≤ x ≤ 0.26) single crystals in the spin-glass regime. Photoionization absorption (PIA) of acceptor-bound magnetic polarons (acceptor-BMPs) is observed to evolve with temperature, which is better accounted for by the classical oscillator model than by the quantum defect method. At low temperatures, p-type Hg1-xMnxTe manifests distinct phenomena of paramagnetic enhancement, negative magnetoresistance, and decrease of the effective binding energy and blueshift of the PIA of the acceptor-BMPs with nearly the same degree as temperature declines. A spin-splitting model is proposed, which can well reproduce the experimentally observed zero-field spin splitting of the acceptor-BMP level at low temperatures and the increase of the spin splitting as temperature drops. The results suggest that the acceptor-BMPs in Hg1-xMnxTe may have potential applications in light-driven polaronic memories, tunable far-infrared lasers, and detectors.

  18. Possible Demonstration of a Polaronic Bose-Einstein(-Mott) Condensate in UO2(+x) by Ultrafast THz Spectroscopy and Microwave Dissipation

    PubMed Central

    Conradson, Steven D.; Gilbertson, Steven M.; Daifuku, Stephanie L.; Kehl, Jeffrey A.; Durakiewicz, Tomasz; Andersson, David A.; Bishop, Alan R.; Byler, Darrin D.; Maldonado, Pablo; Oppeneer, Peter M.; Valdez, James A.; Neidig, Michael L.; Rodriguez, George

    2015-01-01

    Bose-Einstein condensates (BECs) composed of polarons would be an advance because they would combine coherently charge, spin, and a crystal lattice. Following our earlier report of unique structural and spectroscopic properties, we now identify potentially definitive evidence for polaronic BECs in photo- and chemically doped UO2(+x) on the basis of exceptional coherence in the ultrafast time dependent terahertz absorption and microwave spectroscopy results that show collective behavior including dissipation patterns whose precedents are condensate vortex and defect disorder and condensate excitations. That some of these signatures of coherence in an atom-based system extend to ambient temperature suggests a novel mechanism that could be a synchronized, dynamical, disproportionation excitation, possibly via the solid state analog of a Feshbach resonance that promotes the coherence. Such a mechanism would demonstrate that the use of ultra-low temperatures to establish the BEC energy distribution is a convenience rather than a necessity, with the actual requirement for the particles being in the same state that is not necessarily the ground state attainable by other means. A macroscopic quantum object created by chemical doping that can persist to ambient temperature and resides in a bulk solid would be revolutionary in a number of scientific and technological fields. PMID:26472071

  19. Possible Demonstration of a Polaronic Bose-Einstein(-Mott) Condensate in UO2(+x) by Ultrafast THz Spectroscopy and Microwave Dissipation

    DOE PAGES

    Conradson, Steven D.; Gilbertson, Steven M.; Daifuku, Stephanie L.; ...

    2015-10-16

    Bose-Einstein condensates (BECs) composed of polarons would be an advance because they would combine coherently charge, spin, and a crystal lattice. Following our earlier report of unique structural and spectroscopic properties, we now identify potentially definitive evidence for polaronic BECs in photo- and chemically doped UO2(+x) on the basis of exceptional coherence in the ultrafast time dependent terahertz absorption and microwave spectroscopy results that show collective behavior including dissipation patterns whose precedents are condensate vortex and defect disorder and condensate excitations. Furthermore, that some of these signatures of coherence in an atom-based system extend to ambient temperature suggests a novelmore » mechanism that could be a synchronized, dynamical, disproportionation excitation, possibly via the solid state analog of a Feshbach resonance that promotes the coherence. Such a mechanism would demonstrate that the use of ultra-low temperatures to establish the BEC energy distribution is a convenience rather than a necessity, with the actual requirement for the particles being in the same state that is not necessarily the ground state attainable by other means. Interestingly, a macroscopic quantum object created by chemical doping that can persist to ambient temperature and resides in a bulk solid would be revolutionary in a number of scientific and technological fields.« less

  20. Possible Demonstration of a Polaronic Bose-Einstein(-Mott) Condensate in UO2(+x) by Ultrafast THz Spectroscopy and Microwave Dissipation

    SciTech Connect

    Conradson, Steven D.; Gilbertson, Steven M.; Daifuku, Stephanie L.; Kehl, Jeffrey A.; Durakiewicz, Tomasz; Andersson, David A.; Bishop, Alan R.; Byler, Darrin D.; Maldonado, Pablo; Oppeneer, Peter M.; Valdez, James A.; Neidig, Michael L.; Rodriguez, George

    2015-10-16

    Bose-Einstein condensates (BECs) composed of polarons would be an advance because they would combine coherently charge, spin, and a crystal lattice. Following our earlier report of unique structural and spectroscopic properties, we now identify potentially definitive evidence for polaronic BECs in photo- and chemically doped UO2(+x) on the basis of exceptional coherence in the ultrafast time dependent terahertz absorption and microwave spectroscopy results that show collective behavior including dissipation patterns whose precedents are condensate vortex and defect disorder and condensate excitations. Furthermore, that some of these signatures of coherence in an atom-based system extend to ambient temperature suggests a novel mechanism that could be a synchronized, dynamical, disproportionation excitation, possibly via the solid state analog of a Feshbach resonance that promotes the coherence. Such a mechanism would demonstrate that the use of ultra-low temperatures to establish the BEC energy distribution is a convenience rather than a necessity, with the actual requirement for the particles being in the same state that is not necessarily the ground state attainable by other means. Interestingly, a macroscopic quantum object created by chemical doping that can persist to ambient temperature and resides in a bulk solid would be revolutionary in a number of scientific and technological fields.

  1. Lattice Distortion, Polaron Conduction, and Jahn-Teller Effect on teh Magnetoresistance of La(sub 0.7)Ca(sub 0.5)CoO(sub 3) Epitaxial Films

    NASA Technical Reports Server (NTRS)

    Yeh, N. C.; Vasquez, R. P.; Beam, D. A.; Fu, C. C.; Huynh, H.; Beach, G.

    1996-01-01

    In summary, we have investigated the role of lattice distortion, polaron conduction and Jahn-Teller coupling in the occurrence of the colossal negative magnetoresistance in perovskite oxides. We conclude that larger lattice distortion gives rise to larger zero-field resistivity and larger magnitude of negative magnetoresistance.

  2. Effects of the built-in electric field on polaron effects in a wurtzite ZnO/Mg{sub x}Zn{sub 1−x}O quantum well

    SciTech Connect

    Zhao, Feng-qi; Guo, Zi-Zheng

    2015-11-21

    The effects of the built-in electric field on the polarons in wurtzite ZnO/Mg{sub x}Zn{sub 1−x}O quantum wells are studied numerically via the improved Lee-Low-Pines intermediate coupling variational method. The contributions of the different branches of the optical phonons to the polaron energies of the ZnO/Mg{sub x}Zn{sub 1−x}O quantum wells are calculated as functions of well width d and composition x. The anisotropy effects of the electronic effective masses, the dielectric constants, and the frequencies of the different branches of the phonon modes (including both the longitudinal-like and transverse-like confined optical phonon modes, the interface optical phonon modes and the half-space phonon modes) on the polaron energies are considered in the calculations. Comparisons between the cases with and without the built-in electric field (F ≠ 0 and F = 0) are made for the optical phonon contributions to the polaron energies for the different branches of the phonon modes. The results show that the built-in electric field has marked effects on the contributions of the phonons with the different modes; in detail, it makes positive contributions to the interface and the half-space phonons, but negative contributions to the confined phonons, and thus its effect on the total phonon contribution is not obvious. Detailed comparisons of the contributions of the symmetric and antisymmetric phonon modes to the polaron energies as functions of d and x are also presented and a heuristic argument is provided to explain the numerical results.

  3. Neither Goodenough ionic model nor Zener polaron model for Bi 0.5Ca 0.5Mn 1- xNi xO 3- δ system

    NASA Astrophysics Data System (ADS)

    Toulemonde, O.; Skovsen, I.; Mesguich, F.; Gaudin, E.

    2008-04-01

    The magnetic susceptibilities of three Bi 0.5Ca 0.5MnO 3- δ compounds synthesised by three different methods were characterised and analysed. Large magnetic Mn x clusters ( x ≥ 4) were considered to explain the high value of the Curie-Weiss constant. Unlike previous studies on similar systems, Goodenough ionic model or Zener polaron model is not suitable. In all cases, cluster behaviour is observed at low field and at low temperature. The influence of the oxygen stoichiometry and the homogeneity of the cation distribution depending on the method of the synthesis used is discussed. Finally, the effects of nickel doping on the magnetic properties were studied and the cluster behaviour was confirmed. The distribution in size of the clusters depends on the amount of nickel and it induces a glassy magnetic behaviour.

  4. Effects of Anisotropic Parabolic Potential on the Energy Levels and Transition Frequency of Strong-Coupling Polaron in a Quantum Dot

    NASA Astrophysics Data System (ADS)

    Cai, Chun-Yu; Zhao, Cui-Lan; Xiao, Jing-Lin

    2013-07-01

    In the presence of a three-dimensional anisotropic parabolic potential (APP), the energy levels and the transition frequency between relevant levels of the strong-coupling polaron in a quantum dot (QD) are investigated by using the well-known Lee-Low-Pines (LLP) unitary transformation method and the Pekar type variational (PTV) method. The relations of the energy levels and the transition frequency with the electron-phonon (EP) coupling strength and the effective confinement lengths are derived. Numerical calculations show that the energy levels are decreasing functions of the EP coupling strength, whereas the transition frequency is an increasing one of it. And they are all increasing rapidly with decreasing the effective confinement lengths in different directions, which are showing the novel quantum size confining effect of the QD.

  5. Effects of sp-d exchange on a bound polaron and the g-factor of the exciton in a GaMnAs quantum dot

    NASA Astrophysics Data System (ADS)

    Lalitha, D.; John Peter, A.; Yoo, Chang Kyoo

    2013-08-01

    Magneto bound polaron in a GaMnAs/Ga0.6Al0.4As quantum dot is investigated with the inclusion of exchange interaction effects due to Mn alloy content and the geometrical confinement. The exciton binding energy and the optical transition energy are computed as functions of dot radius and the magnetic field strength for a fixed Mn alloy content (x = 0.02) in a GaMnAs quantum dot. Numerical calculations are performed using variational method within a single band effective mass approximation. The spin polaronic energy of the heavy hole exciton is studied with the spatial confinement using a mean field theory in the presence of magnetic field strength. The magnetization as a function of dot radius is investigated in a GaMnAs/Ga0.6Al0.4As quantum dot. The magnetic field induced size dependence of g-factor is studied. The effective g-factor of conduction (valence) band electron (hole) is obtained in the GaMnAs quantum dot. The results bring out that (i) the geometrical dependence on sp-d exchange interaction in the GaMnAs/Ga0.6Al0.4As quantum dot has great influence with the magnetic field strength, (ii) the Landé factor is more sensitive if the geometrical confinement effect is included and (iii) the value of g-factor increases when the magnetic field strength is enhanced for all the dot radii. Our results are in good agreement with the other investigators.

  6. The effects of polaronic mass and conduction band non-parabolicity on a donor binding energy under the simultaneous effect of pressure and temperature basing on the numerical FEM in a spherical quantum dot

    NASA Astrophysics Data System (ADS)

    Sali, A.; Kharbach, J.; Rezzouk, A.; Ouazzani Jamil, M.

    2017-04-01

    Basing on the numerical Finite Element Method (FEM), we have investigated the influences of polaronic mass and conduction band non-parabolicity on the binding energy of the ground state of an on-center hydrogenic donor impurity in a spherical GaAs / Ga1 - x AlxAs quantum dot structure. The calculations have been made with a realistic potential barrier height in the framework of the effective mass approximation including the combined effect of hydrostatic pressure and temperature. The donor binding energy is computed as a function of dot size, Al concentration x , hydrostatic pressure and temperature both in the absence and presence of polaronic mass and conduction band non-parabolicity effects. We have taken into account the electronic effective mass, dielectric constant, and conduction band offset between the dot and barriers varying with pressure and temperature. It has been found that the binding energy is strongly affected by the effect of polaronic mass and conduction band non-parabolicity for narrow quantum dot and large Al concentration x. The results show again that the donor binding energy increases linearly with the pressure in direct gap regime and its variation is larger for narrower dots only and drops slightly with the temperature. A good agreement is obtained with the existing literature values.

  7. Influence of the Guest on Aggregation of the Host by Exciton-Polaron Interactions and Its Effects on the Stability of Phosphorescent Organic Light-Emitting Devices.

    PubMed

    Zhang, Yingjie; Aziz, Hany

    2016-06-08

    The root causes of the differences in electroluminescence stability among phosphorescent organic light-emitting devices (PHOLEDs) utilizing different emitter guests are studied. The results show that the host material plays a more influential role in limiting device stability in comparison to the guest. During the operation of a PHOLED, the host undergoes aggregation as a result of interactions between the excitons and positive polarons. The rate of this aggregation is found to be the limiting factor for device lifetime and is influenced by the choice of the guest material and its concentration. Finally, it is shown that phase segregation between the host and the guest is an important aspect of the aggregation process. As a result of this segregation, energy transfer from the host to the guest becomes increasingly less efficient, resulting in the observed gradual loss in electroluminescence efficiency in the devices over time. The findings explain why PHOLEDs utilizing different guest materials but otherwise identical material systems can have significantly different lifetimes and provide an answer to a long-lasting question in the field.

  8. Time-resolved photoluminescence spectroscopy of localized exciton magnetic polarons in Cd{sub 0.70}Mn{sub 0.30}Te spin glass compound

    SciTech Connect

    Gnatenko, Yu. P. Bukivskij, P. M.; Piryatinski, Yu. P.

    2014-04-07

    We have investigated dynamics of different localized exciton magnetic polarons (LEMPs) in Cd{sub 0.70}Mn{sub 0.30}Te spin glass (SG) compound below the freezing temperature T{sub f} in the crystal regions, where various microscopic magnetic spin states (MMSSs), namely, “loose” spins, finite, and infinite clusters, are formed. It was shown that there is a broad distribution of the LEMPs lifetimes. The presence of the long-lived LEMPs is caused by the admixture of the optically active bright exciton states to the dark exciton states, i.e., the “brightening” of the dark LEMPs which exist along with the bright LEMPs. The lifetimes of the dark LEMPs correspond to hundreds of nanoseconds. It was found that the time decay of photoluminescence band intensity is approximated by the sum of two functions: a single exponential function and the Kohlrausch–Williams–Watts stretched exponential function. The stretched exponential function describes the recombination processes of the LEMPs formed in the crystal regions of the finite clusters as well as the infinite cluster. This reflects the appearance of spatially heterogeneous dynamics in Cd{sub 0.70}Mn{sub 0.30}Te SG compound below T{sub f} which is due to the disorder in the spin distribution caused by the formation of different MMSSs.

  9. Monte Carlo study of efficiency roll-off of phosphorescent organic light-emitting diodes: Evidence for dominant role of triplet-polaron quenching

    SciTech Connect

    Eersel, H. van Coehoorn, R.; Bobbert, P. A.; Janssen, R. A. J.

    2014-10-06

    We present an advanced molecular-scale organic light-emitting diode (OLED) model, integrating both electronic and excitonic processes. Using this model, we can reproduce the measured efficiency roll-off for prototypical phosphorescent OLED stacks based on the green dye tris[2-phenylpyridine]iridium (Ir(ppy){sub 3}) and the red dye octaethylporphine platinum (PtOEP) and study the cause of the roll-off as function of the current density. Both the voltage versus current density characteristics and roll-off agree well with experimental data. Surprisingly, the results of the simulations lead us to conclude that, contrary to what is often assumed, not triplet-triplet annihilation but triplet-polaron quenching is the dominant mechanism causing the roll-off under realistic operating conditions. Simulations for devices with an optimized recombination profile, achieved by carefully tuning the dye trap depth, show that it will be possible to fabricate OLEDs with a drastically reduced roll-off. It is envisaged that J{sub 90}, the current density at which the efficiency is reduced to 90%, can be increased by almost one order of magnitude as compared to the experimental state-of-the-art.

  10. Defects-assisted ferromagnetism due to bound magnetic polarons in Ce into Fe, Co:ZnO nanoparticles and first-principle calculations.

    PubMed

    Verma, Kuldeep Chand; Kotnala, R K

    2016-02-21

    Zn0.94TM0.03Ce0.03O [Zn0.94Fe0.03Ce0.03O (ZFCeO) and Zn0.94Co0.03Ce0.03O (ZCCeO)] nanoparticles were synthesized by a sol-gel process. Elemental analysis of these nanoparticles detects the weight percentage of Zn, Co, Fe, Ce and O in each sample. The Rietveld refinement of the X-ray diffraction pattern obtains the occupancy of dopant atoms, Wurtzite ZnO structure, crystallinity and lattice deformation with doping. The Ce doping into ZFO and ZCO form nanoparticles than nanorods was observed in pure ZnO, ZFO and ZCO samples that described due to chemical and ionic behavior of Ce, Fe, Co and Zn ions. The Raman active modes have peak broadening, intensity changes and peak shifts with metal doping that induces lattice defects. Photoluminescence spectra show blue-shifts at near-band edges and defects that influence broad visible emission with Ce doping. An enhancement in ferromagnetism in the magnetic hysteresis at 5 K is measured. The zero-field cooling and field cooling at H = 500 Oe and T = 300-5 K could confirm antiferromagnetic interactions mediated by defect carriers. The bound magnetic polaron at defect sites is responsible for the observed ferromagnetism. The ac magnetic susceptibility measurements determine the antiferromagnetic to ferromagnetic transition with some magnetic clustered growth in the samples and reveal a frequency independent peak that shows the Neel temperature. Weak room temperature ferromagnetism and optical quenching in ZFCeO are described by valance states of Fe and Ce ions, respectively. Using first-principle calculations, we studied the occupancy of Ce (replacing Zn atoms) in the Wurtzite structure.

  11. Measurement of the resonant polaron effect in the Reststrahlen band of GaAs:Si using far-infrared two-photon excitation

    SciTech Connect

    Wenckebach, W.Th.; Planken, P.C.M.; Son, P.C. van

    1995-12-31

    We present the results of photoconductivity measurements of the resonant electron-phonon interaction in the middle of the Reststrahlen band using two-photon excitation with intense picosecond pulses with frequency around 143 cm{sup -1} (70 {mu}m). We use two photons rather than a single photon for the excitation of the resonant-polaron to avoid the problems of strong reflection and dielectric artifacts encountered in direct single-photon excitation in the Reststrahlen band. The sample is a 10 {mu}m thick Si-doped GaAs epitaxial layer on a 400 {mu}m semi-insulating GaAs substrate. The electronic levels of the Si shallow donor can be tuned by the application of a magnetic field. Intense tunable picosecond pulses with a frequency of around 143 cm{sup -1} from the Dutch free-electron laser FELIX are weakly focussed onto the sample, which is kept at 8 K. Electrons excited to the 3d{sup +2} state via the electric-dipole allowed two-photon transition out of the 1s{sub 0-} ground state, decay to the conduction band and give rise to an increase in the photoconductivity. The figure shows the energy-peak position of the 3d{sup +2} transition thus obtained as a function of the magnetic-field strength. The figure clearly shows the avoided crossing around the LO-phonon energy where the coupling shows the avoided crossing around the LO-phonon energy where the coupling between the 3d{sup +2} state and the LO phonon is strongest. Note that the data between 267 cm{sup -1} and 296 cm{sup -1} are extremely difficult to obtain with single-photon excitation because of their position in the middle of the Reststrahlen band.

  12. Optical transition energy of magneto-polaron in a GaAs{sub 0.9}P{sub 0.1}/GaAs{sub 0.6}P{sub 0.4} quantum dot

    SciTech Connect

    Vinolin, Ada; Peter, A. John

    2015-06-24

    Magneto-LO-polaron in a cylindrical GaAs{sub 0.9} P{sub 0.1} / GaAs{sub 0.6} P{sub 0.4} quantum dot is investigated taking into consideration of geometrical confinement effect. The effects of phonon on the exciton binding energy and the interband emission energy as a function of dot radius are found. The calculations are performed within the single band effective mass approximation using the variational method based on the Lee-Low-Pine LLP transformation.

  13. Optical transition energy of magneto-polaron in a GaAs0.9P0.1/GaAs0.6P0.4 quantum dot

    NASA Astrophysics Data System (ADS)

    Vinolin, Ada; Peter, A. John

    2015-06-01

    Magneto-LO-polaron in a cylindrical GaAs0.9 P0.1 / GaAs0.6 P0.4 quantum dot is investigated taking into consideration of geometrical confinement effect. The effects of phonon on the exciton binding energy and the interband emission energy as a function of dot radius are found. The calculations are performed within the single band effective mass approximation using the variational method based on the Lee-Low-Pine LLP transformation.

  14. Small Families

    MedlinePlus

    ... more emphasis on careers for women, more effective methods of contraception, and the rising cost of rearing and educating children. There are some very clear benefits to having a small family; Each child receives more parental attention and educational advantages, which generally raise her self- ...

  15. Impact of D2O/H2O Solvent Exchange on the Emission of HgTe and CdTe Quantum Dots: Polaron and Energy Transfer Effects.

    PubMed

    Wen, Qiannan; Kershaw, Stephen V; Kalytchuk, Sergii; Zhovtiuk, Olga; Reckmeier, Claas; Vasilevskiy, Mikhail I; Rogach, Andrey L

    2016-04-26

    We have studied light emission kinetics and analyzed carrier recombination channels in HgTe quantum dots that were initially grown in H2O. When the solvent is replaced by D2O, the nonradiative recombination rate changes highlight the role of the vibrational degrees of freedom in the medium surrounding the dots, including both solvent and ligands. The contributing energy loss mechanisms have been evaluated by developing quantitative models for the nonradiative recombination via (i) polaron states formed by strong coupling of ligand vibration modes to a surface trap state (nonresonant channel) and (ii) resonant energy transfer to vibration modes in the solvent. We conclude that channel (i) is more important than (ii) for HgTe dots in either solution. When some of these modes are removed from the relevant spectral range by the H2O to D2O replacement, the polaron effect becomes weaker and the nonradiative lifetime increases. Comparisons with CdTe quantum dots (QDs) served as a reference where the resonant energy loss (ii) a priori was not a factor, also confirmed by our experiments. The solvent exchange (H2O to D2O), however, is found to slightly increase the overall quantum yield of CdTe samples, probably by increasing the fraction of bright dots in the ensemble. The fundamental study reported here can serve as the foundation for the design and optimization principles of narrow bandgap quantum dots aimed at applications in long wavelength colloidal materials for infrared light emitting diodes and photodetectors.

  16. Muon spin relaxation and magnetic measurements on Ba0.63K0.37BiO3 : Evidence for polaronic strong-coupling phonon-mediated pairing

    NASA Astrophysics Data System (ADS)

    Zhao, Guo-Meng

    2007-07-01

    A penetration depth measurement was carried out on the optimally doped bismuthate superconductor Ba0.63K0.37BiO3 (Tc=29.2K) using the muon-spin-relaxation technique. We find that the temperature dependence of the penetration depth λ(T) of this compound is in excellent agreement with strong-coupling phonon-mediated superconductivity with a reduced energy gap of 2Δ(0)/kBTc=4.4 and a retarded electron-phonon coupling constant λe-p=1.4 . The observed large reduced energy gap rules out the possibility of pairing mechanisms based on coupling to high-energy electronic excitations. Quantitative data analyses indicate that high-temperature superconductivity in bismuthates arises from the Cooper pairing of polaronic charge carriers.

  17. First principles study of the crystal, electronic structure, and diffusion mechanism of polaron-Na vacancy of Na3MnPO4CO3 for Na-ion battery applications

    NASA Astrophysics Data System (ADS)

    Debbichi, M.; Debbichi, L.; Dinh, Van An; Lebègue, S.

    2017-02-01

    Based on first principles calculations, we investigate the geometry, electronic structure, and diffusion mechanism of Na ions in Na3MnPO4CO3 using density functional theory with a Hubbard potential correction. Our results suggest that the structure of Na3MnPO4CO3 can be deintercalated with more than one Na ion, and that the removal of a Na ion can form a bound polaron. We find that our calculations of the intercalation voltages for the redox couples Mn2+ /Mn3+ and Mn3+ /Mn4+ agree very well with the experimental data. In addition, we demonstrate that Na in Na3MnPO4CO3 can diffuse in three directions with low activation energy barriers, allowing a fast charging rate.

  18. Strong dependence on doping of a low-activation-energy relaxation process in YBa{sub 2}Cu{sub 3}O{sub 6+{ital x}}: Possible polaron relaxation

    SciTech Connect

    Cannelli, G.; Cantelli, R.; Cordero, F.; Trequattrini, F.; Ferretti, M.

    1996-12-01

    The elastic energy loss of YBa{sub 2}Cu{sub 3}O{sub 6+{ital x}} is measured below room temperature with {ital x} close to the maximum stoichiometry, where three low-activation-energy peaks are present. It is found that the intensity of the process with the lowest activation energy, {ital E}{approximately}0.076 eV decreases very steeply when {ital x} is lowered just below its maximum value; it becomes undetectable when the sample is still in the {ital T}{sub {ital c}}=90 K plateau and all the other peaks are nearly unaffected. The possible mechanisms for this process are discussed, mainly in terms of hopping of polarons or off-center atoms. The characteristics that these defects should possess in order to produce anelastic relaxation are specified. The most natural way to interpret the peak is the assumption of the formation and reorientation of bipolarons among orbitals which are occupied by holes only at the highest O stoichiometries; according to Tolentino {ital et} {ital al}. [Physica C {bold 192}, 115 (1992)], such holes could reside in the {ital p}{sub {ital z}} orbitals of the apical O atoms. {copyright} {ital 1996 The American Physical Society.}

  19. Anomalous electrical relaxation and polaron conduction in nano-crystalline Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4}

    SciTech Connect

    Kumar, N. S. Krishna; Shahid, T. S.; Govindaraj, G.

    2015-06-24

    Nano-crystalline Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} was synthesized by chemical co-precipitation method and characterized with X-ray diffraction. Ac electrical impedance data are taken for the frequency range of 1Hz to 1MHz for various temperatures from 303K to 483K. The ac electrical conduction deviates from the Debye type relaxation which indicates polaron type conduction. In the present study unique anomalous relaxation function in time and frequency domain is used to investigate deviation from the Debye relaxation. The physical basis of anomalous or non-Debye process is explained in terms of change in Debye dipole μ{sub D}=ρr{sub D} of charge ρ into gρ due to the molecular charge interaction and defect disorder. This interaction shifts the Debye relaxation rate τ to a slow relaxation rate τ{sup g}. The fraction 0

  20. Polaron response dominated multiferroic property in 12R-type hexagonal Ba(Ti{sub 1/3}Mn{sub 2/3})O{sub 3-δ} ceramics

    SciTech Connect

    Wei, Xian-Kui E-mail: xiankui.wei@epfl.ch; Su, Yantao; Sui, Yu; Jin, Changqing; Yu, Richeng E-mail: xiankui.wei@epfl.ch

    2015-08-07

    We report the multiferroic properties of 12R-type hexagonal Ba(Ti{sub 1/3}Mn{sub 2/3})O{sub 3-δ} found in Mn-doped BaTiO{sub 3} series samples. Hysteresis measurements reveal the coexistence of weak ferromagnetism and ferroelectricity at room temperature. Furthermore, frequency-driven dynamic ferroelectric phase transition is disclosed around a critical frequency of 220 Hz. Analyses on the dielectric relaxation, leakage current, crystal structure, and magnetic susceptibility lead us to conclude that the response of polarons dominates the observed physical properties, and the dynamic phase transition may ascribe to the response mode changes of the localized electrons. More importantly, we figure out the crucial factors leading to difference of the ferroelectric and magnetic properties of the 12R-type Ba(Ti{sub 1/3}Mn{sub 2/3})O{sub 3-δ} samples from that of the 6H-type Ba(Ti{sub 1-x}M{sub x})O{sub 3-δ} (M = Fe, Mn) samples.

  1. Pressure-induced colossal piezoresistance effect and the collapse of the polaronic state in the bilayer manganite (La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn2O7.

    PubMed

    Thiyagarajan, R; Manivannan, N; Arumugam, S; Esakki Muthu, S; Tamilselvan, N R; Sekar, C; Yoshino, H; Murata, K; Apostu, M O; Suryanarayanan, R; Revcolevschi, A

    2012-04-04

    We have investigated the effect of hydrostatic pressure as a function of temperature on the resistivity of a single crystal of the bilayer manganite (La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn(2)O(7). Whereas a strong insulating behaviour is observed at all temperatures at ambient pressure, a clear transition into a metallic-like behaviour is induced when the sample is subjected to a pressure (P) of ~1.0 GPa at T < 70 K. A huge negative piezoresistance ~10(6) in the low temperature region at moderate pressures is observed. When the pressure is increased further (5.5 GPa), the high temperature polaronic state disappears and a metallic behaviour is observed. The insulator to metal transition temperature exponentially increases with pressure and the distinct peak in the resistivity that is observed at 1.0 GPa almost vanishes for P > 7.0 GPa. A modification in the orbital occupation of the e(g) electron between 3d(x(2)-y(2)) and 3d(z(2)-r(2)) states, as proposed earlier, leading to a ferromagnetic double-exchange phenomenon, can qualitatively account for our data.

  2. Magnetic and electronic properties of La3 MO7 and possible polaron formation in hole-doped La3 MO7 (M  =  Ru and Os)

    NASA Astrophysics Data System (ADS)

    Gao, Bin; Weng, Yakui; Zhang, Jun-Jie; Zhang, Huimin; Zhang, Yang; Dong, Shuai

    2017-03-01

    Oxides with 4d/5d transition metal ions are physically interesting for their particular crystalline structures as well as the spin–orbit coupled electronic structures. Recent experiments revealed a series of 4d/5d transition metal oxides R 3 MO7 (R: rare earth; M: 4d/5d transition metal) with unique quasi-one-dimensional M chains. Here first-principles calculations have been performed to study the electronic structures of La3OsO7 and La3RuO7. Our study confirm both of them to be Mott insulating antiferromagnets with identical magnetic order. The reduced magnetic moments, which are much smaller than the expected value for ideal high-spin state (3 t 2g orbitals occupied), are attributed to the strong p  ‑  d hybridization with oxygen ions, instead of the spin–orbit coupling. The Ca-doping to La3OsO7 and La3RuO7 can not only modulate the nominal carrier density but also affect the orbital order as well as the local distortions. The Coulombic attraction and particular orbital order would prefer to form polarons, which might explain the puzzling insulating behavior of doped 5d transition metal oxides. In addition, our calculations predict that the Ca-doping can trigger ferromagnetism in La3RuO7 but not in La3OsO7.

  3. Temperature and composition dependent density of states extracted using overlapping large polaron tunnelling model in MnxCo1-xFe2O4 (x=0.25, 0.5, 0.75) nanoparticles

    NASA Astrophysics Data System (ADS)

    Jamil, Arifa; Afsar, M. F.; Sher, F.; Rafiq, M. A.

    2017-03-01

    We report detailed ac electrical and structural characterization of manganese cobalt ferrite nanoparticles, prepared by coprecipitation technique. X-ray diffraction (XRD) confirmed single-phase cubic spinel structure of the nanoparticles. Tetrahedral (A) and octahedral (B) group complexes were present in the spinel lattice as determined by Fourier Transform Infrared Spectroscopy (FTIR). Scanning Electron Microscope (SEM) images revealed presence of spherical shape nanoparticles having an average diameter 50-80 nm. Composition, temperature and frequency dependent ac electrical study of prepared nanoparticles interpreted the role of cationic distribution between A and B sites. Overlapping large polaron tunnelling (OLPT) conduction mechanism was observed from 290 to 200 K. Frequency exponent s was fitted theoretically using OLPT model. High values of Density of States (DOS) of the order of 1022-1024 eV-1 cm-3 were extracted from ac conductivity for different compositions. We found that DOS was dependent on distribution of cations in the tunnel-type cavities along the a and b axis.

  4. Lung cancer - small cell

    MedlinePlus

    Cancer - lung - small cell; Small cell lung cancer; SCLC ... About 15% of all lung cancer cases are SCLC. Small cell lung cancer is slightly more common in men than women. Almost all cases of SCLC are ...

  5. Small Scale Organic Techniques

    ERIC Educational Resources Information Center

    Horak, V.; Crist, DeLanson R.

    1975-01-01

    Discusses the advantages of using small scale experimentation in the undergraduate organic chemistry laboratory. Describes small scale filtration techniques as an example of a semi-micro method applied to small quantities of material. (MLH)

  6. Small bowel bacterial overgrowth

    MedlinePlus

    Overgrowth - intestinal bacteria; Bacterial overgrowth - intestine; Small intestinal bacterial overgrowth; SIBO ... intestine does not have a high number of bacteria. Excess bacteria in the small intestine may use ...

  7. Part 1: Synthesis and characterization of magnetic chromium5tellurium nanoparticles Part 2: Local atomic structure studies using theory to simulate polarons in superconducting cuprates and experiment to analyze alternative energy nanomaterials

    NASA Astrophysics Data System (ADS)

    Martucci, Mary B.

    The field of spintronics, the development of spin-based devices that utilize the spin degree of freedom to increase memory capacity, has emerged as a solution to faster more efficient memory storage for electronic devices. One class of materials that has been extensively studied is the half-metallic ferromagnets, compounds that are 100% spin-polarized at the Fermi level. One material in this group that has been investigated is chromium telluride (Cr 1-xTe), whose family of compounds is known to exhibit a wide range of interesting magnetic and electronic properties. We have developed a hot injection solution synthesis of Cr5Te8 nanoplatlets which show similar magnetic behavior to the bulk material. It has also been shown that selenium and sulfur analogues can be obtained without changing the reaction conditions, making progress toward a better understanding of the reaction as well as an interesting family of compounds. Using real-space simulations, the effect of polarons in the high-Tc superconducting cuprates has been studied. The simulations demonstrate energetically favorable sites for the defects and show evidence of longer-range pairing interactions. Variations of the stripe show similar energetic results. X-ray absorption fine structure spectroscopy and neutron scattering have been utilized to examine the local structure of Ni-doped Mg nanoparticles, a hydrogen storage material as well as Cu2ZnSnS4 (CZTS) nanoparticles, a photovoltaic material. The Mg-Ni material shows much local disorder upon hydrogen cycling. The CZTS data demonstrate a loss of sulfur from around the copper sites upon annealing, helping to explain the changes observed in the optical absorption properties resulting from the annealing process.

  8. Small Intestine Disorders

    MedlinePlus

    Your small intestine is the longest part of your digestive system - about twenty feet long! It connects your stomach to ... many times to fit inside your abdomen. Your small intestine does most of the digesting of the foods ...

  9. Small intestine (image)

    MedlinePlus

    The small intestine is the portion of the digestive system most responsible for absorption of nutrients from food into the ... the duodenum. This short first portion of the small intestine is followed by the jejunum and the ileum. ...

  10. Small bowel resection - discharge

    MedlinePlus

    ... chap 26. Read More Colon cancer Crohn disease Intestinal obstruction Small bowel resection Patient Instructions Bland diet Crohn ... Editorial team. Related MedlinePlus Health Topics Intestinal Cancer Intestinal Obstruction Small Intestine Disorders Browse the Encyclopedia A.D. ...

  11. Small Libraries, Big Technology

    ERIC Educational Resources Information Center

    Roberts,Gary

    2005-01-01

    Small libraries don't have the resources to adopt every new technology. It is important that small libraries operate strategically, adopting only those technologies that are the most beneficial to their patrons.

  12. Small Business Pedagogic Practices

    ERIC Educational Resources Information Center

    Billett, Stephen; Hernon-Tinning, Barnie; Ehrich, Lisa

    2003-01-01

    Understanding how learning for small businesses should best proceed constitutes a worthwhile, yet challenging, pedagogic project. In order to maintain their viability, small businesses need to be able to respond to new practices and tasks. Yet small businesses seem neither attracted to nor to value the kinds of taught courses that are the standard…

  13. Small Business Procurement Event

    DTIC Science & Technology

    2014-08-13

    Small Business Procurement Event 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK...distribution unlimited 13. SUPPLEMENTARY NOTES NDIA 27th Navy Gold Coast Small Business Procurement Event , 12-13 Aug 2014, San Diego, CA. 14. ABSTRACT...18 Target the Small Business Accessible Market within the Department of the Navy $77.8B Department of the Navy Total SB Eligible Spend

  14. Small Wastewater Systems Research

    EPA Pesticide Factsheets

    Small communities face barriers to building and maintaining effective wastewater treatment services, challenges include financial/economic limitations, lack of managerial training and geographic isolation/remoteness.

  15. IBM Small Business Survey.

    ERIC Educational Resources Information Center

    International Business Machines Corp., Armonk, NY.

    A telephone survey conducted March 15-22, 1991, examined how small businesses are currently performing. Interviewees were 400 small business owners randomly selected from a Dun and Bradstreet list of companies with 50 or fewer employees. Major findings were as follows: (1) owners were survivors, highly confident in their own abilities, and…

  16. Industrial Education. "Small Engines".

    ERIC Educational Resources Information Center

    Parma City School District, OH.

    Part of a series of curriculum guides dealing with industrial education in junior high schools, this guide provides the student with information and manipulative experiences on small gasoline engines. Included are sections on shop adjustment, safety, small engines, internal combustion, engine construction, four stroke engines, two stroke engines,…

  17. Sensitive Small Area Photometer

    ERIC Educational Resources Information Center

    Levenson, M. D.

    1970-01-01

    Describes a simple photometer capable of measuring small light intensities over small areas. The inexpensive, easy-to- construct instrument is intended for use in a student laboratory to measure the light intensities in a diffraction experiment from single or multiple slits. Typical experimental results are presented along with the theoretical…

  18. Small Schools, Big Future

    ERIC Educational Resources Information Center

    Halsey, R. John

    2011-01-01

    Historically, small schools have played a very important role in the provision of schooling in Australia. Numerically, using an enrollment of 200 or less, small schools represent approximately 45% of the schools in Australia. Population growth and the consequences of this, in particular for food production, water and energy, mean that the…

  19. Small Wind Information (Postcard)

    SciTech Connect

    Not Available

    2011-08-01

    The U.S. Department of Energy's Wind Powering America initiative maintains a website section devoted to information about small wind turbines for homeowners, ranchers, and small businesses. This postcard is a marketing piece that stakeholders can provide to interested parties; it will guide them to this online resource.

  20. Big Project, Small Leaders

    ERIC Educational Resources Information Center

    Schon, Jennifer A.; Eitel, Karla B.; Bingaman, Deirdre; Miller, Brant G.; Rittenburg, Rebecca A.

    2014-01-01

    Donnelly, Idaho, is a small town surrounded by private ranches and Forest Service property. Through the center of Donnelly runs Boulder Creek, a small tributary feeding into Cascade Lake Reservoir. Boulder Creek originates from a mountain lake north of Donnelly. Since 1994 it has been listed as "impaired" by the Environmental Protection…

  1. Small Animal Care.

    ERIC Educational Resources Information Center

    Livesey, Dennis W.; Fong, Stephen

    This small animal care course guide is designed for students who will be seeking employment in veterinary hospitals, kennels, grooming shops, pet shops, and small-animal laboratories. The guide begins with an introductory section that gives the educational philosophy of the course, job categories and opportunities, units of instruction required…

  2. Small Groups in Action

    ERIC Educational Resources Information Center

    Suessmuth, Patrick

    1974-01-01

    Small groups can sometimes be difficult to set up and work with properly. A number of tips for small group instruction are divided into seven areas: (1) presenting tasks; (2) group seating; (3) task time; (4) answering questions; (5) teacher's role in observing groups; (6) group noise level patterns; and (7) serial take-ups. (BP)

  3. Small Soil Animals.

    ERIC Educational Resources Information Center

    Seevers, Elmer R.

    1978-01-01

    Describes an inexpensive technique for providing student opportunities to observe and identify the variety of small animals living in the first few inches below the surface of the soil. A classification key to some small soil animals is also presented. (HM)

  4. Small GTPases and cilia.

    PubMed

    Li, Yujie; Hu, Jinghua

    2011-01-01

    Small GTPases are key molecular switches that bind and hydrolyze GTP in diverse membrane- and cytoskeleton-related cellular processes. Recently, mounting evidences have highlighted the role of various small GTPases, including the members in Arf/Arl, Rab, and Ran subfamilies, in cilia formation and function. Once overlooked as an evolutionary vestige, the primary cilium has attracted more and more attention in last decade because of its role in sensing various extracellular signals and the association between cilia dysfunction and a wide spectrum of human diseases, now called ciliopathies. Here we review recent advances about the function of small GTPases in the context of cilia, and the correlation between the functional impairment of small GTPases and ciliopathies. Understanding of these cellular processes is of fundamental importance for broadening our view of cilia development and function in normal and pathological states and for providing valuable insights into the role of various small GTPases in disease processes, and their potential as therapeutic targets.

  5. Technology for small spacecraft

    NASA Technical Reports Server (NTRS)

    1994-01-01

    This report gives the results of a study by the National Research Council's Panel on Small Spacecraft Technology that reviewed NASA's technology development program for small spacecraft and assessed technology within the U.S. government and industry that is applicable to small spacecraft. The panel found that there is a considerable body of advanced technology currently available for application by NASA and the small spacecraft industry that could provide substantial improvement in capability and cost over those technologies used for current NASA small spacecraft. These technologies are the result of developments by commercial companies, Department of Defense agencies, and to a lesser degree NASA. The panel also found that additional technologies are being developed by these same entities that could provide additional substantial improvement if development is successfully completed. Recommendations for future technology development efforts by NASA across a broad technological spectrum are made.

  6. SmallSat Database

    NASA Technical Reports Server (NTRS)

    Petropulos, Dolores; Bittner, David; Murawski, Robert; Golden, Bert

    2015-01-01

    The SmallSat has an unrealized potential in both the private industry and in the federal government. Currently over 70 companies, 50 universities and 17 governmental agencies are involved in SmallSat research and development. In 1994, the U.S. Army Missile and Defense mapped the moon using smallSat imagery. Since then Smart Phones have introduced this imagery to the people of the world as diverse industries watched this trend. The deployment cost of smallSats is also greatly reduced compared to traditional satellites due to the fact that multiple units can be deployed in a single mission. Imaging payloads have become more sophisticated, smaller and lighter. In addition, the growth of small technology obtained from private industries has led to the more widespread use of smallSats. This includes greater revisit rates in imagery, significantly lower costs, the ability to update technology more frequently and the ability to decrease vulnerability of enemy attacks. The popularity of smallSats show a changing mentality in this fast paced world of tomorrow. What impact has this created on the NASA communication networks now and in future years? In this project, we are developing the SmallSat Relational Database which can support a simulation of smallSats within the NASA SCaN Compatability Environment for Networks and Integrated Communications (SCENIC) Modeling and Simulation Lab. The NASA Space Communications and Networks (SCaN) Program can use this modeling to project required network support needs in the next 10 to 15 years. The SmallSat Rational Database could model smallSats just as the other SCaN databases model the more traditional larger satellites, with a few exceptions. One being that the smallSat Database is designed to be built-to-order. The SmallSat database holds various hardware configurations that can be used to model a smallSat. It will require significant effort to develop as the research material can only be populated by hand to obtain the unique data

  7. Small satellite product assurance

    NASA Astrophysics Data System (ADS)

    Demontlivault, J.; Cadelec, Jacques

    1993-01-01

    In order to increase the interest in small satellites, their cost must be reduced; reducing product assurance costs induced by quality requirements is a major objective. For a logical approach, small satellites are classified in three main categories: satellites for experimental operations with a short lifetime, operational satellites manufactured in small mass with long lifetime requirements, operational satellites (long lifetime required), of which only a few models are produced. The various requirements as regards the product assurance are examined for each satellite category: general requirements for space approach, reliability, electronic components, materials and processes, quality assurance, documentation, tests, and management. Ideal product assurance system integrates quality teams and engineering teams.

  8. Small Bowel Adenocarcinoma.

    PubMed

    Aparicio, Thomas; Zaanan, Aziz; Mary, Florence; Afchain, Pauline; Manfredi, Sylvain; Evans, Thomas Ronald Jeffry

    2016-09-01

    Small bowel adenocarcinomas (SBAs) are rare tumors, but their incidence is increasing. The most common primary location is the duodenum. Even though SBAs are more often sporadic, some diseases are risk factors. Early diagnosis of small bowel adenocarcinoma remains difficult, despite significant radiologic and endoscopic progress. After R0 surgical resection, the main prognostic factor is lymph node invasion. An international randomized trial (BALLAD [Benefit of Adjuvant Chemotherapy For Small Bowel Adenocarcinoma] study) will evaluate the benefit of adjuvant chemotherapy. For metastatic disease, retrospectives studies suggest that platinum-based chemotherapy is the most effective treatment. Phase II studies are ongoing to evaluate targeted therapy in metastatic SBA.

  9. How small are small mutation rates?

    PubMed

    Wu, Bin; Gokhale, Chaitanya S; Wang, Long; Traulsen, Arne

    2012-04-01

    We consider evolutionary game dynamics in a finite population of size N. When mutations are rare, the population is monomorphic most of the time. Occasionally a mutation arises. It can either reach fixation or go extinct. The evolutionary dynamics of the process under small mutation rates can be approximated by an embedded Markov chain on the pure states. Here we analyze how small the mutation rate should be to make the embedded Markov chain a good approximation by calculating the difference between the real stationary distribution and the approximated one. While for a coexistence game, where the best reply to any strategy is the opposite strategy, it is necessary that the mutation rate μ is less than N (-1/2)exp[-N] to ensure that the approximation is good, for all other games, it is sufficient if the mutation rate is smaller than (N ln N)(-1). Our results also hold for a wide class of imitation processes under arbitrary selection intensity.

  10. Small bowel resection

    MedlinePlus

    ... cause inflammation include regional ileitis , regional enteritis , and Crohn disease . Cancer Carcinoid tumor Injuries to the small intestine ... you have a chronic condition, such as cancer, Crohn disease or ulcerative colitis, you may need ongoing medical ...

  11. Small islands adrift

    NASA Astrophysics Data System (ADS)

    Petherick, Anna

    2015-07-01

    With the charismatic former president of the Maldives, Mohamed Nasheed, behind bars on a widely derided terrorism charge, Anna Petherick asks whether small island states can really make themselves heard in Paris.

  12. Small RNAs in spermatogenesis.

    PubMed

    Yadav, Ram Prakash; Kotaja, Noora

    2014-01-25

    Spermatogenesis is characterized by meiotic divisions and major morphological changes to produce spermatozoa that are capable of independent movement and fertilization of an egg. Male germ cell differentiation is governed by orchestrated, phase-specific gene expression patterns that are tightly controlled at transcriptional and post-transcriptional level. Post-transcriptional regulation of protein-coding mRNAs becomes prominent during the late steps of spermatogenesis when the compacting sperm nucleus becomes transcriptionally inhibited. Small non-coding RNAs are important regulators of gene expression that mainly function post-transcriptionally to control the properties of their target mRNAs. Male germ cells express several classes of small RNAs, including Dicer-dependent microRNAs (miRNAs) and endogenous small interfering RNAs (endo-siRNAs), as well as Dicer-independent piwi-interacting RNAs (piRNAs). Increasing evidence supports the essential role of small RNA-mediated RNA regulation in normal spermatogenesis and male fertility.

  13. Small-x physics

    SciTech Connect

    Mueller, A.H.

    1997-06-01

    After a brief review of the kinematics of deep inelastic lepton-proton scattering, the parton model is described. Small-x behavior coming from DGLAP evolution and from BFKL evolution is discussed, and the two types of evolution are contrasted and compared. Then a more detailed discussion of BFKL dynamics is given. The phenomenology of small-x physics is discussed with an emphasis on ways in which BFKL dynamics may be discussed and measured. 45 refs., 12 figs.

  14. Temperature Dependence of Large Polaron Superconductivity.

    DTIC Science & Technology

    1995-07-18

    to explain the variation of critical temperature Tc with chemical composition and the temperature dependence of high-Tc superconductor properties is...One result of this refinement is a clearer picture of the dependence of electron hopping activation energy on crystal-field parameters. A... dependence is more typically exponential. With these improvements, precise fits to penetration depth versus temperature measurements for high-purity YBCO

  15. MINERVA: Small Planets from Small Telescopes

    NASA Astrophysics Data System (ADS)

    Wittenmyer, Robert A.; Johnson, John Asher; Wright, Jason; McCrady, Nate; Swift, Jonathan; Bottom, Michael; Plavchan, Peter; Riddle, Reed; Muirhead, Philip S.; Herzig, Erich; Myles, Justin; Blake, Cullen H.; Eastman, Jason; Beatty, Thomas G.; Lin, Brian; Zhao, Ming; Gardner, Paul; Falco, Emilio; Criswell, Stephen; Nava, Chantanelle; Robinson, Connor; Hedrick, Richard; Ivarsen, Kevin; Hjelstrom, Annie; Vera, Jon De; Szentgyorgyi, Andrew

    2015-09-01

    The Kepler mission has shown that small planets are extremely common. It is likely that nearly every star in the sky hosts at least one rocky planet. We just need to look hard enough-but this requires vast amounts of telescope time. MINERVA (MINiature Exoplanet Radial Velocity Array) is a dedicated exoplanet observatory with the primary goal of discovering rocky, Earth-like planets orbiting in the habitable zone of bright, nearby stars. The MINERVA team is a collaboration among UNSW Australia, Harvard-Smithsonian Center for Astrophysics, Penn State University, University of Montana, and the California Institute of Technology. The four-telescope MINERVA array will be sited at the F.L. Whipple Observatory on Mt Hopkins in Arizona, USA. Full science operations will begin in mid-2015 with all four telescopes and a stabilised spectrograph capable of high-precision Doppler velocity measurements. We will observe ~100 of the nearest, brightest, Sun-like stars every night for at least five years. Detailed simulations of the target list and survey strategy lead us to expect new low-mass planets.

  16. Small Animal Retinal Imaging

    NASA Astrophysics Data System (ADS)

    Choi, WooJhon; Drexler, Wolfgang; Fujimoto, James G.

    Developing and validating new techniques and methods for small animal imaging is an important research area because there are many small animal models of retinal diseases such as diabetic retinopathy, age-related macular degeneration, and glaucoma [1-6]. Because the retina is a multilayered structure with distinct abnormalities occurring in different intraretinal layers at different stages of disease progression, there is a need for imaging techniques that enable visualization of these layers individually at different time points. Although postmortem histology and ultrastructural analysis can be performed for investigating microscopic changes in the retina in small animal models, this requires sacrificing animals, which makes repeated assessment of the same animal at different time points impossible and increases the number of animals required. Furthermore, some retinal processes such as neurovascular coupling cannot be fully characterized postmortem.

  17. A Small as Possible

    NASA Technical Reports Server (NTRS)

    Tibbitts, Scott

    2003-01-01

    This story begins with a bit of serendipity: I was on a trip to see a Shuttle launch and I happened to sit next to a guy who was in charge of batteries for Space Systems/Loral. He told me that they needed to create a new battery bypass switch, the device that takes a battery out of commission if it goes bad. After discussing the conversation back at my company, we decided that we could create the switch. We contacted the folks at Loral and they said, 'Okay, let s see what you can come up with. We need it as small as possible.' We asked, 'How small?' They said, 'We need it as small as you can possibly make it.'

  18. Small-world networks

    NASA Astrophysics Data System (ADS)

    Strogatz, Steven

    Everyone is familiar with the small-world phenomenon: soon after meeting a stranger, we are often suprised to discover that we have a mutual friend, or that we are somehow linked by a short chain of friends. In this talk, I'll present evidence that the small-world phenomenon is more than a curiosity of social networks — it is actually a general property of large, sparse networks whose topology is neither completely regular nor completely random. To check this idea, Duncan Watts and I have analyzed three networks of scientific interest: the neural network of the nematode worm C. elegans, the electrical power grid of the western United States, and the collaboration graph of actors in feature films. All three are small worlds, in the sense that the average number of "handshakes" separating any two members is extremely small (close to the theoretical lower limit set by a random graph). Yet at the same time, all three networks exhibit much more local clustering than a random net, demonstrating that they are not random. I'll also discuss a class of model networks that interpolate between regular lattices and random graphs. Previous theoretical research on complex systems in a wide range of disciplines has focused almost exclusively on networks that are either regular or random. Real networks often lie somewhere in between. Our mathematical model shows that networks in this middle ground tend to exhibit the small-world phenomenon, thanks to the presence of a few long-range edges that link parts of the graph that would otherwise be far apart. Furthermore, we find that when various dynamical systems are coupled in a small-world fashion, they exhibit much greater propagation speed, computational power, and synchronizability than their locally connected, regular counterparts. We explore the implications of these results for simple models of disease spreading, global computation in cellular automata, and collective locking of biological oscillators.

  19. Tracking Small Artists

    NASA Astrophysics Data System (ADS)

    Russell, James C.; Klette, Reinhard; Chen, Chia-Yen

    Tracks of small animals are important in environmental surveillance, where pattern recognition algorithms allow species identification of the individuals creating tracks. These individuals can also be seen as artists, presented in their natural environments with a canvas upon which they can make prints. We present tracks of small mammals and reptiles which have been collected for identification purposes, and re-interpret them from an esthetic point of view. We re-classify these tracks not by their geometric qualities as pattern recognition algorithms would, but through interpreting the 'artist', their brush strokes and intensity. We describe the algorithms used to enhance and present the work of the 'artists'.

  20. Programming in the small.

    PubMed

    Gersten, David B; Langer, Steve G

    2011-02-01

    Academic medical centers, in general, and radiation oncology research, in particular, rely heavily on custom software tools and applications. The code development is typically the responsibility of a single individual or at most a small team. Often these individuals are not professional programmers but physicists, students, and physicians. While they possess domain expertise and algorithm knowledge, they often are not fully aware of general "safe coding" practices--nor do they need the full complexity familiar in large commercial software projects to succeed. Rather, some simple guidelines we refer to as "programming in the small" can be used.

  1. Small Bowel Transplant

    PubMed Central

    2003-01-01

    EXECUTIVE SUMMARY Objective The Medical Advisory Secretariat undertook a review of the evidence on the effectiveness and cost-effectiveness of small bowel transplant in the treatment of intestinal failure. Small Bowel Transplantation Intestinal failure is the loss of absorptive capacity of the small intestine that results in an inability to meet the nutrient and fluid requirements of the body via the enteral route. Patients with intestinal failure usually receive nutrients intravenously, a procedure known as parenteral nutrition. However, long-term parenteral nutrition is associated with complications including liver failure and loss of venous access due to recurrent infections. Small bowel transplant is the transplantation of a cadaveric intestinal allograft for the purpose of restoring intestinal function in patients with irreversible intestinal failure. The transplant may involve the small intestine alone (isolated small bowel ISB), the small intestine and the liver (SB-L) when there is irreversible liver failure, or multiple organs including the small bowel (multivisceral MV or cluster). Although living related donor transplant is being investigated at a limited number of centres, cadaveric donors have been used in most small bowel transplants. The actual transplant procedure takes approximately 12-18 hours. After intestinal transplant, the patient is generally placed on prophylactic antibiotic medication and immunosuppressive regimen that, in the majority of cases, would include tacrolimus, corticosteroids and an induction agent. Close monitoring for infection and rejection are essential for early treatment. Medical Advisory Secretariat Review The Medical Advisory Secretariat undertook a review of 35 reports from 9 case series and 1 international registry. Sample size of the individual studies ranged from 9 to 155. As of May 2001, 651 patients had received small bowel transplant procedures worldwide. According to information from the Canadian Organ Replacement

  2. How Small are Small Stars Really?

    NASA Astrophysics Data System (ADS)

    2002-11-01

    VLT Interferometer Measures the Size of Proxima Centauri and Other Nearby Stars [1] Summary At a distance of only 4.2 light-years, Proxima Centauri is the nearest star to the Sun currently known [2]. It is visible as an 11-magnitude object in the southern constellation of Centaurus and is the faintest member of a triple system, together with Alpha Centauri , the brightest (double) star in this constellation. Proxima Centauri is a very-low-mass star, in fact barely massive enough to burn hydrogen to helium in its interior. It is about seven times smaller than the Sun, and the surface temperature is "only" about 3000 degrees, about half of that of our own star. Consequently, it is also much fainter - the intrinsic brightness is only 1/150th of that of our Sun. Low-mass stars are very interesting objects , also because the physical conditions in their interiors have much in common with those of giant planets, like Jupiter in our solar system. A determination of the sizes of the smallest stars has been impossible until now because of their general faintness and lack of adequate instrumentation. However, astronomers have long been keen to move forward in this direction, since such measurements would provide indirect, crucial information about the behaviour of matter under extreme conditions. When the first observations with the VLT Interferometer (VLTI), combining the light from two of the 8.2-m VLT Unit Telescopes (ANTU and MELIPAL), were made one year ago ( ESO PR 23/01 ), interferometric measurements were also obtained of Proxima Centauri . They formed part of the VLTI commissioning and the data were soon released to the ESO community, cf. the special website. Now, an international team of astronomers from Switzerland, France and ESO/Chile has successfully analysed these observations by means of newly developed, advanced software. For the first time ever, they obtained a highly accurate measurement of the size of such a small star . Three other small stars were also

  3. Automating Small Libraries.

    ERIC Educational Resources Information Center

    Swan, James

    1996-01-01

    Presents a four-phase plan for small libraries strategizing for automation: inventory and weeding, data conversion, implementation, and enhancements. Other topics include selecting a system, MARC records, compatibility, ease of use, industry standards, searching capabilities, support services, system security, screen displays, circulation modules,…

  4. Closed Small Cell Clouds

    Atmospheric Science Data Center

    2013-04-19

    ... (right)   The structure of tightly packed "closed cells" in a layer of marine stratocumulus over the southeastern Pacific Ocean ... into interesting structures such as those shown here. These cells are notably small, with diameters ranging from 10-15 kilometers, instead ...

  5. Small Schools Reform Narratives

    ERIC Educational Resources Information Center

    Lehman, Beth M.; Berghoff, Beth

    2013-01-01

    This study explored complicated personal narratives of school reform generated by participants in response to a particular small schools reform initiative. Narrative data was dialogically generated in interviews with nine past participants of an urban high school conversion project planned and implemented over a span of five years toward the goal…

  6. Measuring Small Leak Holes

    NASA Technical Reports Server (NTRS)

    Koch, D. E.; Stephenson, J. G.

    1983-01-01

    Hole sizes deduced from pressure measurements. Measuring apparatus consists of pitot tube attached to water-filled manometer. Compartment tested is pressurized with air. Pitot probe placed at known distance from leak. Dynamic pressure of jet measured at that point and static pressure measured in compartment. Useful in situations in which small leaks are tolerable but large leaks are not.

  7. Small Business Bibliography.

    ERIC Educational Resources Information Center

    Anderson, Wendell, Ed.

    Intended as a resource for both experienced businesspeople and those new to business, this annotated bibliography provides a list of books, pamphlets, periodicals, and videotapes of value in solving specific business problems. The bibliography begins with a list of resources recommended for the library of every small business and a survey of…

  8. Small satellite radiometric measurements

    SciTech Connect

    Weber, P.G.

    1991-01-01

    A critical need for the Mission to Planet Earth is to provide continuous, well-calibrated radiometric data for the radiation budget. This paper describes a new, compact, flexible radiometer which will provide both spectrally integrated data and data in selected spectral bands. The radiometer design is suitable for use on small satellites, aircraft, or remotely piloted vehicles (RPVs). 12 refs., 2 figs.

  9. Small Business Innovations

    NASA Technical Reports Server (NTRS)

    1993-01-01

    Under an Army Small Business Innovation Research (SBIR) grant, Symbiotics, Inc. developed a software system that permits users to upgrade products from standalone applications so they can communicate in a distributed computing environment. Under a subsequent NASA SBIR grant, Symbiotics added additional tools to the SOCIAL product to enable NASA to coordinate conventional systems for planning Shuttle launch support operations. Using SOCIAL, data may be shared among applications in a computer network even when the applications are written in different programming languages. The product was introduced to the commercial market in 1993 and is used to monitor and control equipment for operation support and to integrate financial networks. The SBIR program was established to increase small business participation in federal R&D activities and to transfer government research to industry. InQuisiX is a reuse library providing high performance classification, cataloging, searching, browsing, retrieval and synthesis capabilities. These form the foundation for software reuse, producing higher quality software at lower cost and in less time. Software Productivity Solutions, Inc. developed the technology under Small Business Innovation Research (SBIR) projects funded by NASA and the Army and is marketing InQuisiX in conjunction with Science Applications International Corporation (SAIC). The SBIR program was established to increase small business participation in federal R&D activities and to transfer government research to industry.

  10. Small Town Renewal Manual.

    ERIC Educational Resources Information Center

    Kenyon, Peter

    Over the last 2 decades, the loss of population and businesses in many small, inland, and remote Australian rural communities has intensified, largely because of the stress and uncertainty of volatile world commodity markets. This manual presents a range of survival and revival strategies that some communities have used to build resilient…

  11. Deburring small intersecting holes

    SciTech Connect

    Gillespie, L.K.

    1980-08-01

    Deburring intersecting holes is one of the most difficult deburring tasks faced by many industries. Only 14 of the 37 major deburring processes are applicable to most intersecting hole applications. Only five of these are normally applicable to small or miniature holes. Basic process capabilities and techniques used as a function of hole sizes and intersection depths are summarized.

  12. Small Gas Engine Repair.

    ERIC Educational Resources Information Center

    Connecticut State Dept. of Education, Hartford. Div. of Vocational-Technical Schools.

    Instructional materials are provided for a small gas engine course. A list of objectives appears first, followed by a list of internal parts and skills/competencies related to those parts for engine work, ignition and electrical systems, fuel system, crankcase lubrication system, arc welding skills, and gas welding skills. Outlines are provided…

  13. Modeling Small Group Learning

    ERIC Educational Resources Information Center

    Draskovic, I.; Holdrinet, R.; Bulte, J.; Bolhuis, S.; Van Leeuwe, J.

    2004-01-01

    This article presents findings from an empirical study on the relations between the variables comprising learning mechanisms in small collaborative groups. Variables comprising the central learning mechanisms component were "task related interactions," "knowledge elaborations," and "subjective estimation of knowledge acquisition." Student related…

  14. Small School Distributive Education.

    ERIC Educational Resources Information Center

    Barnes, Bill

    Information on an atypical 1966-67 Distributive Education pilot program in New Mexico was given. The program was unique since one instructor conducted this program in two schools which were in separate rural districts (Dexter and Hagerman). Since both communities were primarily agricultural, with small student populations, the cost of such a…

  15. Small Public Library Management

    ERIC Educational Resources Information Center

    Pearlmutter, Jane; Nelson, Paul

    2012-01-01

    Anyone at the helm of a small public library knows that every little detail counts. But juggling the responsibilities that are part and parcel of the job is far from easy. Finally, here's a handbook that includes everything administrators need to keep a handle on library operations, freeing them up to streamline and improve how the organization…

  16. Small Wonders Close Encounters

    ERIC Educational Resources Information Center

    Kniseley, MacGregor; Capraro, Karen

    2013-01-01

    This article introduces students to the world of digital microscopy. Looking at small objects through a digital microscope is like traveling through a foreign country for the first time. The experience is new, engaging, and exciting. A handheld digital microscope is an essential tool in a 21st century teacher's toolkit and the perfect tool to…

  17. Small is beautiful

    NASA Astrophysics Data System (ADS)

    Bannister, Nigel; Eves, Stuart

    2009-12-01

    MEETING REPORT While the great space observatories have provided much of the headline news in astronomy and astrophysics in recent years, they are not the whole story. Nigel Bannister reports on an RAS Specialist Discussion Meeting on ``Astronomy with Small Satellites''.

  18. 77 FR 30227 - Small Business Size Regulations, Small Business Innovation Research (SBIR) Program and Small...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-05-22

    ... BUSINESS ADMINISTRATION 13 CFR Part 121 Small Business Size Regulations, Small Business Innovation Research (SBIR) Program and Small Business Technology Transfer (STTR) Program AGENCY: U.S. Small Business... to amend its regulations governing size and eligibility for the Small Business Innovation...

  19. 78 FR 11745 - Small Business Size Regulations, Small Business Innovation Research (SBIR) Program and Small...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-02-20

    ... / Wednesday, February 20, 2013 / Rules and Regulations#0;#0; ] SMALL BUSINESS ADMINISTRATION 13 CFR Part 121 RIN 3245-AG46 Small Business Size Regulations, Small Business Innovation Research (SBIR) Program and Small Business Technology Transfer (STTR) Program; Correction AGENCY: U.S. Small Business...

  20. Small Multiples with Gaps.

    PubMed

    Meulemans, Wouter; Dykes, Jason; Slingsby, Aidan; Turkay, Cagatay; Wood, Jo

    2017-01-01

    Small multiples enable comparison by providing different views of a single data set in a dense and aligned manner. A common frame defines each view, which varies based upon values of a conditioning variable. An increasingly popular use of this technique is to project two-dimensional locations into a gridded space (e.g. grid maps), using the underlying distribution both as the conditioning variable and to determine the grid layout. Using whitespace in this layout has the potential to carry information, especially in a geographic context. Yet, the effects of doing so on the spatial properties of the original units are not understood. We explore the design space offered by such small multiples with gaps. We do so by constructing a comprehensive suite of metrics that capture properties of the layout used to arrange the small multiples for comparison (e.g. compactness and alignment) and the preservation of the original data (e.g. distance, topology and shape). We study these metrics in geographic data sets with varying properties and numbers of gaps. We use simulated annealing to optimize for each metric and measure the effects on the others. To explore these effects systematically, we take a new approach, developing a system to visualize this design space using a set of interactive matrices. We find that adding small amounts of whitespace to small multiple arrays improves some of the characteristics of 2D layouts, such as shape, distance and direction. This comes at the cost of other metrics, such as the retention of topology. Effects vary according to the input maps, with degree of variation in size of input regions found to be a factor. Optima exist for particular metrics in many cases, but at different amounts of whitespace for different maps. We suggest multiple metrics be used in optimized layouts, finding topology to be a primary factor in existing manually-crafted solutions, followed by a trade-off between shape and displacement. But the rich range of possible

  1. Small Animal Bone Biomechanics

    PubMed Central

    Vashishth, Deepak

    2008-01-01

    Animal models, in particular mice, offer the possibility of naturally achieving or genetically engineering a skeletal phenotype associated with disease and conducting destructive fracture tests on bone to determine the resulting change in bone’s mechanical properties. Several recent developments, including nano- and micro- indentation testing, microtensile and microcompressive testing, and bending tests on notched whole bone specimens, offer the possibility to mechanically probe small animal bone and investigate the effects of aging, therapeutic treatments, disease, and genetic variation. In contrast to traditional strength tests on small animal bones, fracture mechanics tests display smaller variation and therefore offer the possibility of reducing sample sizes. This article provides an analysis of what such tests measure and proposes methods to reduce errors associated with testing smaller than ideal specimens. PMID:18672104

  2. Small arms ammunition

    DOEpatents

    Huerta, Joseph

    1992-01-01

    An elongate projectile for small arms use has a single unitary mass with a hollow nose cavity defined by a sharp rigid cutting edge adapted to make initial contact with the target surface and cut therethrough. The projectile then enters the target mass in an unstable flight mode. The projectile base is substantially solid such that the nose cavity, while relatively deep, does not extend entirely through the base and the projectile center of gravity is aft of its geometric center.

  3. Small Business Innovations

    NASA Technical Reports Server (NTRS)

    1992-01-01

    The purpose of QASE RT is to enable system analysts and software engineers to evaluate performance and reliability implications of design alternatives. The program resulted from two Small Business Innovation Research (SBIR) projects. After receiving a description of the system architecture and workload from the user, QASE RT translates the system description into simulation models and executes them. Simulation provides detailed performance evaluation. The results of the evaluations are service and response times, offered load and device utilizations and functional availability.

  4. Small Business Innovations (MISER)

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Lightwave Electronics Corporation, Mountain View, CA, developed the Series 120 and 122 non-planner diode pumped ring lasers based on a low noise ring laser with voltage tuning that they delivered to Jet Propulsion Laboratory under a Small Business Innovation Research (SBIR) contract. The voltage tuning feature allows "phase-locking" the lasers, making them "electronic," similar to radio and microwave electronic oscillators. The Series 120 and 122 can be applied to fiber sensing, coherent communications and laser radar.

  5. Small Business Innovations (Photodetector)

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Epitaxx, Inc. of Princeton, NJ, developed the Epitaxx Near Infrared Room Temperature Indium-Gallium-Arsenide (InGaAs) Photodetector based on their Goddard Space Flight Center Small Business Innovation Research (SBIR) contract work to develop a linear detector array for satellite imaging applications using InGaAs alloys that didn't need to be cooled to (difficult and expensive) cryogenic temperatures. The photodetectors can be used for remote sensing, fiber optic and laser position-sensing applications.

  6. Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    The smaller of two nearby companions of the Milky Way Galaxy that can be seen with the naked eye in the southern hemisphere sky and which are named after the Portuguese navigator, Ferdinand Magellan. Located in the constellation of Tucana, at a distance of about 190 000 light-years, the Small Magellanic Cloud (SMC) has an angular diameter of about three degrees, about half the apparent diameter o...

  7. Small Angle Neutron Scattering

    SciTech Connect

    Urban, Volker S

    2012-01-01

    Small Angle Neutron Scattering (SANS) probes structural details at the nanometer scale in a non-destructive way. This article gives an introduction to scientists who have no prior small-angle scattering knowledge, but who seek a technique that allows elucidating structural information in challenging situations that thwart approaches by other methods. SANS is applicable to a wide variety of materials including metals and alloys, ceramics, concrete, glasses, polymers, composites and biological materials. Isotope and magnetic interactions provide unique methods for labeling and contrast variation to highlight specific structural features of interest. In situ studies of a material s responses to temperature, pressure, shear, magnetic and electric fields, etc., are feasible as a result of the high penetrating power of neutrons. SANS provides statistical information on significant structural features averaged over the probed sample volume, and one can use SANS to quantify with high precision the structural details that are observed, for example, in electron microscopy. Neutron scattering is non-destructive; there is no need to cut specimens into thin sections, and neutrons penetrate deeply, providing information on the bulk material, free from surface effects. The basic principles of a SANS experiment are fairly simple, but the measurement, analysis and interpretation of small angle scattering data involves theoretical concepts that are unique to the technique and that are not widely known. This article includes a concise description of the basics, as well as practical know-how that is essential for a successful SANS experiment.

  8. Small Business Innovations

    NASA Technical Reports Server (NTRS)

    1994-01-01

    A Small Business Innovation Research (SBIR) contract resulted in a series of commercially available lasers, which have application in fiber optic communications, difference frequency generation, fiber optic sensing and general laboratory use. Developed under a Small Business Innovation Research (SBIR) contract, the Phase Doppler Particles Analyzer is a non-disruptive, highly accurate laser-based method of determining particle size, number density, trajectory, turbulence and other information about particles passing through a measurement probe volume. The system consists of an optical transmitter and receiver, signal processor and computer with data acquisition and analysis software. A variety of systems are offered for applications including spray characterization for paint, and agricultural and other sprays. The Microsizer, a related product, is used in medical equipment manufacturing and analysis of contained flows. High frequency components and subsystems produced by Millitech Corporation are marketed for both research and commercial use. These systems, which operate in the upper portion of the millimeter wave, resulted from a number of Small Business Innovation Research (SBIR) projects. By developing very high performance mixers and multipliers, the company has advanced the state of the art in sensitive receiver technology. Components are used in receivers and transceivers for monitoring chlorine monoxides, ozone, in plasma characterization and in material properties characterization.

  9. Astronomy with Small Telescopes

    NASA Astrophysics Data System (ADS)

    Paczynski, Bohdan

    2006-06-01

    While there are more than a dozen telescopes larger than 10 meters there is plenty of interesting astronomy which can be done with much smaller instruments. Notice that the existing SDSS, and the future PanSTARRS and LSST saturate at 15 mag. An example of interesting science is provided with ASAS (All Sky Automated Survey) which used aperture of 7 cm to discover over 50,000 variable stars brighter than 14 mag, covering almost 3/4 of the sky. Most of these are new discoveries.ASAS like instruments are most likely more efficient in a search for afterglows following gamma-ray bursts (GRB) than CFHT and its Megacam. In fact it should be possible to detect the afterglows without a GRB trigger by imaging all visible sky every 15 minutes down to 16 mag using a number of ASAS-like instruments.Another example of small instruments being essential, is their ability to detect 'killer asteroids' prior to their impact. It will take a number of small instruments, somewhat more powerful than ASAS, to detect boulders as small as 10 - 20 meters at a distance of several days prior to their impact. This will provide time to evacuate a region in case of Tunguska-like event, or to provide news of a spectacular but harmless event in case of a more modest impact.

  10. Eccentricity of small exoplanets

    NASA Astrophysics Data System (ADS)

    Van Eylen, Vincent; Albrecht, Simon

    2015-12-01

    Solar system planets move on almost circular orbits. In strong contrast, many massive gas giant exoplanets travel on highly elliptical orbits, whereas the shape of the orbits of smaller, more terrestrial, exoplanets remained largely elusive. This is because the stellar radial velocity caused by these small planets is extremely challenging to measure. Knowing the eccentricity distribution in systems of small planets would be important as it holds information about the planet's formation and evolution. Furthermore the location of the habitable zone depends on eccentricity, and eccentricity also influences occurrence rates inferred for these planets because planets on circular orbits are less likely to transit. We make these eccentricity measurements of small planets using photometry from the Kepler satellite and utilizing a method relying on Kepler's second law, which relates the duration of a planetary transit to its orbital eccentricity, if the stellar density is known.I present a sample of 28 multi-planet systems with precise asteroseismic density measurements, which host 74 planets with an average radius of 2.6 R_earth. We find that the eccentricity of planets in these systems is low and can be described by a Rayleigh distribution with sigma = 0.049 +- 0.013. This is in full agreement with solar system eccentricities, but in contrast to the eccentricity distributions previously derived for exoplanets from radial velocity studies. I further report the first results on the eccentricities of over 50 Kepler single-planet systems, and compare them with the multi-planet systems. I close the talk by showing how transit durations help distinguish between false positives and true planets, and present six new planets.

  11. Small Business Innovations (Helicopters)

    NASA Technical Reports Server (NTRS)

    1992-01-01

    The amount of engine power required for a helicopter to hover is an important, but difficult, consideration in helicopter design. The EHPIC program model produces converged, freely distorted wake geometries that generate accurate analysis of wake-induced downwash, allowing good predictions of rotor thrust and power requirements. Continuum Dynamics, Inc., the Small Business Innovation Research (SBIR) company that developed EHPIC, also produces RotorCRAFT, a program for analysis of aerodynamic loading of helicopter blades in forward flight. Both helicopter codes have been licensed to commercial manufacturers.

  12. Small obstacle avoidance sensor.

    PubMed

    Vollmerhausen, Richard H

    2013-01-01

    This paper describes a laser ranging sensor that is suitable for applications like small unmanned aerial vehicles. The hardware consists of a diode emitter array and line-scan charge coupled devices. A structured-light technique measures ranges up to 30 meters for 64 field angles in a 90 degree field of view. Operation is eye safe, and the laser wavelength is not visible to night vision goggles. This paper describes a specific sensor design in order to illustrate performance for a given package size.

  13. Supernumerary small ring chromosome.

    PubMed Central

    Kaffe, S; Kim, H J; Hsu, L Y; Brill, C B; Hirschhorn, K

    1977-01-01

    A supernumerary small ring chromosome was found in 30% of cultured peripheral leucocytes and 50% of skin fibroblasts in a 6-year-old boy with mild mental retardation and midline cleft palate. The extra chromosome appeared to carry a densely staining region on Giemsa banding. The banding patterns of the remaining 46 chromosomes were normal. C banding indicated that the ring chromosome contained mainly centromeric constitutive heterochromatin. Chromosome analysis of both parents showed normal karyotypes by both conventional and banding techniques; thus the origin of the ring chromosome could not be determined. Images PMID:604496

  14. Rapid small lot manufacturing

    SciTech Connect

    Harrigan, R.W.

    1998-05-09

    The direct connection of information, captured in forms such as CAD databases, to the factory floor is enabling a revolution in manufacturing. Rapid response to very dynamic market conditions is becoming the norm rather than the exception. In order to provide economical rapid fabrication of small numbers of variable products, one must design with manufacturing constraints in mind. In addition, flexible manufacturing systems must be programmed automatically to reduce the time for product change over in the factory and eliminate human errors. Sensor based machine control is needed to adapt idealized, model based machine programs to uncontrolled variables such as the condition of raw materials and fabrication tolerances.

  15. Small Business Innovations

    NASA Technical Reports Server (NTRS)

    1995-01-01

    The PER-Force Handcontroller was originally developed for the International Space Station under a Johnson Space Center Small Business Innovation Research (SBIR) contract. Produced by Cybernet Systems Corporation, the unit is a force-reflecting system that manipulates robots or objects by "feel." The Handcontroller moves in six degrees of freedom, with real and virtual reality forces simulated by a 3-D molecular modeling software package. It is used in molecular modeling in metallurgy applications, satellite docking research, and in research on military unmanned ground vehicles.

  16. Small Unit Operations

    DTIC Science & Technology

    2007-11-02

    best demonstrated value for small (< AA size) lithium - thionyl - chloride batteries (Halpert 1993). Equation (2-3) shows that the solar power...However, this energy den- sity this is only ~ 3 times larger than the demonstrated performance of the best lithium batteries , and the fuel cells are...Units 13 2.2.2 ASIC Capability 15 2.2.3 Power and Size 17 2.2.4 Cost 19 2.3 Power Sources 20 2.3.1 Batteries 21 2.3.2 Solar Augmentation

  17. Small Business Innovations (Cryostat)

    NASA Technical Reports Server (NTRS)

    1991-01-01

    General Pneumatics Corporation, Scottsdale, AZ, developed an anti- clogging cryostat that liquifies gases by expansion for high pressure through a nozzle to produce cryorefrigeration based on their Kennedy Space Center Small Business Innovation Research (SBIR) work to develop a Joule-Thomson (JT) expansion valve that is less susceptible to clogging by particles or condensed contaminants in the flow than a non-contaminating compressor in a closed cycle Linde-Hampson cryocooler used to generate cryogenic cooling for infrared sensors, super conductors, supercooled electronics and cryosurgery.

  18. NIF small mirror mount

    SciTech Connect

    McCarville, T

    1999-07-01

    A number of small mirror mounts have been identified that meet the stringent stability, wave front, and cleanliness standards of the NIF. These requirements are similar to those required in other performance critical optical design applications. Future design teams would conserve time and effort if recognized standards were established for mirror mount design and performance characteristics. Standards for stability, physical features, wave front distortion, and cleanliness would simplify the qualification process considerably. At this point such standards are not difficult to define, as the technical support work has been performed repeatedly by mirror mount consumers and suppliers.

  19. Small circuits for cryptography.

    SciTech Connect

    Torgerson, Mark Dolan; Draelos, Timothy John; Schroeppel, Richard Crabtree; Miller, Russell D.; Anderson, William Erik

    2005-10-01

    This report examines a number of hardware circuit design issues associated with implementing certain functions in FPGA and ASIC technologies. Here we show circuit designs for AES and SHA-1 that have an extremely small hardware footprint, yet show reasonably good performance characteristics as compared to the state of the art designs found in the literature. Our AES performance numbers are fueled by an optimized composite field S-box design for the Stratix chipset. Our SHA-1 designs use register packing and feedback functionalities of the Stratix LE, which reduce the logic element usage by as much as 72% as compared to other SHA-1 designs.

  20. Small modulation ellipsometry

    NASA Technical Reports Server (NTRS)

    Ducharme, Stephen P. (Inventor); El Hajj, Hassanayn M. (Inventor); Johs, Blaine D. (Inventor); Woollam, John A. (Inventor)

    1995-01-01

    In an ellipsometer, a phase-modulated, polarized light beam is applied to a sample, electrical signals are obtained representing the orthogonal planes of polarization of the light after it has interacted with the sample and the constants of the sample are calculated from the two resulting electrical signals. The phase modulation is sufficiently small so that the calibration errors are negligible. For this purpose, the phase modulator phase modulates the light within a range of no more than ten degrees modulations peak to peak. The two electrical signals are expanded by Fourier analysis and the coefficients thereof utilized to calculate psi and delta.

  1. Small Landslide in Kasei

    NASA Technical Reports Server (NTRS)

    2004-01-01

    21 February 2004 The finger-shaped lobe just right of center in this Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image is the deposit of a small landslide that came down a dark, layered slope. Landslides are common on Mars in areas of steep topography; this one is located in the Kasei Valles region near 23.9oN, 67.1oW. Sunlight illuminates the scene from the lower left; the picture covers an area 3 km (1.9 mi) wide.

  2. Small satellite space operations

    NASA Technical Reports Server (NTRS)

    Reiss, Keith

    1994-01-01

    CTA Space Systems has played a premier role in the development of the 'lightsat' programs of the 80's and 90's. The high costs and development times associated with conventional LEO satellite design, fabrication, launch, and operations continue to motivate the development of new methodologies, techniques, and generally low cost and less stringently regulated satellites. These spacecraft employ low power 'lightsat' communications (versus TDRSS for NASA's LEO's) and typically fly missions with payload/experiment suites that can succeed, for example, without heavily redundant backup systems and large infrastructures of personnel and ground support systems. Such small yet adaptable satellites are also typified by their very short contract-to-launch times (often one to two years). This paper reflects several of the methodologies and perspectives of our successful involvement in these innovative programs and suggests how they might relieve NASA's mounting pressures to reduce the cost of both the spacecraft and their companion mission operations. It focuses on the use of adaptable, sufficiently powerful yet inexpensive PC-based ground systems for wide ranging user terminal (UT) applications and master control facilities for mission operations. These systems proved themselves in successfully controlling more than two dozen USAF, USN, and ARPA satellites at CTA/SS. UT versions have linked with both GEO and LEO satellites and functioned autonomously in relay roles often in remote parts of the world. LEO applications particularly illustrate the efficacy of these concepts since a user can easily mount a lightweight antenna, usually an omni or helix with light duty rotors and PC-based drivers. A few feet of coax connected to a small transceiver module (the size of a small PC) and a serial line to an associated PC establishes a communications link and together with the PC constitute a viable ground station. Applications included geomagnetic mapping; spaceborne solid state

  3. SmallSat Lab

    DTIC Science & Technology

    2014-03-05

    CubeSat. Mr. Alvarez worked with four students on the PCB layout for the solar panels and the construction of the 6U CubeSat mockup . Support for Mr...Hull and Mr. Alvarez was $49k including fringe benefits. !! Purchases: During this time period a license for MatLab software and the Princeton...Satellite ToolBox was purchased using funds from this award. This software adds tremendous capability to the SmallSat Lab by enabling students to analyze

  4. Small engine technology programs

    NASA Technical Reports Server (NTRS)

    Niedzwiecki, Richard W.

    1990-01-01

    Described here is the small engine technology program being sponsored at the Lewis Research Center. Small gas turbine research is aimed at general aviation, commuter aircraft, rotorcraft, and cruise missile applications. The Rotary Engine program is aimed at supplying fuel flexible, fuel efficient technology to the general aviation industry, but also has applications to other missions. The Automotive Gas Turbine (AGT) and Heavy-Duty Diesel Transport Technology (HDTT) programs are sponsored by DOE. The Compound Cycle Engine program is sponsored by the Army. All of the programs are aimed towards highly efficient engine cycles, very efficient components, and the use of high temperature structural ceramics. This research tends to be generic in nature and has broad applications. The HDTT, rotary technology, and the compound cycle programs are all examining approaches to minimum heat rejection, or 'adiabatic' systems employing advanced materials. The AGT program is also directed towards ceramics application to gas turbine hot section components. Turbomachinery advances in the gas turbine programs will benefit advanced turbochargers and turbocompounders for the intermittent combustion systems, and the fundamental understandings and analytical codes developed in the research and technology programs will be directly applicable to the system projects.

  5. Small engine technology programs

    NASA Technical Reports Server (NTRS)

    Niedzwiecki, Richard W.

    1987-01-01

    Small engine technology programs being conducted at the NASA Lewis Research Center are described. Small gas turbine research is aimed at general aviation, commutercraft, rotorcraft, and cruise missile applications. The Rotary Engine Program is aimed at supplying fuel flexible, fuel efficient technology to the general aviation industry, but also has applications to other missions. There is a strong element of synergism between the various programs in several respects. All of the programs are aimed towards highly efficient engine cycles, very efficient components, and the use of high temperature structural ceramics. This research tends to be generic in nature and has broad applications. The Heavy Duty Diesel Transport (HDTT), rotary technology, and the compound cycle programs are all examining approached to minimum heat rejection, or adiabatic systems employing advanced materials. The Automotive Gas Turbine (AGT) program is also directed towards ceramics application to gas turbine hot section components. Turbomachinery advances in the gas turbines will benefit advanced turbochargers and turbocompounders for the intermittent combustion systems, and the fundamental understandings and analytical codes developed in the research and technology programs will be directly applicable to the system projects.

  6. Small Impact Crater

    NASA Technical Reports Server (NTRS)

    2005-01-01

    22 June 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a small impact crater with a 'butterfly' ejecta pattern. The butterfly pattern results from an oblique impact. Not all oblique impacts result in an elliptical crater, but they can result in a non-radial pattern of ejecta distribution. The two-toned nature of the ejecta -- with dark material near the crater and brighter material further away -- might indicate the nature of subsurface materials. Below the surface, there may be a layer of lighter-toned material, underlain by a layer of darker material. The impact throws these materials out in a pattern that reflects the nature of the underlying layers.

    Location near: 3.7oN, 348.2oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Autumn

  7. Small Business Innovations

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Under a Small Business Innovation Research (SBIR) contract to Kennedy Space Center, EIC Laboratories invented a Raman Spectrograph with fiber optic sampling for space applications such as sensing hazardous fuel vapors and making on-board rapid analyses of chemicals and minerals. Raman spectroscopy is a laser-based measurement technique that provides through a unique vibrational spectrum a molecular 'fingerprint,' and can function in aqueous environments. EIC combined optical fiber technology with Raman methods to develop sensors that can be operated at a distance from the spectrographic analysis instruments and the laser excitation source. EIC refined and commercialized the technology to create the Fiber Optic Raman Spectrograph and the RamanProbe. Commercial applications range from process control to monitoring hazardous materials.

  8. Modular small hydro configuration

    NASA Astrophysics Data System (ADS)

    1981-09-01

    Smaller sites (those under 750 kilowatts) which previously were not attractive to develop using equipment intended for application at larger scale sites, were the focal point in the conception of a system which utilizes standard industrial components which are generally available within short procurement times. Such components were integrated into a development scheme for sites having 20 feet to 150 feet of head. The modular small hydro configuration maximizes the use of available components and minimizes modification of existing civil works. A key aspect of the development concept is the use of a vertical turbine multistage pump, used in the reverse mode as a hydraulic turbine. The configuration allows for automated operation and control of the hydroelectric facilities with sufficient flexibility for inclusion of potential hydroelectric sites into dispersed storage and generation (DSG) utility grid systems.

  9. Small transport aircraft technology

    NASA Technical Reports Server (NTRS)

    Williams, L. J.

    1983-01-01

    Information on commuter airline trends and aircraft developments is provided to upgrade the preliminary findings of a NASA-formed small transport aircraft technology (STAT) team, established to determine whether the agency's research and development programs could help commuter aircraft manufacturers solve technical problems related to passenger acceptance and use of 19- to 50-passenger aircraft. The results and conclusions of the full set of completed STAT studies are presented. These studies were performed by five airplane manufacturers, five engine manufacturers, and two propeller manufacturers. Those portions of NASA's overall aeronautics research and development programs which are applicable to commuter aircraft design are summarized. Areas of technology that might beneficially be expanded or initiated to aid the US commuter aircraft manufacturers in the evolution of improved aircraft for the market are suggested.

  10. Small Syrian Volcano

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-498, 29 September 2003

    Today, 29 September 2003, is the first day of southern summer, and the first day of northern winter on Mars. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a small volcano in Syria Planum near 12.9oS, 102.7oW. The volcano and surrounding terrain have been thickly mantled by dust; this dust has subsequently been eroded so that it appears textured rather than smooth. The thin, light streaks that crisscross the image are the tracks left by passing dust devils. Not all dust devils on Mars make streaks, and not all streaks are darker than their surroundings--those found in Syria Planum are invariably lighter in tone. The picture covers an area 3 km (1.9 mi) across; sunlight illuminates the scene from the upper left.

  11. [Is allastrim small pox?].

    PubMed

    Tiexeira, L A

    2000-01-01

    Between 1910 and 1913, two renowned physicians in the city of Sao Paulo found themselves engaged in a scientific controversy regarding the classification of a disease then assailing the state. Antonio Carini, director of the Instituto Pasteur de Sao Paulo, believed the illness to be small pox, while Emilio Ribas, director of the Servico Sanitario, claimed it was allastrim, or milk pox. The controversy started in the Sociedade de Medicina e Cirurgia but later migrated to other forums and came to incorporate other figures as well. This presentation and discussion of the polemic is meant as a contribution to our understanding of the process by which a scientific consensus is constructed and solidified within the field of the biomedical sciences.

  12. Friction at small displacement.

    NASA Technical Reports Server (NTRS)

    Campbell, W. E.; Aronstein, J.

    1972-01-01

    Low contact resistance between metal surfaces is often observed in spite of interposed lubricant and/or oxide films. To study this effect an apparatus is used with which normal force and tangential microdisplacement are applied between a small lead rider and a gold flat with various surface film conditions. Under nonoxidized and nonlubricated conditions, and with either oxide or stearic acid lubricant film alone, friction is high and contact resistance is low. With oxide and lubricant together, friction is much lower and slide is smooth, but contact resistance remains low and Ohm's law is obeyed. The results are consistent with Greenwood's theory of contact resistance for a cluster of minute metallic contact spots within the load-supporting area. The contact resistance of such a cluster is indistinguishable, for practical purposes, from that given by complete metallic contact.

  13. Small caliber guided projectile

    DOEpatents

    Jones, James F.; Kast, Brian A.; Kniskern, Marc W.; Rose, Scott E.; Rohrer, Brandon R.; Woods, James W.; Greene, Ronald W.

    2010-08-24

    A non-spinning projectile that is self-guided to a laser designated target and is configured to be fired from a small caliber smooth bore gun barrel has an optical sensor mounted in the nose of the projectile, a counterbalancing mass portion near the fore end of the projectile and a hollow tapered body mounted aft of the counterbalancing mass. Stabilizing strakes are mounted to and extend outward from the tapered body with control fins located at the aft end of the strakes. Guidance and control electronics and electromagnetic actuators for operating the control fins are located within the tapered body section. Output from the optical sensor is processed by the guidance and control electronics to produce command signals for the electromagnetic actuators. A guidance control algorithm incorporating non-proportional, "bang-bang" control is used to steer the projectile to the target.

  14. Small Active Radiation Monitor

    NASA Technical Reports Server (NTRS)

    Badhwar, Gautam D.

    2004-01-01

    A device, named small active radiation monitor, allows on-orbit evaluations during periods of increased radiation, after extravehicular activities, or at predesignated times for crews on such long-duration space missions as on the International Space Station. It also permits direct evaluation of biological doses, a task now performed using a combination of measurements and potentially inaccurate simulations. Indeed the new monitor can measure a full array of radiation levels, from soft x-rays to hard galactic cosmic-ray particles. With refinement, it will benefit commercial (nuclear power-plant workers, airline pilots, medical technicians, physicians/dentists, and others) and military personnel as well as the astronauts for whom thermoluminescent dosimeters are inadequate. Civilian and military personnel have long since graduated from film badges to thermoluminescent dosimeters. Once used, most dosimeters must be returned to a central facility for processing, a step that can take days or even weeks. While this suffices for radiation workers for whom exposure levels are typically very low and of brief duration, it does not work for astronauts. Even in emergencies and using express mail, the results can often be delayed by as much as 24 hours. Electronic dosimeters, which are the size of electronic oral thermometers, and tattlers, small electronic dosimeters that sound an alarm when the dose/dose rate exceeds preset values, are also used but suffer disadvantages similar to those of thermoluminescent dosimeters. None of these devices fully answers the need of rapid monitoring during the space missions. Instead, radiation is monitored by passive detectors, which are read out after the missions. Unfortunately, these detectors measure only the absorbed dose and not the biologically relevant dose equivalent. The new monitor provides a real-time readout, a time history of radiation exposures (both absorbed dose and biologically relevant dose equivalent), and a count of the

  15. Small intestine contrast injection (image)

    MedlinePlus

    ... and throat, through the stomach into the small intestine. When in place, contrast dye is introduced and ... means of demonstrating whether or not the small intestine is normal when abnormality is suspected.

  16. Small intestine aspirate and culture

    MedlinePlus

    ... ency/article/003731.htm Small intestine aspirate and culture To use the sharing features on this page, please enable JavaScript. Small intestine aspirate and culture is a lab test to check for infection ...

  17. Small rover exploration capabilities

    NASA Astrophysics Data System (ADS)

    Salotti, Jean-Marc; Laithier, Corentin; Machut, Benoit; Marie, Aurélien; Bruneau, Audrey; Grömer, Gernot; Foing, Bernard H.

    2015-05-01

    For a human mission to the Moon or Mars, an important question is to determine the best strategy for the choice of surface vehicles. Recent studies suggest that the first missions to Mars will be strongly constrained and that only small unpressurized vehicles will be available. We analyze the exploration capabilities and limitations of small surface vehicles from the user perspective. Following the “human centered design” paradigm, the team focused on human systems interactions and conducted the following experiments: - Another member of our team participated in the ILEWG EuroMoonMars 2013 simulation at the Mars Desert Research Station in Utah during the same period of time. Although the possible traverses were restricted, a similar study with analog space suits and quads has been carried out. - Other experiments have been conducted in an old rock quarry close to Bordeaux, France. An expert in the use of quads for all types of terrains performed a demonstration and helped us to characterize the difficulties, the risks and advantages and drawbacks of different vehicles and tools. The vehicles that will be used on the surface of Mars have not been defined yet. Nevertheless, the results of our project already show that using a light and unpressurized vehicle (in the order of 150 kg) for the mobility on the Martian surface can be a true advantage. Part of the study was dedicated to the search for appropriate tools that could be used to make

  18. All Shops Great and Small.

    ERIC Educational Resources Information Center

    Carman, Bernard R.

    1994-01-01

    The functions of public relations offices are described for four small colleges and one small private school: Spelman College (Georgia); North Harris County College (Texas); Scripps College (California); Lafayette College (Pennsylvania); and Maumee Valley Country Day School (Ohio). Focus is on creative and effective use of a small staff and…

  19. Small Business Management. Teacher Edition.

    ERIC Educational Resources Information Center

    Oklahoma State Dept. of Vocational and Technical Education, Stillwater. Curriculum and Instructional Materials Center.

    This instructor's guide, which is designed to assist teachers in providing instruction and technical support to small business owners and managers, contains 17 competency-based units of instruction on the following areas that both small business instructors and small business owners have deemed critical to the success of any business:…

  20. Small scale sanitation technologies.

    PubMed

    Green, W; Ho, G

    2005-01-01

    Small scale systems can improve the sustainability of sanitation systems as they more easily close the water and nutrient loops. They also provide alternate solutions to centrally managed large scale infrastructures. Appropriate sanitation provision can improve the lives of people with inadequate sanitation through health benefits, reuse products as well as reduce ecological impacts. In the literature there seems to be no compilation of a wide range of available onsite sanitation systems around the world that encompasses black and greywater treatment plus stand-alone dry and urine separation toilet systems. Seventy technologies have been identified and classified according to the different waste source streams. Sub-classification based on major treatment methods included aerobic digestion, composting and vermicomposting, anaerobic digestion, sand/soil/peat filtration and constructed wetlands. Potential users or suppliers of sanitation systems can choose from wide range of technologies available and examine the different treatment principles used in the technologies. Sanitation systems need to be selected according to the local social, economic and environmental conditions and should aim to be sustainable.

  1. 48 CFR 970.1907 - Subcontracting with Small Business, Small Disadvantaged Business and Woman-Owned Small Business...

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Business, Small Disadvantaged Business and Woman-Owned Small Business Concerns. 970.1907 Section 970.1907... MANAGEMENT AND OPERATING CONTRACTS Small, Small Disadvantaged and Women-Owned Small Business Concerns 970.1907 Subcontracting with Small Business, Small Disadvantaged Business and Woman-Owned Small...

  2. Small Thermophotovoltaic Prototype Systems

    NASA Astrophysics Data System (ADS)

    Durisch, Wilhelm; Bitnar, Bernd; von Roth, Fritz; Palfinger, Günther

    2003-01-01

    In an earlier paper [1], we reported on a small grid-connected thermophotovoltaic (TPV) system consisting of an ytterbia mantle emitter and silicon solar cells with 16 % efficiency (under solar irradiance at Standard Test Conditions, STC). The emitter was heated up using a butane burner with a rated thermal power of 1.35 kW (referring to the lower heating value). This system produced an electrical output of 15 W, which corresponds to a thermal to electric (direct current) conversion efficiency of 1.1 %. In the interim, further progress has been made, and significantly higher efficiencies have been achieved. The most important development steps are: 1) The infrared radiation-absorbing water filter between emitter and silicon cells (to protect the cells against overheating and against contact with flue gasses) has been replaced by a suitable glass tube. By doing this, it has been possible to prevent losses of convertible radiation in water. 2) Cell cooling has been significantly improved, in order to reduce cell temperature, and therefore increase conversion efficiency. 3) The shape of the emitter has been changed from spherical to a quasi-cylindrical geometry, in order to obtain a more homogeneous irradiation of the cells. 4) The metallic burner tube, on which the ytterbia emitter was fixed in the initial prototypes, has been replaced by a heat-resistant metallic rod, carrying ceramic discs as emitter holders. This has prevented the oxidation and clogging of the perforated burner tube. 5) Larger reflectors have been used to reduce losses in useful infrared radiation. 6) Smaller cells have been used, to reduce electrical series resistance losses. Applying all these improvements to the basic 1.35 kW prototype, we attained a system efficiency of 1.5 %. By using preheated air for combustion (at approximately 370 °C), 1.8 % was achieved. In a subsequent step, a photocell generator was constructed, consisting of high-efficiency silicon cells (21% STC efficiency). In this

  3. Small angle neutron scattering

    NASA Astrophysics Data System (ADS)

    Cousin, Fabrice

    2015-10-01

    Small Angle Neutron Scattering (SANS) is a technique that enables to probe the 3-D structure of materials on a typical size range lying from ˜ 1 nm up to ˜ a few 100 nm, the obtained information being statistically averaged on a sample whose volume is ˜ 1 cm3. This very rich technique enables to make a full structural characterization of a given object of nanometric dimensions (radius of gyration, shape, volume or mass, fractal dimension, specific area…) through the determination of the form factor as well as the determination of the way objects are organized within in a continuous media, and therefore to describe interactions between them, through the determination of the structure factor. The specific properties of neutrons (possibility of tuning the scattering intensity by using the isotopic substitution, sensitivity to magnetism, negligible absorption, low energy of the incident neutrons) make it particularly interesting in the fields of soft matter, biophysics, magnetic materials and metallurgy. In particular, the contrast variation methods allow to extract some informations that cannot be obtained by any other experimental techniques. This course is divided in two parts. The first one is devoted to the description of the principle of SANS: basics (formalism, coherent scattering/incoherent scattering, notion of elementary scatterer), form factor analysis (I(q→0), Guinier regime, intermediate regime, Porod regime, polydisperse system), structure factor analysis (2nd Virial coefficient, integral equations, characterization of aggregates), and contrast variation methods (how to create contrast in an homogeneous system, matching in ternary systems, extrapolation to zero concentration, Zero Averaged Contrast). It is illustrated by some representative examples. The second one describes the experimental aspects of SANS to guide user in its future experiments: description of SANS spectrometer, resolution of the spectrometer, optimization of spectrometer

  4. Small 'l' leadership.

    PubMed

    Parsons, Jenni

    2009-05-01

    Recently I attended the RACGP Leadership Masterclass in Sydney. When I enrolled, I thought, 'Yes... sounds interesting...good speakers... I need to learn something about leadership...'As the time drew closer I started to get a bit anxious about the whole thing. I realised that the title, 'Masterclass', probably implied that the attendees were expected to already know something about leadership and its theories, if not have considerable expertise and experience in leadership. I also wondered how the workshop sessions were going to go and I started to feel a bit sorry for the facilitators. Imagine trying to facilitate a group of 10 aspiring leaders... a bit like trying to herd cats. A few days later I received a call from the organisers,saying they were a bit short of facilitators and could I help out if necessary. Great... better do a crash course in cat herding! Then there was the first 'predisposing activity'. Step 1: think of leaders you admire. Easy enough. Leaders of social justice and social change on a world stage, people who have shown great courage of their convictions and great orators popped into my head... Ghandi, Martin Luther King, Mandela, JFK. Step 2:describe the ways in which you are like these leaders. Whoa!Never going to measure up here. I wondered if there was going to be sessions on 'leadership for introverts', or 'leadership of small things', or 'leaders without grand vision or fabulous oratory skills', or perhaps 'leadership for people who are deeply suspicious of the corrupting influence of power'.

  5. Small Mercury Relativity Orbiter

    NASA Technical Reports Server (NTRS)

    Bender, Peter L.; Vincent, Mark A.

    1989-01-01

    The accuracy of solar system tests of gravitational theory could be very much improved by range and Doppler measurements to a Small Mercury Relativity Orbiter. A nearly circular orbit at roughly 2400 km altitude is assumed in order to minimize problems with orbit determination and thermal radiation from the surface. The spacecraft is spin-stabilized and has a 30 cm diameter de-spun antenna. With K-band and X-band ranging systems using a 50 MHz offset sidetone at K-band, a range accuracy of 3 cm appears to be realistically achievable. The estimated spacecraft mass is 50 kg. A consider-covariance analysis was performed to determine how well the Earth-Mercury distance as a function of time could be determined with such a Relativity Orbiter. The minimum data set is assumed to be 40 independent 8-hour arcs of tracking data at selected times during a two year period. The gravity field of Mercury up through degree and order 10 is solved for, along with the initial conditions for each arc and the Earth-Mercury distance at the center of each arc. The considered parameters include the gravity field parameters of degree 11 and 12 plus the tracking station coordinates, the tropospheric delay, and two parameters in a crude radiation pressure model. The conclusion is that the Earth-Mercury distance can be determined to 6 cm accuracy or better. From a modified worst-case analysis, this would lead to roughly 2 orders of magnitude improvement in the knowledge of the precession of perihelion, the relativistic time delay, and the possible change in the gravitational constant with time.

  6. Small quenches and thermalization

    NASA Astrophysics Data System (ADS)

    Kennes, D. M.; Pommerening, J. C.; Diekmann, J.; Karrasch, C.; Meden, V.

    2017-01-01

    We study the expectation values of observables and correlation functions at long times after a global quantum quench. Our focus is on metallic ("gapless") fermionic many-body models and small quenches. The system is prepared in an eigenstate of an initial Hamiltonian, and the time evolution is performed with a final Hamiltonian which differs from the initial one in the value of one global parameter. We first derive general relations between time-averaged expectation values of observables as well as correlation functions and those obtained in an eigenstate of the final Hamiltonian. Our results are valid to linear and quadratic order in the quench parameter g and generalize prior insights in several essential ways. This allows us to develop a phenomenology for the thermalization of local quantities up to a given order in g . Our phenomenology is put to a test in several case studies of one-dimensional models representative of four distinct classes of Hamiltonians: quadratic ones, effectively quadratic ones, those characterized by an extensive set of (quasi-) local integrals of motion, and those for which no such set is known (and believed to be nonexistent). We show that for each of these models, all observables and correlation functions thermalize to linear order in g . The more local a given quantity, the longer the linear behavior prevails when increasing g . Typical local correlation functions and observables for which the term O (g ) vanishes thermalize even to order g2. Our results show that lowest-order thermalization of local observables is an ubiquitous phenomenon even in models with extensive sets of integrals of motion.

  7. Nematode endogenous small RNA pathways

    PubMed Central

    Hoogstrate, Suzanne W; Volkers, Rita JM; Sterken, Mark G; Kammenga, Jan E; Snoek, L Basten

    2014-01-01

    The discovery of small RNA silencing pathways has greatly extended our knowledge of gene regulation. Small RNAs have been presumed to play a role in every field of biology because they affect many biological processes via regulation of gene expression and chromatin remodeling. Most well-known examples of affected processes are development, fertility, and maintenance of genome stability. Here we review the role of the three main endogenous small RNA silencing pathways in Caenorhabditis elegans: microRNAs, endogenous small interfering RNAs, and PIWI-interacting RNAs. After providing an entry-level overview on how these pathways function, we discuss research on other nematode species providing insight into the evolution of these small RNA pathways. In understanding the differences between the endogenous small RNA pathways and their evolution, a more comprehensive picture is formed of the functions and effects of small RNAs. PMID:25340013

  8. Small Bowel Hamartoma: A Huge Diverticulum of Small Bowel

    PubMed Central

    Eltweri, Amar M.; Salama, Yahya; Gorgees, Neshtman; Naidu, Leena; Bowrey, David J.

    2013-01-01

    A-20-year old male, with no significant medical history, presented with clinical features mimicking a perforated acute appendicitis. Because of features of peritonitis, a laparotomy was performed which showed a segment of small bowel with multiple large diverticula and mesenteric cysts. A segmental small bowel resection was performed. The patient made an uneventful recovery from surgery. Histology revealed features of a small bowel hamartoma. PMID:24454405

  9. Jupiter small satellite montage

    NASA Technical Reports Server (NTRS)

    2000-01-01

    A montage of images of the small inner moons of Jupiter from the camera onboard NASA's Galileo spacecraft shows the best views obtained of these moons during Galileo's 11th orbit around the giant planet in November 1997. At that point, Galileo was completing its first two years in Jupiter orbit--known as the Galileo 'prime mission'--and was about to embark on a successful two-year extension, called the Galileo Europa Mission.

    The top two images show the moon Thebe. Thebe rotates by approximately 50 degrees between the time these two images were taken, so that the same prominent impact crater is seen in both views; this crater, which has been given the provisional name Zethus, is near the point on Thebe that faces permanently away from Jupiter.

    The next two images show the moon Amalthea; they were taken with the Sun directly behind the observer, an alignment that emphasizes patterns of intrinsically bright or dark surface material. The third image from the top is a view of Amalthea's leading side, the side of the moon that 'leads' as Amalthea moves in its orbit around Jupiter. This image looks 'noisy' because it was obtained serendipitously during an observation of the Jovian satellite Io (Amalthea and Io shared the same camera frame but the image was exposed for bright Io rather than for the much darker Amalthea). The fourth image from the top emphasizes prominent 'spots' of relatively bright material that are located near the point on Amalthea that faces permanently away from Jupiter. The bottom image is a view of the tiny moon Metis.

    In all the images, north is approximately up, and the moons are shown in their correct relative sizes. The images are, from top to bottom: Thebe taken on November 7, 1997 at a range of 504,000 kilometers (about 313,000 miles); Thebe on November 7, 1997 at a range of 548,000 kilometers (about 340,000 miles); Amalthea on November 6, 1997 at a range of about 650,000 kilometers (about 404,000 miles); Amalthea on November

  10. Small business innovation, research & development

    SciTech Connect

    Colvin, D.P.

    1995-12-31

    Historically, small businesses have been the innovation engine of the United States (US). The author provides statistical data that indicates that small business is really big business in the U.S. Small businesses are responsible for much of the applied research necessary for new product development. The author examines productivity, academic research and teaming as a cost-effective and time effective way to develop new products and technologies.

  11. Small Wind Site Assessment Guidelines

    SciTech Connect

    Olsen, Tim; Preus, Robert

    2015-09-01

    Site assessment for small wind energy systems is one of the key factors in the successful installation, operation, and performance of a small wind turbine. A proper site assessment is a difficult process that includes wind resource assessment and the evaluation of site characteristics. These guidelines address many of the relevant parts of a site assessment with an emphasis on wind resource assessment, using methods other than on-site data collection and creating a small wind site assessment report.

  12. Small white matter lesion detection in cerebral small vessel disease

    NASA Astrophysics Data System (ADS)

    Ghafoorian, Mohsen; Karssemeijer, Nico; van Uden, Inge; de Leeuw, Frank E.; Heskes, Tom; Marchiori, Elena; Platel, Bram

    2015-03-01

    Cerebral small vessel disease (SVD) is a common finding on magnetic resonance images of elderly people. White matter lesions (WML) are important markers for not only the small vessel disease, but also neuro-degenerative diseases including multiple sclerosis, Alzheimer's disease and vascular dementia. Volumetric measurements such as the "total lesion load", have been studied and related to these diseases. With respect to SVD we conjecture that small lesions are important, as they have been observed to grow over time and they form the majority of lesions in number. To study these small lesions they need to be annotated, which is a complex and time-consuming task. Existing (semi) automatic methods have been aimed at volumetric measurements and large lesions, and are not suitable for the detection of small lesions. In this research we established a supervised voxel classification CAD system, optimized and trained to exclusively detect small WMLs. To achieve this, several preprocessing steps were taken, which included a robust standardization of subject intensities to reduce inter-subject intensity variability as much as possible. A number of features that were found to be well identifying small lesions were calculated including multimodal intensities, tissue probabilities, several features for accurate location description, a number of second order derivative features as well as multi-scale annular filter for blobness detection. Only small lesions were used to learn the target concept via Adaboost using random forests as its basic classifiers. Finally the results were evaluated using Free-response receiver operating characteristic.

  13. Patient Safety Outcomes in Small Urban and Small Rural Hospitals

    ERIC Educational Resources Information Center

    Vartak, Smruti; Ward, Marcia M.; Vaughn, Thomas E.

    2010-01-01

    Purpose: To assess patient safety outcomes in small urban and small rural hospitals and to examine the relationship of hospital and patient factors to patient safety outcomes. Methods: The Nationwide Inpatient Sample and American Hospital Association annual survey data were used for analyses. To increase comparability, the study sample was…

  14. Small Business at EPA Bulletin

    EPA Pesticide Factsheets

    A list of monthly bulletins that highlight information on Agency activities, rulemakings, and to share information about ongoing initiatives from the State Small Business Environmental Assistance Programs.

  15. Small Molecular as SIRT Modulators.

    PubMed

    Yao, Lei; Xu, Xiangming; Chen, Kai

    2016-06-19

    Sirtuins are class III histone deacetylases, they involve in many important biological functions. Small molecules that can modulate sirtuin activity have been shown to have potential for treating many human diseases. In the article, recent development of small molecular as SIRT modulators has been reviewed.

  16. [Pain therapy in small pets].

    PubMed

    Tacke, Sabine; Gollwitzer, Andrea; Grammel, Lukas; Henke, Julia

    2017-02-09

    Although many advances in pain therapy have been made in recent years, pain therapy is more difficult in the small domestic animal than in cats and dogs. However, there is the ethical obligation that these animals also receive adequate pain therapy. An analgesic is rarely authorized for use in small pets, with pharmacological investigations often lacking and dosages frequently only determined empirically. The small size of the animals often requires a higher dose per kilogram bodyweight compared to cats and dogs. The dosage itself is also difficult to apply in small animals, because many analgesics must be diluted before their use. In addition, frequent manipulation of small animals for analgesic administration induces stress in the patient, which can intensify the pain. In the present article, those analgesics suitable for use in the small domestic animal are described and the indications for the use of the various types of analgesics are explained. A specialized section concentrates on pain detection and algesimetry in the small domestic animal. The detection of pain is much more difficult in small domestic animals. In the last few years so-called "grimace scales" have been developed which are used to assess the facial expression of the animals.

  17. Resourcing Change in Small Schools

    ERIC Educational Resources Information Center

    Anderson, Michelle; White, Simone

    2011-01-01

    The theme of this article is the challenge that school leaders face in creating the conditions for learning in small schools. We draw on the concepts of "social capital" and "social entrepreneurship" to identify tensions and possibilities for school leaders in a case study of a small rural school as they seek to find resources…

  18. Small Gas Turbine Engine Technology

    DTIC Science & Technology

    1991-01-01

    Highly advanced small turbine engines will require novel and innovative concepts that minimize the cost and complexity of variable geometry if full...Enhanced computational tools development, verification and application to advanced concepts are rsquired to provide highly advanced, effi- cient... concepts . 3 EFFICIENT ENGINE CYCLES Small vs. large. - Previous investments in technology programs by govern- ment and industry have led to significant

  19. Role Transitions in Small Groups.

    ERIC Educational Resources Information Center

    Moreland, Richard L.; Levine, John M.

    This paper analyzes role transitions in small groups within the context of a more general model of group socialization that is based on the psychological processes of evaluation, commitment, and decision making. The major advantage of such an approach is that it specifies why role transitions in small groups occur. According to the model, groups…

  20. Small bowel obstruction- a surprise.

    PubMed

    Mathew, Jeffrey Daniel; Cp, Ganesh Babu; M, Balachandar; M, Ramanathan

    2015-01-01

    Trans - omental hernia is very rare, accounting to 1-4% of all internal hernias which is an unusual cause of small bowel obstruction. Here we present a case report of a small bowel obstruction in a female due to trans - omental hernia presenting with central abdominal pain, distension and bilious vomiting. She had no previous history of trauma, surgery. Plain X-ray abdomen erect showed multiple air fluid levels with dilated small bowel loops. Emergency laparotomy revealed a segment of congested small bowel loop (ileum) through a defect in greater omentum. On table the herniated bowel loop was reduced and the defect in greater omentum was closed primarily. There was no necessity for bowel resection as it regained normal colour after reduction. Postoperative period was uneventful with complete resolution of symptoms. This case is presented for its rarity and its importance in clinical differential diagnosis of acute abdomen due to small bowel obstruction.

  1. Small-world brain networks.

    PubMed

    Bassett, Danielle Smith; Bullmore, Ed

    2006-12-01

    Many complex networks have a small-world topology characterized by dense local clustering or cliquishness of connections between neighboring nodes yet a short path length between any (distant) pair of nodes due to the existence of relatively few long-range connections. This is an attractive model for the organization of brain anatomical and functional networks because a small-world topology can support both segregated/specialized and distributed/integrated information processing. Moreover, small-world networks are economical, tending to minimize wiring costs while supporting high dynamical complexity. The authors introduce some of the key mathematical concepts in graph theory required for small-world analysis and review how these methods have been applied to quantification of cortical connectivity matrices derived from anatomical tract-tracing studies in the macaque monkey and the cat. The evolution of small-world networks is discussed in terms of a selection pressure to deliver cost-effective information-processing systems. The authors illustrate how these techniques and concepts are increasingly being applied to the analysis of human brain functional networks derived from electroencephalography/magnetoencephalography and fMRI experiments. Finally, the authors consider the relevance of small-world models for understanding the emergence of complex behaviors and the resilience of brain systems to pathological attack by disease or aberrant development. They conclude that small-world models provide a powerful and versatile approach to understanding the structure and function of human brain systems.

  2. Characterization of dopant diffusion within semiconducting polymer and small-molecule films using infrared-active vibrational modes and attenuated total reflectance infrared spectroscopy.

    PubMed

    Maliakal, Ashok J

    2013-09-11

    Understanding dopant diffusion within organic and polymeric semiconductors is of great importance toward the development of organic photovoltaic and electronic devices, many of which require layered structures with controlled doping profiles (e.g., p-n and p-i-n structures). The current paper demonstrates a new method to determine the diffusion and permeability coefficients for dopant diffusion within polymeric and small-molecule organic semiconductors using attenuated total reflectance infrared (ATR-IR) spectroscopy and taking advantage of the intense IR-active vibrational bands created when dopants such as iodine accept charge from a semiconducting polymer to generate polaronic species. The diffusion and permeability coefficients for iodine within poly(3-hexylthiophene) (P3HT) are determined to be 2.5×10(-11)±1.2×10(-11) cm2/s and 2.4×10(-8)±1.2×10(-8) cm2/s·atm, respectively. The approach is applied to P3HT/PCBM (1:1 mass ratio) films, and the diffusion and permeability coefficients through these composite films are determined to be 7.8×10(-11)±2.8×10(-11) cm2/s and 4.8×10(-8)±1.3×10(-8) cm2/s·atm, respectively. Finally, the approach is extended to determining iodine diffusion within the polycrystalline semiconductor tetraphenylporphyrin (TPP) in a bilayer film with P3HT, and the diffusion coefficient of iodine through TPP is determined to be 7.1×10(-14)±1.1×10(-14) cm2/s. Although the current paper determines diffusion and permeability for the dopant iodine, this approach should be applicable to a wide array of dopants and polymeric and small-molecule semiconductors of interest in photovoltaic and electronic applications.

  3. Small Solid Rocket Motor Test

    NASA Video Gallery

    It was three-two-one to brilliant fire as NASA's Marshall Space Flight Center tested a small solid rocket motor designed to mimic NASA's Space Launch System booster. The Mar. 14 test provides a qui...

  4. Small- x resummation from HELL

    NASA Astrophysics Data System (ADS)

    Bonvini, Marco; Marzani, Simone; Peraro, Tiziano

    2016-11-01

    Small- x logarithmic enhancements arising from high-energy gluon emissions affect both the evolution of collinearly-factorized parton densities and partonic coefficient functions. With the higher collider energy reached by the LHC, the prospect of a future high-energy collider, and the recent deep-inelastic scattering (DIS) results at small- x from HERA, providing phenomenological tools for performing small- x resummation has become of great relevance. In this paper we discuss a framework to perform small- x resummation for both parton evolution and partonic coefficient functions and we describe its implementation in a computer code named High-Energy Large Logarithms ( HELL). We present resummed and matched results for the DGLAP splitting functions and, as a proof of principle, for the massless structure functions in DIS. Furthermore, we discuss the uncertainty from subleading terms on our results.

  5. Environmental Justice Small Grants Program

    EPA Pesticide Factsheets

    The Environmental Justice Small Grants Program provides financial assistance to eligible organizations to build collaborative partnerships, to identify the local environmental and/or public health issues, and to envision solutions and empower the community

  6. Learn about Small Wastewater Systems

    EPA Pesticide Factsheets

    Many small and rural communities, including those in Indian Country and along the U.S.-Mexico border, struggle with aging or inadequate wastewater treatment systems, or do not have access to basic wastewater services.

  7. Unsteady swimming of small organisms

    NASA Astrophysics Data System (ADS)

    Wang, Shiyan; Ardekani, Arezoo

    2012-11-01

    Small planktonic organisms ubiquitously display unsteady or impulsive motion to attack a prey or escape a predator in natural environments. Despite this, the role of unsteady hydrodynamic forces such as history and added mass forces on the low Reynolds number propulsion of small organisms is poorly understood. In this paper, we derive the fundamental equation of motion for an organism swimming by the means of surface distortion in a nonuniform flow at a low Reynolds number regime. We show that the history and added mass forces, that where traditionally neglected in the literature for small swimming organisms, cannot be neglected as the Stokes number increases above unity. For example, these unsteady inertial forces are of the same order as quasi-steady Stokes forces for Paramecium. Finally, we quantify the effects of convective inertial forces in the limit of small, but nonzero, Reynolds number regime. This work is supported by NSF grant CBET-1066545.

  8. Urban Waters Small Grants 101

    EPA Pesticide Factsheets

    General information on Urban Waters Small Grants is provided in this document. Grantees are listed by themes, including Environmental Justice, Water Quality, Job Training and Creation, and Green Infrastructure.

  9. Small Airframe Manufacturer's Icing Perspective

    NASA Technical Reports Server (NTRS)

    Hoppins, Jim

    2009-01-01

    This viewgraph presentation describes the icing effects, risk mitigation practices, and icing certifications for various Cessna small aircraft models. NASA's role in the development of simulation tools for icing certifications is also discussed.

  10. Small amplitude quasibreathers and oscillons

    SciTech Connect

    Fodor, Gyula; Lukacs, Arpad; Forgacs, Peter; Horvath, Zalan

    2008-07-15

    Quasibreathers (QB) are time-periodic solutions with weak spatial localization introduced in G. Fodor et al. in [Phys. Rev. D 74, 124003 (2006)]. QB's provide a simple description of oscillons (very long-living spatially localized time dependent solutions). The small amplitude limit of QB's is worked out in a large class of scalar theories with a general self-interaction potential, in D spatial dimensions. It is shown that the problem of small amplitude QB's is reduced to a universal elliptic partial differential equation. It is also found that there is the critical dimension, D{sub crit}=4, above which no small amplitude QB's exist. The QB's obtained this way are shown to provide very good initial data for oscillons. Thus these QB's provide the solution of the complicated, nonlinear time dependent problem of small amplitude oscillons in scalar theories.

  11. Small and Rural Wastewater Systems

    EPA Pesticide Factsheets

    Many tools, training, technical assistance, and funding resources are available to develop and maintain reliable and affordable wastewater treatment systems in small and rural communities including in tribal and U.S.-Mexico Border area.

  12. Small bowel and colon perforation.

    PubMed

    Brown, Carlos V R

    2014-04-01

    For patients with small bowel and colonic perforations, a definitive diagnosis of the cause of perforation is not necessary before operation. Bowel obstruction and inflammatory bowel disease are the most common causes of nontraumatic intestinal perforations in industrialized countries, whereas infectious causes of intestinal perforations are more common in developing countries. Treatment of small bowel and colonic perforations generally includes intravenous antibiotics and fluid resuscitation, but the specific management of the bowel depends on the underlying cause of the perforation.

  13. Spring Small Grains Area Estimation

    NASA Technical Reports Server (NTRS)

    Palmer, W. F.; Mohler, R. J.

    1986-01-01

    SSG3 automatically estimates acreage of spring small grains from Landsat data. Report describes development and testing of a computerized technique for using Landsat multispectral scanner (MSS) data to estimate acreage of spring small grains (wheat, barley, and oats). Application of technique to analysis of four years of data from United States and Canada yielded estimates of accuracy comparable to those obtained through procedures that rely on trained analysis.

  14. Ab initio calculations of SrTiO3, BaTiO3, PbTiO3, CaTiO3, SrZrO3, PbZrO3 and BaZrO3 (001), (011) and (111) surfaces as well as F centers, polarons, KTN solid solutions and Nb impurities therein

    NASA Astrophysics Data System (ADS)

    Eglitis, R. I.

    2014-03-01

    In this paper, the review of recent results of calculations of surface relaxations, energetics, and bonding properties for ABO3 perovskite (001), (011) and (111) surfaces using mostly a hybrid description of exchange and correlation is presented. Both AO and BO2-terminations of the nonpolar (001) surface and A, BO, and O terminations of the polar (011) surface, as well as B and AO3-terminations of the polar (111) surface were considered. On the AO-terminated (001) surface, all upper-layer A atoms relax inwards, while all second layer atoms relax outwards. For the BO2-terminated (001) surface, in most cases, the largest relaxations are on the second-layer metal atoms. For almost all ABO3 perovskites, the surface rumpling is much larger for the AO-terminated than for the BO2-terminated (001) surface, but their surface energies are always quite similar. In contrast, different terminations of the (011) ABO3 surface lead to very different surface energies for the O-terminated, A-terminated, and BO-terminated (011) surface, respectively. A considerable increase in the Ti-O or Zr-O, respectively, chemical bond covalency near the (011) surface as compared both to the bulk and to the (001) surface in ABO3 perovskites were predicted. According to the results of ab initio calculations for Nb doped SrTiO3, Nb is a shallow donor; six nearest O ions are slightly displaced outwards from the Nb ion. The F center in ABO3 perovskites resembles electron defects in the partially-covalent SiO2 crystal rather than usual F centers in ionic crystals like MgO and alkali halides. The results of calculations for several perovskite KNbxTa1-xO3 (KTN) solid solutions, as well as hole and electron polarons in ABO3 perovskites are analyzed.

  15. Chartering Launchers for Small Satellites

    NASA Astrophysics Data System (ADS)

    Hernandez, Daniel

    The question of how to launch small satellites has been solved over the years by the larger launchers offering small satellites the possibility of piggy-backing. Specific fixtures have been developed and commercialized: Arianespace developed the ASAP interface, the USAF studied ESPA, NASA has promoted Shuttle launch possibilities, Russian authorities and companies have been able to find solutions with many different launchers... It is fair to say that most launcher suppliers have worked hard and finally often been able to find solutions to launch most small satellites into orbit. It is also true, however, that most of these small satellites were technology demonstration missions capable of accepting a wide range of orbit and launch characteristics: orbit altitude and inclination, launch date, etc. In some cases the small satellite missions required a well-defined type of orbit and have therefore been obliged to hire a small launcher on which they were the prime passenger. In our paper we would like to propose an additional solution to all these possibilities: launchers could plan well in advance (for example about 3 years), trips to precisely defined orbits to allow potential passengers to organize themselves and be ready on the D-Day. On the scheduled date the chartered launcher goes to the stated orbit while on another date, another chartered launcher goes to another orbit. The idea is to organize departures for space like trains or airplanes leaving on known schedules for known destinations.

  16. Severe adhesive small bowel obstruction.

    PubMed

    Di Saverio, Salomone; Catena, Fausto; Kelly, Michael D; Tugnoli, Gregorio; Ansaloni, Luca

    2012-12-01

    Adhesive small bowel obstruction is a frequent cause of hospital admission. Water soluble contrast studies may have diagnostic and therapeutic value and avoid challenging demanding surgical operations, but if bowel ischemia is suspected, prompt surgical intervention is mandatory. A 58-year-old patient was operated for extensive adhesive small bowel obstruction after having had two previous laparotomies for colorectal surgery, and had a complex clinical course with multiple operations and several complications. Different strategies of management have been adopted, including non-operative management with the use of hyperosmolar water soluble contrast medium, multiple surgical procedures, total parenteral nutrition (TPN) support, and finally use of antiadherences icodextrin solution. After 2 years follow-up the patient was doing well without presenting recurrent episodes of adhesive small bowel obstruction. For patients admitted several times for adhesive small bowel obstruction, the relative risk of recurring obstruction increases in relation to the number of prior episodes. Several strategies for non-operative conservative management of adhesive small bowel obstruction have already addressed diagnostic and therapeutic value of hyperosmolar water soluble contrast. According to the most recent evidence-based guidelines, open surgery is the preferred method for surgical treatment of strangulating adhesive small bowel obstruction as well as after failed conservative management. Research interest and clinical evidence are increasing in adhesions prevention. Hyaluronic acid-carboxycellulose membrane and icodextrin may reduce incidence of adhesions.

  17. Small

    SciTech Connect

    Montoya, Joseph

    2013-07-18

    Representing the Center on Nanostructuring for Efficient Energy Conversion (CNEEC), this document is one of the entries in the Ten Hundred and One Word Challenge. As part of the challenge, the 46 Energy Frontier Research Centers were invited to represent their science in images, cartoons, photos, words and original paintings, but any descriptions or words could only use the 1000 most commonly used words in the English language, with the addition of one word important to each of the EFRCs and the mission of DOE energy. The mission of CNEEC is to understand how nanostructuring can enhance efficiency for energy conversion and solve fundamental cross-cutting problems in advanced energy conversion and storage systems.

  18. Small rocket flowfield diagnostic chambers

    NASA Technical Reports Server (NTRS)

    Morren, Sybil; Reed, Brian

    1993-01-01

    Instrumented and optically-accessible rocket chambers are being developed to be used for diagnostics of small rocket (less than 440 N thrust level) flowfields. These chambers are being tested to gather local fluid dynamic and thermodynamic flowfield data over a range of test conditions. This flowfield database is being used to better understand mixing and heat transfer phenomena in small rockets, influence the numerical modeling of small rocket flowfields, and characterize small rocket components. The diagnostic chamber designs include: a chamber design for gathering wall temperature profiles to be used as boundary conditions in a finite element heat flux model; a chamber design for gathering inner wall temperature and static pressure profiles; and optically-accessible chamber designs, to be used with a suite of laser-based diagnostics for gathering local species concentration, temperature, density, and velocity profiles. These chambers were run with gaseous hydrogen/gaseous oxygen (GH2/GO2) propellants, while subsequent versions will be run on liquid oxygen/hydrocarbon (LOX/HC) propellants. The purpose, design, and initial test results of these small rocket flowfield diagnostic chambers are summarized.

  19. Small gas turbine engine technology

    NASA Technical Reports Server (NTRS)

    Niedzwiecki, Richard W.; Meitner, Peter L.

    1988-01-01

    Performance of small gas turbine engines in the 250 to 1,000 horsepower size range is significantly lower than that of large engines. Engines of this size are typically used in rotorcraft, commutercraft, general aviation, and cruise missile applications. Principal reasons for the lower efficiencies of a smaller engine are well known: component efficients are lower by as much as 8 to 10 percentage points because of size effects. Small engines are designed for lower cycle pressures and temperatures because of smaller blading and cooling limitations. The highly developed analytical and manufacturing techniques evolved for large engines are not directly transferrable to small engines. Thus, it was recognized that a focused effort addressing technologies for small engies was needed and could significantly impact their performance. Recently, in-house and contract studies were undertaken at the NASA Lewis Research Center to identify advanced engine cycle and component requirements for substantial performance improvement of small gas turbines for projected year 2000 applications. The results of both in-house research and contract studies are presented. In summary, projected fuel savings of 22 to 42 percent could be obtained. Accompanying direct operating cost reductions of 11 to 17 percent, depending on fuel cost, were also estimated. High payoff technologies are identified for all engine applications, and recent results of experimental research to evolve the high payoff technologies are described.

  20. Energy Conservation in Small Schools. Small Schools Digest.

    ERIC Educational Resources Information Center

    Gardener, Clark

    Information concerning methods and available materials for conserving energy is needed by small, rural schools to offset continued increasing energy costs and lack of financial support and technical assistance. The first step in developing an energy conservation policy is to obtain school board commitment and to establish an energy saving policy.…

  1. Marketing the Uniqueness of Small Towns. Small Town Strategy.

    ERIC Educational Resources Information Center

    Hogg, David H.; Dunn, Douglas

    A small town can strengthen its local economy as a result of business people and concerned citizens collectively identifying that community's uniqueness and then capitalizing on it via advertising, personal selling, sales promotion, or publicity. This publication relates the science of marketing to communities. Seven simple techniques are provided…

  2. Industry Research and Recommendations for Small Buildings and Small Portfolios

    SciTech Connect

    Langner, Rois; Hendron, Bob; Pless, Shanti; Huppert, Mark; Cochrane, Ric

    2013-12-01

    Small buildings have been left behind in the energy efficiency marketplace because financial and technical resources have flowed to larger commercial buildings. DOE's Building Technologies Office works with the commercial building industry to accelerate the uptake of energy efficiency technologies and techniques in existing and new commercial buildings (DOE 2013). BTO recognizes the SBSP sector'spotential for significant energy savings and the need for investments in resources that are tailored to this sector's unique needs. The industry research and recommendations described in this report identify potential approaches and strategic priorities that BTO could explore over the next 3-5 years that will support the implementation of high-potential energy efficiency opportunities for thisimportant sector. DOE is uniquely positioned to provide national leadership, objective information, and innovative tools, technologies, and services to support cost-effective energy savings in the fragmented and complex SBSP sector. Properly deployed, the DOE effort could enhance and complement current energy efficiency approaches. Small portfolios are loosely and qualitatively defined asportfolios of buildings that include only a small number of small buildings. This distinction is important because the report targets portfolio owners and managers who generally do not have staff and other resources to track energy use and pursue energy efficiency solutions.

  3. Small Molecule CXCR3 Antagonists.

    PubMed

    Andrews, Stephen P; Cox, Rhona J

    2016-04-14

    Chemokines and their receptors are known to play important roles in disease. More than 40 chemokine ligands and 20 chemokine receptors have been identified, but, to date, only two small molecule chemokine receptor antagonists have been approved by the FDA. The chemokine receptor CXCR3 was identified in 1996, and nearly 20 years later, new areas of CXCR3 disease biology continue to emerge. Several classes of small molecule CXCR3 antagonists have been developed, and two have shown efficacy in preclinical models of inflammatory disease. However, only one CXCR3 antagonist has been evaluated in clinical trials, and there remain many opportunities to further investigate known classes of CXCR3 antagonists and to identify new chemotypes. This Perspective reviews the known CXCR3 antagonists and considers future opportunities for the development of small molecules for clinical evaluation.

  4. Mycoplasma infections in small ruminants.

    PubMed

    Ruffin, D C

    2001-07-01

    Mycoplasmas have complex mechanisms of antigenic variation that allow them to evade the immune system. These organisms cause a variety of clinical syndromes that can have a significant economic effect on small ruminant production. The syndromes range from acute septicemia and death to chronic infection resulting in decreased production. Recent research findings have shed light on the means by which these organisms evade the host immune response and cause or contribute to the development of disease in the host. This article provides a review of the pathogenesis, clinical signs, and treatment options for common disease syndromes involving Mycoplasma spp. in small ruminants.

  5. Orbit Mechanics about Small Asteroids

    NASA Technical Reports Server (NTRS)

    Scheeres, D. J.

    2007-01-01

    Space missions to small solar system bodies must deal with multiple perturbations acting on the spacecraft. These include strong perturbations from the gravity field and solar tide, but for small bodies the most important perturbations may arise from solar radiation pressure (SRP) acting on the spacecraft. Previous research has generally investigated the effect of the gravity field, solar tide, and SRP acting on a spacecraft trajectory about an asteroid in isolation and has not considered their joint effect. In this paper a more general theoretical discussion of the joint effects of these forces is given.

  6. Ectoparasites in small exotic mammals.

    PubMed

    Fehr, Michael; Koestlinger, Saskia

    2013-09-01

    Ectoparasites inhabiting the skin are responsible for significant problems in small mammals, owing to ingestion of blood, lymph, sebaceous secretions, and scavenging skin debris, as well as a hypersensitivity reaction to parasite antigen resulting in severe pruritus and subsequent self-trauma-induced lesions. In general practice, the most common diagnosis in exotic pets is an unspecified mite infestation, but other ectoparasites such as lice, fleas, insects, or even helminths may cause dermatologic diseases. If treatment with topical insecticides is planned, the small mammal should be isolated for a few hours to enable drying and spreading of the product.

  7. Purchasing cooperatives for small employers.

    PubMed

    Mallozzi, J

    1997-12-01

    Despite a booming economy, the number of uninsured Americans is rising. It hit nearly 42 million in 1996. Many of the uninsured work at businesses with fewer than 50 employees. Because small firms have traditionally found it difficult to provide health benefits, purchasing cooperatives have grown in scope and size across the country in recent years. By bringing small businesses together to buy insurance as a group, these organizations can help employers provide greater choice to their workers at a lower cost. However, to operate well in the insurance market, purchasing cooperatives must be well-designed and provided with adequate legal protections.

  8. Small intestinal physiology and pathophysiology.

    PubMed

    Sarna, S K; Otterson, M F

    1989-06-01

    The small intestine, like the rest of the gastrointestinal tract, is an intelligent organ. It generates a wide variety of motor patterns to meet motility requirements in different situations. Its basic motor function after a meal is to mix the chyme with exocrine and intestinal secretions, agitate its contents to uniformly and evenly expose them to the mucosal surface, and to propel them distally at a rate that allows optimal absorption of food components, and reabsorption of bile. Most of these functions are performed by individual phasic contractions. In humans, the phasic contractions are largely disorganized in time and space. These contractions may cause mixing and agitation of luminal contents with slow distal propulsion. Occasionally, an individual contraction of large amplitude and long duration migrates over several centimeters and may rapidly propel the contents over this distance. In general, the spatial and temporal relationships of individual phasic contractions become less organized distally, resulting in a slower propulsion rate in the distal small intestine than in the proximal small intestine. The migrating clustered contractions generated after a meal may also be propulsive, but because of their unpredictable and irregular occurrence, their precise role in postprandial propulsion is incompletely understood. Rapidly migrating contractions may occur when the electrical control activity is obliterated by pharmacologic agents or during parasitic infections. Their effects on motility are not known yet. Between meals, when digestion is complete, the small intestine generates migrating motor complexes that help keep the small intestine clean by dislodging debris from the villi and dumping them into the colon. This may prevent decay of these materials in the small intestine and limit their contribution to bacterial overgrowth. Giant migrating contractions may perform a similar function in the distal small intestine as well as return any refluxed fecal

  9. Small Business Administration Semiannual Regulatory Agenda

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-12-20

    ... Small Business Jobs Act: Multiple Award Contracts and Small Business Set-Asides (Reg 3245-AG20 Plan Seq... Development/Small Disadvantaged 3245-AF53 Business Status Determination (Reg Plan Seq No. 161) 484 Small... Appeal Regulations 485 Small Business Jobs Act: 504 Loan Program Debt Refinancing (Reg Plan Seq No....

  10. 76 FR 74749 - Small Business Subcontracting

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-12-01

    ...; ] SMALL BUSINESS ADMINISTRATION 13 CFR Parts 121 and 125 RIN 3245-AG22 Small Business Subcontracting AGENCY: U.S. Small Business Administration. ACTION: Proposed rule; reopening of comment period. SUMMARY... of the Small Business Jobs Act of 2010 (Jobs Act) pertaining to small business subcontracting....

  11. Department of the Navy Small Business Programs

    DTIC Science & Technology

    2014-08-13

    small business concerns and to women -owned small business concerns eligible under the Women -Owned Small Business Program. The dollar...2014 For All US-Based Women Owned Small Business Awards Over $ 200M Over $ 100M Over...Department of the Navy Small Business Programs Gold Coast August 13, 2014 Report Documentation Page Form ApprovedOMB No. 0704-0188

  12. Biological productivity in small impoundments

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Most ponds and small impoundments are built or used with a principal use in mind. That use may be recreational fishing, commercial aquaculture, waterfowl hunting, potable water storage, irrigation water supply, livestock watering, stormwater retention, landscaping, swimming, or others. In practice, ...

  13. 1999 Shuttle Small Payloads Symposium

    NASA Technical Reports Server (NTRS)

    Daelemans, Gerard (Editor); Mosier, Frances L. (Editor)

    1999-01-01

    The 1999 Shuttle Small Payloads Symposium is a combined symposia of the Get Away Special (GAS), Space Experiment Module (SEM), and Hitchhiker programs, and is proposed to continue as an annual conference. The focus of this conference is to educate potential Space Shuttle Payload Bay users as to the types of carrier systems provided and for current users to share experiment concepts.

  14. Small, Lightweight, Collapsible Glove Box

    NASA Technical Reports Server (NTRS)

    James, Jerry

    2009-01-01

    A small, lightweight, collapsible glove box enables its user to perform small experiments and other tasks. Originally intended for use aboard a space shuttle or the International Space Station (ISS), this glove box could also be attractive for use on Earth in settings in which work space or storage space is severely limited and, possibly, in which it is desirable to minimize weight. The development of this glove box was prompted by the findings that in the original space-shuttle or ISS setting, (1) it was necessary to perform small experiments in a large general-purpose work station, so that, in effect, they occupied excessive space; and it took excessive amounts of time to set up small experiments. The design of the glove box reflects the need to minimize the space occupied by experiments and the time needed to set up experiments, plus the requirement to limit the launch weight of the box and the space needed to store the box during transport into orbit. To prepare the glove box for use, the astronaut or other user has merely to insert hands through the two fabric glove ports in the side walls of the box and move two hinges to a locking vertical position (see figure). The user could do this while seated with the glove box on the user fs lap. When stowed, the glove box is flat and has approximately the thickness of two pieces of 8-in. (.20 cm) polycarbonate.

  15. Small artery remodelling in diabetes

    PubMed Central

    Rosei, Enrico Agabiti; Rizzoni, Damiano

    2010-01-01

    Abstract The aim of this article is to briefly review available data regarding changes in the structure of microvessels observed in patients with diabetes mellitus, and possible correction by effective treatment. The development of structural changes in the systemic vasculature is the end result of established hypertension. In essential hypertension, small arteries of smooth muscle cells are restructured around a smaller lumen and there is no net growth of the vascular wall, although in some secondary forms of hypertension, a hypertrophic remodelling may be detected. Moreover, in non-insulin-dependent diabetes mellitus a hypertrophic remodelling of subcutaneous small arteries is present. Indices of small resistance artery structure, such as the tunica media to internal lumen ratio, may have a strong prognostic significance in hypertensive and diabetic patients, over and above all other known cardiovascular risk factors. Therefore, regression of vascular alterations is an appealing goal of antihypertensive treatment. Different antihypertensive drugs seem to have different effect on vascular structure. In diabetic hypertensive patients, a significant regression of structural alterations of small resistance arteries with drugs blocking the renin–angiotensin system (angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers) was demonstrated. Alterations in the microcirculation represent a common pathological finding, and microangiopathy is one of the most important mechanisms involved in the development of organ damage as well as of clinical events in patients with diabetes mellitus. Renin–angiotensin system blockade seems to be effective in preventing/regressing alterations in microvascular structure. PMID:20646125

  16. SMALL DRINKING WATER SYSTEMS RESEARCH

    EPA Science Inventory

    There are 159,796 Community Water Systems (CWSs) in the United States. Ninety-three percent of CWSs are considered very small to medium-sized systems that serve roughly 19% of the CWS population. In contrast, large to very large systems comprise just 7% of CWSs, but serve 81% of ...

  17. Big Opportunities in Small Science

    ERIC Educational Resources Information Center

    Dewey, T. Gregory

    2007-01-01

    A transformation is occurring that will have a major impact on how academic science is done and how scientists are trained. That transformation--driven by declining federal funds, as well as by the rising cost of technology and the need for costly, labor-intensive interdisciplinary approaches--is from small science to big science. It is…

  18. SEGREGATION IN SMALL STEEL CASTINGS

    DTIC Science & Technology

    Carbon segregation in small castings often occurs near riser necks. Systematic studies were continued to determine effect on segregation of such...intensity of carbon segregation under ’neck-down’ risers varies directly as the neck length and inversely as the neck diameter. The degree of segregation

  19. ADA Guide for Small Businesses.

    ERIC Educational Resources Information Center

    Department of Justice, Washington, DC. Civil Rights Div.

    This guide presents an informal overview of some basic Americans with Disabilities Act (ADA) requirements for small businesses that provide goods or services to the public. References to key sections of the regulations or other information are included. The first section describes the ADA briefly. Section two lists the 12 categories of public…

  20. Consciousness & the small network argument.

    PubMed

    Herzog, Michael H; Esfeld, Michael; Gerstner, Wulfram

    2007-11-01

    The last decade has experienced a vivid enthusiasm to unravel the mystery of consciousness believed to be one of the major puzzles of human kind. We share this enthusiasm. Still, we feel that current models are incomplete suffering from a problem that we call the "small network argument".

  1. Final Barrier: Small System Compliance

    EPA Science Inventory

    This presentation will discuss the use of point-of-use (POU) technology for small drinking water systems. Information will be provided on the USEPA regulations that allow the use of POU for compliance and the technologies that are listed as SSCT for radium and arsenic. Listing o...

  2. Netbooks: Small but Powerful Friends

    ERIC Educational Resources Information Center

    Descy, Don E.

    2009-01-01

    Netbooks, sometimes called "mini-notebooks," are lightweight, small, and low-priced computers. Some writers ridicule them by calling them "one of the hottest tech toys of the year" (Saltzman, 2008). Others enthusiastically embrace them as "my perfect new travel companion" (Grossman, 2009). Netbooks are not toys. They are honest-to-goodness real…

  3. Modeling Interactions in Small Groups

    ERIC Educational Resources Information Center

    Heise, David R.

    2013-01-01

    A new theory of interaction within small groups posits that group members initiate actions when tension mounts between the affective meanings of their situational identities and impressions produced by recent events. Actors choose partners and behaviors so as to reduce the tensions. A computer model based on this theory, incorporating reciprocal…

  4. Groundwater vulnerability on small islands

    NASA Astrophysics Data System (ADS)

    Holding, S.; Allen, D. M.; Foster, S.; Hsieh, A.; Larocque, I.; Klassen, J.; van Pelt, S. C.

    2016-12-01

    The majority of naturally occurring freshwater on small islands is groundwater, which is primarily recharged by precipitation. Recharge rates are therefore likely to be impacted by climate change. Freshwater resources on small islands are particularly vulnerable to climate change because they are limited in size and easily compromised. Here we have compiled available aquifer system characteristics and water-use data for 43 small island developing states distributed worldwide, based on local expert knowledge, publications and regional data sets. Current vulnerability was assessed by evaluating the recharge volume per capita. For future vulnerability, climate change projections were used to estimate changes in aquifer recharge. We find that 44% of islands are in a state of water stress, and while recharge is projected to increase by as much as 117% on 12 islands situated in the western Pacific and Indian Ocean, recharge is projected to decrease by up to 58% on the remaining 31 islands. Of great concern is the lack of enacted groundwater protection legislation for many of the small island developing states identified as highly vulnerable to current and future conditions. Recharge indicators, shown alongside the state of legal groundwater protections, provide a global picture of groundwater supply vulnerability under current and future climate change conditions.

  5. Calculator. Owning a Small Business.

    ERIC Educational Resources Information Center

    Parma City School District, OH.

    Seven activities are presented in this student workbook designed for an exploration of small business ownership and the use of the calculator in this career. Included are simulated situations in which students must use a calculator to compute property taxes; estimate payroll taxes and franchise taxes; compute pricing, approximate salaries,…

  6. VEGA, a small launch vehicle

    NASA Astrophysics Data System (ADS)

    Duret, François; Fabrizi, Antonio

    1999-09-01

    Several studies have been performed in Europe aiming to promote the full development of a small launch vehicle to put into orbit one ton class spacecrafts. But during the last ten years, the european workforce was mainly oriented towards the qualification of the heavy class ARIANE 5 launch vehicle.Then, due also to lack of visibility on this reduced segment of market, when comparing with the geosatcom market, no proposal was sufficiently attractive to get from the potentially interrested authorities a clear go-ahead, i.e. a financial committment. The situation is now rapidly evolving. Several european states, among them ITALY and FRANCE, are now convinced of the necessity of the availability of such a transportation system, an important argument to promote small missions, using small satellites. Application market will be mainly scientific experiments and earth observation; some telecommunications applications may be also envisaged such as placement of little LEO constellation satellites, or replacement after failure of big LEO constellation satellites. FIAT AVIO and AEROSPATIALE have proposed to their national agencies the development of such a small launch vehicle, named VEGA. The paper presents the story of the industrial proposal, and the present status of the project: Mission spectrum, technical definition, launch service and performance, target development plan and target recurring costs, as well as the industrial organisation for development, procurement, marketing and operations.

  7. OSHA Handbook for Small Businesses

    DTIC Science & Technology

    1996-01-01

    27601 PHONE: (919)715-7272 FAX: (919)715-7777 E-MAIL: srdaughe.sbdc@mhs.unc.e North Dakota Walter Kearns (Wally) State Director North Dakota Small...Road Telephone: (516) 334-3344 64 North Carolina Raleigh, NC 27601 Century Station, Room 438 300 Fayetteville Street Mall Telephone: (919) 856-4770

  8. UV Treatment for Small Systems

    EPA Science Inventory

    The Center for Environmental Education, Conservation and Research (CECIA) at InterAmerican University of Puerto Rico (IAUPR) has organized the 10th CECIA-IAUPR Biennial Symposium on Potable Water Issues in Puerto Rico. This presentation on UV Treatment for Small Systems will be ...

  9. SMALL CRAFT OPERATION AND NAVIGATION.

    ERIC Educational Resources Information Center

    Louisiana State Dept. of Education, Baton Rouge.

    THIS REFERENCE TEXTBOOK WAS PREPARED FOR USE IN THE FIRST PART OF A TWO-PART COURSE IN MARINE NAVIGATION AND SMALL CRAFT OPERATION ON INLAND AND INTERNATIONAL WATERS. THE MATERIAL WAS DEVELOPED BY AN INDIVIDUAL AUTHOR FOR USE IN TRADE SCHOOL PREPARATORY AND EXTENSION CLASSES FOR MALE ADULTS WHO PLAN TO OPERATE BOATS. IT IS MAINLY CONCERNED WITH…

  10. Small Business. Lesson Plan Three.

    ERIC Educational Resources Information Center

    Dicke, Thomas S.

    1996-01-01

    Presents a lesson plan that requires students to use their research and analytical skills in studying the social and economic importance of small business. Activities include interviewing local business owners and producing a written summary, developing a survey showing and explaining area land use, and researching opposition to Wal-Mart stores.…

  11. Reimagining Education in Small Towns

    ERIC Educational Resources Information Center

    Carr, Patrick J.; Kefalas, Maria J.

    2010-01-01

    Things are not going so well in small-town America. While the so-called "Great Recession" of the moment has focused considerable attention on the travails of Main Street and Middle America, the truth is that the troubles that plague such places have been a long time in the making. For the past 30 years, nonmetropolitan counties and the…

  12. Big Ideas and Small Solutions

    ERIC Educational Resources Information Center

    Tennant, Roy

    2004-01-01

    Small solutions solve discrete, well-bounded problems and can be pieces of larger solutions. They can move things forward by mixing and matching available components in new and previously unimagined ways. A number of innovations, which at first glance are completely unrelated, can come together and create important synergics. This article…

  13. Hispanic Women Small Business Owners.

    ERIC Educational Resources Information Center

    Sarason, Yolanda; Koberg, Christine

    1994-01-01

    A survey of 22 Hispanic women who owned small businesses in a western state found that most were located in metropolitan areas, were new to business ownership, had started the business themselves, engaged in "miscellaneous services," and generated lower than average revenues. Respondents were similar to nonminority owners in educational…

  14. Small Business Innovations (Crystal Components)

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Scientific Materials Corporation, Bozeman, MT developed the SciMax line of improved Nd:Yag crystals under an Small Business Innovation Research (SBIR) contract with Langley Research Center. They reduced the amount of water trapped in the crystals during growth to improve the optical quality and efficiency. Applications of the crystals include fiber optics, telecommunications, welding, drilling, eye surgery and medical instrumentation.

  15. A Small Computer for Teaching.

    ERIC Educational Resources Information Center

    Mastascusa, E. J.; Snyder, W. J.

    1984-01-01

    Describes an easily constructed, small laboratory computer that can be programed in BASIC. The computer is easy to use with analog to digital and digital to analog converters so that it can serve as a control or data logging computer. (Author/JN)

  16. Small rocket research and technology

    NASA Technical Reports Server (NTRS)

    Schneider, Steven; Biaglow, James

    1993-01-01

    Small chemical rockets are used on nearly all space missions. The small rocket program provides propulsion technology for civil and government space systems. Small rocket concepts are developed for systems which encompass reaction control for launch and orbit transfer systems, as well as on-board propulsion for large space systems and earth orbit and planetary spacecraft. Major roles for on-board propulsion include apogee kick, delta-V, de-orbit, drag makeup, final insertions, north-south stationkeeping, orbit change/trim, perigee kick, and reboost. The program encompasses efforts on earth-storable, space storable, and cryogenic propellants. The earth-storable propellants include nitrogen tetroxide (NTO) as an oxidizer with monomethylhydrazine (MMH) or anhydrous hydrazine (AH) as fuels. The space storable propellants include liquid oxygen (LOX) as an oxidizer with hydrazine or hydrocarbons such as liquid methane, ethane, and ethanol as fuels. Cryogenic propellants are LOX or gaseous oxygen (GOX) as oxidizers and liquid or gaseous hydrogen as fuels. Improved performance and lifetime for small chemical rockets are sought through the development of new predictive tools to understand the combustion and flow physics, the introduction of high temperature materials to eliminate fuel film cooling and its associated combustion inefficiency, and improved component designs to optimize performance. Improved predictive technology is sought through the comparison of both local and global predictions with experimental data. Results indicate that modeling of the injector and combustion process in small rockets needs improvement. High temperature materials require the development of fabrication processes, a durability data base in both laboratory and rocket environments, and basic engineering property data such as strength, creep, fatigue, and work hardening properties at both room and elevated temperature. Promising materials under development include iridium-coated rhenium and a

  17. Small rocket research and technology

    NASA Astrophysics Data System (ADS)

    Schneider, Steven; Biaglow, James

    1993-11-01

    Small chemical rockets are used on nearly all space missions. The small rocket program provides propulsion technology for civil and government space systems. Small rocket concepts are developed for systems which encompass reaction control for launch and orbit transfer systems, as well as on-board propulsion for large space systems and earth orbit and planetary spacecraft. Major roles for on-board propulsion include apogee kick, delta-V, de-orbit, drag makeup, final insertions, north-south stationkeeping, orbit change/trim, perigee kick, and reboost. The program encompasses efforts on earth-storable, space storable, and cryogenic propellants. The earth-storable propellants include nitrogen tetroxide (NTO) as an oxidizer with monomethylhydrazine (MMH) or anhydrous hydrazine (AH) as fuels. The space storable propellants include liquid oxygen (LOX) as an oxidizer with hydrazine or hydrocarbons such as liquid methane, ethane, and ethanol as fuels. Cryogenic propellants are LOX or gaseous oxygen (GOX) as oxidizers and liquid or gaseous hydrogen as fuels. Improved performance and lifetime for small chemical rockets are sought through the development of new predictive tools to understand the combustion and flow physics, the introduction of high temperature materials to eliminate fuel film cooling and its associated combustion inefficiency, and improved component designs to optimize performance. Improved predictive technology is sought through the comparison of both local and global predictions with experimental data. Results indicate that modeling of the injector and combustion process in small rockets needs improvement. High temperature materials require the development of fabrication processes, a durability data base in both laboratory and rocket environments, and basic engineering property data such as strength, creep, fatigue, and work hardening properties at both room and elevated temperature. Promising materials under development include iridium-coated rhenium and a

  18. Native Small Airways Secrete Bicarbonate

    PubMed Central

    Quinton, Paul M.

    2014-01-01

    Since the discovery of Cl− impermeability in cystic fibrosis (CF) and the cloning of the responsible channel, CF pathology has been widely attributed to a defect in epithelial Cl− transport. However, loss of bicarbonate (HCO3−) transport also plays a major, possibly more critical role in CF pathogenesis. Even though HCO3− transport is severely affected in the native pancreas, liver, and intestines in CF, we know very little about HCO3− secretion in small airways, the principle site of morbidity in CF. We used a novel, mini-Ussing chamber system to investigate the properties of HCO3− transport in native porcine small airways (∼ 1 mm φ). We assayed HCO3− transport across small airway epithelia as reflected by the transepithelial voltage, conductance, and equivalent short-circuit current with bilateral 25-mM HCO3− plus 125-mM NaGlu Ringer’s solution in the presence of luminal amiloride (10 μM). Under these conditions, because no major transportable anions other than HCO3− were present, we took the equivalent short-circuit current to be a direct measure of active HCO3− secretion. Applying selective agonists and inhibitors, we show constitutive HCO3− secretion in small airways, which can be stimulated significantly by β-adrenergic– (cAMP) and purinergic (Ca2+) -mediated agonists, independently. These results indicate that two separate components for HCO3− secretion, likely via CFTR- and calcium-activated chloride channel–dependent processes, are physiologically regulated for likely roles in mucus clearance and antimicrobial innate defenses of small airways. PMID:24224935

  19. Small is beautiful: models of small neuronal networks

    PubMed Central

    Lamb, Damon G; Calabrese, Ronald L

    2013-01-01

    Modeling has contributed a great deal to our understanding of how individual neurons and neuronal networks function. In this review, we focus on models of the small neuronal networks of invertebrates, especially rhythmically active CPG networks. Models have elucidated many aspects of these networks, from identifying key interacting membrane properties to pointing out gaps in our understanding, for example missing neurons. Even the complex CPGs of vertebrates, such as those that underlie respiration, have been reduced to small network models to great effect. Modeling of these networks spans from simplified models, which are amenable to mathematical analyses, to very complicated biophysical models. Some researchers have now adopted a population approach, where they generate and analyze many related models that differ in a few to several judiciously chosen free parameters; often these parameters show variability across animals and thus justify the approach. Models of small neuronal networks will continue to expand and refine our understanding of how neuronal networks in all animals program motor output, process sensory information and learn. PMID:22364687

  20. Small Bodies, Big Discoveries: NASA's Small Bodies Education Program

    NASA Astrophysics Data System (ADS)

    Mayo, L.; Erickson, K. J.

    2014-12-01

    2014 is turning out to be a watershed year for celestial events involving the solar system's unsung heroes, small bodies. This includes the close flyby of comet C/2013 A1 / Siding Spring with Mars in October and the historic Rosetta mission with its Philae lander to comet 67P/Churyumov-Gerasimenko. Beyond 2014, the much anticipated 2015 Pluto flyby by New Horizons and the February Dawn Mission arrival at Ceres will take center stage. To deliver the excitement and wonder of our solar system's small bodies to worldwide audiences, NASA's JPL and GSFC education teams in partnership with NASA EDGE will reach out to the public through multiple venues including broadcast media, social media, science and math focused educational activities, observing challenges, interactive visualization tools like "Eyes on the Solar System" and more. This talk will highlight NASA's focused education effort to engage the public in small bodies mission science and the role these objects play in our understanding of the formation and evolution of the solar system.

  1. Small is beautiful: models of small neuronal networks.

    PubMed

    Lamb, Damon G; Calabrese, Ronald L

    2012-08-01

    Modeling has contributed a great deal to our understanding of how individual neurons and neuronal networks function. In this review, we focus on models of the small neuronal networks of invertebrates, especially rhythmically active CPG networks. Models have elucidated many aspects of these networks, from identifying key interacting membrane properties to pointing out gaps in our understanding, for example missing neurons. Even the complex CPGs of vertebrates, such as those that underlie respiration, have been reduced to small network models to great effect. Modeling of these networks spans from simplified models, which are amenable to mathematical analyses, to very complicated biophysical models. Some researchers have now adopted a population approach, where they generate and analyze many related models that differ in a few to several judiciously chosen free parameters; often these parameters show variability across animals and thus justify the approach. Models of small neuronal networks will continue to expand and refine our understanding of how neuronal networks in all animals program motor output, process sensory information and learn.

  2. 77 FR 28520 - Small Business Size Regulations, Small Business Innovation Research (SBIR) Program and Small...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-05-15

    ... businesses to understand and a bright-line test by which small businesses can easily determine whether they..., bright-line test for SBIR and STTR applicants to apply when determining eligibility with respect to size... owns 33% or more of the company) in order to create a bright-line test for applicants; (2)...

  3. Knowledge Management in Small Firms

    NASA Astrophysics Data System (ADS)

    Panyasorn, Jessada; Panteli, Niki; Powell, Philip

    This paper explores knowledge management in small and medium-sized firms (SMEs). It investigates the use of Lotus Notes in SMEs of a developing country as a counterpoint to the large firm, developed country emphasis of existing research. It develops taxonomy of Lotus Notes use within the context of different knowledge management processes; notably communicating, co-ordinating and collaborating. The study employs an interpretive approach using three case studies. The key findings suggest that publishing, searching, sharing and retrieving are the user modes for enabling sharing and storing information. Evidence of knowledge creation is found at the departmental level but not at the organizational level. Further, small firms may explore more groupware potential than large organizations and this reflects their different context. Finally, implications for further research are identified.

  4. Small satellite radiometric measurement system

    SciTech Connect

    Weber, P.G.

    1992-01-01

    A critical need for the US Global Change Research Program is to provide continuous, well-calibrated radiometric data for the earth`s radiation budget. This paper describes a new, compact, relatively light-weight, adaptable radiometer which will provide both spectrally integrated measurements and data in selected spectral bands. The radiometer design is suitable for use on small satellites, aircraft, or remotely piloted aircraft (RPAs). An example of the implementation of this radiometer on a small satellite is given. Significant benefits derive from simultaneous measurements of specific narrow (in wavelength) spectral features; such data may be obtained by combining LARI with a compact spectrometer on the same platform. Well-chosen satellite orbits allow one to use data from other satellites (e.g. DMSP) to enhance the data product, or to provide superior coverage of specific locations. 23 refs.

  5. Avionics for a small satellite

    NASA Astrophysics Data System (ADS)

    Abbott, Larry; Jochim, David; Shuler, Robert

    2001-02-01

    This paper discusses a small, seven and a half (7.5) inch diameter, satellite that NASA-JSC is developing as a technology demonstrator for an astronaut assistant. The free flyer, the Mini-AERCam, is designed to off load the flight crew's workload by performing inspections of the exteriors of the Space Shuttle or International Space Station. The Mini-AERCam is intended to be operated by the flight crew, thereby reducing the number of Extra Vehicle Activities (EVA) and reducing crew workload as a result. The paper focuses on the design constraints for a small satellite and the technology approach used to achieve the set of high performance requirements specified for the Mini-AERCam. Particular attention is paid to the flight computer as it is the system integration point of the Mini-AERCam. .

  6. Small sets of complementary observables

    NASA Astrophysics Data System (ADS)

    Grassl, M.; McNulty, D.; Mišta, L.; Paterek, T.

    2017-01-01

    Two observables are called complementary if preparing a physical object in an eigenstate of one of them yields a completely random result in a measurement of the other. We investigate small sets of complementary observables that cannot be extended by yet another complementary observable. We construct explicit examples of unextendible sets up to dimension 16 and conjecture certain small sets to be unextendible in higher dimensions. Our constructions provide three complementary measurements, only one observable away from the ultimate minimum of two. Almost all our examples in finite dimensions are useful for discriminating pure states from some mixed states, and they help to shed light on the complex topology of the Bloch space of higher-dimensional quantum systems.

  7. Small satellite radiometric measurement system

    SciTech Connect

    Weber, P.G.

    1992-01-01

    A critical need for the US Global Change Research Program is to provide continuous, well-calibrated radiometric data for the earth's radiation budget. This paper describes a new, compact, relatively light-weight, adaptable radiometer which will provide both spectrally integrated measurements and data in selected spectral bands. The radiometer design is suitable for use on small satellites, aircraft, or remotely piloted aircraft (RPAs). An example of the implementation of this radiometer on a small satellite is given. Significant benefits derive from simultaneous measurements of specific narrow (in wavelength) spectral features; such data may be obtained by combining LARI with a compact spectrometer on the same platform. Well-chosen satellite orbits allow one to use data from other satellites (e.g. DMSP) to enhance the data product, or to provide superior coverage of specific locations. 23 refs.

  8. VSATs - Very small aperture terminals

    NASA Astrophysics Data System (ADS)

    Everett, John L.

    The present volume on very small aperture terminals (VSATs) discusses antennas, semiconductor devices, and traveling wave tubes and amplifiers for VSAT systems, VSAT low noise downconverters, and modems and codecs for VSAT systems. Attention is given to multiaccess protocols for VSAT networks, protocol software in Ku-band VSAT network systems, system design of VSAT data networks, and the policing of VSAT networks. Topics addressed include the PANDATA and PolyCom systems, APOLLO - a satellite-based information distribution system, data broadcasting within a satellite television channel, and the NEC NEXTAR VSAT system. Also discussed are small aperture military ground terminals, link budgets for VSAT systems, capabilities and experience of a VSAT service provider, and developments in VSAT regulation.

  9. Small Payload Flight Systems (SPFS)

    NASA Technical Reports Server (NTRS)

    Mitchell, R. A. K.

    1984-01-01

    The Small Payload Flight System (SPFS) provides a simple and cost-effective approach to carrying small size experiments on the space shuttle. The system uses a bridge-like structure which spans the orbiter cargo bay but is only 3 feet in length. The structure can carry up to 4300 lb of payload weight and can be positioned at any location along the length of the cargo bay. In addition to the structural support, the SPFS provides avionics services to experiments. These include electrical power distribution and control, command and telemetry for control of the experiments and subsystem health monitoring, and software computations. The avionics system includes a flight qualified electrical power branching distributor, and a system control unit based on the Intel 8086 microprocessor. Data can be recorded on magnetic tape or transmitted to the ground. Finally, a Freon pump and cold plate system provides environmental control for both the avionics hardware and the experiments as necessary.

  10. Avionics for a Small Satellite

    NASA Technical Reports Server (NTRS)

    Abbott, Larry; Jochim, David; Schuler, Robert

    2001-01-01

    This paper discusses a small. seven and a half (7.5) inch diameter. satellite that NASA-JSC is developing as a technology demonstrator for an astronaut assistant free flyer. The Free Flyer is designed to off load flight crew work load by performing inspections of the exterior of Space Shuttle or International Space Station. The Free Flyer is designed to be operated by the flight crew thereby reducing the number of Extra Vehicle Activities (EVA) or by an astronaut on the ground further reducing crew work load. The paper focuses on the design constraint of a small satellite and the technology approach used to achieve the set of high performance requirements specified for the Free Flyer. Particular attention is paid to the processor card as it is the heart and system integration point of the Free Flyer.

  11. Wastewater services for small communities.

    PubMed

    Gray, S; Booker, N

    2003-01-01

    Connection to centralised regional sewage systems has been too expensive for small-dispersed communities, and these townships have traditionally been serviced by on-site septic tank systems. The conventional on-site system in Australia has consisted of an anaerobic holding tank followed by adsorption trenches. This technique relies heavily on the uptake of nutrients by plants for effective removal of nitrogen and phosphorus from the effluent, and is very seasonal in its efficiency. Hence, as these small communities have grown in size, the environmental effects of the septic tank discharges have become a problem. In locations throughout Australia, such as rural Victoria and along the Hawkesbury-Nepean River, septic tanks as being replaced with the transport of sewage to regional treatment plants. For some isolated communities, this can mean spending 20,000 dollars-40,000 dollars/household, as opposed to more common connection prices of 7,000 dollars/household. This paper explores some alternative options that might be suitable for these small communities, and attempts to identify solutions that provide acceptable environmental outcomes at lower cost. The types of alternative systems that are assessed in the paper include local treatment systems, separate blackwater and greywater collection and treatment systems both with and without non-potable water recycling, a small township scale treatment plant compared to either existing septic tank systems or pumping to a remote regional treatment facility. The work demonstrated the benefits of a scenario analysis approach for the assessment of a range of alternative systems. It demonstrated that some of the alternatives systems can achieve better than 90% reductions in the discharge of nutrients to the environment at significantly lower cost than removing the wastewater to a remote regional treatment plant. These concepts allow wastewater to be retained within a community allowing for local reuse of treated effluent.

  12. Small Business Innovations (Integrated Database)

    NASA Technical Reports Server (NTRS)

    1992-01-01

    Because of the diversity of NASA's information systems, it was necessary to develop DAVID as a central database management system. Under a Small Business Innovation Research (SBIR) grant, Ken Wanderman and Associates, Inc. designed software tools enabling scientists to interface with DAVID and commercial database management systems, as well as artificial intelligence programs. The software has been installed at a number of data centers and is commercially available.

  13. Small-Scale-Field Dynamo

    SciTech Connect

    Gruzinov, A.; Cowley, S.; Sudan, R. ||

    1996-11-01

    Generation of magnetic field energy, without mean field generation, is studied. Isotropic mirror-symmetric turbulence of a conducting fluid amplifies the energy of small-scale magnetic perturbations if the magnetic Reynolds number is high, and the dimensionality of space {ital d} satisfies 2.103{lt}{ital d}{lt}8.765. The result does not depend on the model of turbulence, incompressibility, and isotropy being the only requirements. {copyright} {ital 1996 The American Physical Society.}

  14. Twisted Yangians of small rank

    NASA Astrophysics Data System (ADS)

    Guay, Nicolas; Regelskis, Vidas; Wendlandt, Curtis

    2016-04-01

    We study quantized enveloping algebras called twisted Yangians associated with the symmetric pairs of types CI, BDI, and DIII (in Cartan's classification) when the rank is small. We establish isomorphisms between these twisted Yangians and the well known Olshanskii's twisted Yangians of types AI and AII, and also with the Molev-Ragoucy reflection algebras associated with symmetric pairs of type AIII. We also construct isomorphisms with twisted Yangians in Drinfeld's original presentation.

  15. Small-particle-size cement

    SciTech Connect

    Ewert, D.P.; Almond, S.W.; Blerhaus, W.M. II )

    1991-05-01

    Successful remedial cementing has historically been difficult in wells with large-interval, multizone, gravel-packed completions. The reason is the inability of conventional oilfield cements to penetrate gravel packs adequately. Small-particle-size cement (SPSC) was developed to penetrate gravel packs and to provide the zonal isolation required. This paper details the laboratory work, job design, and field implementation of this new cement.

  16. Small Business Innovations (Robotic Wrist)

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Under a Langley Research Center Small Business Innovation Research (SBIR) contract, Ross-Hime Designs, Inc. Minneapolis, MN, developed the Omni-Wrist actuator, which has a 25-pound capacity, 180 degrees of pitch/yaw, and 360 degrees of roll. Company literature calls it "the first successful singularity-free high-precision (robotic) wrist." Applications include spray painting, sealing, ultrasonic testing, welding and a variety of nuclear industry, aerospace and military uses.

  17. Implantable telemetry for small animals

    NASA Technical Reports Server (NTRS)

    1982-01-01

    A series of totally implantable telemetry devices for use in measuring deep body parameters in small animals were developed. Under a collaborative agreement with NASA, several of these systems; the continuous wave Doppler ultrasonic flowmeter, the multichannel telemetry system, and the inductively-powered dual channel cardiac pacer were evaluated in a series of ten mongrel dogs (15 to 20 kg.). These systems were used to measure ascending aortic and coronary blood flow, aortic pressure, and subcutaneous EKG.

  18. Metagenomic small molecule discovery methods

    PubMed Central

    Charlop-Powers, Zachary; Milshteyn, Aleksandr; Brady, Sean F.

    2014-01-01

    Metagenomic approaches to natural product discovery provide the means of harvesting bioactive small molecules synthesized by environmental bacteria without the requirement of first culturing these organisms. Advances in sequencing technologies and general metagenomic methods are beginning to provide the tools necessary to unlock the unexplored biosynthetic potential encoded by the genomes of uncultured environmental bacteria. Here, we highlight recent advances in sequence- and functional- based metagenomic approaches that promise to facilitate antibiotic discovery from diverse environmental microbiomes. PMID:25000402

  19. Implantable telemetry for small animals

    NASA Astrophysics Data System (ADS)

    1982-03-01

    A series of totally implantable telemetry devices for use in measuring deep body parameters in small animals were developed. Under a collaborative agreement with NASA, several of these systems; the continuous wave Doppler ultrasonic flowmeter, the multichannel telemetry system, and the inductively-powered dual channel cardiac pacer were evaluated in a series of ten mongrel dogs (15 to 20 kg.). These systems were used to measure ascending aortic and coronary blood flow, aortic pressure, and subcutaneous EKG.

  20. Small Business Innovations (Fiber Optics)

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Foster-Miller, Inc. Waltham, MA developed the In-Situ Fiber Optic Polymer Reaction Monitor which could lead to higher yields and lower costs in complex composite manufacturing. The monitor, developed under a Small Business Innovation Research (SBIR) contract with Langley Research Center, uses an infrared, fiber optic sensor to track the molecular vibrational characteristics of a composite part while it is being cured. It is the first analytical system capable of directly measuring the chemistry of advanced composite materials.

  1. Small Break Air Ingress Experiment

    SciTech Connect

    Chang Oh; Eung Soo Kim

    2011-09-01

    The small break air-ingress experiment, described in this report, is designed to investigate air-ingress phenomena postulated to occur in pipes in a very high temperature gas-cooled reactor (VHTRs). During this experiment, air-ingress rates were measured for various flow and break conditions through small holes drilled into a pipe of the experimental apparatus. The holes were drilled at right angles to the pipe wall such that a direction vector drawn from the pipe centerline to the center of each hole was at right angles with respect to the pipe centerline. Thus the orientation of each hole was obtained by measuring the included angle between the direction vector of each hole with respect to a reference line anchored on the pipe centerline and pointing in the direction of the gravitational force. Using this reference system, the influence of several important parameters on the air ingress flow rate were measured including break orientation, break size, and flow velocity . The approach used to study the influence of these parameters on air ingress is based on measuring the changes in oxygen concentrations at various locations in the helium flow circulation system as a function of time using oxygen sensors (or detectors) to estimate the air-ingress rates through the holes. The test-section is constructed of a stainless steel pipe which had small holes drilled at the desired locations.

  2. Atmospheric holes and small comets

    NASA Technical Reports Server (NTRS)

    Frank, L. A.; Sigwarth, J. B.

    1993-01-01

    Global images of Earth's UV dayglow as gained with an imaging photometer on board Dynamics Explorer 1 exhibit transient decreases, or atmospheric holes, in the dayglow intensities over areas with diameters about 50 km. Features of these atmospheric holes include (1) preferential motion in the east-to-west direction across the sunlit face of Earth, (2) similar diurnal variations in occurrence rates as those for radar meteors, (3) correlation of the occurrence rates with the nonshower rates as determined with forward scatter radar, and (4) larger angular diameters for these atmospheric holes when the spacecraft approaches Earth during its perigee passes. These atmospheric holes are interpreted in terms of obscuration of the dayglow by water clouds from the disruption and subsequent vaporization of small comets at low altitudes above the atmosphere. Supporting evidence for the existence of these small comets is given by their telescopic sighting at greater altitudes before disruption and the detection of water bursts in Earth's upper atmosphere. The small-comet hypothesis and its relationship to geophysical, lunar, and interplanetary phenomena are discussed.

  3. Evolution of small prokaryotic genomes.

    PubMed

    Martínez-Cano, David J; Reyes-Prieto, Mariana; Martínez-Romero, Esperanza; Partida-Martínez, Laila P; Latorre, Amparo; Moya, Andrés; Delaye, Luis

    2014-01-01

    As revealed by genome sequencing, the biology of prokaryotes with reduced genomes is strikingly diverse. These include free-living prokaryotes with ∼800 genes as well as endosymbiotic bacteria with as few as ∼140 genes. Comparative genomics is revealing the evolutionary mechanisms that led to these small genomes. In the case of free-living prokaryotes, natural selection directly favored genome reduction, while in the case of endosymbiotic prokaryotes neutral processes played a more prominent role. However, new experimental data suggest that selective processes may be at operation as well for endosymbiotic prokaryotes at least during the first stages of genome reduction. Endosymbiotic prokaryotes have evolved diverse strategies for living with reduced gene sets inside a host-defined medium. These include utilization of host-encoded functions (some of them coded by genes acquired by gene transfer from the endosymbiont and/or other bacteria); metabolic complementation between co-symbionts; and forming consortiums with other bacteria within the host. Recent genome sequencing projects of intracellular mutualistic bacteria showed that previously believed universal evolutionary trends like reduced G+C content and conservation of genome synteny are not always present in highly reduced genomes. Finally, the simplified molecular machinery of some of these organisms with small genomes may be used to aid in the design of artificial minimal cells. Here we review recent genomic discoveries of the biology of prokaryotes endowed with small gene sets and discuss the evolutionary mechanisms that have been proposed to explain their peculiar nature.

  4. Galileo's Exploration of Small Bodies

    NASA Astrophysics Data System (ADS)

    Johnson, Torrence

    The Galileo mission to the Jupiter system afforded the opportunity to make the first ever flyby observations of main belt asteroids. The first encounter with 951 Gaspra revealed an irregular cratered surface that shows evidence of regolith optical space weatering processes. The second encounter with 243 Ida resulted in the discovery of the first confirmed satellite of an asteroid Dactyl. Measruements of Dactyl's orbit also allowed a useful determination of mass and density for Ida. In addition to these pioneering asteroid observations Galileo also made observations of Jupiter's small inner moons and found that they were the major source for material in Jupiter's tenuous ring system. During it's final data taking orbit in 2002 Galileo passed within about 250 km of the irregularly shaped satellite Amalthea. Determination of Amalthea's mass from tracking data yields a bulk density for this small body of less than 1 gm/cc suggesting a body of relatively high porosity. This is consistent with the growing body of data on small asteroid densities and estimates of their porosity

  5. Galileo's Exploration of Small Bodies

    NASA Astrophysics Data System (ADS)

    Johnson, Torrence

    2005-01-01

    The Galileo mission to the Jupiter system afforded the opportunity to make the first ever flyby observations of main belt asteroids. The first encounter with 951 Gaspra revealed an irregular cratered surface that shows evidence of regolith optical space weatering processes. The second encounter with 243 Ida resulted in the discovery of the first confirmed satellite of an asteroid Dactyl. Measruements of Dactyl's orbit also allowed a useful determination of mass and density for Ida. In addition to these pioneering asteroid observations Galileo also made observations of Jupiter's small inner moons and found that they were the major source for material in Jupiter's tenuous ring system. During it's final data taking orbit in 2002 Galileo passed within about 250 km of the irregularly shaped satellite Amalthea. Determination of Amalthea's mass from tracking data yields a bulk density for this small body of less than 1 gm/cc suggesting a body of relatively high porosity. This is consistent with the growing body of data on small asteroid densities and estimates of their porosity.

  6. Evolution of small prokaryotic genomes

    PubMed Central

    Martínez-Cano, David J.; Reyes-Prieto, Mariana; Martínez-Romero, Esperanza; Partida-Martínez, Laila P.; Latorre, Amparo; Moya, Andrés; Delaye, Luis

    2015-01-01

    As revealed by genome sequencing, the biology of prokaryotes with reduced genomes is strikingly diverse. These include free-living prokaryotes with ∼800 genes as well as endosymbiotic bacteria with as few as ∼140 genes. Comparative genomics is revealing the evolutionary mechanisms that led to these small genomes. In the case of free-living prokaryotes, natural selection directly favored genome reduction, while in the case of endosymbiotic prokaryotes neutral processes played a more prominent role. However, new experimental data suggest that selective processes may be at operation as well for endosymbiotic prokaryotes at least during the first stages of genome reduction. Endosymbiotic prokaryotes have evolved diverse strategies for living with reduced gene sets inside a host-defined medium. These include utilization of host-encoded functions (some of them coded by genes acquired by gene transfer from the endosymbiont and/or other bacteria); metabolic complementation between co-symbionts; and forming consortiums with other bacteria within the host. Recent genome sequencing projects of intracellular mutualistic bacteria showed that previously believed universal evolutionary trends like reduced G+C content and conservation of genome synteny are not always present in highly reduced genomes. Finally, the simplified molecular machinery of some of these organisms with small genomes may be used to aid in the design of artificial minimal cells. Here we review recent genomic discoveries of the biology of prokaryotes endowed with small gene sets and discuss the evolutionary mechanisms that have been proposed to explain their peculiar nature. PMID:25610432

  7. 78 FR 48537 - Small Business Innovation Research and Small Business Technology Transfer Programs...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-08

    ... ADMINISTRATION Small Business Innovation Research and Small Business Technology Transfer Programs... Administration (SBA) is publishing the Small Business Innovation Research (SBIR) and Small Business Technology... Business Administration, 409 Third Street SW., Washington, DC 20416; or send an email to...

  8. 75 FR 29393 - Small Business Week, 2010

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-26

    ... 8525 of May 20, 2010 Small Business Week, 2010 By the President of the United States of America A.... During Small Business Week, we reaffirm our support for America's small businesses and celebrate the... that have helped small business owners acquire loans and hire workers. This week, we celebrate the...

  9. History of the Oregon Small Schools Program.

    ERIC Educational Resources Information Center

    Oregon State Board of Education, Salem.

    Development of the Oregon Small Schools Program is traced against the background of other small-school projects, such as the Western States Small Schools Project and the Texas Small Schools Project. Information is given on the various procedures involved in the organization's development and on problems (e.g., high turnover of teachers and high…

  10. 76 FR 61626 - Small Business Subcontracting

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-05

    ... From the Federal Register Online via the Government Publishing Office SMALL BUSINESS ADMINISTRATION 13 CFR Parts 121 and 125 RIN 3245-AG22 Small Business Subcontracting AGENCY: U.S. Small Business Administration. ACTION: Proposed rule. SUMMARY: The U.S. Small Business Administration (SBA or Agency)...

  11. Helicity Evolution at Small x

    NASA Astrophysics Data System (ADS)

    Sievert, Michael; Kovchegov, Yuri; Pitonyak, Daniel

    2017-01-01

    We construct small- x evolution equations which can be used to calculate quark and anti-quark helicity TMDs and PDFs, along with the g1 structure function. These evolution equations resum powers of ln2(1 / x) in the polarization-dependent evolution along with the powers of ln(1 / x) in the unpolarized evolution which includes saturation effects. The equations are written in an operator form in terms of polarization-dependent Wilson line-like operators. While the equations do not close in general, they become closed and self-contained systems of non-linear equations in the large-Nc and large-Nc &Nf limits. After solving the large-Nc equations numerically we obtain the following small- x asymptotics for the flavor-singlet g1 structure function along with quarks hPDFs and helicity TMDs (in absence of saturation effects): g1S(x ,Q2) ΔqS(x ,Q2) g1L S(x ,kT2) (1/x) > αh (1/x) 2.31√{αsNc/2 π. We also give an estimate of how much of the proton's spin may be at small x and what impact this has on the so-called ``spin crisis.'' Work supported by the U.S. DOE, Office of Science, Office of Nuclear Physics under Award Number DE-SC0004286 (YK), the RIKEN BNL Research Center, and TMD Collaboration (DP), and DOE Contract No. DE-SC0012704 (MS).

  12. Small animal models of xenotransplantation.

    PubMed

    Wang, Hao

    2012-01-01

    Organ transplantation has become a successful and acceptable treatment for end-stage organ failure. Such success has allowed transplant patients to resume a normal lifestyle. The demands for transplantation have been steadily increasing, as more patients and new diseases are being deemed eligible for treatment via transplantation. However, it is clear that human organs will never meet the increasing demand of transplantation. Therefore, scientists must continue to pursue alternative therapies and explore new treatments to meet the growing demand for the limited number of organs available. Transplanting organs from animals into humans (xenotransplantation) is one such therapy. The observed enthusiasm for xenotransplantation, irrespective of the severe shortage of human organs and tissues available for transplantation, can be said to stem from at least two factors. First, there is the possibility that animal organs and tissues might be less susceptible than those of humans to the recurrence of disease processes. Second, a xenograft might be used as a vehicle for introducing novel genes or biochemical processes which could be of therapeutic value for the transplant recipient.To date, millions of lives have been saved by organ transplantation. These remarkable achievements would have been impossible without experimental transplantation research in animal models. Presently, more than 95% of organ transplantation research projects are carried out using rodents, such as rats and mice. The key factor to ensure the success of these experiments lies in state-of-the art experimental surgery. Small animal models offer unique advantages for the mechanistic study of xenotransplantation rejection. Currently, multiple models have been developed for investigating the different stages of immunological barriers in xenotransplantation. In this chapter, we describe six valuable small animal models that have been used in xenotransplantation research. The methodology for the small animal

  13. Rain on small tropical islands

    NASA Astrophysics Data System (ADS)

    Sobel, A. H.; Burleyson, C. D.; Yuter, S. E.

    2011-04-01

    A high-resolution rainfall climatology based on observations from the Tropical Rainfall Measuring Mission's Precipitation Radar (PR) instrument is used to evaluate the influence of small tropical islands on climatological rainfall. Islands with areas between one hundred and several thousand km2 are considered in both the Indo-Pacific Maritime Continent and Caribbean regions. Annual mean climatological (1997-2007) rainfall over each island is compared with that over the surrounding ocean region, and the difference is expressed as a percentage. In addition to total rainfall, rain frequency and intensity are also analyzed. Results are stratified into two 12 h halves of the diurnal cycle as well as eight 3 h periods, and also by a measure of each island's topographic relief. In both regions, there is a clear difference between larger islands (areas of a few hundred km2 or greater) and smaller ones. Both rain frequency and total rainfall are significantly enhanced over larger islands compared to the surrounding ocean. For smaller islands the enhancement is either negligibly small, statistically insignificant, or, in the case of Caribbean rain frequency, negative. The enhancement in total rainfall over larger islands is partly attributable to greater frequency and partly to greater intensity. A diurnal cycle in island enhancement is evident in frequency but not intensity, except over small Caribbean islands where the converse is true. For the larger islands, higher orography is associated with greater rainfall enhancements. The orographic effect is larger (percentagewise) in the Caribbean than in the Maritime Continent. Orographic precipitation enhancement manifests more strongly as increased frequency of precipitation rather than increased intensity and is present at night as well as during the day. The lack of a clear diurnal cycle in orographic enhancement suggests that much of the orographic rainfall enhancement is attributable to mechanically forced upslope flow

  14. ATFSR: a small torsatron reactor

    SciTech Connect

    Houlberg, W.A.; Lacatski, J.T.; Uckan, N.A.

    1985-01-01

    A small (average minor radius anti a approx. = 1 m), moderate-aspect-ratio torsatron reactor based on the Advanced Toroidal Facility (ATF) is proposed as a starting point for improved stellarator reactor designs. The major limitation of the compact size is the lack of space under the helical coils for the blanket and shield. Neoclassical confinement models for helically trapped particles show that a large electric potential (radial electric field) is necessary to achieve ignition in a device of this size, although high-Q operation is still attainable with more modest potentials.

  15. Ionene modified small polymeric beads

    NASA Technical Reports Server (NTRS)

    Rembaum, Alan (Inventor)

    1977-01-01

    Linear ionene polyquaternary cationic polymeric segments are bonded by means of the Menshutkin reaction (quaternization) to biocompatible, extremely small, porous particles containing halide or tertiary amine sites which are centers for attachment of the segments. The modified beads in the form of emulsions or suspensions offer a large, positively-charged surface area capable of irreversibly binding polyanions such as heparin, DNA, RNA or bile acids to remove them from solution or of reversibly binding monoanions such as penicillin, pesticides, sex attractants and the like for slow release from the suspension.

  16. GEF small grants programme - overview

    SciTech Connect

    1997-12-01

    This paper describes the GEF small grants program which seeks to enhance the role of households and communities in conserving global biodiversity, mitigating global climate change, and protecting international waters. Grants up to $50k have been granted for projects in 33 countries, with plans for 12 other countries. The author describes the framework that the program works under, and the methodology followed in developing and planning projects. The approach to climate change concerns is to emphasize the development of non-carbon energy development activities to provide energy sources and economic development.

  17. Small satellite radiation budget instrumentation

    SciTech Connect

    Weber, P.G.

    1992-01-01

    A major diagnostic in understanding the response of the Earth's climate to natural or anthropogenic changes is the radiative balance at the top of the atmosphere. Two classes of measurements may be undertaken: (1) a monitoring of the radiation balance over decade-long long time-scales, and (2) measurements designed to provide a sufficiently complete data set to validate or improve models. This paper discusses some of the important ingredients in obtaining such data, and presents a description of some candidate instrumentation for use on a small satellite. 23 refs.

  18. Small satellite radiation budget instrumentation

    SciTech Connect

    Weber, P.G.

    1992-05-01

    A major diagnostic in understanding the response of the Earth`s climate to natural or anthropogenic changes is the radiative balance at the top of the atmosphere. Two classes of measurements may be undertaken: (1) a monitoring of the radiation balance over decade-long long time-scales, and (2) measurements designed to provide a sufficiently complete data set to validate or improve models. This paper discusses some of the important ingredients in obtaining such data, and presents a description of some candidate instrumentation for use on a small satellite. 23 refs.

  19. Theory problems at small x

    SciTech Connect

    Collins, J.C.

    1984-01-01

    It is shown how the standard methods of perturbative QCD are valid to extremely small x. The methods are valid provided a quantity we call the packing fraction of partons in a hadron is much less than one. One surprising consequence is that the cross-section for production of jets of a few GeV energy can be reliably calculated. Since this cross-section in tens of millibarns, the phenomenology of minimum bias events at the SSC will be different than at lower energy; this will have a significant effect on the backgrounds for new physics events. 8 references.

  20. Restricted Transport in Small Pores

    PubMed Central

    Anderson, John L.; Quinn, John A.

    1974-01-01

    The basic hydrodynamic equations governing transport in submicron pores are reexamined. Conditions necessary for a simplified, one-dimensional treatment of the diffusion/convection process are established. Steric restrictions and Brownian motion are incorporated directly into the resulting model. Currently available fluid mechanical results are used to evaluate an upper limit on hindered diffusion; this limit is valid for small particle-to-pore ratios. Extensions of the analysis are shown to depend on numerical solutions of the related hydrodynamic problem, that of asymmetrical particle motion in a bounded fluid. PMID:4813157