Science.gov

Sample records for impurity-bound small polarons

  1. Influence of the image charge effect on the hydrogen-like impurity-bound polaron in a spherical quantum dot in the presence of an electric field

    NASA Astrophysics Data System (ADS)

    Vartanian, Arshak L.; Vardanyan, Lyudvig A.

    2016-01-01

    We have investigated the influence of an external electric field on the binding energies and polaronic shifts of the ground and some first few excited states of a hydrogenic impurity in a spherical quantum dot by taking into account the image charge effect. By using Landau-Pekar variational method the general analytical expression is obtained for the impurity bound-polaron energies. It has been numerically identified the conditions (electric field, nominal radius of quantum dot, etc.) in which the bound-polaron states can be existence in GaAs quantum dot. We have shown that the polaronic shifts in the binding energy of 1s-like state are the same in cases with and without image charge effect while they for 2s-like state are not coincide and have different monotonic behavior versus confinement potential. Electron-phonon interaction lifts the degeneracy of the 2px-, 2py-, and 2pz-like states of a donor impurity and reduces their binding energies.

  2. The Effective Mass of Impurity-bound Polaron in a Two- and Three-Dimensional Quantum Dot

    NASA Astrophysics Data System (ADS)

    Chen, Shi-Hua

    2013-01-01

    Within the framework of the Landau-Pekar variational method we have derived an analytical expression for the ground-state binding energies and the effective mass of an electron bound to a Coulomb impurity in a polar semiconductor quantum dot (QD) with parabolic confinement in both two and three dimensions. We have also calculated the number of phonons in the cloud of this bound polaron. It is found that the effective mass increase with increasing the Coulomb binding parameter and increase with the decrease in size of the QD. The results also indicate that this effect becomes much more pronounced with decreasing dimensionality.

  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. 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

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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. PMID:19811399

  10. Criteria for the accuracy of small polaron quantum master equation in simulating excitation energy transfer dynamics

    SciTech Connect

    Chang, Hung-Tzu; Cheng, Yuan-Chung; Zhang, Pan-Pan

    2013-12-14

    The small polaron quantum master equation (SPQME) proposed by Jang et al. [J. Chem. Phys. 129, 101104 (2008)] is a promising approach to describe coherent excitation energy transfer dynamics in complex molecular systems. To determine the applicable regime of the SPQME approach, we perform a comprehensive investigation of its accuracy by comparing its simulated population dynamics with numerically exact quasi-adiabatic path integral calculations. We demonstrate that the SPQME method yields accurate dynamics in a wide parameter range. Furthermore, our results show that the accuracy of polaron theory depends strongly upon the degree of exciton delocalization and timescale of polaron formation. Finally, we propose a simple criterion to assess the applicability of the SPQME theory that ensures the reliability of practical simulations of energy transfer dynamics with SPQME in light-harvesting systems.

  11. Charge reorganization energy and small polaron binding energy of rubrene thin films by ultraviolet photoelectron spectroscopy.

    PubMed

    Duhm, Steffen; Xin, Qian; Hosoumi, Shunsuke; Fukagawa, Hirohiko; Sato, Kazushi; Ueno, Nobuo; Kera, Satoshi

    2012-02-14

    The hole–phonon coupling of a rubrene monolayer on graphite is measured by means of angle resolved ultraviolet photoelectron spectroscopy. Thus, the charge reorganization energy λ and the small polaron binding energy is determined, which allows insight into the nature of charge transport in condensed rubrene. PMID:22403829

  12. Small polarons and point defects in LaFeO3

    NASA Astrophysics Data System (ADS)

    Zhu, Zhen; Peelaers, Hartwin; van de Walle, Chris G.

    The proton-conductive perovskite-type LaFeO3 is a promising negative-electrode material for Ni/metal-hydride (Ni-MH) batteries. It has a discharge capacity up to 530 mAhg-1 at 333 K, which is significantly higher than commercialized AB5-type alloys. To elucidate the underlying mechanism of this performance, we have investigated the structural and electronic properties of bulk LaFeO3, as well as the effect of point defects, using hybrid density functional methods. LaFeO3 is antiferromagnetic in the ground state with a band gap of 3.54 eV. Small hole and electron polarons can form through self- or point-defect-assisted trapping. We find that La vacancies and Sr substitutional on La sites are shallow acceptors with the induced holes trapped as small polarons, while O and Fe vacancies are deep defect centers. Hydrogen interstitials behave like shallow donors, with the donor electrons localized on nearby iron sites as electron polarons. With a large trapping energy, these polarons can act as electron or hole traps and affect the electrical performance of LaFeO3 as the negative electrode for Ni-MH batteries. We acknowledge DOE for financial support.

  13. Small polaron effect on carrier recombination in perovskite manganite thin films

    NASA Astrophysics Data System (ADS)

    Wu, G.-R.; Sasaki, M.; Isa, T.; Negishi, H.; Inoue, M.; Gao, W.-X.; Xiong, G.-C.

    2001-05-01

    Photoinduced 'transient thermoelectric effect (TTE)' in perovskite manganite La 0.6Ca 0.4MnO 3 thin film has been measured under magnetic fields. The fast decay process of TTE signals is due to a recombination of photogenerated electron-hole pairs through Mn 4+ ions as capture centers, whose evaluated cross section σ obeys the power law σ∝ T- n ( n=0.75) in the ferromagnetic phase far below Tc and in the paramagnetic phase. From the observed relaxation time τ1, we evaluated the parameter α characterizing a small polaron effect and the effective mass m∗; both are enhanced appreciably near Tc. Such anomaly is attributed to the change in the thermal velocity of diffusing holes with downspin due to a small polaron effect.

  14. 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.

  15. Temperature dependence of small polaron population decays in iron-doped lithium niobate by Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Mhaouech, I.; Guilbert, L.

    2016-10-01

    The population decay of light-induced small polarons in iron-doped lithium niobate is simulated by a Monte-Carlo method on the basis of Holstein's theory. The model considers random walks of both bound polarons (NbLi4+) and free polarons (NbNb4+) ending to deep traps (FeLi3+). The thermokinetic interplay between polaron species is introduced by trapping and de-trapping rates at niobium antisites (NbLi). The decay of the NbLi4+ population proceeds by three possible channels: direct trapping at FeLi3+ sites, hopping on niobium antisites and hopping on Nb regular sites after conversion to the free state. Up to three regimes, each one reflecting the predominance of one of these processes, appear with different activation energies in the Arrhenius plots of the decay time. The influence of FeLi and NbLi concentrations on the transition temperatures is evidenced. For both polaron species, the length of the final hop (trapping length) is found much larger than the usual hopping length and decreases at rising temperature. This trap size effect is a natural consequence of Holstein's theory and may explain some unclear features of polaron-related light-induced phenomena, such as the temperature-dependent stretching exponent of light-induced absorption decays and the anomalous increase of the photoconductivity at high doping levels.

  16. Electrochromism and small-polaron hopping in oxygen deficient and lithium intercalated amorphous tungsten oxide films

    NASA Astrophysics Data System (ADS)

    Triana, C. A.; Granqvist, C. G.; Niklasson, G. A.

    2015-07-01

    Thin films of Li x WO 3 - z with 0 ≤ x ≤ 0.27 and 0 ≤ z ≤ 0.27 were prepared by sputter deposition followed by electrochemical lithiation. Kramers-Kronig-consistent complex dielectric functions were obtained for these films by numerical inversion of experimental spectra of optical transmittance and reflectance by using a superposition of Tauc-Lorentz and Lorentz oscillator models. Low-energy optical absorption bands were induced by oxygen vacancies and/or by electrochemical intercalation of Li+ species together with charge compensating electrons. The experimental optical conductivity was fitted to a small-polaron model for disordered systems with strong electron-phonon interaction, taking into account transitions near the Fermi level. The optical absorption is due to small-polaron hopping and associated with the formation of W5+ states due to transfer of electrons from oxygen vacancies and/or insertion of Li+ species. The results also show increases in the Fermi level, caused by oxygen deficiency or Li+ insertion, which occur along with a band gap shift towards higher energies for the Li+ intercalated films.

  17. 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.

  18. The conversion of the small magnetic polarons into the large polaron as the cause of the unusual transport properties of layered manganites La1.2Sr1.8Mn2O7

    NASA Astrophysics Data System (ADS)

    Solin, N. I.

    2016-03-01

    The paper is aimed at clarification of nature of unusual transport properties of the layered manganites. Magnetic and magnetotransport properties of the Mn-deficient quasi-two-dimensional manganites La1,2Sr1,8Mn2(1-z)O7 are investigated at 5-400 K in magnetic fields up to 9 T. The studied single crystals show properties typical to layered manganites. Semiconductor-metal-like transition near the Curie temperature (TC), non-metal type of resistance ρ(T) at low temperatures, enormous magnetoresistance near TC, the negative magnetoresistance in the studied temperature range are observed in these single crystals. The obtained results are discussed in the framework of the magnetic polaron conductivity. It is assumed that in quasi-two-dimensional manganites the polarons are preserved in the magnetically ordered state as well, and that small magnetic polarons become big polaron at low temperatures. The increase of size of the magnetic polaron under magnetic ordering or application of a magnetic field explains the basic transport properties of layered manganites La1.2Sr1.8Mn2O7. The temperature and field dependencies of the polaron sizes, defined from the magnetotransport properties, are reasonably described in the model of phase separation.

  19. Anisotropic spin dephasing of impurity-bound electron spins in ZnO

    SciTech Connect

    Lee, Jieun; Sih, Vanessa; Venugopal, Aneesh

    2015-01-05

    We investigate the electron spin dynamics of n-type c-axis oriented bulk zinc oxide (ZnO) by using time-resolved Kerr rotation and resonant spin amplification measurements. Calculating resonant spin amplification using an anisotropic spin dephasing model reveals that there are two species involved in the spin dynamics, which we attribute to conduction and impurity-bound electron spins, respectively. We find that the impurity-bound electron spin dephasing mechanism is strongly anisotropic due to anisotropic exchange interactions. The identification of the two spin species and their dephasing mechanisms is further supported by the temperature, power, and wavelength dependence of the spin coherence measurements.

  20. Electron small polarons and their mobility in iron (oxyhydr)oxide nanoparticles

    SciTech Connect

    Katz, Jordan E.; Zhang, Xiaoyi; Attenkofer, Klaus; Chapman, Karena W.; Frandsen, Cathrine; Zarzycki, Piotr P.; Rosso, Kevin M.; Falcone, Roger; Waychunas, Glenn; Gilbert, Benjamin

    2012-09-07

    Redox-active transition metal (TM) oxides, hydroxide and oxyhydroxides semiconductors typically posses wide p-d charge-transfer band gaps and exhibit poor charge carrier mobility. Nevertheless, there is increasing evidence that electron mobility within TM (oxyhydr)oxides is a crucial feature of their redox reactivity, affecting the rates of interfacial reactions, outcomes of redox-driven phase transformations and enabling charge transfer between reactions occurring at widely-separated surface sites 1,2. In order to determine the links between crystal structure and charge transport efficiency on solid-phase redox reactivity we have applied a pump-probe method to observe directly the fate of electrons introduced into ferric iron (oxyhydr)oxide nanoparticles via ultrafast interfacial electron transfer3. Time-resolved X-ray spectroscopy observes the formation of reduced and structurally distorted metal sites consistent with small polarons. By tracking the lifetime of the reduced metal states, rate constants for thermally-activated cation-to-cation electron hopping in the solid can be measured with subnanosecond accuracy. Comparisons between different phases revealed that short-range structural topology, not long-range order, dominates the electron-hopping rate, and shed new insight into the structure and properties of the naturally-formed nanomaterial, ferrihydrite4. Lattice Monte Carlo simulations revealed that, on timescales relevant to solid-phase reactions, surface charge plays a commanding role in biasing electron conduction trajectories.

  1. Electron transport in pure and substituted iron oxyhydroxides by small-polaron migration

    SciTech Connect

    Alexandrov, Vitali Y.; Rosso, Kevin M.

    2014-08-12

    Iron oxyhydroxides (FeOOH) are common crystalline forms of iron that play a critical role in technology and the natural environment via a variety of important reduction-oxidation reactions, including electrical semiconduction as an aspect. However, a basic understanding of the electron transport properties of these systems is still lacking. We examine the electron mobility in goethite (α-FeOOH), akaganéite (β-FeOOH), and lepidocrocite (γ -FeOOH) polymorphs by means of density functional theory based (DFT+U) calculations.We show that room temperature charge transport should be dominated by the small-polaron hopping type, and that the attendant mobility should be highest for pure goethite and akaganéite. Hopping pathways through the various lattices are discussed in terms of individual electron exchange steps and rates for each. Given the usual occurrence of compositional impurities in natural iron oxyhydroxides, we also investigate the effect of common stoichiometric defects on the electron hopping activation energies such as Al and Cr substitutional cations in goethite, and Cl anions in the channels of akaganéite.

  2. Electron transport in pure and substituted iron oxyhydroxides by small-polaron migration

    SciTech Connect

    Alexandrov, Vitaly Rosso, Kevin M.

    2014-06-21

    Iron oxyhydroxides (FeOOH) are common crystalline forms of iron that play a critical role in technology and the natural environment via a variety of important reduction-oxidation reactions, including electrical semiconduction as an aspect. However, a basic understanding of the electron transport properties of these systems is still lacking. We examine the electron mobility in goethite (α-FeOOH), akaganéite (β-FeOOH), and lepidocrocite (γ-FeOOH) polymorphs by means of density functional theory based (DFT+U) calculations. We show that room temperature charge transport should be dominated by the small-polaron hopping type, and that the attendant mobility should be highest for pure goethite and akaganéite. Hopping pathways through the various lattices are discussed in terms of individual electron exchange steps and rates for each. Given the usual occurrence of compositional impurities in natural iron oxyhydroxides, we also investigate the effect of common stoichiometric defects on the electron hopping activation energies such as Al and Cr substitutional cations in goethite, and Cl anions in the channels of akaganéite.

  3. Transmon-based simulator of nonlocal electron-phonon coupling: A platform for observing sharp small-polaron transitions

    NASA Astrophysics Data System (ADS)

    Stojanović, Vladimir M.; Vanević, Mihajlo; Demler, Eugene; Tian, Lin

    2014-04-01

    We propose an analog superconducting quantum simulator for a one-dimensional model featuring momentum-dependent (nonlocal) electron-phonon couplings of Su-Schrieffer-Heeger and "breathing-mode" types. Because its corresponding coupling vertex function depends on both the electron and phonon quasimomenta, this model does not belong to the realm of validity of the Gerlach-Löwen theorem that rules out any nonanalyticities in single-particle properties. The superconducting circuit behind the proposed simulator entails an array of transmon qubits and microwave resonators. By applying microwave driving fields to the qubits, a small-polaron Bloch state with an arbitrary quasimomentum can be prepared in this system within times several orders of magnitude shorter than the typical qubit decoherence times. We demonstrate that—by varying the externally tunable parameters—one can readily reach the critical coupling strength required for observing the sharp transition from a nondegenerate (single-particle) ground state corresponding to zero quasimomentum (Kgs=0) to a twofold-degenerate small-polaron ground state at nonzero quasimomenta Kgs and -Kgs. Through exact numerical diagonalization of our effective Hamiltonian, we show how this nonanalyticity is reflected in the relevant single-particle properties (ground-state energy, quasiparticle residue, average number of phonons). We also show that the proposed setup provides an ideal testbed for studying the nonequilibrium dynamics of small-polaron formation in the presence of strongly momentum-dependent electron-phonon interactions.

  4. Coexistence of Anderson localization and small polarons in the normal phase of La 2-xSr xCuO 4

    NASA Astrophysics Data System (ADS)

    Tateno, Jun

    1993-09-01

    The feature of the electrical resistivity in the normal phase of La 2- xSr xCuO 4 is explained by the coexistence model of Anderson localization and small polarons. The estimated concentration of the small polarons from this model attains a maximum at the optimum concentration, where the superconducting transition temperature attains its maximum. The variation of the activation energy of the hopping conduction with x is explained by taking into account the transfer mechanism accompanied with a change of states between Anderson localization and a small polaron state. From this analysis the Bose condensation of bipolarons is considered to be valid as the origin of superconductivity in this material.

  5. Self-trapping of holes in p-type oxides: Theory for small polarons in MnO

    NASA Astrophysics Data System (ADS)

    Peng, Haowei; Lany, Stephan

    2012-02-01

    Employing the p-d repulsion to increase the valence band dispersion and the energy of the VBM is an important design principle for p-type oxides, as manifested in prototypical p-type oxides like Cu2O or CuAlO2 which show a strong Cu-d/O-p interaction. An alternative opportunity to realize this design principle occurs for Mn(+II) compounds, where the p-d orbital interaction occurs dominantly in the fully occupied d^5 majority spin direction of Mn. However, the ability of Mn to change the oxidation state from +II to +III can lead to a small polaron mechanism for hole transport which hinders p-type conductivity. This work addresses the trends of hole self-trapping for MnO between octahedral (rock-salt structure) and tetrahedral coordination (zinc-blende structure). We employ an on-site hole-state potential so to satisfy the generalized Koopmans condition. This approach avoids the well-known difficulty of density-functional calculations to describe correctly the localization of polaronic states, and allows to quantitatively predict the self-trapping energies. We find that the tetrahedrally coordinated Mn is less susceptible to hole self-trapping than the octahedrally coordinated Mn.

  6. Charge carriers and small-polaron migration as the origin of intrinsic dielectric anomalies in multiferroic TbMnO3 polycrystals.

    PubMed

    Silveira, L G D; Dias, G S; Cótica, L F; Eiras, J A; Garcia, D; Sampaio, J A; Yokaichiya, F; Santos, I A

    2013-11-27

    Temperature-dependent and frequency-dependent dielectric investigations have been performed in TbMnO3 polycrystals sintered in either oxidative or reductive atmospheres. The results revealed the occurrence of two dielectric anomalies above 100 K, which are caused by the thermal activation of charge carriers and their motion in grain cores and grain boundaries. The temperature dependence of the bulk dc conductivity was also analysed and indicates that charge carriers move between inequivalent sites according to a variable-range-hopping mechanism. Also, a strong correlation between dielectric properties and crystalline structure was observed. Furthermore, a low-temperature dielectric relaxation, commonly reported in rare-earth manganite crystals, was observed in both samples. This relaxation follows the empirical Cole-Cole model and was attributed to small-polaron tunnelling. Polaron motion was observed to be affected by the magnetic transitions, structural properties and intrinsic anisotropies in TbMnO3. It is also worth mentioning that the dielectric anomaly due to motion of charge carriers in grain boundaries is the only one of extrinsic origin, while the anomalies related to carrier motion in grain cores and small-polaron tunnelling are intrinsic to TbMnO3.

  7. Nonadiabatic small-polaron hopping conduction in Li-doped and undoped Bi4Sr3Ca3CuyOx (0<=y<=5)

    NASA Astrophysics Data System (ADS)

    Mollah, S.; Som, K. K.; Bose, K.; Chakravorty, A. K.; Chaudhuri, B. K.

    1992-11-01

    Detailed experimental results of temperature- and CuO-concentration-dependent dc conductivities of semiconducting Bi4Sr3Ca3CuyOx (y=0 to 5) and Li-doped Bi4Sr3Ca3-zLizCu4Ox (z=0.1, 0.5, and 1.0) glasses are reported. The variation of activation energy with glass compositions dominates the conductivity. Unlike many glasses with transition-metal ions, a strong preexponential factor containing the ``small-polaron'' tunneling term [exp(-2αR)] is observed. Nonadiabatic small-polaron hopping mechanism is found to be appropriate for explaining the conductivity data of both glass systems. Addition of alkali-metal ions decreases the conductivities and causes appreciable change of some model parameters obtained from least-squares fittings of the experimental data. The overall thermal behavior of the electrical conductivities of the glasses, however, remains unaltered. This indicates that small (less than 10 wt.%) amount of Li or other alkali-metal ions in these glasses acts as a flux to keep the oxygen content fixed in the corresponding glass-ceramic (superconducting) phases. This in turn helps increase the superconducting transition temperature of the glass ceramics and also lower the sintering and melting temperatures of the glasses.

  8. Small-polaron transport and thermoelectric properties of the misfit-layer composite (BiSe)109TaSe2 / TaSe2

    NASA Astrophysics Data System (ADS)

    Kim, Jin-Hee; Song, Yoo Jang; Rhyee, Jong-Soo; Kim, Bong-Seo; Park, Su-Dong; Lee, Hyeung Jin; Shin, Jae-Wook

    2014-03-01

    We studied the thermoelectric properties of the composite of misfit-layered compounds (BiSe)109TaSe2 and TaSe2. The x-ray diffraction pattern on the cross-sectional plane of the sintered body shows a preferred orientation of the (00 l) direction for (BiSe)109TaSe2 / TaSe2 indicating anisotropic alignment during hot pressing. Because of the crystallographic alignment, the temperature-dependent electrical resistivity ρ (T) , Seebeck coefficient S (T) , and the thermal conductivity κ (T) exhibit in-plane and out-of-plane anisotropic transport behavior. The Seebeck coefficient is very low because of the coexistence of electron and hole mixing, as confirmed by the two-carrier model. The lattice thermal conductivity κLof the covalent bonding layer (in-plane) is lower than those of the layer with van der Waals bonding (out-of-plane) implying the existence of a charge density wave along the in-plane. We observed a sign anomaly of the positive Hall coefficient RH and negative Seebeck coefficient S. According to Holstein's small-polaron model, the sign anomaly may come from the odd number of small-polaron hopping sites.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Engineering Polarons at a Metal Oxide Surface.

    PubMed

    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 TiO_{2}(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. PMID:27661706

  14. Engineering Polarons at a Metal Oxide Surface.

    PubMed

    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 TiO_{2}(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.

  15. 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.

  16. 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.

  17. Two-dimensional polaronic behavior in the binary oxides m-HfO2 and m-ZrO2.

    PubMed

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

    2012-03-16

    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 zero-dimensional 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.

  18. 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

  19. Photogeneration of polaron pairs in conducting polymers

    NASA Astrophysics Data System (ADS)

    Conwell, E. M.; Mizes, H. A.

    1995-03-01

    It is usually assumed that when photogeneration in a conducting polymer results in an electron and hole on separate chains they form negative and positive polarons that can move independently of each other. We show, on the basis of the small carrier yield per photon seen in picosecond photoconductivity, the different behavior of photoinduced absorption (PA) in dilute solution and thin films, and the spectral distribution of the PA in thin films, that photogenerated positive and negative polarons in poly(p-phenylene vinylene), polythiophene, and polyacetylene are, for the most part, bound in pairs by their Coulomb attraction. We also show that PA data give evidence for a gap of 2.8 eV, and thus an exciton binding energy of 0.4 eV, in poly(p-phenylene vinylene).

  20. Effective Masses of Vector Polarons

    NASA Astrophysics Data System (ADS)

    Foell, Charles; Clougherty, Dennis

    2006-03-01

    We consider the vector polarons of a one-dimensional model of an electron in a doubly (or nearly) degenerate band that couples to two elastic distortions, as described previously by Clougherty and Foell [1]. A variational approach is used to analytically and numerically calculate effective masses of the three types of vector polarons. [1] D. P. Clougherty and C. A. Foell, Phys. Rev. B 70, 052301 (2004).

  1. Monotonicity of the Polaron Energy

    NASA Astrophysics Data System (ADS)

    Miyao, Tadahiro

    2014-12-01

    In condensed matter physics, the polaron is described by the Hamiltonian of H. Fröhlich. In this paper, the Fröhlich Hamiltonian is investigated from a viewpoint of operator inequalities proposed in [36]. This point of view clarifies the monotonicity of polaron energy, i.e. denoting the lowest energy of the Fröhlich Hamiltonian with the ultraviolet cutoff Λ by EΛ, we prove that EΛ, >EΛ‧ for Λ < Λ‧.

  2. Bound Polaron Pair Formation in Poly (phenylenevinylenes)

    NASA Astrophysics Data System (ADS)

    Rothberg, Lewis

    The following sections are included: * INTRODUCTION * PHOTOGENERATED YIELD OF SINGLET EXCITONS * AGGREGRATION EFFECTS ON EXCITED STATE PHOTO-GENERATION * ASSIGNMENT TO BOUND POLARON PAIRS AND DISCUSSION * PROBLEMS WITH THE BOUND POLARON PAIR PICTURE AND CONCLUSION * REFERENCES

  3. Excitonic polarons in low-dimensional transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Thilagam, A.

    2015-05-01

    We examine the excitonic polaron properties of common monolayer transition metal dichalcogenides (MoS2, MoSe2, WS2 and WSe2). The excitonic polaron is formed when excitons interact with acoustic or optical phonons via coupling to the deformation potentials associated with the conduction and valence bands. A unitary transformation which performs an approximate diagonalization of the exciton-phonon operator is used to evaluate the ground state energy of the excitonic polaron. We derive analytical expressions of the changes in the excitonic polaron energy and mass at small exciton wavevectors involving the deformation potential due to optical phonons. The polaronic effect of the monolayer transition metal dichalcogenides is examined by comparing changes in the energy gap shift and effective masses based on known deformation potential constants for carrier-phonon interactions. Our results indicate the occurrence of comparable energy shifts when the ground state exciton interacts with optical or acoustic phonons. We extend our calculations to explore the influence of exciton-lattice interactions on the binding energies and the self-trapping of excitons in two-dimensional layers of transition metal dichalcogenides.

  4. Ab initio Lattice Results for Fermi Polarons in Two Dimensions.

    PubMed

    Bour, Shahin; Lee, Dean; Hammer, H-W; Meißner, Ulf-G

    2015-10-30

    We investigate the attractive Fermi polaron problem in two dimensions using nonperturbative Monte Carlo simulations. We introduce a new Monte Carlo algorithm called the impurity lattice Monte Carlo method. This algorithm samples the path integral in a computationally efficient manner and has only small sign oscillations for systems with a single impurity. As a benchmark of the method, we calculate the universal polaron energy in three dimensions in the scale-invariant unitarity limit and find agreement with published results. We then present the first fully nonperturbative calculations of the polaron energy in two dimensions and density correlations between the impurity and majority particles in the limit of zero-range interactions. We find evidence for a smooth crossover transition from fermionic quasiparticle to molecular state as a function of the interaction strength. PMID:26565472

  5. Vector polarons in a degenerate electron system

    NASA Astrophysics Data System (ADS)

    Clougherty, Dennis P.; Foell, Charles A.

    2004-08-01

    We consider a one-dimensional model of an electron in a doubly (or nearly) degenerate band that interacts with elastic distortions. We show that the electron equations of motion reduce to a set of coupled nonlinear Schrödinger equations. For the case of interband electron-phonon coupling stemming from local Jahn-Teller interactions, multicomponent self-localized polaron solutions-vector polarons- are described and classified. The phase diagram for the different types of vector polarons in this model is presented. By interpreting the components of the orbital doublet as those of spin- (1)/(2) , our results can also be used to describe bound magnetic polarons.

  6. Dynamics of photogenerated polarons in conjugated polymers.

    PubMed

    An, Z; Wu, C Q; Sun, X

    2004-11-19

    Within a tight-binding electron-phonon interacting model, we investigate the dynamics of photoexcitations to address the generation mechanism of charged polarons in conjugated polymers by using a nonadiabatic evolution method. Besides the neutral polaron exciton which is well known, we identify a novel product of lattice dynamic relaxation from the photoexcited states in a few hundreds of femtoseconds, which is a mixed state composed of both charged polarons and neutral excitons. Our results show that the charged polarons are generated directly with a yield of about 25%, which is independent of the excitation energies, in good agreement with results from experiments. Effects of the conjugation length are also discussed.

  7. Dynamics of Photogenerated Polarons in Conjugated Polymers

    NASA Astrophysics Data System (ADS)

    An, Z.; Wu, C. Q.; Sun, X.

    2004-11-01

    Within a tight-binding electron-phonon interacting model, we investigate the dynamics of photoexcitations to address the generation mechanism of charged polarons in conjugated polymers by using a nonadiabatic evolution method. Besides the neutral polaron exciton which is well known, we identify a novel product of lattice dynamic relaxation from the photoexcited states in a few hundreds of femtoseconds, which is a mixed state composed of both charged polarons and neutral excitons. Our results show that the charged polarons are generated directly with a yield of about 25%, which is independent of the excitation energies, in good agreement with results from experiments. Effects of the conjugation length are also discussed.

  8. Bose Polarons in the Strongly Interacting Regime.

    PubMed

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

    2016-07-29

    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 ^{87}Rb with a much lower density gas of fermionic ^{40}K 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. PMID:27517776

  9. 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.

  10. Topological phases and polaron physics in ultracold quantum gases

    NASA Astrophysics Data System (ADS)

    Grusdt, Fabian

    2016-05-01

    The description of quantum many-body systems poses a formidable theoretical challenge. A seemingly simple problem is the coupling of a single impurity atom to non-interacting Bogoliubov phonons in a surrounding Bose-Einstein condensate. The system can be described by a polaron model at intermediate couplings - an 80 year problem. The situation has been realized experimentally, but when the impurity mass is small compared to the Boson mass, neither mean-field nor strong-coupling expansions are valid anymore. Now the impurity acts as an exchange particle, mediating phonon-phonon interactions. In this talk I present a semi-analytical solution to the polaron problem. I will show that the approach can be generalized to solve far-from equilibrium polaron problems, too, and elaborate on connections with recent experiments involving ultracold atoms and photons. A completely different class of many-body problems are systems with topological order. In recent years we have seen an uprise of cold-atomic or photonic implementations of artificial gauge fields, providing a corner stone for the realization of topological phases of matter. In the second part of my talk, I will address the challenging problem how non-local topological orders can be detected. It will be demonstrated that many-body topological invariants can be measured, making use of mobile impurities as coherent probes of the highly entangled groundstates. I will discuss Laughlin states and comment on possible realizations using ultracold atoms.

  11. 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.

  12. Comments on polaron-phonon scattering theory

    NASA Astrophysics Data System (ADS)

    Tulub, A. V.

    2015-10-01

    We use the polaron state function described in terms of coupled classical and quantum fields to calculate the cross section of phonon scattering on a polaron. The value of the resonance momentum is determined by asymptotic values of several integrals. Calculating them with crystal parameters taken into account leads to bounds on the maximum value of the coupling constant. We confirm that the applicability domain of the strong-coupling approximation is near zero.

  13. Properties of a polaron confined in a spherical quantum dot

    NASA Astrophysics Data System (ADS)

    Melnikov, Dmitriy V.

    A Frohlich Hamiltonian describing the electron-phonon interaction in a spherical quantum dot embedded in another polar material is derived, taking into account interactions with both bulk longitudinal optical and surface optical phonons. The Hamiltonian is appropriate to the general case of a finite confining potential originating from a bandgap mismatch between the materials of the dot and the surrounding matrix. This Hamiltonian is then applied to treat the electron-phonon interaction in the adiabatic approximation for various quantum dot systems. It was found that, as the radius of the dot decreases, the magnitude of the electron-phonon interaction energy first increases, passes through a maximum, and then gradually decreases to the value appropriate to the situation where the electron is weakly localized inside the dot. For most dot radii the polaron properties are described well by a model assuming perfect electron confinement. Based on this result, the problem of the bound polaron confined perfectly in the quantum dot was investigated within the adiabatic and all-coupling variational approaches. The polaron properties have been studied performing both analytical and numerical calculations for various radii of the quantum dot and for different impurity positions inside the dot. Within the adiabatic approximation, it was found that the magnitude of the electron-phonon interaction increases as the radius decreases for any impurity position. It was also shown that the input from the electron-surface-phonon interaction to the total polaron energy is much larger than was found earlier for the free polaron confined in the dot. As a function of the impurity position, the electron-surface-phonon interaction energy increases as the impurity is shifted towards the surface, reaches its maximum when the impurity is positioned inside the dot and then decreases as the impurity moved close to surface. The all-coupling approach gave rise to the following results: for any

  14. 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.

  15. 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

    2013-04-01

    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.

  16. 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.

  17. 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.

  18. Photogeneration of Polarons in Sexithiophene Oligomers

    NASA Astrophysics Data System (ADS)

    Ehrenfreund, Eitan

    1996-03-01

    We present photoexcitation studies of vacuum deposited neutral films of sexithiophene (6T) using photoinduced absorption spectroscopy and photoinduced absorption detected magnetic resonance (PADMR) techniques. We find evidence for photoinduced polarons (photoexcited ``radical ions'') having spin 1/2, with two absorption bands at 0.80 and 1.54 eV, respectively, and with negative PADMR signal at g~=2. Similar absorption bands are observed in lightly p-doped sexithiophene, and are interpreted as due to 6T^ -- + radical cations. In addition, a photoinduced absorption band is found at ~=1.1 eV, which is shorter lived and decreases faster with increasing temperature than the polaron bands. We identify this band as due to spinless bipolarons (photoexcited ``di-ions''). A similar di-cation (6T^++) band has been identified in heavily p-doped sexithiophene. Each of the polaron and bipolaron peaks, observed here, is accompanied by a secondary shoulder on its low energy side. This observation may indicate a possible breaking of charge conjugation symmetry, with negatively charged polarons (bipolarons) having lower energy transitions than positively charged polarons (bipolarons). Finally, we have identified triplet excitons (S=1) with triplet-triplet transition energy at ~=1.45 eV. Work done in collaboration with J. Poplawski (Technion), X. Wei, P. Lane and Z.V. Vardeny (University of Utah, Salt Lake City, UT), M. Ibrahim and A.J. Frank (NREL, Golden, CO). Supported by the US--Israel Binational Science Foundation (BSF 94--256).

  19. Polaron Properties in Armchair Graphene Nanoribbons.

    PubMed

    da Cunha, Wiliam F; Acioli, Paulo H; de Oliveira Neto, Pedro H; Gargano, Ricardo; E Silva, Geraldo M

    2016-07-14

    By means of a 2-D tight-binding model with lattice relaxation in a first-order expansion, we report different polaron properties depending on the armchair graphene nanoribbons width family as well as on its size. We find that representatives of the 3p+2 family do not present a polaronic-mediated charge transport. As for 3p and 3p+1 families, the polaron behavior was completely dependent on the system's width. In particular, we observed a greater degree of delocalization for broader nanoribbons; narrower nanoribbons of both families, on the contrary, typically presented a more localized polaronic-type transport. Energy levels and occupation numbers analysis are performed to rigorously assess the nature of the charge carrier. Time evolution in the scope of the Ehrenfest molecular dynamics was also carried out to confirm the collective behavior and stability of the carrier as a function of time. We were able to determine that polarons in nanoribbons of 3p family present higher mobility than those in 3p+1 nanoribbons. These results identify the transport process that takes place for each system, and they allow the prediction of the mobility of the charge carriers as a function of the structural properties of the system, thus providing guidance on how to improve the efficiency of graphene nanoribbon-based devices. PMID:26918483

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

    PubMed

    Shadkhoo, Shahriar; Bruinsma, Robijn

    2015-09-25

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

  1. Plasmon-Polaron Coupling in Conjugated Polymer on Infrared Nanoantennas.

    PubMed

    Wang, Zilong; Zhao, Jun; Frank, Bettina; Ran, Qiandong; Adamo, Giorgio; Giessen, Harald; Soci, Cesare

    2015-08-12

    We propose and demonstrate a novel type of coupling between polarons in a conjugated polymer and localized surface plasmons in infrared (IR) nanoantennas. The near-field interaction between plasmons and polarons is revealed by polarized photoinduced absorption measurements, probing mid-IR polaron transitions, and infrared-active vibrational modes of the polymer, which directly gauge the density of photogenerated charge carriers. This work proves the possibility of tuning the polaronic properties of organic semiconductors with plasmonic nanostructures.

  2. Polarons and solitons in Jahn Teller systems

    NASA Astrophysics Data System (ADS)

    Clougherty, Dennis P.

    2007-07-01

    Using a semiclassical continuum model of an electron in a deformable molecular crystal, some properties of multicomponent generalizations of the polaron - "vector polarons" - are elucidated. Analytical solutions for the case of two electronic bands coupled to two vibrational modes are given in detail. Within the model considered, the vector polaron can be classified by its wavefunction into several types and can have features that include: (1) a spatial variation in the electronic and vibrational character, and (2) low-energy internal degrees of freedom. For the case of electronic and vibrational degeneracy, local Jahn-Teller interactions can also lead to a novel spatiotemporal soliton, a long-lived excited state of the many-electron system stabilized by the conservation law resulting from degeneracy.

  3. 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. PMID:26089510

  4. 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.

  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. Role of photogenerated meta-stable polarons in organic magnetoresistance: evidence for polaron pair mechanism

    NASA Astrophysics Data System (ADS)

    Gautam, Bhoj; Nguyen, Tho; Valy Vardeny, Z.

    2010-03-01

    We studied the magneto-conductance (MC) in homopolar organic diodes based on semiconductor polymers MEH-PPV and DOO-PPV. In dark we measured negative MC in both MEH-PPV and DOO-PPV homopolar devices, which was previously interpreted as due to magnetic field effect on singlet yield of polaron pairs having the same charge, known in the literature as the ``bipolaron'' mechanism. We investigated the role of photogenerated meta-stable polarons on the MC, when illuminating the device with a cw laser beam at various intensities and illumination times. Such illumination is known to produce metastable polarons that are deep-trapped in MEH-PPV polymer, but less so in DOO-PPV polymer. Upon illumination we obtained a gradual change in the MC magnitude and magnetic field response, where the MC first decreases then changes sign from negative to positive with the illumination time. Similar effects were not obtained in DOO-PPV devices. We therefore conclude that the metastable polarons in the illuminated polymer initiate the formation of polaron pairs with opposite charge in the homopolar device upon current injection; and these are therefore responsible for positive MC. This photoinduced MC is in agreement with a similar effect found in MC of bipolar organic diodes upon increasing the bias voltage beyond the threshold for bipolar injection.

  7. Photogenerated polarons in poly(paraphenylene vinylene)

    NASA Astrophysics Data System (ADS)

    Murata, K.; Shimoi, Y.; Abe, S.; Kuroda, S.; Noguchi, T.; Ohnishi, T.

    1998-02-01

    Photo-induced spin species in poly(paraphenylene vinylene) (PPV) and its derivative have been investigated by means of the light-induced ESR (LESR) technique using variable excitation energy. LESR spectra at the X and K bands for stretch-oriented PPV samples exhibit clear anisotropy, which is well explained in terms of the anisotropic g-value and hyperfine coupling of unpaired π electron on the conjugated chain. The X band spectra were well reproduced by theoretical ESR spectra using a polaron spin density obtained from the Pariser-Parr-Pople model. The LESR signal increases significantly above around 3 eV. This threshold is interpreted as the interband gap above which free electron-hole pairs are created efficiently. From these results, we conclude that the observed light-induced spin species are polarons.

  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. Ground state energy of large polaron systems

    SciTech Connect

    Benguria, Rafael D.; Frank, Rupert L.; Lieb, Elliott H.

    2015-02-15

    The last unsolved problem about the many-polaron system, in the Pekar–Tomasevich approximation, is the case of bosons with the electron-electron Coulomb repulsion of strength exactly 1 (the “neutral case”). We prove that the ground state energy, for large N, goes exactly as −N{sup 7/5}, and we give upper and lower bounds on the asymptotic coefficient that agree to within a factor of 2{sup 2/5}.

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

    PubMed

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

    2016-02-01

    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.

  11. 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

  12. Polaronic conduction and Anderson localization in reduced strontium barium niobate

    NASA Astrophysics Data System (ADS)

    Dandeneau, Christopher S.; Yang, YiHsun; Olmstead, Marjorie A.; Bordia, Rajendra K.; Ohuchi, Fumio S.

    2015-12-01

    Electron transport mechanisms in reduced Sr0.5Ba0.5Nb2O6 (SBN50) are investigated from ˜100 to 955 K through an analysis of the electrical conductivity (σ) and the Seebeck coefficient (S) with respect to temperature (T). Notably, experimental evidence is presented that supports a scenario of Anderson localization below 600 K and carrier excitation across a mobility edge at higher temperature. As a relaxor ferroelectric, stoichiometric SBN has intrinsic disorder associated with both the distribution of Sr/Ba vacancies and the formation of polarized nanoregions. The removal of oxygen through reduction generates conduction electrons in SBN. At the lowest temperatures measured (100-155 K), the electrical conductivity exhibits a temperature dependence characteristic of variable range hopping, followed by a transition to small polaron hopping at intermediate temperatures (250-545 K). In both the variable range and small polaron hopping regimes, a semiconductor-like temperature dependence of the electrical conductivity (dσ/dT > 0) was observed. However, above 615 K, dσ/dT decreases dramatically and eventually becomes metal-like (dσ/dT < 0). Concomitantly, the Seebeck coefficient exhibits a linear dependence on lnT from 615 to 955 K with the same slope (˜104 μ V/K) for both polycrystalline SBN50 and single crystalline SBN61 (both reduced), indicating a similar, constant density of states near the Fermi level for both compositions. The application of Seebeck coefficient theory to this inherently disordered material reveals that the excitation of carriers across a mobility edge is likely responsible for the change in dσ/dT at high temperature. Such findings may have a significant impact in the field of conductive ferroelectrics.

  13. One dimensional polaron effects and current inhomogeneities in sequential phonon emission

    SciTech Connect

    Hellman, E.S.; Harris, J.S.; Hanna, C.; Laughlin, R.B.

    1985-07-01

    We have constructed a physical model to explain the tunneling current oscillations reported by Hickmott et al., for GaAs/AlGaAs heterostructures in high magnetic fields. We propose that the periodic structure observed is due to space charge which builds up in the undepleted layer when electrons enter it with energy just below the phonon emission threshold. Such electrons interact with the lattice to form polarons whose energy is pinned to the phonon energy, and thus has a very small group velocity. The polaron effect is strongly enhanced by the confinement of the electrons by the strong magnetic field. We infer from the current-voltage data that most of the tunneling current flows through a small area of the sample. The combined model gives reasonable quantitative agreement with experiment. 6 refs., 6 figs.

  14. Accuracy of second order perturbation theory in the polaron and variational polaron frames

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

    In the study of open quantum systems, the polaron transformation has recently attracted a renewed interest as it offers the possibility to explore the strong system-bath coupling regime. Despite this interest, a clear and unambiguous analysis of the regimes of validity of the polaron transformation is still lacking. Here we provide such a benchmark, comparing second order perturbation theory results in the original untransformed frame, the polaron frame, and the variational extension with numerically exact path integral calculations of the equilibrium reduced density matrix. Equilibrium quantities allow a direct comparison of the three methods without invoking any further approximations as is usually required in deriving master equations. It is found that the second order results in the original frame are accurate for weak system-bath coupling; the results deteriorate when the bath cut-off frequency decreases. The full polaron results are accurate for the entire range of coupling for a fast bath but only in the strong coupling regime for a slow bath. The variational method is capable of interpolating between these two methods and is valid over a much broader range of parameters.

  15. 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.

  16. 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.

  17. Size dependent polaronic conduction in hematite

    NASA Astrophysics Data System (ADS)

    Sharma, Monika; Banday, Azeem; Murugavel, Sevi

    2016-05-01

    Lithium Ion Batteries have been attracted as the major renewable energy source for all portable electronic devices because of its advantages like superior energy density, high theoretical capacity, high specific energy, stable cycling and less memory effects. Recently, α-Fe2O3 has been considered as a potential anode material due to high specific capacity, low cost, high abundance and environmental benignity. We have synthesized α-Fe2O3 with various sizes by using the ball milling and sol-gel procedure. Here, we report the dc conductivity measurement for the crystallite size ranging from 15 nm to 50nm. It has been observed that the enhancement in the polaronic conductivity nearly two orders in magnitude while reducing the crystallite size from bulk into nano scale level. The enhancement in the conductivity is due to the augmented to compressive strain developed in the material which leads to pronounced decrease in the hopping length of polarons. Thus, nanocrystaline α-Fe2O3 may be a better alternative anode material for lithium ion batteries than earlier reported systems.

  18. Polaronic effects in one- and two-band quantum systems

    NASA Astrophysics Data System (ADS)

    Yin, Tao; Cocks, Daniel; Hofstetter, Walter

    2015-12-01

    In this work, we study the formation and dynamics of polarons in a system with a few impurities in a lattice immersed in a Bose-Einstein condensate (BEC). This system has been experimentally realized using ultracold atoms and optical lattices. Here, we consider a two-band model for the impurity atoms, along with a Bogoliubov approximation for the BEC, with phonons coupled to impurities via both intraband and interband transitions. We decouple this Fröhlich-type term by an extended two-band Lang-Firsov polaron transformation using a variational method. The new effective Hamiltonian with two (polaron) bands differs from the original Hamiltonian by modified coherent transport, polaron energy shifts, and induced long-range interaction. A Lindblad master-equation approach is used to take into account residual incoherent coupling between polaron and bath. This polaronic treatment yields a renormalized interband relaxation rate compared to Fermi's golden rule. For a strongly coupled two-band Fröhlich Hamiltonian, the polaron is tightly dressed in each band and can not tunnel between them, leading to an interband self-trapping effect.

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

    PubMed

    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

    2016-06-01

    Solution-processed organometallic perovskites have rapidly developed into a top candidate for the active layer of photovoltaic devices. Despite 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. Here 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. 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. PMID:27224519

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

    PubMed

    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

    2016-06-01

    Solution-processed organometallic perovskites have rapidly developed into a top candidate for the active layer of photovoltaic devices. Despite 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. Here 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. 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. Massive polarons in large-energy-gap polymers

    NASA Astrophysics Data System (ADS)

    McCall, R. P.; Ginder, J. M.; Roe, M. G.; Asturias, G. E.; Scherr, E. M.; MacDiarmid, A. G.; Epstein, A. J.

    1989-05-01

    We present evidence for the existence of defect states with large mass and low mobility in the conducting polymer polyaniline. This large-energy-gap polymer has been shown to have properties significantly different from many other conducting polymers. Photoinduced infrared absorption studies presented here are consistent with the photogeneration of charged polarons. Analysis within the amplitude mode (Peierls) formalism indicates that these polarons are massive (Mpol~60me), while use of a bond-order or Holstein polaron formalism leads to even larger estimates of Mpol.

  2. Dynamics of Photogenerated Polaron-Excitons in Organic Semiconductors

    NASA Astrophysics Data System (ADS)

    Junior, Luiz A. Ribeiro; Neto, Pedro H. Oliveira; da Cunha, Wiliam F.; Silva, Geraldo M. e.

    In this work we performed numerical simulations of one π-conjugated polymer chain subjected to photogeneration. Within the SSH model modified to include the Brazoviskii-Kirova symmetry breaking term, we investigate the dynamics of photoexcitations to address the generation mechanism of polaron-excitons using the unrestricted Hartree-Fock approximation. It was obtained that after the photoexcitation the system relaxes spontaneously into a polaron-exciton in a transient state in a range of 200 fs. Our results also show that charged polarons are generated directly after this transient state.

  3. Quantum Dynamics of Ultracold Bose Polarons.

    PubMed

    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. PMID:27661684

  4. 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.

  5. 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.

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

    PubMed

    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

    2016-06-28

    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.

  7. Mixed polaronic-ionic conduction in lithium borate glasses and glass-ceramics containing copper oxide

    NASA Astrophysics Data System (ADS)

    Khalil, M. M. I.

    2007-03-01

    The effect of electric field strength on conduction in lithium borate glasses doped with CuO with different concentration was studied and the value of the jump distance of charge carrier was calculated. The conductivity measurements indicate that the conduction is due to non-adiabatic hopping of polarons and the activation energies are found to be temperature and concentration dependent. Lithium borate glasses are subjected to carefully-programmed thermal treatments which cause the nucleation and growth of crystalline phases. X-ray diffraction analysis confirmed the amorphous nature for the investigated glass sample and the formation of crystalline phase for annealed samples at 650 °C. The main separated crystalline phase is Li2B8O13. The scanning electron micrographs of some selected glasses showed a significant change in the morphology of the films investigated due to heat treatment of the glass samples. It was found that the dc-conductivity decreases with an increase of the HT temperature. The decrease of dc conductivity, with an increase of the HT temperature, can be related to the decrease in the number of free ions in the glass matrix. There is deviation from linearity at high temperature regions in the logσ-1/T plots for all investigated doped samples at a certain temperature at which the transition from polaronic to ionic conduction occurs. The hopping of small polarons is dominant at low temperatures, whereas the hopping of Li+ ions dominates at high temperatures.

  8. Vast Hole- and Electron-Polaron Spatial Extent in Oligomeric π-Conjugated Porphyrin Arrays

    NASA Astrophysics Data System (ADS)

    Angiolillo, Paul; Rawson, Jeff; Therien, Michael

    meso-Ethyne bridged π-conjugated zinc porphyrin oligomers (PZnn compounds) have been demonstrated to evince lowest excited singlet states that are globally delocalized. It has also previously been shown that hole-polaron states of these oligomers exhibit delocalization lengths that mirror the molecular spatial dimension, 7.5 nm in the case of the heptamer. Here we demonstrate that the electron-polaron states in PZnn compounds also 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. These results are buttressed by electron spin relaxation measurements of PZnn electron polarons that show that both T1 and T2 relaxation times are unusually large, on the order of 103 ns and 102 ns, respectively. Since rapid charge delocalization defines an important mechanism that mitigates Coulombic stabilization of photogenerated electron-hole pairs to create separated free charge carriers, and spin polarization lifetimes feature prominently in spin currents, these findings identify conjugated materials with exceptional optical, electronic, and spintronic properties.

  9. 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.

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

    PubMed

    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

    2016-01-01

    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. PMID:27349567

  11. 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.

  12. Evidence for photogenerated intermediate hole polarons in ZnO

    NASA Astrophysics Data System (ADS)

    Sezen, Hikmet; Shang, Honghui; Bebensee, Fabian; Yang, Chengwu; Buchholz, Maria; Nefedov, Alexei; Heissler, Stefan; Carbogno, Christian; Scheffler, Matthias; Rinke, Patrick; Wöll, Christof

    2015-04-01

    Despite their pronounced importance for oxide-based photochemistry, optoelectronics and photovoltaics, only fairly little is known about the polaron lifetimes and binding energies. Polarons represent a crucial intermediate step populated immediately after dissociation of the excitons formed in the primary photoabsorption process. Here we present a novel approach to studying photoexcited polarons in an important photoactive oxide, ZnO, using infrared (IR) reflection-absorption spectroscopy (IRRAS) with a time resolution of 100 ms. For well-defined (10-10) oriented ZnO single-crystal substrates, we observe intense IR absorption bands at around 200 meV exhibiting a pronounced temperature dependence. On the basis of first-principles-based electronic structure calculations, we assign these features to hole polarons of intermediate coupling strength.

  13. Evidence for photogenerated intermediate hole polarons in ZnO.

    PubMed

    Sezen, Hikmet; Shang, Honghui; Bebensee, Fabian; Yang, Chengwu; Buchholz, Maria; Nefedov, Alexei; Heissler, Stefan; Carbogno, Christian; Scheffler, Matthias; Rinke, Patrick; Wöll, Christof

    2015-04-22

    Despite their pronounced importance for oxide-based photochemistry, optoelectronics and photovoltaics, only fairly little is known about the polaron lifetimes and binding energies. Polarons represent a crucial intermediate step populated immediately after dissociation of the excitons formed in the primary photoabsorption process. Here we present a novel approach to studying photoexcited polarons in an important photoactive oxide, ZnO, using infrared (IR) reflection-absorption spectroscopy (IRRAS) with a time resolution of 100 ms. For well-defined (10-10) oriented ZnO single-crystal substrates, we observe intense IR absorption bands at around 200 meV exhibiting a pronounced temperature dependence. On the basis of first-principles-based electronic structure calculations, we assign these features to hole polarons of intermediate coupling strength.

  14. Bipolar polaron pair recombination in polymer/fullerene solar cells

    NASA Astrophysics Data System (ADS)

    Kupijai, Alexander J.; Behringer, Konstantin M.; Schaeble, Florian G.; Galfe, Natalie E.; Corazza, Michael; Gevorgyan, Suren A.; Krebs, Frederik C.; Stutzmann, Martin; Brandt, Martin S.

    2015-12-01

    We present a study of the rate-limiting spin-dependent charge-transfer processes in different polymer/fullerene bulk-heterojunction solar cells at 10 K . Observing central spin-locking signals in pulsed electrically detected magnetic resonance and an inversion of Rabi oscillations in multifrequency electron-double-resonance spectroscopy, we find that the spin response of both spin-coated and printed P3HT/PCBM and spin-coated PCDTBT/PCBM solar cells at low temperatures is governed by bipolar polaron pair recombination and quantitatively determine the polaron-polaron coupling strength with double electron-electron resonance experiments. Furthermore spin Hahn echo decay and inversion recovery measurements are performed to measure spin coherence and recombination times of the polaron pairs, respectively.

  15. Evidence for photogenerated intermediate hole polarons in ZnO.

    PubMed

    Sezen, Hikmet; Shang, Honghui; Bebensee, Fabian; Yang, Chengwu; Buchholz, Maria; Nefedov, Alexei; Heissler, Stefan; Carbogno, Christian; Scheffler, Matthias; Rinke, Patrick; Wöll, Christof

    2015-01-01

    Despite their pronounced importance for oxide-based photochemistry, optoelectronics and photovoltaics, only fairly little is known about the polaron lifetimes and binding energies. Polarons represent a crucial intermediate step populated immediately after dissociation of the excitons formed in the primary photoabsorption process. Here we present a novel approach to studying photoexcited polarons in an important photoactive oxide, ZnO, using infrared (IR) reflection-absorption spectroscopy (IRRAS) with a time resolution of 100 ms. For well-defined (10-10) oriented ZnO single-crystal substrates, we observe intense IR absorption bands at around 200 meV exhibiting a pronounced temperature dependence. On the basis of first-principles-based electronic structure calculations, we assign these features to hole polarons of intermediate coupling strength. PMID:25902307

  16. Tunable polaronic conduction in anatase TiO2.

    PubMed

    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

    2013-05-10

    Oxygen vacancies created in anatase TiO(2) 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. PMID:23705725

  17. 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.

  18. 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

  19. Attractive and repulsive Fermi polarons in two dimensions.

    PubMed

    Koschorreck, Marco; Pertot, Daniel; Vogt, Enrico; Fröhlich, Bernd; Feld, Michael; Köhl, Michael

    2012-05-31

    The dynamics of a single impurity in an environment is a fundamental problem in many-body physics. In the solid state, a well known case is an impurity coupled to a bosonic bath (such as lattice vibrations); the impurity and its accompanying lattice distortion form a new entity, a polaron. This quasiparticle plays an important role in the spectral function of high-transition-temperature superconductors, as well as in colossal magnetoresistance in manganites. For impurities in a fermionic bath, studies have considered heavy or immobile impurities which exhibit Anderson's orthogonality catastrophe and the Kondo effect. More recently, mobile impurities have moved into the focus of research, and they have been found to form new quasiparticles known as Fermi polarons. The Fermi polaron problem constitutes the extreme, but conceptually simple, limit of two important quantum many-body problems: the crossover between a molecular Bose-Einstein condensate and a superfluid with BCS (Bardeen-Cooper-Schrieffer) pairing with spin-imbalance for attractive interactions, and Stoner's itinerant ferromagnetism for repulsive interactions. It has been proposed that such quantum phases (and other elusive exotic states) might become realizable in Fermi gases confined to two dimensions. Their stability and observability are intimately related to the theoretically debated properties of the Fermi polaron in a two-dimensional Fermi gas. Here we create and investigate Fermi polarons in a two-dimensional, spin-imbalanced Fermi gas, measuring their spectral function using momentum-resolved photoemission spectroscopy. For attractive interactions, we find evidence for a disputed pairing transition between polarons and tightly bound dimers, which provides insight into the elementary pairing mechanism of imbalanced, strongly coupled two-dimensional Fermi gases. Additionally, for repulsive interactions, we study novel quasiparticles--repulsive polarons--the lifetime of which determines the

  20. Role of triplet polaron pairs in conjugated polymer photophysics

    NASA Astrophysics Data System (ADS)

    Wesely, Elizabeth; Rothberg, Lewis; Marchetti, Alfred; Chen, Shaw; Geng, Yanhou; Culligan, Sean

    2007-03-01

    We measure the decay of the long-lived fluorescence of a conjugated oligofluorene at temperatures from 300 K to 20 K. We conclude that nearly all of this emission arises from geminate recombination of photogenerated polaron pairs to reform the singlet exciton, and that charge pair recombination represents a significant contribution to the overall fluorescence quantum yield. The unusual nonmonotonic decay dynamics of the delayed fluorescence can be explained if we assume interconversion between singlet and triplet polaron pairs on the submicrosecond time scale. (˜500 ns.) We are able to model the decay of the delayed fluorescence by assuming activated recombination from a Gaussian energy distribution of singlet polaron pairs centered 0.2 eV below the excited state and having a standard deviation of 0.12 eV. The model is relevant to recent work involving the measurement of singlet-triplet branching ratios and to the yields of electroluminescent devices.

  1. Magnetic frustration in itinerant systems: the Kondo polaron problem

    NASA Astrophysics Data System (ADS)

    Isaev, Leonid; Batista, Cristian; Vekhter, Ilya

    2013-03-01

    We study the interplay between magnetic frustration and Kondo screening in Kondo lattices by analyzing the J1-J2 antiferromagnetic chain coupled to a conduction band. The system is tuned to the Majumdar-Ghosh point J2 =J1 / 2 which stabilizes a dimer valence-bond solid at weak Kondo coupling JK. We use an effective low-energy theory to demonstrate that sufficiently large JK results in a proliferation of ``Kondo polarons'', i.e. Kondo-screened domain-wall excitations of the dimer state, and collapse of the dimer order via a 2nd order quantum phase transition. At the quantum critical point, JK =JKc , these polarons become gapless, and we argue that the transition itself belongs to a 2D Ising universality class. For JK >JKc increasing concentration of the polarons leads to a continuous growth of the electron Fermi momentum until all spins are absorbed by the Fermi sea.

  2. Reentrant formation of magnetic polarons in quantum dots

    NASA Astrophysics Data System (ADS)

    Pientka, J. M.; Oszwałdowski, R.; Petukhov, A. G.; Han, J. E.; Žutić, Igor

    2012-10-01

    We propose a model of magnetic polaron formation in semiconductor quantum dots doped with magnetic ions. A wetting layer serves as a reservoir of photogenerated holes, which can be trapped by the adjacent quantum dots. For certain hole densities, the temperature dependence of the magnetization induced by the trapped holes is reentrant: it disappears for some temperature range and reappears at higher temperatures. We demonstrate that this peculiar effect is not an artifact of the mean-field approximation and persists after statistical spin fluctuations are accounted for. We predict fingerprints of reentrant magnetic polarons in photoluminescence spectra.

  3. 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.

  4. 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.

  5. 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. PMID:23902411

  6. 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.

  7. Deep electron and hole polarons and bipolarons in amorphous oxide

    NASA Astrophysics Data System (ADS)

    Kaviani, Moloud; Strand, Jack; Afanas'ev, Valery V.; Shluger, Alexander L.

    2016-07-01

    Amorphous (a)-HfO2 is a prototype high dielectric constant insulator with wide technological applications. Using ab initio calculations we show that excess electrons and holes can trap in a-HfO2 in energetically much deeper polaron states than in the crystalline monoclinic phase. The electrons and holes localize at precursor sites, such as elongated Hf-O bonds or undercoordinated Hf and O atoms, and the polaronic relaxation is amplified by the local disorder of amorphous network. Single electron polarons produce states in the gap at ˜2 eV below the bottom of the conduction band with average trapping energies of 1.0 eV. Two electrons can form even deeper bipolaron states on the same site. Holes are typically localized on undercoordinated O ions with average trapping energies of 1.4 eV. These results advance our general understanding of charge trapping in amorphous oxides by demonstrating that deep polaron states are inherent and do not require any bond rupture to form precursor sites.

  8. 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)

  9. 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.

  10. Polaron Localization in Conjugated Polymers by Hybrid DFT Methods

    NASA Astrophysics Data System (ADS)

    Shao, Nan; Wu, Qin; Theorey; Computation Group Team

    2013-03-01

    Reliable application of density functional theory (DFT) to study the electronic properties of polarons remains controversial. A proper description should exhibit both the formation of a charge-localized electronic state and saturation of the polaron size for increasing oligomer length. The aim of this work is to find a proper hybrid DFT method to study the chain length related electronic properties of charged conjugated polymer system. Using oligopyrrole cations as a test case, global hybrid functionals such as BHandHLYP can show charge localization, but a well-defined polaron size does not emerge when the length of the oligomer is increased; the saturation effect was not predicted correctly. By applying 100% long-range corrected hybrid functionals, LRC-PBE, the saturation of charge distribution has been achieved, implying that the LRC-PBE is a better way to describe the spatial extent of the electronic state of polypyrrole than the conventional hybrid functionals. The tuning of the range parameter and the study of other polymer polaron systems will be discussed. Supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.

  11. 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

  12. Polaron hopping in olivine phosphates studied by nuclear resonant scattering

    NASA Astrophysics Data System (ADS)

    Tracy, Sally June

    Valence fluctuations of Fe2+ and Fe3+ were studied in a solid solution of LixFePO4 by nuclear resonant forward scattering of synchrotron x rays while the sample was heated in a diamond-anvil pressure cell. The spectra acquired at different temperatures and pressures were analyzed for the frequencies of valence changes using the Blume-Tjon model of a system with a fluctuating Hamiltonian. These frequencies were analyzed to obtain activation energies and an activation volume for polaron hopping. There was a large suppression of hopping frequency with pressure, giving an anomalously large activation volume. This large, positive value is typical of ion diffusion, which indicates correlated motions of polarons, and Li+ ions that alter the dynamics of both. In a parallel study of NaxFePO4, the interplay between sodium ordering and electron mobility was investigated using a combination of synchrotron x-ray diffraction and nuclear resonant scattering. Conventional Mossbauer spectra were collected while the sample was heated in a resistive furnace. An analysis of the temperature evolution of the spectral shapes was used to identify the onset of fast electron hopping and determine the polaron hopping rate. Synchrotron x-ray diffraction measurements were carried out in the same temperature range. Reitveld analysis of the diffraction patterns was used to determine the temperature of sodium redistribution on the lattice. The diffraction analysis also provides new information about the phase stability of the system. The temperature evolution of the iron site occupancies from the Mossbauer measurements, combined with the synchrotron diffraction results give strong evidence for a relationship between the onset of fast electron dynamics and the redistribution of sodium in the lattice. Measurements of activation barriers for polaron hopping gave fundamental insights about the correlation between electronic carriers and mobile ions. This work established that polaron-ion interactions

  13. 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

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

    PubMed

    Chuev, G N; Lakhno, V D

    1993-07-01

    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.

  15. Polaron and bipolaron of uniaxially strained one dimensional zigzag ladder

    NASA Astrophysics Data System (ADS)

    Yavidov, B. Ya.

    2016-09-01

    An influence of the uniaxial strains in one dimensional zigzag ladder (1DZL) on the properties of polarons and bipolarons is considered. It is shown that strain changes all the parameters of the system, in particular, spectrum, existing bands and the masses of charge carriers. Numerical results obtained by taking into an account the Poisson effect clearly indicate that the properties of the (bi)polaronic system can be tuned via strain. Mass of bipolaron can be manipulated by the strain too which in turn leads to the way of tuning Bose-Einstein condensation temperature TBEC of bipolarons. It is shown that TBEC of bipolarons in strained 1DZL reasonably correlates with the values of critical temperature of superconductivity of certain perovskites.

  16. Diagrammatic Monte Carlo Method for Many-Polaron Problems

    NASA Astrophysics Data System (ADS)

    Mishchenko, Andrey S.; Nagaosa, Naoto; Prokof'ev, Nikolay

    2014-10-01

    We introduce the first bold diagrammatic Monte Carlo approach to deal with polaron problems at a finite electron density nonperturbatively, i.e., by including vertex corrections to high orders. Using the Holstein model on a square lattice as a prototypical example, we demonstrate that our method is capable of providing accurate results in the thermodynamic limit in all regimes from a renormalized Fermi liquid to a single polaron, across the nonadiabatic region where Fermi and Debye energies are of the same order of magnitude. By accounting for vertex corrections, the accuracy of the theoretical description is increased by orders of magnitude relative to the lowest-order self-consistent Born approximation employed in most studies. We also find that for the electron-phonon coupling typical for real materials, the quasiparticle effective mass increases and the quasiparticle residue decreases with increasing the electron density at constant electron-phonon coupling strength.

  17. The properties of strong couple bound polaron in monolayer graphene

    NASA Astrophysics Data System (ADS)

    Ding, Zhao-Hua; Zhao, Ying; Xiao, Jing-Lin

    2016-09-01

    Based on the Hamiltonian of the interaction energy between electron on the surface of the graphene and longitudinal acoustic phonon on the surface of the substrate, the paper studies the properties of strong couple polaron in monolayer graphene considering the coulomb doping problem. The conventional Lee-Low-Pine unitary transformation method and linear combination operator method are used to calculate the ground state energy of the polaron. The results show that the ground state energy of the system has a linear relationship with the magnetic field strength, the cut-off wave number, the coulomb bound parameter, the distance between the graphene and the substrates, meanwhile, the ground state energy will split into two branches near the Dirac point.

  18. Charge transport in DNA in solution: The role of polarons

    PubMed Central

    Conwell, Esther M.

    2005-01-01

    Since the discovery a decade ago of rapid photoinduced electron transfer in DNA over a distance >4 nm, a large number of experiments and theories have been advanced in the attempt to characterize the transfer, mainly of a radical cation or hole. Particularly influential experiments were carried out by Giese [Giese, B. (2000) Acc. Chem. Res. 33, 631–636] on the sequence G(A)nGGG, where G is guanine and A is adenine. These experiments were interpreted as showing that for n > 3, after the holes tunnel through the first three As, they hop onto the bridge of As, where they are localized on a single A and travel further by hopping between neighboring As. Recent experiments of Barton and coworkers [Shao, F., O'Neill, M. A. & Barton, J. K. (2004) Proc. Natl. Acad. Sci. USA 101, 17914–17919] have, however, established that the hole wavefunctions are delocalized. One of the mechanisms based on delocalized hole wavefunctions that had been investigated, both experimentally and theoretically, is transport by polarons. For one type of polaron, the properties are determined by polarization of the surrounding medium (water and ions, in this case). Theory predicts that this type of polaron is delocalized over approximately four bases in DNA. Transport by these polarons could explain the results of Giese et al. [Giese, B., Amaudrut, J., Köhler, A.-K., Spormann, M. & Wessely, S. (2001) Nature 412, 318–320], recent experimental results of O'Neill and Barton [O'Neill, M. A. & Barton, J. K. (2004) J. Am. Chem. Soc. 126, 11471–11483] concerning the size of the region over which the hole is delocalized, and other experimental observations. PMID:15956188

  19. Numerical study of polaron problem in the adiabatic limit

    NASA Astrophysics Data System (ADS)

    Marsiglio, Frank; Li, Zhou; Blois, Cindy; Baillie, Devin

    2010-03-01

    We study the polaron problem in a one dimensional chain and on a two dimensional square lattice. The models we have used are the Holstein model and the Su-Schrieffer-Heeger (SSH) model. By a variational procedure based on the Lanczos method, we are able to examine the polaron problem in the limit when the mass of the ion is very large, i.e. close to the adiabatic limit. It is known that for the Holstein model there is no phase transition [1] for any nonzero phonon energy. It is also known that for the one dimensional Holstein or SSH model there will be long range order [2] (e.g. dimerization) in the adiabatic limit at half-filling. It is then interesting to study the long range order on a two dimensional square lattice in and away from the adiabatic limit. Moreover, recent progress for the single polaron near an impurity (disorder) [3] make it an interesting problem for studying bond length disorder which can change the hopping energy in a specific direction in the Holstein model. Reference: [1] H. Lowen, Phys.Rev.B 37, 8661 (1988) [2] J.E.Hirsch and E. Frandkin, Phys. Rev. Lett. 49, 402 (1982) [3]A.S.Mishchenko et.al Phys.Rev.B 79(2009) 180301(R)

  20. 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.

  1. 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.

  2. Carrier generation/recombination processes and polaron effect in perovskite manganite thin films

    NASA Astrophysics Data System (ADS)

    Wu, Guang-Ri; Inoue, Masasi; Sasaki, Minoru; Negishi, Hiroshi; Xiong, Guang-Cheng

    2000-07-01

    Pulsed-laser-induced transient thermoelectric effect (TTE) for perovskite manganite films, La 0.6Ca 0.4MnO 3 (LCMO), Pr 0.67Sr 0.33MnO 3 (PSMO), La 0.7Sr 0.3MnO 3 (LSMO), has been measured under DC electric and magnetic fields. The photoinduced TTE voltage and its sign are strongly dependent on both temperature and magnetic field, which is due to the formation of a bipolar state of photogenerated electrons and holes. It is found that Jahn-Teller and polaron effects are appreciable near the Curie temperature for the carrier recombination, in particular, for LCMO with small ionic radius of Ca 2+ ions.

  3. Large low-symmetry polarons of the high-Tc, copper oxides: Formation, mobility and ordering

    NASA Astrophysics Data System (ADS)

    Bersuker, Gennadi I.; Goodenough, John B.

    1997-02-01

    A microscopic model of the evolution from antiferromagnetic insulator to superconductor on oxidation of the parent-phase (CuO 2) 2- sheets of a cuprate superconductor starts with the assumption that strong electron-lattice interactions are dominant and give a heterogeneous electronic distribution. Introduction of pseudo-Jahn-Teller vibronic coupling associated with the δ holes in the (CuO 2) (2-δ) - sheets is shown to stabilize, below a critical temperature Tp ≈ 850 K, large non-adiabatic polarons containing 5 to 7 copper centers; cooperative low-symmetry in-plane vibrations also stabilize an elastic attractive force between polarons that can overcome the longer-range Coulomb repulsion between polarons. Utilizing established parameters for isolated CuO 6 complexes gives a calculated polaron size of 5 to 7 copper centers, which compares with a measured mean size of 5.3 copper centers in underdoped samples 0 < δ ≤ 0.10. A large polaron is shown to move by a piece-wise tunneling of a fraction of itself across a peripheral CuO vibronic bond rather than by an activated hopping. This type of motion, which is not described by conventional transport theories, gives a linear increase of the resistivity with temperature above a temperature Tϱ due to scattering of the polaron at its own border, which separates regions inside and outside the polaron of slightly different mean CuO bond length. At lower temperatures, the polaron mobility becomes activated, but at higher concentrations this change is obscured because the elastic interpolaron attractive force causes the polarons to condense into a “polaron liquid,” and below some critical temperature Td ≥ Tc the polarons undergo long-range ordering into one-dimensional <110> polaronic stripes separated by stripes of the parent phase, which support antiferromagnetic spin fluctuations. The zig-zag polaron stripes consist of polaron pairs oriented alternately along [100] and [010] axes of a CuO 2 sheet. Formation

  4. Truncated phase-space approach to polaron response.

    PubMed

    Sels, Dries; Brosens, Fons

    2014-01-01

    A method is presented to obtain the linear response coefficients of a system coupled to a bath. The method is based on a systematic truncation of the Liouville equation for the reduced distribution function. The first-order truncation results are expected to be accurate in the low-temperature and weak-coupling regime. Explicit expressions for the conductivity of the Fröhlich polaron are obtained, and the discrepancy between the Kadanoff and the Feynman-Hellwarth-Iddings-Platzman mobility is elucidated. PMID:24580189

  5. On uniqueness and non-degeneracy of anisotropic polarons

    NASA Astrophysics Data System (ADS)

    Ricaud, Julien

    2016-05-01

    We study the anisotropic Choquard-Pekar equation which describes a polaron in an anisotropic medium. We prove the uniqueness and non-degeneracy of minimizers in a weakly anisotropic medium. In addition, for a wide range of anisotropic media, we derive the symmetry properties of minimizers and prove that the kernel of the associated linearized operator is reduced, apart from three functions coming from the translation invariance, to the kernel on the subspace of functions that are even in each of the three principal directions of the medium.

  6. The origin of ferromagnetic interaction between bound magnetic polarons in diluted magnetic semiconductors: A minimal model

    NASA Astrophysics Data System (ADS)

    Bednarski, Henryk

    2014-01-01

    We present a detailed analysis of the role of various interaction mechanisms contributing to the bound magnetic polaron (BMP) molecule Hamiltonian with the purpose of gaining an insight into the origin of the ferromagnetic interaction between BMPs. Explicitly, it appears that the BMP molecule Hamiltonian without interatomic direct exchange interaction does not lead to appearance of the parallel alignment of polaronic clouds in the lowest energy state even for large magnitudes of the polaronic exchange fields (up to ~65 meV in Cd0.95Mn0.05Se). Also, it appears that for the range of moderate values of polaronic exchange fields (16-25 meV in Cd0.95Mn0.05Se), the regular Hubbard BMP pair Hamiltonian must be supplemented with the direct interatomic (Heisenberg) exchange interaction to form a minimal model Hamiltonian of BMP molecule with the parallel alignment of the polaronic clouds in the lowest energy state.

  7. 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.

  8. "Watching" Polaron Pair Formation from First-Principles Electron-Nuclear Dynamics.

    PubMed

    Donati, Greta; Lingerfelt, David B; Petrone, Alessio; Rega, Nadia; Li, Xiaosong

    2016-09-22

    The formation of polaron pairs is one of the important photophysical processes that take place after the excitation in semiconducting organic polymers. First-principles Ehrenfest excited-state dynamics is a unique tool to investigate ultrafast photoinduced charge carrier dynamics and related nonequilibrium processes involving correlated electron-nuclear dynamics. In this work the formation of polaron pairs and their dynamical evolution in an oligomer of seven thiophene units is investigated with a combined approach of first-principles exciton-nuclear dynamics and wavelet analysis. The real-time formation of a polaron pair can be observed in the dipole evolution during the excited-state dynamics. The possible driving force of the polaron pair formation is investigated through qualitative correlation between the structural dynamics and the dipole evolution. The time-dependent characteristics and spectroscopic consequences of the polaron pair formation are probed using the wavelet analysis. PMID:27571540

  9. Additional evidence for complex 2-site polarons in CMR manganites.

    NASA Astrophysics Data System (ADS)

    Bridges, Frank; Kurczveil, Geza; Downward, Lisa; Neumeier, John J.

    2007-03-01

    Recently we have proposed a complex 2-site polaron model (which we call a dimeron) that exists for temperatures near and above the ferromagnetic transition temperature, Tc [1]. The dimeron has a hole delocalized over two Mn sites (i.e. a hole and an electron share the two Mn sites) and the two Mn sites have a reduced distortion compared to the remaining Jahn-Teller distorted electron sites. Magnetic clusters just above Tc are likely clusters of these dimeron quasiparticles. The average valance of the two Mn sites in the dimeron is 3.5 and the spin is 7/2. We show that the Mn K-absorption edge is much better described as a sum of a 3.5 valence edge (fraction 2x) plus a 3 valance edge (fraction 1-2x), compared to earlier simulations using x CaMnO3 plus 1-x LaMnO3. We also show that fitting the Mn-O peak to a sum of two experimental Mn-O standards leads to a similar result as in the earlier study - a fraction 2x of lower distorted Mn sites (dimerons) and a fraction 1-2x of more distorted sites with 1 eg electron. Both support the proposed complex - 2-site polaron model.Supported under NSF grant DMR0301971.[1] L. Downward et. al., Phys Rev Lett 95, 106401 (2005).

  10. Spin relaxation via exchange with donor impurity-bound electrons

    NASA Astrophysics Data System (ADS)

    Appelbaum, Ian

    In the Bir-Aronov-Pikus depolarization process affecting conduction electrons in p-type cubic semiconductors, spin relaxation is driven by exchange with short-lived valence band hole states. We have identified an analogous spin relaxation mechanism in nominally undoped silicon at low temperatures, when many electrons are bound to dilute dopant ion potentials. Inelastic scattering with externally injected conduction electrons accelerated by electric fields can excite transitions into highly spin-orbit-mixed bound excited states, driving strong spin relaxation of the conduction electrons via exchange interaction. We reveal the consequences of this spin depolarization mechanism both below and above the impact ionization threshold, where conventional charge and spin transport are restored. Based upon: Lan Qing, Jing Li, Ian Appelbaum, and Hanan Dery, Phys Rev. B 91, 241405(R) (2015). We acknowledge support from NSF, DTRA, and ONR.

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

    NASA Astrophysics Data System (ADS)

    Murugavel, Sevi; Sharma, Monika; Shahid, Raza

    2016-01-01

    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 LiFePO4 (LFP) and delithiated heterosite FePO4 (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.

  12. Recombination lifetime of free polarons in polymer/fullerene bulk heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Li, Kejia; Li, Lijun; Campbell, Joe C.

    2012-02-01

    The recombination lifetime of free polarons was measured using three different methods: electrical field-dependent photoresponse, transient photoconductivity, and forward-to-zero bias transient-current response. The average free polaron recombination lifetime is estimated to be a few microseconds for poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) solar cells. The competition between sweep-out by the internal field and the loss of photogenerated carriers by recombination is analyzed. The short-circuit free polaron collection efficiency for P3HT:PCBM bulk heterojunction material was determined to be in the range of 80% to 90%.

  13. Dispersed Polaron Simulations of Electron Transfer in Photosynthetic Reaction Centers

    NASA Astrophysics Data System (ADS)

    Warshel, A.; Chu, Z. T.; Parson, W. W.

    1989-10-01

    A microscopic method for simulating quantum mechanical, nuclear tunneling effects in biological electron transfer reactions is presented and applied to several electron transfer steps in photosynthetic bacterial reaction centers. In this ``dispersed polaron'' method the fluctuations of the protein and the electron carriers are projected as effective normal modes onto an appropriate reaction coordinate and used to evaluate the quantum mechanical rate constant. The simulations, based on the crystallographic structure of the reaction center from Rhodopseudomonas viridis, focus on electron transfer from a bacteriopheophytin to a quinone and the subsequent back-reaction. The rates of both of these reactions are almost independent of temperature or even increase with decreasing temperature. The simulations reproduce this unusual temperature dependence in a qualitative way, without the use of adjustable parameters for the protein's Franck-Condon factors. The observed dependence of the back-reaction on the free energy of the reaction also is reproduced, including the special behavior in the ``inverted region.''

  14. Study of spin-polaron formation in 1D systems

    SciTech Connect

    Arredondo, Y.; Navarro, O.; Vallejo, E.

    2014-05-15

    We study numerically the formation of spin-polarons in low-dimensional systems. We consider a ferromagnetic Kondo lattice model with Hund coupling J{sub H} and localized spins interacting antiferromagnetically with coupling constant J. We investigate the ground state phase diagram as a function of the exchange couplings J{sub H} and J and as a function of the band filling, since it has been observed that doping either on the ferromagnetic or antiferromagnetic regime lead to formation of magnetic domains [1]. We explore the quasi-particle formation and phase separation using the density-matrix renormalization group method, which is a highly efficient method to investigate quasi-one-dimensional strongly correlated systems.

  15. 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.

  16. Origin of the Efficient Polaron-Pair Dissociation in Polymer-Fullerene Blends

    NASA Astrophysics Data System (ADS)

    Deibel, Carsten; Strobel, Thomas; Dyakonov, Vladimir

    2009-07-01

    The separation of photogenerated polaron pairs in organic bulk heterojunction solar cells is the intermediate but crucial step between exciton dissociation and charge transport to the electrodes. In state-of-the-art devices, above 80% of all polaron pairs are separated at fields of below 107V/m. In contrast, considering just the Coulomb binding of the polaron pair, electric fields above 108V/m would be needed to reach similar yields. In order to resolve this discrepancy, we performed kinetic Monte Carlo simulations of polaron-pair dissociation in donor-acceptor blends, considering delocalized charge carriers along conjugated polymer chain segments. We show that the resulting fast local charge carrier transport can indeed explain the high experimental quantum yields in polymer solar cells.

  17. Illumination induced metastable polaron-supporting phase in poly p-phenylene- vinylene films

    NASA Astrophysics Data System (ADS)

    Ehrenfreund, E.; Gershman, E.; Eichen, Y.; Drori, T.; Sheng, C. X.; Vardeny, Z. V.

    2007-03-01

    We found a new illumination induced metastable polaron-supporting phase in pristine films of a soluble derivative of poly-p-phenylene vinylene (MEH-PPV). In the pristine, un-illuminated MEH-PPV phase A, the polymer films do not show any long-lived photogenerated polarons. Prolonged UV illumination, however, was found to induce a reversible, metastable phase B, characterized by its ability to support the existence of abundant long-lived photogenerated polarons. In the dark, films of phase B revert back to the original phase A within about thirty minutes at room temperature. Relying on the well-established ubiquitous reversible photoinduced cyclization of diarylethenes into dihyrophenanthrene derivatives, we propose a reversible mechanism in which UV illumination creates metastable deep defects that substantially increase the photogenerated polaron lifetime.

  18. Illumination-induced metastable polaron-supporting state in poly( p -phenylene vinylene) films

    NASA Astrophysics Data System (ADS)

    Drori, T.; Gershman, E.; Sheng, C. X.; Eichen, Y.; Vardeny, Z. V.; Ehrenfreund, E.

    2007-07-01

    We found an illumination-induced metastable polaron-supporting state in films of a soluble derivative of poly- p -phenylene vinylene (MEH-PPV). Pristine, nonilluminated MEH-PPV polymer films do not show long-lived photogenerated polarons. Prolonged UV illumination, however, is found to induce a reversible, metastable state characterized by its ability to support abundant long-lived photogenerated polarons. In the dark, the illumination-induced metastable state reverts back to the state of the original MEH-PPV within about 30min at room temperature. Relying on the well-established ubiquitous reversible photoinduced cyclization of diarylethenes into dihyrophenanthrene derivatives, we propose a reversible mechanism in which UV illumination transforms cis native defects in the polymer chains into metastable deep traps that substantially increase the photogenerated polaron lifetime in the film.

  19. Origin of the efficient polaron-pair dissociation in polymer-Fullerene blends.

    PubMed

    Deibel, Carsten; Strobel, Thomas; Dyakonov, Vladimir

    2009-07-17

    The separation of photogenerated polaron pairs in organic bulk heterojunction solar cells is the intermediate but crucial step between exciton dissociation and charge transport to the electrodes. In state-of-the-art devices, above 80% of all polaron pairs are separated at fields of below 10(7) V/m. In contrast, considering just the Coulomb binding of the polaron pair, electric fields above 10(8) V/m would be needed to reach similar yields. In order to resolve this discrepancy, we performed kinetic Monte Carlo simulations of polaron-pair dissociation in donor-acceptor blends, considering delocalized charge carriers along conjugated polymer chain segments. We show that the resulting fast local charge carrier transport can indeed explain the high experimental quantum yields in polymer solar cells.

  20. Evidence for Polaron Transport from Hall Effect, Resistivity and Thermopower in CMR Perovskite Materials

    NASA Astrophysics Data System (ADS)

    Jaime, Marcelo

    1998-03-01

    The experimental transport properties of so called colossal magnetoresistance (CMR) perovskite materials of composition A_1-xB_xMnO3 (A: La, Gd ; B: Sr,Ca,Pb) with x ~ 0.33, classically described in the context of the double exchange model by Zener(C. Zener, Phys. Rev. 82), 403 (1951), were studied over an extensive temperature range from a small fraction of the Curie temperature (T_C) to several times T_C. In the ferromagnetic state of La_2/3(Ca,Pb)_1/3MnO3 single crystals the resistivity reveals electron-magnon scattering processes that vanish below 20 K. The failure of single magnon scattering processes to be completely suppressed suggests the persistence of partially spin-polarized electronic bands at low temperatures. In this regime the thermopower shows evidence for mass-enhanced hole-like transport. Our high temperature thermopower measurements(M. Jaime et al. Appl. Phys. Lett. 68), 1576 (1996); Phys. Rev. B54, 11914 (1996), on the other hand, were the first unmistakable evidence for polaronic effects in CMR. Confirming the thermopower results, the Hall coefficient of Gd-doped La_2/3Ca_1/3MnO3 exhibits Arrhenius behavior over a temperature range from 2 TC to 4 T_C, with an activation energy very close to 2/3 that of the electrical conductivity. Although both the doping level and thermoelectric coefficient indicate hole-like conduction, the Hall coefficient is electron-like. This unusual result provides strong evidence in favor of small-polaronic conduction in the paramagnetic regime of the manganites(M. Jaime et al. Phys. Rev. Lett. 78) 951 (1997). La_2/3(Ca,Pb)_1/3MnO3 single crystals high temperature thermopower Hall coefficient of Gd-doped La_2/3Ca_1/3MnO_3 http://xxx.lanl.gov/abs/cond-mat/9609194

  1. Laser Asisted Scattering of an Optical Polaron in Presence of an Impurity Center

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, S.; Sinha, C.

    2012-11-01

    Momentum transfer cross-sections are studied for polarons inside a polar medium in presence of a coulomb impurity center as well as an external linerly polarised,homogeneous annd monochromatic laser field. The strongly bound polaron is found to be reluctant to contribute to the conductivity which is justified physically. The present study may find application in development of electronic devices using polar materials like organic semiconductors.

  2. [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.

  3. Light-induced polaron magnetization in EuTe at temperatures reaching 150 K

    NASA Astrophysics Data System (ADS)

    Henriques, A. B.; Galgano, G. D.; Rappl, P. H. O.; Abramof, E.

    2016-05-01

    We demonstrate that light creates a highly magnetized region in a magnetic semiconductor far above its critical temperature. A near-gap photon generates a quasiparticle of nonzero magnetic moment, named magnetic polaron, which is constituted by the photoexcited electron and about 1000 spin-polarized lattice atoms surrounding the photoexcited electron. The photoinduced magnetization follows a Langevin function, whose shape uniquely determines the magnetic moment of an individual polaron. In EuTe at 5 K the magnetic moment reaches a giant value of over 500 Bohr magnetons, thus the photoinduced magnetization saturates with a magnetic field of only 50 mT, which characterizes the magnetic polaron system as superparamagnetic. The polaron has an average lifetime of 15 μ s . When temperature is increased its magnetic moment decreases, but at 150 K it still has a large value of about 80 Bohr magnetons. The paramagnet of polarons is fully controlled by light. Because the magnetic polaron affects only spin orientation, but not the charge distribution, in the superparamagnetic state the ideal optical quality of the host semiconductor is preserved.

  4. 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.

  5. Unusual isotope effects on the pseudogap in high-Tc cuprate superconductors as support for the BCS-like pairing theory of large polarons above Tc

    NASA Astrophysics Data System (ADS)

    Dzhumanov, S.; Baimatov, P. J.; Djumanov, Sh. S.

    2015-06-01

    The BCS-like pairing theory is extended to the intermediate coupling regime and to the cases of exotic cuprate superconductors with large and small Fermi surfaces, so as to describe the pairing correlations above Tc , the opening of a pseudogap (PG) at a mean-field temperature T∗ >Tc and the unusual isotope effects on the PG in these materials within the large polaron model and two different BCS-like approaches. We argue that unconventional electron-phonon interactions are responsible for the polaron formation and the separation between temperatures T∗ (the onset of precursor Cooper pairing) and Tc (the onset of the superconducting transition) in exotic cuprate superconductors. Using the extended BCS-like approaches, we calculate the PG formation temperature T∗ , isotope shifts ΔT∗ , oxygen and copper isotope exponents and show that isotope effects on the PG basically depend on strengths of Coulomb and electron-phonon interactions, doping levels and dielectric constants of the cuprates. The new BCS-like pairing theory of polaronic carriers predicts the existence of small and sizable positive oxygen isotope effect and very large negative oxygen and copper isotope effects on the PG in the cuprates with large Fermi surfaces. The calculated results for T∗ , isotope shifts and exponents are compared with experimental data on various cuprate superconductors. For all the considered cases, a good quantitative agreement was found between theory and experimental data. We also predict the existence of small and sizable negative isotope effects on T∗ in deeply underdoped cuprates with small Fermi surfaces. Further, we find that the isotope effects on T∗ (=Tc) in heavily overdoped cuprates just like in some metals are relatively small positive or become even negative.

  6. 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

  7. 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.

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

    PubMed

    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. PMID:26894712

  9. 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.

  10. Ultrafast photogeneration of charged polarons on conjugated polymer chains in dilute solution

    NASA Astrophysics Data System (ADS)

    Miranda, Paulo B.; Moses, Daniel; Heeger, Alan J.

    2004-08-01

    Ultrafast photoinduced absorption by infrared-active vibrational modes is used to study the photogeneration of polarons on semiconducting polymer chains in dilute solutions and in solid films of a soluble derivative of poly(para-phenylene vinylene). In dilute solutions, polaron pairs are photogenerated on the conjugated polymer within less than 250fs with quantum efficiencies ϕch˜3% , about one-third of that for solid films of the same polymer. The excitation spectra of ϕch for both solutions and films show that ϕch is weakly dependent on photon energy between 2.2eV (the onset of absorption) and 4.7eV . The recombination dynamics of polarons is very fast and highly dependent on the excitation density for polymer films, but it is significantly slower and less sensitive to pump intensity for the semiconducting polymer in dilute solution. We conclude that the positive and negative polarons on a single chain in solution are typically separated by hundreds of monomer repeat units and that their one-dimensional diffusion along the chain is inhibited by the intervening excitons. This, together with the suppression of interchain recombination, explains the surprisingly slower polaron recombination in isolated chains.

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

    PubMed

    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.

  12. 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.

  13. Magnetization steps and bound magnetic polarons in diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    McCabe, Gao Hua

    1997-09-01

    Magnetization measurements and computer simulations were used to address several current problems in the area of the Diluted Magnetic Semiconductors (DMS). The method of Magnetization Steps (MSTs) was used to study Jahn-Teller Distortions in Zn1-xCrxTe, and exchange constants in Pb1-xEuxSe and Pb1- xEuxTe. Bound magnetic polarons in Cu2MnxZn1-xSnS4 were studied by conventional magnetometry. Jahn-Teller Distortions in cubic Zn1- xCrxTe were studied using MSTs. Possible Jahn- Teller Distortions in this material are along the three equivalent /langle 100/rangle axes. Energy states for the three distortion directions are equivalent at H = 0, but are different for finite H. The main issue is whether the populations of three possible distortions will vary with field, or remain frozen at their values in zero- field. The data showed that the populations of the distortions changed significantly. The dominant antiferomagnetic exchange constants J between Eu2+ ions in IV-VI Pb1- xEuxSe and Pb1-xEuxTe were determined using the MST method. Measurements were made at 0.6 K in fields up to 150 kOe. Supplementary data by our collaborators were taken at much lower temperatures. Simulations of various MSTs (from isolated Eu2+ ions, pairs of ions, and triplets) were performed to fit the experimental data. Because J is determined from the MSTs for pairs, the effects of other anisotropies and exchange interactions on these MSTs were considered. They were found to bring little change to the values of J. The exchange constants were J/kB = -0/24 ± 0.03 K for Ph 1-xEu xSe amd os J/KB = -0.264 ± 0.018 K for Ph1-xEuxTe. The dominant AF exchange constants were identified as J1, between nearest-neighbors, by comparing the experimental magnetization curves to the theoretical simulations using the single J model. The dominant antiferromagnetic exchange constants J between Eu2+ ions in IV-VI Pb1- xEuxSe and Pb1-xEuxTe were determined using the MST method. Measurements were made at 0.6 K in

  14. 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.

  15. High-voltage thermionic polaron emission in the presence of adsorbed nonmetal nanofilm on a cathode

    NASA Astrophysics Data System (ADS)

    Barengolts, Yu. A.; Beril, S. I.

    2016-07-01

    The equation of thermionic emission has been derived, which takes into account the presence of thin films of adsorbed gas-environment molecules on a cathode under conditions of high-voltage gas discharge. It is shown that the consideration of electron polaron tunneling mechanism leads to a significant (by more than an order of magnitude) decrease in the emission-current density. A comparison with the classical Richardson-Schottky equation is performed. The role of the polaron effect is shown to strongly increase with an increase in the applied electric field strength and a decrease in temperature, which is due to an increase in the electron work function because of polaron nature.

  16. 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.

  17. 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 PAGESBeta

    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 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

  18. 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.

  19. On the drift mobility of a molecular polaron in the presence of Coulomb traps

    NASA Astrophysics Data System (ADS)

    Rackovsky, S.; Scher, H.

    1999-08-01

    We study the drift mobility of a molecular polaron in the presence of an external applied field and Coulomb traps. The model is based on one previously developed for geminate recombination of photogenerated charge carriers. It is shown that the unusual combination of Poole-Frenkel-like field dependence and non-Arrhenius temperature dependence of the mobility, measured experimentally in molecular films, is well reproduced by this model. Our key result is that this nearly universal experimental behavior of the mobility arises from competition between rates of polaron trapping and release from a very low density of Coulomb traps.

  20. Electron Spin Resonance Spectra of Photogenerated Polarons in Poly(Paraphenylene Vinylene)

    NASA Astrophysics Data System (ADS)

    Murata, Kazuhiro; Kuroda, Shin-ichi; Shimoi, Yukihiro; Abe, Shuji; Noguchi, Takanobu; Ohnishi, Toshihiro

    1996-12-01

    Light-induced ESR (LESR) measurements have been performed on undoped poly(parapheny- lene vinylene) (PPV) down to 4 K. The ESR signal increases significantly for the excitation energy above 3.1 3.2 eV, as in the case of the excitation spectra of photocarriers reported in PPV derivatives. The anisotropic light-induced ESR spectra in oriented samples are well reproduced by the spectra calculated using a theoretical polaron spin distribution in the case of finite electron-electron interaction. These spectral features indicate that the observed spins are photogenerated polarons.

  1. Determination of free polaron lifetime in organic bulk heterojunction solar cells by transient time analysis

    SciTech Connect

    Li, Kejia; Shen, Yang; Majumdar, Nabanita; Hu, Chong; Gupta, Mool C.; Campbell, Joe C.

    2010-01-01

    A transient response technique that is widely used to measure the minority carrier lifetime in inorganic semiconductors is proposed to measure the lifetime of free polarons in a polymer:fullerene bulk heterojunction (BHJ) solar cell. A numerical model that can be used to describe the transient behavior of BHJ devices has been developed. Using the proposed method, the lifetime of free polarons in poly (3-hexylthiophene) and [6, 6]-phenyl C61-butyric acid methyl ester blend film is estimated to be in the range of 300–400 ns.

  2. Electronic structure and polaronic excitation in FeVO{sub 4}

    SciTech Connect

    Dixit, A.; Lawes, G.; Chen, P.; Musfeldt, J. L.

    2011-10-03

    We investigated the electronic properties of FeVO{sub 4} films using optical, valence band x-ray photoelectron, and infrared spectroscopies. These studies show that FeVO{sub 4} is a direct bandgap system with a 2.7 eV gap with the Fermi level in the middle of the valence band maximum and conduction band minimum. A polaronic excitation is also observed in the middle infrared, indicating the importance of charge-lattice coupling in this multiferroic material. Fits to a model for the optical response of large polarons yield a binding energy of approximately 130 meV.

  3. 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.

  4. 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

  5. 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.

  6. Quantitative measurements of magnetic polaron binding on acceptors in CdMnTe alloys

    NASA Astrophysics Data System (ADS)

    Nhung, Tran Hong; Planel, R.

    1983-03-01

    The acceptor binding energy is measured as a function of Temperature and composition in Cd1-x Mnx Te alloys, by time resolved spectroscopy. The Bound magnetic polaron effect is measured and compared with a theory accouting for magnetic saturation and fluctuations.

  7. Polaronic effects at finite temperatures in the B850 ring of the LH2 complex.

    PubMed

    Chorošajev, Vladimir; Rancova, Olga; Abramavicius, Darius

    2016-03-21

    Energy transfer and relaxation dynamics in the B850 ring of LH2 molecular aggregates are described, taking into account the polaronic effects, by a stochastic time-dependent variational approach. We explicitly include the finite temperature effects in the model by sampling the initial conditions of the vibrational states randomly. This is in contrast to previous applications of the variational approach, which consider only the zero-temperature case. The method allows us to obtain both the microscopic dynamics at the single-wavefunction level and the thermally averaged picture of excitation relaxation over a wide range of temperatures. Spectroscopic observables such as temperature dependent absorption and time-resolved fluorescence spectra are calculated. Microscopic wavefunction evolution is quantified by introducing the exciton participation (localization) length and the exciton coherence length. Their asymptotic temperature dependence demonstrates that the environmental polaronic effects range from exciton self-trapping and excitonic polaron formation at low temperatures to thermally induced state delocalization and decoherence at high temperatures. While the transition towards the polaronic state can be observed on the wavefunction level, it does not produce a discernible effect on the calculated spectroscopic observables.

  8. Time-resolved magnetophotoluminescence studies of magnetic polaron dynamics in type-II quantum dots

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    We used continuous wave photoluminescence (cw-PL) and time-resolved photoluminescence (TR-PL) spectroscopy to compare the properties of magnetic polarons (MP) in two related spatially indirect II-VI epitaxially grown quantum dot systems. In the ZnTe /(Zn ,Mn )Se system the holes are confined in the nonmagnetic ZnTe quantum dots (QDs), and the electrons reside in the magnetic (Zn,Mn)Se matrix. On the other hand, in the (Zn ,Mn )Te /ZnSe system, the holes are confined in the magnetic (Zn,Mn)Te QDs, while the electrons remain in the surrounding nonmagnetic ZnSe matrix. The magnetic polaron formation energies EMP in both systems were measured from the temporal redshift of the band-edge emission. The magnetic polaron exhibits distinct characteristics depending on the location of the Mn ions. In the ZnTe /(Zn ,Mn )Se system the magnetic polaron shows conventional behavior with EMP decreasing with increasing temperature T and increasing magnetic field B . In contrast, EMP in the (Zn ,Mn )Te /ZnSe system has unconventional dependence on temperature T and magnetic field B ; EMP is weakly dependent on T as well as on B . We discuss a possible origin for such a striking difference in the MP properties in two closely related QD systems.

  9. Competition between polaron pair formation and singlet fission observed in amorphous rubrene films

    NASA Astrophysics Data System (ADS)

    Jankus, Vygintas; Snedden, Edward W.; Bright, Daniel W.; Arac, Erhan; Dai, DeChang; Monkman, Andrew P.

    2013-06-01

    In this paper, we investigate excited state dynamics in amorphous rubrene vacuum sublimed films. We report the direct observation of singlet fission in amorphous rubrene films. We have determined the fission rate to be >2.5×1012 s-1. Simultaneously, we observe strong polaron pair absorption and propose that polaron pair formation could be competing with singlet fission. Another possible conclusion from our experiments could be that two triplets from singlet fission might arise via polaron pairs. In either case, polaron pairs play an important role in singlet fission in an amorphous rubrene film. We also observe that triplets created by singlet fission fuse to regenerate a singlet, giving delayed fluorescence (DF) scaling linearly with initial laser energy (i.e., one singlet gives two triplets and two triplets give back one singlet). This is a strong evidence of S1n→2T1. We did not observe substantial temperature dependence of DF decay curve shape, indicating that triplet migration in amorphous rubrene films is not hopping limited and that triplets undergo fusion before their migration.

  10. Luminescence properties of magnetic polarons in EuTe: Theoretical description and experiments in magnetic fields up to 28 T

    NASA Astrophysics Data System (ADS)

    Henriques, A. B.; Moraes, F. C. D.; Galgano, G. D.; Meaney, A. J.; Christianen, P. C. M.; Maan, J. C.; Abramof, E.; Rappl, P. H. O.

    2014-10-01

    The recent discovery of a polaron-associated zero phonon line in the band-edge photoluminescence of high optical quality EuTe crystals opens up the prospect of answering long-standing questions about the polaron internal structure, thermal stability, and generation efficiency. Here, a Schrödinger equation for the polaron was formulated and resolved by using both variational and self-consistent methods. The theory is in good agreement with measurements of the zero phonon line as a function of magnetic field and temperature, and it could be applied to other polaronic systems. It is deduced that, in EuTe, at 0K, a polaron carries a magnetic moment of 610μB, and its binding energy is 27 meV. However, this binding energy does not carry the usual meaning of thermal stability, because it decreases drastically when the sample is warmed up. For instance, at T =100K, the binding energy is already reduced to only 6 meV. The thermal destruction of a polaron is brought about by thermal fluctuations of the spin lattice that suppress the electron's self-energy. Photoluminescence excitation spectra of EuTe demonstrate that the photogeneration of polarons becomes increasingly inefficient when the energy of the pumping photon is increased above the band gap.

  11. Optical orientation of hole magnetic polarons in (Cd,Mn)Te/(Cd,Mn,Mg)Te quantum wells

    NASA Astrophysics Data System (ADS)

    Zhukov, E. A.; Kusrayev, Yu. G.; Kavokin, K. V.; Yakovlev, D. R.; Debus, J.; Schwan, A.; Akimov, I. A.; Karczewski, G.; Wojtowicz, T.; Kossut, J.; Bayer, M.

    2016-06-01

    The optically induced spin polarization in (Cd,Mn)Te/(Cd,Mn,Mg)Te diluted-magnetic-semiconductor quantum wells is investigated by means of picosecond pump-probe Kerr rotation. At 1.8 K temperature, additionally to the oscillatory signals from photoexcited electrons and manganese spins precessing about an external magnetic field, a surprisingly long-lived (up to 60 ns) nonoscillating spin polarization is detected. This polarization is related to optical orientation of equilibrium magnetic polarons involving resident holes. The suggested mechanism for the optical orientation of the equilibrium magnetic polarons indicates that the detected polaron dynamics originates from unexcited magnetic polarons. The polaron spin dynamics is controlled by the anisotropic spin structure of the heavy hole resulting in a freezing of the polaron magnetic moment in one of the two stable states oriented along the structure growth axis. Spin relaxation between these states is prohibited by a potential barrier, which depends on temperature and magnetic field. The magnetic polaron relaxation is accelerated with increasing temperature and in magnetic field.

  12. Criteria for validating polaron pair dissociation in polymer-fullerene bulk heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Inche Ibrahim, M. L.

    2016-04-01

    The dissociation of polaron pairs into free charge carriers in organic bulk heterojunction solar cells is a fundamental step in generating photocurrent and is still in debate. In this study, we propose two simple criteria that can be used to test the validity of any polaron pair dissociation model for polymer-fullerene bulk heterojunction solar cells. The first criterion states that the ratio of the bimolecular recombination current density to the maximum photocurrent density should increase as a function of applied voltage. The second criterion states that the ratio of the bimolecular recombination current density to the maximum photocurrent density at short circuit should not be larger than 1. We apply these criteria to test the validity of the widely used Onsager-Braun model by using the experimental current-voltage data of poly[2-methoxy-5-(3'-7'-dimethyloctyloxy)-p-phenylene vinylene] (OC1C10-PPV) and [6,6]-phenyl C61-butyric acid methylester (PCBM) based solar cells. We find that our numerical analysis is not suitable to employ these criteria. Our analytical analysis, on the other hand, clearly demonstrates that the Onsager-Braun model simply cannot fulfill the first criteria. The reason is because the polaron pair dissociation given by the Onsager-Braun model is too strongly influenced by the electric field (i.e., decreases too rapidly as the electric field decreases). The analysis provides a further evidence against the widely used Onsager-Braun model. The proposed criteria can help us to determine the correct model for polaron pair dissociation by serving as a guideline on how strongly the electric field is allowed to influence the polaron pair dissociation.

  13. 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

  14. Many-polaron description of impurities in a Bose-Einstein condensate in the weak-coupling regime

    SciTech Connect

    Casteels, W.; Devreese, J. T.; Tempere, J.

    2011-12-15

    The weak-coupling many-polaron formalism is applied to the case of the polaronic system consisting of impurities in a Bose-Einstein condensate. This allows investigating the ground-state properties and the response of the system to Bragg spectroscopy. Then, this theory is applied to the system of spin-polarized fermionic lithium-6 impurities in a sodium condensate. The Bragg spectrum reveals a peak that corresponds to the emission of Bogoliubov excitations. Both the ground-state properties and the response spectrum show that the polaronic effect vanishes at high densities. We also look at two possibilities to define the polaronic effective mass and observe that this results in a different quantitative behavior if multiple impurities are involved.

  15. 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.

  16. 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

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

    PubMed

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

    2015-07-17

    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.

  18. Laser assisted bound-free transition of a polaron bound to an impurity center

    NASA Astrophysics Data System (ADS)

    Sinha, C.; Biswas, R.; Mukhopadhyay, S.

    2013-12-01

    The scattering of a bound Frohlich large polaron in the presence of a coulomb impurity center as well as a linearly polarized laser field is studied. The differential (DCS) as well as the momentum transfer cross sections (MTCS) and the conductivity depend remarkably on the electron-phonon coupling (αP) and the strength of the coulomb impurity (β). The strongly bound polaron is found to be reluctant to contribute to the conductivity which is justified physically. The curves for MTCS and conductivity verses αP and β appear to be complementary, indicating the possibility of controlling the mobility and thereby conductivity by varying one of the parameters. This behavior indicates the possibility of optimizing the composition of optoelectronic materials where laser is the dominant source of excitation.

  19. Magnetic field tuning of polaron losses in Fe doped BaTiO3 single crystals

    NASA Astrophysics Data System (ADS)

    Anand Theerthan, R.; Artemenko, Alla; Maglione, Mario

    2012-10-01

    Artificial tuning of dielectric parameters can result from interface conductivity in polycrystalline materials. In ferroelectric single crystals, it has already been shown that ferroelectric domain walls can be the source of such artificial coupling. We show here that low-temperature dielectric losses can be tuned by a dc magnetic field. Since such losses were previously ascribed to polaron relaxation we suggest this results from the interaction of hopping polarons with the magnetic field. The fact that this loss alteration has no counterpart in the real part of the dielectric permittivity confirms that no interface is involved in this purely dynamical effect. The contribution of mobile charges hopping among Fe-related centers was confirmed by ESR spectroscopy, showing a maximum intensity at ca T ˜ 40 K.

  20. Reducing exciton-polaron annihilation in organic planar heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Verreet, Bregt; Bhoolokam, Ajay; Brigeman, Alyssa; Dhanker, Rijul; Cheyns, David; Heremans, Paul; Stesmans, Andre; Giebink, Noel C.; Rand, Barry P.

    2014-09-01

    We investigate the relationship between charge concentration, exciton concentration, and photocurrent generation in fullerene-containing heterojunction diodes. Impedance measurements on C60 diodes reveal a charge buildup at the C60/bathocuproine (BCP) interface that can be swept out under reverse bias. In solar cell structures, a similar charge buildup is observed in dark conditions, and increases as a function of incident light intensity. Photoluminescence measurements reveal that the C60 exciton concentration is voltage dependent, explained via the process of exciton-polaron annihilation. This process has a negative impact on the generated photocurrent of the solar cells and thereby decreases the fill factor. A combination of electroabsorption, photoluminescence, and impedance measurements reveal a decrease in charge buildup and the associated exciton-polaron annihilation through the use of a BCP/3,4,9,10-perylenetetracarboxylic bis-benzimidazole/Ag cathode.

  1. Finite-temperature Wigner solid and other phases of ripplonic polarons on a helium film

    NASA Astrophysics Data System (ADS)

    Klimin, Serghei N.; Tempere, Jacques; Misko, Vyacheslav R.; Wouters, Michiel

    2016-07-01

    Electrons on liquid helium can form different phases depending on density, and temperature. Also the electron-ripplon coupling strength influences the phase diagram, through the formation of so-called "ripplonic polarons", that change how electrons are localized, and that shifts the transition between the Wigner solid and the liquid phase. We use an all-coupling, finite-temperature variational method to study the formation of a ripplopolaron Wigner solid on a liquid helium film for different regimes of the electron-ripplon coupling strength. In addition to the three known phases of the ripplopolaron system (electron Wigner solid, polaron Wigner solid, and electron fluid), we define and identify a fourth distinct phase, the ripplopolaron liquid. We analyse the transitions between these four phases and calculate the corresponding phase diagrams. This reveals a reentrant melting of the electron solid as a function of temperature. The calculated regions of existence of the Wigner solid are in agreement with recent experimental data.

  2. Translation invariant theory of polaron (bipolaron) and the problem of quantizing near the classical solution

    SciTech Connect

    Lakhno, V. D.

    2013-06-15

    A physical interpretation of translation-invariant polarons and bipolarons is presented, some results of their existence are discussed. Consideration is given to the problem of quantization in the vicinity of the classical solution in the quantum field theory. The lowest variational estimate is obtained for the bipolaron energy E({eta}) with E(0) = -0.440636{alpha}{sup 2}, where {alpha} is a constant of electron-phonon coupling, {eta} is a parameter of ion binding.

  3. Femtosecond dynamics of photogenerated solitons and polarons in trans-polyacetylene

    NASA Astrophysics Data System (ADS)

    Rothberg, L.; Jedju, T. M.; Townsend, P. D.; Etemad, S.; Baker, G. L.

    1990-07-01

    Intrachain and interchain excitations are clearly identified by polarized time-resolved absorption studies of photoinduced midgap bands in well-aligned trans-polyacetylene. We report spectroscopic evidence of the lattice deformation during intrachain photogeneration of charged soliton pairs, and see these pairs recombine geminatley in <2 ps. For incident polarization perpendicular to the chain direction, our data also show that interchain electron-hole pair excitation occurs with fairly high quantum yield and leads to polaron formation.

  4. Transient spectroscopy of excitons and polarons in C[sub 60] films from femtoseconds to milliseconds

    SciTech Connect

    Dick, D.; Wei, X.; Jeglinski, S.; Benner, R.E.; Vardeny, Z.V. ); Moses, D.; Srdanov, V.I.; Wudl, F. )

    1994-11-14

    We have studied photoexcitations in C[sub 60] films using transient photomodulation and photoluminescence from 100 fs to 50 ms and absorption-detected magnetic resonance (ADMR). We show that singlet Frenkel excitons are the primary photoexcitations; their recombination kinetics in the picosecond time domain are dispersive as a result of inhomogeneity. The long-lived photoexcitations, however, are shown to be triplet excitons and charged polarons (C[sub 60][sup [minus plus

  5. Polaron-like vortices, dissociation transition, and self-induced pinning in magnetic superconductors

    SciTech Connect

    Bulaevskii, L. N. Lin, S.-Z.

    2013-09-15

    Vortices in magnetic superconductors polarize spins nonuniformly and repolarize them when moving. At a low spin relaxation rate and at low bias currents, vortices carrying magnetic polarization clouds become polaron-like and their velocities are determined by the effective drag coefficient that is significantly bigger than the Bardeen-Stephen (BS) one. As the current increases, vortices release polarization clouds and the velocity as well as the voltage in the I-V characteristics jump to values corresponding to the BS drag coefficient at a critical current J{sub c}. The nonuniform components of the magnetic field and magnetization drop as the velocity increases, resulting in weaker polarization and a discontinuous dynamic dissociation depinning transition. Experimentally, the jump shows up as a depinning transition and the corresponding current at the jump is the depinning current. As the current decreases, on the way back, vortices are retrapped by polarization clouds at the current J{sub r} < J{sub c}. As a result, the polaronic effect suppresses dissipation and enhances the critical current. Borocarbides (RE)Ni{sub 2}B{sub 2}C with a short penetration length and highly polarizable rare earth spins seem to be optimal systems for a detailed study of vortex polaron formation by measuring I-V characteristics. We also propose to use a superconductor-magnet multilayer structure to study polaronic mechanism of pinning with the goal to achieve high critical currents. The magnetic layers should have large magnetic susceptibility to enhance the coupling between vortices and magnetization in magnetic layers while the relaxation of the magnetization should be slow. For Nb and a proper magnet multilayer structure, we estimate the critical current density J{sub c} {approx} 10{sup 9} A/m{sup 2} at the magnetic field B Almost-Equal-To 1 T.

  6. Negative Polaron and Triplet Exciton Diffusion inOrganometallic “Molecular Wires”

    SciTech Connect

    Schanze, K.S.; Miller, J.; Keller, J.M.; Sean McIlroy, S.; Sreearuothai, P.; Danilov, E.O.; Jiang, H.; Glusac, K.D.; Miller, J.R.

    2011-07-27

    The dynamics of negative polaron and triplet exciton transport within a series of monodisperse platinum (Pt) acetylide oligomers is reported. The oligomers consist of Pt-acetylide repeats, [PtL{sub 2}-C {triple_bond} C-Ph-C {triple_bond} C-]{sub n} (where L = PBu{sub 3} and Ph = 1,4-phenylene, n = 2, 3, 6, and 10), capped with naphthalene diimide (NDI) end groups. The Pt-acetylide segments are electro- and photoactive, and they serve as conduits for transport of electrons (negative polaron) and triplet excitons. The NDI end groups are relatively strong acceptors, serving as traps for the carriers. Negative polaron transport is studied by using pulse radiolysis/transient absorption at the Brookhaven National Laboratory Laser-Electron Accelerator Facility (LEAF). Electrons are rapidly attached to the oligomers, with some fraction initially residing upon the Pt-acetylide chains. The dynamics of transport are resolved by monitoring the spectral changes associated with transfer of electrons from the chain to the NDI end group. Triplet exciton transport is studied by femtosecond-picosecond transient absorption spectroscopy. Near-UV excitation leads to rapid production of triplet excitons localized on the Pt-acetylide chains. The excitons transport to the chain ends, where they are annihilated by charge separation with the NDI end group. The dynamics of triplet transport are resolved by transient absorption spectroscopy, taking advantage of the changes in spectra associated with decay of the triplet exciton and rise of the charge-separated state. The results indicate that negative polarons and excitons are transported rapidly, on average moving distances of 3 nm in less than 200 ps. Analysis of the dynamics suggests diffusive transport by a site-to-site hopping mechanism with hopping times of 27 ps for triplets and <10 ps for electrons.

  7. Photogeneration of superparaelectric large polarons in dielectrics with soft anharmonic T1u phonons

    NASA Astrophysics Data System (ADS)

    Nasu, Keiichiro

    2003-05-01

    In connection with the recent experiments on photoenhancements of the electronic conductivity and the quasistatic electric susceptibility of SrTiO3, we theoretically study global versus local parity violation of a photogenerated electron in this dielectric. The photogenerated electron, being quite itinerant in the 3d band of Ti, is assumed to couple weakly but quadratically with soft-anharmonic T1u phonons in this dielectric. The electron is also assumed to couple strongly but linearly to the breathing (A1g) type high energy phonons. We will show that these two types of electron-phonon (e-p) couplings result in two types of polarons, a “superparaelectric large polaron” with a quasiglobal parity violation, and an “off-center type self-trapped polaron” with only a local parity violation. These two states are shown to be separated by an adiabatic potential barrier, if these e-p couplings are short in their force ranges. Without the T1u phonon, these two states reduce to the well-known large polaron and the self-trapped one, both of which have even parities. We will also show that this superparaelectric large polaron enhances both the electronic conductivity and the quasistatic electric susceptibility, in qualitative agreements with the experiments.

  8. Structural correlations in the generation of polaron pairs in low-bandgap polymers for photovoltaics

    NASA Astrophysics Data System (ADS)

    Tautz, Raphael; da Como, Enrico; Limmer, Thomas; Feldmann, Jochen; Egelhaaf, Hans-Joachim; von Hauff, Elizabeth; Lemaur, Vincent; Beljonne, David; Yilmaz, Seyfullah; Dumsch, Ines; Allard, Sybille; Scherf, Ullrich

    2012-07-01

    Polymeric semiconductors are materials where unique optical and electronic properties often originate from a tailored chemical structure. This allows for synthesizing conjugated macromolecules with ad hoc functionalities for organic electronics. In photovoltaics, donor-acceptor co-polymers, with moieties of different electron affinity alternating on the chain, have attracted considerable interest. The low bandgap offers optimal light-harvesting characteristics and has inspired work towards record power conversion efficiencies. Here we show for the first time how the chemical structure of donor and acceptor moieties controls the photogeneration of polaron pairs. We show that co-polymers with strong acceptors show large yields of polaron pair formation up to 24% of the initial photoexcitations as compared with a homopolymer (η=8%). π-conjugated spacers, separating the donor and acceptor centre of masses, have the beneficial role of increasing the recombination time. The results provide useful input into the understanding of polaron pair photogeneration in low-bandgap co-polymers for photovoltaics.

  9. 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.

  10. 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.

  11. 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.

  12. {sup 139}La NMR in lanthanum manganites: Indication of the presence of magnetic polarons from spectra and nuclear relaxations

    SciTech Connect

    Allodi, G.; De Renzi, R.; Guidi, G.

    1998-01-01

    We present {sup 139}La NMR experiments on five powder samples of lanthanum manganites, with a Mn{sup 4+} concentration ranging from the antiferromagnetic-insulator (AFM) to the ferromagnetic-conducting (FM) region of the phase diagram. We measure a positive hyperfine coupling C=0.13 T/{mu}{sub B}. A signal from nuclei in a FM environment is present at all compositions, as evidenced by a hyperfine frequency in zero-field experiments, by a positive hyperfine shift in NMR experiments below T{sub c}, and by a paramagnetic frequency shift following Curie-Weiss law. A signal from nuclei in an AFM environment is identified by a similar negative intercept Curie-Weiss law. The NMR spectra reveal a large temperature dependent fraction of static spin defects below T{sub c} in the FM domains. Nuclear relaxation indicates that the FM regions are influenced by diffusing, AFM-correlated excitations, while the AFM regions probe spin fluctuations from diffusing, FM correlated excitations. These results are interpreted in terms of electronic inhomogeneities due to the presence of a magnetic small polaron. {copyright} {ital 1998} {ital The American Physical Society}

  13. Time-resolved photoluminescence spectroscopy of NbNb4 + and O- polarons in LiNbO3 single crystals

    NASA Astrophysics Data System (ADS)

    Kämpfe, T.; Haußmann, A.; Eng, L. M.; Reichenbach, P.; Thiessen, A.; Woike, T.; Steudtner, R.

    2016-05-01

    We probe here the optical relaxation properties of Mg-doped wide-band-gap LiNbO3 single crystals with both a high spectral and temporal resolution at cryogenic temperatures. Surprisingly, we observe the photoluminescence to decay in a two-step process: a fast relaxation and a slower one centered around an energy Emax = 2.62 ±0.05 eV. Both decays fit well to the stretched-exponential behavior. Moreover, we are able to associate these energies to the recombination of light-induced NbNb4 + and O- small polarons. Also, we checked the stability of our findings by using LiNbO3 single crystals that show on-purpose modified radiative recombination processes, i.e., with a Mg doping both above and below the optical damage resistance threshold, as well as with different poling histories of inverted domains.

  14. Luttinger liquid of polarons in one-dimensional boson-fermion mixtures.

    PubMed

    Mathey, L; Wang, D-W; Hofstetter, W; Lukin, M D; Demler, Eugene

    2004-09-17

    We use the bosonization approach to investigate quantum phases of boson-fermion mixtures (BFM) of atoms confined to one dimension by an anisotropic optical lattice. For a BFM with a single species of fermions we find a charge-density wave phase, a fermion pairing phase, and a phase separation regime. We also obtain the rich phase diagram of a BFM with two species of fermions. We demonstrate that these phase diagrams can be understood in terms of polarons, i.e., atoms "dressed" by screening clouds of the other atom species. Techniques to detect the resulting quantum phases are discussed.

  15. Polaron hopping in some biomolecular solids and their charge transfer complexes.

    PubMed

    Solanki, G K; Amin, Anand; Padhiyar, Ashvin; Ray, A K; Oza, A T

    2008-12-01

    The solid state spectroscopy of charge transfer complexes of biomolecules such as fatty acids, tripalmitin, lysozyme. folic acid, beta-carotene, cytochrome c, valinomycin and gramicidin has been carried out. The absorption coefficient is related with electronic conductivity. A half-power beta density is found common among these macromolecular solids, indicating photon-induced polaron hopping or hopping of a charge carrier between two branches of a polariton. Band gap vs full width at half-maximum of the mid-IR peak also reveals a linear relation.

  16. Electron spin resonance and electron nuclear double resonance of photogenerated polarons in polyfluorene and its fullerene composite

    NASA Astrophysics Data System (ADS)

    Marumoto, K.; Kato, M.; Kondo, H.; Kuroda, S.; Greenham, N. C.; Friend, R. H.; Shimoi, Y.; Abe, S.

    2009-06-01

    Electron spin resonance (ESR) and electron-nuclear double resonance (ENDOR) of photogenerated polarons in poly(9,9-dioctylfluorene) (PFO) and its composite with fullerene (C60) using variable photoexcitation energy up to 4.1 eV are reported. For PFO, a light-induced ESR (LESR) signal (g=2.003) is observed below 60 K, and its transient response and excitation spectrum indicate that the observed spins are photogenerated polarons on PFO. For the PFO-C60 composite, two LESR signals of photogenerated positive polarons on PFO (g1=2.003) and radical anions on C60 (g2=1.999) , respectively, are observed below 120 K, which are caused by photoinduced electron transfer from PFO to C60 . A remarkable enhancement of the LESR signals in the excitation spectrum at ˜2.8eV is observed compared with the case of pure PFO. The bimolecular-recombination kinetics of photogenerated charge carriers in the composite are confirmed by the dependence of the LESR on excitation-light intensity and by the decay dynamics. Light-induced ENDOR (LENDOR) signals are clearly observed for excitation around 2.8 eV owing to the highly efficient photoinduced electron transfer in the composite. Broad LENDOR shifts directly reflect the spin-density distribution of the polarons in PFO. We have determined its maximum shift using LENDOR-induced ESR, and have evaluated the maximum spin density on the carbon site coupled to the proton as 0.032. This value is consistent with the theoretical result obtained by Pariser-Parr-Pople (PPP) model, where the spatial extent of the polarons is calculated as ˜3 monomer units of PFO. The calculated LESR spectra of PFO based on the PPP model are consistent with the experimental spectra, which confirm the above spatial extension of the polaron in PFO.

  17. 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.

  18. Real Space Imaging of Spin Polarons in Zn-Doped SrCu2(BO3)2

    NASA Astrophysics Data System (ADS)

    Yoshida, M.; Kobayashi, H.; Yamauchi, I.; Takigawa, M.; Capponi, S.; Poilblanc, D.; Mila, F.; Kudo, K.; Koike, Y.; Kobayashi, N.

    2015-02-01

    We report on the real space profile of spin polarons in the quasi-two-dimensional frustrated dimer spin system SrCu2(BO3)2 doped with 0.16% of Zn. The 11B nuclear magnetic resonance spectrum exhibits 15 additional boron sites near nonmagnetic Zn impurities. With the help of exact diagonalizations of finite clusters, we have deduced from the boron spectrum, the distribution of local magnetizations at the Cu sites with fine spatial resolution, providing direct evidence for an extended spin polaron. The results are confronted with those of other experiments performed on doped and undoped samples of SrCu2(BO3)2.

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

    PubMed

    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

  20. Polaron absorption for photovoltaic energy conversion in a manganite-titanate pn heterojunction

    NASA Astrophysics Data System (ADS)

    Saucke, Gesine; Norpoth, Jonas; Jooss, Christian; Su, Dong; Zhu, Yimei

    2012-04-01

    The relation among structure, electric transport, and photovoltaic effect is investigated for a pn heterojunction with strong correlation interactions. A perovskite interface is chosen as a model system consisting of the p-doped strongly correlated manganite Pr0.64Ca0.36MnO3 (PCMO) and the n-doped titanate SrTi1-yNbyO3 (y=0.002 and 0.01). High-resolution electron microscopy and spectroscopy reveal a nearly dislocation-free, epitaxial interface and give insight into the local atomic and electronic structure. The presence of a photovoltaic effect under visible light at room temperature suggests the existence of mobile excited polarons within the band-gap-free PCMO absorber. The temperature-dependent rectifying current-voltage characteristics prove to be mainly determined by the presence of an interfacial energy spike in the conduction band and are affected by the colossal electroresistance effect. From the comparison of photocurrents and spatiotemporal distributions of photogenerated carriers (deduced from optical absorption spectroscopy), we discuss the range of the excited polaron diffusion length.

  1. Ideal Diode Equation for Organic Heterojunctions. II. The Role of Polaron Pair Recombination

    SciTech Connect

    Giebink, Noel C; Wiederrecht, Gary P; Wasielewski, Michael R; Forrest, Stephen R.

    2010-10-04

    In paper I [N. C. Giebink, G. P. Wiederrecht, M. R. Wasielewski, and S. R. Forrest, Phys. Rev. B 82, 155305 (2010)], we proposed that current transport in a donor-acceptor heterojunction (HJ) depends on the balance of polaron pair (PP) dissociation and recombination. Here, we directly investigate these processes in archetype planar copper phthalocyanine (CuPc)/C{sub 60} and boron subpthalocyanine chloride (SubPc)/C{sub 60} HJs. Using intensity-modulated photocurrent spectroscopy (IMPS) along with emission from interfacial Pc/C{sub 60} exciplex states, we monitor the geminate PP density at the HJ as a function of bias and illumination intensity. We find that the SubPc/C{sub 60} PP density is limited by the dynamics of dissociation, where it increases from short circuit, and peaks at open circuit. In contrast, that of CuPc/C{sub 60} is dominated by faster recombination kinetics and declines monotonically over the same voltage domain. We conclude that the PP recombination rate depends on electric field, and propose a simple expression that qualitatively explains the observed exciplex luminescence and IMPS behavior for these HJs. Our results provide insight into polaron pair recombination, which governs the current-voltage characteristics of organic heterojunctions in the dark and under illumination.

  2. Ideal diode equation for organic heterojunctions. II. The role of polaron pair recombination

    SciTech Connect

    Giebink, Noel C; Lassiter, Brian E; Wiederrecht, Gary P; Wasielewski, Michael R; Forrest, Stephen R.

    2010-10-04

    In paper I [N. C. Giebink, G. P. Wiederrecht, M. R. Wasielewski, and S. R. Forrest, Phys. Rev. B 82, 155305 (2010)], we proposed that current transport in a donor-acceptor heterojunction (HJ) depends on the balance of polaron pair (PP) dissociation and recombination. Here, we directly investigate these processes in archetype planar copper phthalocyanine (CuPc)/C{sub 60} and boron subpthalocyanine chloride (SubPc)/C{sub 60} HJs. Using intensity-modulated photocurrent spectroscopy (IMPS) along with emission from interfacial Pc/C{sub 60} exciplex states, we monitor the geminate PP density at the HJ as a function of bias and illumination intensity. We find that the SubPc/C{sub 60} PP density is limited by the dynamics of dissociation, where it increases from short circuit, and peaks at open circuit. In contrast, that of CuPc/C{sub 60} is dominated by faster recombination kinetics and declines monotonically over the same voltage domain. We conclude that the PP recombination rate depends on electric field, and propose a simple expression that qualitatively explains the observed exciplex luminescence and IMPS behavior for these HJs. Our results provide insight into polaron pair recombination, which governs the current-voltage characteristics of organic heterojunctions in the dark and under illumination.

  3. Polyaniline emeraldine salt in the amorphous solid state: polaron versus bipolaron.

    PubMed

    Canales, Manel; Torras, Juan; Fabregat, Georgina; Meneguzzi, Alvaro; Alemán, Carlos

    2014-10-01

    The polaronic and bipolaronic forms of polyaniline emeraldine salt (PAni-ES) in the amorphous solid state have been simulated using classical molecular dynamics (MD) and hybrid quantum mechanical/molecular mechanical-molecular dynamics (QM/MM-MD) approaches. It should be remarked that the electronic state of PAni-ES has been theoretically investigated in the gas phase, solution phase, and crystalline state, but this is the first study in the amorphous solid state, which is the most typical for this conducting polymer. MD simulations were carried out using force-field parametrizations explicitly developed for polaronic and bipolaronic models. QM/MM-MD calculations were performed using a quantum mechanical zone defined by four repeat units. In addition of the structural and electronic characteristics of the two forms of PAni-ES, MD and QM/MM-MD simulations indicate that the bipolaronic is the most stable state of amorphous PAni-ES. Complementary studies have been carried out using different experimental techniques. Although the morphology and topography of doped and undoped PAni are very similar, comparison of their UV-vis spectra supports the preference toward the bipolaronic form of PAni-ES.

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

    NASA Astrophysics Data System (ADS)

    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.

    2016-09-01

    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.

  5. 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

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

    PubMed

    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

    2016-09-01

    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.

  7. 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

  8. 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.

  9. Evidence for transition from polaron to bipolaron conduction in electroactive Li{sub x}Cr{sub 0.11}V{sub 2}O{sub 5.16} powders: A dynamic study from 10 to 10{sup 10} Hz

    SciTech Connect

    Badot, J.C.; Dubrunfaut, O.

    2011-12-15

    This paper presents a study on the electrical transport properties of lithiated Cr{sub 0.11}V{sub 2}O{sub 5.16}, which can be used as a rechargeable cathodic material in lithium batteries. Dielectric and conductivity spectra of Li{sub x}Cr{sub 0.11}V{sub 2}O{sub 5.16} powders (x=0, 0.05, 0.40 and 1.20) were recorded in a broad frequency range of 10-10{sup 10} Hz at temperature varying between 300 and 400 K. Complex resistivity diagrams have enabled to obtain thermal behaviors of bulk dc-conductivity. Dielectric relaxations were found, attributed to small polarons and (intersite) bipolarons hopping. The transport properties are shown to be consistent with small polaron and bipolaron conduction models. The change from polaronic to bipolaronic conduction has been evidenced with the increase of the lithium content x from 0.40 to 1.20. This work opens up new prospects for a more fundamental understanding of the electronic transport in relation with the electrochemical properties of Cr{sub 0.11}V{sub 2}O{sub 5.16}. - Graphical Abstract: Schematic structure of Cr{sub 0.11}V{sub 2}O{sub 5.16}. Highlights: Black-Right-Pointing-Pointer Chromium-vanadium mixed oxide as cathodic material. Black-Right-Pointing-Pointer Broadband dielectric spectroscopy from low frequencies to microwaves. Black-Right-Pointing-Pointer Transition from polaron to bipolaron conduction as lithium content increases.

  10. 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.

  11. Trimers, Molecules, and Polarons in Mass-Imbalanced Atomic Fermi Gases

    SciTech Connect

    Mathy, Charles J. M.; Parish, Meera M.; Huse, David A.

    2011-04-22

    We consider the ground state of a single ''spin-down'' impurity atom interacting attractively with a ''spin-up'' atomic Fermi gas. By constructing variational wave functions for polarons, molecules, and trimers, we perform a detailed study of the transitions between these dressed bound states as a function of mass ratio r=m{sub {up_arrow}}/m{sub {down_arrow}} and interaction strength. Crucially, we find that the presence of a Fermi sea enhances the stability of the p-wave trimer, which can be viewed as a Fulde-Ferrell-Larkin-Ovchinnikov molecule that has bound an additional majority atom. For sufficiently large r, we find that the transitions lie outside the region of phase separation of the imbalanced Fermi gas and should thus be observable in experiment, unlike the well-studied equal-mass case.

  12. Polaron-molecule transitions in a two-dimensional Fermi gas

    SciTech Connect

    Parish, Meera M.

    2011-05-15

    We address the problem of a single 'spin-down' impurity atom interacting attractively with a spin-up Fermi gas in two dimensions (2D). We consider the case where the mass of the impurity is greater than or equal to the mass of a spin-up fermion. Using a variational approach, we resolve the questions raised by previous studies and show that there is, in fact, a transition between polaron and molecule (dimer) ground states in 2D. For the molecule state, we use a variational wave function with a single particle-hole excitation on the Fermi sea and we find that its energy matches that of the exact solution in the limit of infinite impurity mass. Thus, we expect the variational approach to provide a reliable tool for investigating 2D systems.

  13. Single-polaron properties for double-well electron-phonon coupling

    NASA Astrophysics Data System (ADS)

    Adolphs, Clemens; Berciu, Mona

    2014-03-01

    We introduce a new model to describe electron-phonon coupling in systems such as one-dimensional intercalated chains or two-dimensional CuO2 planes, where symmetry dictates that the linear coupling term vanishes. We show that, under certain conditions, an additional charge carrier dynamically changes the local lattice potential from a harmonic well into a double well. We use the Momentum Average approximation to study the properties of this model in the single-polaron limit. A detailed analysis reveals that despite some qualitative similarities to the linear Holstein model, a renormalized Holstein model cannot account for all of the physics of the double-well model. We thank NSERC and QMI for financial support.

  14. Tunable spin-polaron state in a singly clamped semiconducting carbon nanotube

    NASA Astrophysics Data System (ADS)

    Pistolesi, F.; Shekhter, R.

    2015-07-01

    We consider a semiconducting carbon nanotube (CNT) lying on a ferromagnetic insulating substrate with one end passing the substrate and suspended over a metallic gate. We assume that the polarized substrate induces an exchange interaction acting as a local magnetic field for the electrons in the nonsuspended CNT side. Generalizing the approach of I. Snyman and Yu.V. Nazarov [Phys. Rev. Lett. 108, 076805 (2012), 10.1103/PhysRevLett.108.076805], we show that one can generate electrostatically a tunable spin-polarized polaronic state localized at the bending end of the CNT. We argue that at low temperatures manipulation and detection of the localized quantum spin state are possible.

  15. Polaronic quantum master equation theory of inelastic and coherent resonance energy transfer for soft systems.

    PubMed

    Yang, Lei; Devi, Murali; Jang, Seogjoo

    2012-07-14

    This work extends the theory of coherent resonance energy transfer [S. Jang, J. Chem. Phys. 131, 164101 (2009)] by including quantum mechanical inelastic effects due to modulation of donor-acceptor electronic coupling. Within the approach of the second order time local quantum master equation (QME) in the polaron picture and under the assumption that the bath degrees of freedom modulating the electronic coupling are independent of other modes, a general time evolution equation for the reduced system density operator is derived. Detailed expressions for the relaxation operators and inhomogeneous terms of the QME are then derived for three specific models of modulation in distance, axial angle, and dihedral angle, which are all approximated by harmonic oscillators. Numerical tests are conducted for a set of model parameters. Model calculation shows that the torsional modulation can make significant contribution to the relaxation and dephasing mechanisms.

  16. Direct observation of the spatial and temporal dynamics of polaron diffusion in SrTiO3

    NASA Astrophysics Data System (ADS)

    Kohmoto, T.; Ikeda, D.; Liang, X.; Moriyasu, T.

    2013-06-01

    The generation, relaxation, and diffusion dynamics of optically induced lattice distortion in the relaxed excited state of SrTiO3 are studied by using polarization spectroscopy with the pump-probe technique. The relaxed excited state is generated with a rise time on the order of 100 ps. Three kinds of thermal activation processes of the localized lattice distortion are found, and these processes are considered to be caused by photogenerated carriers in trapped states, which play important roles in photoluminescence or photoconductivity. We observed the lattice distortion induced by a separated pump beam from the probe beam to investigate its itineracy. The lattice-distortion signal appears later as the separation along the [100] axis becomes larger. The temperature dependence of the mobility suggests that the observed diffusive lattice distortion is caused by photogenerated electrons accompanied by lattice distortion, or electron polarons. Thus, the spatial and temporal dynamics of polaron diffusion were observed directly in our experiment.

  17. Real space imaging of spin polarons in Zn-doped SrCu(2)(BO(3))(2).

    PubMed

    Yoshida, M; Kobayashi, H; Yamauchi, I; Takigawa, M; Capponi, S; Poilblanc, D; Mila, F; Kudo, K; Koike, Y; Kobayashi, N

    2015-02-01

    We report on the real space profile of spin polarons in the quasi-two-dimensional frustrated dimer spin system SrCu(2)(BO(3))(2) doped with 0.16% of Zn. The (11)B nuclear magnetic resonance spectrum exhibits 15 additional boron sites near nonmagnetic Zn impurities. With the help of exact diagonalizations of finite clusters, we have deduced from the boron spectrum, the distribution of local magnetizations at the Cu sites with fine spatial resolution, providing direct evidence for an extended spin polaron. The results are confronted with those of other experiments performed on doped and undoped samples of SrCu(2)(BO(3))(2). PMID:25699459

  18. Long-lived localized magnetic polarons in ZnMnSe/ZnSSe type-II superlattices

    SciTech Connect

    Maksimov, A. A. Pashkov, A. V.; Brichkin, A. S.; Kulakovskii, V. D.; Tartakovskii, I. I.; Toropov, A. A.; Ivanov, S. V.

    2008-06-15

    The kinetics and polarized spectra of low-temperature photoluminescence in semiconductor type-II superlattices based on ZnMnSe/ZnSSe structures have been studied in detail. Processes responsible for the formation of short-lived (about 1 ns) and long-lived (above 10 ns) localized exciton-type magnetic polarons (EMPs) in these systems are determined, and the relative contributions due to magnetic and nonmagnetic localization of heavy holes to the formation of such polarons are evaluated. A phenomenological model is constructed that takes into account the energy distribution of charge-carrier traps with respect to their level depths and employs the EMP parameters determined for ZnMnSe quantum wells. Within the proposed model, all spectral, temporal, and temperature-dependent features in the behavior of magnetophotoluminescence observed for the system under consideration can be consistently and quantitatively described.

  19. New insights on the nature of two-dimensional polarons in semiconducting polymers: Infrared absorption in poly(3-hexylthiophene)

    SciTech Connect

    Pochas, Christopher M.; Spano, Frank C.

    2014-06-28

    Infrared absorption of positively charged polarons in conjugated polymer chains and π-stacked aggregates is investigated theoretically, employing a Holstein-based Hamiltonian which treats electronic coupling, electron-vibrational coupling, and disorder on equal footing. The spectra evaluated from the Hamiltonian expressed in a one- and two-particle basis set are essentially exact, insofar as the main, aromatic-quinoidal vibrational mode is treated fully nonadiabatically. Diagonal and off-diagonal (“paracrystalline”) disorder are resolved along the polymer axis (x) and the aggregate stacking axis (y). Disorder along the polymer axis selectively attenuates the x-polarized spectrum, which is dominated by the polaron peak P{sub 1}. Disorder along the stacking axis selectively attenuates the y-polarized spectrum, which is dominated by the lower-energy charge-transfer peak, DP{sub 1}. Calculated spectra are in excellent agreement with the measured induced-absorption and charge-modulation spectra, reproducing the peak positions and relative peak intensities within a line shape rich in vibronic structure. Our nonadiabatic approach predicts the existence of a weak, x-polarized peak P{sub 0}, slightly blueshifted from DP{sub 1}. The peak is intrinsic to single polymer chains and appears in a region of the spectrum where narrow infrared active vibrational modes have been observed in nonaggregated conjugated polymers. The polaron responsible for P{sub 0} is composed mainly of two-particle wave functions and cannot be accounted for in the more conventional adiabatic treatments.

  20. New insights on the nature of two-dimensional polarons in semiconducting polymers: Infrared absorption in poly(3-hexylthiophene)

    NASA Astrophysics Data System (ADS)

    Pochas, Christopher M.; Spano, Frank C.

    2014-06-01

    Infrared absorption of positively charged polarons in conjugated polymer chains and π-stacked aggregates is investigated theoretically, employing a Holstein-based Hamiltonian which treats electronic coupling, electron-vibrational coupling, and disorder on equal footing. The spectra evaluated from the Hamiltonian expressed in a one- and two-particle basis set are essentially exact, insofar as the main, aromatic-quinoidal vibrational mode is treated fully nonadiabatically. Diagonal and off-diagonal ("paracrystalline") disorder are resolved along the polymer axis (x) and the aggregate stacking axis (y). Disorder along the polymer axis selectively attenuates the x-polarized spectrum, which is dominated by the polaron peak P1. Disorder along the stacking axis selectively attenuates the y-polarized spectrum, which is dominated by the lower-energy charge-transfer peak, DP1. Calculated spectra are in excellent agreement with the measured induced-absorption and charge-modulation spectra, reproducing the peak positions and relative peak intensities within a line shape rich in vibronic structure. Our nonadiabatic approach predicts the existence of a weak, x-polarized peak P0, slightly blueshifted from DP1. The peak is intrinsic to single polymer chains and appears in a region of the spectrum where narrow infrared active vibrational modes have been observed in nonaggregated conjugated polymers. The polaron responsible for P0 is composed mainly of two-particle wave functions and cannot be accounted for in the more conventional adiabatic treatments.

  1. Pseudogap formation and unusual quasiparticle tunneling in cuprate superconductors: Polaronic and multiple-gap effects on the tunneling spectra

    NASA Astrophysics Data System (ADS)

    Dzhumanov, S.; Ganiev, O. K.; Djumanov, Sh. S.

    2013-10-01

    We propose new simple and generalized multiple-gap models of quasiparticle tunneling across the high-Tc cuprate superconductor (HTSC)/insulator/normal metal (SIN) junction based on the two different mechanisms for tunneling at positive and negative bias voltages, and the gap inhomogeneity (i.e., multiple-gap) picture. The tunneling of electrons from the normal metal into the quasiparticle states in HTSC with the BCS-type density of states (DOSs) takes place at V>0, while the tunneling of Cooper pairs and large polarons from the HTSC with the BCS DOS and quasi-free state DOS (which appears only in the dissociation of polarons) into the normal metal occurs at V<0. We show that most of the unusual features of tunneling spectra such as nearly U- and V-shaped subgap features, peak-dip-hump structure (appearing systematically at V<0) and asymmetry of the conductance peaks and their temperature and doping dependences, and shoulder-like features inside the main conductance peaks arise naturally in our specific models of SIN tunneling. The experimental tunneling spectra of Bi2Sr2CaCu2O8+δ are adequately reproduced by using the specific multiple-gap models and taking into account the distribution of BCS and polaronic gap values.

  2. Intermediate-coupling theory of the spin polaron in the t-J model

    NASA Astrophysics Data System (ADS)

    Barentzen, Heinz

    1996-03-01

    The spin polaron in the t-J model, i.e., a hole dressed by a cloud of virtual magnons of the antiferromagnetic spin background, is treated within the framework of intermediate-coupling theory. To this end the original t-J model is first reformulated in terms of spinless fermions and bosons by means of the generalized Dyson-Maleev representation (DMR). The latter may be regarded as the natural extension of the ordinary DMR of pure (undoped) spin systems to the case where holes are present, and is similar to the one originally proposed by Schmitt-Rink, Varma, and Ruckenstein. The reformulated t-J model, which is reminiscent of the Fröhlich Hamiltonian, is then subjected to a series of unitary transformations, analogous to those employed by Lee, Low, and Pines in their treatment of the Fröhlich polaron. Our approach yields an approximate quasiparticle energy E(k) as well as the corresponding eigenvector. To explore the range of validity of the theory presented here, the analytic expressions are then further analyzed for intermediate (J/t=0.4) and strong (J/t=0.08) coupling, where special attention is paid to the quasiparticle bandwidth W. The intermediate-coupling result for E(k) is in excellent agreement with the dispersion curve recently obtained by Dagotto and co-workers by means of a Green function Monte Carlo method. Surprisingly, even in the strong-coupling range the bandshape remains qualitatively correct. The bandwidth W is rather accurate for weak coupling (J/t>~3), as expected, and still reasonable in the intermediate range 0.4<~J/t<=3, where it deviates from the correct values by some 10-20 %. Our theory fails, however, to describe the proper behavior of W in the strong-coupling regime. This shows that the limitations of our approach manifest themselves in the bandwidths rather than in the shapes of the dispersion curves. Our conclusion is that intermediate-coupling theory is appropriate for J/t>~0.4, whereas a genuine strong-coupling theory is required

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

    PubMed

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

    2015-06-14

    The 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. PMID:25971627

  4. 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

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

    DOE PAGESBeta

    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.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

  6. 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.

  7. 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.

  8. Thickness dependent absorption and polaron photogeneration in poly-(2-metoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene-vinylene)

    NASA Astrophysics Data System (ADS)

    Petrović, J. P.; Matavulj, P. S.; Pinto, L. R.; Thapa, A.; Živanović, S. R.

    2012-06-01

    A comprehensive photocurrent spectra analysis of the ITO/PEDOT:PSS/MEH-PPV/Al devices with three different poly-(2-metoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene-vinylene) or MEH-PPV thin-film thicknesses is used to investigate charge carrier photogeneration in this polymer. The photocurrent is calculated based on the hole polaron drift-diffusion model including Poole-Frenkel (P-F) transport. Two mechanisms (monomolecular and Langevin-type bimolecular) for hole polaron recombination are considered separately. The MEH-PPV absorption coefficient spectra dependence on the thin film thickness is experimentally determined and included in our model. By comparing the simulated photocurrent spectra to measured data in the wide range of bias voltages and for devices with different MEH-PPV film thicknesses the polaron photogeneration quantum efficiency (θp) as a function of the electric field is extracted. The θp curves obtained for different devices are perfectly fitted by the P-F expression. It is shown that polaron photogeneration process in the thin MEH-PPV films is affected by the film thickness. A unique polaron photogeneration model which accounts for the field and thickness dependences is achieved when one of the P-F parameters is left to be thickness dependent.

  9. 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

  10. Excitons, polarons, and laser action in poly(p-phenylene vinylene) films

    NASA Astrophysics Data System (ADS)

    Österbacka, R.; Wohlgenannt, M.; Shkunov, M.; Chinn, D.; Vardeny, Z. V.

    2003-05-01

    We have used a multitude of linear and nonlinear cw optical spectroscopies to study the optical properties of water precursor poly(p-phenylene vinylene) (PPV) thin films. These spectroscopies include absorption, photoluminescence, photoinduced absorption and their respective optically detected magnetic resonance, and electroabsorption spectroscopy. We have studied singlet and triplet excitons, polarons, and laser action in PPV films. We found that the lowest-lying absorption band is excitonic in origin. It consists of two absorption components due to a bimodal distribution of the polymer chain conjugation lengths. Electroabsorption spectroscopy unambiguously shows the positions of the lowest-lying odd parity exciton 1Bu at 2.59 eV and two of the higher-lying even-parity excitons, namely, mAg at 3.4 eV and kAg at 3.7 eV. From these exciton energies we obtained a lower bound for the exciton binding energy in PPV, Eb(min)=E(mAg)-E(1Bu)=0.8 eV. The quantum efficiency spectrum for triplet exciton photogeneration consists of two contributions; the intersystem crossing and, at higher energies, singlet fission. From the onset of the singlet fission process at ESF=2ET, we could estimate the energy of the lowest-lying triplet exciton, 1 3Bu, at 1.55 eV, with a singlet-triplet splitting as large as 0.9 eV. From photoinduced absorption spectroscopy we measured the triplet-triplet transition, T→T*, to be 1.45 eV. The quantum efficiency spectrum for polaron photogeneration also consists of two contributions: one extrinsic and the other intrinsic. The latter shows a monotonically increasing function of energy with an energy onset at 3.3 eV. The intrinsic photogeneration process is analyzed with a model of free-electron-hole pair photogeneration, which separate more effectively at higher energy. The carrier generation quantum yield at 3.65 eV is estimated to be 0.5%. The quantum efficiency for photoluminescence, on the other hand, shows one single step-function process, with an

  11. New Models of Magnetic Interactions for Bound Magnetic Polarons in Dilute Magnetic Semiconductors

    NASA Astrophysics Data System (ADS)

    McIntyre, Cynthia R.

    The goal of the first part of this thesis is to develop a solvable model that better approximates the true exchange Hamiltonian of bound magnetic polarons (BMPs). The model replaces the single exchange constant (one-step) of the previous model by two exchange parameters (two-steps) of different coupling strengths. This formulation of the Hamiltonian breaks up some of the degeneracy of the one -step model. Determination of the relevant parameters is done using a Feynman (17) variational method. This method gives the optimal values for parameters in the model. A comparison of parameters, significant to the one-step model, using Feynman's variational method and a technique by Ryabchenko (14) will be presented. The second part of this thesis will focus on the effects of anisotropic exchange interaction, Dzyaloshinski (15) -Moriya (16) (DM) interaction, on the magnetization of the dilute magnetic semiconductors. Anisotropic exchange (DM) is the largest of the known non-spin conserving interactions. Because of its non-spin conserving property, anisotropic exchange is a probable mechanism for affecting the magnetization of Mn^{+2} pairs. Recent experimental research (22) on these materials has focused on the contribution of the DM interaction at the energy level crossings of Mn^{+2} pairs. We calculate the contribution of DM to the magnetization and compare to the linewidth of magnetization steps obtained from experiment. Also, we theoretically investigate the role of spin-lattice interactions on the relaxation of Mn^{+2} pairs and compare the theoretical time to the estimated experimental time (22). (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.) (Abstract shortened with permission of school.).

  12. Polaron-induced lattice distortion of (In,Ga)As/GaAs quantum dots by optically excited carriers.

    PubMed

    Tiemeyer, S; Bombeck, M; Göhring, H; Paulus, M; Sternemann, C; Nase, J; Wirkert, F J; Möller, J; Büning, T; Seeck, O H; Reuter, D; Wieck, A D; Bayer, M; Tolan, M

    2016-10-21

    We report on a high resolution x-ray diffraction study unveiling the effect of carriers optically injected into (In,Ga)As quantum dots on the surrounding GaAs crystal matrix. We find a tetragonal lattice expansion with enhanced elongation along the [001] crystal axis that is superimposed on an isotropic lattice extension. The isotropic contribution arises from excitation induced lattice heating as confirmed by temperature dependent reference studies. The tetragonal expansion on the femtometer scale is tentatively attributed to polaron formation by carriers trapped in the quantum dots.

  13. Polaron-induced lattice distortion of (In,Ga)As/GaAs quantum dots by optically excited carriers

    NASA Astrophysics Data System (ADS)

    Tiemeyer, S.; Bombeck, M.; Göhring, H.; Paulus, M.; Sternemann, C.; Nase, J.; Wirkert, F. J.; Möller, J.; Büning, T.; Seeck, O. H.; Reuter, D.; Wieck, A. D.; Bayer, M.; Tolan, M.

    2016-10-01

    We report on a high resolution x-ray diffraction study unveiling the effect of carriers optically injected into (In,Ga)As quantum dots on the surrounding GaAs crystal matrix. We find a tetragonal lattice expansion with enhanced elongation along the [001] crystal axis that is superimposed on an isotropic lattice extension. The isotropic contribution arises from excitation induced lattice heating as confirmed by temperature dependent reference studies. The tetragonal expansion on the femtometer scale is tentatively attributed to polaron formation by carriers trapped in the quantum dots.

  14. Polaron-induced lattice distortion of (In,Ga)As/GaAs quantum dots by optically excited carriers.

    PubMed

    Tiemeyer, S; Bombeck, M; Göhring, H; Paulus, M; Sternemann, C; Nase, J; Wirkert, F J; Möller, J; Büning, T; Seeck, O H; Reuter, D; Wieck, A D; Bayer, M; Tolan, M

    2016-10-21

    We report on a high resolution x-ray diffraction study unveiling the effect of carriers optically injected into (In,Ga)As quantum dots on the surrounding GaAs crystal matrix. We find a tetragonal lattice expansion with enhanced elongation along the [001] crystal axis that is superimposed on an isotropic lattice extension. The isotropic contribution arises from excitation induced lattice heating as confirmed by temperature dependent reference studies. The tetragonal expansion on the femtometer scale is tentatively attributed to polaron formation by carriers trapped in the quantum dots. PMID:27622774

  15. 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.

  16. 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.

  17. 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.

  18. Formation of polaron pairs and time-resolved photogeneration of free charge carriers in π-conjugated polymers

    NASA Astrophysics Data System (ADS)

    Frankevich, Eugene; Ishii, Hisao; Hamanaka, Yasushi; Yokoyama, Takahiro; Fuji, Akihiko; Li, Sergey; Yoshino, Katsumi; Nakamura, Arao; Seki, Kazuhiko

    2000-07-01

    We have performed in the present work time-resolved experiments on poly(3-dodecyl-thiophene) (P3DDT) and poly(2,5-dioctyloxy-p-phenylene vinylene) (OO-PPV) films by directly probing the formation of charge carriers responsible for the cw photoconductivity within the time domain of -10 ps to 1 ns. Laser light pulses of 400 nm wavelength, 150 fs width, induced photoconductivity in a sample with a frequency 1 kHz. Red 800 nm light pulses delayed in respect to blue ones were revealed to affect the photoconductivity. The effect of the second pulses increased with the delay time. Red light induced changes of the photoconductivity were positive in OO-PPV, and negative in P3DDT. These results are rationalized as an evidence of delayed not immediate formation of free charge carriers. The carriers seem to be formed within 10 ps after the pumping pulse. A mechanism of formation of free polarons from polaron pair is suggested, which has permitted to explain main feature of the results including different signs of the effect of the red light in different polymers.

  19. High Pressure Study of Delocalized Polarons in 2-D Lamellar Structure of Regio-Regular Poly(3-alkylthiophene) Films

    NASA Astrophysics Data System (ADS)

    An, C. P.; Jiang, X. M.; Vardeny, Z. V.

    2001-03-01

    The long-lived photoexcitations in poly(3-alkylthiophene) [P3AT] having a high head-to-tail ratio, the so called regio-regular (RR) P3AT, have been extensively studied by the photoinduced absorption (PA) spectroscopy using a FTIR spectrometer. In particular, delocalized polarons with DP1 (low energy) and DP2 (high energy) PA bands were observed in the self-assembled two-dimensional lamellar structure of RR P3AT films.(R. Osterbacka et al, Science, 287), p839 (2000) DP1 with a peak at ~0.1 eV is expected to red-shift as the interlayer distance decreases. This was indirectly confirmed before in the experiments by observing a red-shift in DP1 band as the aklyl sidegroup of the P3AT polymer decreases from dodecyl to hexyl.^2 In the present work we have succeeded, for the first time, to measure infrared PA spectra down to 400 cm-1 under high hydrostatic pressure up to 50 kbar with a diamond anvil cell. This technique was applied to RR P3AT in order to test the effect of the change in the interlayer distance for the same alkyl sidegroup, which is induced by the high pressure. We found that the first moment of the DP1 band red-shifts as the pressure increases. This result is in agreement with the delocalized polaron model in the lamellar structure.

  20. Electron and hole polaron accumulation in low-bandgap ambipolar donor-acceptor polymer transistors imaged by infrared microscopy

    NASA Astrophysics Data System (ADS)

    Khatib, O.; Mueller, A. S.; Stinson, H. T.; Yuen, J. D.; Heeger, A. J.; Basov, D. N.

    2014-12-01

    A resurgence in the use of the donor-acceptor approach in synthesizing conjugated polymers has resulted in a family of high-mobility ambipolar systems with exceptionally narrow energy bandgaps below 1 eV. The ability to transport both electrons and holes is critical for device applications such as organic light-emitting diodes and transistors. Infrared spectroscopy offers direct access to the low-energy excitations associated with injected charge carriers. Here we use a diffraction-limited IR microscope to probe the spectroscopic signatures of electron and hole injection in the conduction channel of an organic field-effect transistor based on an ambipolar DA polymer polydiketopyrrolopyrrole-benzobisthiadiazole. We observe distinct polaronic absorptions for both electrons and holes and spatially map the carrier distribution from the source to drain electrodes for both unipolar and ambipolar biasing regimes. For ambipolar device configurations, we observe the spatial evolution of hole-induced to electron-induced polaron absorptions throughout the transport path. Our work provides a platform for combined transport and infrared studies of organic semiconductors on micron length scales relevant to functional devices.

  1. Polaron and ion diffusion in a poly(3-hexylthiophene) thin-film transistor gated with polymer electrolyte dielectric

    NASA Astrophysics Data System (ADS)

    Mills, T.; Kaake, L. G.; Zhu, X.-Y.

    2009-04-01

    Electrolytes are finding applications as dielectric materials in low-voltage organic thin-film transistors (OTFT). The presence of mobile ions in these materials (polymer electrolytes or ion gels) gives rise to very high capacitance (>10 μF/cm2) and thus low transistor turn-on voltage. In order to establish fundamental limits in switching speeds of electrolyte gated OFETs, we carry out in situ optical spectroscopy measurement of a poly(3-hexylthiophene) (P3HT) OTFT gated with a LiClO4:poly(ethyleneoxide) (PEO) dielectric. Based on spectroscopic signatures of molecular vibrations and polaron transitions, we quantitatively determine charge carrier concentration and diffusion constants. We find two distinctively different regions: at V G≥-1.5 V, drift-diffusion (parallel to the semiconductor/dielectric interface) of hole-polarons in P3HT controls charging of the device; at V G<-1.5 V, electrochemical doping of the entire P3HT film occurs and charging is controlled by drift/diffusion (perpendicular to the interface) of ClO4 - counter ions into the polymer semiconductor.

  2. Role of polaron hopping in leakage current behavior of a SrTiO3 single crystal

    NASA Astrophysics Data System (ADS)

    Cao, Y.; Bhattacharya, S.; Shen, J.; Randall, C. A.; Chen, L. Q.

    2013-12-01

    We studied the ionic/electronic transport and resistance degradation behavior of dielectric oxides by solving the electrochemical transport equations. Here, we took into account the non-periodical boundary conditions for the transport equations using the Chebyshev collocation algorithm. A sandwiched Ni|SrTiO3|Ni capacitor is considered as an example under the condition of 1.0 V, 1.0 μm thickness for SrTiO3 layer, and a temperature of 150 °C. The applied voltage resulted in the migration of ionic defects (oxygen vacancies) from anode towards cathode. The simulated electric potential profile at steady state is in good agreement with the recent experimental observation. We introduced the possibility of polaron-hopping between Ti3+ and Ti4+ at the electrode interface. It is shown that both the oxygen vacancy transport and the polaron-hopping contribute to the resistance degradation of single crystal SrTiO3, which is consistent with the experimental observations.

  3. Role of polaron hopping in leakage current behavior of a SrTiO{sub 3} single crystal

    SciTech Connect

    Cao, Y. Randall, C. A.; Chen, L. Q.; Bhattacharya, S.; Shen, J.

    2013-12-14

    We studied the ionic/electronic transport and resistance degradation behavior of dielectric oxides by solving the electrochemical transport equations. Here, we took into account the non-periodical boundary conditions for the transport equations using the Chebyshev collocation algorithm. A sandwiched Ni|SrTiO{sub 3}|Ni capacitor is considered as an example under the condition of 1.0 V, 1.0 μm thickness for SrTiO{sub 3} layer, and a temperature of 150 °C. The applied voltage resulted in the migration of ionic defects (oxygen vacancies) from anode towards cathode. The simulated electric potential profile at steady state is in good agreement with the recent experimental observation. We introduced the possibility of polaron-hopping between Ti{sup 3+} and Ti{sup 4+} at the electrode interface. It is shown that both the oxygen vacancy transport and the polaron-hopping contribute to the resistance degradation of single crystal SrTiO{sub 3}, which is consistent with the experimental observations.

  4. 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.

  5. 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. PMID:25933748

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    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.

  7. Effect of Förster-mediated triplet-polaron quenching and triplet-triplet annihilation on the efficiency roll-off of organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    We report the results of a systematic study of the interplay of triplet-polaron quenching (TPQ) and triplet-triplet annihilation (TTA) on the efficiency roll-off of organic light-emitting diodes (OLEDs) with increasing current density. First, we focus on OLEDs based on the green phosphorescent emitter tris[2-phenylpyridine]iridium(III) (Ir(ppy)3) and the red phosphorescent dye platinum octaethylporphyrin. It is found that the experimental data can be reproduced using kinetic Monte Carlo (kMC) simulations within which TPQ and TTA are due to a nearest-neighbor (NN) interaction, or due to a more long-range Förster-type process. Furthermore, we find a subtle interplay between TPQ and TTA: decreasing the contribution of one process can increase the contribution of the other process, so that the roll-off is not significantly reduced. Furthermore, we find that just analyzing the shape of the roll-off is insufficient for determining the relative role of TPQ and TTA. Subsequently, we investigate the wider validity of this picture using kMC simulations for idealized but realistic symmetric OLEDs, with an emissive layer containing a small concentration of phosphorescent dye molecules in a matrix material. Whereas for NN-interactions the roll-off can be reduced when the dye molecules act as shallow hole and electron traps, we find that such an approach becomes counterproductive for long-range TTA and TPQ. Developing well-founded OLED design rules will thus require that more quantitative information is available on the rate and detailed mechanism of the TPQ and TTA processes.

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

    PubMed Central

    2009-01-01

    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 (P2at 1.45 eV) and delocalized (DP2at 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. PMID:20652147

  9. 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

  10. 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

  11. 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.

  12. Nonlinear lattice relaxation of photogenerated charge-transfer excitation in halogen-bridged mixed-valence metal complexes. II. Polaron channel

    NASA Astrophysics Data System (ADS)

    Mishima, A.; Nasu, K.

    1989-03-01

    The one-dimensional extended Peierls-Hubbard model with half-filled-band electrons is studied in order to clarify the lattice relaxation path of the photogenerated charge-transfer excitation in halogen-bridged mixed-valence metal complexes. The ground and excited states are calculated within mean-field theory for electrons and the adiabatic approximation for phonons. It is concluded that the main origin of the photoinduced absorption is a distant pair of the hole-polaron and the electron-polaron. This distant pair is created not from the ground state of the self-trapped exciton (STE), but from the excited states of the STE through their autodissociation. This is consistent with the experiment on the excitation energy dependence of the photoinduced absorption yield.

  13. Photogeneration of self-localized polarons in YBa2Cu3O(7-delta) and La2CuO4

    NASA Astrophysics Data System (ADS)

    Kim, Y. H.; Foster, C. M.; Heeger, A. J.; Cox, S.; Acedo, L.

    1989-01-01

    Photoinduced IR absorption measurements of YBa2Cu3O(7-delta) (delta = 0.75) and La2CuO4 are reported. Photoinduced IR active vibrational modes and associated phonon bleachings which indicate the formation of a localized structural distortion in the Cu-O plane around the photogenerated carriers are observed. In both materials, an associated electronic transition indicates that this structural distortion causes the formation of a self-localized electronic state in the energy gap. The photoinduced distortion and the associated self-localized gap state demonstrate that the photoexcitations are relatively long-lived polarons (or bipolarons). It is found that polaron (or bipolaron) formation plays an important role in the high temperature superconductivity.

  14. 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

  15. 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.

  16. Kinetic Monte Carlo Study of Ambipolar Lithium Ion and Electron–Polaron Diffusion into Nanostructured TiO2

    SciTech Connect

    Yu, Jianguo; Sushko, Maria L.; Kerisit, Sebastien N.; Rosso, Kevin M.; Liu, Jun

    2012-08-02

    Nanostructured titania (TiO2) polymorphs have proved to be promising electrode materials for next generation lithium-ion batteries. However, there is still a lack of understanding of the fundamental microscopic processes that control charge transport in these materials. Here we present microscopic simulations of the collective dynamics of lithium-ion (Li+) and charge compensating electron polarons (e-) in rutile TiO2 nanoparticles in contact with idealized conductive matrix and electrolyte. Kinetic Monte Carlo simulations are used, parameterized by molecular dynamics-based predictions of activation energy barriers for Li+ and e- diffusion. Simulations reveal the central role of electrostatic coupling between Li+ and e- on their collective drift diffusion at the nanoscale. They also demonstrate that high contact area between conductive matrix and rutile nanoparticles leads to undesirable coupling-induced surface saturation effects during Li+ insertion, which limits the overall capacity and conductivity of the material. These results help provide guidelines for design of nanostructured electrode materials with improved electrochemical performance.

  17. Optimal Shell Thickness of Metal@Insulator Nanoparticles for Net Enhancement of Photogenerated Polarons in P3HT Films.

    PubMed

    Goh, Wei-Peng; Williams, Evan L; Yang, Ren-Bin; Koh, Wee-Shing; Mhaisalkar, Subodh; Ooi, Zi-En

    2016-02-01

    Embedding metal nanoparticles in the active layer of organic solar cells has been explored as a route for improving charge carrier generation, with localized field enhancement as a proposed mechanism. However, embedded metal nanoparticles can also act as charge recombination sites. To suppress such recombination, the metal nanoparticles are commonly coated with a thin insulating shell. At the same time, this insulating shell limits the extent that the localized enhanced electric field influences charge generation in the organic medium. It is presumed that there is an optimal thickness which maximizes field enhancement effects while suppressing recombination. Atomic Layer Deposition (ALD) was used to deposit Al2O3 layers of different thicknesses onto silver nanoparticles (Ag NPs), in a thin film of P3HT. Photoinduced absorption (PIA) spectroscopy was used to study the dependence of the photogenerated P3HT(+) polaron population on the Al2O3 thickness. The optimal thickness was found to be 3-5 nm. This knowledge can be further applied in the design of metal nanoparticle-enhanced solar cells.

  18. 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.

  19. 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. PMID:27367366

  20. 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.

  1. 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.

  2. 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

  3. 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

  4. Triplets in extended nematic liquid crystals and polarons in their blends

    NASA Astrophysics Data System (ADS)

    Tsoi, Wing C.; O'Neill, Mary; Aldred, Matthew P.; Vlachos, Panos; Kelly, Stephen M.

    2007-09-01

    Photoinduced absorption shows that triplets are the primary photoexcited species in a series of conjugated liquid crystals containing thiophene and fluorene groups. We find that the triplet generation rate can be varied substantially by molecular design. The introduction of extra thiophene groups into the elongated molecules changes the intersystem crossing rate by over two orders of magnitude, while modifying the singlet and triplet energies by only small amounts. This result is attributed to the high spin-orbit coupling constant of sulfur: An increase in the number of sulfur atoms increases the spin-orbit coupling between the singlet and triplet states. These results are relevant to the design of organic light emitting diodes, lasers, and other devices where triplet formation has a major impact on device performance. The molecules are shown to act as effective electron donors when blended with a perylene molecule which acts as an electron acceptor. The electron transfer rate is faster than the singlet lifetime so that the blend shows the efficient charge separation required for a photovoltaic device.

  5. 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.

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

    DOE PAGESBeta

    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.; et al

    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

  7. Photogeneration of self-localized polarons in YBa2 Cu3O7-delta and La2CuO4

    NASA Astrophysics Data System (ADS)

    Kim, Y. H.; Foster, C. M.; Heeger, A. J.; Cox, S.; Acedo, L.

    1988-08-01

    Photoinduced infrared absorption measurements of YBa2Cu3O7-delta (delta=0.75) and La2CuO4 are reported. We have observed photoinduced infrared active vibrational modes and associated phonon bleachings which indicate the formation of a localized structural distortion in the Cu-O plane around the photogenerated carriers. In both materials, an associated electronic transition indicates that this structural distortion causes the formation of a self-localized electronic state in the energy gap. The photoinduced distortion and the associated self-localized gap state demonstrate that the photoexcitations are relatively long-lived polarons (or bipolarons). The dynamic mass associated with the distortion is smaller in YBa2Cu3O7-delta than in La2CuO4 (smaller dynamic mass implies a longer range distortion). Since these features are not observed in the isostructural compound, La2NiO4, we suggest that polaron (or bipolaron) formation may play an important role in the high temperature superconductivity.

  8. 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

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

    NASA Astrophysics Data System (ADS)

    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

    2015-10-01

    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.

  10. 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.

  11. 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.

  12. Photogenerated carriers in La 2CuO 4, YBa 2Cu 3O 7-δ, and Tl 2Ba 2Ca (1-x)Gd xCu 2O 8: Polarizability-induced pairing of polarons

    NASA Astrophysics Data System (ADS)

    Foster, C. M.; Heeger, A. J.; Kim, Y. H.; Stucky, G.; Herron, N.

    1989-12-01

    Photoinduced absorption measurements have been carried out on Tl 2Ba 2Ca (1-x)Gd xCu 2O 8 (x=0.02), YBa 2Cu 3O 7-δ (δ=0.75) and La 2CuO 4. The observation of infrared active vibrational (IRAV) modes and an associated electronic transition with common intensity and temperature dependence indicate the formation of self-localized polarons as photogenerated carriers. The photoinduced electronic transition deep in the infrared implies a major shift of oscillator strength leading to a large local polarizability in the vicinity of the polaron. We suggest that the enhanced local polarizability may provide an important mechanism for pairing.

  13. Self-localization of a small number of Bose particles in a superfluid Fermi system

    SciTech Connect

    Targonska, Katarzyna; Sacha, Krzysztof

    2010-09-15

    We consider self-localization of a small number of Bose particles immersed in a large homogeneous superfluid mixture of fermions in three- and one-dimensional space. Bosons distort the density of surrounding fermions and create a potential well where they can form a bound state analogous to a small polaron state. In the three-dimensional volume, we observe the self-localization for repulsive interactions between bosons and fermions. In the one-dimensional case, bosons self-localize as well for attractive interactions, thereby forming, together with a pair of fermions at the bottom of the Fermi sea, a vector soliton. We analyze also thermal effects and show that small nonzero temperature affects the pairing function of the Fermi subsystem and has little influence on the self-localization phenomena.

  14. 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.

  15. 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.

  16. Small Wins.

    ERIC Educational Resources Information Center

    Rhatigan, James J.; Schuh, John H.

    2003-01-01

    Examines how it easy for people to overlook small successes when they are overwhelmed by and preoccupied with large projects and goals. Explores the concept of "small wins" in organizational theory, which have the potential to become a prominent part of institutional culture and impact organizational behavior and change. (GCP)

  17. Small Cultures.

    ERIC Educational Resources Information Center

    Holliday, Adrian

    1999-01-01

    Presents a notion of small culture as an alternative to what has become the default notion of large culture in applied linguistics, social science, and popular usage. A small-culture view of English-language curriculum settings reveals mismatches between professional-academic and organizational cultures at the mezzo level of the institution. (VWL)

  18. 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.

  19. 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. PMID:26831598

  20. 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.

  1. Small satellites

    NASA Technical Reports Server (NTRS)

    Thomas, P.; Veverka, J.; Dermott, S.

    1986-01-01

    Satellites smaller than Mimas (r = 195 km) are distinguished by irregular overall shapes and by rough limb topography. Material properties and impact cratering dominate the shaping of these objects. Long fragmentation histories can produce a variety of internal structures, but so far there is no direct evidence that any small satellite is an equilibrium ellipsoid made up of noncohesive gravitationally bound rubble. One many bodies that orbit close to their primary the tidal and rotational components of surface gravity strongly affect the directions of local g and thereby affect the redistribution of regolith by mass wasting. Downslope movement of regolith is extensive on Deimos, and is probably effective on many other small satellites. It is shown that in some cases observed patterns of downslope mass wasting cold produce useful constraints on the satellite's mean density. The diversity of features seen in the few high-resolution images of small satellites currently available suggests that these objects have undergone complex histories of cratering, fragmentation, and regolith evolution.

  2. The effects of optical phonon on the binding energy of bound polaron in a wurtzite ZnO/Mg{sub x}Zn{sub 1–x}O quantum well

    SciTech Connect

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

    2014-07-07

    An improved Lee-Low-Pines intermediate coupling method is used to study the energies and binding energies of bound polarons in a wurtzite ZnO/Mg{sub x}Zn{sub 1–x}O quantum well. The contributions from different branches of long-wave optical phonons, i.e., confined optical phonons, interface optical phonons, and half-space optical phonons are considered. In addition to electron-phonon interaction, the impurity-phonon interaction, and the anisotropy of material parameters, such as phonon frequency, electron effective mass, and dielectric constant, are also included in our computation. Ground-state energies, binding energies and detailed phonon contributions from various phonons as functions of well width, impurity position and composition are presented. Our result suggests that total phonon contribution to ground state and binding energies in the studied wurtzite ZnO/Mg₀.₃Zn₀.₇O quantum wells varies between 28–23 meV and 62–45 meV, respectively, which are much larger than the corresponding values (about 3.2–1.8 meV and 1.6–0.3 meV) in GaAs/Al₀.₃Ga₀.₇As quantum wells. For a narrower quantum well, the phonon contribution mainly comes from interface and half-space phonons, for a wider quantum well, most of phonon contribution originates from confined phonons. The contribution from all the phonon modes to binding energies increases slowly either when impurity moves far away from the well center in the z direction or with the increase in magnesium composition (x). It is found that different phonons have different influences on the binding energies of bound polarons. Furthermore, the phonon contributions to binding energies as functions of well width, impurity position, and composition are very different from one another. In general, the electron-optical phonon interaction and the impurity center-optical phonon interaction play an important role in electronic states of ZnO-based quantum wells and cannot be neglected.

  3. 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.

  4. 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

  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 resection

    MedlinePlus

    Small intestine surgery; Bowel resection - small intestine; Resection of part of the small intestine; Enterectomy ... her hand inside your belly to feel the intestine or remove the diseased segment. Your belly is ...

  7. Small bowel bacterial overgrowth

    MedlinePlus

    Overgrowth - intestinal bacteria; Bacterial overgrowth - intestine; Small intestinal bacterial overgrowth; SIBO ... Most of the time, the small intestine does not have a high number ... in the small intestine may use up the nutrients needed by the ...

  8. 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 ...

  9. Peculiar oxygen and copper isotope effects on the pseudogap formation temperature in underdoped to overdoped cuprates: Pseudogap induced by pairing correlations above Tc in cuprates with large and small Fermi surfaces

    NASA Astrophysics Data System (ADS)

    Dzhumanov, S.; Khudayberdiev, Z. S.; Djumanov, Sh. S.

    2015-05-01

    We investigate the pseudogap (PG) state and the peculiar oxygen and copper isotope effects on the PG onset temperature T* in cuprate superconductors with large and small Fermi surfaces within the polaron model and two different BCS-based approaches extended to the intermediate coupling regime. We argue that the unconventional electron-phonon interactions are responsible for the polaron formation and BCS-like pairing correlations above Tc in underdoped to overdoped cuprates, which are exotic (non-BCS) superconductors. Using the generalized BCS-like theory, we calculate pseudogap formation temperatures T*, isotope shifts ΔT*, oxygen and copper isotope exponents (i.e. αT*O and αT*Cu) and show that isotope effects on T* strongly depend on strengths of Coulomb and electron-phonon interactions, doping levels and dielectric constants of the cuprates. This theory explains the existence of small positive or sign reversed oxygen isotope effect, sizable and very large negative oxygen and copper isotope effects on T* in cuprates with large Fermi surfaces. Further, we use another version of the extended BCS-like model to study the PG formation and the peculiar isotope effects on T* in deeply underdoped cuprates with small Fermi surfaces and predict the existence of small and sizable negative oxygen and copper isotope effects on T* in such underdoped cuprates. The results for T*, isotope shifts ΔT* and exponents (αT*O and αT*Cu) in different classes of high-Tc cuprates are in good agreement with the existing well-established experimental data and explain the controversy between various experiments on isotope effects for T* in the cuprates.

  10. Small Claims Court.

    ERIC Educational Resources Information Center

    McKitric, Eloise; Davis, Janet

    The study examined individuals and companies who used small claims courts and the results of decisions reached in small claims cases. A review of studies including an empirical study of two Ohio small claims courts monitored for 12 months made it clear that small claims courts need to be examined to determine if utilization and accessibility to…

  11. 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.

  12. Localization properties of electronic states in a polaron model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers.

    PubMed

    Yamada, H; Starikov, E B; Hennig, D; Archilla, J F R

    2005-06-01

    We numerically investigate localization properties of electronic states in a static model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with realistic parameters obtained by quantum-chemical calculation. The randomness in the on-site energies caused by the electron-phonon coupling is completely correlated to the off-diagonal parts. In the single electron model, the effect of the hydrogen-bond stretchings, the twist angles between the base pairs and the finite system size effects on the energy dependence of the localization length and on the Lyapunov exponent are given. The localization length is reduced by the influence of the fluctuations in the hydrogen bond stretchings. It is also shown that the helical twist angle affects the localization length in the poly(dG)-poly(dC) DNA polymer more strongly than in the poly(dA)-poly(dT) one. Furthermore, we show resonance structures in the energy dependence of the localization length when the system size is relatively small. PMID:15906117

  13. Small bowel resection - discharge

    MedlinePlus

    Eat small amounts of food several times a day. DO NOT eat 3 big meals. You should: Space out your small meals. Wait the same amount of time between each one. Add new foods back into your diet slowly, one ...

  14. 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 ...

  15. 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…

  16. Small Colleges, Big Missions.

    ERIC Educational Resources Information Center

    Griffin, W. A., Jr., Ed.

    This monograph by the members of the American Association of Community Colleges' Commission on Small and/or Rural Community Colleges shares small and rural community college experiences. In "Leaders through Community Service," Jacqueline D. Taylor provides a model for how small and rural community colleges can be involved in building leaders…

  17. Small turbines, big unknown

    SciTech Connect

    Gipe, P.

    1995-07-01

    While financial markets focus on the wheeling and dealing of the big wind companies, the small wind turbine industry quietly keeps churning out its smaller but effective machines. Some, the micro turbines, are so small they can be carried by hand. Though worldwide sales of small wind turbines fall far short of even one large windpower plant, figures reach $8 million to $10 million annually and could be as much as twice that if batteries and engineering services are included.

  18. Is Small Business Doomed?

    ERIC Educational Resources Information Center

    Business Education Forum, 1979

    1979-01-01

    Provides a sampling of viewpoints from businessmen, economists, futurists, and government experts on the future of small business presented at hearings before the Subcommittee on Antitrust, Consumers, and Employment, Committee on Small Business, House of Representatives. Problems of taxes, the economy, and government regulations are discussed from…

  19. 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…

  20. Small Group Inquiry.

    ERIC Educational Resources Information Center

    Koller, Martin M.

    Learning in small groups is a practical way to bring about behavior change. The inquiry learning process is perceived to be the most natural and scientific way of learning. Skills developed include those of problem-solving task analysis, decision-making, value formation and adaptability. The art of small group interaction is developed. Factual…

  1. 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…

  2. 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,…

  3. 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…

  4. 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…

  5. 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…

  6. Veterans in Small Business.

    ERIC Educational Resources Information Center

    American Association of Community and Junior Colleges, Washington, DC. National Small Business Training Network.

    These materials provide information on conducting small business training seminars for veterans. First, a discussion is presented of the development of the guide based on 1983 field testing of the seminar and evaluations conducted by Small Business Administration (SBA) officials, the seminar contracts, and trainers. The next sections deal with the…

  7. 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.

  8. The Small Business Tradition.

    ERIC Educational Resources Information Center

    Dicke, Thomas S.

    1996-01-01

    Recognizes and discusses the special place that small business occupies, not only in American history, but also in American thought and culture. Examines the various conflicts between big and small business. Notes that the division of territory, products, and services between the two is largely defined by economies of scale. (MJP)

  9. 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.

  10. Small intestinal ischemia and infarction

    MedlinePlus

    ... small intestine; Atherosclerosis - small intestine; Hardening of the arteries - small intestine ... Embolus: Blood clots can block one of the arteries supplying the intestine. People who have had a ...

  11. 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

  12. Small Intestinal Bacterial Overgrowth

    PubMed Central

    Dukowicz, Andrew C.; Levine, Gary M.

    2007-01-01

    Small intestinal bacterial overgrowth (SIBO), defined as excessive bacteria in the small intestine, remains a poorly understood disease. Initially thought to occur in only a small number of patients, it is now apparent that this disorder is more prevalent than previously thought. Patients with SIBO vary in presentation, from being only mildly symptomatic to suffering from chronic diarrhea, weight loss, and malabsorption. A number of diagnostic tests are currently available, although the optimal treatment regimen remains elusive. Recently there has been renewed interest in SIBO and its putative association with irritable bowel syndrome. In this comprehensive review, we will discuss the epidemiology, pathogenesis, clinical manifestations, diagnosis, and treatment of SIBO. PMID:21960820

  13. Polaron models of high-temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Mott, N. F.

    1993-01-01

    A review is given of theories of high-temperature superconductors in which the current is carried by bipolarons, which form a condensed Bose gas below Tc and a non-degenerate gas above it. Such theories were first proposed by Schafroth, Alexandrov, Ranninger and de Jongh; the present author has, for the copper oxide materials, proposed spin bipolarons. Experimental work has, however, shown no magnetic moments in the superconducting and “spin glass” ranges of composition; a modification of the spin bipolaron model is proposed to take account of these observations. Other aspects of the model are discussed, particularly heat conduction and the effect of disorder. A comparison is made with the cubic bismuth materials.

  14. Magnetic monopole polarons in artificial spin ices

    NASA Astrophysics Data System (ADS)

    Chern, Gia-Wei; Mellado, Paula

    2016-05-01

    Emergent quasiparticles that arise from the fractionalization of the microscopic degrees of freedom have been one of the central themes in modern condensed-matter physics. The notion of magnetic monopoles, freely moving quasiparticles fragmented from local dipole excitations, has enjoyed much success in understanding the thermodynamic, static, and transport properties of the so-called spin-ice materials. The artificial version of spin ice, where a lattice of nanoscale magnetic dipoles is sculpted out of a ferromagnetic film, provides a unique opportunity to study these unusual quasiparticles in a material-by-design approach. Here we show that the elementary excitations in the ice phase of a nano-magnetic array arranged in the pentagonal lattice are composite objects comprised of the emergent monopole and a surrounding cloud of opposite uncompensated magnetic charges.

  15. 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.

  16. Small intestine (image)

    MedlinePlus

    The small intestine is the portion of the digestive system most responsible for absorption of nutrients from food into the bloodstream. The pyloric sphincter governs the passage of partly digested food ...

  17. 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.

  18. 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.

  19. Small Intestinal Infections.

    PubMed

    Munot, Khushboo; Kotler, Donald P

    2016-06-01

    Small intestinal infections are extremely common worldwide. They may be bacterial, viral, or parasitic in etiology. Most are foodborne or waterborne, with specific etiologies differing by region and with diverse pathophysiologies. Very young, very old, and immune-deficient individuals are the most vulnerable to morbidity or mortality from small intestinal infections. There have been significant advances in diagnostic sophistication with the development and early application of molecular diagnostic assays, though these tests have not become mainstream. The lack of rapid diagnoses combined with the self-limited nature of small intestinal infections has hampered the development of specific and effective treatments other than oral rehydration. Antibiotics are not indicated in the absence of an etiologic diagnosis, and not at all in the case of some infections. PMID:27168147

  20. [Small-Bowel Cancer].

    PubMed

    Kagaya, Yuka; Sakamoto, Hirotsugu; Yamamoto, Hironori

    2016-05-01

    Diagnosis of small-bowel cancer has become easier thanks to the development of both balloon-assisted endoscopy and capsule endoscopy. Balloon-assisted endoscopy allows not only for observation of the deep intestine but also for biopsies and for establishing a histological diagnosis. Although endoscopic diagnosis is reported to improve the prognosis of small-bowel cancer by early detection, it is still difficult and the prognosis in general is poor. Surgery and chemotherapy protocols for this disease are similar to those for colon cancer. At present, the response rate to chemotherapy for small-bowel cancer is low. There is an urgent need in this patient population to establish a new diagnostic and therapeutic algorithm using balloon-assisted endoscopy and capsule endoscopy. PMID:27210079

  1. 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.

  2. 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.'

  3. 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

  4. 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

  5. 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…

  6. Benign small bowel tumor.

    PubMed Central

    Wilson, J M; Melvin, D B; Gray, G; Thorbjarnarson, B

    1975-01-01

    The clinical record and histologic sections of 84 cases of benign small bowel tumor are reviewed. Manifestations of systemic diseases, congenital anomalies, and lesions of either the ileocecal valve or periampullary region were excluded. In the same time span there were 96 small bowel malignancies. Clinical presentation, pathologic findings, management and result are compared to the collected published experience of about 2000 cases. There were 36 leiomyomas, 22 lipomas, 9 angiomas, 6 neurofibromas and 4 fibromas. Thirty-six men and 48 women were affected; the majority in their fifth and sixth decade. Seventy-eight were operative and 6 autopsy diagnoses. The most common symptom was obstruction (42%) followed by hemorrhage (34%) and pain (22%), relative frequency differing for the various specific tumors. There were rarely significant physical findings. A diagnosis of small bowel tumor was made radiologically in 30 patients. Because of the nonspecificity of other signs and symptoms, an acute awareness of the possibility of small bowel tumor is mandatory for preoperative anticipation of the diagnosis. Local resection was performed in all with no deaths or significant postoperative complications. PMID:1078626

  7. 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.

  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 Intestine Cancer Treatment

    MedlinePlus

    ... small intestine cancer include unexplained weight loss and abdominal pain. These and other signs and symptoms may be ... doctor if you have any of the following: Pain or cramps in the middle of the abdomen. Weight loss with no known reason. A lump ...

  10. Small intestinal fungal overgrowth.

    PubMed

    Erdogan, Askin; Rao, Satish S C

    2015-04-01

    Small intestinal fungal overgrowth (SIFO) is characterized by the presence of excessive number of fungal organisms in the small intestine associated with gastrointestinal (GI) symptoms. Candidiasis is known to cause GI symptoms particularly in immunocompromised patients or those receiving steroids or antibiotics. However, only recently, there is emerging literature that an overgrowth of fungus in the small intestine of non-immunocompromised subjects may cause unexplained GI symptoms. Two recent studies showed that 26 % (24/94) and 25.3 % (38/150) of a series of patients with unexplained GI symptoms had SIFO. The most common symptoms observed in these patients were belching, bloating, indigestion, nausea, diarrhea, and gas. The underlying mechanism(s) that predisposes to SIFO is unclear but small intestinal dysmotility and use of proton pump inhibitors has been implicated. However, further studies are needed; both to confirm these observations and to examine the clinical relevance of fungal overgrowth, both in healthy subjects and in patients with otherwise unexplained GI symptoms. Importantly, whether eradication or its treatment leads to resolution of symptoms remains unclear; at present, a 2-3-week course of antifungal therapy is recommended and may be effective in improving symptoms, but evidence for eradication is lacking. PMID:25786900

  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. Pancreatic small cell cancer.

    PubMed

    El Rassy, Elie; Tabchi, Samer; Kourie, Hampig Raphael; Assi, Tarek; Chebib, Ralph; Farhat, Fadi; Kattan, Joseph

    2016-06-01

    Small cell carcinoma (SCC) is most commonly associated with lung cancer. Extra-pulmonary SCC can originate in virtually any organ system, with the gastrointestinal tract being the most common site of involvement. We review the clinical presentation, pathogenesis, histology, imaging modalities and optimal therapeutic management of PSCC in light of available evidence. PMID:26566245

  13. Swedish small satellites

    NASA Astrophysics Data System (ADS)

    Lundahl, K.; von Scheele, F.

    2004-11-01

    In 1986 the first Swedish small satellite VIKING was launched on the Ariane 1 rocket together with the French remote sensing satellite SPOT-1. This paper describes the development of Swedish small satellites in an international framework. The satellites have delivered excellent scientific data to a low cost by using e.g. streamlined project organisations, competitive procurement programs and piggy-back launch opportunities. The first micro satellite Astrid-1 was launched in January 1995 and was followed by the launch of Astrid-2 in December 1998. The capable Odin small satellite was launched in February 2001. SSC was also contracted for ESA's SMART-1 probe destined to the Moon. SMART-1, launched in September 2003, is used for both research and as a technology demonstrator for future projects. Future proposed projects include micro and small satellites for climate research as the Atmosphere and Climate Explorer Plus (ACE+), the Stratosphere-Troposphere Exchange And climate Monitor (STEAM) and PRISMA, a technology demonstrator for formation flying, new propulsion system and commercial development methods.

  14. Small animal disease surveillance.

    PubMed

    Sánchez-Vizcaíno, Fernando; Jones, Philip H; Menacere, Tarek; Heayns, Bethaney; Wardeh, Maya; Newman, Jenny; Radford, Alan D; Dawson, Susan; Gaskell, Rosalind; Noble, Peter J M; Everitt, Sally; Day, Michael J; McConnell, Katie

    2015-12-12

    This is the first UK small animal disease surveillance report from SAVSNET. Future reports will expand to other syndromes and diseases. As data are collected for longer, the estimates of changes in disease burden will become more refined, allowing more targeted local and perhaps national interventions. Anonymised data can be accessed for research purposes by contacting the authors. SAVSNET welcomes feedback on this report.

  15. 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,…

  16. 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…

  17. 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 ...

  18. 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…

  19. 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…

  20. Libraries for Small Museums.

    ERIC Educational Resources Information Center

    Anderson, Linda M.

    Presented are the very basic requirements for establishing a small special library operating under a limited budget. Physical plant organization, cataloging, book processing, circulation procedures, book selection and ordering and instructions for typists are covered. Although the practices discussed were established for a museum library, what is…

  1. Small Modular Biomass Systems

    SciTech Connect

    2002-12-01

    This fact sheet provides information about modular biomass systems. Small modular biomass systems can help supply electricity to rural areas, businesses, and the billions of people who live without power worldwide. These systems use locally available biomass fuels such as wood, crop waste, animal manures, and landfill gas.

  2. 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''.

  3. 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…

  4. Small reentry vehicles

    NASA Astrophysics Data System (ADS)

    Sudmeijer, K. J.

    1987-12-01

    The design and potential applications of a small modular unguided reentry vehicle (SMURV) being developed for ESA are discussed. The first studies of the SMURV concept in the Spacemail program (for transporting small payloads from the Space Shuttle to earth) are recalled; the steps in a typical Spacemail operation are listed and briefly characterized; and the smaller version of SMURV (40 kg instead of 120 kg) developed for a Space Station Spacemail project (requiring 1000-1500 SMURVs) is described. This SMURV configuration comprises a detachable propulsion module and a reentry module (containing the parachute system and the recovery module). Consideration is given to a SMURV-type vehicle to return microgravity processing samples from the ESA Interim Flight Opportunity spacecraft, the technological challenges posed by SMURV design, and SMURV applications to the Comet Nucleus Sample Return and Cassini Titan Lander missions. Diagrams and drawings are provided.

  5. Aerodynamics of Small Vehicles

    NASA Astrophysics Data System (ADS)

    Mueller, Thomas J.

    In this review we describe the aerodynamic problems that must be addressed in order to design a successful small aerial vehicle. The effects of Reynolds number and aspect ratio (AR) on the design and performance of fixed-wing vehicles are described. The boundary-layer behavior on airfoils is especially important in the design of vehicles in this flight regime. The results of a number of experimental boundary-layer studies, including the influence of laminar separation bubbles, are discussed. Several examples of small unmanned aerial vehicles (UAVs) in this regime are described. Also, a brief survey of analytical models for oscillating and flapping-wing propulsion is presented. These range from the earliest examples where quasi-steady, attached flow is assumed, to those that account for the unsteady shed vortex wake as well as flow separation and aeroelastic behavior of a flapping wing. Experiments that complemented the analysis and led to the design of a successful ornithopter are also described.

  6. Structuring small projects

    SciTech Connect

    Pistole, C.O.

    1995-11-01

    One of the most difficult hurdles facing small project developers is obtaining financing. Many major banks and institutional investors are unwilling to become involved in projects valued at less than $25 million. To gain the interest of small project investors, developers will want to present a well-considered plan and an attractive rate of return. Waste-to-energy projects are one type that can offer diversified revenue sources that assure maximum profitability. The Ripe Touch Greenhouse project, a $14.5 million waste tire-to-energy facility in Colorado, provides a case study of how combining the strengths of the project partners can help gain community and regulatory acceptance and maximize profit opportunities.

  7. The small turbine revolution

    SciTech Connect

    Williams, P.L.

    1995-07-01

    Until the mid-1960s, improvements in technology and economies of scale made each new generating unit installed less expensive than the previous one. Later, bigger was still better. Larger units cost less per kilowatt than smaller units. Today, that may be changing. In some situations, distributed generation -the use of small, dispersed units (usually gas turbines) in the place of large central stations- can be the most attractive option.

  8. 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...

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. NIF small mirror mounts

    NASA Astrophysics Data System (ADS)

    McCarville, Tom J.

    1999-11-01

    The most prominent physical characteristics of the 192-beam NIF laser are the 123 m length of the main laser and 400 mm aperture of each beam line. The main laser is illustrated in Figure 1, which shows half the total beam lines. Less visible are the many small optics (less than 100-mm diameter) used to align and diagnose each beam line. Commercial mounts can be used for most of the small aperture turning mirrors. This paper reviews the NIF projects effort to identify suitable commercial mirror mounts. The small mirror mounts have stability, wave front, space, and cleanliness requirements similar to the large aperture optics. While cost favors use of commercial mounts, there is little other than user experience to guide the mount qualification process. At present, there is no recognizable qualification standard with which to compare various products. In a large project like NIF, different user experience leads to different product selection. In some cases the differences are justified by application needs, but more often the selection process is somewhat random due to a lack of design standards. The result is redundant design and testing by project staff and suppliers. Identification of suitable mirror mounts for large projects like NIF would be streamlined if standards for physical and performance criteria were available, reducing cost for both the project and suppliers. Such standards could distinguish mounts for performance critical applications like NIF from laboratory applications, where ease of use and flexibility is important.

  15. Why Small Catholic Schools Succeed.

    ERIC Educational Resources Information Center

    Kealey, Robert J., Ed.

    This book grew out of presentations at the 1997 National Catholic Educational Association convention. "Twelve Reasons Why Small Catholic Schools Are Successful" (Donald F. Novotney) and "Advantages of a Small Catholic School" (Wayne A. Pelzel) focus on the advantages and climate of small schools. "Staffing and Scheduling in a Small Catholic…

  16. 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.

  17. 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

  18. Small intestinal bacterial overgrowth.

    PubMed

    Johnston, K L

    1999-03-01

    It is clear that the exact definition of small intestinal bacterial overgrowth (SIBO) needs to be reappraised in veterinary medicine. Antibiotic responsive enteropathies due to SIBO must be distinguished from those that are not associated with SIBO, such as those caused by a lack of immune tolerance. Once appropriate definitions and criteria for diagnosis are in place, the wide variety of diagnostic procedures that may facilitate the diagnosis can be evaluated with respect to their sensitivity and specificity, and statements about the prevalence and significance of this disorder can be made.

  19. Small Martian Mesa

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-381, 4 June 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image was acquired during the first week of June 2003. It shows a small mesa surrounded by a plain of dust-mantled dunes and ripples near 5.9oS, 202.8oW. Large, house-sized boulders have tumbled down the mesa slopes. This one of the highest resolution images from Mars, each pixel covers an area of 1.5 meters (5 feet) across. Sunlight illuminates the scene from the left.

  20. 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.

  1. Small Obstacle Avoidance Sensor

    PubMed Central

    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. PMID:23878527

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Using small glass catalogs

    NASA Astrophysics Data System (ADS)

    Tesar, John C.

    2000-07-01

    Changes in glass catalogs from the major manufacturers, Schott, Ohara, Hoya, Corning, and Summita, are a future certainty. The ongoing efforts of these companies to eliminate arsenic, lead, and other environmentally unfriendly materials may well have an additional effect on the size of their catalogs also. We should not assume a zero-sum game, however. Environmental concerns may not lead to permanently smaller catalogs, though many have speculated that in the near term this might be so. However, from the designer's perspective, very small, abbreviated class catalogs, constructed for special purposes, can speed the glass selection process. Several examples will be discussed, based on derivative libraries suggested by Zhang, Shannon, and Walker. Streamlined libraries tailored for special purposes can be used effectively in the latest lens design software. Future software tools may speed this selection process by the use of algorithms that treat the problem as a `black box' using logic tools derived from probability studies of the patent literature.

  12. 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.

  13. [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.

  14. 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

  15. 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.

  16. 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.

  17. 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

  18. The Case for Small Universities--"Is Small Beautiful?"

    ERIC Educational Resources Information Center

    Birt, L. M.; Stewart, R. F.

    1981-01-01

    Options available to small universities in Australia in order to maximize their efficiency in lean times are discussed: staying small with better funding; staying small with standard funding; federation with another institution or institutions but with internal differentiation; merger; and closing. (MSE)

  19. Going Small: Progress & Challenges of Philadelphia's Small High Schools

    ERIC Educational Resources Information Center

    Hartmann, Tracey; Reumann-Moore, Rebecca; Evans, Shani Adia; Haxton, Clarisse; Maluk, Holly; Neild, Ruth Curran

    2009-01-01

    Between 2003 and 2007, and without significant outside funding, the School District of Philadelphia created 25 new small high schools. This study, begun by Research for Action in 2006, follows the start-up and early implementation of these small high schools in Philadelphia. The study found that parents and students are interested in small high…

  20. 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 ...

  1. Small Business's Big Training Needs.

    ERIC Educational Resources Information Center

    Kelly, Leslie

    1984-01-01

    Discusses the training needs of small businesses in light of their high failure rate (50 percent). Includes characteristics of successful small businesses, potential training needs, training methods, and topics for seminars. (JOW)

  2. 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.

  3. 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

  4. Introduction to Small Group Discussion.

    ERIC Educational Resources Information Center

    Millar, Dan Pyle

    To bring educational research into focus with tested classroom practice, this booklet provides an introduction to small group discussion. The theory and research section discusses the importance of small group discussion, characteristics of small group discussions, group attraction based on Maslow's hierarchy of basic human needs, group decision…

  5. Small Cell Lung Cancer.

    PubMed

    Bernhardt, Erica B; Jalal, Shadia I

    2016-01-01

    Small cell lung cancer (SCLC) is an aggressive cancer of neuroendocrine origin, which is strongly associated with cigarette smoking. Patients typically present with a short duration of symptoms and frequently (60-65 %) with metastatic disease. SCLC is a heterogeneous disease including extremely chemosensitive and chemoresistant clones. For this reason, a high percentage of patients respond to first-line chemotherapy but rapidly succumb to the disease. SCLC is generally divided into two stages, limited and extensive. Standard treatment of limited stage disease includes combination chemotherapy with cisplatin and etoposide for four cycles, thoracic radiation initiated early with the first cycle of chemotherapy, and consideration of prophylactic cranial irradiation (PCI) in the subset of patients with good response. Surgery may play a role in TNM stages I and II. In extensive disease, platinum agents and etoposide, used in combination, are again the first-line standard of care in the USA. However, thoracic radiation therapy is used predominately in patients where local control is important and PCI is of uncertain benefit. Despite these treatments, prognosis remains poor and novel therapies are needed to improve survival in this disease. PMID:27535400

  6. Small Stirling Cycle Convertors

    NASA Astrophysics Data System (ADS)

    Penswick, L. Barry; Schreiber, Jeffery

    2005-02-01

    The Stirling convertor concept continues to be a viable potential candidate for various space power applications at electrical power levels ranging from greater than 100 KW to on the order of 10+watts. Various development efforts, both in the past and currently underway, have clearly demonstrated the potential for long operating life of this concept, its high efficiency in comparison to alternative power systems (>50% of Carnot based on electric power out to heat in), and its excellent specific power characteristics. A truly unique attribute of the Stirling convertor is the ability to maintain many of these same advantages at significantly lower electrical power levels (on the order of 1 watt and below). This provides the opportunity for a wider range of potential space power applications and the use of alternative heat sources operating at dramatically lower hot-end temperatures (about 250 °C vs. current values of about 650 °C). An overview of low-power Stirling convertors and related Stirling cooler technology is provided with an emphasis on assessing the technical maturity of this concept's key components at the low power level of interest. A conceptual design of a small, 1-watt (electrical output) Stirling convertor utilizing multiple Low Weight Radioisotope Heater Unit heat sources will be described. Key technical issues in the development of this power level Stirling convertor are discussed.

  7. 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

    ... 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 Business... Business, Small Disadvantaged Business and Woman-Owned Small Business Concerns. 970.1907 Section...

  8. Small diameter carbon nanopipettes

    NASA Astrophysics Data System (ADS)

    Singhal, Riju; Bhattacharyya, Sayan; Orynbayeva, Zulfiya; Vitol, Elina; Friedman, Gary; Gogotsi, Yury

    2010-01-01

    Nanoscale multifunctional carbon probes facilitate cellular studies due to their small size, which makes it possible to interrogate organelles within living cells in a minimally invasive fashion. However, connecting nanotubes to macroscopic devices and constructing an integrated system for the purpose of fluid and electrical signal transfer is challenging, as is often the case with nanoscale components. We describe a non-catalytic chemical vapor deposition based method for batch fabrication of integrated multifunctional carbon nanopipettes (CNPs) with tip diameters much smaller (10-30 nm) than previously reported (200 nm and above) and approaching those observed for multiwalled carbon nanotubes. This eliminates the need for complicated attachment/assembly of nanotubes into nanofluidic devices. Variable tip geometries and structures were obtained by controlled deposition of carbon inside and outside quartz pipettes. We have shown that the capillary length and gas flow rate have a marked effect on the carbon deposition. This gives us a flexible protocol, useful for growing carbon layers of different thicknesses at selective locations on a glass pipette to yield a large variety of cellular probes in bulk quantities. The CNPs possess an open channel for fluid transfer with the carbon deposited inside at 875 °C behaving like an amorphous semiconductor. Vacuum annealing of the CNP tips at temperatures up to 2000 °C yields graphitic carbon structures with an increase in conductivity of two orders of magnitude. Penetration of the integrated carbon nanoprobes into cells was shown to produce minimal Ca2+ signals, fast recovery of basal Ca2+ levels and no adverse activation of the cellular metabolism during interrogation times as long as 0.5-1 h.

  9. 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.

  10. 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

  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. Standard Deviation for Small Samples

    ERIC Educational Resources Information Center

    Joarder, Anwar H.; Latif, Raja M.

    2006-01-01

    Neater representations for variance are given for small sample sizes, especially for 3 and 4. With these representations, variance can be calculated without a calculator if sample sizes are small and observations are integers, and an upper bound for the standard deviation is immediate. Accessible proofs of lower and upper bounds are presented for…

  15. How Small Is a Billionth?

    ERIC Educational Resources Information Center

    Gough, John

    2007-01-01

    Children's natural curiosity about numbers, big and small can lead to exploring place-value ideas. But how can these abstract concepts be experienced more concretely? This article presents some practical approaches for conceptualising very small numbers using linear models, area models, volume models, and diagrams.

  16. The Big Benefits of Smallness.

    ERIC Educational Resources Information Center

    Meier, Deborah W.

    1996-01-01

    Small schools (300 to 400 students) offer a real panacea for America's educational ills. New York City's celebrated Central Park East schools lack separate buildings, but have the climate and culture for developing democratic habits of heart and mind. Smallness can facilitate governance, respect, simplicity, safety, parent involvement,…

  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 for school-community…

  18. Arthropod viruses and small RNAs.

    PubMed

    Vijayendran, Diveena; Airs, Paul M; Dolezal, Kelly; Bonning, Bryony C

    2013-10-01

    The recently characterized small RNAs provide a new paradigm for physiological studies. These molecules have been shown to be integral players in processes as diverse as development and innate immunity against bacteria and viruses in eukaryotes. Several of the well-characterized small RNAs including small interfering RNAs, microRNAs and PIWI-interacting RNAs are emerging as important players in mediating arthropod host-virus interactions. Understanding the role of small RNAs in arthropod host-virus molecular interactions will facilitate manipulation of these pathways for both management of arthropod pests of agricultural and medical importance, and for protection of beneficial arthropods such as honey bees and shrimp. This review highlights recent research on the role of small RNAs in arthropod host-virus interactions with reference to other host-pathogen systems. PMID:23932976

  19. 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.

  20. Small Bowel Obstruction- A Surprise

    PubMed Central

    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. PMID:25738033

  1. 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.

  2. Small systems and SDWA reauthorization

    SciTech Connect

    Shanaghan, P.E. )

    1994-05-01

    Small systems issues have been a prominent feature of deliberations on the Safe Drinking Water Act (SDWA) since its initial formulation. In 1993 the US Environmental Protection Agency (USEPA) prepared a report to Congress that contained a detailed discussion of the SDWA compliance challenges faced by small water systems. This article focuses on three of the major small system issues identified in the report to congress--viability, lower-cost technology, and financing--and discusses how USEPA's reauthorization recommendations would address these issues. 51 refs.

  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 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.

  5. 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.

  6. Public Relations for Small Schools.

    ERIC Educational Resources Information Center

    Seifert, Edward H.; Lott, Chester N.

    1981-01-01

    Discusses economically feasible and sensible methods of school-community relations for implementation in small schools; a multifaceted communication approach should be implemented which includes news releases, newsletters, advisory committees, and internal communication. (Author/LC)

  7. Leadership Development for Small Organizations.

    ERIC Educational Resources Information Center

    Tarley, Marshall

    2002-01-01

    Discusses how a small to mid-sized organization can create a leadership development program using the same approach that is used in large companies like General Electric. Identifies the factors that can transfer successfully to smaller organizations. (JOW)

  8. Matrix Theory of Small Oscillations

    ERIC Educational Resources Information Center

    Chavda, L. K.

    1978-01-01

    A complete matrix formulation of the theory of small oscillations is presented. Simple analytic solutions involving matrix functions are found which clearly exhibit the transients, the damping factors, the Breit-Wigner form for resonances, etc. (BB)

  9. Widespread expression of conserved small RNAs in small symbiont genomes

    PubMed Central

    Hansen, Allison K; Degnan, Patrick H

    2014-01-01

    Genome architecture of a microbe markedly changes when it transitions from a free-living lifestyle to an obligate symbiotic association within eukaryotic cells. These symbiont genomes experience numerous rearrangements and massive gene loss, which is expected to radically alter gene regulatory networks compared with those of free-living relatives. As such, it remains unclear whether and how these small symbiont genomes regulate gene expression. Here, using a label-free mass-spec quantification approach we found that differential protein regulation occurs in Buchnera, a model symbiont with a reduced genome, when it transitions between two distinct life stages. However, differential mRNA expression could not be detected between Buchnera life stages, despite the presence of a small number of putative transcriptional regulators. Instead a comparative analysis of small RNA expression profiles among five divergent Buchnera lineages, spanning a variety of Buchnera life stages, reveals 140 novel intergenic and antisense small RNAs and 517 untranslated regions that were significantly expressed, some of which have been conserved for ∼65 million years. In addition, the majority of these small RNAs exhibit both sequence covariation and thermodynamic stability, indicators of a potential structural RNA role. Together, these data suggest that gene regulation at the post-transcriptional level may be important in Buchnera. This is the first study to empirically identify Buchnera small RNAs, and we propose that these novel small RNAs may facilitate post-transcriptional regulation through translational inhibition/activation, and/or transcript stability. Ultimately, post-transcriptional regulation may shape metabolic complementation between Buchnera and its aphid host, thus impacting the animal's ecology and evolution. PMID:25012903

  10. 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.

  11. Very small ionization pressure gauge

    SciTech Connect

    Edwards, D. Jr.

    1982-01-01

    A very small ionization pressure gauge has been developed to operate in the pressure range 10/sup -6/ Torr to 100..mu... A metal construction and external cooling fins result in a very rugged device with exceptionally small outgassing properties. The gauge also incorporates a replaceable filament-grid assembly on a single plug which allows the simple replacement of both the filament and the grid when needed.

  12. 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.

  13. 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.

  14. Maybe Small Is Too Small a Term: Introduction to Advancing Small Sample Prevention Science.

    PubMed

    Fok, Carlotta Ching Ting; Henry, David; Allen, James

    2015-10-01

    Prevention research addressing health disparities often involves work with small population groups experiencing such disparities. The goals of this special section are to (1) address the question of what constitutes a small sample; (2) identify some of the key research design and analytic issues that arise in prevention research with small samples; (3) develop applied, problem-oriented, and methodologically innovative solutions to these design and analytic issues; and (4) evaluate the potential role of these innovative solutions in describing phenomena, testing theory, and evaluating interventions in prevention research. Through these efforts, we hope to promote broader application of these methodological innovations. We also seek whenever possible, to explore their implications in more general problems that appear in research with small samples but concern all areas of prevention research. This special section includes two sections. The first section aims to provide input for researchers at the design phase, while the second focuses on analysis. Each article describes an innovative solution to one or more challenges posed by the analysis of small samples, with special emphasis on testing for intervention effects in prevention research. A concluding article summarizes some of their broader implications, along with conclusions regarding future directions in research with small samples in prevention science. Finally, a commentary provides the perspective of the federal agencies that sponsored the conference that gave rise to this special section.

  15. 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.

  16. Small satellites for tropical applications

    NASA Astrophysics Data System (ADS)

    Montpetit, Marie-Jose; Bonn, Ferdinand

    1993-11-01

    A number of mission studies were performed to assess the suitability of small satellite systems for tropical data acquisition. These studies took into account the specifics of the tropical user communities and were focused on remote sensing and resource management issues. The requirements and potential solutions for four application areas are discussed. For monitoring of forest and agricultural vegetation, a small synthetic aperture radar is considered with P, C, or X band imaging, possibly supplemented by a high resolution multispectral imager. The radar would have the capability to monitor below cloud cover which is often found in tropical regions. Optical, microwave, or spectrographic imaging would also be useful in small satellites for disaster monitoring (notably of floods), land management, and air pollution monitoring. A small satellite with data storage and forwarding capability is also envisioned to collect data from dependable, low-power, and low-cost ground sensors via a simple ultrahigh frequency uplink and download the data on a very high frequency downlink. All the small satellites would be launched in low inclination orbits to ensure a number of consecutive passes over the targeted tropical area.

  17. 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.

  18. 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.…

  19. Small but Pristine--Lessons for Small Library Automation.

    ERIC Educational Resources Information Center

    Clement, Russell; Robertson, Dane

    1990-01-01

    Compares the more positive library automation experiences of a small public library with those of a large research library. Topics addressed include collection size; computer size and the need for outside control of a data processing center; staff size; selection process for hardware and software; and accountability. (LRW)

  20. 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…

  1. Measurement of small intestinal damage.

    PubMed

    Takeuchi, Koji; Satoh, Hiroshi

    2010-08-01

    Many animal models have been devised for investigating the pathogenesis of intestinal lesions and for screening drugs for the treatment of intestinal ulcers in humans. Recently, particular attention has been focused on NSAID-induced intestinal lesions as a result of the development of the capsule endoscope and double-balloon endoscope. Ischemic enteritis, one of the most dramatic abdominal emergencies, is known to cause severe damage to the small intestine by a significant decrease of arterial blood flow in the small intestine. In this unit, two animal models for small intestinal damage induced by NSAIDs or intestinal ischemia are described. Also included are methods for lesion induction and evaluation of the damage as well as the measurement of pathogenic functional and biochemical changes.

  2. Health Promotion in Small Business

    PubMed Central

    McCoy, Kira; Stinson, Kaylan; Scott, Kenneth; Tenney, Liliana; Newman, Lee S.

    2015-01-01

    Objective To assess the evidence regarding the adoption and efficacy of worksite health promotion programs (WHPPs) in small businesses. Methods Peer-reviewed research articles were identified from a database search. Included articles were published before July 2013, described a study that used an experimental or quasiexperimental design and either assessed adoption of WHPPs or conducted interventions in businesses with fewer than 500 employees. A review team scored the study’s rigor using the WHO-adapted GRADEprofiler “quality of evidence” criteria. Results Of the 84 retrieved articles, 19 met study inclusion criteria. Of these, only two met criteria for high rigor. Conclusions Fewer small businesses adopt WHPPs compared with large businesses. Two high-rigor studies found that employees were healthier postintervention. Higher quality research is needed to better understand why small businesses rarely adopt wellness programs and to demonstrate the value of such programs. PMID:24905421

  3. Small group discussion: Students perspectives

    PubMed Central

    Annamalai, Nachal; Manivel, Rajajeyakumar; Palanisamy, Rajendran

    2015-01-01

    Context: Various alternative methods are being used in many medical colleges to reinforce didactic lectures in physiology. Small group teaching can take on a variety of different tasks such as problem-solving, role play, discussions, brainstorming, and debate. Research has demonstrated that group discussion promotes greater synthesis and retention of materials. Aims: The aims of this study were to adopt a problem-solving approach by relating basic sciences with the clinical scenario through self-learning. To develop soft skills, to understand principles of group dynamics, and adopt a new teaching learning methodology. Subjects and Methods: Experimental study design was conducted in Phase I 1st year medical students of 2014–2015 batch (n = 120). On the day of the session, the students were grouped into small groups (15 each). The session started with the facilitator starting off the discussion. Feedback forms from five students in each group was taken (n = 40). A five point Likert scale was used ranging from strongly agree to strongly disagree. Data were analyzed using IBM SPSS Statistics for Windows, Version 21.0. Armonk, NY: IBM Corp. Results: Our results show that 70% of the students opined that small group discussion were interactive, friendly, innovative, built interaction between teacher and student. Small group discussion increased their thought process and helped them in better communication. Conclusions: The small group discussion was interactive, friendly, and bridged the gap between the teacher and student. The student's communication skills are also improved. In conclusion, small group discussion is more effective than the traditional teaching methods. PMID:26380202

  4. 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.

  5. Polynomials with small Mahler measure

    NASA Astrophysics Data System (ADS)

    Mossinghoff, M. J.

    1998-10-01

    We describe several searches for polynomials with integer coefficients and small Mahler measure. We describe the algorithm used to test Mahler measures. We determine all polynomials with degree at most 24 and Mahler measure less than 1.3, test all reciprocal and antireciprocal polynomials with height 1 and degree at most 40, and check certain sparse polynomials with height 1 and degree as large as 181. We find a new limit point of Mahler measures near 1.309, four new Salem numbers less than 1.3, and many new polynomials with small Mahler measure. None has measure smaller than that of Lehmer's degree 10 polynomial.

  6. Small GTPases in vesicle trafficking.

    PubMed

    Molendijk, Arthur J; Ruperti, Benedetto; Palme, Klaus

    2004-12-01

    Plant small GTPases belonging to the Rop, Arf, and Rab families are regulators of vesicle trafficking. Rop GTPases regulate actin dynamics and modulate H(2)O(2) production in polar cell growth and pathogen defence. A candidate Rop GDP to Rop GTP exchange factor (RopGEF) SPIKE1 is involved in the morphogenesis of leaf epidermal cells. The ArfGEF GNOM regulates the endosomal recycling of the PIN proteins, which are involved in polar auxin transport. Intracellular localisation of small GTPases and functional studies using dominant mutant versions of Arf and Rab GTPases are defining novel plant-specific membrane compartments, especially those that participate in endosomal vesicle trafficking.

  7. Starting a Small Instrument Company

    NASA Astrophysics Data System (ADS)

    Warburton, W. K.

    1997-03-01

    The author is now the owner of an 8 person company that develops specialized electronics to support the detectors used at synchrotron radiation facilities and is spinning this expertise off into developing spectrometry instruments for specialized medical markets. This talk will begin with a short history illustrating the random walk processes leading to the present situation and then consider some of the issues which a small company must deal with in order to survive. From this perspective, the author will then extract a list of steps the prospective physicist/entreprenuer can take, while still a student or post-doc, to prepare for success in growing a small business.

  8. 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 towns that…

  9. 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...

  10. 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)

  11. Small amplitude quasibreathers and oscillons

    NASA Astrophysics Data System (ADS)

    Fodor, Gyula; Forgács, Péter; Horváth, Zalán; Lukács, Árpád

    2008-07-01

    Quasibreathers (QB) are time-periodic solutions with weak spatial localization introduced in G. Fodor et al. in [Phys. Rev. D 74, 124003 (2006)PRVDAQ0556-282110.1103/PhysRevD.74.124003]. 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, Dcrit=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.

  12. Neoplasms of the Small Bowel

    PubMed Central

    Silberman, Howard; Crichlow, Robert W.; Caplan, Howard S.

    1974-01-01

    Small bowel tumors are unusual lesions exhibiting nonspecific clinical features often diagnosed at an advanced stage. In the cases studied at the Hospital of the University of Pennsylvania nearly all the 32 patients with malignancies were symptomatic whereas in the 34 patients with benign lesions the condition was discovered as an incidental finding in about half of the patients. Weight loss, palpable mass or anemia usually indicated malignancy. Small bowel radiography was the most useful diagnostic aid in the present series. While the etiology of these lesions is unknown, villous adenomas probably bear a relationship to carcinoma. The association between chronic regional enteritis and small bowel tumors is unestablished but suggestive. An analysis of reported series reveals a disproportionate incidence of additional primary tumors in patients with small bowel neoplasms. Surgical extirpation is indicated for curative treatment. In the present series, resection in hope of cure was carried out in 25 of 32 malignant tumors resulting in eight five-year survivals. One of these latter lived nine years with disseminated malignant carcinoid reflecting the occasional indolent course of this tumor. PMID:4842978

  13. Social Planning for Small Cities.

    ERIC Educational Resources Information Center

    Meyers, James

    Derived mainly from publications by the League of California Cities, this guide to social planning for small cities presents the following: (1) social planning definitions; (2) a checklist of social planning concerns (provision for: adequate income and economic opportunity; optimal environmental conditions for basic material needs; optimal health…

  14. Research at Small Canadian Universities.

    ERIC Educational Resources Information Center

    Owen, Michael

    1992-01-01

    There are many excellent scientists in the natural and human sciences in Canada's small universities. If the institutions implement internal procedures to encourage and foster a research climate and if research councils consider alternative strategies for research funding, research productivity could expand greatly in quality and scope. (MSE)

  15. Stages of Small Intestine Cancer

    MedlinePlus

    ... small intestine cancer include unexplained weight loss and abdominal pain. These and other signs and symptoms may be ... doctor if you have any of the following: Pain or cramps in the middle of the abdomen. Weight loss with no known reason. A lump ...

  16. 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.

  17. The Anatomy of Small Groups.

    ERIC Educational Resources Information Center

    Lewis, Harry A.

    1979-01-01

    Five studies on the advantages and disadvantages of small groups in teaching in higher education are discussed. These include works by M. L. Johnson Abercrombie; Barbara Cockburn and Alex Ross; M. L. J. Abercrombie and P. M. Terry; and Jean Rudduck. (JMF)

  18. 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,…

  19. 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…

  20. Microwave Levitation Of Small Objects

    NASA Technical Reports Server (NTRS)

    Watkins, John L.; Jackson, Henry W.

    1991-01-01

    Microwave radiation in resonant cavities used to levitate small objects, according to proposal. Feedback control and atmosphere not needed. Technique conceived for use in experiments on processing of materials in low gravitation of outer space, also used in normal Earth gravitation, albeit under some limitations.

  1. INDIVIDUALIZING INSTRUCTION IN SMALL SCHOOLS.

    ERIC Educational Resources Information Center

    Western States Small Schools Project, Salt Lake City, UT.

    THIS DOCUMENT DISCUSSES PROCEDURES AND POTENTIALS FOR INDIVIDUALIZING INSTRUCTIONAL PROGRAMS IN SMALL RURAL SCHOOLS. FOUR FACTORS ARE SEEN TO BE OPERANT IN THE INDIVIDUALIZATION PROCESS. THESE ARE THE INSTRUCTOR, THE CURRICULUM AND SUPPLEMENTARY MATERIALS, ADMINISTRATIVE PRACTICE, AND PHYSICAL FACILITIES. NEW INSTRUCTIONAL PROCEDURES SHOULD BE…

  2. 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, ...

  3. 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.

  4. 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 ...

  5. Disability Management in Small Firms.

    ERIC Educational Resources Information Center

    Drury, David

    1991-01-01

    Notes that American research has paid relatively little attention to prospects for adapting disability management practices to financial and management environment of smaller employers. Compares large and small firms in terms of employer disability practices and characteristics of disabled workers; discusses barriers to rehabilitation and…

  6. 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…

  7. 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 ...

  8. 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…

  9. 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.

  10. Small Schools: Size or Community?

    ERIC Educational Resources Information Center

    Strike, Kenneth A.

    2008-01-01

    Small schools are not just about size. They are also about authentic instruction, portfolio evaluation, and a thematic curriculum. Their agendas overlap with that of charter schools. They have an uncomfortable and sometimes adversarial relationship with standards, accountability, and the No Child Left Behind Act. They have migrated from their…

  11. Small-Town Rock Trade

    ERIC Educational Resources Information Center

    Robarge, Thomas J.

    1977-01-01

    Describes an eighth grade rock exchange project in which small groups of students researched, then wrote letters to schools throughout the United States requesting samples of local rocks and minerals. Provides experience in use of the atlas and letter writing. (CS)

  12. 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.…

  13. 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…

  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 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

  16. 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.

  17. 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.

  18. Genetics Home Reference: small fiber neuropathy

    MedlinePlus

    ... Home Health Conditions small fiber neuropathy small fiber neuropathy Enable Javascript to view the expand/collapse boxes. ... PDF Open All Close All Description Small fiber neuropathy is a condition characterized by severe pain attacks ...

  19. Small-scale explosive welding of aluminum

    NASA Technical Reports Server (NTRS)

    Bement, L. J.

    1972-01-01

    Welding technique uses very small quantities of explosive ribbon to accomplish small-scale lap-welding of aluminum plates. Technique can perform small controlled welding with no length limitations and requires minimal protective shielding.

  20. Small Business Administration Semiannual Regulatory Agenda

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-26

    ... businesses. Timetable: Action Date FR Cite NPRM 08/00/10 Regulatory Flexibility Analysis Required: Yes Agency... Manufacturing Assistance Act of 2004 (Reauthorization Act) to regulate Small Business Lending Companies (SBLCs... Part XVI Small Business Administration Semiannual Regulatory Agenda ] SMALL...

  1. 77 FR 76215 - Small Business Size Regulations, Small Business Innovation Research (SBIR) Program and Small...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-27

    ... to sizestandards@SBA.gov . SUPPLEMENTARY INFORMATION: I. Background On May 15, 2012, at 77 FR 28520 (available at http://www.gpo.gov/fdsys/pkg/FR-2012-05-15/pdf/2012-11586.pdf ), the U.S. Small Business... FR 30227 (May 22, 2012). SBA held these outreach sessions in Washington, DC; Boston,...

  2. 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.

  3. 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.

  4. Small crater populations on Vesta

    NASA Astrophysics Data System (ADS)

    Marchi, S.; Bottke, W. F.; O'Brien, D. P.; Schenk, P.; Mottola, S.; De Sanctis, M. C.; Kring, D. A.; Williams, D. A.; Raymond, C. A.; Russell, C. T.

    2014-11-01

    The NASA Dawn mission has extensively examined the surface of asteroid Vesta, the second most massive body in the main belt. The high quality of the gathered data provides us with a unique opportunity to determine the surface and internal properties of one of the most important and intriguing main belt asteroids (MBAs). In this paper, we focus on the size frequency distributions (SFDs) of sub-kilometer impact craters observed at high spatial resolution on several selected young terrains on Vesta. These small crater populations offer an excellent opportunity to determine the nature of their asteroidal precursors (namely MBAs) at sizes that are not directly observable from ground-based telescopes (i.e., below ∼100 m diameter). Moreover, unlike many other MBA surfaces observed by spacecraft thus far, the young terrains examined had crater spatial densities that were far from empirical saturation. Overall, we find that the cumulative power-law index (slope) of small crater SFDs on Vesta is fairly consistent with predictions derived from current collisional and dynamical models down to a projectile size of ∼10 m diameter (e.g., Bottke et al., 2005a, b). The shape of the impactor SFD for small projectile sizes does not appear to have changed over the last several billions of years, and an argument can be made that the absolute number of small MBAs has remained roughly constant (within a factor of 2) over the same time period. The apparent steady state nature of the main belt population potentially provides us with a set of intriguing constraints that can be used to glean insights into the physical evolution of individual MBAs as well as the main belt as an ensemble.

  5. 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.

  6. 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.

  7. 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. PMID

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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

  18. 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 Transfer (STTR) program Commercialization Benchmark for the 11 participating agencies for public...

  19. 78 FR 59410 - Small Business Innovation Research and Small Business Technology Transfer Programs...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-09-26

    ... ADMINISTRATION Small Business Innovation Research and Small Business Technology Transfer Programs... period for the Small Business Innovation Research (SBIR) and Small Business Technology Transfer (STTR... submitting comments. Mail/Hand Delivery/Courier: Edsel Brown, Jr., Assistant Director, Office of...

  20. Advances in small bowel neuroendocrine neoplasia Banck and Small intestine

    PubMed Central

    Banck, Michaela S.; Beutler, Andreas S.

    2015-01-01

    Purpose of review this review aims at summarizing progress in clinical trials and basic science redefining the diagnosis and treatment of well differentiated small intestine neuroendocrine tumors (SI-NET). Recent findings Two clinical trials demonstrated antitumor activity of the long-acting somatostatin analogues octreotide LAR and lanreotide for advanced SI-NET. The mTOR inhibitor everolimus is another treatment option for patients with SI-NET, but awaits definitive proof of benefit in the ongoing RADIANT-4 study. Two whole exome/genome-sequencing studies reported in the past year provided the first genome-wide analysis of large sets of SI-NET at nucleotide resolution. Candidate therapeutically relevant alterations were found to affect SRC, SMAD genes, AURKA, EGFR, HSP90, and PDGFR as well as mutually exclusive amplification of AKT1 or AKT2 and other alterations of PI3K/Akt/mTOR signaling genes. The gene CDKN1B is inactivated by small insertions/deletions in 8% of patients with SI-NET suggesting cell cycle inhibitors as new candidate drugs for SI-NET. Circulating tumor cells and tumor-derived RNA in the blood are promising clinical tests for SI-NET. Summary Clinical and genomic research may merge in the near future to re-shape clinical trials and to define the ‘personalized’ treatment options for patients with SI-NET. PMID:24441281

  1. Small Group Communication in the 1980's.

    ERIC Educational Resources Information Center

    Neer, Michael R., Ed.

    1981-01-01

    This special edition of "Communication" brings together the work of nine leading scholars of small group communication. The following topics are discussed: (1) small group communication research in the 1980s; (2) unanswered questions in research on communication in the small group; (3) emerging trends in small group research; (4) structure in…

  2. Small intestinal bacterial overgrowth syndrome

    PubMed Central

    Bures, Jan; Cyrany, Jiri; Kohoutova, Darina; Förstl, Miroslav; Rejchrt, Stanislav; Kvetina, Jaroslav; Vorisek, Viktor; Kopacova, Marcela

    2010-01-01

    Human intestinal microbiota create a complex polymicrobial ecology. This is characterised by its high population density, wide diversity and complexity of interaction. Any dysbalance of this complex intestinal microbiome, both qualitative and quantitative, might have serious health consequence for a macro-organism, including small intestinal bacterial overgrowth syndrome (SIBO). SIBO is defined as an increase in the number and/or alteration in the type of bacteria in the upper gastrointestinal tract. There are several endogenous defence mechanisms for preventing bacterial overgrowth: gastric acid secretion, intestinal motility, intact ileo-caecal valve, immunoglobulins within intestinal secretion and bacteriostatic properties of pancreatic and biliary secretion. Aetiology of SIBO is usually complex, associated with disorders of protective antibacterial mechanisms (e.g. achlorhydria, pancreatic exocrine insufficiency, immunodeficiency syndromes), anatomical abnormalities (e.g. small intestinal obstruction, diverticula, fistulae, surgical blind loop, previous ileo-caecal resections) and/or motility disorders (e.g. scleroderma, autonomic neuropathy in diabetes mellitus, post-radiation enteropathy, small intestinal pseudo-obstruction). In some patients more than one factor may be involved. Symptoms related to SIBO are bloating, diarrhoea, malabsorption, weight loss and malnutrition. The gold standard for diagnosing SIBO is still microbial investigation of jejunal aspirates. Non-invasive hydrogen and methane breath tests are most commonly used for the diagnosis of SIBO using glucose or lactulose. Therapy for SIBO must be complex, addressing all causes, symptoms and complications, and fully individualised. It should include treatment of the underlying disease, nutritional support and cyclical gastro-intestinal selective antibiotics. Prognosis is usually serious, determined mostly by the underlying disease that led to SIBO. PMID:20572300

  3. Small GTPases in peroxisome dynamics.

    PubMed

    Just, Wilhelm W; Peränen, Johan

    2016-05-01

    In this review article, we summarize current knowledge on peroxisome biogenesis/functions and the role that small GTPases may play in these processes. Precise intracellular distribution of cell organelles requires their regulated association to microtubules and the actin cytoskeleton. In this respect, RhoGDP/RhoGTP favor binding of peroxisomes to microtubules and actin filaments. In its GTP-bound form, RhoA activates a regulatory cascade involving Rho kinaseII and non-muscle myosinIIA. Such interactions frequently depend on phosphoinositides (PIs) of which PI4P, PI(4,5)P2, and PI(3,5)P2 were found to be present in the peroxisomal membrane. PIs are pivotal determinants of intracellular signaling and known to regulate a wide range of cellular functions. In many of these functions, small GTPases are implicated. The small GTPase ADP-ribosylation factor 1 (Arf1), for example, is known to stimulate synthesis of PI4P and PI(4,5)P2 on the Golgi to regulate protein and lipid sorting. In vitro binding assays localized Arf1 and the COPI complex to peroxisomes. In light of the recent discussion of pre-peroxisomal vesicle generation at the ER, peroxisomal Arf1-COPI vesicles may serve retrograde transport of ER-resident components. A mass spectrometric screen localized various Rab proteins to peroxisomes. Overexpression of these proteins in combination with laser-scanning fluorescence microscopy co-localized Rab6, Rab8, Rab10, Rab14, and Rab18 with peroxisomal structures. By analogy to the role these proteins play in other organelle dynamics, we may envisage what the function of these proteins may be in relation to the peroxisomal compartment.

  4. 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.

  5. Apparatus for blending small particles

    DOEpatents

    Bradley, R.A.; Reese, C.R.; Sease, J.D.

    1975-08-26

    An apparatus is described for blending small particles and uniformly loading the blended particles in a receptacle. Measured volumes of various particles are simultaneously fed into a funnel to accomplish radial blending and then directed onto the apex of a conical splitter which collects the blended particles in a multiplicity of equal subvolumes. Thereafter the apparatus sequentially discharges the subvolumes for loading in a receptacle. A system for blending nuclear fuel particles and loading them into fuel rod molds is described in a preferred embodiment. (auth)

  6. 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.

  7. Hanford Small Building Demolition Program

    SciTech Connect

    Diebel, J.A.; Douglas, L.M.; Shuck, R.G.

    1993-09-01

    Over 1,100 buildings currently exist on the Hanford Site. Many of these structures are outdated and no longer needed to support the environmental restoration mission. The Hanford Small Building Demolition Program is part of a combined effort of an Accelerated Decontamination and Decommissioning (D and D) Program and Landlord Site Preparation and Stabilization Program aimed at reducing the inventory of noncontaminated surplus facilities onsite. The reduction of surplus facilities results in reduced surveillance and maintenance (S and M) costs and eliminates the safety and environmental hazards associated with aging buildings. The project involves decommissioning up to 80 surplus facilities over the next five years.

  8. Small Bowel Imaging: an Update.

    PubMed

    Rimola, Jordi; Panés, Julián

    2016-07-01

    Bowel imaging had experienced relevant technical advances during the last decade. The developments in the field of cross-sectional imaging had a particular impact on the assessment of Crohn's disease. The purpose of this manuscript is to provide a review of the main progress of cross-sectional imaging in the assessment of Crohn's disease and other small bowel diseases with relevance in clinical practice and in research. Also, we outline the technical advances, trends, and potential contributions of new technological cross-sectional imaging improvements that may have potential impact and contribution in the near future. PMID:27315216

  9. Small lasers in flow cytometry.

    PubMed

    Telford, William G

    2004-01-01

    Laser technology has made tremendous advances in recent years, particularly in the area of diode and diode-pumped solid state sources. Flow cytometry has been a direct beneficiary of these advances, as these small, low-maintenance, inexpensive lasers with reasonable power outputs are integrated into flow cytometers. In this chapter we review the contribution and potential of solid-state lasers to flow cytometry, and show several examples of these novel sources integrated into production flow cytometers. Technical details and critical parameters for successful application of these lasers for biomedical analysis are reviewed. PMID:14976380

  10. Small-Signal ac Analysis

    NASA Technical Reports Server (NTRS)

    Jagielski, James M.; Chen, Jess

    1987-01-01

    Program simulates power circuits and systems. Small Signal A.C. Analysis program (SSAC) valuable tool for design and analysis of electrical-power-system circuits. By combining "black box" power-system components operating in specified manner, user characterizes system modeled. Menu-driven program proved simple and cost effective in development and modification of arbitrary power-system configurations. Package includes sample data from Dynamic Explorer satellite family. Results compared favorable to calculations from such general circuit-analysis programs as SPICE. Written in FORTRAN 77.

  11. Radiation emission from small particles

    NASA Astrophysics Data System (ADS)

    Egan, W. G.; Hilgeman, T. W.

    1984-04-01

    Measurements have been made of the IR radiation from monodisperse optically absorbing spherical particles of di-2-ethylhexyl sebacate. The purpose was to validate the Mie emission theory for particles that are small compared with the radiation wavelength. In contradiction to the Mie theory, McGregor has theoretically concluded that radiation absorption or emission is not possible at wavelengths longer than pi times the square root of 2 times the particle diameter for spherical particles. The present results on monodisperse spherical particles of 3, 1, and 0.5 microns emitting at a wavelength of 3.4 microns support the Mie theory predictions.

  12. Small but sturdy: small RNAs in cellular memory and epigenetics

    PubMed Central

    Stuwe, Evelyn; Tóth, Katalin Fejes; Aravin, Alexei A.

    2014-01-01

    Cells in multicellular organisms have distinct identities characterized by their profiles of expressed genes. Cell identities can be stable over a long time and through multiple cellular divisions but are also responsive to extracellular signals. Since the DNA sequence is identical in all cells, a “cellular memory” of expression profiles is achieved by what are defined as epigenetic mechanisms. Two major molecular principles—networks of transcription factors and maintenance of cis-chromatin modifications—have been implicated in maintaining cellular memory. Here we describe recent studies demonstrating that short noncoding RNAs can also provide molecular signals that define epigenetic states of cells. Small RNAs can act independently or cooperate with chromatin modifications to achieve long-lasting effects necessary for cellular memory and transgenerational inheritance. PMID:24589774

  13. Reactions of small molecular systems

    SciTech Connect

    Wittig, C.

    1993-12-01

    This DOE program remains focused on small molecular systems relevant to combustion. Though a number of experimental approaches and machines are available for this research, the authors` activities are centered around the high-n Rydberg time-of-flight (HRTOF) apparatus in this laboratory. One student and one postdoc carry out experiments with this machine and also engage in small intra-group collaborations involving shared equipment. This past year was more productive than the previous two, due to the uninterrupted operation of the HRTOF apparatus. Results were obtained with CH{sub 3}OH, CH{sub 3}SH, Rg-HX complexes, HCOOH, and their deuterated analogs where appropriate. One paper is in print, three have been accepted for publication, and one is under review. Many preliminary results that augur well for the future were obtained with other systems such as HNO{sub 3}, HBr-HI complexes, toluene, etc. Highlights from the past year are presented below that display some of the features of this program.

  14. The DSI small satellite launcher

    NASA Technical Reports Server (NTRS)

    Nichols, S.; Gibbons, D.; Wise, J.; Nguyen, D.

    1992-01-01

    A new launcher has been developed by DSI, that is compatible with the GAS canisters. It has the proven capability to deploy a satellite from an orbiting Shuttle that is 18 inches in diameter, 31 inches long, and weighing 190 pounds. These DSI Launchers were used aboard the Discovery (STS-39) in May 1991 as part of the Infrared Background Signature Survey (IBSS) to deploy three small satellites known as Chemical Release Observation (CRO) satellites A, B, and C. Because the satellites contained hazardous liquids (MMH, UDMH, and MON-10) and were launched from GAS Cylinders without motorized doors, the launchers were required to pass NASA Shuttle Payload safety and verification requirements. Some of the more interesting components of the design were the V-band retention and separation mechanism, the separation springs, and the launcher electronics which provided a properly inhibited release sequence operated through the Small Payload Accommodations Switch Panel (SPASP) on board the Orbiter. The original plan for this launcher was to use a motorized door. The launcher electronics, therefore has the capability to be modified to accommodate the door, if desired.

  15. Small Satellites for Secondary Students

    NASA Astrophysics Data System (ADS)

    Zack, Kevin; Cominsky, Lynn

    2012-11-01

    Small Satellites for Secondary Students is a program funded by a three-year grant from NASA to bridge the gap in STEM education for secondary-school students. This is accomplished by creating the educational resources that are needed to support the development of a small scientific payload in alignment with scientific and technological education standards. The prototype payloads are flexible multi-experiment platforms designed to accommodate a wide range of student abilities with minimal resource requirements. The heart of each payload is an Arduino microcontroller which communicates with components that provide sensor data, Global Positioning System information, and which offer on-board data storage. The payload is built with off-the-shelf components and a pre-etched, custom-designed connector board. The platform also supports real-time telemetry updates through the use of Wi-Fi. To date, the prototype payloads have been tested on both high-powered rockets reaching over 3km and weather balloons tethered at 300m. Multiple successful rocket test runs reaching 1km have been conducted in partnership with amateur rocket clubs including the Association of Experimental Rocketry of the Pacific. From these flights, we are continuing to improve the payload design in order to increase the likelihood of student success.

  16. Spin polarons in the t-t'-J model

    NASA Astrophysics Data System (ADS)

    Bała, Jan; Oleś, Andrzej M.; Zaanen, Jan

    1995-08-01

    Treating the hole-magnon interaction within the self-consistent Born approximation, we demonstrate that the low-energy quasiparticles that occur in the t-J model due to quantum fluctuations of the spin system survive in the models including free hole propagation on the sublattices. The quasiparticle dispersion and weight are found to be strongly dependent on the next-neighbor hopping parameter. The flat band observed near the X point in the high-temperature superconductors is reproduced, but not for the realistic parameters that correspond to the hole-doped system.

  17. Polaron pair mediated triplet generation in polymer/fullerene blends

    PubMed Central

    Dimitrov, Stoichko D.; Wheeler, Scot; Niedzialek, Dorota; Schroeder, Bob C.; Utzat, Hendrik; Frost, Jarvist M.; Yao, Jizhong; Gillett, Alexander; Tuladhar, Pabitra S.; McCulloch, Iain; Nelson, Jenny; Durrant, James R.

    2015-01-01

    Electron spin is a key consideration for the function of organic semiconductors in light-emitting diodes and solar cells, as well as spintronic applications relying on organic magnetoresistance. A mechanism for triplet excited state generation in such systems is by recombination of electron-hole pairs. However, the exact charge recombination mechanism, whether geminate or nongeminate and whether it involves spin-state mixing is not well understood. In this work, the dynamics of free charge separation competing with recombination to polymer triplet states is studied in two closely related polymer-fullerene blends with differing polymer fluorination and photovoltaic performance. Using time-resolved laser spectroscopic techniques and quantum chemical calculations, we show that lower charge separation in the fluorinated system is associated with the formation of bound electron-hole pairs, which undergo spin-state mixing on the nanosecond timescale and subsequent geminate recombination to triplet excitons. We find that these bound electron-hole pairs can be dissociated by electric fields. PMID:25735188

  18. Temperature scaling of effective polaron mobility in energetically disordered media.

    PubMed

    Seki, Kazuhiko; Wojcik, Mariusz

    2016-07-21

    We study effective mobility in 2 dimensional (2D) and 3 dimensional (3D) systems, where hopping transitions of carriers are described by the Marcus equation under a Gaussian density of states in the dilute limit. Using an effective medium approximation (EMA), we determined the coefficient Cd for the effective mobility expressed by μeff∝exp-λ/4kBT-Cdσ(2)/kBT(2)/λ(kBT)(3/2), where λ is the reorganization energy, σ is the standard deviation of the Gaussian density of states, and kBT takes its usual meaning. We found Cd = 1/2 for both 2D and 3D. While various estimates of the coefficient Cd for 3D systems are available in the literature, we provide for the first time the expected Cd value for a 2D system. By means of kinetic Monte-Carlo simulations, we show that the effective mobility is well described by the equation shown above under certain conditions on λ. We also give examples of analysis of experimental data for 2D and 3D systems based on our theoretical results. PMID:27448873

  19. Small number preference in guiding attention.

    PubMed

    Cai, Yong-Chun; Li, Shuang-Xia

    2015-02-01

    Healthy individuals are usually biased toward small numbers when they are asked to mentally bisect number intervals or generate number sequences. Number magnitude may be represented spatially along a left-to-right mental number line. The preference for small numbers is believed to reflect the leftward spatial bias of this numerical representation. This study examined whether small numbers captured visual attention more than larger numbers. Participants were asked to detect a target pre-cued by a small or a large number. We found that the response was faster when the target was pre-cued by a small number than when pre-cued by a large number, suggesting that visual attention is preferentially allocated to small numbers. In addition, this attentional preference for small numbers was distinct for participants of different educational backgrounds. For science or engineering participants, this small number preference was enhanced by left-hand responding and was positively correlated with the small number preference in a random number generation task, suggesting that the small number preference was attributable to a leftward bias of the spatial representation. For liberal arts participants, however, left-hand responding did not enhance the small number preference and no correlations were found between the attention task and the random number generation task, suggesting that non-spatial processing mediated the small number preference. Our findings show that the small number preference occurs as early as the perceptual processing stage and distinct mechanisms underlie the preference for small numbers for participants with different educational backgrounds.

  20. A Survey of Small Factories*

    PubMed Central

    Jefferys, Margot; Wood, C. H.

    1960-01-01

    This survey was undertaken by a group of doctors, nurses, and lecturers in the Department of Public Health of the London School of Hygiene and Tropical Medicine as part of the teaching programme for the Diploma in Public Health. Fifty small factories in an area of a metropolitan borough were invited to answer questions concerning their industrial processes, their labour force, their premises, their first-aid provision, and the visits they received from officials of local and central government. Forty-eight of these factories responded and observations were made by teams of three recording independently of each other in 45. A variety of industries was represented in these 48 firms, half of which employed less than 10 workers. The working environment, in respect of sanitary arrangements, cleanliness and tidiness, lighting on stairs and passage ways, was considered to be unsatisfactory in many firms. Some instances of inadequate safeguards of machines were seen. The accident rate was found to be rather less than the computed national rate for manufacturing industry in 1956. First-aid equipment and workers were also considered to be deficient in a number of instances. In case of accident and for the treatment of minor ailments most firms made use of a local casualty and out-patient department of a general hospital. This service was considered quite adequate. Many firms had not been visited by the Factory Inspector or his deputy during the previous year. Rather more had received visits from the local authority health inspectors. Many firms expressed confusion about the duties and functions of their various official visitors. The conclusions drawn from this limited enquiry were that the working conditions in small factories are often unsatisfactory; that in areas such as the one surveyed it is unrealistic to think in terms of development of an industrial health service similar to those operating in Slough and Harlow; and that the greatest impact on environmental