Sample records for band edge statecalculation

  1. The use of bulk states to accelerate the band edge statecalculation of a semiconductor quantum dot

    Energy Technology Data Exchange (ETDEWEB)

    Vomel, Christof; Tomov, Stanimire Z.; Wang, Lin-Wang; Marques,Osni A.; Dongarra, Jack J.


    We present a new technique to accelerate the convergence of the folded spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We use bulk band states of the materials constituent of the quantum dot to construct initial vectors and a preconditioner. We apply these to accelerate the convergence of the folded spectrum method for the interior states at the top of the valence and the bottom of the conduction band. For large CdSe quantum dots, the number of iteration steps until convergence decreases by about a factor of 4 compared to previous calculations.

  2. New Kronig-Penney Equation Emphasizing the Band Edge Conditions (United States)

    Szmulowicz, Frank


    The Kronig-Penney problem is a textbook example for discussing band dispersions and band gap formation in periodic layered media. For example, in photonic crystals, the behaviour of bands next to the band edges is important for further discussions of such effects as inhibited light emission, slow light and negative index of refraction. However,…

  3. The Red Edge Problem in asteroid band parameter analysis (United States)

    Lindsay, Sean S.; Dunn, Tasha L.; Emery, Joshua P.; Bowles, Neil E.


    Near-infrared reflectance spectra of S-type asteroids contain two absorptions at 1 and 2 μm (band I and II) that are diagnostic of mineralogy. A parameterization of these two bands is frequently employed to determine the mineralogy of S(IV) asteroids through the use of ordinary chondrite calibration equations that link the mineralogy to band parameters. The most widely used calibration study uses a Band II terminal wavelength point (red edge) at 2.50 μm. However, due to the limitations of the NIR detectors on prominent telescopes used in asteroid research, spectral data for asteroids are typically only reliable out to 2.45 μm. We refer to this discrepancy as "The Red Edge Problem." In this report, we evaluate the associated errors for measured band area ratios (BAR = Area BII/BI) and calculated relative abundance measurements. We find that the Red Edge Problem is often not the dominant source of error for the observationally limited red edge set at 2.45 μm, but it frequently is for a red edge set at 2.40 μm. The error, however, is one sided and therefore systematic. As such, we provide equations to adjust measured BARs to values with a different red edge definition. We also provide new ol/(ol+px) calibration equations for red edges set at 2.40 and 2.45 μm.

  4. Edge-Induced Shear Banding in Entangled Polymeric Fluids (United States)

    Hemingway, Ewan J.; Fielding, Suzanne M.


    Despite decades of research, the question of whether solutions and melts of highly entangled polymers exhibit shear banding as their steady state response to a steadily imposed shear flow remains controversial. From a theoretical viewpoint, an important unanswered question is whether the underlying constitutive curve of shear stress σ as a function of shear rate γ ˙ (for states of homogeneous shear) is monotonic, or has a region of negative slope, d σ /d γ ˙ edge fracture." Here we show by numerical simulation that in fact even only very modest edge disturbances—which are the precursor of full edge fracture but might well, in themselves, go unnoticed experimentally—can cause strong secondary flows in the form of shear bands that invade deep into the fluid bulk. Crucially, this is true even when the underlying constitutive curve is monotonically increasing, precluding true bulk shear banding in the absence of edge effects.

  5. Band Edge Dynamics and Multiexciton Generation in Narrow Band Gap HgTe Nanocrystals. (United States)

    Livache, Clément; Goubet, Nicolas; Martinez, Bertille; Jagtap, Amardeep; Qu, Junling; Ithurria, Sandrine; Silly, Mathieu G; Dubertret, Benoit; Lhuillier, Emmanuel


    Mercury chalcogenide nanocrystals and especially HgTe appear as an interesting platform for the design of low cost mid-infrared (mid-IR) detectors. Nevertheless, their electronic structure and transport properties remain poorly understood, and some critical aspects such as the carrier relaxation dynamics at the band edge have been pushed under the rug. Some of the previous reports on dynamics are setup-limited, and all of them have been obtained using photon energy far above the band edge. These observations raise two main questions: (i) what are the carrier dynamics at the band edge and (ii) should we expect some additional effect (multiexciton generation (MEG)) as such narrow band gap materials are excited far above the band edge? To answer these questions, we developed a high-bandwidth setup that allows us to understand and compare the carrier dynamics resonantly pumped at the band edge in the mid-IR and far above the band edge. We demonstrate that fast (>50 MHz) photoresponse can be obtained even in the mid-IR and that MEG is occurring in HgTe nanocrystal arrays with a threshold around 3 times the band edge energy. Furthermore, the photoresponse can be effectively tuned in magnitude and sign using a phototransistor configuration.

  6. Wild Band Edges: The Role of Bandgap Grading and Band-Edge Fluctuations in High-Efficiency Chalcogenide Devices: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Repins, Ingrid; Mansfield, Lorelle; Kanevce, Ana; Jensen, Soren A.; Kuciauskas, Darius; Glynn, Stephen; Barnes, Teresa; Metzger, Wyatt; Burst, James; Jiang, Chun-Sheng; Dippo, Patricia; Harvey, Steve; Teeter, Glenn; Perkins, Craig; Egaas, Brian; Zakutayev, Andriy; Alsmeier, J.-H.; Lussky, T.; Korte, L.; Wilks, R. G.; Bar, M.; Yan, Y.; Lany, Stephan; Zawadzki, Pawel; Park, Ji-Sang; Wei, Suhuai


    Band-edge effects -- including grading, electrostatic fluctuations, bandgap fluctuations, and band tails -- affect chalcogenide device efficiency. These effects now require more careful consideration as efficiencies increase beyond 20%. Several aspects of the relationships between band-edge phenomena and device performance for NREL absorbers are examined. For Cu(In,Ga)Se2 devices, recent increases in diffusion length imply changes to optimum bandgap profile. The origin, impact, and modification of electrostatic and bandgap fluctuations are also discussed. The application of the same principles to devices based on CdTe, kesterites, and emerging absorbers (Cu2SnS3, CuSbS2), considering differences in materials properties and defect formation energies, is examined.

  7. Validity of the concept of band edge in organic semiconductors (United States)

    Horowitz, Gilles


    Because most organic semiconductors are disordered, the more appropriate function to describe their density of states (DOS) is the Gaussian distribution. A striking difference between the Gaussian DOS and the parabolic DOS found in conventional inorganic semiconductors is the fact that it does not allow for a simple and straightforward definition of the band edge. The most usual way found in the literature to define the band edge of a Gaussian DOS consists of extrapolating the tangent to the inflection point of the Gaussian curve. The aim of this paper is to discuss the validity of such a way of conduct. An analysis of data found in the literature shows that the width of the Gaussian distribution is significantly larger than what usually retained in transport models. It is also shown that the validity of the usual definition for the band edge is questioned by the fact that the density of charge carriers behave as a degenerate distribution, even at relatively low doping levels.

  8. Degenerate-band-edge engineering inspired by nonlocal transformation optics

    Directory of Open Access Journals (Sweden)

    Moccia Massimo


    Full Text Available We address the engineering of degenerate-band-edge effects in nonlocal metamaterials. Our approach, inspired by nonlocal-transformation-optics concepts, is based on the approximation of analytically-derived nonlocal constitutive “blueprints”. We illustrate the synthesis procedure, and present and validate a possible implementation based on multilayered metamaterials featuring anisotropic constituents. We also elucidate the physical mechanisms underlying our approach and proposed configuration, and highlight the substantial differences with respect to other examples available in the topical literature.

  9. Band-edge utilization of C-band video transponder for high speed data network (United States)

    Todd, Stephen R.; Seo, Jong-Soo

    International Datacasting Corporation (IDC) has developed a 512 kbits per second C-band satellite transceiver that will operate using the band-edge of video transponders on commercial satellites such as the Anik D series. The system benefits users such as video transponder operators who wish to derive incremental revenue opportunities by expanding their services to include high speed data distribution for digital audio or local area network interconnection with no additional satellite costs. The band-edge system has been tested at IDC's facilities in Ottawa on Anik D1 with the technical support of Satellite Communications Inc. (CANCOM) and Telesat Canada. This paper describes the experimental results using IDC's 512 kbits per second superposed quadrature amplitude modulation (SQAM) transceiver equipped with 3/4 rate foreward error coding (FEC) codec. The discussion highlights the system parameters that optimized the data performance and maintained the video quality. The data link provided 99.8 percent error free minutes when the interference from the video carrier was minimized. Video picture and subcarrier quality were not affected by signal to noise ratio degradation due to intermodulation. This intermodulation could be eliminated by adjusting the video uplink level. The results support the use of SQAM as the digital modulation technique because of its excellent performance in a nonlinear and band-edge environment.

  10. Role of Interlayer Coupling on the Evolution of Band Edges in Few-Layer Phosphorene. (United States)

    Wang, V; Liu, Y C; Kawazoe, Y; Geng, W T


    Using first-principles calculations, we have investigated the evolution of band edges in few-layer phosphorene as a function of the number of P layers. Our results predict that monolayer phosphorene is an indirect band gap semiconductor and its valence band edge is extremely sensitive to strain. Its band gap could undergo an indirect-to-direct transition under a lattice expansion as small as 1% along the zigzag direction. A semiempirical interlayer coupling model is proposed, which can reproduce the evolution of valence band edges obtained by first-principles calculations well. We conclude that the interlayer coupling plays a dominant role in the evolution of the band edges via decreasing both band gap and carrier effective masses with the increase of phosphorene thickness. Scrutiny of the orbital-decomposed band structure provides a better understanding of the upward shift of the valence band maximum, surpassing that of the conduction band minimum.

  11. Band-edge lasing in Rh6G-doped dichromated gelatin at different excitations (United States)

    Ying, Cui-Feng; Zhou, Wen-Yuan; Ye, Qing; Zhang, Xiao-Liang; Tian, Jian-Guo


    One-dimensional photonic crystal band-edge lasing at different excitations was studied experimentally by altering the excitation angle. We considered almost every condition including in-band, out-of-band and near the band edge while keeping the density of states unchanged. Holographic rhodamin 6G-doped dichromated gelatin was used for creating low-threshold photonic band-edge lasing (PBEL). Lasing actions excited near the high-energy and low-energy band edges were observed simultaneously, and their full widths at half maximum were different. The results show that the PBEL intensity and pump efficiency are sensitive to the excitation angle, enhanced obviously at the excitation near the band edge and suppressed distinctly in the band which agreed well with the theoretical prediction. We also demonstrated for the first time that active matters exist not only in the air voids but also in the high-index regions of the gelatin.

  12. Coherent control of spontaneous emission near a photonic band edge

    International Nuclear Information System (INIS)

    Woldeyohannes, Mesfin; John, Sajeev


    We demonstrate the coherent control of spontaneous emission for a three-level atom located within a photonic band gap (PBG) material, with one resonant frequency near the edge of the PBG. Spontaneous emission from the three-level atom can be totally suppressed or strongly enhanced depending on the relative phase between the steady-state control laser coupling the two upper levels and the pump laser pulse used to create an excited state of the atom in the form of a coherent superposition of the two upper levels. Unlike the free-space case, the steady-state inversion of the atomic system is strongly dependent on the externally prescribed initial conditions. This non-zero steady-state population is achieved by virtue of the localization of light in the vicinity of the emitting atom. It is robust to decoherence effects provided that the Rabi frequency of the control laser field exceeds the rate of dephasing interactions. As a result, such a system may be relevant for a single-atom, phase-sensitive optical memory device on the atomic scale. The protected electric dipole within the PBG provides a basis for a qubit to encode information for quantum computations. A detailed literature survey on the nature, fabrication and applications of PBG materials is presented to provide context for this research. (phd tutorial)

  13. Self-consistent study of localization near band edges

    International Nuclear Information System (INIS)

    Brezini, A.


    The localization criterion of Kumar et al. is applied to the case of a uniform distribution for the site energies and particular attention is given to the behaviour of the mobility edge in the limit of weak disorder. The results are similar to other theories but disagree with that of Abou-Chacra and Thouless in the limit of zero disorder. (author)

  14. Electron charge densities at conduction-band edges of semiconductors

    International Nuclear Information System (INIS)

    Richardson, S.L.; Cohen, M.L.; Louie, S.G.; Chelikowsky, J.R.


    We demonstrate that both the empirical pseudopotential method (EPM) and the linear combination of atomiclike orbitals (LCAO) approach are capable of producing consistent electronic charge distributions in a compound semiconductor. Since the EPM approach is known to produce total valence electron charge densities which compare well with experimental x-ray data (e.g., Si), this work serves as a further test for the LCAO method. In particular, the EPM scheme, which uses an extended plane-wave basis, and the LCAO scheme, which employs a localized Gaussian basis, are used, with the same empirical potential as input, to analyze both the total valence electron charge density and the charge density of the first conduction band at the GAMMA, L, and X k points of the Brillouin zone. These charge densities are decomposed into their s-, p-, and d-orbital contributions, and this information is used to interpret the differences in the topologies of the conduction bands at GAMMA, L, and X. Such differences are crucial for a comprehensive understanding of interstitial impurities and the response of specific band states to perturbations in compound semiconductors

  15. Anomalies in the 1D Anderson model: Beyond the band-centre and band-edge cases (United States)

    Tessieri, L.; Izrailev, F. M.


    We consider the one-dimensional Anderson model with weak disorder. Using the Hamiltonian map approach, we analyse the validity of the random-phase approximation for resonant values of the energy, E = 2 cos(πr) , with r a rational number. We expand the invariant measure of the phase variable in powers of the disorder strength and we show that, contrary to what happens at the centre and at the edges of the band, for all other resonant energies the leading term of the invariant measure is uniform. When higher-order terms are taken into account, a modulation of the invariant measure appears for all resonant values of the energy. This implies that, when the localisation length is computed within the second-order approximation in the disorder strength, the Thouless formula is valid everywhere except at the band centre and at the band edges.

  16. Enhancement of broadband optical absorption in photovoltaic devices by band-edge effect of photonic crystals. (United States)

    Tanaka, Yoshinori; Kawamoto, Yosuke; Fujita, Masayuki; Noda, Susumu


    We numerically investigate broadband optical absorption enhancement in thin, 400-nm thick microcrystalline silicon (µc-Si) photovoltaic devices by photonic crystals (PCs). We realize absorption enhancement by coupling the light from the free space to the large area resonant modes at the photonic band-edge induced by the photonic crystals. We show that multiple photonic band-edge modes can be produced by higher order modes in the vertical direction of the Si photovoltaic layer, which can enhance the absorption on multiple wavelengths. Moreover, we reveal that the photonic superlattice structure can produce more photonic band-edge modes that lead to further optical absorption. The absorption average in wavelengths of 500-1000 nm weighted to the solar spectrum (AM 1.5) increases almost twice: from 33% without photonic crystal to 58% with a 4 × 4 period superlattice photonic crystal; our result outperforms the Lambertian textured structure.

  17. Band-edge engineering for controlled multi-modal nanolasing in plasmonic superlattices (United States)

    Wang, Danqing; Yang, Ankun; Wang, Weijia; Hua, Yi; Schaller, Richard D.; Schatz, George C.; Odom, Teri W.


    Single band-edge states can trap light and function as high-quality optical feedback for microscale lasers and nanolasers. However, access to more than a single band-edge mode for nanolasing has not been possible because of limited cavity designs. Here, we describe how plasmonic superlattices—finite-arrays of nanoparticles (patches) grouped into microscale arrays—can support multiple band-edge modes capable of multi-modal nanolasing at programmed emission wavelengths and with large mode spacings. Different lasing modes show distinct input-output light behaviour and decay dynamics that can be tailored by nanoparticle size. By modelling the superlattice nanolasers with a four-level gain system and a time-domain approach, we reveal that the accumulation of population inversion at plasmonic hot spots can be spatially modulated by the diffractive coupling order of the patches. Moreover, we show that symmetry-broken superlattices can sustain switchable nanolasing between a single mode and multiple modes.

  18. Experimental Study of Electronic Quantum Interference, Photonic Crystal Cavity, Photonic Band Edge Effects for Optical Amplification (United States)


    EDGE EFFECTS FOR OPTICAL AMPLIFICATION Shawn-Yu Lin Rensselaer Polytechnic Institute 110 8th Street Troy, New York 12180 26 Jan 2016 Final Report...2014 – 11 Jan 2016 4. TITLE AND SUBTITLE Experimental Study of Electronic Quantum Interference, Photonic Crystal Cavity, Photonic Band Edge Effects...Approved for public release; distribution is unlimited. i Approved for public release; distribution is unlimited. Table of Contents 1.0 Summary

  19. Enhancement of Faraday rotation at photonic-band-gap edge in garnet-based magnetophotonic crystals

    International Nuclear Information System (INIS)

    Zhdanov, A.G.; Fedyanin, A.A.; Aktsipetrov, O.A.; Kobayashi, D.; Uchida, H.; Inoue, M.


    Spectral dependences of Faraday rotation angle in one-dimensional garnet-based magnetophotonic crystals are considered. The enhancement of Faraday angle is demonstrated at the photonic band gap (PBG) edge both theoretically and experimentally. It is shown to be associated with the optical field localization in the magnetic layers of the structure. The advantages of magnetophotonic crystals in comparison with traditional magnetic microcavities are discussed. The specially designed microcavity structures optimized for the Faraday effect enhancement at the PBG edge are suggested

  20. Band-gap and band-edge engineering of multicomponent garnet scintillators from first principles

    Czech Academy of Sciences Publication Activity Database

    Yadav, S.K.; Uberuaga, B.P.; Nikl, Martin; Jiang, C.; Stanek, C.R.


    Roč. 4, č. 5 (2015), "054012-1"-"054012-9" ISSN 2331-7019 R&D Projects: GA ČR GAP204/12/0805 Institutional support: RVO:68378271 Keywords : scintillator * electronic band gap structure * garnets * band gap engineering Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 4.061, year: 2015

  1. Plasmonic band edge effects on the transmission properties of metal gratings

    Directory of Open Access Journals (Sweden)

    D. de Ceglia


    Full Text Available We present a detailed analysis of the optical properties of one-dimensional arrays of slits in metal films. Although enhanced transmission windows are dominated by Fabry-Perot cavity modes localized inside the slits, the periodicity introduces surface modes that can either enhance or inhibit light transmission. We thus illustrate the interaction between cavity modes and surface modes in both finite and infinite arrays of slits. In particular we study a grating that clearly separates surface plasmon effects from Wood-Rayleigh anomalies. The periodicity of the grating induces a strong plasmonic band gap that inhibits coupling to the cavity modes for frequencies near the center of the band gap, thereby reducing the transmission of the grating. Strong field localization at the high energy plasmonic band edge enhances coupling to the cavity modes while field localization at the low energy band edge leads to weak cavity coupling and reduced transmission.

  2. Tuning colloidal quantum dot band edge positions through solution-phase surface chemistry modification (United States)

    Kroupa, Daniel M.; Vörös, Márton; Brawand, Nicholas P.; McNichols, Brett W.; Miller, Elisa M.; Gu, Jing; Nozik, Arthur J.; Sellinger, Alan; Galli, Giulia; Beard, Matthew C.


    Band edge positions of semiconductors determine their functionality in many optoelectronic applications such as photovoltaics, photoelectrochemical cells and light emitting diodes. Here we show that band edge positions of lead sulfide (PbS) colloidal semiconductor nanocrystals, specifically quantum dots (QDs), can be tuned over 2.0 eV through surface chemistry modification. We achieved this remarkable control through the development of simple, robust and scalable solution-phase ligand exchange methods, which completely replace native ligands with functionalized cinnamate ligands, allowing for well-defined, highly tunable chemical systems. By combining experiments and ab initio simulations, we establish clear relationships between QD surface chemistry and the band edge positions of ligand/QD hybrid systems. We find that in addition to ligand dipole, inter-QD ligand shell inter-digitization contributes to the band edge shifts. We expect that our established relationships and principles can help guide future optimization of functional organic/inorganic hybrid nanostructures for diverse optoelectronic applications.

  3. Edge states in lateral p -n junctions in inverted-band HgTe quantum wells (United States)

    Piatrusha, S. U.; Khrapai, V. S.; Kvon, Z. D.; Mikhailov, N. N.; Dvoretsky, S. A.; Tikhonov, E. S.


    We investigate lateral p -n junctions, electrostatically defined in 14-nm-wide HgTe-based quantum wells (QWs) with inverted band structure. The p -n junction resistances are close to h /2 e2 , consistent with some previous experiments on 8 -10 nm QWs, and the current-voltage characteristics are highly linear, indicating the transport via ballistic helical edge states. Shot noise measurements are performed in order to further verify the underlying transport mechanism. We discuss the role of unknown inelastic relaxation rates in the leads and in the edge channels for the correct interpretation of the noise data. Although the interpretation in favor of the helical edge states seems more consistent, a definite conclusion cannot be drawn based on the present experiment. Our approach looks promising for the study of short quasiballistic edges in topological insulators in suitable geometry.

  4. Effect of edge defects on band structure of zigzag graphene nanoribbons (United States)

    Wadhwa, Payal; Kumar, Shailesh; Dhilip Kumar, T. J.; Shukla, Alok; Kumar, Rakesh


    In this article, we report band structure studies of zigzag graphene nanoribbons (ZGNRs) on introducing defects (sp3 hybridized carbon atoms) in different concentrations at edges by varying the ratio of sp3 to sp2 hybridized carbon atoms. On the basis of theoretical analyses, bandgap values of ZGNRs are found to be strongly dependent on the relative arrangement of sp3 to sp2 hybridized carbon atoms at the edges for a defect concentration; so the findings would greatly help in understanding the bandgap of nanoribbons for their electronic applications.

  5. Conduction band edge effective mass of La-doped BaSnO3 (United States)

    James Allen, S.; Raghavan, Santosh; Schumann, Timo; Law, Ka-Ming; Stemmer, Susanne


    BaSnO3 has attracted attention as a promising material for applications requiring wide band gap, high electron mobility semiconductors, and moreover possesses the same perovskite crystal structure as many functional oxides. A key parameter for these applications and for the interpretation of its properties is the conduction band effective mass. We measure the plasma frequency of La-doped BaSnO3 thin films by glancing incidence, parallel-polarized resonant reflectivity. Using the known optical dielectric constant and measured electron density, the resonant frequency determines the band edge electron mass to be 0.19 ± 0.01. The results allow for testing band structure calculations and transport models.

  6. Lifshitz singularities in random harmonic chains: periodic amplitudes near the band edge and near special frequencies

    International Nuclear Information System (INIS)

    Nieuwenhuizen, T.M.; Luck, J.M.


    The authors give a complete description of the scaling behavior of the integrated density of states of random harmonic chains with random masses near the band edge omega/sub max/ and near special frequencies omega/sub s/. There are four different situations: omega upward arrow omega/sub max/, omega upward arrow omega/sub s/, omega upward arrow omega/sub s/ (critical case), omega upward arrow omega/sub s/ (general case). Their analytic results have the form of infinite sums involving Fourier coefficients of the scaling behavior of the Dyson-Schmidt function at the special frequency or the band edge. Binary mass distributions are considered in detail in the limit of a small fraction rho of light masses. Their predictions are compared with extensive numerical data

  7. Experimental verification of directional liquid surface wave emission at band edge frequencies

    International Nuclear Information System (INIS)

    Wang, Zhenyu; Zhang, Pei; Zhang, Yongqiang; Nie, Xiaofei


    Directional liquid surface wave emission at band edge frequencies is an interesting physical phenomenon and has already been studied in theoretical research. There has been no experimental validation of it to date, however. This paper has as its subject the experimental investigation of the emission effect when a point source is placed inside a finite square array of rigid cylinders standing vertically in liquid. Both the wave patterns and spatial intensities are obtained by experiment and compared with simulated results calculated by using the finite element method. We can see from this comparison that the two results correspond closely both at lower and upper band edge frequency. Obvious directional wave emission along a desired direction is observed in the source structures, confirming previous theoretical predictions. In the future, this method could serve as a directional liquid wave source in applications used in hydraulic and ocean engineering for the concentration of wave energy

  8. Atom-atom interactions around the band edge of a photonic crystal waveguide. (United States)

    Hood, Jonathan D; Goban, Akihisa; Asenjo-Garcia, Ana; Lu, Mingwu; Yu, Su-Peng; Chang, Darrick E; Kimble, H J


    Tailoring the interactions between quantum emitters and single photons constitutes one of the cornerstones of quantum optics. Coupling a quantum emitter to the band edge of a photonic crystal waveguide (PCW) provides a unique platform for tuning these interactions. In particular, the cross-over from propagating fields [Formula: see text] outside the bandgap to localized fields [Formula: see text] within the bandgap should be accompanied by a transition from largely dissipative atom-atom interactions to a regime where dispersive atom-atom interactions are dominant. Here, we experimentally observe this transition by shifting the band edge frequency of the PCW relative to the [Formula: see text] line of atomic cesium for [Formula: see text] atoms trapped along the PCW. Our results are the initial demonstration of this paradigm for coherent atom-atom interactions with low dissipation into the guided mode.

  9. Atom–atom interactions around the band edge of a photonic crystal waveguide (United States)

    Hood, Jonathan D.; Goban, Akihisa; Asenjo-Garcia, Ana; Lu, Mingwu; Yu, Su-Peng; Chang, Darrick E.; Kimble, H. J.


    Tailoring the interactions between quantum emitters and single photons constitutes one of the cornerstones of quantum optics. Coupling a quantum emitter to the band edge of a photonic crystal waveguide (PCW) provides a unique platform for tuning these interactions. In particular, the cross-over from propagating fields E(x)∝e±ikxx outside the bandgap to localized fields E(x)∝e−κx|x| within the bandgap should be accompanied by a transition from largely dissipative atom–atom interactions to a regime where dispersive atom–atom interactions are dominant. Here, we experimentally observe this transition by shifting the band edge frequency of the PCW relative to the D1 line of atomic cesium for N¯=3.0±0.5 atoms trapped along the PCW. Our results are the initial demonstration of this paradigm for coherent atom–atom interactions with low dissipation into the guided mode. PMID:27582467

  10. Band-edge lasing and miniband lasing in 1-D dual-periodic photonic crystal (United States)

    Ying, Cui-Feng; Zhou, Wen-Yuan; Li, Yi; Ye, Qing; Zhang, Chun-Ping; Tian, Jian-Guo


    Herein, we report two different dual-periodic Photonic Crystals (PCs) in dichromated gelatin emulsion which are fabricated by four-beam holography and double-exposure holography. The minibands with high Q-factors have been evidently located in both two structures. By taking into account the non-uniform distribution of material, the numerical results agree quite well with the experimental results. We also compared the band-edge lasing in single-periodic PC and miniband lasing in Moiré dual-periodic PC. Due to extremely flat dispersion and large mode volume of the miniband, high optical conversion efficiency in miniband lasing is achieved as compared with that of band-edge lasing. Such effect may provide potential applications in low-threshold lasers and ultra-sensitive fluorescent probes in biological assays.

  11. Optical constants and band edge of amorphous zinc oxide thin films

    International Nuclear Information System (INIS)

    Khoshman, Jebreel M.; Kordesch, Martin E.


    The optical characteristics of amorphous zinc oxide (a-ZnO) thin films grown by radio frequency reactive magnetron sputtering on various substrates at temperature -8 -0.32, respectively. The band edge of the films on Si (100) and quartz has been determined by spectroscopic ellipsometry (3.39 ± 0.05 eV) and spectrophotometric (3.35 ± 0.05 eV) methods, respectively. From the angle dependence of the p-polarized reflectivity we deduce a Brewster angle of 60.5 deg. Measurement of the polarized optical properties shows a high transmissivity (81%-99%) and low absorptivity (< 5%) in the visible and near infrared regions at different angles of incidence. Also, we found that there was a higher absorptivity for wavelength < 370 nm. This wavelength, ∼ 370 nm, therefore indicated that the band edge for a-ZnO thin films is about 3.35 eV

  12. Band edges determination of CuInS2 thin films prepared by electrodeposition

    International Nuclear Information System (INIS)

    Martinez, A.M.; Arriaga, L.G.; Fernandez, A.M.; Cano, U.


    A CuInS 2 (CIS) semiconductor thin film was growth by electrodeposition on a stainless steel substrate. In order to improve the polycrystallinity the samples were annealed in a N 2 atmosphere. The films were characterized by electrochemical techniques and X ray diffraction and their band gaps were determined by photocurrent spectroscopy. When the electrolytic bath has the same concentration [Cu 2+ ] = [In 3+ ] the resulting film was of the n-type, while for different concentrations of Cu and In ions the film was of the p-type. A depletion zone during capacitance-voltage measurements at 10 kHz frequency was seen over the voltage range used. Using C-V plots in the depletion zone, flat-band potentials and the energetic position of band edges were calculated

  13. Biologically inspired band-edge laser action from semiconductor with dipole-forbidden band-gap transition (United States)

    Wang, Cih-Su; Liau, Chi-Shung; Sun, Tzu-Ming; Chen, Yu-Chia; Lin, Tai-Yuan; Chen, Yang-Fang


    A new approach is proposed to light up band-edge stimulated emission arising from a semiconductor with dipole-forbidden band-gap transition. To illustrate our working principle, here we demonstrate the feasibility on the composite of SnO2 nanowires (NWs) and chicken albumen. SnO2 NWs, which merely emit visible defect emission, are observed to generate a strong ultraviolet fluorescence centered at 387 nm assisted by chicken albumen at room temperature. In addition, a stunning laser action is further discovered in the albumen/SnO2 NWs composite system. The underlying mechanism is interpreted in terms of the fluorescence resonance energy transfer (FRET) from the chicken albumen protein to SnO2 NWs. More importantly, the giant oscillator strength of shallow defect states, which is served orders of magnitude larger than that of the free exciton, plays a decisive role. Our approach therefore shows that bio-materials exhibit a great potential in applications for novel light emitters, which may open up a new avenue for the development of bio-inspired optoelectronic devices. PMID:25758749

  14. Sharp edge broad-band lasers for ``white-light`` cooling in storage rings

    Energy Technology Data Exchange (ETDEWEB)

    Atutov, S.N.; Calabrese, R.; Guidi, V.; Lenisa, P.; Petruio, S. [Ferrara Univ. (Italy). Dipt. di Fisica]|[Istituto Nazionale di Fisica Nucleare, Ferrara (Italy); Mariotti, E.; Moi, L. [INFM, Siena (Italy)]|[Dipt. di Fisica, Univ. di Siena (Italy)


    We have developed broad-band laser sources which show a sharp edge in their spectra and are particularly suitable for ``white-laser`` cooling of ions in storage rings. They allow for a very large velocity capture range by maintaining the same cooling rate allowed by the single mode lasers. A large fraction of the circulating ions are expected to be cooled both in coasting and bunched beams. The device, which does not use an active medium, can easily operate at any frequency from UV to IR spectral region. (orig.). 13 refs.

  15. Paired modes of heterostructure cavities in photonic crystal waveguides with split band edges

    DEFF Research Database (Denmark)

    Mahmoodian, Sahand; Sukhorukov, Andrey A.; Ha, Sangwoo


    We investigate the modes of double heterostructure cavities where the underlying photonic crystal waveguide has been dispersion engineered to have two band-edges inside the Brillouin zone. By deriving and using a perturbative method, we show that these structures possess two modes. For unapodized...... cavities, the relative detuning of the two modes can be controlled by changing the cavity length, and for particular lengths, a resonant-like effect makes the modes degenerate. For apodized cavities no such resonances exist and the modes are always non-degenerate....

  16. Dirac Cones, Topological Edge States, and Nontrivial Flat Bands in Two-Dimensional Semiconductors with a Honeycomb Nanogeometry

    Directory of Open Access Journals (Sweden)

    E. Kalesaki


    Full Text Available We study theoretically two-dimensional single-crystalline sheets of semiconductors that form a honeycomb lattice with a period below 10 nm. These systems could combine the usual semiconductor properties with Dirac bands. Using atomistic tight-binding calculations, we show that both the atomic lattice and the overall geometry influence the band structure, revealing materials with unusual electronic properties. In rocksalt Pb chalcogenides, the expected Dirac-type features are clouded by a complex band structure. However, in the case of zinc-blende Cd-chalcogenide semiconductors, the honeycomb nanogeometry leads to rich band structures, including, in the conduction band, Dirac cones at two distinct energies and nontrivial flat bands and, in the valence band, topological edge states. These edge states are present in several electronic gaps opened in the valence band by the spin-orbit coupling and the quantum confinement in the honeycomb geometry. The lowest Dirac conduction band has S-orbital character and is equivalent to the π-π^{⋆} band of graphene but with renormalized couplings. The conduction bands higher in energy have no counterpart in graphene; they combine a Dirac cone and flat bands because of their P-orbital character. We show that the width of the Dirac bands varies between tens and hundreds of meV. These systems emerge as remarkable platforms for studying complex electronic phases starting from conventional semiconductors. Recent advancements in colloidal chemistry indicate that these materials can be synthesized from semiconductor nanocrystals.

  17. Electrochemical determination of CdS band edges and semiconducting parameters

    International Nuclear Information System (INIS)

    Miandari, Somaieh; Jafarian, Majid; Mahjani, Mohammad Ghasem; Heidaripour, Ashraf; Gobal, Fereydoon


    Cadmium sulfide (CdS) thin film was electrodeposited on indium tin oxide (ITO) by chronoamperometry. The SEM images showed that hexagonal sheets of CdS deposited on the ITO surface. The X-ray diffraction (XRD) analysis confirmed this structure for CdS crystals and the average of crystalline size and the lattice constant parameters are approximately 39.54 and a = 0.4136, c = 0.6696 nm respectively. Photo-electrochemical investigations were performed by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) techniques. CdS band edges and density of states (DOS) were determined by CV technique. The band gap energy (E bg ) was measured by ultraviolet–visible (UV–vis) spectroscopy and electrochemical methods. Mott–Schottky plots were used to find the values of flat band potential (E fb ), donor density (N D ) and Debye length (L D ). Also, the position of surface states was investigated by Mott–Schottky and LSV techniques. EIS was employed to confirm our electrochemical findings and investigate the charge transfer mechanism. (author)

  18. Suppression of near band edge emission in specially engineered ZnO twin nanorods. (United States)

    Singh, Avanendra; Senapati, Kartik; Satpati, Biswarup; Sahoo, Pratap K


    We report the synthesis of a unique zinc oxide nanorod structure in which an amorphous ZnO layer is sandwiched between two identical crystalline segments of ZnO. A simple hydrothermal reaction method was used for this purpose, which allowed us to tune the amorphous and crystalline sections of the nanorods via reaction temperature. A systematic study of the morphology and dimensions of the nanorods grown under various conditions was performed using a combination of scanning and transmission electron microscopy. Transmission electron microscopy (TEM) clearly showed an amorphous separation between the two crystalline segments. UV-vis absorption spectroscopy of the twin nanorods (TNRs) showed a redshift in the optical band gap as a function of the growth duration, indicating slightly stressed growth of the crystalline segments. For a longer growth duration, as the amorphous gap starts to get bridged by crystalline growth, redshift in optical band gap becomes constant. This confirms a true mechanical gap between the two crystalline segments of the nanorods. Temperature dependent photoluminescence (PL) spectra of the TNRs showed a variation in free exciton (FX) emission energy, which fitted very well to a model incorporating lattice dilation in addition to the standard electron-phonon interactions. At low temperatures (below ∼180 K) we observed the appearance of visible emission peaks due to localization of defect levels. A loss in the near band edge emission intensity was observed at low temperatures, commensurate with the appearance of defect emission in the visible range.

  19. Microscopic bosonization of band structures: x-ray processes beyond the Fermi edge (United States)

    Snyman, Izak; Florens, Serge


    Bosonization provides a powerful analytical framework to deal with one-dimensional strongly interacting fermion systems, which makes it a cornerstone in quantum many-body theory. However, this success comes at the expense of using effective infrared parameters, and restricting the description to low energy states near the Fermi level. We propose a radical extension of the bosonization technique that overcomes both limitations, allowing computations with microscopic lattice Hamiltonians, from the Fermi level down to the bottom of the band. The formalism rests on the simple idea of representating the fermion kinetic term in the energy domain, after which it can be expressed in terms of free bosonic degrees of freedom. As a result, one- and two-body fermionic scattering processes generate anharmonic boson-boson interactions, even in the forward channel. We show that up to moderate interaction strengths, these non-linearities can be treated analytically at all energy scales, using the x-ray emission problem as a showcase. In the strong interaction regime, we employ a systematic variational solution of the bosonic theory, and obtain results that agree quantitatively with an exact diagonalization of the original one-particle fermionic model. This provides a proof of the fully microscopic character of bosonization, on all energy scales, for an arbitrary band structure. Besides recovering the known x-ray edge singularity at the emission threshold, we find strong signatures of correlations even at emission frequencies beyond the band bottom.

  20. The northern edge of the band of solar wind variability: Ulysses at ∼4.5AU

    International Nuclear Information System (INIS)

    Gosling, J.T.; Bame, S.J.; Feldman, W.C.; McComas, D.J.; Riley, P.; Goldstein, B.E.; Neugebauer, M.


    Ulysses observations reveal that the northern edge of the low-latitude band of solar wind variability at ∼4.5AU was located at N30 degree in the latter part of 1996 when solar activity was at a minimum. This edge latitude is intermediate between edge latitudes found during previous encounters with the band edge along different portions of Ulysses close-quote polar orbit about the Sun. Corotating interaction regions, CIRs, near the northern edge of the band were tilted in such a manner that the forward and reverse shocks bounding the CIRs were propagating equatorward and poleward, respectively, providing definite confirmation that CIRs have opposed tilts in the opposite solar hemispheres. No shocks or coronal mass ejections, CMEs, were detected during the ∼1.5y traverse of the northern, high-latitude northern hemisphere; however, at the northern edge of the band of variability an expanding CME was observed that was driving a shock into the high-speed wind.copyright 1997 American Geophysical Union

  1. Thermally switchable photonic band-edge to random laser emission in dye-doped cholesteric liquid crystals (United States)

    Ye, Lihua; Wang, Yan; Feng, Yangyang; Liu, Bo; Gu, Bing; Cui, Yiping; Lu, Yanqing


    By changing the doping concentration of the chiral agent to adjust the relative position of the reflection band of cholesteric liquid crystals and the fluorescence emission spectrum of the dye, photonic band-edge and random lasing were observed, respectively. The reflection band of the cholesteric phase liquid crystal can also be controlled by adjusting the temperature: the reflection band is blue-shifted with increasing temperature, and a reversible switch from photonic band-edge to random lasing is obtained. Furthermore, the laser line width can be thermally adjusted from 1.1 nm (at 27 °C) to 4.6 nm (at 32.1 °C). A thermally tunable polarization state of a random laser from dual cells was observed, broadening the field of application liquid crystal random lasers.

  2. Giant amplification in degenerate band edge slow-wave structures interacting with an electron beam

    Energy Technology Data Exchange (ETDEWEB)

    Othman, Mohamed A. K.; Veysi, Mehdi; Capolino, Filippo [Department of Electrical Engineering and Computer Science, University of California, Irvine, California 92697 (United States); Figotin, Alexander [Department of Mathematics, University of California, Irvine, California 92697 (United States)


    We propose a new amplification regime based on a synchronous operation of four degenerate electromagnetic (EM) modes in a slow-wave structure and the electron beam, referred to as super synchronization. These four EM modes arise in a Fabry-Pérot cavity when degenerate band edge (DBE) condition is satisfied. The modes interact constructively with the electron beam resulting in superior amplification. In particular, much larger gains are achieved for smaller beam currents compared to conventional structures based on synchronization with only a single EM mode. We demonstrate giant gain scaling with respect to the length of the slow-wave structure compared to conventional Pierce type single mode traveling wave tube amplifiers. We construct a coupled transmission line model for a loaded waveguide slow-wave structure exhibiting a DBE, and investigate the phenomenon of giant gain via super synchronization using the Pierce model generalized to multimode interaction.

  3. Largely enhanced near band edge emission of ultrathin zinc oxide nanowire/gold nanoparticles composites by surface plasmon resonance (United States)

    Li, Lei; Wang, Chenying; Han, Feng; Yang, Shuming; Jing, Weixuan; Jiang, Zhuangde


    Ultrathin zinc oxide nanowires with diameter less than 50 nm were synthesized by polyethyleneimine assisted solution method. Zinc oxide nanowire near band edge emission was enhanced obviously by gold nanoparticles coating, and a max 26 times enhancement was realized. The defects caused visible light emission was also quenched to noise level when gold was deposited more than 10 s. The large near band edge emission enhancement was caused by surface plasmon resonance mediated luminescent energy transfer, which absorbed the visible light energy and transferred to the near band edge emission. The large surface to volume ratio enhanced the coupling strength between gold nanoparticles and ultrathin zinc oxide nanowires. This research provide a method to improve the luminescent efficiency of zinc oxide nanowires.

  4. Band edge electronic structure of transition metal/rare earth oxide dielectrics (United States)

    Lucovsky, Gerald


    This article addresses band edge electronic structure of transition metal/rare earth (TM/RE) non-crystalline and nano-crystalline elemental and complex oxide high- k dielectrics for advanced semiconductor devices. Experimental approaches include X-ray absorption spectroscopy (XAS) from TM, RE and oxygen core states, photoconductivity (PC), and visible/vacuum ultra-violet (UV) spectroscopic ellipsometry (SE) combined with ab initio theory is applied to small clusters. These measurements are complemented by Fourier transform infra-red absorption (FTIR), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). Two issues are highlighted: Jahn-Teller term splittings that remove d-state degeneracies of states at the bottom of the conduction band, and chemical phase separation and crystallinity in Zr and Hf silicates and ternary (Zr(Hf)O 2) x(Si 3N 4) y(SiO 2) 1- x- y alloys. Engineering solutions for optimization of both classes of high- k dielectric films, including limits imposed on the continued and ultimate scaling of the equivalent oxide thickness (EOT) are addressed.

  5. Adjustment of Sentinel-2 Multi-Spectral Instrument (MSI Red-Edge Band Reflectance to Nadir BRDF Adjusted Reflectance (NBAR and Quantification of Red-Edge Band BRDF Effects

    Directory of Open Access Journals (Sweden)

    David P. Roy


    Full Text Available Optical wavelength satellite data have directional reflectance effects over non-Lambertian surfaces, described by the bidirectional reflectance distribution function (BRDF. The Sentinel-2 multi-spectral instrument (MSI acquires data over a 20.6° field of view that have been shown to have non-negligible BRDF effects in the visible, near-infrared, and short wave infrared bands. MSI red-edge BRDF effects have not been investigated. In this study, they are quantified by an examination of 6.6 million (January 2016 and 10.7 million (April 2016 pairs of forward and back scatter reflectance observations extracted over approximately 20° × 10° of southern Africa. Non-negligible MSI red-edge BRDF effects up to 0.08 (reflectance units across the 290 km wide MSI swath are documented. A recently published MODIS BRDF parameter c-factor approach to adjust MSI visible, near-infrared, and short wave infrared reflectance to nadir BRDF-adjusted reflectance (NBAR is adapted for application to the MSI red-edge bands. The red-edge band BRDF parameters needed to implement the algorithm are provided. The parameters are derived by a linear wavelength interpolation of fixed global MODIS red and NIR BRDF model parameters. The efficacy of the interpolation is investigated using POLDER red, red-edge, and NIR BRDF model parameters, and is shown to be appropriate for the c-factor NBAR generation approach. After adjustment to NBAR, red-edge MSI BRDF effects were reduced for the January data (acquired close to the solar principal where BRDF effects are maximal and the April data (acquired close to the orthogonal plane for all the MSI red-edge bands.

  6. The use of bulk states to accelerate the band edge state calculation of a semiconductor quantum dot

    International Nuclear Information System (INIS)

    Voemel, Christof; Tomov, Stanimire Z.; Wang, Lin-Wang; Marques, Osni A.; Dongarra, Jack J.


    We present a new technique to accelerate the convergence of the folded spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We use bulk band states of the materials constituent of the quantum dot to construct initial vectors and a preconditioner. We apply these to accelerate the convergence of the folded spectrum method for the interior states at the top of the valence and the bottom of the conduction band. For large CdSe quantum dots, the number of iteration steps until convergence decreases by about a factor of 4 compared to previous calculations

  7. Opposing effects of stacking faults and antisite domain boundaries on the conduction band edge in kesterite quaternary semiconductors (United States)

    Park, Ji-Sang; Kim, Sunghyun; Walsh, Aron


    We investigated stability and the electronic structure of extended defects including antisite domain boundaries and stacking faults in the kesterite-structured semiconductors, Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe). Our hybrid density functional theory calculations show that stacking faults in CZTS and CZTSe induce a higher conduction band edge than the bulk counterparts, and thus the stacking faults act as electron barriers. Antisite domain boundaries, however, accumulate electrons as the conduction band edge is reduced in energy, having an opposite role. An Ising model was constructed to account for the stability of stacking faults, which shows the nearest-neighbor interaction is stronger in the case of the selenide.

  8. A Short Course on Topological Insulators: Band-structure topology and edge states in one and two dimensions


    Asbóth, János K.; Oroszlány, László; Pályi, András


    This course-based primer provides newcomers to the field with a concise introduction to some of the core topics in the emerging field of topological band insulators in one and two dimensions. The aim is to provide a basic understanding of edge states, bulk topological invariants, and of the bulk--boundary correspondence with as simple mathematical tools as possible. We use noninteracting lattice models of topological insulators, building gradually on these to arrive from the simplest one-dime...

  9. Band Edge Energetics of Heterostructured Nanorods: Photoemission Spectroscopy and Waveguide Spectroelectrochemistry of Au-Tipped CdSe Nanorod Monolayers. (United States)

    Ehamparam, Ramanan; Pavlopoulos, Nicholas G; Liao, Michael W; Hill, Lawrence J; Armstrong, Neal R; Pyun, Jeffrey; Saavedra, S Scott


    Conduction and valence band energies (ECB, EVB) for CdSe nanorods (NRs) functionalized with Au nanoparticle (NP) tips are reported here, referenced to the vacuum scale. We use (a) UV photoemission spectroscopy (UPS) to measure EVB for NR films, utilizing advanced approaches to secondary electron background correction, satellite removal to enhance spectral contrast, and correction for shifts in local vacuum levels; and (b) waveguide-based spectroelectrochemistry to measure ECB from onset potentials for electron injection into NR films tethered to ITO. For untipped CdSe NRs, both approaches show EVB = 5.9-6.1 eV and ECB = 4.1-4.3 eV. Addition of Au tips alters the NR band edge energies and introduces midgap states, in ways that are predicted to influence the efficiency of these nanomaterials as photoelectrocatalysts. UPS results show that Au tipping shifts EVB closer to vacuum by up to 0.4 eV, shifts the apparent Fermi energy toward the middle of the band gap, and introduces additional states above EVB. Spectroelectrochemical results confirm these trends: Au tipping shifts ECB closer to vacuum, by 0.4-0.6 eV, and introduces midgap states below ECB, which are assigned as metal-semiconductor interface (MSI) states. Characterization of these band edge energies and understanding the origins of MSI states is needed to design energy conversion systems with proper band alignment between the light absorbing NR, the NP catalyst, and solution electron donors and acceptors. The complementary characterization protocols presented here should be applicable to a wide variety of thin films of heterogeneous photoactive nanomaterials, aiding in the identification of the most promising material combinations for photoelectrochemical energy conversion.

  10. Band edge tuned ZnxCd1-xS solid solution nanopowders for efficient solar photocatalysis. (United States)

    Ghosh, Shrabani; Sarkar, Samrat; Das, Bikram Kumar; Sen, Dipayan; Samanta, Madhupriya; Chattopadhyay, Kalyan Kumar


    This work highlights the synthesis of zinc blende Zn x Cd 1-x S ternary solid solutions with a tunable bandgap. Composition dependent band gaps are realized due to the effective band edge tuning of the solid solutions which in turn show decent photocatalytic behaviour. The bandgap of Zn x Cd 1-x S increases as Zn composition increases. It is interesting to note that the highest catalytic activity is observed for Zn 0.8 Cd 0.2 S (E g = 2.83 eV) in the visible spectra due to the presence of defect states in the bandgap around 2.35 eV which has been explicated according to the results of photoluminescence spectra. Density of states (DOS) analysis provides further theoretical insight into the more negative conduction band edge for x = 0.8 than other samples. It also determines generation of intermediate states due to sulfur vacancy which is responsible for more electron-hole generation and the highest rate of Methyl Orange (MO) degradation under natural sunlight irradiation.

  11. Single Pixel, Single Band Microstrip Antenna for Sub-Millimeter Wavelength Detection Using Transition Edge Superconducting Bolometric Receivers (United States)

    Hunt, Cynthia; Bock, Jamie J.; Day, Peter K.; Goldin, Alexey; Lange, Andrew E.; Leduc, Henry G.; Vayonakis, Anastasios; Zmuidzinas, Jonas

    We are developing a single pixel antenna coupled bolometric detector as a precursor to the SAMBA (Superconducting Antenna-coupled Multi-frequency Bolometric Array) instrument. Our device consists of a dual slot microstrip antenna coupled to an Al/Ti/Au voltage-biased transition edge superconducting bolometer (TES). The coupling architecture involves propagating the signal along superconducting microstrip lines and terminating the lines at a normal metal resistor on a thermally isolated island. The device, which is inherently polarization sensitive, is optimized to for 100GHz band measurements, ideal for future implementation as an astronomical sub-millimeter instrument. We will present recent tests of these single pixel detectors.

  12. Spontaneous emission near the band edge of a three-dimensional photonic crystal: a fractional calculus approach

    International Nuclear Information System (INIS)

    Cheng, S-C; Wu, J-N; Tsai, M-R; Hsieh, W-F


    We suggest a better mathematical method, fractional calculus, for studying the behavior of the atom-field interaction in photonic crystals. By studying the spontaneous emission of an atom in a photonic crystal with a one-band isotropic model, we found that the long-time inducing memory of the spontaneous emission is a fractional phenomenon. This behavior could be well described by fractional calculus. The results show no steady photon-atom bound state for the atomic resonant transition frequency lying in the proximity of the allowed band edge which was encountered in a previous study (Woldeyohannes and John 2003 J. Opt. B: Quantum Semiclass. Opt. 5 R43). The correctness of this result is validated by the 'cut-off smoothing' density of photon states (DOS) with fractional calculus. By obtaining a rigorous solution without the multiple-valued problem for the system, we show that the method of fractional calculus has a logically concise property.

  13. Direct measurement of band edge discontinuity in individual core-shell nanowires by photocurrent spectroscopy. (United States)

    Chen, Guannan; Sun, Guan; Ding, Yujie J; Prete, Paola; Miccoli, Ilio; Lovergine, Nico; Shtrikman, Hadas; Kung, Patrick; Livneh, Tsachi; Spanier, Jonathan E


    Group III-V coaxial core-shell semiconducting nanowire heterostructures possess unique advantages over their planar counterparts in logic, photovoltaic, and light-emitting devices. Dimensional confinement of electronic carriers and interface complexity in nanowires are known to produce local electronic potential landscapes along the radial direction that deviate from those along the normal to planar heterojunction interfaces. However, understanding of selected electronic and optoelectronic carrier transport properties and device characteristics remains lacking without a direct measurement of band alignment in individual nanowires. Here, we report on, in the GaAs/AlxGa1-xAs and GaAs/AlAs core-shell nanowire systems, how photocurrent and photoluminescence spectroscopies can be used together to construct a band diagram of an individual heterostructure nanowire with high spectral resolution, enabling quantification of conduction band offsets.

  14. Selective tuning of enhancement in near band edge emission in hydrothermally grown ZnO nanorods coated with gold

    Energy Technology Data Exchange (ETDEWEB)

    Dixit, Tejendra, E-mail: [Molecular and Nanoelectronics Research Group (MNRG), Department of Electrical Engineering, IIT Indore, Indore, Madhya Pradesh (India); Palani, I.A., E-mail: [Mechatronics and Instrumentation Lab, Department of Mechanical Engineering, IIT Indore, Indore, Madhya Pradesh (India); Centre of Material Science and Engineering, IIT Indore, Indore, Madhya Pradesh (India); Singh, Vipul, E-mail: [Molecular and Nanoelectronics Research Group (MNRG), Department of Electrical Engineering, IIT Indore, Indore, Madhya Pradesh (India); Centre of Material Science and Engineering, IIT Indore, Indore, Madhya Pradesh (India)


    The room-temperature photoluminescence (PL) spectra of hydrothermally grown ZnO nanorods (NRs) coated with Au using dc sputtering and thermal evaporation were systematically investigated. Au coated (via dc sputtering) ZnO NRs were found to exhibit very large near band edge emission enhancement, on the contrary Au coated (via thermal evaporation) ZnO NRs showed suppression in the near band edge emission peak. These observed results were further confirmed by excitation intensity (EI) dependent PL spectra of different samples. Further using Raman spectra it has been observed that the longitudinal optical (LO) phonons exhibit an enhancement and a weakening by the Au coatings, using dc sputtering and thermal evaporation respectively. Finally by controlling the concentration of KMnO{sub 4} as an additive during the hydrothermal growth, selective tuning in the defect density was carried out, which was later utilized to probe the effect of defect density of the Au–ZnO plasmonic coupling. Moreover, our results strongly suggest that the EI dependent PL has a strong dependence on the metal coating technique. The findings presented in this article clearly indicate the dependence of Au–ZnO plasmonic coupling on the overall defect density and the process of Au deposition.

  15. Selective tuning of enhancement in near band edge emission in hydrothermally grown ZnO nanorods coated with gold

    International Nuclear Information System (INIS)

    Dixit, Tejendra; Palani, I.A.; Singh, Vipul


    The room-temperature photoluminescence (PL) spectra of hydrothermally grown ZnO nanorods (NRs) coated with Au using dc sputtering and thermal evaporation were systematically investigated. Au coated (via dc sputtering) ZnO NRs were found to exhibit very large near band edge emission enhancement, on the contrary Au coated (via thermal evaporation) ZnO NRs showed suppression in the near band edge emission peak. These observed results were further confirmed by excitation intensity (EI) dependent PL spectra of different samples. Further using Raman spectra it has been observed that the longitudinal optical (LO) phonons exhibit an enhancement and a weakening by the Au coatings, using dc sputtering and thermal evaporation respectively. Finally by controlling the concentration of KMnO 4 as an additive during the hydrothermal growth, selective tuning in the defect density was carried out, which was later utilized to probe the effect of defect density of the Au–ZnO plasmonic coupling. Moreover, our results strongly suggest that the EI dependent PL has a strong dependence on the metal coating technique. The findings presented in this article clearly indicate the dependence of Au–ZnO plasmonic coupling on the overall defect density and the process of Au deposition.

  16. Wavelength-tuned light emission via modifying the band edge symmetry: Doped SnO2 as an example

    KAUST Repository

    Zhou, Hang


    We report the observation of ultraviolet photoluminescence and electroluminescence in indium-doped SnO2 thin films with modified "forbidden" bandgap. With increasing indium concentration in SnO 2, dominant visible light emission evolves into the ultraviolet regime in photoluminescence. Hybrid functional first-principles calculations demonstrate that the complex of indium dopant and oxygen vacancy breaks "forbidden" band gap to form allowed transition states. Furthermore, undoped and 10% indium-doped SnO2 layers are synthesized on p-type GaN substrates to obtain SnO2-based heterojunction light-emitting diodes. A dominant visible emission band is observed in the undoped SnO 2-based heterojunction, whereas strong near-ultraviolet emission peak at 398 nm is observed in the indium-doped SnO2-based heterojunction. Our results demonstrate an unprecedented doping-based approach toward tailoring the symmetry of band edge states and recovering ultraviolet light emission in wide-bandgap oxides. © 2014 American Chemical Society.

  17. Band Edge Positions and Their Impact on the Simulated Device Performance of ZnSnN2-Based Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Arca, Elisabetta [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Fioretti, Angela [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Lany, Stephan [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Tamboli, Adele C [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Teeter, Glenn R [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Melamed, Celeste [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Pan, Jie [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Wood, Kevin [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Toberer, Eric [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Zakutayev, Andriy A [National Renewable Energy Laboratory (NREL), Golden, CO (United States)


    ZnSnN2 (ZTN) has been proposed as a new earth abundant absorber material for PV applications. While carrier concentration has been reduced to values suitable for device implementation, other properties such as ionization potential, electron affinity and work function are not known. Here, we experimentally determine the value of ionization potential (5.6 eV), electron affinity (4.1 eV) and work function (4.4 eV) for ZTN thin film samples with Zn cation composition Zn/(Zn+Sn) = 0.56 and carrier concentration n = 2x10^19 cm^-3. Using both experimental and theoretical results, we build a model to simulate the device performance of a ZTN/Mg:CuCrO2 solar cell, showing a potential efficiency of 23% in the limit of no defects present. We also investigate the role of band tails and recombination centers on the cell performance. In particular device simulations show that band tails are highly detrimental to the cell efficiency, and recombination centers are a major limitation if present in concentration comparable to the net carrier density. The effect of the position of the band edges of the p-type junction partner was assessed too. Through this study, we determine the major bottlenecks for the development of ZTN-based solar cell and identify avenues to mitigate them.

  18. n-GaAs Band-Edge Repositioning by Modification with Metalloporphyrin/Polysiloxane Matrices

    Directory of Open Access Journals (Sweden)

    Hikmat S. Hilal


    system was annealed under nitrogen and used for photoelectrochemical study in water/LiCIO4/Fe(CN63-/Fe(CN64− system. The results indicated a positive shift in the value of the flat-band potential of the semiconductor due to MnP. This was manifested by shifting the values of the dark-current onset potential and the photo-current open-circuit potential towards more positive values. These findings are potentially valuable in future applications of solar energy in hydrogen and oxygen production from water.

  19. Mach bands and multiscale models of spatial vision: the role of first, second, and third derivative operators in encoding bars and edges. (United States)

    Wallis, Stuart A; Georgeson, Mark A


    Ernst Mach observed that light or dark bands could be seen at abrupt changes of luminance gradient in the absence of peaks or troughs in luminance. Many models of feature detection share the idea that bars, lines, and Mach bands are found at peaks and troughs in the output of even-symmetric spatial filters. Our experiments assessed the appearance of Mach bands (position and width) and the probability of seeing them on a novel set of generalized Gaussian edges. Mach band probability was mainly determined by the shape of the luminance profile and increased with the sharpness of its corners, controlled by a single parameter (n). Doubling or halving the size of the images had no significant effect. Variations in contrast (20%-80%) and duration (50-300 ms) had relatively minor effects. These results rule out the idea that Mach bands depend simply on the amplitude of the second derivative, but a multiscale model, based on Gaussian-smoothed first- and second-derivative filtering, can account accurately for the probability and perceived spatial layout of the bands. A key idea is that Mach band visibility depends on the ratio of second- to first-derivative responses at peaks in the second-derivative scale-space map. This ratio is approximately scale-invariant and increases with the sharpness of the corners of the luminance ramp, as observed. The edges of Mach bands pose a surprisingly difficult challenge for models of edge detection, but a nonlinear third-derivative operation is shown to predict the locations of Mach band edges strikingly well. Mach bands thus shed new light on the role of multiscale filtering systems in feature coding.

  20. A short course on topological insulators band structure and edge states in one and two dimensions

    CERN Document Server

    Asbóth, János K; Pályi, András


    This course-based primer provides newcomers to the field with a concise introduction to some of the core topics in the emerging field of topological insulators. The aim is to provide a basic understanding of edge states, bulk topological invariants, and of the bulk--boundary correspondence with as simple mathematical tools as possible. The present approach uses noninteracting lattice models of topological insulators, building gradually on these to arrive from the simplest one-dimensional case (the Su-Schrieffer-Heeger model for polyacetylene) to two-dimensional time-reversal invariant topological insulators (the Bernevig-Hughes-Zhang model for HgTe). In each case the discussion of simple toy models is followed by the formulation of the general arguments regarding topological insulators. The only prerequisite for the reader is a working knowledge in quantum mechanics, the relevant solid state physics background is provided as part of this self-contained text, which is complemented by end-of-chapter problems.

  1. Simulation study of CD variation caused by field edge effects and out-of-band radiation in EUVL (United States)

    Gao, Weimin; Niroomand, Ardavan; Lorusso, Gian F.; Boone, Robert; Lucas, Kevin; Demmerle, Wolfgang


    Although extreme ultraviolet lithography (EUVL) remains a promising candidate for semiconductor device manufacturing of the 1x nm half pitch node and beyond, many technological burdens have to be overcome. The "field edge effect" in EUVL is one of them. The image border region of an EUV mask,also known as the "black border" (BB), reflects a few percent of the incident EUV light, resulting in a leakage of light into neighboring exposure fields, especially at the corner of the field where three adjacent exposures take place. This effect significantly impacts on CD uniformity (CDU) across the exposure field. To avoid this phenomenon, a light-shielding border is introduced by etching away the entire absorber and multi-layer (ML)at the image border region of the EUV mask. In this paper, we present a method of modeling the field edge effect (also called the BB effect) by using rigorous lithography simulation with a calibrated resist model. An additional "flare level" at the field edge is introduced on top of the exposure tool flare map to account for the BB effect. The parameters in this model include the reflectivity and the width of the BB, which are mainly determining the leakage of EUV light and its influence range, respectively. Another parameter is the transition width which represents the half shadow effect of the reticle masking blades. By setting the corresponding parameters, the simulation results match well the experimental results obtained at the imec's NXE:3100 EUV exposure tool. Moreover, these results indicate that the out-of-band (OoB) radiation also contributes to the CDU. Using simulation we can also determine the OoB effect rigorouslyusing the methodology of an "effective mask blank". The study in this paper demonstrates that the impact of BB and OoB effects on CDU can be well predicted by simulations.

  2. Visualizing band offsets and edge states in bilayer–monolayer transition metal dichalcogenides lateral heterojunction

    KAUST Repository

    Zhang, Chendong


    Semiconductor heterostructures are fundamental building blocks for many important device applications. The emergence of two-dimensional semiconductors opens up a new realm for creating heterostructures. As the bandgaps of transition metal dichalcogenides thin films have sensitive layer dependence, it is natural to create lateral heterojunctions (HJs) using the same materials with different thicknesses. Here we show the real space image of electronic structures across the bilayer–monolayer interface in MoSe2 and WSe2, using scanning tunnelling microscopy and spectroscopy. Most bilayer–monolayer HJs are found to have a zig-zag-orientated interface, and the band alignment of such atomically sharp HJs is of type-I with a well-defined interface mode that acts as a narrower-gap quantum wire. The ability to utilize such commonly existing thickness terraces as lateral HJs is a crucial addition to the tool set for device applications based on atomically thin transition metal dichalcogenides, with the advantage of easy and flexible implementation.

  3. Modulation of valence band maximum edge and photocatalytic activity of BiOX by incorporation of halides. (United States)

    Lv, Jiaxin; Hu, Qingsong; Cao, Chengjin; Zhao, Yaping


    To better know the photocatalytic performance of bismuth oxyhalides (BiOX, X = Cl, Br, I) regulated by incorporation of halides within nanostructures, BiOX nanosheets were synthesized through morphology controllable solvothermal method and characterized systematically. The organic structural property greatly influences the photocatalytic activity of BiOX: 1) as for neutral molecular phenol, BiOX shows photocatalytic activity in the order of BiOCl > BiOBr > BiOI under simulated sun light irradiation, and the photo-oxidation kinetics follow Eley-Rideal mechanism; and 2) for adsorbed anionic orange II (OII) and cationic methylene blue (MB), BiOX shows photocatalytic activity in the order of BiOCl > BiOBr > BiOI, and the photo-oxidation kinetics follow Langmuir-Hinshelwood mechanism. The crystal structure of the catalyst also greatly influences the photocatalytic activity of BiOX: 1) The relative photo-oxidation power of O 2 •- radicals or HO radicals involved in this study were different which were quantitatively detected using typical radical trapping agent, separately; 2) The relative oxidation power of photogenerated holes (h + ) in this study were in the order of BiOCl > BiOBr > BiOI, which may be ascribed to lowering the valence band maximum edge of BiOX through incorporation of halides as the atomic number of halides decreased. This study provides novel explanation for fabricating BiOX heterojunctions with tunable photocatalytic reactivity via regulating the halides ratio. Copyright © 2017 Elsevier Ltd. All rights reserved.

  4. Band-edge electronic structure of β-In2S3: the role of s or p orbitals of atoms at different lattice positions. (United States)

    Zhao, Zongyan; Cao, Yuechan; Yi, Juan; He, Xijia; Ma, Chenshuo; Qiu, Jianbei


    As a promising solar-energy material, the electronic structure and optical properties of Beta phase indium sulfide (β-In(2)S(3)) are still not thoroughly understood. This paper devotes to solve these issues using density functional theory calculations. β-In(2)S(3) is found to be an indirect band gap semiconductor. The roles of its atoms at different lattice positions are not exactly identical because of the unique crystal structure. Additonally, a significant phenomenon of optical anisotropy was observed near the absorption edge. Owing to the low coordination numbers of the In3 and S2 atoms, the corresponding In3-5s states and S2-3p states are crucial for the composition of the band-edge electronic structure, leading to special optical properties and excellent optoelectronic performances. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Defect induced structural inhomogeneity, ultraviolet light emission and near-band-edge photoluminescence broadening in degenerate In2O3 nanowires (United States)

    Mukherjee, Souvik; Sarkar, Ketaki; Wiederrecht, Gary P.; Schaller, Richard D.; Gosztola, David J.; Stroscio, Michael A.; Dutta, Mitra


    We demonstrate here defect induced changes on the morphology and surface properties of indium oxide (In2O3) nanowires and further study their effects on the near-band-edge (NBE) emission, thereby showing the significant influence of surface states on In2O3 nanostructure based device characteristics for potential optoelectronic applications. In2O3 nanowires with cubic crystal structure (c-In2O3) were synthesized via carbothermal reduction technique using a gold-catalyst-assisted vapor-liquid-solid method. Onset of strong optical absorption could be observed at energies greater than 3.5 eV consistent with highly n-type characteristics due to unintentional doping from oxygen vacancy ({V}{{O}}) defects as confirmed using Raman spectroscopy. A combination of high resolution transmission electron microscopy, x-ray photoelectron spectroscopy and valence band analysis on the nanowire morphology and stoichiometry reveals presence of high-density of {V}{{O}} defects on the surface of the nanowires. As a result, chemisorbed oxygen species can be observed leading to upward band bending at the surface which corresponds to a smaller valence band offset of 2.15 eV. Temperature dependent photoluminescence (PL) spectroscopy was used to study the nature of the defect states and the influence of the surface states on the electronic band structure and NBE emission has been discussed. Our data reveals significant broadening of the NBE PL peak consistent with impurity band broadening leading to band-tailing effect from heavy doping.

  6. Defect induced structural inhomogeneity, ultraviolet light emission and near-band-edge photoluminescence broadening in degenerate In 2 O 3 nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Mukherjee, Souvik; Sarkar, Ketaki; Wiederrecht, Gary P.; Schaller, Richard D.; Gosztola, David J.; Stroscio, Michael A.; Dutta, Mitra


    We demonstrate here defect induced changes on the morphology and surface properties of indium oxide (In2O3) nanowires and further study their effects on the near-band-edge (NBE) emission, thereby showing the significant influence of surface states on In2O3 nanostructure based device characteristics for potential optoelectronic applications. In2O3 nanowires with cubic crystal structure (c-In2O3) were synthesized via carbothermal reduction technique using a gold-catalyst-assisted vapor–liquid–solid method. Onset of strong optical absorption could be observed at energies greater than 3.5 eV consistent with highly n-type characteristics due to unintentional doping from oxygen vacancy (VO) defects as confirmed using Raman spectroscopy. A combination of high resolution transmission electron microscopy, x-ray photoelectron spectroscopy and valence band analysis on the nanowire morphology and stoichiometry reveals presence of high-density of VO defects on the surface of the nanowires. As a result, chemisorbed oxygen species can be observed leading to upward band bending at the surface which corresponds to a smaller valence band offset of 2.15 eV. Temperature dependent photoluminescence (PL) spectroscopy was used to study the nature of the defect states and the influence of the surface states on the electronic band structure and NBE emission has been discussed. Our data reveals significant broadening of the NBE PL peak consistent with impurity band broadening leading to band-tailing effect from heavy doping.

  7. Evaluating the influence of the Red Edge band from RapidEye sensor in quantifying leaf area index for hydrological applications specifically focussing on plant canopy interception (United States)

    Dube, Timothy; Mutanga, Onisimo; Sibanda, Mbulisi; Shoko, Cletah; Chemura, Abel


    Reliable and accurate quantification of plant Leaf Area Index (LAI) is critical in understanding its role in reducing runoff. The main aim of the present study was to evaluate the ability of the Red Edge (RE) band derived from RapidEye in estimating LAI for applications in quantifying canopy interception at landscape scale. To achieve this objective, the study also compares the predictive power of two machine learning algorithms (Random Forest-RF and Stochastic Gradient Boosting-SGB) in estimating LAI. Comparatively, the results of the study have demonstrated that the inclusion of spectral information derived from the Red Edge band yields high accurate LAI estimates, when compared to the use of traditional traditional Red, Green, Blue and Near Infra-Red (traditional RGBNIR) spectral information. The results indicate that the use of the four traditional RGBNIR bands yielded comparatively lower R2 values and high Root Mean Squares, Mean Absolute Error (Pinus taeda: R2 of 0.60; the lowest RMSE (0.35 m2/m2) and MAE of 28); whereas the use of integration of traditional RGBNIR + RE in more accurate LAI estimates (Pinus taeda: R2 = 0.65; RMSE = 0.30 m2/m2) and the lowest MAE of 0.23). These findings therefore underscores the importance of new generation multispectral sensors with strategically-position bands and machine learning algorithms in estimating LAI for quantifying canopy interception, especially in resource-poor areas.

  8. Near-Band-Edge Optical Responses of CH3NH3PbCl3 Single Crystals: Photon Recycling of Excitonic Luminescence (United States)

    Yamada, Takumi; Aharen, Tomoko; Kanemitsu, Yoshihiko


    The determination of the band gap and exciton energies of lead halide perovskites is very important from the viewpoint of fundamental physics and photonic device applications. By using photoluminescence excitation (PLE) spectra, we reveal the optical properties of CH3NH3PbCl3 single crystals in the near-band-edge energy regime. The one-photon PLE spectrum exhibits the 1 s exciton peak at 3.11 eV. On the contrary, the two-photon PLE spectrum exhibits no peak structure. This indicates photon recycling of excitonic luminescence. By analyzing the spatial distribution of the excitons and photon recycling, we obtain 3.15 eV for the band gap energy and 41 meV for the exciton binding energy.

  9. Valence and conduction band edges of selenide and sulfide-based kesterites—a study by x-ray based spectroscopy and ab initio theory (United States)

    Olar, Tetiana; Manoharan, Archana; Draxl, Claudia; Calvet, Wolfram; Ümsur, Bünyamin; Parvan, Vladimir; Chacko, Binoy; Xie, Haibing; Saucedo, Edgardo; Valle-Rios, Laura Elisa; Neldner, Kai; Schorr, Susan; Lux-Steiner, Martha Ch; Lauermann, Iver


    Thin film solar cells based on the kesterite material with the general composition Cu2ZnSn(Se,S)4 can be a substitute for the more common chalcopyrites (Cu(In,Ga)(Se,S)2) with a similar band gap range. When replacing the anion sulfide with selenide, the optical band gap of kesterite changes from 1.5 to 1 eV. Here we report on a study of the valence band maximum and conduction band minimum energies of kesterites with either S or Se as the anion. Knowing these positions is crucial for the design of solar cells in order to match the bands of the absorber material with those of the subsequent functional layers like buffer or window layer. Their relative positions were studied using photoelectron spectroscopy of the valence band edge and x-ray absorption spectroscopy of the cations Cu, Zn, and Sn, respectively. The experimental results are interpreted and confirmed in terms of calculations based on density-functional theory and the GW approach of the many-body theory.

  10. Exploring the Potential of WorldView-2 Red-Edge Band-Based Vegetation Indices for Estimation of Mangrove Leaf Area Index with Machine Learning Algorithms

    Directory of Open Access Journals (Sweden)

    Yuanhui Zhu


    Full Text Available To accurately estimate leaf area index (LAI in mangrove areas, the selection of appropriate models and predictor variables is critical. However, there is a major challenge in quantifying and mapping LAI using multi-spectral sensors due to the saturation effects of traditional vegetation indices (VIs for mangrove forests. WorldView-2 (WV2 imagery has proven to be effective to estimate LAI of grasslands and forests, but the sensitivity of its vegetation indices (VIs has been uncertain for mangrove forests. Furthermore, the single model may exhibit certain randomness and instability in model calibration and estimation accuracy. Therefore, this study aims to explore the sensitivity of WV2 VIs for estimating mangrove LAI by comparing artificial neural network regression (ANNR, support vector regression (SVR and random forest regression (RFR. The results suggest that the RFR algorithm yields the best results (RMSE = 0.45, 14.55% of the average LAI, followed by ANNR (RMSE = 0.49, 16.04% of the average LAI, and then SVR (RMSE = 0.51, 16.56% of the average LAI algorithms using 5-fold cross validation (CV using all VIs. Quantification of the variable importance shows that the VIs derived from the red-edge band consistently remain the most important contributor to LAI estimation. When the red-edge band-derived VIs are removed from the models, estimation accuracies measured in relative RMSE (RMSEr decrease by 3.79%, 2.70% and 4.47% for ANNR, SVR and RFR models respectively. VIs derived from red-edge band also yield better accuracy compared with other traditional bands of WV2, such as near-infrared-1 and near-infrared-2 band. Furthermore, the estimated LAI values vary significantly across different mangrove species. The study demonstrates the utility of VIs of WV2 imagery and the selected machine-learning algorithms in developing LAI models in mangrove forests. The results indicate that the red-edge band of WV2 imagery can help alleviate the saturation

  11. Gate-last TiN/HfO2 band edge effective work functions using low-temperature anneals and selective cladding to control interface composition

    KAUST Repository

    Hinkle, C. L.


    Silicon N-metal-oxide-semiconductor (NMOS) and P-metal-oxide-semiconductor (PMOS) band edge effective work functions and the correspondingly low threshold voltages (Vt) are demonstrated using standard fab materials and processes in a gate-last scheme employing low-temperature anneals and selective cladding layers. Al diffusion from the cladding to the TiN/HfO2interface during forming gas anneal together with low O concentration in the TiN enables low NMOS Vt. The use of non-migrating W cladding along with experimentally detected N-induced dipoles, produced by increased oxygen in the TiN, facilitates low PMOS Vt.

  12. Nitrogen and Fluorine Codoped, Colloidal TiO2Nanoparticle: Tunable Doping, Large Red-Shifted Band Edge, Visible Light Induced Photocatalysis, and Cell Death. (United States)

    Biswas, Aritra; Chakraborty, Atanu; Jana, Nikhil R


    Visible light photocatalysis by TiO 2 requires efficient doping of other elements with red-shifted band edge to the visible region. However, preparation of such TiO 2 with tunable doping is challenging. Here we report a method of making nitrogen (N) and fluorine (F) codoped TiO 2 nanoparticle with tunable doping between 1 and 7 at. %. The preparation of N, F codoped TiO 2 nanoparticle involves reaction of colloidal TiO 2 nanorods with an ammonium fluoride-urea mixture at 300 °C, and the extent of N/F doping is tuned by varying the amount of ammonium fluoride-urea and the reaction time. Resultant colloidal N, F codoped TiO 2 nanoparticles show doping dependent shifting of the band edge from the UV to near-IR region, visible light induced generation of reactive oxygen species (ROS), and visible light photodegradation of bisphenol A. A colloidal form of doped TiO 2 nanoparticle offers labeling of cells, visible light induced ROS generation inside a cell, and successive cell death. This work shows the potential advantage of anisotropic nanoparticle precursor for tunable doping and colloidal form of N, F codoped TiO 2 nanoparticle as a visible light photocatalyst.

  13. Determining the Conduction Band-Edge Potential of Solar-Cell-Relevant Nb2O5Fabricated by Atomic Layer Deposition. (United States)

    Hoffeditz, William L; Pellin, Michael J; Farha, Omar K; Hupp, Joseph T


    Often key to boosting photovoltages in photoelectrochemical and related solar-energy-conversion devices is the preferential slowing of rates of charge recombination-especially recombination at semiconductor/solution, semiconductor/polymer, or semiconductor/perovskite interfaces. In devices featuring TiO 2 as the semiconducting component, a common approach to slowing recombination is to install an ultrathin metal oxide barrier layer or trap-passivating layer atop the semiconductor, with the needed layer often being formed via atomic layer deposition (ALD). A particularly promising barrier layer material is Nb 2 O 5 . Its conduction-band-edge potential E CB is low enough that charge injection from an adsorbed molecular, polymeric, or solid-state light absorber and into the semiconductor can still occur, but high enough that charge recombination is inhibited. While a few measurements of E CB have been reported for conventionally synthesized, bulk Nb 2 O 5 , none have been described for ALD-fabricated versions. Here, we specifically determine the conduction-band-edge energy of ALD-fabricated Nb 2 O 5 relative to that of TiO 2 . We find that, while the value for ALD-Nb 2 O 5 is indeed higher than that for TiO 2 , the difference is less than anticipated based on measurements of conventionally synthesized Nb 2 O 5 and is dependent on the thermal history of the material. The implications of the findings for optimization of competing interfacial rate processes, and therefore photovoltages, are briefly discussed.

  14. Can We Afford These Affordances? GarageBand and the Double-Edged Sword of the Digital Audio Workstation (United States)

    Bell, Adam Patrick


    The proliferation of computers, tablets, and smartphones has resulted in digital audio workstations (DAWs) such as GarageBand in being some of the most widely distributed musical instruments. Positing that software designers are dictating the music education of DAW-dependent music-makers, I examine the fallacy that music-making applications such…

  15. Photoreflectance study of the near-band-edge transitions of chemical vapor deposition-grown mono- and few-layer MoS{sub 2} films

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Kuang-I, E-mail: [Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan 70101, Taiwan (China); Chen, Yen-Jen; Wang, Bo-Yan; Cheng, Yung-Chen [Department of Materials Science, National University of Tainan, Tainan 70005, Taiwan (China); Chen, Chang-Hsiao, E-mail: [Department of Automatic Control Engineering, Feng Chia University, Taichung 40724, Taiwan (China)


    Room-temperature photoreflectance (PR) and reflectance (R) spectroscopy are utilized to investigate the near-band-edge transitions of molybdenum disulfide (MoS{sub 2}) thin films grown on sapphire substrates by a hot-wall chemical vapor deposition system. The layer thickness and optical properties of the MoS{sub 2} thin films are confirmed by Raman spectroscopy, atomic force microscope, and photoluminescence (PL) analysis. The B exciton shows relatively weak PL intensity in comparing with the A exciton even for monolayer MoS{sub 2} films. In the R spectrum of few‐layer MoS{sub 2}, it is not possible to clearly observe exciton related features. The PR spectra have two sharp, derivative-like features on a featureless background. Throughout the PR lineshape fitting, the transition energies are designated as the A and B excitons at the K-point of the Brillouin zone, but at room temperature there seems to be no distinguishable feature corresponding to an H‐point transition for the mono- and few-layer MoS{sub 2} films unlike in bulk. These transition energies are slightly larger than those obtained by PL, which is attributed to the Stokes shifts related to doping level. The obtained values of valence-band spin-orbit splitting are in good agreement with those from other experimental methods. By comparing the PR lineshapes, the dominant modulation mechanism is attributed to variations of the exciton transition energies due to change in the built-in electric field. On the strength of this study, PR spectroscopy is demonstrated as a powerful technique for characterizing the near-band-edge transitions of MoS{sub 2} from monolayer to bulk.

  16. Role of band states and trap states in the electrical properties of organic semiconductors: Hopping versus mobility edge model

    KAUST Repository

    Mehraeen, Shafigh


    We compare the merits of a hopping model and a mobility edge model in the description of the effect of charge-carrier concentration on the electrical conductivity, carrier mobility, and Fermi energy of organic semiconductors. We consider the case of a composite electronic density of states (DOS) that consists of a superposition of a Gaussian DOS and an exponential DOS. Using kinetic Monte Carlo simulations, we apply the two models in order to interpret the recent experimental data reported for n-doped C60 films. While both models are capable of reproducing the experimental data very well and yield qualitatively similar characteristic parameters for the density of states, some discrepancies are found at the quantitative level. © 2013 American Physical Society.

  17. A novel hybrid organic/inorganic photonic crystal slab showing a resonance action at the band edge (United States)

    Petti, L.; Rippa, M.; Zhou, J.; Manna, L.; Mormile, P.


    Here we propose and experimentally demonstrate a hybrid photonic crystal (PC) slab consisting of air rods in a nanocomposite prepared by incorporating CdSe/CdS core/shell NRs (NR) in a polymer. Since the styrene methyl acrylate based polymer (ZEP) is transparent in the visible spectral range and is an electron-sensitive material, it was chosen as the embedding matrix for the NRs. Scanning electron microscopy and luminance measurements were used to characterize the experimental structure. The vertical extraction of the light, by the coupling of the modes guided by the PC slab to the free radiation via Bragg scattering, consists of a narrow orange emission band at 592 nm with a full width at half-maximum (FWHM) of 17 nm. The original characteristics of hybrid materials based on polymers and colloidal NRs, able to combine the unique optical properties of the inorganic moiety with the processability of the host matrix, are extremely appealing in view of their technological impact on the development of new high performing optical devices such as organic light-emitting diodes, ultra-low threshold lasers and non-linear devices.

  18. Band edge states, intrinsic defects, and dopants in monolayer HfS2 and SnS2 (United States)

    Lu, Haichang; Guo, Yuzheng; Robertson, John


    Although monolayer HfS2 and SnS2 do not have a direct bandgap like MoS2, they have much higher carrier mobilities. Their band offsets are favorable for use with WSe2 in tunnel field effect transistors. Here, we study the effective masses, intrinsic defects, and substitutional dopants of these dichalcogenides. We find that HfS2 has surprisingly small effective masses for a compound that might appear partly ionic. The S vacancy in HfS2 is found to be a shallow donor while that in SnS2 is a deep donor. Substitutional dopants at the S site are found to be shallow. This contrasts with MoS2 where donors and acceptors are not always shallow or with black phosphorus where dopants can reconstruct into deep non-doping configurations. It is pointed out that HfS2 is more favorable than MoS2 for semiconductor processing because it has the more convenient CVD precursors developed for growing HfO2.

  19. Surface sensing behavior and band edge properties of AgAlS2: Experimental observations in optical, chemical, and thermoreflectance spectroscopy

    Directory of Open Access Journals (Sweden)

    Ching-Hwa Ho


    Full Text Available Optical examination of a chaocogenide compound AgAlS2 which can spontaneously transfer to a AgAlO2 oxide has been investigated by thermoreflectance (TR spectroscopy herein. The single crystals of AgAlS2 were grown by chemical vapor transport (CVT method using ICl3 as a transport agent sealed in evacuated quartz tubes. The as-grown AgAlS2 crystals essentially possess a transparent and white color in vacuum. The crystal surface of AgAlS2 becomes darkened and brownish when putting AgAlS2 into atmosphere for reacting with water vapor or hydrogen gas. Undergoing the chemical reaction process, oxygen deficient AgAlO2-2x with brownish and reddish-like color on surface of AgAlS2 forms. The transition energy of deficient AgAlO2-2x was evaluated by TR experiment. The value was determined to be ∼2.452 eV at 300 K. If the sample is kept dry and moved away from moisture, AgAlS2 crystal can stop forming more deficient AgAlO2-2x surface oxides. The experimental TR spectra for the surface-reacted sample show clearly two transition features at EW=2.452 eV for deficient AgAlO2-2x and EU=3.186 eV for AgAlS2, respectively. The EU transition belongs to direct band-edge exciton of AgAlS2. Alternatively, for surface-oxidation process of AgAlS2 lasting for a long time, a AgAlO2 crystal with yellowish color will eventually form. The TR measurements show mainly a ground-state band edge exciton of E OX 1 detected for AgAlO2. The energy was determined to be E OX 1=2.792 eV at 300 K. The valence-band electronic structure of AgAlS2 has been detailed characterized using polarized-thermoreflectance (PTR measurements in the temperature range between 30 and 340 K. Physical chemistry behaviors of AgAlS2 and AgAlO2 have been comprehensively studied via detailed analyses of PTR and TR spectra. Based on the experimental analyses, optical and chemical behaviors of the AgAlS2 crystals under atmosphere are realized. A possible optical-detecting scheme for using AgAlS2 as a humidity

  20. Linear analysis of an X-band backward wave oscillator with a circular-edge disk-loaded cylindrical waveguide driven by an annular electron beam (United States)

    Hasan Sagor, Rakibul; Ruhul Amin, Md.


    An X-band backward wave oscillator (BWO) with a circular-edge disk-loaded periodic metallic slow wave structure (CDSWS) is proposed and studied numerically. The structure is the modified version of our previously modeled semi-circularly corrugated slow wave structure (SCCSWS). The CDSWS is energized by an intense relativistic electron beam (IREB) which is directed by a strong magnetic field. The electromagnetic (EM) wave of the slow wave structure (SWS) merges with the space charge wave of the beam under the guidance of the strong axial magnetic field. The inner wall contour of CDSWS is modeled by a finite Fourier series and the dispersion characteristics of different TM modes are solved by utilizing the linear Rayleigh-Fourier (R-F) technique, which is verified by a commercial EM solver. To study the temporal growth rate (TGR) for the fundamental TM01 mode, the dispersion equation is solved for the beam current of 0.1-1.0kA and the beam energy of 205-665kV. For the TM01 mode, the TGR that occurs at the unstable region, which provides a qualitative index of the strength of the microwave generation, is compared with those of the BWOs with sinusoidally corrugated SWS (SCSWS), disk-loaded SWS (DLSWS) and triangularly corrugated SWS (TrCSWS) for different beam parameters. The dimension of the CDSWS is determined by comparing the dispersion characteristics of fundamental TM01 mode with DLSWS and SCSWS. For the same set of beam parameters, an average of 3.5%, 7%, 1.5% and more than 50% higher TGR have been obtained with the proposed CDSWS than that of SCSWS, DLSWS, TrCSWS and SCCSWS respectively. Moreover, the presented structure also provides an advantage in the fabrication process and is less prone to RF breakdown since it has no sharp edges in the inner wall where the electric field intensity can be infinitely high.


    Directory of Open Access Journals (Sweden)

    V. Marshall


    Full Text Available Our goals is to determine if Worldview-2 8-band multispectral imagery can be used to discriminate an invasive grass species namely, Buffel grass (Cenchrus ciliaris in the subtropical arid parts of central Australia and whether it offers a tangible improvement on 4-band (visible and near infra red multispectral imagery. A Worldview-2 scene was acquired for a 10*10km area just west of Alice Springs in central Australia following heavy rains of early Summer. Mixture Tuned Matched Filtering was used to classify the image. Target and background spectra were selected in the field and extracted from the image. Linear discriminate analysis (LDA was used to examine the spectral separability of each group of the target/ background spectra. The importance of the additional spectral bands on the image classification was assessed by running LDA for both 8 and 4 bands (red, green, blue and NIR. LDA did not indicate improved separability between groups when additional spectral bands were applied. Preliminary classification results indicate that Buffel grass (Cenchrus ciliaris is detected with an omission error 44%, commission error of 11.8% and overall accuracy of 59.5%. We were surprised that the additional spectral bands did not improve spectral separability and in part attribute this to the high degree of variance we observed within groups of spectra, which was particularly observable in the NIR2 and Yellow bands. The analyses may be significantly improved by acquiring imagery following the first big rains at the end of the dry season. At this time, phonological differences between our focal species and the surrounding native vegetation should be maximised. We suspect that Worldview-2 will offer even greater potential for the discrimination of Buffel grass under these conditions, being able to fully utilise the yellow-band in particular.

  2. Benefits of Red-Edge Spectral Band and Texture Features for the Object-based Classification using RapidEye sSatellite Image data (United States)

    Kim, H. O.; Yeom, J. M.


    Space-based remote sensing in agriculture is particularly relevant to issues such as global climate change, food security, and precision agriculture. Recent satellite missions have opened up new perspectives by offering high spatial resolution, various spectral properties, and fast revisit rates to the same regions. Here, we examine the utility of broadband red-edge spectral information in multispectral satellite image data for classifying paddy rice crops in South Korea. Additionally, we examine how object-based spectral features affect the classification of paddy rice growth stages. For the analysis, two seasons of RapidEye satellite image data were used. The results showed that the broadband red-edge information slightly improved the classification accuracy of the crop condition in heterogeneous paddy rice crop environments, particularly when single-season image data were used. This positive effect appeared to be offset by the multi-temporal image data. Additional texture information brought only a minor improvement or a slight decline, although it is well known to be advantageous for object-based classification in general. We conclude that broadband red-edge information derived from conventional multispectral satellite data has the potential to improve space-based crop monitoring. Because the positive or negative effects of texture features for object-based crop classification could barely be interpreted, the relationships between the textual properties and paddy rice crop parameters at the field scale should be further examined in depth.

  3. Effects of adsorbed pyridine derivatives and ultrathin atomic-layer-deposited alumina coatings on the conduction band-edge energy of TiO2 and on redox-shuttle-derived dark currents. (United States)

    Katz, Michael J; Vermeer, Michael J D; Farha, Omar K; Pellin, Michael J; Hupp, Joseph T


    Both the adsorption of t-butylpyridine and the atomic-layer deposition of ultrathin conformal coatings of insulators (such as alumina) are known to boost open-circuit photovoltages substantially for dye-sensitized solar cells. One attractive interpretation is that these modifiers significantly shift the conduction-edge energy of the electrode, thereby shifting the onset potential for dark current arising from the interception of injected electrons by solution-phase redox shuttle components such as Co(phenanthroline)(3)(3+) and triiodide. For standard, high-area, nanoporous photoelectrodes, band-edge energies are difficult to measure directly. In contrast, for flat electrodes they are readily accessible from Mott-Schottky analyses of impedance data. Using such electrodes (specifically TiO(2)), we find that neither organic nor inorganic electrode-surface modifiers shift the conduction-band-edge energy sufficiently to account fully for the beneficial effects on electrode behavior (i.e., the suppression of dark current). Additional experiments reveal that the efficacy of ultrathin coatings of Al(2)O(3) arises chiefly from the passivation of redox-catalytic surface states. In contrast, adsorbed t-butylpyridine appears to suppress dark currents mainly by physically blocking access of shuttle molecules to the electrode surface. Studies with other derivatives of pyridine, including sterically and/or electronically diverse derivatives, show that heterocycle adsorption and the concomitant suppression of dark current does not require the coordination of surface Ti(IV) or Al(III) atoms. Notably, the favorable (i.e., negative) shifts in onset potential for the flow of dark current engendered by organic and inorganic surface modifiers are additive. Furthermore, they appear to be largely insensitive to the identity of shuttle molecules.

  4. Graphene edges; localized edge state and electron wave interference

    Directory of Open Access Journals (Sweden)

    Enoki Toshiaki


    Full Text Available The electronic structure of massless Dirac fermion in the graphene hexagonal bipartite is seriously modified by the presence of edges depending on the edge chirality. In the zigzag edge, strongly spin polarized nonbonding edge state is created as a consequence of broken symmetry of pseudo-spin. In the scattering at armchair edges, the K-K’ intervalley transition gives rise to electron wave interference. The presence of edge state in zigzag edges is observed in ultra-high vacuum STM/STS observations. The electron wave interference phenomenon in the armchair edge is observed in the Raman G-band and the honeycomb superlattice pattern with its fine structure in STM images.

  5. Improved performance of dye sensitized solar cells using Cu-doped TiO2 as photoanode materials: Band edge movement study by spectroelectrochemistry (United States)

    Zhou, Li; Wei, Liguo; Yang, Yulin; Xia, Xue; Wang, Ping; Yu, Jia; Luan, Tianzhu


    Cu-doped TiO2 nanoparticles are prepared and used as semiconductor materials of photoanode to improve the performance of dye sensitized solar cells (DSSCs). UV-Vis spectroscopy and variable temperature spectroelectrochemistry study are used to characterize the influence of copper dopant with different concentrations on the band gap energies of TiO2 nanoparticles. The prepared Cu-doped TiO2 semiconductor has avoided the formation of CuO during hydrothermal process and lowered the conduction band position of TiO2, which contribute to increase the short circuit current density of DSSCs. At the optimum Cu concentration of 1.0 at.%, the short circuit current density increased from 12.54 to 14.98 mA cm-2, full sun solar power conversion efficiencies increased from 5.58% up to 6.71% as compared to the blank DSSC. This showed that the presence of copper in DSSCs leads to improvements of up to 20% in the conversion efficiency of DSSCs.

  6. Living edge

    DEFF Research Database (Denmark)

    Earon, Ofri


    on the ground level, but there is a lack of recognition in the significance of communicative characters as well at the higher part of the edge. The city’s planning approach is “Consider urban life before urban space. Consider urban space before buildings” This urban strategy neglects the possible architectural...... is a collection of material from the case study of an ongoing PhD study titled: LIVING EDGE - The Architectural and Urban Prospect of Domestic Borders. The paper includes a description of the problem analysis, research question, method, discussion and conclusion.......“What is an edge? We can think about an edge as having been of two sorts. In one, it is a border. In the other, it is a boundary. A border is a zone of interaction where things meet and intersect. A boundary is a place where something ends” Architects and planners normally approach domestic borders...

  7. Edge Matters

    DEFF Research Database (Denmark)

    Earon, Ofri


    and outside the contemporary urban house? And what is the interplay between them? The research argues for re-thinking the edge zone between inside and outside the urban house. Therefore, although, residential buildings in the city are the objects of study, the focal point here is the edge zone along...... the building. The research explores and develops the architectural characteristics of correlations between the resident, the singular unit, the building and the given location at the edge zone. It approaches the edge zone of the urban house as a platform for dynamic interactions between these behaviours...... of this container is to separate inside from outside and to protect and provide privacy, psychological as well as physical (Venturi, 1966). But, if dwelling phenomenon takes place both inside and outside the private house – why is the urban house an enclosed box? What is the differentiation between inside...

  8. Edge Matters

    DEFF Research Database (Denmark)

    Earon, Ofri


    of this container is to separate inside from outside and to protect and provide privacy, psychological as well as physical (Venturi, 1966). But, if dwelling phenomenon takes place both inside and outside the private house – why is the urban house an enclosed box? What is the differentiation between inside...... and outside the contemporary urban house? And what is the interplay between them? The research argues for re-thinking the edge zone between inside and outside the urban house. Therefore, although, residential buildings in the city are the objects of study, the focal point here is the edge zone along...... the building. The research explores and develops the architectural characteristics of correlations between the resident, the singular unit, the building and the given location at the edge zone. It approaches the edge zone of the urban house as a platform for dynamic interactions between these behaviours...

  9. Living edge

    DEFF Research Database (Denmark)

    Earon, Ofri


    “What is an edge? We can think about an edge as having been of two sorts. In one, it is a border. In the other, it is a boundary. A border is a zone of interaction where things meet and intersect. A boundary is a place where something ends” Architects and planners normally approach domestic borders...... of the involved actors at the border. By doing so, the study underlines a forgotten, yet important, role of this edge zone – being a zone of commonality between the house and city, between indoors and outdoors, between the man at home and the man at the street. The city of Copenhagen promotes porous borders...... on the ground level, but there is a lack of recognition in the significance of communicative characters as well at the higher part of the edge. The city’s planning approach is “Consider urban life before urban space. Consider urban space before buildings” This urban strategy neglects the possible architectural...

  10. Edge modulation of electronics and transport properties of cliff-edge phosphorene nanoribbons (United States)

    Guo, Caixia; Wang, Tianxing; Xia, Congxin; Liu, Yufang


    Based on the first-principles calculations, we study the electronic structures and transport properties of cliff-like edge phosphorene nanoribbons (CPNRs), considering different types of edge passivation. The band structures of bare CPNRs possess the metallic features; while hydrogen (H), fluorine (F), chlorine (Cl) and oxygen (O) atoms-passivated CPNRs are semiconductor materials, and the band gap values monotonically decrease when the ribbon width increases. Moreover, the H and F-passivated CPNRs exhibit the direct band gap characteristics, while the Cl and O-passivated cases show the features of indirect band gap. In addition, the edge passivated CPNRs are more energetically stable than bare edge case. Meanwhile, our results also show that the transport properties of the CPNRs can be obviously influenced by the different edge passivation.

  11. Edge Detection, (United States)


    PROJECT. T ASK0 Artificial Inteligence Laboratory AREA It WORK UNIT NUMBERS V 545 Technology Square ( Cambridge, HA 02139 I I* CONTOOL1LIN@4OFFICE NAME...ARD-A1t62 62 EDGE DETECTION(U) NASSACNUSETTS INST OF TECH CAMBRIDGE 1/1 ARTIFICIAL INTELLIGENCE LAB E C HILDRETH SEP 85 AI-M-8 N99SI4-8S-C-6595...used to carry out this analysis. cce~iO a N) ’.~" D LI’BL. P p ------------ Sj. t i MASSACHUSETTS INSTITUTE OF TECHNOLOGY i ARTIFICIAL INTELLIGENCE

  12. Edge effects on the electronic properties of phosphorene nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Peng, Xihong, E-mail: [School of Letters and Sciences, Arizona State University, Mesa, Arizona 85212 (United States); Copple, Andrew [Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States); Wei, Qun [School of Letters and Sciences, Arizona State University, Mesa, Arizona 85212 (United States); School of Physics and Optoelectronic Engineering, Xidian University, Xi' an 710071 (China)


    Two dimensional few-layer black phosphorus crystal structures have recently been fabricated and have demonstrated great potential in electronic applications. In this work, we employed first principles density functional theory calculations to study the edge and quantum confinement effects on the electronic properties of the phosphorene nanoribbons (PNR). Different edge functionalization groups, such as H, F, Cl, OH, O, S, and Se, in addition to a pristine case were studied for a series of ribbon widths up to 3.5 nm. It was found that the armchair-PNRs (APNRs) are semiconductors for all edge groups considered in this work. However, the zigzag-PNRs (ZPNRs) show either semiconductor or metallic behavior in dependence on their edge chemical species. Family 1 edges (i.e., H, F, Cl, OH) form saturated bonds with P atoms in the APNRs and ZPNRs, and the edge states keep far away from the band gap. However, Family 2 edges (pristine, O, S, Se) form weak unsaturated bonds with the p{sub z} orbital of the phosphorus atoms and bring edge states within the band gap of the ribbons. For the ZPNRs, the edge states of Family 2 are present around the Fermi level within the band gap, which close up the band gap of the ZPNRs. For the APNRs, these edge states are located at the bottom of the conduction band and result in a reduced band gap.

  13. High-energy band structure of gold

    DEFF Research Database (Denmark)

    Christensen, N. Egede


    The band structure of gold for energies far above the Fermi level has been calculated using the relativistic augmented-plane-wave method. The calculated f-band edge (Γ6-) lies 15.6 eV above the Fermi level is agreement with recent photoemission work. The band model is applied to interpret...

  14. Edge-based correlation image registration for multispectral imaging (United States)

    Nandy, Prabal [Albuquerque, NM


    Registration information for images of a common target obtained from a plurality of different spectral bands can be obtained by combining edge detection and phase correlation. The images are edge-filtered, and pairs of the edge-filtered images are then phase correlated to produce phase correlation images. The registration information can be determined based on these phase correlation images.

  15. Red edge parameters as indicators of rice nitrogen levels (United States)

    Huang, Jingfeng; Wang, Xiuzhen; Wang, Renchao


    The canopy spectra of rice under different nitrogen levels were studied. Some red edge parameters in the first derivative reflectance curve (wavelength, amplitude and area of the red edge peak) were used to evaluate rice leaf chlorophyll, LAI. Red edge positions move to longer wave bands till booting stage and move to short bands after booting stage. A high correlation was found between chlorophyll content of top leaves and the wavelength of the red edge position and between LAI and the red edge parameter. Then, the red edge was found valuable for assessment of rice above stand leaves chlorophyll contents. But a correlation was not found between chlorophyll b content of leaves or carotenoid or albumen-nitrogen or non-albumen-nitrogen and the wavelength of the red parameters. Some red edge parameters are one of the best remote sensing descriptors.

  16. Magnetism of zigzag edge phosphorene nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Zhili, E-mail:, E-mail:; Li, Chong; Yu, Weiyang; Chang, Dahu; Sun, Qiang; Jia, Yu, E-mail:, E-mail: [International Joint Research Laboratory for Quantum Functional Materials of Henan, and School of Physics and Engineering, Zhengzhou University, Zhengzhou 450001 (China)


    We have investigated, by means of ab initio calculations, the electronic and magnetic structures of zigzag edge phosphorene nanoribbons (ZPNRs) with various widths. The stable magnetic state was found in pristine ZPNRs by allowing the systems to be spin-polarized. The ground state of pristine ZPNRs prefers ferromagnetic order in the same edge but antiferromagnetic order between two opposite edges. The magnetism arises from the dangling bond states as well as edge localized π-orbital states. The presence of a dangling bond is crucial to the formation of the magnetism of ZPNRs. The hydrogenated ZPNRs get nonmagnetic semiconductors with a direct band gap. While, the O-saturated ZPNRs show magnetic ground states due to the weak P-O bond in the ribbon plane between the p{sub z}-orbitals of the edge O and P atoms.

  17. Grain size dependent optical band gap of CdI2 films

    Indian Academy of Sciences (India)


    direct band gap in conformity with band structure calcula- tions. However, a smaller indirect band gap can also be determined from part of absorption data near the band edge for the purpose of comparison with earlier analyses of absorption data as well as the band structure calcula- tions. The decreasing band gap with film ...

  18. Optical excitation processes in the near band-edge region of KAlSi3O8 and NaAlSi3O8 feldspar

    DEFF Research Database (Denmark)

    Poolton, N.R.J.; Mauz, B.; Lang, A.


    -stimulated phosphorescence and energy-dependent photo-transferred optically stimulated luminescence. The photo-transferred OSL confirms the bandgap energy of alkali feldspars to be 7.7eV at 10K, and highlights the role played by a dominant optically active defect 4.4 eV below the conduction band, associated with blue......)) yielding a characteristically narrow feature at 4.61 eV: significantly, excitation to this level allows photo-transferred OSL to take place, a process that is not obviously identifiable with the other transitions of the set. The conclusion of the work is that synchrotron-based luminescence methods can...

  19. Imaging edges of nanostructured graphene

    DEFF Research Database (Denmark)

    Kling, Jens; Cagliani, Alberto; Booth, T. J.

    Graphene, as the forefather of 2D-materials, attracts much attention due to its extraordinary properties like transparency, flexibility and outstanding high conductivity, together with a thickness of only one atom. However, graphene also possesses no band gap, which makes it unsuitable for many...... electronic applications like transistors. It has been shown theoretically that by nanostructuring pristine graphene, e.g. with regular holes, the electronic properties can be tuned and a band gap introduced. The size, distance and edge termination of these “defects” influence the adaptability....... Such nanostructuring can be done experimentally, but especially characterization at atomic level is a huge challenge. High-resolution TEM (HRTEM) is used to characterize the atomic structure of graphene. We optimized the imaging conditions used for the FEI Titan ETEM. To reduce the knock-on damage of the carbon atoms...

  20. Edge-on! (United States)


    Peering at Uranus's Rings as they Swing Edge-on to Earth for the First Time Since their Discovery in 1977 As Uranus coasts through a brief window of time when its rings are edge-on to Earth - a view of the planet we get only once every 42 years - astronomers peering at the rings with ESO's Very Large Telescope and other space or ground-based telescopes are getting an unprecedented view of the fine dust in the system, free from the glare of the bright rocky rings. They may even find a new moon or two. ESO PR Photo 37/07 ESO PR Photo 37/07 The Uranus System "ESO's VLT took data at the precise moment when the rings were edge-on to Earth," said Imke de Pater, of University of California, Berkeley who coordinated the worldwide campaign. She worked with two team members observing in Chile: Daphne Stam of the Technical University Delft in the Netherlands and Markus Hartung of ESO. The observations were done with NACO, one of the adaptive optics instruments installed at the VLT. With adaptive optics, it is possible to obtain images almost free from the blurring effect of the atmosphere. It is as if the 8.2-m telescope were observing from space. Observations were also done with the Keck telescope in Hawaii, the Hubble Space Telescope, and at the Palomar Observatory. "Using different telescopes around the world allows us to observe as much of the changes during the ring-plane crossing as possible: when Uranus sets as seen from the VLT, it can still be observed by the Keck," emphasised Stam. Uranus orbits the Sun in 84 years. Twice during a Uranian year, the rings appear edge-on to Earth for a brief period. The rings were discovered in 1977, so this is the first time for a Uranus ring-crossing to be observed from Earth. The advantage of observations at a ring-plane crossing is that it becomes possible to look at the rings from the shadowed or dark side. From that vantage point, the normally bright outer rings grow fainter because their centimetre- to metre-sized rocks obscure

  1. Stability of edge states and edge magnetism in graphene nanoribbons


    Kunstmann, Jens; Özdoğan, Cem; Quandt, Alexander; Fehske, Holger


    We critically discuss the stability of edge states and edge magnetism in zigzag edge graphene nanoribbons (ZGNRs). We point out that magnetic edge states might not exist in real systems, and show that there are at least three very natural mechanisms - edge reconstruction, edge passivation, and edge closure - which dramatically reduce the effect of edge states in ZGNRs or even totally eliminate them. Even if systems with magnetic edge states could be made, the intrinsic magnetism would not be ...

  2. Unconventional quantized edge transport in the presence of inter-edge coupling in intercalated graphene


    Li, Yuanchang


    It is generally believed that the inter-edge coupling destroys the quantum spin Hall (QSH) effect along with the gap opening at the Dirac points. Using first-principles calculations, we find that the quantized edge transport persists in the presence of inter-edge coupling in Ta intercalated epitaxial graphene on SiC(0001), being a QSH insulator with the non-trivial gap of 81 meV. In this case, the band is characterized by two perfect Dirac cones with different Fermi velocities, yet only one m...

  3. The marginal band system in nymphalid butterfly wings. (United States)

    Taira, Wataru; Kinjo, Seira; Otaki, Joji M


    Butterfly wing color patterns are highly complex and diverse, but they are believed to be derived from the nymphalid groundplan, which is composed of several color pattern systems. Among these pattern systems, the marginal band system, including marginal and submarginal bands, has rarely been studied. Here, we examined the color pattern diversity of the marginal band system among nymphalid butterflies. Marginal and submarginal bands are usually expressed as a pair of linear bands aligned with the wing margin. However, a submarginal band can be expressed as a broken band, an elongated oval, or a single dot. The marginal focus, usually a white dot at the middle of a wing compartment along the wing edge, corresponds to the pupal edge spot, one of the pupal cuticle spots that signify the locations of color pattern organizing centers. A marginal band can be expressed as a semicircle, an elongated oval, or a pair of eyespot-like structures, which suggest the organizing activity of the marginal focus. Physical damage at the pupal edge spot leads to distal dislocation of the submarginal band in Junonia almana and in Vanessa indica, suggesting that the marginal focus functions as an organizing center for the marginal band system. Taken together, we conclude that the marginal band system is developmentally equivalent to other symmetry systems. Additionally, the marginal band is likely a core element and the submarginal band a paracore element of the marginal band system, and both bands are primarily specified by the marginal focus organizing center.

  4. The reconstructed edges of the hexagonal BN (United States)

    Zhao, Ruiqi; Gao, Junfeng; Liu, Zhongfan; Ding, Feng


    and ZZN57 are more stable. The pristine edges are more stable in bare BN in most cases if saturated with hydrogen. By applying the theory of Wulff construction, we predicted that an unpassivated BN domain prefers the hexagonal shape enclosed with bare AC edges i.e., AC-Ns, AC, AC-Bs if the feedstock varies from N-rich to B-rich. However, the evolution from ZZN edged triangular domain, to hexagonal domain enclosed with AC edges, and ZZB edged triangle may occur if the edges are terminated by hydrogen atoms. Further calculation shows that these edges present rich type-dependent properties and thus are important for various applications. This theoretical study showed that controlling the morphologies of BN domains and BN edges is crucial for various applications. Electronic supplementary information (ESI) available: Models, definitions and calculations of edge energies; edge energies, band gaps (Eg), electronic and magnetic properties. See DOI: 10.1039/c5nr02143j

  5. An edge pedestal model

    International Nuclear Information System (INIS)

    Stacev, W.M.


    A new model for calculation of the gradient scale lengths in the edge pedestal region and of the edge transport barrier width in H-mode tokamak plasmas will be described. Model problem calculations which demonstrate the promise of this model for predicting experimental pedestal properties will be discussed. The density and Prague gradient scale lengths (L) in the edge are calculated from the particle and ion and electron energy radial transport equations, making use of (presumed) known particle and energy fluxes flowing across the edge transport barrier from the core into the SOL and of edge transport coefficients. The average values of the particle and heat fluxes in the edge transport barrier are calculated in terms of the fluxes crossing into the SOL and the atomic physics reaction rates (ionisation, charge-exchange, elastic scattering, impurity radiation) in the edge by integrating the respective transport equations from the pedestal to the separatrix. An important implication of this model is that the pedestal gradient scale lengths depend not just on local pedestal platers properties but also on particle and energy fluxes from the core plasma and on recycling neutral fluxes that penetrate into the plasma edge, both of which in turn depend on the pedestal properties. The MHD edge pressure gradient constraint α≤ α C is used to determine the pressure width of the edge transport barrier, Δ TB = Δ TB (α c ). Three different models for the MHD edge pressure gradient constraint have been investigated: (1) nominal ideal ballooning mode theory, (2) ballooning mode theory taking into account the edge geometry and shear to access He second stability region; and pedestal β-limit theory when the ballooning modes are stabilised by diamagnetic effects. A series of calculations have been made for a DIII-D model problem. The calculated gradient scale lengths and edge transport barrier widths are of the magnitude of values observed experimentally, and certain trends

  6. Polygonal deformation bands in sandstone (United States)

    Antonellini, Marco; Nella Mollema, Pauline


    We report for the first time the occurrence of polygonal faults in sandstone, which is compelling given that layer-bound polygonal fault systems have been observed so far only in fine-grained sediments such as clay and chalk. The polygonal faults are dm-wide zones of shear deformation bands that developed under shallow burial conditions in the lower portion of the Jurassic Entrada Fm (Utah, USA). The edges of the polygons are 1 to 5 meters long. The shear deformation bands are organized as conjugate faults along each edge of the polygon and form characteristic horst-like structures. The individual deformation bands have slip magnitudes ranging from a few mm to 1.5 cm; the cumulative average slip magnitude in a zone is up to 10 cm. The deformation bands heaves, in aggregate form, accommodate a small isotropic horizontal extension (strain Crosscutting relationships are rare. The interactions of the deformation bands are similar to those of mode I opening fractures. Density inversion, that takes place where under-compacted and over-pressurized layers (Carmel Fm) lay below normally compacted sediments (Entrada Sandstone), may be an important process for polygonal deformation bands formation. The gravitational sliding and soft sediment structures typically observed within the Carmel Fm support this hypothesis. Soft sediment deformation may induce polygonal faulting in the section of the Entrada Sandstone just above the Carmel Fm. The permeability of the polygonal deformation bands is approximately 10-14 to 10-13 m2, which is less than the permeability of the host, Entrada Sandstone (range 10-12 to 10-11 m2). The documented fault networks have important implications for evaluating the geometry of km-scale polygonal fault systems in the subsurface, top seal integrity, as well as constraining paleo-tectonic stress regimes.

  7. Strain-activated edge reconstruction of graphene nanoribbons

    KAUST Repository

    Cheng, Yingchun


    The edge structure and width of graphene nanoribbons (GNRs) are crucial factors for the electronic properties. A combination of experiment and first-principles calculations allows us to determine the mechanism of the hexagon-hexagon to pentagon-heptagon transformation. GNRs thinner than 2 nm have been fabricated by bombardment of graphene with high-energetic Au clusters. The edges of the GNRs are modified in situ by electron irradiation. Tensile strain along the edge decreases the transformation energy barrier. Antiferromagnetism and a direct band gap are found for a zigzag GNR, while a fully reconstructed GNR shows an indirect band gap. A GNR reconstructed on only one edge exhibits ferromagnetism. We propose that strain is an effective method to tune the edge and, therefore, the electronic structure of thin GNRs for graphene-based electronics.

  8. Doping and bond length contributions to Mn K-edge shift in La1 ...

    Indian Academy of Sciences (India)

    ... corresponds to the shift in the center of gravity of the unoccupied Mn 4-band contributing to the Mn K-absorption edge region. This correspondence is then used to separate the doping and size contributions to the edge shift due to variation in the number of electrons in valence band and Mn-O bond lengths, respectively, ...

  9. Determinação de diagramas de bandas de energia e da borda de absorção em SnO2, depositado via sol-gel, sobre quartzo Determination of the band energy diagram and absorption fundamental edge in SnO2, deposited via sol-gel, on quartz

    Directory of Open Access Journals (Sweden)

    E. A. Floriano


    Full Text Available Propriedades ópticas e estruturais de filmes finos de SnO2, depositados sobre substratos de quartzo, são apresentadas. Os filmes são preparados pela técnica de molhamento via sol-gel. Uma avaliação das propriedades eletrônicas do cristal (bulk e das superfícies (110 e (101 do material é também efetuada, através de cálculos baseados em um método mecânico-quântico que utiliza a Teoria do Funcional da Densidade (DFT em conjunto com o funcional hibrido B3LYP. A borda fundamental de absorção, obtida experimentalmente, é então comparada com os diagramas de bandas de energia do bulk e superfícies (110 e (101, calculadas.Optical and structural properties of SnO2 thin films, deposited on quartz substrates, are presented. Films are prepared by the sol-gel-dip-coating technique. An evaluation of the electronic properties of bulk and surfaces (110 and (101 of the material is also carried out, through calculation based on a quantum-mechanical method using the Density Functional Theory (DFT in conjunction with the hybrid functional B3LYP. The absorption fundamental edge, experimentally obtained, is compared to the calculated band energy diagram of bulk and surfaces (110 and (101.

  10. Topological edge modes in multilayer graphene systems

    KAUST Repository

    Ge, Lixin


    Plasmons can be supported on graphene sheets as the Dirac electrons oscillate collectively. A tight-binding model for graphene plasmons is a good description as the field confinement in the normal direction is strong. With this model, the topological properties of plasmonic bands in multilayer graphene systems are investigated. The Zak phases of periodic graphene sheet arrays are obtained for different configurations. Analogous to Su-Schrieffer-Heeger (SSH) model in electronic systems, topological edge plasmon modes emerge when two periodic graphene sheet arrays with different Zak phases are connected. Interestingly, the dispersion of these topological edge modes is the same as that in the monolayer graphene and is invariant as the geometric parameters of the structure such as the separation and period change. These plasmonic edge states in multilayer graphene systems can be further tuned by electrical gating or chemical doping. © 2015 Optical Society of America.

  11. Floquet edge states in germanene nanoribbons

    KAUST Repository

    Tahir, M.


    We theoretically demonstrate versatile electronic properties of germanene monolayers under circularly, linearly, and elliptically polarized light. We show for the high frequency regime that the edge states can be controlled by tuning the amplitude of the light and by applying a static electric field. For circularly polarized light the band gap in one valley is reduced and in the other enhanced, enabling single valley edge states. For linearly polarized light spin-split states are found for both valleys, being connected by time reversal symmetry. The effects of elliptically polarized light are similar to those of circularly polarized light. The transport properties of zigzag nanoribbons in the presence of disorder confirm a nontrivial nature of the edge states under circularly and elliptically polarized light.

  12. Interfacial band-edge energetics for solar fuels production


    Smith, Wilson A.; Sharp, Ian D.; Strandwitzd, Nicholas C.; Bisquert, Juan


    Photoelectrochemical (PEC) water splitting has received growing attention as a potential pathway to replace fossil fuels and produce a clean, renewable, and sustainable source of fuel. To achieve overall water splitting and the associated production of solar fuels, complex devices are needed to efficiently capture light from the sun, separate photogenerated charges, and catalyze reduction and oxidation reactions. To date, the highest performing solar fuels devices rely on multi-component syst...

  13. InAs Band-Edge Exciton Fine Structure (United States)


    with a 100x near- infrared corrected long working distance objective (Mi- tutoyo, Plan Apo NIR), using a 640 nm pulsed diode laser for excitation...Fernée, M. J.; Louyer, Y.; Tamarat, P.; Lounis, B. Comment on “Spin-Flip Limited Exciton Dephasing in CdSe/ ZnS Colloidal Quantum Dots”. Phys. Rev. Lett... Spectroscopy of single nanocrystals. Chem. Soc. Rev. 2014, 43, 1311–1337. [10] Bruns, O. T.; Bischof, T. S.; Harris, D. K.; Shi, Y.; Riedemann, L.; Reiberger

  14. Edge effects in composites

    International Nuclear Information System (INIS)

    Guz, A.N.; Kokhanenko, Yu.V.


    In the present article we survey papers on edge effects investigated by the rigorous approach. We interpret edge effects as stressed states created in a composite as a result of zones in which the stresses exhibit a rapidly changing behavior in comparison with the slow variation of the stresses outside such zones. Here the range of the edge effect is defined as the distance from the point of its inception to the boundary of the edge zone in a given direction. The transition of the stresses to the slowly varying state is determined within prescribed error limits. The size and configuration of the edge zone depends on the tolerated error. Clearly, the main difficulty associated with the rigorous approach is finding solutions of the elasticity problems. The finite-difference approach is suggested for the approximate solution of these problems. In light of the comparative time consumption of the finite-difference approach, it is best directed at certain classes of problems rather than at particular individual problems. Not too many papers on the investigation of edge effects by the rigorous approach have been published to date. Below, following in their footsteps, we formulate edge effect problems in composites, determine classes of problems, and investigate edge effects in composite materials and structural elements using them in Cartesian (planar and three-dimensional problems) and cylindrical (axisymmetric problems) coordinate frames. We note that the division of approaches to the study of edge effects into qualitative (nonrigorous) and quantitative (rigorous) reflects the authors own point of view. Of course, other schemes of classification of the approaches to the investigation of the regions of rapidly varying states in composites are possible

  15. Adobe Edge Quickstart Guide

    CERN Document Server

    Labrecque, Joseph


    Adobe Edge Quickstart Guide is a practical guide on creating engaging content for the Web with Adobe's newest HTML5 tool. By taking a chapter-by-chapter look at each major aspect of Adobe Edge, the book lets you digest the available features in small, easily understandable chunks, allowing you to start using Adobe Edge for your web design needs immediately. If you are interested in creating engaging motion and interactive compositions using web standards with professional tooling, then this book is for you. Those with a background in Flash Professional wanting to get started quickly with Adobe

  16. Adobe Edge Preview 3

    CERN Document Server

    Grover, Chris


    Want to use an Adobe tool to design animated web graphics that work on iPhone and iPad? You've come to the right book. Adobe Edge Preview 3: The Missing Manual shows you how to build HTML5 graphics using simple visual tools. No programming experience? No problem. Adobe Edge writes the underlying code for you. With this eBook, you'll be designing great-looking web elements in no time. Get to know the workspace. Learn how Adobe Edge Preview 3 performs its magic.Create and import graphics. Make drawings with Edge's tools, or use art you designed in other programs.Work with text. Build menus, lab

  17. Edge Simulation Laboratory

    Energy Technology Data Exchange (ETDEWEB)

    Krasheninnikov, Sergei I. [Univ. of California, San Diego, CA (United States); Angus, Justin [Univ. of California, San Diego, CA (United States); Lee, Wonjae [Univ. of California, San Diego, CA (United States)


    The goal of the Edge Simulation Laboratory (ESL) multi-institutional project is to advance scientific understanding of the edge plasma region of magnetic fusion devices via a coordinated effort utilizing modern computing resources, advanced algorithms, and ongoing theoretical development. The UCSD team was involved in the development of the COGENT code for kinetic studies across a magnetic separatrix. This work included a kinetic treatment of electrons and multiple ion species (impurities) and accurate collision operators.

  18. Quantum electrodynamics near a photonic band-gap (United States)

    Liu, Yanbing; Houck, Andrew

    Quantum electrodynamics predicts the localization of light around an atom in photonic band-gap (PBG) medium or photonic crystal. Here we report the first experimental realization of the strong coupling between a single artificial atom and an one dimensional PBG medium using superconducting circuits. In the photonic transport measurement, we observe an anomalous Lamb shift and a large band-edge avoided crossing when the artificial atom frequency is tuned across the band-edge. The persistent peak within the band-gap indicates the single photon bound state. Furthermore, we study the resonance fluorescence of this bound state, again demonstrating the breakdown of the Born-Markov approximation near the band-edge. This novel architecture can be directly generalized to study many-body quantum electrodynamics and to construct more complicated spin chain models.

  19. Green's function asymptotics near the internal edges of spectra of periodic elliptic operators. Spectral edge case

    KAUST Repository

    Kuchment, Peter


    Precise asymptotics known for the Green\\'s function of the Laplace operator have found their analogs for periodic elliptic operators of the second order at and below the bottom of the spectrum. Due to the band-gap structure of the spectra of such operators, the question arises whether similar results can be obtained near or at the edges of spectral gaps. As the result of this work shows, this is possible at a spectral edge when the dimension d ≥ 3. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. The Edge supersonic transport (United States)

    Agosta, Roxana; Bilbija, Dushan; Deutsch, Marc; Gallant, David; Rose, Don; Shreve, Gene; Smario, David; Suffredini, Brian


    As intercontinental business and tourism volumes continue their rapid expansion, the need to reduce travel times becomes increasingly acute. The Edge Supersonic Transport Aircraft is designed to meet this demand by the year 2015. With a maximum range of 5750 nm, a payload of 294 passengers and a cruising speed of M = 2.4, The Edge will cut current international flight durations in half, while maintaining competitive first class, business class, and economy class comfort levels. Moreover, this transport will render a minimal impact upon the environment, and will meet all Federal Aviation Administration Part 36, Stage III noise requirements. The cornerstone of The Edge's superior flight performance is its aerodynamically efficient, dual-configuration design incorporating variable-geometry wingtips. This arrangement combines the benefits of a high aspect ratio wing at takeoff and low cruising speeds with the high performance of an arrow-wing in supersonic cruise. And while the structural weight concerns relating to swinging wingtips are substantial, The Edge looks to ever-advancing material technologies to further increase its viability. Heeding well the lessons of the past, The Edge design holds economic feasibility as its primary focus. Therefore, in addition to its inherently superior aerodynamic performance, The Edge uses a lightweight, largely windowless configuration, relying on a synthetic vision system for outside viewing by both pilot and passengers. Additionally, a fly-by-light flight control system is incorporated to address aircraft supersonic cruise instability. The Edge will be produced at an estimated volume of 400 aircraft and will be offered to airlines in 2015 at $167 million per transport (1992 dollars).

  1. Theory of edge radiation

    Energy Technology Data Exchange (ETDEWEB)

    Geloni, G.; Kocharyan, V.; Saldin, E.; Schneidmiller, E.; Yurkov, M.


    We formulate a complete theory of Edge Radiation based on a novel method relying on Fourier Optics techniques. Similar types of radiation like Transition UndulatorRadiation are addressed in the framework of the same formalism. Special attention is payed in discussing the validity of approximations upon which the theory is built. Our study makes consistent use of both similarity techniques and comparisons with numerical results from simulation. We discuss both near and far zone. Physical understanding of many asymptotes is discussed. Based on the solution of the field equation with a tensor Green's function technique, we also discuss an analytical model to describe the presence of a vacuum chamber. In particular, explicit calculations for a circular vacuum chamber are reported. Finally, we consider the use of Edge Radiation as a tool for electron beam diagnostics. We discuss Coherent Edge Radiation, Extraction of Edge Radiation by a mirror, and other issues becoming important at high electron energy and long radiation wavelength. Based on this work we also study the impact of Edge Radiation on XFEL setups and we discuss recent results. (orig.)

  2. Assessment of Multipath and Shadowing Effects on UHF Band in ...

    African Journals Online (AJOL)


    mobile (GSM) and Wideband Code Division Multiple. Access (WCDMA) bands. Although, (Abhayawardhana, 2005) carried out measurements in the VHF and UHF bands within the urban clutter, still, only empirical models were considered and the work did not incorporate semi- empirical models such as Knife Edge Model.

  3. High Speed Edge Detection (United States)

    Prokop, Norman F (Inventor)


    Analog circuits for detecting edges in pixel arrays are disclosed. A comparator may be configured to receive an all pass signal and a low pass signal for a pixel intensity in an array of pixels. A latch may be configured to receive a counter signal and a latching signal from the comparator. The comparator may be configured to send the latching signal to the latch when the all pass signal is below the low pass signal minus an offset. The latch may be configured to hold a last negative edge location when the latching signal is received from the comparator.

  4. HYBASE : HYperspectral BAnd SElection

    NARCIS (Netherlands)

    Schwering, P.B.W.; Bekman, H.H.P.T.; Seijen, H.H. van


    Band selection is essential in the design of multispectral sensor systems. This paper describes the TNO hyperspectral band selection tool HYBASE. It calculates the optimum band positions given the number of bands and the width of the spectral bands. HYBASE is used to assess the minimum number of

  5. Band structures in fractal grading porous phononic crystals (United States)

    Wang, Kai; Liu, Ying; Liang, Tianshu; Wang, Bin


    In this paper, a new grading porous structure is introduced based on a Sierpinski triangle routine, and wave propagation in this fractal grading porous phononic crystal is investigated. The influences of fractal hierarchy and porosity on the band structures in fractal graidng porous phononic crystals are clarified. Vibration modes of unit cell at absolute band gap edges are given to manifest formation mechanism of absolute band gaps. The results show that absolute band gaps are easy to form in fractal structures comparatively to the normal ones with the same porosity. Structures with higher fractal hierarchies benefit multiple wider absolute band gaps. This work provides useful guidance in design of fractal porous phononic crystals.

  6. Swords with Blunt Edges (United States)

    Popham, W. James


    Many U.S. educators now wonder whether they're teachers or targets. This mentality stems from the specter of their school being sanctioned for failing the state accountability tests mandated under No Child Left Behind (NCLB). According to this author, most of those tests are like blunt-edged swords: They function badly in two directions. While…

  7. Edge effects in magnetoplasmas

    NARCIS (Netherlands)

    Suttorp, L.G.; Kraeft, W.D.; Schlanges, M.


    Edge effects in magnetized charged-particle systems are discussed with the help of a multiple-reflection expansion for the Green function. The profiles of the density and the electric current are determined both for the non-degenerate and the highly degenerate case. The asymptotic form of the

  8. The Inner Urban Edge (United States)

    Ferebee, Ann; Carpenter, Edward K.


    In this article, renewal of the inner urban edge is discussed. Norfolk (Virginia) is attempting to blur the difference between old and new neighbor hoods through zoning and architectural controls. Cincinnati (Ohio) is developing an environmentally sound hillside design. Reading (Pennsylvania) is utilizing old railyards for greenbelts of hiking and…

  9. Topological edge states for disordered bosonic systems (United States)

    Peano, Vittorio; Schulz-Baldes, Hermann


    Quadratic bosonic Hamiltonians over a one-particle Hilbert space can be described by a Bogoliubov-de Gennes (BdG) Hamiltonian on a particle-hole Hilbert space. In general, the BdG Hamiltonian is not self-adjoint, but only J-self-adjoint on the particle-hole space viewed as a Krein space. Nevertheless, its energy bands can have non-trivial topological invariants like Chern numbers or winding numbers. By a thorough analysis for tight-binding models, it is proved that these invariants lead to bosonic edge modes which are robust to a large class of possibly disordered perturbations. Furthermore, general scenarios are presented for these edge states to be dynamically unstable even though the bulk modes are stable.

  10. Smoothness in Binomial Edge Ideals

    Directory of Open Access Journals (Sweden)

    Hamid Damadi


    Full Text Available In this paper we study some geometric properties of the algebraic set associated to the binomial edge ideal of a graph. We study the singularity and smoothness of the algebraic set associated to the binomial edge ideal of a graph. Some of these algebraic sets are irreducible and some of them are reducible. If every irreducible component of the algebraic set is smooth we call the graph an edge smooth graph, otherwise it is called an edge singular graph. We show that complete graphs are edge smooth and introduce two conditions such that the graph G is edge singular if and only if it satisfies these conditions. Then, it is shown that cycles and most of trees are edge singular. In addition, it is proved that complete bipartite graphs are edge smooth.

  11. Chiral topological excitons in a Chern band insulator (United States)

    Chen, Ke; Shindou, Ryuichi


    A family of semiconductors called Chern band insulators are shown to host exciton bands with nonzero topological Chern integers and chiral exciton edge modes. Using a prototypical two-band Chern insulator model, we calculate a cross-correlation function to obtain the exciton bands and their Chern integers. The lowest exciton band acquires Chern integers such as ±1 and ±2 in the electronic Chern insulator phase. The nontrivial topology can be experimentally observed both by a nonlocal optoelectronic response of exciton edge modes and by a phase shift in the cross-correlation response due to the bulk mode. Our result suggests that magnetically doped HgTe, InAs/GaSb quantum wells, and (Bi,Sb)2Te3 thin films are promising candidates for a platform of topological excitonics.

  12. Band-gap measurements of bulk and nanoscale hematite by soft x-ray spectroscopy

    DEFF Research Database (Denmark)

    Gilbert, B.; Frandsen, Cathrine; Maxey, E.R.


    Chemical and photochemical processes at semiconductor surfaces are highly influenced by the size of the band gap, and ability to control the band gap by particle size in nanomaterials is part of their promise. The combination of soft x-ray absorption and emission spectroscopies provides band......-edge to reveal band-edge electronic structure of bulk and nanoscale hematite. Good agreement is found between the hematite band gap derived from optical spectroscopy and the energy separation of the first inflection points in the x-ray absorption and emission onset regions. By applying this method to two sizes...

  13. Urbach absorption edge in epitaxial erbium-doped silicon

    Energy Technology Data Exchange (ETDEWEB)

    Shmagin, V. B., E-mail:; Kudryavtsev, K. E.; Shengurov, D. V.; Krasilnik, Z. F. [Institute for Physics of Microstructures, Russian Academy of Sciences, 603950, GSP-105, Nizhniy Novgorod, Russia and Nizhniy Novgorod State University, 603950, 23 Gagarin ave., Nizhniy Novgorod (Russian Federation)


    We investigate the dependencies of the photocurrent in Si:Er p-n junctions on the energy of the incident photons. The exponential absorption edge (Urbach edge) just below fundamental edge of silicon was observed in the absorption spectra of epitaxial Si:Er layers grown at 400–600 C. It is shown that the introduction of erbium significantly enhances the structural disorder in the silicon crystal which was estimated from the slope of the Urbach edge. We discuss the possible nature of the structural disorder in Si:Er and a new mechanism of erbium excitation, which does not require the presence of deep levels in the band gap of silicon.

  14. Coupling and manipulation of edge states in multilayer phosphorene nanoribbons (United States)

    Lv, Z. T.; Gao, J. H.; Zhang, X. D.; Jiang, Z. T.


    We investigate the couplings among the edge states of the normal zigzag and skewed armchair multilayer phosphorene nanoribbons, as well as the effect of the electric field on the corresponding energy levels, by using the tight-binding Hamiltonian approach. It is found that there appear different transitions from the coupled to uncoupled edge states in the normal zigzag and skewed armchair nanoribbons with the increasing of the nanoribbon width, which is fundamentally attributed to the edge asymmetry of the multilayer phosphorene nanoribbons. Moreover, the energy bands of the multilayer phosphorene nanoribbons can be effectively adjusted by applying the perpendicular electric field. Therefore, this research should be thought of as a useful reference for determining the width, the edge types, and the layer numbers of the nanoribbons in manipulating the properties of the multilayer phosphorene nanoribbons.

  15. Saturn's Rings Edge-on (United States)


    In one of nature's most dramatic examples of 'now-you see-them, now-you-don't', NASA's Hubble Space Telescope captured Saturn on May 22, 1995 as the planet's magnificent ring system turned edge-on. This ring-plane crossing occurs approximately every 15 years when the Earth passes through Saturn's ring plane.For comparison, the top picture was taken by Hubble on December 1, 1994 and shows the rings in a more familiar configuration for Earth observers.The bottom picture was taken shortly before the ring plane crossing. The rings do not disappear completely because the edge of the rings reflects sunlight. The dark band across the middle of Saturn is the shadow of the rings cast on the planet (the Sun is almost 3 degrees above the ring plane.) The bright stripe directly above the ring shadow is caused by sunlight reflected off the rings onto Saturn's atmosphere. Two of Saturn's icy moons are visible as tiny starlike objects in or near the ring plane. They are, from left to right, Tethys (slightly above the ring plane) and Dione.This observation will be used to determine the time of ring-plane crossing and the thickness of the main rings and to search for as yet undiscovered satellites. Knowledge of the exact time of ring-plane crossing will lead to an improved determination of the rate at which Saturn 'wobbles' about its axis (polar precession).Both pictures were taken with Hubble's Wide Field Planetary Camera 2. The top image was taken in visible light. Saturn's disk appears different in the bottom image because a narrowband filter (which only lets through light that is not absorbed by methane gas in Saturn's atmosphere) was used to reduce the bright glare of the planet. Though Saturn is approximately 900 million miles away, Hubble can see details as small as 450 miles across.The Wide Field/Planetary Camera 2 was developed by the Jet Propulsion Laboratory and managed by the Goddard Spaced Flight Center for NASA's Office of Space Science.This image and other images and

  16. On Detecting Edges. (United States)


    size / uo;1 ) 9 2.5, it has subpixel posi- tion localization (b , < 1/3) and an angular localization better ".- than 10; further, it is designed to be...detection is robust with respect to noise; for (step-size / o.,, ) 2 2.5, it has subpixel posi- tion localization (u, oi. < 1/3) and an angular localization...34"..".- . ’ Page 48 On Detecting Edges *.% intensities photoelectronic noise may dominate thermal noise, rendering our noise-model invalid. Under such

  17. The amniotic band syndrome: antenatal sonographic diagnosis and potential pitfalls. (United States)

    Mahony, B S; Filly, R A; Callen, P W; Golbus, M S


    Amniotic band syndrome causes a variety of fetal malformations involving the limbs, craniofacial region, and trunk. Six prenatally diagnosed cases of amniotic band syndrome are discussed. The diagnosis was based on sonographic visualization of either amniotic sheets or bands associated with fetal deformation or deformities in nonembryologic distributions known to characterize the amniotic band syndrome. Seven additional cases are considered in which an aberrant sheet of tissue with a free edge was visualized within the amniotic cavity but no restriction of fetal motion or subsequent deformity was demonstrated.

  18. Band structure of semiconductors

    CERN Document Server

    Tsidilkovski, I M


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

  19. X-ray absorption near edge spectroscopy at the Mn K-edge in highly homogeneous GaMnN diluted magnetic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Sancho-Juan, O.; Cantarero, A.; Garro, N.; Cros, A. [Materials Science Institute, University of Valencia, PO Box 22085, 46071 Valencia (Spain); Martinez-Criado, G.; Salome, M.; Susini, J. [ESRF, Polygone Scientifique Louis Neel, 6 rue Jules Horowitz, 38000 Grenoble (France); Olguin, D. [Dept. de Fisica, CINVESTAV-IPN, 07300 Mexico D.F. (Mexico); Dhar, S.; Ploog, K. [Paul Drude Institute, Hausvogteiplatz 5-7, 10117 Berlin (Germany)


    We have studied by X-ray absorption spectroscopy the local environment of Mn in highly homogeneous Ga{sub 1-x}Mn{sub x}N (0.06edges. In this report, we focus our attention to the X-ray absorption near edge spectroscopy (XANES) results. The comparison of the XANES spectra corresponding to the Ga and Mn edges indicates that Mn is substitutional to Ga in all samples studied. The XANES spectra measured at the Mn absorption edge shows in the near-edge region a double peak and a shoulder below the absorption edge and the main absorption peak after the edge, separated around 15 eV above the pre-edge structure. We have compared the position of the edge with that of MnO (Mn{sup 2+}) and Mn{sub 2}O{sub 3} (Mn{sup 3+}). All samples studied present the same Mn oxidation state, 2{sup +}. In order to interprete the near-edge structure, we have performed ab initio calculations with a 2 x 2 x 1supercell ({proportional_to}6% Mn) using the full potential linear augmented plane wave method as implemented in the Wien2k code. The calculations show the appearance of Mn anti-bonding t{sub 2g} bands, which are responsible for the pre-edge absorption. The shoulder and main absorption peaks are due to transitions from the valence band 1s-states of Mn to the p-contributions of the conduction bands. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Effect of Edge Roughness on Static Characteristics of Graphene Nanoribbon Field Effect Transistor

    Directory of Open Access Journals (Sweden)

    Yaser M. Banadaki


    Full Text Available In this paper, we present a physics-based analytical model of GNR FET, which allows for the evaluation of GNR FET performance including the effects of line-edge roughness as its practical specific non-ideality. The line-edge roughness is modeled in edge-enhanced band-to-band-tunneling and localization regimes, and then verified for various roughness amplitudes. Corresponding to these two regimes, the off-current is initially increased, then decreased; while, on the other hand, the on-current is continuously decreased by increasing the roughness amplitude.

  1. Determination of density of band-gap states of hydrogenated amorphous silicon suboxide thin films

    International Nuclear Information System (INIS)

    Bacioglu, A.


    Variation of density of gap states of PECVD silicon suboxide films with different oxygen concentrations was evaluated through electrical and optical measurements. Optical transmission and constant photocurrent method (CPM) were used to determine absorption coefficient as a function of photon energy. From these measurements the localized density of states between the valance band mobility edge and Fermi level has been determined. To determine the variation of conduction band edge, steady state photoconductivity (SSPC), photoconductivity response time (PCRT) and transient photoconductivity (TPC) measurements were utilized. Results indicate that the conduction and valance band edges, both, widen monotonically with oxygen content

  2. Anomalous edge states and the bulk-edge correspondence for periodically-driven two dimensional systems

    DEFF Research Database (Denmark)

    Rudner, Mark Spencer; Lindner, Netanel; Berg, Erez


    revealed phenomena that cannot be characterized by analogy to the topological classification framework for static systems. In particular, in driven systems in two dimensions (2D), robust chiral edge states can appear even though the Chern numbers of all the bulk Floquet bands are zero. Here, we elucidate...... the crucial distinctions between static and driven 2D systems, and construct a new topological invariant that yields the correct edge-state structure in the driven case. We provide formulations in both the time and frequency domains, which afford additional insight into the origins of the “anomalous” spectra...... that arise in driven systems. Possibilities for realizing these phenomena in solid-state and cold-atomic systems are discussed....

  3. Edge remap for solids

    Energy Technology Data Exchange (ETDEWEB)

    Kamm, James R.; Love, Edward; Robinson, Allen C; Young, Joseph G.; Ridzal, Denis


    We review the edge element formulation for describing the kinematics of hyperelastic solids. This approach is used to frame the problem of remapping the inverse deformation gradient for Arbitrary Lagrangian-Eulerian (ALE) simulations of solid dynamics. For hyperelastic materials, the stress state is completely determined by the deformation gradient, so remapping this quantity effectively updates the stress state of the material. A method, inspired by the constrained transport remap in electromagnetics, is reviewed, according to which the zero-curl constraint on the inverse deformation gradient is implicitly satisfied. Open issues related to the accuracy of this approach are identified. An optimization-based approach is implemented to enforce positivity of the determinant of the deformation gradient. The efficacy of this approach is illustrated with numerical examples.

  4. Performance characterization of edge detectors (United States)

    Ramesh, Visvanathan; Haralick, Robert M.


    Edge detection is the most fundamental step in vision algorithms. A number of edge detectors have been discussed in the computer vision literature. Examples of classic edge detectors include the Marr-Hildreth edge operator, facet edge operator, and the Canny edge operator. Edge detection using morphological techniques are attractive because they can be efficiently implemented in near real time machine vision systems that have special hardware support. However, little performance characterization of edge detectors has been done. In general, performance characterization of edge detectors has been done mainly by plotting empirical curves of performance. Quantitative performance evaluation of edge detectors was first performed by Abdou and Pratt. It is the goal of this paper to perform a theoretical comparison of gradient based edge detectors and morphological edge detectors. By assuming that an ideal edge is corrupted with additive noise we derive theoretical expressions for the probability of misdetection (the probability of labeling of a true edge pixel as a nonedge pixel in the output). Further, we derive theoretical expressions for the probability of false alarm (the probability of labeling of a nonedge pixel as an output edge pixel) by assuming that the input to the operator is a region of flat graytone intensity corrupted with additive Gaussian noise of zero mean and variance (sigma) 2. Even though the blurring step in the morphological operator introduces correlation in the additive noise, we make an approximation that the output samples after blurring are i.i.d. Gaussian random variables with zero mean and variance (sigma) 2/M where M is the window size of the blurring kernel. The false alarm probabilities obtained by using this approximation can be shown to be upperbounds of the false alarm probabilities computed without the approximation. The theory indicates that the blur- min operator is clearly superior when a 3 X 3 window size is used. Since we only have

  5. Strong coupling between a permalloy ferromagnetic contact and helical edge channel in a narrow HgTe quantum well

    Energy Technology Data Exchange (ETDEWEB)

    Kononov, A.; Egorov, S. V. [Russian Academy Sciences, Institute of Solid State Physics (Russian Federation); Kvon, Z. D.; Mikhailov, N. N.; Dvoretsky, S. A. [Institute of Semiconductor Physics (Russian Federation); Deviatov, E. V., E-mail: [Russian Academy Sciences, Institute of Solid State Physics (Russian Federation)


    We experimentally investigate spin-polarized electron transport between a permalloy ferromagnet and the edge of a two-dimensional electron system with band inversion, realized in a narrow, 8 nm wide, HgTe quantum well. In zero magnetic field, we observe strong asymmetry of the edge potential distribution with respect to the ferromagnetic ground lead. This result indicates that the helical edge channel, specific for the structures with band inversion even at the conductive bulk, is strongly coupled to the ferromagnetic side contact, possibly due to the effects of proximity magnetization. This allows selective and spin-sensitive contacting of helical edge states.

  6. Edge colouring by total labellings

    DEFF Research Database (Denmark)

    Brandt, Stephan; Rautenbach, D.; Stiebitz, M.


    We introduce the concept of an edge-colouring total k-labelling. This is a labelling of the vertices and the edges of a graph G with labels 1, 2, ..., k such that the weights of the edges define a proper edge colouring of G. Here the weight of an edge is the sum of its label and the labels of its...... two endvertices. We define χ (G) to be the smallest integer k for which G has an edge-colouring total k-labelling. This parameter has natural upper and lower bounds in terms of the maximum degree Δ of G : ⌈ (Δ + 1) / 2 ⌉ ≤ χ (G) ≤ Δ + 1. We improve the upper bound by 1 for every graph and prove χ (G...

  7. Band-gap engineering in fluorographene nanoribbons under uniaxial strain

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yan, E-mail:, E-mail:; Li, Qunxiang, E-mail:, E-mail: [Hefei National Laboratory for Physical Sciences at Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)


    Based on extensive first-principles calculations, we report the structural and electronic properties of fluorinated graphene, i.e., fluorographene nanoribbons (FGNRs) under uniaxial strain. Our results indicate that the FGNRs are semiconductors with wide direct band gaps regardless of their edge structures. Moreover, the band gap of FGNR can be effectively modulated nonlinearly with the applied uniaxial elastic strain, where the band gap value increases first and then reduces when the applied strain changes from −10.0% to 10.0%. This abnormal behavior mainly originates from the electronic structures of valence and conduction band edges, which is quite different from previously reported linear behavior on graphene nanoribbon. Our results imply the great potential applications of FGNRs in the optical electronics.

  8. Cutting Edge Localisation in an Edge Profile Milling Head

    NARCIS (Netherlands)

    Fernandez Robles, Laura; Azzopardi, George; Alegre, Enrique; Petkov, Nicolai


    Wear evaluation of cutting tools is a key issue for prolonging their lifetime and ensuring high quality of products. In this paper, we present a method for the effective localisation of cutting edges of inserts in digital images of an edge profile milling head. We introduce a new image data set of

  9. Band warping, band non-parabolicity, and Dirac points in electronic and lattice structures (United States)

    Resca, Lorenzo; Mecholsky, Nicholas A.; Pegg, Ian L.


    We illustrate at a fundamental level the physical and mathematical origins of band warping and band non-parabolicity in electronic and vibrational structures. We point out a robust presence of pairs of topologically induced Dirac points in a primitive-rectangular lattice using a p-type tight-binding approximation. We analyze two-dimensional primitive-rectangular and square Bravais lattices with implications that are expected to generalize to more complex structures. Band warping is shown to arise at the onset of a singular transition to a crystal lattice with a larger symmetry group, which allows the possibility of irreducible representations of higher dimensions, hence band degeneracy, at special symmetry points in reciprocal space. Band warping is incompatible with a multi-dimensional Taylor series expansion, whereas band non-parabolicities are associated with multi-dimensional Taylor series expansions to all orders. Still band non-parabolicities may merge into band warping at the onset of a larger symmetry group. Remarkably, while still maintaining a clear connection with that merging, band non-parabolicities may produce pairs of conical intersections at relatively low-symmetry points. Apparently, such conical intersections are robustly maintained by global topology requirements, rather than any local symmetry protection. For two p-type tight-binding bands, we find such pairs of conical intersections drifting along the edges of restricted Brillouin zones of primitive-rectangular Bravais lattices as lattice constants vary relatively to each other, until these conical intersections merge into degenerate warped bands at high-symmetry points at the onset of a square lattice. The conical intersections that we found appear to have similar topological characteristics as Dirac points extensively studied in graphene and other topological insulators, even though our conical intersections have none of the symmetry complexity and protection afforded by the latter more

  10. Edge-edge interactions in stacked graphene nanoplatelets

    Energy Technology Data Exchange (ETDEWEB)

    Cruz Silva, Eduardo [ORNL; Terrones Maldonado, Humberto [ORNL; Terrones Maldonado, Mauricio [ORNL; Jia, Xiaoting [Massachusetts Institute of Technology (MIT); Sumpter, Bobby G [ORNL; Dresselhaus, M [Massachusetts Institute of Technology (MIT); Meunier, V. [Rensselaer Polytechnic Institute (RPI)


    High-resolution transmission electron microscopy (HRTEM) studies show the dynamics of small graphene platelets on larger graphene layers. The platelets move nearly freely to eventually lock in at well-defined positions close to the edges of the larger underlying graphene sheet. While such movement is driven by a shallow potential energy surface described by an interplane interaction, the lock-in position occurs by via edge-edge interactions of the platelet and the graphene surface located underneath. Here we quantitatively study this behavior using van der Waals density functional calculations. Local interactions at the open edges are found to dictate stacking configurations that are different from Bernal (AB) stacking. These stacking configurations are known to be otherwise absent in edge-free two-dimensional (2D) graphene. The results explain the experimentally observed platelet dynamics and provide a detailed account of the new electronic properties of these combined systems.

  11. Band alignments of graphene-like III-nitride semiconductors (United States)

    Ota, Yuichi


    Band alignment in graphene-like III-nitride semiconductors was investigated using first principles calculations and an empirical formula. We estimated the band edge positions using two simple approaches based on the energy of the band gap center (BGC) and electron affinity rules. The energy positions relative to the vacuum level were determined from the BGC and Mulliken electronegativities. These methods provided similar trends in the band lineup. The valence band and conduction band offsets determined by the first principles calculations agreed with the empirical results to within 0.5 eV. The findings suggest that the first principles and empirical methods provide a useful guide for high-throughput device design.

  12. Finite size effects on the helical edge states on the Lieb lattice

    International Nuclear Information System (INIS)

    Chen Rui; Zhou Bin


    For a two-dimensional Lieb lattice, that is, a line-centered square lattice, the inclusion of the intrinsic spin–orbit (ISO) coupling opens a topologically nontrivial gap, and gives rise to the quantum spin Hall (QSH) effect characterized by two pairs of gapless helical edge states within the bulk gap. Generally, due to the finite size effect in QSH systems, the edge states on the two sides of a strip of finite width can couple together to open a gap in the spectrum. In this paper, we investigate the finite size effect of helical edge states on the Lieb lattice with ISO coupling under three different kinds of boundary conditions, i.e., the straight, bearded and asymmetry edges. The spectrum and wave function of edge modes are derived analytically for a tight-binding model on the Lieb lattice. For a strip Lieb lattice with two straight edges, the ISO coupling induces the Dirac-like bulk states to localize at the edges to become the helical edge states with the same Dirac-like spectrum. Moreover, it is found that in the case with two straight edges the gapless Dirac-like spectrum remains unchanged with decreasing the width of the strip Lieb lattice, and no gap is opened in the edge band. It is concluded that the finite size effect of QSH states is absent in the case with the straight edges. However, in the other two cases with the bearded and asymmetry edges, the energy gap induced by the finite size effect is still opened with decreasing the width of the strip. It is also proposed that the edge band dispersion can be controlled by applying an on-site potential energy on the outermost atoms. (paper)

  13. Effects of band-tails on the subthreshold characteristics of nanowire band-to-band tunneling transistors (United States)

    Khayer, M. Abul; Lake, Roger K.


    High source doping is required to support the high electric fields necessary to provide sufficient drive currents in interband tunnel field effect transistors (TFETs). High doping is associated with band-tails in the density of states that decay exponentially into the bandgap with decay constants that can be comparable to the room temperature thermal energy kBT. This compromises the core operational principal of a TFET of a hard energy cut-off to the injected channel carrier distribution provided by the source valence band edge. If the band-tails are limited to the source region, they have minimal effect for short channels ≤10 nm, since the leakage current is dominated by direct, coherent tunneling through the channel. For longer 20 nm channels, source band-tails can double the inverse subthreshold slope but still leave it below the ideal 60 mV/decade value with on-off current ratios greater than 106 using a supply voltage of 0.4 V. Band-tails both in the source and channel are more detrimental for both 10 and 20 nm channels. On-off current ratios are reduced to ≥103 and ≥104 for the 10 nm and 20 nm channel devices, respectively.

  14. Wide Band to ''Double Band'' upgrade

    International Nuclear Information System (INIS)

    Kasper, P.; Currier, R.; Garbincius, P.; Butler, J.


    The Wide Band beam currently uses electrons obtained from secondary photon conversions to produce the photon beam incident on the experimental targets. By transporting the positrons produced in these conversions as well as the electrons it is possible to almost double the number of photons delivered to the experiments per primary beam proton. 11 figs

  15. Highly Efficient Photocatalytic Water Splitting over Edge-Modified Phosphorene Nanoribbons. (United States)

    Hu, Wei; Lin, Lin; Zhang, Ruiqi; Yang, Chao; Yang, Jinlong


    Two-dimensional phosphorene with desirable optoelectronic properties (ideal band gap, high carrier mobility, and strong visible light absorption) is a promising metal-free photocatalyst for water splitting. However, the band edge positions of the valence band maximum (VBM) and conduction band maximum (CBM) of phosphorene are higher than the redox potentials in photocatalytic water splitting reactions. Thus, phosphorene can only be used as the photocathode for hydrogen evolution reaction as a low-efficiency visible-light-driven photocatalyst for hydrogen production in solar water splitting cells. Here, we propose a new mechanism to improve the photocatalytic efficiency of phosphorene nanoribbons (PNRs) by modifying their edges for full reactions in photocatalytic water splitting. By employing first-principles density functional theory calculations, we find that pseudohalogen (CN and OCN) passivated PNRs not only show desired VBM and CBM band edge positions induced by edge electric dipole layer, but also possess intrinsic optoelectronic properties of phosphorene, for both water oxidation and hydrogen reduction in photocatalytic water splitting without using extra energy. Furthermore, our calculations also predict that the maximum energy conversion efficiency of heterojunction solar cells consisting of different edge-modified PNRs can be as high as 20% for photocatalytic water splitting.

  16. Extremal characterization of band gaps in nonlinear gratings

    NARCIS (Netherlands)

    van Groesen, Embrecht W.C.; Sopaheluwakan, A.

    In this paper we present an explicit extremal characterization of the edges of the lowest band gap in gratings; we restrict here to the case of TE-modes, but the TM case can be treated similarly. The characterization is valid for linear and Kerr-nonlinear gratings, for smooth as well as for

  17. Predictive intelligence to the edge: impact on edge analytics


    Harth, Natascha; Anagnostopoulos, Christos; Pezaros, Dimitrios


    We rest on the edge computing paradigm where pushing processing and inference to the edge of the Internet of Things (IoT) allows the complexity of predictive analytics to be distributed into smaller pieces physically located at the source of the contextual information. This enables a huge amount of rich contextual data to be processed in real time that would be prohibitively complex and costly to deliver on a traditional centralized Cloud. We propose a lightweight, distributed, predictive int...

  18. The edge of space time

    International Nuclear Information System (INIS)

    Hawking, S.


    What happened at the beginning of the expansion of the universe. Did space time have an edge at the Big Bang. The answer is that, if the boundary conditions of the universe are that it has no boundary, time ceases to be well-defined in the very early universe as the direction ''north'' ceases to be well defined at the North Pole of the Earth. The quantity that we measure as time has a beginning but that does not mean spacetime has an edge, just as the surface of the Earth does not have an edge at the North Pole. 8 figs

  19. Edges, curvature, and primal sketches. (United States)

    Watt, Roger


    Marr described two versions of the primal sketch: the basic image-processing level in human vision. In line with his broader view of how one should construct explanatory theories in vision, he provided some details of the computational theory for this stage, the algorithms used, and how they might be implemented in neural systems. In this paper I consider how Marr ideas have continued over the past 30 years. In this regard, I pay particular attention to three stages: locating edges; describing edge curvature; linking local edge segments into elongated contours.

  20. Band - Weg interactie

    NARCIS (Netherlands)

    de Boer, Andries; ter Huerne, Henderikus L.; Noordermeer, Jacobus W.M.; Schipper, Dirk J.; Molenaar, A.A.A.


    De huidige infrastructuur van wegen waarover men zich snel en comfortabel kan verplaatsen is niet meer weg te denken uit onze maatschappij. Twee “componenten” die hierbij een belangrijke rol spelen zijn het wegdek en de band. Het contact tussen band en wegdek is mede bepalend voor de veiligheid. De

  1. Photonic band structure computations. (United States)

    Hermann, D; Frank, M; Busch, K; Wolfle, P


    We introduce a novel algorithm for band structure computations based on multigrid methods. In addition, we demonstrate how the results of these band structure calculations may be used to compute group velocities and effective photon masses. The results are of direct relevance to studies of pulse propagation in such materials.


    NARCIS (Netherlands)



    Banding techniques were carried out on metaphase chromosomes of zebrafish (Danio rerio) embryos. The karyotypes with the longest chromosomes consist of 12 metacentrics, 26 submetacentrics, and 12 subtelocentrics (2n = 50). All centromeres are C-band positive. Eight chromosomes have a pericentric

  3. DAVs: Red Edge and Outbursts (United States)

    Luan, Jing


    As established by ground based surveys, white dwarfs with hydrogen atmospheres pulsate as they cool across the temperature range, 12500Kred edge is a two-decade old puzzle. Recently, Kepler discovered a number of cool DAVs exhibiting sporadic outbursts separated by days, each lasting several hours, and releasing \\sim 10^{33}-10^{34} {erg}. We provide quantitative explanations for both the red edge and the outbursts. The minimal frequency for overstable modes rises abruptly near the red edge. Although high frequency overstable modes exist below the red edge, their photometric amplitudes are generally too small to be detected by ground based observations. Nevertheless, these overstable parent modes can manifest themselves through nonlinear mode couplings to damped daughter modes which generate limit cycles giving rise to photometric outbursts.

  4. Fast tracking using edge histograms (United States)

    Rokita, Przemyslaw


    This paper proposes a new algorithm for tracking objects and objects boundaries. This algorithm was developed and applied in a system used for compositing computer generated images and real world video sequences, but can be applied in general in all tracking systems where accuracy and high processing speed are required. The algorithm is based on analysis of histograms obtained by summing along chosen axles pixels of edge segmented images. Edge segmentation is done by spatial convolution using gradient operator. The advantage of such an approach is that it can be performed in real-time using available on the market hardware convolution filters. After edge extraction and histograms computation, respective positions of maximums in edge intensity histograms, in current and previous frame, are compared and matched. Obtained this way information about displacement of histograms maximums, can be directly converted into information about changes of target boundaries positions along chosen axles.

  5. Diffraction at a Straight Edge

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 20; Issue 5. Diffraction at a Straight Edge: A Gem from Sommerfeld's Work in Classical Physics. Rajaram Nityananda. General Article Volume 20 Issue 5 May 2015 pp 389-400 ...

  6. Edge equilibrium code for tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Li, Xujing [Institute of Computational Mathematics and Scientific/Engineering Computing, Academy of Mathematics and Systems Science, Chinese Academy of Sciences, P.O. Box 2719, Beijing 100190 (China); Zakharov, Leonid E. [Princeton Plasma Physics Laboratory Princeton, MS-27 P.O. Box 451, New Jersey (United States); Drozdov, Vladimir V. [Euratom/CCFE Fusion Association, Culham Science Centre, Abingdon OX14 3DB (United Kingdom)


    The edge equilibrium code (EEC) described in this paper is developed for simulations of the near edge plasma using the finite element method. It solves the Grad-Shafranov equation in toroidal coordinate and uses adaptive grids aligned with magnetic field lines. Hermite finite elements are chosen for the numerical scheme. A fast Newton scheme which is the same as implemented in the equilibrium and stability code (ESC) is applied here to adjust the grids.

  7. Extruded edge members for honeycombs (United States)

    Haskell, D. R.


    Edge members in bonded honeycomb panel structures are conventionally made by machining channels in aluminum bars. Open ends are stuffed with honeycomb core, using intumescent adhesive. Less expensive technique eliminates need for stuffing. Extended edges are more reliable, lighter, and easier to install. New manufacturing method may prove useful in fabricating structures such as air-frames, recreational-vehicle frame members, and the like in which weight savings is primary goal.

  8. Effects of edge reconstruction on the common groups terminated zigzag phosphorene nanoribbon

    International Nuclear Information System (INIS)

    Xiao, Huaping; Guo, Sumei; Zhang, Chunxiao; He, Chaoyu; Zhong, Jianxin


    Edge configuration plays an important role in the electronic properties of nano-structures. In this work, we perform first-principles calculations to study the effects of the cooperation between neighbor groups on the edge configuration and the electronic properties of zigzag-PNRs (ZPNRs) terminated by common groups H, F, O, S and OH. We find that the cooperation has little effect on the H(F)-terminated ZPNRs, but gives rise to an edge reconstruction for the O(S)-terminated ZPNRs. The edge reconstruction derives from the repulsion between neighbor O atoms and the distortion of the P skeleton induced by the p state coupling among the edge, second edge and third edge P atoms. In comparison to the H-terminated ZPNRs, O-terminated ZPNRs are also a semiconductor and enlarge the band gap, but bring about an extra transport channel for the charge transport at the edge and decreases the effective mass of the electron and hole. OH-terminated ZPNRs also undergo a doubling of the unit cell (UC) along the periodic direction because of the different directions of the neighbor O–H bonds. In comparison with the H-terminated ZPNRs, OH-terminated ZPNRs show a similar band gap and electronic effective mass, but increase the effective mass of the hole. (paper)

  9. [Road Extraction in Remote Sensing Images Based on Spectral and Edge Analysis]. (United States)

    Zhao, Wen-zhi; Luo, Li-qun; Guo, Zhou; Yue, Jun; Yu, Xue-ying; Liu, Hui; Wei, Jing


    Roads are typically man-made objects in urban areas. Road extraction from high-resolution images has important applications for urban planning and transportation development. However, due to the confusion of spectral characteristic, it is difficult to distinguish roads from other objects by merely using traditional classification methods that mainly depend on spectral information. Edge is an important feature for the identification of linear objects (e. g. , roads). The distribution patterns of edges vary greatly among different objects. It is crucial to merge edge statistical information into spectral ones. In this study, a new method that combines spectral information and edge statistical features has been proposed. First, edge detection is conducted by using self-adaptive mean-shift algorithm on the panchromatic band, which can greatly reduce pseudo-edges and noise effects. Then, edge statistical features are obtained from the edge statistical model, which measures the length and angle distribution of edges. Finally, by integrating the spectral and edge statistical features, SVM algorithm is used to classify the image and roads are ultimately extracted. A series of experiments are conducted and the results show that the overall accuracy of proposed method is 93% comparing with only 78% overall accuracy of the traditional. The results demonstrate that the proposed method is efficient and valuable for road extraction, especially on high-resolution images.

  10. Edge of polar cap patches (United States)

    Hosokawa, K.; Taguchi, S.; Ogawa, Y.


    On the night of 4 December 2013, a sequence of polar cap patches was captured by an all-sky airglow imager (ASI) in Longyearbyen, Norway (78.1°N, 15.5°E). The 630.0 nm airglow images from the ASI of 4 second exposure time, oversampled the emission of natural lifetime (with quenching) of at least ˜30 sec, introduce no observational blurring effects. By using such high-quality ASI images, we succeeded in visualizing an asymmetry in the gradients between the leading/trailing edges of the patches in a 2-D fashion. The gradient in the leading edge was found to be 2-3 times steeper than that in the trailing edge. We also identified fingerlike structures, appearing only along the trailing edge of the patches, whose horizontal scale size ranged from 55 to 210 km. These fingers are considered to be manifestations of plasma structuring through the gradient-drift instability (GDI), which is known to occur only along the trailing edge of patches. That is, the current 2-D observations visualized, for the first time, how GDI stirs the patch plasma and such a mixing process makes the trailing edge more gradual. This result strongly implies a close connection between the GDI-driven plasma stirring and the asymmetry in the large-scale shape of patches and then suggests that the fingerlike structures can be used as markers to estimate the fine-scale structure in the plasma flow within patches.

  11. Trailing edge noise estimation by tomographic Particle Image Velocimetry (United States)

    Pröbsting, Stefan; Tuinstra, Marthijn; Scarano, Fulvio


    The feasibility of estimating broadband trailing edge noise with high-speed tomographic Particle Image Velocimetry (PIV) measurements is studied. A thin plate terminating in a sharp trailing edge provides a generic test case for turbulent boundary layer trailing edge interaction noise. Far-field noise is linked to the wavenumber-frequency spectrum of the surface pressure fluctuations in proximity of the trailing edge through diffraction theory. High-speed tomographic PIV measurements return volumetric and time-resolved information about all velocity components for the resolved spatio-temporal scales and can therefore provide the required statistical quantities. For the turbulent boundary layer interacting with the trailing edge, these statistics include the auto-spectral density, spanwise correlation length, and convection velocity of the unsteady surface pressure, which are thus estimated. Acoustic phased array measurements in an anechoic environment provide a reference for comparison. Over the resolved frequency band, PIV based noise estimation results compare favorably with the reference measurements. Especially at lower frequencies, where existing, empirical models for the unsteady surface pressure spectrum are not accurate, tomographic PIV can offer an alternative approach to complex and intrusive model instrumentation for assessing the relevant statistical quantities.

  12. Domination Edge Lift Critical Trees | Desormeaux | Quaestiones ...

    African Journals Online (AJOL)

    stract. Let uxv be an induced path with center x in a graph G. The edge lifting of uv off x is defined as the action of removing edges ux and vx from the edge set of G, while adding the edge uv to the edge set of G. We study trees for which every possible edge lift changes the domination number. We show that there are no ...

  13. Effects of edge magnetism on the Kohn anomalies of zigzag graphene nanoribbons. (United States)

    Culchac, F J; Capaz, Rodrigo B


    The effects of edge magnetism on the Kohn anomaly (KA) of the G-band phonons of zigzag graphene nanoribbons (ZGNRs) are studied using a combination of the tight-binding and mean-field Hubbard models. We show that the opening of an energy gap, induced by magnetic ordering, significantly changes the KA effects, particularly for narrow ribbons in which the gap is larger than the phonon energy. Therefore, the G-band phonon frequency and lifetime are altered for a magnetically-ordered edge state with respect to an unpolarized edge state. The effects of temperature, ZGNR width, doping and transverse electric fields are systematically investigated. We propose using this effect to probe the magnetic order of edge states in graphene nanoribbons using Raman spectroscopy.

  14. Dendrometer bands made easy: using modified cable ties to measure incremental growth of trees (United States)

    Anemaet, Evelyn R.; Middleton, Beth A.


    Dendrometer bands are a useful way to make sequential repeated measurements of tree growth, but traditional dendrometer bands can be expensive, time consuming, and difficult to construct in the field. An alternative to the traditional method of band construction is to adapt commercially available materials. This paper describes how to construct and install dendrometer bands using smooth-edged, stainless steel, cable tie banding and attachable rollerball heads. As a performance comparison, both traditional and cable tie dendrometer bands were installed on baldcypress trees at the National Wetlands Research Center in Lafayette, Louisiana, by both an experienced and a novice worker. Band installation times were recorded, and growth of the trees as estimated by the two band types was measured after approximately one year, demonstrating equivalence of the two methods. This efficient approach to dendrometer band construction can help advance the knowledge of long-term tree growth in ecological studies.

  15. Band parameters of phosphorene

    DEFF Research Database (Denmark)

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


    Phosphorene is a two-dimensional nanomaterial with a direct band-gap at the Brillouin zone center. In this paper, we present a recently derived effective-mass theory of the band structure in the presence of strain and electric field, based upon group theory. Band parameters for this theory...... are computed using a first-principles theory based upon the generalized-gradient approximation to the density-functional theory. These parameters and Hamiltonian will be useful for modeling physical properties of phosphorene....

  16. Laparoscopic gastric banding (United States)

    ... eat by making you feel full after eating small amounts of food. After surgery, your doctor can adjust the band ... You will feel full after eating just a small amount of food. The food in the small upper pouch will ...

  17. Decay of superdeformed bands

    International Nuclear Information System (INIS)

    Carpenter, M.P.; Khoo, T.L.; Lauritsen, T.


    One of the major challenges in the study of superdeformation is to directly connect the large number of superdeformed bands now known to the yrast states. In this way, excitation energies, spins and parities can be assigned to the levels in the second well which is essential to establish the collective and single-particle components of these bands. This paper will review some of the progress which has been made to understand the decay of superdeformed bands using the new arrays including the measurement of the total decay spectrum and the establishment of direct one-step decays from the superdeformed band to the yrast line in 194 Hg. 42 refs., 5 figs

  18. HYBASE - HYperspectral BAnd SElection tool

    NARCIS (Netherlands)

    Schwering, P.B.W.; Bekman, H.H.P.T.; Seijen, H.H. van


    Band selection is essential in the design of multispectral sensor systems. This paper describes the TNO hyperspectral band selection tool HYBASE. It calculates the optimum band positions given the number of bands and the width of the spectral bands. HYBASE is used to calculate the minimum number of

  19. Hurricane Spiral Bands. (United States)

    Guinn, Thomas A.; Schubert, Wayne H.


    The spiral bands that occur in tropical cyclones can be conveniently divided into two classes-outer bands and inner bands. Evidence is presented here that the outer bands form as the result of nonlinear effects during the breakdown of the intertropical convergence zone (ITCZ) through barotropic instability. In this process a zonal strip of high potential vorticity (the ITCZ shear zone or monsoon trough) begins to distort in a varicose fashion, with the potential vorticity (PV) becoming pooled in local regions that are connected by filaments of high PV. As the pooled regions become more axisymmetric, the filaments become thinner and begin to wrap around the PV centers.It is argued that inner bands form in a different manner. As a tropical cyclone intensifies due to latent heat release, the PV field becomes nearly circular with the highest values of PV in the cyclone center. The radial gradient of PV provides a state on which PV waves (the generalization of Rossby waves) can propagate. The nonlinear breaking of PV waves then leads to an irreversible distortion of the PV contours and a downgradient flux of PV. The continuation of this proem tends to erode the high PV core of the tropical cyclone, to produce a surrounding surf zone, and hence to spread the PV horizontally. In a similar fashion, inner bands can also form by the merger of a vortex with a patch of relatively high PV air. As the merger proem occurs the patch of PV is quickly elongated and wrapped around the vortex. The resulting vortex is generally larger in horizontal extent and exhibits a spiral band of PV.When the formation of outer and inner bands is interpreted in the context of a normal-mode spectral model, they emerge as slow manifold phenomena; that is, they have both rotational and (balanced or slaved) gravitational mode aspects. In this sense, regarding them as simply gravity waves leads to an incomplete dynamical picture.

  20. Novel Dual-band Slot Antenna Design for Bluetooth and UWB Applications (United States)

    Huang, Hai-Yan; Shao, Wei; Wang, Bing-Zhong; Ma, Xiao-Liang


    A novel technique to introduce an additional low frequency band to compact ultra wideband (UWB) slot antennas is proposed in this paper. To get an additional Bluetooth band, a parasitic strip is mounted on the back side of the slot edge. Because of the interaction of the strip and the slot edge, the Bluetooth band can be obtained while a notch band between the Bluetooth band and UWB band also appears. Two types of feeding, coplanar waveguide and microstrip line, are investigated. The proposed antennas are both fabricated on a low-cost FR4 substrate and have compact size (24 mm × 28 mm × 1 mm). The good agreement between measured and simulated results verifies our design.

  1. Band Anticrossing in Highly Mismatched Compound Semiconductor Alloys (United States)

    Yu, Kin Man; Wu, J.; Walukiewicz, W.; Ager, J. W.; Haller, E. E.; Miotkowski, I.; Su, Ching-Hua; Curreri, Peter A. (Technical Monitor)


    Compound semiconductor alloys in which metallic anions are partially replaced with more electronegative isoelectronic atoms have recently attracted significant attention. Group IIIN(sub x)V(sub 1-x) alloys with a small amount of the electronegative N substituting more metallic column V elements has been the most extensively studied class of such Highly Mismatched Alloys (HMAs). We have shown that many of the unusual properties of the IIIN(sub x)V(sub 1-x) alloys can be well explained by the Band Anticrossing (BAC) model that describes the electronic structure in terms of an interaction between highly localized levels of substitutional N and the extended states of the host semiconductor matrix. Most recently the BAC model has been also used to explain similar modifications of the electronic band structure observed in Te-rich ZnS(sub x)Te(sub 1-x) and ZnSe(sub y)Te(sub 1-y) alloys. To date studies of HMAs have been limited to materials with relatively small concentrations of highly electronegative atoms. Here we report investigations of the electronic structure of ZnSe(sub y)Te(sub 1-y) alloys in the entire composition range, y between 0 and 1. The samples used in this study are bulk ZnSe(sub y)Te(sub 1-y) crystals grown by either a modified Bridgman method or by physical vapor transport. Photomodulated reflection (PR) spectroscopy was used to measure the composition dependence of optical transitions from the valence band edge and from the spin-orbit split off band to the conduction band. The pressure dependence of the band gap was measured using optical absorption in a diamond anvil cell. We find that the energy of the spin-orbit split off valence band edge does not depend on composition and is located at about 3 eV below the conduction band edge of ZnSe. On the Te-rich side the pressure and the composition dependence of the optical transitions are well explained by the BAC model which describes the downward shift of the conduction band edge in terms of the

  2. Protected Edge Modes without Symmetry

    Directory of Open Access Journals (Sweden)

    Michael Levin


    Full Text Available We discuss the question of when a gapped two-dimensional electron system without any symmetry has a protected gapless edge mode. While it is well known that systems with a nonzero thermal Hall conductance, K_{H}≠0, support such modes, here we show that robust modes can also occur when K_{H}=0—if the system has quasiparticles with fractional statistics. We show that some types of fractional statistics are compatible with a gapped edge, while others are fundamentally incompatible. More generally, we give a criterion for when an electron system with Abelian statistics and K_{H}=0 can support a gapped edge: We show that a gapped edge is possible if and only if there exists a subset of quasiparticle types M such that (1 all the quasiparticles in M have trivial mutual statistics, and (2 every quasiparticle that is not in M has nontrivial mutual statistics with at least one quasiparticle in M. We derive this criterion using three different approaches: a microscopic analysis of the edge, a general argument based on braiding statistics, and finally a conformal field theory approach that uses constraints from modular invariance. We also discuss the analogous result for two-dimensional boson systems.

  3. All-graphene edge contacts

    DEFF Research Database (Denmark)

    Jacobsen, Kåre Wedel; Falkenberg, Jesper Toft; Papior, Nick Rübner


    Using ab-initio methods we investigate the possibility of three-terminalgraphene "T-junction" devices and show that these all-graphene edge contactsare energetically feasible when the 1D interface itself is free from foreignatoms. We examine the energetics of various junction structures as a func......Using ab-initio methods we investigate the possibility of three-terminalgraphene "T-junction" devices and show that these all-graphene edge contactsare energetically feasible when the 1D interface itself is free from foreignatoms. We examine the energetics of various junction structures...... to be in therange of 1-10 kΩμm which is comparable to the best contact resistance reportedfor edge-contacted graphene-metal contacts. We conclude that conductingall-carbon T-junctions should be feasible....

  4. Photonic band gap materials (United States)

    Cassagne, D.

    Photonic band gap materials Photonic band gap materials are periodic dielectric structures that control the propagation of electromagnetic waves. We describe the plane wave method, which allows to calculate the band structures of photonic crystals. By symmetry analysis and a perturbative approach, we predict the appearance of the low energy photonic band gaps of hexagonal structures. We propose new two-dimensional structures called graphite and boron nitride. Using a transfer matrix method, we calculate the transmission of the graphite structure and we show the crucial role of the coupling with external modes. We study the appearance of allowed modes in the photonic band gap by the introduction of localized defects in the periodicity. Finally, we discuss the properties of opals formed by self-organized silica microspheres, which are very promising for the fabrication of three-dimensional photonic crystals. Les matériaux à bandes interdites photoniques sont des structures diélectriques périodiques qui contrôlent la propagation des ondes électromagnétiques. Nous décrivons la méthode des ondes planes qui permet de calculer les structures de bandes des cristaux photoniques. Par une analyse de la symétrie et une approche perturbative, nous précisons les conditions d'existence des bandes interdites de basse énergie. Nous proposons de nouvelles structures bidimensionnelles appelées graphite et nitrure de bore. Grâce à une méthode de matrices de transfert, nous calculons la transmission de la structure graphite et nous mettons en évidence le rôle fondamental du couplage avec les modes extérieurs. Nous étudions l'apparition de modes permis dans la bande interdite grâce à l'introduction de défauts dans la périodicité. Enfin, nous discutons les propriétés des opales constituées de micro-billes de silice auto-organisées, qui sont très prometteuses pour la fabrication de cristaux photoniques tridimensionnels.

  5. Restrictive techniques: gastric banding

    Directory of Open Access Journals (Sweden)

    Katia Cristina da Cunha


    Full Text Available Surgery for the treatment of severe obesity has a definite role onthe therapeutic armamentarium all over the world. Initiated 40years ago, bariatric surgery has already a long way thanks tohundred of surgeons, who had constantly searched for the besttechnique for the adequate control of severe obesity. Among theimportant breakthroughs in obesity surgery there is theadjustable gastric band. It is a sylastic band, inflatable andadjustable, which is placed on the top of the stomach in order tocreate a 15-20 cc pouch, with an outlet of 1.3cm. The adjustablegastric band has also a subcutaneous reservoir through whichadjustments can be made, according to the patient evolution.The main feature of the adjustable gastric band is the fact thatis minimal invasive, reversible, adjustable and placedlaparoscopically. Then greatly diminishing the surgical traumato the severe obese patient. Belachew and Favretti’s techniqueof laparoscopic application of the adjustable gastric band isdescribed and the evolution of the technique during this years,as we has been practiced since 1998. The perioperative care ofthe patient is also described, as well as the follow-up and shortand long term controls.

  6. Invariance of the mobility edge in anodic titanium oxides

    International Nuclear Information System (INIS)

    Tit, N.; Halley, J.W.; Shore, H.B.


    We present a theoretical investigation to explain the electronic and optical properties of anodic rutile TiO 2 thin films of different thicknesses (ranging from 5nm to 20nm). There is experimental evidence that the observed gap state at 0.7eV below the edge of conduction-band is due to an oxygen vacancy. For this reason, oxygen vacancies are used as defects in our model. A comparison of the calculated bulk-photoconductivity to photospectroscopy experiment reveals that the films have bulk-like transport properties with a bandgap E g =3.0eV. On the other hand, a fit of the surface density of states to the scanning tunneling microscopy (STM) experiment on the (001) surfaces has suggested a surface defect density of 5% of oxygen vacancies. To resolve this discrepancy, we calculated the dc-conductivity where localization effects are included. Our results show an impurity band formation at about p c =9% of oxygen vacancies. We concluded that the studied films have defect densities below the threshold of impurity band formation. As a consequence the gap states seen in STM are localized (i.e. the oxygen vacancies are playing the role of trapping centers, deep levels) and the mobility edge is invariant. (author). 11 refs, 3 figs

  7. The giant Stark effect in armchair-edge phosphorene nanoribbons under a transverse electric field (United States)

    Zhou, Benliang; Zhou, Benhu; Liu, Pu; Zhou, Guanghui


    We study the variation of electronic properties for armchair-edge phosphorene nanoribbons (APNRs) modulated by a transverse electric field. Within the tight-binding model Hamiltonian, and by solving the differential Schrödinger equation, we find that a band gap closure appears at the critical field due to the giant Stark effect for an APNR. The gap closure has no field polarity, and the gap varies quadratically for small fields but becomes linear for larger ones. We attribute the giant Stark effect to the broken edge degeneracy, i.e., the charge redistributions of the conduction band minimum and valence band maximum states localized at opposite edges induced by the field. By combined with the Green's function approach, it is shown that in the presence of the critical field a gap of density of states (DOS) disappears and a high value DOS turns up at the energy position of the band gap closure. Finally, as the field increases, we find the band gap decreases more rapidly and the gap closure occurs at smaller fields for wider ribbons. Both the band gap and DOS variations with the field show an insulator-metal transition induced by a transverse electric field for the APNR. Our results show that wider APNRs are more appreciable to design field-effect transistors.

  8. Capillary Sharp Inner Edge Manufacturing

    Czech Academy of Sciences Publication Activity Database

    Hošek, Jan; Studenovský, K.; Najdek, D.


    Roč. 19, č. 35 (2009), s. 19-25 ISSN 1584-5982. [MECAHITECH 09 /1./. Bukurešť, 08.10.2009-09.10.2009] R&D Projects: GA AV ČR IAA200760905 Institutional research plan: CEZ:AV0Z20760514 Keywords : capillary * edge * manufacturing Subject RIV: JR - Other Machinery

  9. Diffraction at a Straight Edge

    Indian Academy of Sciences (India)

    IAS Admin

    integral is a complex number which is a function of the lower limit. We have named it ... (b) Straight edge diffraction according to Young: In this figure, the plane wave from the source simply continues with ... discontinuity in the amplitude at the shadow, which exactly compensates for the discontinuity in the plane wavefront ...

  10. Morpho (?) phono (?) logical fuzzy edges

    African Journals Online (AJOL)

    Open Access DOWNLOAD FULL TEXT Subscription or Fee Access. Morpho (?) phono (?) logical fuzzy edges: The case of {-/}/{-/U/} semantic (?) contrast in Shona. K. G. Mkangwanwi. Abstract. (ZAMBEZIA: Journal of Humanities of the Univ of Zimbabwe, 2000 27(1): 47-54). Full Text: EMAIL FULL TEXT EMAIL FULL TEXT

  11. On the Edge of Existence

    DEFF Research Database (Denmark)

    Richter, Line


    Based on ethnographic fieldwork among Malian migrants and migration brokers in Mali, Algeria, Morocco, and France, this article investigates life in exile on the edge of Europe. Zooming in on the experiences of interlocutors in Morocco and Algeria, the article will explore the experiential...

  12. Ultra wide band antennas

    CERN Document Server

    Begaud, Xavier


    Ultra Wide Band Technology (UWB) has reached a level of maturity that allows us to offer wireless links with either high or low data rates. These wireless links are frequently associated with a location capability for which ultimate accuracy varies with the inverse of the frequency bandwidth. Using time or frequency domain waveforms, they are currently the subject of international standards facilitating their commercial implementation. Drawing up a complete state of the art, Ultra Wide Band Antennas is aimed at students, engineers and researchers and presents a summary of internationally recog

  13. Development of edge effects around experimental ecosystem hotspots is affected by edge density and matrix type (United States)

    Ecological edge effects are sensitive to landscape context. In particular, edge effects can be altered by matrix type and by the presence of other nearby edges. We experimentally altered patch configurations in an African savanna to determine how edge density and matrix type influence edge effect de...

  14. Topological edge states of distorted photonic Kagome lattices (United States)

    Ni, Xiang; Alu, Andrea; Khanikaev, Alexander B.


    We demonstrate that the distorted Kagome lattice formed by two-dimensional(2d) array of dielectric rods embedded in air exhibits a new class of topological states characterized by a topological invariant number in Pauli vector space. The Kagome lattice can be considered as a 2d analogue of the Su-Schrieffer-Heeger (SSH) model, which displays a phase transition by detuning the relative amplitudes of the inter-cell and intra-cell hopping terms. The phase transition is accompanied by the opening of a complete band gap in the Brillouin zone, which may host topological edge states on either the truncated end of the lattice or at the domain walls between topological nontrivial and trivial domains. To further reveal the connection between the bulk invariance and edge states, polarizations of shrunken and expanded effects are calculated. Our first-principles simulations based on finite element method (FEM) are used to design the lattice and confirm the analytic prediction.

  15. Design lithium storage materials by lithium adatoms adsorption at the edges of zigzag silicene nanoribbon: A first principle study

    International Nuclear Information System (INIS)

    Guo, Gang; Mao, Yuliang; Zhong, Jianxin; Yuan, Jianmei; Zhao, Hongquan


    Highlights: • Edge-adsorption of Li adatoms on zigzag silicene nanoribbon is preferred in energy to form new type lithium storage materials. • Significant charge transfer from Li adatoms to Si atoms is found, indicating the main ionic interactions. • The band structures of zigzag silicene nanoribbon are sensitive with the variation of sites of Li adatoms at the two edges. • The local magnetic moments at the two edges of zigzag silicene nanoribbon are suppressed by the adsorptions of Li adatoms. - Abstract: First-principles spin-polarized calculations are performed to design lithium storage materials using the active edges of zigzag silicene nanoribbon (ZSiNR). We predict that edge-adsorption of Li adatoms on zigzag silicene nanoribbon is preferred in energy to form new type lithium storage materials. Significant charge transfer from Li adatoms to Si atoms at the edges of ZSiNR is found, indicating the main ionic interactions. It is found that the band structures of ZSiNR with Li adsorptions are sensitive with the variation of sites of adatoms at the two edges. Ferro-magnetic to antiferro-magnetic change is found in ZSiNR with symmetrical adsorption of Li adatoms at its two edges. Other unsymmetrical Li adsorptions at the edges of ZSiNR prefer to stay in ferro-magnetic state as that in narrow pristine ZSiNR.

  16. Design lithium storage materials by lithium adatoms adsorption at the edges of zigzag silicene nanoribbon: A first principle study

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Gang [Hunan Key Laboratory for Micro–Nano Energy Materials and Devices, School of Physics and Optoelectronic Engineering, Xiangtan University, Hunan, 411105 (China); Mao, Yuliang, E-mail: [Hunan Key Laboratory for Micro–Nano Energy Materials and Devices, School of Physics and Optoelectronic Engineering, Xiangtan University, Hunan, 411105 (China); Zhong, Jianxin [Hunan Key Laboratory for Micro–Nano Energy Materials and Devices, School of Physics and Optoelectronic Engineering, Xiangtan University, Hunan, 411105 (China); Yuan, Jianmei [Hunan Key Laboratory for Computation and Simulation in Science and Engineering, School of Mathematics and Computational Science, Xiangtan University, Hunan, 411105 (China); Zhao, Hongquan, E-mail: [Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing, 401120 (China)


    Highlights: • Edge-adsorption of Li adatoms on zigzag silicene nanoribbon is preferred in energy to form new type lithium storage materials. • Significant charge transfer from Li adatoms to Si atoms is found, indicating the main ionic interactions. • The band structures of zigzag silicene nanoribbon are sensitive with the variation of sites of Li adatoms at the two edges. • The local magnetic moments at the two edges of zigzag silicene nanoribbon are suppressed by the adsorptions of Li adatoms. - Abstract: First-principles spin-polarized calculations are performed to design lithium storage materials using the active edges of zigzag silicene nanoribbon (ZSiNR). We predict that edge-adsorption of Li adatoms on zigzag silicene nanoribbon is preferred in energy to form new type lithium storage materials. Significant charge transfer from Li adatoms to Si atoms at the edges of ZSiNR is found, indicating the main ionic interactions. It is found that the band structures of ZSiNR with Li adsorptions are sensitive with the variation of sites of adatoms at the two edges. Ferro-magnetic to antiferro-magnetic change is found in ZSiNR with symmetrical adsorption of Li adatoms at its two edges. Other unsymmetrical Li adsorptions at the edges of ZSiNR prefer to stay in ferro-magnetic state as that in narrow pristine ZSiNR.

  17. Research on the Band Gap Characteristics of Two-Dimensional Phononic Crystals Microcavity with Local Resonant Structure

    Directory of Open Access Journals (Sweden)

    Mao Liu


    Full Text Available A new two-dimensional locally resonant phononic crystal with microcavity structure is proposed. The acoustic wave band gap characteristics of this new structure are studied using finite element method. At the same time, the corresponding displacement eigenmodes of the band edges of the lowest band gap and the transmission spectrum are calculated. The results proved that phononic crystals with microcavity structure exhibited complete band gaps in low-frequency range. The eigenfrequency of the lower edge of the first gap is lower than no microcavity structure. However, for no microcavity structure type of quadrilateral phononic crystal plate, the second band gap disappeared and the frequency range of the first band gap is relatively narrow. The main reason for appearing low-frequency band gaps is that the proposed phononic crystal introduced the local resonant microcavity structure. This study provides a good support for engineering application such as low-frequency vibration attenuation and noise control.

  18. X-ray absorption near-edge structure of GaN with high Mn concentration grown on SiC

    International Nuclear Information System (INIS)

    Sancho-Juan, O; Cantarero, A; Garro, N; Cros, A; Martinez-Criado, G; Salome, M; Susini, J; Olguin, D; Dhar, S


    By means of x-ray absorption near-edge structure (XANES) several Ga 1-x Mn x N (0.03 2 ↑ band localized in the gap region, and the corresponding anti-bonding state t 2 ↓, which seem to be responsible for the double structure which appears at the pre-edge absorption region. The shoulders and main absorption peak of the XANES spectra are attributed to transitions from the Mn(1s) band to the conduction bands, which are partially dipole allowed because of the Mn(4p) contribution to these bands.

  19. Band-notched spiral antenna

    Energy Technology Data Exchange (ETDEWEB)

    Jeon, Jae; Chang, John


    A band-notched spiral antenna having one or more spiral arms extending from a radially inner end to a radially outer end for transmitting or receiving electromagnetic radiation over a frequency range, and one or more resonance structures positioned adjacent one or more segments of the spiral arm associated with a notch frequency band or bands of the frequency range so as to resonate and suppress the transmission or reception of electromagnetic radiation over said notch frequency band or bands.

  20. Topological magnon bands in ferromagnetic star lattice (United States)

    Owerre, S. A.


    The experimental observation of topological magnon bands and thermal Hall effect in a kagomé lattice ferromagnet Cu(1-3, bdc) has inspired the search for topological magnon effects in various insulating ferromagnets that lack an inversion center allowing a Dzyaloshinskii-Moriya (DM) spin-orbit interaction. The star lattice (also known as the decorated honeycomb lattice) ferromagnet is an ideal candidate for this purpose because it is a variant of the kagomé lattice with additional links that connect the up-pointing and down-pointing triangles. This gives rise to twice the unit cell of the kagomé lattice, and hence more interesting topological magnon effects. In particular, the triangular bridges on the star lattice can be coupled either ferromagnetically or antiferromagnetically which is not possible on the kagomé lattice ferromagnets. Here, we study DM-induced topological magnon bands, chiral edge modes, and thermal magnon Hall effect on the star lattice ferromagnet in different parameter regimes. The star lattice can also be visualized as the parent material from which topological magnon bands can be realized for the kagomé and honeycomb lattices in some limiting cases.

  1. Nonreciprocity of edge modes in 1D magnonic crystal

    Energy Technology Data Exchange (ETDEWEB)

    Lisenkov, I., E-mail: [Kotelnikov Institute of Radio-engineering and Electronics of RAS, 11-7 Mokhovaya st., Moscow 125009 (Russian Federation); Department of Physics, Oakland University, 2200 N. Squirrel Rd., Rochester, MI 48309 (United States); Moscow Institute of Physics and Technology, 9 Instituskij per., Dolgoprudny, 141700, Moscow Region (Russian Federation); Kalyabin, D., E-mail: [Kotelnikov Institute of Radio-engineering and Electronics of RAS, 11-7 Mokhovaya st., Moscow 125009 (Russian Federation); Moscow Institute of Physics and Technology, 9 Instituskij per., Dolgoprudny, 141700, Moscow Region (Russian Federation); Osokin, S. [Kotelnikov Institute of Radio-engineering and Electronics of RAS, 11-7 Mokhovaya st., Moscow 125009 (Russian Federation); Moscow Institute of Physics and Technology, 9 Instituskij per., Dolgoprudny, 141700, Moscow Region (Russian Federation); Klos, J.W.; Krawczyk, M. [Adam Mickiewicz University in Poznan, Umultowska 85, Poznan 61-614 (Poland); Nikitov, S., E-mail: [Kotelnikov Institute of Radio-engineering and Electronics of RAS, 11-7 Mokhovaya st., Moscow 125009 (Russian Federation); Moscow Institute of Physics and Technology, 9 Instituskij per., Dolgoprudny, 141700, Moscow Region (Russian Federation); Saratov State University, 112 Bol' shaya Kazach' ya, Saratov 410012 (Russian Federation)


    Spin waves propagation in 1D magnonic crystals is investigated theoretically. Mathematical model based on plane wave expansion method is applied to different types of magnonic crystals, namely bi-component magnonic crystal with symmetric/asymmetric boundaries and ferromagnetic film with periodically corrugated top surface. It is shown that edge modes in magnonic crystals may exhibit nonreciprocal behaviour at much lower frequencies than in homogeneous films. - Highlights: • Magnetostatic surface spin waves in 1D magnonic crystals were studied theoretically. • Mathematical model is based on plane wave method. • Mathematical model was applied to different types of magnonic crystals. • Stop band formation and nonreciprocity were obtained.

  2. Design of transition edge sensor microcalorimeters for optimal performance

    Energy Technology Data Exchange (ETDEWEB)

    Bandler, S.R. E-mail:; Figueroa-Feliciano, E.; Stahle, C.K.; Boyce, K.; Brekosky, R.; Chervenak, J.; Finkbeiner, F.; Kelley, R.; Lindeman, M.; Porter, F.S.; Saab, T


    We have developed a model for transition edge sensors to optimize performance under a variety of different conditions. There are three design trade-offs when engineering a microcalorimeter for a particular application: energy resolution, energy range and maximum count rate. All three are interdependent and are determined by various design parameters such as the detector heat capacity, the sharpness of the transition, and the thermal conductance of the detector to the frame. Our model includes all known sources of intrinsic noise in our calorimeters including the observed broad band excess noise. We will present the results of this model, and its predictions for optimally designed microcalorimeters.

  3. Neutral hydrogen and optical observations of edge-on galaxies : Hunting for warps

    NARCIS (Netherlands)

    Garcia-Ruiz, [No Value; Sancisi, R; Kuijken, K


    We present 21-cm HI line and optical R-band observations for a sample of 26 edge-on galaxies. The HI observations were obtained with the Westerbork Synthesis Radio Telescope, and are part of the WHISP database (Westerbork HI Survey of Spiral and Irregular Galaxies). We present HI maps, optical

  4. All-optical materials design of chiral edge modes in transition-metal dichalcogenides (United States)

    Claassen, Martin; Jia, Chunjing; Moritz, Brian; Devereaux, Thomas P.


    Monolayer transition-metal dichalcogenides are novel materials which at low energies constitute a condensed-matter realization of massive relativistic fermions in two dimensions. Here, we show that this picture breaks for optical pumping--instead, the added complexity of a realistic materials description leads to a new mechanism to optically induce topologically protected chiral edge modes, facilitating optically switchable conduction channels that are insensitive to disorder. In contrast to graphene and previously discussed toy models, the underlying mechanism relies on the intrinsic three-band nature of transition-metal dichalcogenide monolayers near the band edges. Photo-induced band inversions scale linearly in applied pump field and exhibit transitions from one to two chiral edge modes on sweeping from red to blue detuning. We develop an ab initio strategy to understand non-equilibrium Floquet-Bloch bands and topological transitions, and illustrate for WS2 that control of chiral edge modes can be dictated solely from symmetry principles and is not qualitatively sensitive to microscopic materials details.

  5. Magnetism and bonding in graphene nanodots with H modified interior, edge, and apex (United States)

    Philpott, Michael R.; Prabhat, Kawazoe, Yoshiyuki


    Ab initio density functional theory calculations of hexagonal shaped zigzag edged graphene nanodot molecules, modified by the addition of atomic H to interior and perimeter sites, predict significant changes to the hexagonally sectored spin distribution and chemical bonding of the originals. The redistribution of Kohn-Sham levels at the top of the valence manifold from parent to derivative hint at large changes in the electronic structure. A centrally added H atom creates an occupied level in the middle of the 0.3 eV band gap of the parent molecule and is surrounded by an island of spins. The latter is isolated enough from the perimeter to provide a calibration of the edge spins of the modified parent. Mid-edge addition of a H atom "quenches" the spin on the edge by drawing a pz-electron into the C-H bond without reducing the spin on the other edges. Addition of H to an apex carbon atom results in a localized spin freed from the double bond that coexists with the parent spin on the same edge. Saturating the apex double bond by adding two H atoms, returns π-levels shifted in energy and index and parent-like spin patterns on all edges, intact except for small changes on the edges joined at the apex. Taken in unison these results demonstrate how atomic hydrogen and other groups could be used to engineer the magnetism of graphene nanodots.

  6. Symmetrical metallic and magnetic edge states of nanoribbon from semiconductive monolayer PtS2 (United States)

    Liu, Shan; Zhu, Heyu; Liu, Ziran; Zhou, Guanghui


    Transition metal dichalcogenides (TMD) MoS2 or graphene could be designed to metallic nanoribbons, which always have only one edge show metallic properties due to symmetric protection. In present work, a nanoribbon with two parallel metallic and magnetic edges was designed from a noble TMD PtS2 by employing first-principles calculations based on density functional theory (DFT). Edge energy, bonding charge density, band structure, density of states (DOS) and simulated scanning tunneling microscopy (STM) of four possible edge states of monolayer semiconductive PtS2 were systematically studied. Detailed calculations show that only Pt-terminated edge state among four edge states was relatively stable, metallic and magnetic. Those metallic and magnetic properties mainly contributed from 5d orbits of Pt atoms located at edges. What's more, two of those central symmetric edges coexist in one zigzag nanoribbon, which providing two atomic metallic wires thus may have promising application for the realization of quantum effects, such as Aharanov-Bohm effect and atomic power transmission lines in single nanoribbon.

  7. Edge imaging in intense beams

    Directory of Open Access Journals (Sweden)

    S. Bernal


    Full Text Available The appearance of rings of charge observed near the edge of beams from high-perveance guns is described with a simple ray tracing technique inspired by the particle-core model. We illustrate the technique, which has no analog in light optics, with examples from experiments employing solenoid focusing of an electron beam. The rings of charge result from the combined effects of external focusing and space-charge forces acting on paraxial fringe particles with relatively large initial transverse velocities. The model is independent of the physical mechanisms responsible for the fringe particles. Furthermore, the focal length for edge imaging in a uniform focusing channel is derived using a linearized trajectory equation for the motion of fringe particles. Counterintuitively, the focal length decreases as the beam current increases.

  8. Nonreference Medical Image Edge Map Measure

    Directory of Open Access Journals (Sweden)

    Karen Panetta


    Full Text Available Edge detection is a key step in medical image processing. It is widely used to extract features, perform segmentation, and further assist in diagnosis. A poor quality edge map can result in false alarms and misses in cancer detection algorithms. Therefore, it is necessary to have a reliable edge measure to assist in selecting the optimal edge map. Existing reference based edge measures require a ground truth edge map to evaluate the similarity between the generated edge map and the ground truth. However, the ground truth images are not available for medical images. Therefore, a nonreference edge measure is ideal for medical image processing applications. In this paper, a nonreference reconstruction based edge map evaluation (NREM is proposed. The theoretical basis is that a good edge map keeps the structure and details of the original image thus would yield a good reconstructed image. The NREM is based on comparing the similarity between the reconstructed image with the original image using this concept. The edge measure is used for selecting the optimal edge detection algorithm and optimal parameters for the algorithm. Experimental results show that the quantitative evaluations given by the edge measure have good correlations with human visual analysis.

  9. Galaxies on the Blue Edge


    Cabanela, J. E.; Dickey, J. M.


    We have successfully constructed a catalog of HI-rich galaxies selected from the Minnesota Automated Plate Scanner Catalog of the Palomar Observatory Sky Survey (POSS I) based solely on optical criteria. We identify HI-rich candidates by selecting the bluest galaxies at a given apparent magnitude, those galaxies on the "blue edge" of POSS I color-magnitude parameter space. Subsequent 21-cm observations on the upgraded Arecibo 305m dish detected over 50% of the observed candidates. The detecte...

  10. Edge effects and delamination failures (United States)

    Herakovich, C. T.


    The fundamental relationship between the morphology of a composite laminate and the resulting free edge effects is explored and related to delamination failures. Cross-ply, angle-ply, and quasi-isotropic laminates are discussed in detail. It is shown that the local mismatch in elastic properties of adjacent layers and the global stacking sequence of a laminate both have a significant influence on the interlaminar stresses and delamination failures.

  11. Diffraction at a Straight Edge

    Indian Academy of Sciences (India)

    IAS Admin

    have to integrate exp(ikx) × exp(ik(y − y′)2/2x) with respect to y′, from zero to infinity. It is natural to change variables using u2 ... sudden changeover from a continuous line to a dashed line on the circular arc. It might appear difficult to reconcile ... using integration by parts, it precisely gave rise to the. Young edge wave!

  12. Design lithium storage materials by lithium adatoms adsorption at the edges of zigzag silicene nanoribbon: A first principle study (United States)

    Guo, Gang; Mao, Yuliang; Zhong, Jianxin; Yuan, Jianmei; Zhao, Hongquan


    First-principles spin-polarized calculations are performed to design lithium storage materials using the active edges of zigzag silicene nanoribbon (ZSiNR). We predict that edge-adsorption of Li adatoms on zigzag silicene nanoribbon is preferred in energy to form new type lithium storage materials. Significant charge transfer from Li adatoms to Si atoms at the edges of ZSiNR is found, indicating the main ionic interactions. It is found that the band structures of ZSiNR with Li adsorptions are sensitive with the variation of sites of adatoms at the two edges. Ferro-magnetic to antiferro-magnetic change is found in ZSiNR with symmetrical adsorption of Li adatoms at its two edges. Other unsymmetrical Li adsorptions at the edges of ZSiNR prefer to stay in ferro-magnetic state as that in narrow pristine ZSiNR.

  13. Flap--edge flowfield measurements (United States)

    Pye, John D.; Cantwell, Brian J.


    Recent studies of airframe noise suggest that the wing and flap trailing--edges as well as the flap side--edge are areas of significant noise generation. To identify the fluid dynamic processes associated with these noise sources, we are examining the flow--field around a NACA 63--215 Mod B main element airfoil configured with a half--span Fowler flap. The tests are performed in a low--speed wind tunnel at a Reynolds number of ~ 6.0×10^5. A hot wire traverse system is used to map the mean velocities and turbulence intensities in the near wake region of the flow. Measurements of the pressure fluctuations along the flap side--edge and in the cove of the airfoil configuration are made with pressure transducers mounted inside the airfoil. The experimental data are in good qualitative agreement with the numerical simulation of a slightly higher Reynolds number flow ( ~ 1.5×10^6) around a geometrically similar airfoil configuration.

  14. Leading Edge Device Aerodynamic Optimization

    Directory of Open Access Journals (Sweden)

    Marius Gabriel COJOCARU


    Full Text Available Leading edge devices are conventionally used as aerodynamic devices that enhance performances during landing and in some cases during takeoff. The need to increase the efficiency of the aircrafts has brought the idea of maintaining as much as possible a laminar flow over the wings. This is possible only when the leading edge of the wings is free from contamination, therefore using the leading edge devices with the additional role of shielding during takeoff. Such a device based on the Krueger flap design is aerodynamically analyzed and optimized. The optimization comprises three steps: first, the positioning of the flap such that the shielding criterion is kept, second, the analysis of the flap size and third, the optimization of the flap shape. The first step is subject of a gradient based optimization process of the position described by two parameters, the position along the line and the deflection angle. For the third step the Adjoint method is used to gain insight on the shape of the Krueger flap that will extend the most the stall limit. All these steps have been numerically performed using Ansys Fluent and the results are presented for the optimized shape in comparison with the baseline configuration.

  15. Edge effect on weevils and spiders

    Directory of Open Access Journals (Sweden)

    R. Horváth


    Full Text Available The edge effect on weevils and spiders was tested along oak forest – meadow transects using sweep-net samples at the Síkfökút Project in Hungary. For spiders the species richness was significantly higher in the forest edge than either in the meadow or the forest interior. For weevils the species richness of the forest edge was higher than that of the meadow, but the difference was not statistically significant whereas the species richness of the forest interior was significantly lower than that of the forest edge and the meadow. The composition of the spider assemblage of the edge was more similar to the forest, while the composition of weevils in the edge was more similar to the meadow. Our results based on two invertebrate groups operating on different trophic levels suggest that there is a significant edge effect for the studied taxa resulting in higher species richness in the edge.

  16. Edge-based perceptual image coding. (United States)

    Niu, Yi; Wu, Xiaolin; Shi, Guangming; Wang, Xiaotian


    We develop a novel psychovisually motivated edge-based low-bit-rate image codec. It offers a compact description of scale-invariant second-order statistics of natural images, the preservation of which is crucial to the perceptual quality of coded images. Although being edge based, the codec does not explicitly code the edge geometry. To save bits on edge descriptions, a background layer of the image is first coded and transmitted, from which the decoder estimates the trajectories of significant edges. The edge regions are then refined by a residual coding technique based on edge dilation and sequential scanning in the edge direction. Experimental results show that the new image coding technique outperforms the existing ones in both objective and perceptual quality, particularly at low bit rates.

  17. Environmental Dataset Gateway (EDG) REST Interface (United States)

    U.S. Environmental Protection Agency — Use the Environmental Dataset Gateway (EDG) to find and access EPA's environmental resources. Many options are available for easily reusing EDG content in other...

  18. Environmental Dataset Gateway (EDG) Search Widget (United States)

    U.S. Environmental Protection Agency — Use the Environmental Dataset Gateway (EDG) to find and access EPA's environmental resources. Many options are available for easily reusing EDG content in other...

  19. Organizing on the Edge: Appreciation and Critique

    National Research Council Canada - National Science Library

    Scott, W. R


    .... Hayes, "Power to the Edge: Command, Control in the Information Age" (2003). The author places the "edge" perspective in the broader context of organizational studies, noting both its strengths and limitations...

  20. Urbach's rule derived from thermal fluctuations in the band-gap energy

    DEFF Research Database (Denmark)

    Skettrup, Torben


    The exponential absorption edge (known as Urbach's rule) observed in most materials is interpreted in terms of thermal fluctuations in the band-gap energy. The main contribution to the temperature shift of the band-gap energy is due to the temperature-dependent self-energies of the electrons...... and holes interacting with the phonons. Since the phonon number is fluctuating in thermal equilibrium, the band-gap energy is also fluctuating resulting in an exponential absorption tail below the average band-gap energy. These simple considerations are applied to derive Urbach's rule at high temperatures...

  1. Theoretical band alignment in an intermediate band chalcopyrite based material (United States)

    Castellanos Águila, J. E.; Palacios, P.; Conesa, J. C.; Arriaga, J.; Wahnón, P.


    Band alignment is key to enhance the performance of heterojunction for chalcopyrite thin film solar cells. In this paper we report ab initio calculations of the electronic structures of CuGaS2:Cr with various Cr compositions, CuAlSe2 and ZnSe and the band alignment between their interfaces. We use density functional theory and the more accurate self-consistent GW scheme to obtain improved bulk band-gaps and band offsets. Band alignments of the interfacial region for CuGaS2:Cr/CuAlSe2 and CuGaS2:Cr/ZnSe systems were aligned with respect of an average electrostatic potential. Our results are in good agreement with experimental values for the bulk band-gaps. These theoretical band alignments show a characteristic staggered band alignment for the design of heterojunction devices in photovoltaic applications.

  2. CFAR Edge Detector for Polarimetric SAR Images

    DEFF Research Database (Denmark)

    Schou, Jesper; Skriver, Henning; Nielsen, Allan Aasbjerg


    Finding the edges between different regions in an image is one of the fundamental steps of image analysis, and several edge detectors suitable for the special statistics of synthetic aperture radar (SAR) intensity images have previously been developed. In this paper, a new edge detector for polar...

  3. Nature of the fundamental band gap in GaNxP1-x alloys

    International Nuclear Information System (INIS)

    Shan, W.; Walukiewicz, W.; Yu, K. M.; Wu, J.; Ager, J. W. III; Haller, E. E.; Xin, H. P.; Tu, C. W.


    The optical properties of GaN x P 1-x alloys (0.007≤x≤0.031) grown by gas-source molecular-beam epitaxy have been studied. An absorption edge appears in GaN x P 1-x at energy below the indirect Γ V -X C transition in GaP, and the absorption edge shifts to lower energy with increasing N concentration. Strong photomodulation signals associated with the absorption edges in GaN x P 1-x indicate that a direct fundamental optical transition is taking place, revealing that the fundamental band gap has changed from indirect to direct. This N-induced transformation from indirect to direct band gap is explained in terms of an interaction between the highly localized nitrogen states and the extended states at the Γ conduction-band minimum. (c) 2000 American Institute of Physics

  4. Edge and coupled core-edge transport modelling in tokamaks

    International Nuclear Information System (INIS)

    Lodestro, L.L.; Casper, T.A.; Cohen, R.H.


    Recent advances in the theory and modelling of tokamak edge, scrape-off-layer (SOL) and divertor plasmas are described. The effects of the poloidal ExB drift on inner/outer divertor-plate asymmetries within a 1D analysis are shown to be in good agreement with experimental trends; above a critical v ExB, the model predicts transitions to supersonic SOL flow at the inboard midplane. 2D simulations show the importance of ExB flow in the private-flux region and of ∇ B-drifts. A theory of rough plasma-facing surfaces is given, predicting modifications to the SOL plasma. The parametric dependence of detached-plasma states in slab geometry has been explored; with sufficient pumping, the location of the ionization front can be controlled; otherwise only fronts near the plate or the X-point are stable. Studies with a more accurate Monte-Carlo neutrals model and a detailed non-LTE radiation-transport code indicate various effects are important for quantitative modelling. Detailed simulations of the DIII-D core and edge are presented; impurity and plasma flow are discussed and shown to be well modelled with UEDGE. (author)

  5. Edge and coupled core/edge transport modelling in tokamaks

    International Nuclear Information System (INIS)

    Lodestro, L.L.; Casper, T.A.; Cohen, R.H.


    Recent advances in the theory and modelling of tokamak edge, scrape-off-layer (SOL) and divertor plasmas are described. The effects of the poloidal E x B drift on inner/outer divertor-plate asymmetries within a 1D analysis are shown to be in good agreement with experimental trends; above a critical v ExB , the model predicts transitions to supersonic flow at the inboard midplane. 2D simulations show the importance of E x B flow in the private-flux region and of ∇ B-drifts. A theory of rough plasma-facing surfaces is given, predicting modifications to the SOL plasma. The parametric dependence of detached-plasma states in slab geometry has been explored; with sufficient pumping, the location of the ionization front can be controlled; otherwise only fronts near the plate or the X-point are stable. Studies with a more accurate Monte-Carlo neutrals model and a detailed non-LTE radiation-transport code indicate various effects are important for quantitative modelling. Detailed simulations of the DIII-D core and edge are presented; impurity and plasma flow are discussed and shown to be well modelled with UEDGE. (author)

  6. Thermal stability of the optical band gap and structural order in hot-wire-deposited amorphous silicon

    CSIR Research Space (South Africa)

    Arendse, CJ


    Full Text Available and that the structural disorder increases upon annealing. The increase in the structural disorder results in a broadening of the valence and conduction band tails, thereby pinning the valence and conduction band edges closer together, resulting in a decrease...

  7. K-edge densitometer (KED)

    Energy Technology Data Exchange (ETDEWEB)

    Sprinkle, J.K.; Hansen, W.J.


    In 1979, a K-edge densitometer (KED) was installed by the Safeguards Assay group from Los Alamos National Laboratory in the PNC reprocessing plant at Tokai-mura, Japan. It uses an active nondestructive assay technique, KED, to measure the plutonium concentration of the product solution. The measurement uncertainty of an assay depends on the count time chosen, but can be 0.5% or better. The computer hardware and software were upgraded in 1992. This manual describes the operation of the instrument, with an emphasis on the user interface to the software.

  8. Instant Adobe Edge Inspect starter

    CERN Document Server

    Khan, Joseph


    Get to grips with a new technology, understand what it is and what it can do for you, and then get to work with the most important features and tasks. This easy-to-understand Starter guide will get you up to speed with Adobe Edge Inspect quickly and with little effort.This book is for frontend web developers and designers who are developing and testing web applications targeted for mobile browsers. It's assumed that you have a basic understanding of creating web applications using HTML, CSS, and JavaScript, as well as being familiar with running web pages from local HTTP servers. Readers are a

  9. At the edge of intonation

    DEFF Research Database (Denmark)

    Niebuhr, Oliver


    The paper is concerned with the 'edge of intonation' in a twofold sense. It focuses on utterance-final F0 movements and crosses the traditional segment-prosody divide by investigating the interplay of F0 and voiceless fricatives in speech production. An experiment was performed for German with four...... types of voiceless fricatives: /f/, /s/, /ʃ/ and /x/. They were elicited with scripted dialogues in the contexts of terminal falling statement and high rising question intonations. Acoustic analyses show that fricatives concluding the high rising question intonations had higher mean centres of gravity...

  10. Semiconductors bonds and bands

    CERN Document Server

    Ferry, David K


    As we settle into this second decade of the twenty-first century, it is evident that the advances in micro-electronics have truly revolutionized our day-to-day lifestyle. The technology is built upon semiconductors, materials in which the band gap has been engineered for special values suitable to the particular application. This book, written specifically for a one semester course for graduate students, provides a thorough understanding of the key solid state physics of semiconductors. It describes how quantum mechanics gives semiconductors unique properties that enabled the micro-electronics revolution, and sustain the ever-growing importance of this revolution.

  11. Microstrip microwave band gap structures

    Indian Academy of Sciences (India)

    Microwave band gap structures exhibit certain stop band characteristics based on the periodicity, impedance contrast and effective refractive index contrast. These structures though formed in one-, two- and three-dimensional periodicity, are huge in size. In this paper, microstrip-based microwave band gap structures are ...

  12. Quantum Manifestations of Graphene Edge Stress and Edge Instability: A First-Principles Study


    Huang, Bing; Liu, Miao; Su, Ninghai; Wu, Jian; Duan, Wenhui; Gu, Bing-lin; Liu, Feng


    We have performed first-principles calculations of graphene edge stresses, which display two interesting quantum manifestations absent from the classical interpretation: the armchair edge stress oscillates with a nanoribbon width, and the zigzag edge stress is noticeably reduced by spin polarization. Such quantum stress effects in turn manifest in mechanical edge twisting and warping instability, showing features not captured by empirical potentials or continuum theory. Edge adsorption of H a...

  13. Single-band negative differential resistance in metallic armchair MoS2 nanoribbons

    International Nuclear Information System (INIS)

    Chen, Cheng; Wang, Xue-Feng; Li, Yao-Sheng; Cheng, Xue-Mei; Yao, A-Long


    Semiconductor armchair MoS 2 nanoribbons can be converted into conductors by edge functionalization of H atoms or OH groups. Those metallic nanoribbons exhibit I – V characteristics of a single half-filled band with strong negative differential resistance (NDR) under a voltage bias less than 1 V. This originates from the spatial separation between electrons in the conduction and valence bands. The NDR becomes spin dependent if the H atoms or OH groups are not uniformly adsorbed on the edge. Furthermore, the spin polarization can be greatly enhanced in heterojunctions of H- and OH-passivated nanoribbons. (paper)

  14. Morphologies of omega band auroras (United States)

    Sato, Natsuo; Yukimatu, Akira Sessai; Tanaka, Yoshimasa; Hori, Tomoaki


    We examined the morphological signatures of 315 omega band aurora events observed using the Time History of Events and Macroscale Interactions during Substorm ground-based all-sky imager network over a period of 8 years. We find that omega bands can be classified into the following three subtypes: (1) classical (O-type) omega bands, (2) torch or tongue (T-type) omega bands, and (3) combinations of classical and torch or tongue (O/T-type) omega bands. The statistical results show that T-type bands occur the most frequently (45%), followed by O/T-type bands (35%) and O-type bands (18%). We also examined the morphologies of the omega bands during their formation, from the growth period to the declining period through the maximum period. Interestingly, the omega bands are not stable, but rather exhibit dynamic changes in shape, intensity, and motion. They grow from small-scale bumps (seeds) at the poleward boundary of preexisting east-west-aligned auroras, rather than via the rotation or shear motion of preexisting east-west-aligned auroras, and do not exhibit any shear motion during the periods of auroral activity growth. Furthermore, the auroral luminosity is observed to increase during the declining period, and the total time from the start of the growth period to the end of the declining period is found to be about 20 min. Such dynamical signatures may be important in determining the mechanism responsible for omega band formation.

  15. Band-to-band and inner shell excitation VIS-UV photoluminescence of quaternary InAlGaN alloys

    International Nuclear Information System (INIS)

    Fukui, K.; Naoe, S.; Okada, K.; Hamada, S.; Hirayama, H.


    Visible and ultraviolet photoluminescence and photoluminescence excitation spectra of quaternary InAlGaN alloys were measured. The excitation photon energy covers from band edge to 180 eV, near both nitrogen K (∝400 eV) and aluminium K (∝1.5 keV) inner shell energy region. From photoluminescence excitation spectra photoluminescence intensity per incident photon number varies in proportion to incident photon energy. This result implies that many conduction band electron - valence band hole pairs which are responsible for photoluminescence are produced by high energy excitation. Time resolved decay curves were also measured in the same energy region. No effect of high energy excitation on time resolved decay measurements suggests a role of indium on the photoluminescence mechanism in InAlGaN system. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Band-to-band tunneling distance analysis in the heterogate electron–hole bilayer tunnel field-effect transistor

    Energy Technology Data Exchange (ETDEWEB)

    Padilla, J. L., E-mail: [Nanoelectronic Devices Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015 (Switzerland); Departamento de Electrónica y Tecnología de los Computadores, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain); Palomares, A. [Departamento de Matemática Aplicada, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain); Alper, C.; Ionescu, A. M. [Nanoelectronic Devices Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015 (Switzerland); Gámiz, F. [Departamento de Electrónica y Tecnología de los Computadores, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain)


    In this work, we analyze the behavior of the band-to-band tunneling distance between electron and hole subbands resulting from field-induced quantum confinement in the heterogate electron–hole bilayer tunnel field-effect transistor. We show that, analogously to the explicit formula for the tunneling distance that can be easily obtained in the semiclassical framework where the conduction and valence band edges are allowed states, an equivalent analytical expression can be derived in the presence of field-induced quantum confinement for describing the dependence of the tunneling distance on the body thickness and material properties of the channel. This explicit expression accounting for quantum confinement holds valid provided that the potential wells for electrons and holes at the top and bottom of the channel can be approximated by triangular profiles. Analytical predictions are compared to simulation results showing very accurate agreement.

  17. Predicted solar cell edge radiation effects

    International Nuclear Information System (INIS)

    Gates, M.T.


    The Advanced Solar Cell Orbital Test (ASCOT) will test six types of solar cells in a high energy proton environment. During the design of the experiment a question was raised about the effects of proton radiation incident on the edge of the solar cells and whether edge radiation shielding was required. Historical geosynchronous data indicated that edge radiation damage is not detectable over the normal end of life solar cell degradation; however because the ASCOT radiation environment has a much higher and more energetic fluence of protons, considerably more edge damage is expected. A computer analysis of the problem was made by modeling the expected radiation damage at the cell edge and using a network model of small interconnected solar cells to predict degradation in the cell's electrical output. The model indicated that the deepest penetration of edge radiation was at the top of the cell near the junction where the protons have access to the cell through the low density cell/cover adhesive layer. The network model indicated that the cells could tolerate high fluences at their edge as long as there was high electrical resistance between the edge radiated region and the contact system on top of the cell. The predicted edge radiation related loss was less than 2% of maximum power for GaAs/Ge solar cells. As a result, no edge radiation protection was used for ASCOT

  18. Photonic band control in a quantum metamaterial (United States)

    Felbacq, Didier; Rousseau, Emmanuel


    In the present work, we present a metamaterial made of a periodic collection of dielectric resonators in which a quantum oscillator (denoted QO in the following) is inserted. The geometry at stake here is much more complicated than the textbook 1D cavity usually dealt with theoretically in quantum optics. We do provide a treatment essentially based on the scattering matrix non-perturbative approach, in order to investigate the various effects that could be expected to exist in such structures.The theoretical methods used are the Feshbach projection method associated with multiple scattering theory. First, the phenomenology for one scatterer with a QO inserted is presented, then the collective behavior of a finite periodic set of such scatterers is investigated and it is shown that it is possible to open and close a conduction band according to the state of the oscillators when the inserted quantum oscillators are put in the inversion regime by means of a pump field. They add gain to the system, allowing to reach the amplification regime in the vicinity of the Mie resonances of the dielectric resonators. When the transition frequency is situated at the photonic band gap edge, it creates switchable conducting modes within the bandgap.

  19. A Novel Hammer-Shaped UWB Antenna with Triple Notched-Band for Rejecting RLS, WLAN and XSCS bands

    Directory of Open Access Journals (Sweden)

    H. S. Mewara


    Full Text Available A novel hammer-shaped UWB printed antenna with triple notched stop bands is presented and fabricated on FR-4 substrate with size of 40×40×1.6 mm3. The proposed antenna is composed of hammer-shaped patch with C-shaped slot, U-shaped slot on feed line, and inverted stepped notch and bevel edges with pair of L-shaped slots in partial ground plane. The fabricated antenna is tested and obtained impedance bandwidth 2.89 ̶ 11.6 GHz with three notched stop bands 3.15 ̶ 3.7 GHz, 5.45 ̶ 6.8 GHz, and 7.5 ̶  8.8 GHz, for radiolocation system (RLS, wireless local area networks (WLAN, and X-band satellite communication system (XSCS bands, respectively. Moreover, the antenna result shows omnidirectional radiation pattern, average gain of 3.10 dBi over the whole UWB band except at the notched frequency bands.

  20. Robust and adaptive band-to-band image transform of UAS miniature multi-lens multispectral camera (United States)

    Jhan, Jyun-Ping; Rau, Jiann-Yeou; Haala, Norbert


    Utilizing miniature multispectral (MS) or hyperspectral (HS) cameras by mounting them on an Unmanned Aerial System (UAS) has the benefits of convenience and flexibility to collect remote sensing imagery for precision agriculture, vegetation monitoring, and environment investigation applications. Most miniature MS cameras adopt a multi-lens structure to record discrete MS bands of visible and invisible information. The differences in lens distortion, mounting positions, and viewing angles among lenses mean that the acquired original MS images have significant band misregistration errors. We have developed a Robust and Adaptive Band-to-Band Image Transform (RABBIT) method for dealing with the band co-registration of various types of miniature multi-lens multispectral cameras (Mini-MSCs) to obtain band co-registered MS imagery for remote sensing applications. The RABBIT utilizes modified projective transformation (MPT) to transfer the multiple image geometry of a multi-lens imaging system to one sensor geometry, and combines this with a robust and adaptive correction (RAC) procedure to correct several systematic errors and to obtain sub-pixel accuracy. This study applies three state-of-the-art Mini-MSCs to evaluate the RABBIT method's performance, specifically the Tetracam Miniature Multiple Camera Array (MiniMCA), Micasense RedEdge, and Parrot Sequoia. Six MS datasets acquired at different target distances and dates, and locations are also applied to prove its reliability and applicability. Results prove that RABBIT is feasible for different types of Mini-MSCs with accurate, robust, and rapid image processing efficiency.

  1. Band structure, band offsets, substitutional doping, and Schottky barriers of bulk and monolayer InSe (United States)

    Guo, Yuzheng; Robertson, John


    We present a detailed study of the electronic structure of the layered semiconductor InSe. We calculate the band structure of the monolayer and bulk material using density functional theory, hybrid functionals, and G W . The band gap of the monolayer InSe is calculated to be 2.4 eV in screened exchange hybrid functional, close to the experimental photoluminescence gap. The electron affinities and band offsets are calculated for vertical stacked-layer heterostructures, and are found to be suitable for tunnel field effect transistors (TFETs) in combination with WS e2 or similar. The valence-band edge of InSe is calculated to lie 5.2 eV below the vacuum level, similar to that for the closed shell systems HfS e2 or SnS e2 . Hence InSe would be suitable to act as a p -type drain in the TFET. The intrinsic defects are calculated. For Se-rich layers, the Se adatom (interstitial) is found to be the most stable defect, whereas for In-rich layers, the Se vacancy is the most stable for the neutral state. Antisites tend to have energies just above those of vacancies. The Se antisite distorts towards a bond-breaking distortion as in the EL2 center of GaAs. Both substitutional donors and acceptors are calculated to be shallow, and effective dopants. They do not reconstruct to form nondoping configurations as occurs in black phosphorus. Finally, the Schottky barriers of metals on InSe are found to be strongly pinned by metal induced gap states (MIGS) at ˜0.5 eV above the valence-band edge. Any interfacial defects would lead to a stronger pinning at a similar energy. Overall, InSe is an effective semiconductor combining the good features of 2D (lack of dangling bonds, etc.) with the good features of 3D (effective doping), which few others achieve.

  2. Edge-Corrected Mean-Field Hubbard Model: Principle and Applications in 2D Materials (United States)

    Zhang, Xi; Wang, Tianlei; Chen, Wencong; Wang, Sanmei; Peng, Da


    This work reviews the current progress of tight-binding methods and the recent edge-modified mean-field Hubbard model. Undercoordinated atoms and nonbonding electrons exist widely in nanomaterials and in network-structural materials with their impact under-estimated. A quantum theory was proposed to calculate the under-coordinated effects on the electronic structure of materials by incorporating bond order-length-strength (BOLS) correlation theory to mean-field Hubbard model, i.e. BOLS-HM. Consistency between the BOLS-HM calculation and density functional theory (DFT) calculation on 2D materials verified that i) bond contractions and potential well depression occur at the edge of graphene, phosphorene, and antimonene nanoribbons; ii) the physical origin of the band gap opening of graphene, phosphorene, and antimonene nanoribbons lays in the enhancement of edge potentials and hopping integrals due to the shorter and stronger bonds between undercoordinated atoms; iii) the band gap of 2D material nanoribbons expand as the width decreases due to the increasing under-coordination effects of edges which modulates the conductive behaviors; and iv) nonbond electrons at the edges and atomic vacancies of 2D material accompanied with the broken bond contribute to the Dirac-Fermi polaron (DFP) with a local magnetic moment.

  3. Edge magnetism impact on electrical conductance and thermoelectric properties of graphenelike nanoribbons (United States)

    Krompiewski, Stefan; Cuniberti, Gianaurelio


    Edge states in narrow quasi-two-dimensional nanostructures determine, to a large extent, their electric, thermoelectric, and magnetic properties. Nonmagnetic edge states may quite often lead to topological-insulator-type behavior. However, another scenario develops when the zigzag edges are magnetic and the time reversal symmetry is broken. In this work we report on the electronic band structure modifications, electrical conductance, and thermoelectric properties of narrow zigzag nanoribbons with spontaneously magnetized edges. Theoretical studies based on the Kane-Mele-Hubbard tight-binding model show that for silicene, germanene, and stanene both the Seebeck coefficient and the thermoelectric power factor are strongly enhanced for energies close to the charge neutrality point. A perpendicular gate voltage lifts the spin degeneracy of energy bands in the ground state with antiparallel magnetized zigzag edges and makes the electrical conductance significantly spin polarized. Simultaneously the gate voltage worsens the thermoelectric performance. Estimated room-temperature figures of merit for the aforementioned nanoribbons can exceed a value of 3 if phonon thermal conductances are adequately reduced.

  4. Edge-Corrected Mean-Field Hubbard Model: Principle and Applications in 2D Materials

    Directory of Open Access Journals (Sweden)

    Xi Zhang


    Full Text Available This work reviews the current progress of tight-binding methods and the recent edge-modified mean-field Hubbard model. Undercoordinated atoms (atoms not fully coordinated exist at a high rate in nanomaterials with their impact overlooked. A quantum theory was proposed to calculate electronic structure of nanomaterials by incorporating bond order-length-strength (BOLS correlation to mean-field Hubbard model, i.e., BOLS-HM. Consistency between the BOLS-HM calculation and density functional theory (DFT calculation on 2D materials verified that (i bond contractions and potential well depression occur at the edge of graphene, phosphorene, and antimonene nanoribbons; (ii the physical origin of the band gap opening of graphene, phosphorene, and antimonene nanoribbons lays in the enhancement of edge potentials and hopping integrals due to the shorter and stronger bonds between undercoordinated atoms; (iii the band gap of 2D material nanoribbons expand as the width decreases due to the increasing under-coordination effects of edges which modulates the conductive behaviors; and (iv non-bond electrons at the edges and atomic vacancies of 2D material accompanied with the broken bond contribute to the Dirac-Fermi polaron (DFP with a local magnetic moment.

  5. Modeling cell elongation during germ band retraction: cell autonomy versus applied anisotropic stress

    International Nuclear Information System (INIS)

    Lynch, Holley E; Shane Hutson, M; Veldhuis, Jim; Wayne Brodland, G


    The morphogenetic process of germ band retraction in Drosophila embryos involves coordinated movements of two epithelial tissues—germ band and amnioserosa. The germ band shortens along its rostral–caudal or head-to-tail axis, widens along its perpendicular dorsal-ventral axis, and uncurls from an initial ‘U’ shape. The amnioserosa mechanically assists this process by pulling on the crook of the U-shaped germ band. The amnioserosa may also provide biochemical signals that drive germ band cells to change shape in a mechanically autonomous fashion. Here, we use a finite-element model to investigate how these two contributions reshape the germ band. We do so by modeling the response to laser-induced wounds in each of the germ band’s spatially distinct segments (T1–T3, A1–A9) during the middle of retraction when segments T1–A3 form the ventral arm of the ‘U’, A4–A7 form its crook, and A8–A9 complete the dorsal arm. We explore these responses under a range of externally applied stresses and internal anisotropy of cell edge tensions—akin to a planar cell polarity that can drive elongation of cells in a direction parallel to the minimum edge tension—and identify regions of parameter space (edge-tension anisotropy versus stress anisotropy) that best match previous experiments for each germ band segment. All but three germ band segments are best fit when the applied stress anisotropy and the edge-tension anisotropy work against one another—i.e., when the isolated effects would elongate cells in perpendicular directions. Segments in the crook of the germ band (A4–A7) have cells that elongate in the direction of maximum external stress, i.e., external stress anisotropy is dominant. In most other segments, the dominant factor is internal edge-tension anisotropy. These results are consistent with models in which the amnioserosa pulls on the crook of the germ band to mechanically assist retraction. In addition, they suggest a mechanical cue for

  6. High Selectivity Dual-Band Bandpass Filter with Tunable Lower Passband


    Pan, Wei-Qiang; Zhao, Xiao-Lan; Zhang, Yao; Xu, Jin-Xu


    This paper presents a novel method to design dual-band bandpass filters with tunable lower passband and fixed upper passband. It utilizes a trimode resonator with three controllable resonant modes. Discriminating coupling is used to suppress the unwanted mode to avoid the interference. Varactors are utilized to realize tunable responses. The bandwidth of the two bands can be controlled individually. Transmission zeros are generated near the passband edges, resulting in high selectivity. For d...

  7. Wide band ENDOR spectrometer

    International Nuclear Information System (INIS)

    Mendonca Filho, C.


    The construction of an ENDOR spectrometer operating from 0,5 to 75 MHz within a single band, with ore Klystron and homodine detection, and no fundamental changes on the electron spin resonance spectrometer was described. The ENDOR signal can be detected both by amplitude modulation of the frequency field, or direct detection of the ESR output, which is taken to a signal analyser. The signal-to-noise ratio is raised by averaging rather than filtering avoiding the use of long time constants, providing natural line widths. The experimental apparatus and the spectra obtained are described. A discussion, relating the ENDOR line amplitudes with the experimental conditions is done and ENDOR mechanism, in which there is a relevant presence of cross relaxation is proposed

  8. Wide Band Artificial Pulsar (United States)

    Parsons, Zackary


    The Wide Band Artificial Pulsar (WBAP) is an instrument verification device designed and built by the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virgina. The site currently operates the Green Bank Ultimate Pulsar Processing Instrument (GUPPI) and the Versatile Green Bank Astronomical Spectrometer (VEGAS) digital backends for their radio telescopes. The commissioning and continued support for these sophisticated backends has demonstrated a need for a device capable of producing an accurate artificial pulsar signal. The WBAP is designed to provide a very close approximation to an actual pulsar signal. This presentation is intended to provide an overview of the current hardware and software implementations and to also share the current results from testing using the WBAP.

  9. Ethical decisions at the edge. (United States)

    Gillett, Grant


    Medicine grows incrementally in its ability to treat patients and at the growing edge it poses problems about the appropriateness of treatments that are different from those where good practice conforms to widely agreed standards. The growth of access to medical knowledge and the diversity of contemporary theoretical and clinical medicine have spawned deep divisions in the profession and divergent opinions about what constitutes reasonable care. That hallmark of acceptable practice is also under pressures from the threat of litigation, a highly commercialised contemporary medical environment, patient demands based on medical journalism and the internet and the exponential growth of bio-medical technology. Patient empowerment can result in complaints arising in new and complex areas and expert opinion can often differ markedly depending on where on the medical spectrum the experts are aligned. This column lays out some broad-brush principles to assess the adequacy of medical advice in such a climate.

  10. Electronic properties and relative stabilities of heterogeneous edge-decorated zigzag boron nitride nanoribbons

    International Nuclear Information System (INIS)

    Li, L.L.; Yu, X.F.; Yang, X.J.; Zhang, X.H.; Xu, X.W.; Jin, P.; Zhao, J.L.; Wang, X.X.; Tang, C.C.


    The wide band gap of boron nitride (BN) materials has been a major bottleneck for a wider application of BN in electronics. In this work, density functional theory computations were used to study the band structure of zigzag BN nanoribbons (BNNRs). Due to the ionic origin of the BN band gap, a heterogeneous edge decoration is an effective way to modulate the electronic band structure of BNNRs. This study demonstrates that a metallic behavior and magnetism can be realized by applying a NO 2 –NH 2 pair edge decoration. Although the lone electron pair of the NH 2 group is partly responsible for the metallic behavior, the effective potential difference induced by the donor–acceptor pair is also crucial for metallic behavior. Furthermore, these newly formed BNNRs were found to be more stable than H-passivated BNNRs. This simple chemical modification method offers great opportunities for the development of future BNNR-based electronic devices. - Graphical abstract: Due to the ionic origin of a BN band gap, heterogeneous edge decoration is an effective way to modulate its electronic structures. Metallicity and magnetism can be realized by NO 2 –NH 2 pair decoration. Although the N lone pair electrons in NH 2 group are responsible for the metallicity, the effective potential difference induced by a donor–acceptor pair is crucial for the formation of metallicity. - Highlights: • Heterogeneous edge decoration is effective for tuning BNNRs' electronic structures. • NO 2 –NH 2 pair decoration can lead to metallic behavior and magnetism for BNNRs. • The effective potential difference is crucial for the formation of metallicity. • NO 2 –NH 2 pair decorated BNNRs is more stable than H-passivated ones

  11. Characterization of edge plasma fluctuations in ASDEX

    International Nuclear Information System (INIS)

    Qin, J.; Carlson, A.; Endler, M.; Giannone, L.; Niedermeyer, H.; Rudyj, A.; Theimer, G.


    Nonlinear dynamical characterizations of the edge plasma fluctuations measured by both H α -light diagnostic and Langmuir probes in ASDEX are presented. The edge plasma fluctuations are stochastic rather than chaotic, they have a higher-dimensional structure in phase space. In time, the edge turbulence is found to have memory properties, the time required to lose the memory is different in the different cases. (orig.)

  12. Edge effect on weevils and spiders


    R. Horváth; T. Magura; G. Péter; B. Tóthmérész


    The edge effect on weevils and spiders was tested along oak forest – meadow transects using sweep-net samples at the Síkfökút Project in Hungary. For spiders the species richness was significantly higher in the forest edge than either in the meadow or the forest interior. For weevils the species richness of the forest edge was higher than that of the meadow, but the difference was not statistically significant whereas the species richness of the forest...

  13. Edge Segment-Based Automatic Video Surveillance

    Directory of Open Access Journals (Sweden)

    Oksam Chae


    Full Text Available This paper presents a moving-object segmentation algorithm using edge information as segment. The proposed method is developed to address challenges due to variations in ambient lighting and background contents. We investigated the suitability of the proposed algorithm in comparison with the traditional-intensity-based as well as edge-pixel-based detection methods. In our method, edges are extracted from video frames and are represented as segments using an efficiently designed edge class. This representation helps to obtain the geometric information of edge in the case of edge matching and moving-object segmentation; and facilitates incorporating knowledge into edge segment during background modeling and motion tracking. An efficient approach for background initialization and robust method of edge matching is presented, to effectively reduce the risk of false alarm due to illumination change and camera motion while maintaining the high sensitivity to the presence of moving object. Detected moving edges are utilized along with watershed algorithm for extracting video object plane (VOP with more accurate boundary. Experiment results with real image sequence reflect that the proposed method is suitable for automated video surveillance applications in various monitoring systems.

  14. Visible imaging of edge turbulence in NSTX

    International Nuclear Information System (INIS)

    S. Zweben; R. Maqueda; K. Hill; D. Johnson; S. Kaye; H. Kugel; F. Levinton; R. Maingi; L. Roquemore; S. Sabbagh; G. Wurden


    Edge plasma turbulence in tokamaks and stellarators is believed to cause the radial heat and particle flux across the separatrix and into the scrape-off-layers of these devices. This paper describes initial measurements of 2-D space-time structure of the edge density turbulence made using a visible imaging diagnostic in the National Spherical Torus Experiment (NSTX). The structure of the edge turbulence is most clearly visible using a method of ''gas puff imaging'' to locally illuminate the edge density turbulence

  15. Object detection using categorised 3D edges

    DEFF Research Database (Denmark)

    Kiforenko, Lilita; Buch, Anders Glent; Bodenhagen, Leon


    categorisation algorithm for describing objects in terms of its different edge types. Relying on edge information allow our system to deal with objects with little or no texture or surface variation. We show that edge categorisation improves matching performance due to the higher level of discrimination, which...... is made possible by the explicit use of edge categories in the feature descriptor. We quantitatively compare our approach with the state-of-the-art template based Linemod method, which also provides an effective way of dealing with texture-less objects, tests were performed on our own object dataset. Our...

  16. Edge passivation induced single-edge ferromagnetism of zigzag MoS{sub 2} nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Rui; Sun, Hui; Ma, Ben; Hu, Jingguo, E-mail:; Pan, Jing, E-mail:


    We performed density functional theory study on electronic structure, magnetic properties and stability of zigzag MoS{sub 2} nanoribbons (ZMoS{sub 2}NRs) with and without oxygen (O) passivation. The bare ZMoS{sub 2}NRs are magnetic metal with ferromagnetic edge states, edge passivation decreases their magnetism because of the decrease of edge unsaturated electrons. Obviously, the electronic structure and magnetic properties of ZMoS{sub 2}NRs greatly depend on edge states. When both edges are passivated by O atoms, ZMoS{sub 2}NRs are nonmagnetic metals. When either edge is passivated by O atoms, the systems exhibit single-edge ferromagnetism and magnetism concentrates on the non-passivated edge. Edge passivation can not only tune the magnetism of ZMoS{sub 2}NRs, but also enhance their stability by eliminating dangling bonds. These interesting findings on ZMoS{sub 2}NRs may open the possibility of their application in nanodevices and spintronics. - Highlights: • Edge passivation for tuning magnetism of zigzag MoS{sub 2} nanoribbons (ZMoS{sub 2}NRs) is proposed. • Edge passivation can tune ZMoS{sub 2}NRs from nonmagnetic metal to ferromagnetic metal. • When either edge is passivated, the systems exhibit single-edge ferromagnetic states. • These findings may inspire great interest in the community of ZMoS{sub 2}NRs and motivate numerous experimental researches.

  17. Feasibility of compensating for EUV field edge effects through OPC (United States)

    Maloney, Chris; Word, James; Fenger, Germain L.; Niroomand, Ardavan; Lorusso, Gian F.; Jonckheere, Rik; Hendrickx, Eric; Smith, Bruce W.


    As EUV Lithography (EUVL) continues to evolve, it offers a possible solution to the problems of additional masks and lithography steps that drive up the cost and complexity of 193i multiple patterning. EUVL requires a non-telecentric reflective optical system for operation. This requirement causes EUV specific effects such as shadowing. The absorber physically shadows the reflective multilayer (ML) on an EUV reticle resulting in pattern fidelity degradation. To reduce this degradation, a thinner absorber may help. Yet, as the absorber thickness decreases, reflectivity increases in the `dark' region around the image field, resulting in a loss of contrast. The region around the edge of the die on the mask of unpatterned absorber material deposited on top of ML, known as the image border, is also susceptible to undesirable reflections in an ideally dark region. For EUVL to be enabled for high-volume manufacturing (HVM), reticle masking (REMA) blades are used to shield light from the image border to allow for the printing of densely spaced die. When die are printed densely, the image border of each neighboring die will overlap with the edge of a given die resulting in an increase of dose that overexposes features at the edge of the field. This effect is convolved with a fingerprint from the edge of the REMA blades. This phenomenon will be referred to as a field edge effect. One such mitigation strategy that has been investigated to reduce the field edge effect is to fully remove the ML along the image border to ensure that no actinic-EUV radiation can be reflected onto neighboring die. This has proven to suppress the effect, but residual out-of-band radiation still provides additional dose to features near the image border, especially in the corners where three neighboring fields overlap. Measurements of dense contact holes (CHs) have been made along the image border with and without a ML-etched border at IMEC in collaboration with Micron using the ASML NXE:3100. The

  18. Ultrafast carrier dynamics in band edge and broad deep defect emission ZnSe nanowires (United States)

    Othonos, Andreas; Lioudakis, Emmanouil; Philipose, U.; Ruda, Harry E.


    Ultrafast carrier dynamics of ZnSe nanowires grown under different growth conditions have been studied. Transient absorption measurements reveal the dependence of the competing effects of state filling and photoinduced absorption on the probed energy states. The relaxation of the photogenerated carriers occupying defect states in the stoichiometric and Se-rich samples are single exponentials with time constants of 3-4ps. State filling is the main contribution for probe energies below 1.85eV in the Zn-rich grown sample. This ultrafast carrier dynamics study provides an important insight into the role that intrinsic point defects play in the observed photoluminescence from ZnSe nanowires.

  19. Efficient light amplification in low gain materials due to a photonic band edge effect

    Czech Academy of Sciences Publication Activity Database

    Ondič, Lukáš; Pelant, Ivan


    Roč. 20, č. 7 (2012), s. 7071-7080 ISSN 1094-4087 R&D Projects: GA MŠk LC510; GA AV ČR(CZ) IAA101120804; GA AV ČR KJB100100903 Institutional research plan: CEZ:AV0Z10100521 Keywords : photonic crystals * nanostructures * theory and design Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.546, year: 2012

  20. Femtosecond Pulse Characterization as Applied to One-Dimensional Photonic Band Edge Structures (United States)

    Fork, Richard L.; Gamble, Lisa J.; Diffey, William M.


    The ability to control the group velocity and phase of an optical pulse is important to many current active areas of research. Electronically addressable one-dimensional photonic crystals are an attractive candidate to achieve this control. This report details work done toward the characterization of photonic crystals and improvement of the characterization technique. As part of the work, the spectral dependence of the group delay imparted by a GaAs/AlAs photonic crystal was characterized. Also, a first generation an electrically addressable photonic crystal was tested for the ability to electronically control the group delay. The measurement technique, using 100 femtosecond continuum pulses was improved to yield high spectral resolution (1.7 nanometers) and concurrently with high temporal resolution (tens of femtoseconds). Conclusions and recommendations based upon the work done are also presented.

  1. Water splitting and the band edge positions of TiO2

    Czech Academy of Sciences Publication Activity Database

    Deák, P.; Kullgren, J.; Aradi, B.; Frauenheim, T.; Kavan, Ladislav


    Roč. 199, MAY 2016 (2016), s. 27-34 ISSN 0013-4686 R&D Projects: GA ČR GA13-07724S Grant - others:COST(XE) CM1104 Institutional support: RVO:61388955 Keywords : water splitting * rutile * anatase Subject RIV: CG - Electrochemistry Impact factor: 4.798, year: 2016

  2. "High Quantum Efficiency of Band-Edge Emission from ZnO Nanowires"

    Energy Technology Data Exchange (ETDEWEB)



    External quantum efficiency (EQE) of photoluminescence as high as 20 percent from isolated ZnO nanowires were measured at room temperature. The EQE was found to be highly dependent on photoexcitation density, which underscores the importance of uniform optical excitation during the EQE measurement. An integrating sphere coupled to a microscopic imaging system was used in this work, which enabled the EQE measurement on isolated ZnO nanowires. The EQE values obtained here are significantly higher than those reported for ZnO materials in forms of bulk, thin films or powders. Additional insight on the radiative extraction factor of one-dimensional nanostructures was gained by measuring the internal quantum efficiency of individual nanowires. Such quantitative EQE measurements provide a sensitive, noninvasive method to characterize the optical properties of low-dimensional nanostructures and allow tuning of synthesis parameters for optimization of nanoscale materials.

  3. CMS kinematic edge from sbottoms

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Peisi; Wagner, Carlos E. M.


    We present two scenarios in the Minimal Supersymmetric Extension of the Standard Model (MSSM) that can lead to an explanation of the excess in the invariant mass distribution of two opposite charged, same flavor leptons, and the corresponding edge at an energy of about 78 GeV, recently reported by the CMS Collaboration. In both scenarios, sbottoms are pair produced, and decay to neutralinos and a b-jet. The heavier neutralinos further decay to a pair of leptons and the lightest neutralino through on-shell sleptons or off-shell neutral gauge bosons. These scenarios are consistent with the current limits on the sbottoms, neutralinos, and sleptons. Assuming that the lightest neutralino is stable we discuss the predicted relic density as well as the implications for darkmatter direct detection. We show that consistency between the predicted and the measured value of the muon anomalous magnetic moment may be obtained in both scenarios. Finally, we define the signatures of these models that may be tested at the 13 TeV run of the LHC

  4. Atomically Thin Ordered Alloys of Transition Metal Dichalcogenides: Stability and Band Structures

    DEFF Research Database (Denmark)

    Pandey, Mohnish; Jacobsen, Karsten Wedel; Thygesen, Kristian Sommer


    We explore the possibility of modulating the electronic band edges of the transition metal dichalcogenides (TMD) via alloying of different semiconductors within the same group (intra-group alloying). The stability of the ordered alloys is assessed from the calculated mixing enthalpy which is found...

  5. Propagation losses in photonic crystal waveguides: Effects of band tail absorption and waveguide dispersion

    DEFF Research Database (Denmark)

    Rigal, F.; Joanesarson, Kristoffer Bitsch; Lyasota, A.


    Propagation losses in GaAs-based photonic crystal (PhC) waveguides are evaluated near the semiconductor band-edge by measuring the finesse of corresponding Ln cavities. This approach yields simultaneously the propagation losses and the mode reflectivity at the terminations of the cavities. We...... is important for the monolithic integration of light sources with such optical elements....

  6. Effect of Al doping on microstructure and optical band gap of ZnO ...

    Indian Academy of Sciences (India)

    % AZO indicating a blue-shift for 1% AZO film. However, for 2% AZO film, a decrease in band gap compared to pure ZnO is observed indicating a red-shift of fundamental absorption edge. Electrical resistance shows an initial decrease with.

  7. Product of normal edge transitive Cayley graphs

    Directory of Open Access Journals (Sweden)

    Amir Assari


    Full Text Available For two normal edge transitive Cayley graphs on two groups H and K whichhave no common direct factor and gcd(|H|/|H'|, |Z(K| = 1 = gcd(|K=K′|,|Z(H|,we consider four standard product of them and proved that only tensor product ofthem can be normal edge transitive.

  8. An investigation of the flap edge flowfield (United States)

    Pye, John David

    To identify and understand the fluid dynamic processes associated with flow in the region of a flap side edge, a NACA 63-215 Mod B main element with a half-span Fowler flap was tested in the JIAA Low Speed Wind Tunnel at Stanford University. Measurements were made using a variety of techniques to capture the effects of the flap edge vortex. Pressure sensitive paint was applied to the upper surface of both the flap and main element, as well as to the flap side edge. Fast response pressure transducers were mounted interior to the model to measure surface pressure fluctuations on the flap side edge. Single component hotwire data was taken in the near wake region of the flap edge. In addition to the data experimentally obtained, a computational data set of a geometrically similar model at a flight Reynolds number was used for comparison. The data indicates the presence of a dual vortex structure along the flap side edge. This structure is seen to grow, merge, and ultimately become a single symmetric vortex as it progresses downstream. Surface pressure fluctuations on the side edge scale as three power laws with free stream velocity as different flow regions are encountered. By varying the model rigging, indications of a confined source region for the pressure fluctuations were observed. A spatial survey of the correlation between flap side edge surface pressure fluctuations and the near-wake fluctuating velocity field shows increased correlation coefficients for the region surrounding the vortex core.

  9. Leading edge gypsy moth population dynamics (United States)

    M. R. Carter; F. W. Ravlin; M. L. McManus


    Leading edge gypsy moth populations have been the focus of several intervention programs (MDIPM, AIPM). Knowledge of gypsy moth population dynamics in leading edge area is crucial for effective management. Populations in these areas tend to reach outbreak levels (noticeable defoliation) within three to four years after egg masses are first detected. Pheromone traps...

  10. Development of planar detectors with active edge

    International Nuclear Information System (INIS)

    Povoli, M.; Bagolini, A.; Boscardin, M.; Dalla Betta, G.-F.; Giacomini, G.; Vianello, E.; Zorzi, N.


    We report on the first batch of planar active edge sensors fabricated at Fondazione Bruno Kessler (Trento, Italy) on the way to the development of full 3D detectors with active edges. The main design and technological aspects are reported, along with selected results from the electrical characterization of detectors and test structures.

  11. Development of planar detectors with active edge

    Energy Technology Data Exchange (ETDEWEB)

    Povoli, M., E-mail: [Dipartimento di Ingegneria e Scienza dell' Informazione, Universita di Trento, Via Sommarive, 14, I-38123 Povo di Trento (Italy); INFN, Sezione di Padova (Gruppo Collegato di Trento) (Italy); Bagolini, A.; Boscardin, M. [Fondazione Bruno Kessler, Centro per i Materiali e i Microsistemi (FBK-CMM), Via Sommarive, 18, I-38123 Povo di Trento (Italy); Dalla Betta, G.-F. [Dipartimento di Ingegneria e Scienza dell' Informazione, Universita di Trento, Via Sommarive, 14, I-38123 Povo di Trento (Italy); INFN, Sezione di Padova (Gruppo Collegato di Trento) (Italy); Giacomini, G.; Vianello, E.; Zorzi, N. [Fondazione Bruno Kessler, Centro per i Materiali e i Microsistemi (FBK-CMM), Via Sommarive, 18, I-38123 Povo di Trento (Italy)


    We report on the first batch of planar active edge sensors fabricated at Fondazione Bruno Kessler (Trento, Italy) on the way to the development of full 3D detectors with active edges. The main design and technological aspects are reported, along with selected results from the electrical characterization of detectors and test structures.

  12. Annotated Bibliography of EDGE2D Use

    International Nuclear Information System (INIS)

    Strachan, J.D.; Corrigan, G.


    This annotated bibliography is intended to help EDGE2D users, and particularly new users, find existing published literature that has used EDGE2D. Our idea is that a person can find existing studies which may relate to his intended use, as well as gain ideas about other possible applications by scanning the attached tables

  13. Edge effects in Bilayer Graphene Nanoribbons (United States)

    Lima, Matheus P.; Fazzio, Adalberto; da Silva, Antonio J. R.


    We investigate the geometrical and electronic structure of zigzag bilayer graphene nanoribbons (B-ZGNR), with widths that range from w=0.6 to w=4.5 nm. The layers are in the Bernal stacking, which means that there are two types of C atoms, those that are positioned above the center of the hexagons of the other layer, defining a B-sublattice, and those right on top of the C atoms of the other layer, forming an A-sublattice. When we cut the layer along the zigzag edge, there are two possible alignments, α, where the outermost edge atoms belong to the A- sublattice, and β, where the outermost edge atoms belong to the B-sublattice. Thus, only the inter-layer edge interaction differs. We found that the α alignment is energetically favorable, with an inter-layer edges attraction, whereas for the β there is an inter-layer edges repulsion. These edge-related forces cause a deviation from the exact Bernal stacking, resulting in a non-monotonic behavior of the energy gap with the width w for the α B-ZGNR, with a maximum value at w 3.5nm. This is a consequence of the competition between bulk and strongly attractive edge interactions. All results were obtained using density functional theory calculations with the inclusion of parametrized van der Waals interactions.

  14. Connected domination stable graphs upon edge addition ...

    African Journals Online (AJOL)

    A set S of vertices in a graph G is a connected dominating set of G if S dominates G and the subgraph induced by S is connected. We study the graphs for which adding any edge does not change the connected domination number. Keywords: Connected domination, connected domination stable, edge addition ...

  15. Direct Band Gap Gallium Antimony Phosphide (GaSbxP1−x) Alloys


    H. B. Russell; A. N. Andriotis; M. Menon; J. B. Jasinski; A. Martinez-Garcia; M. K. Sunkara


    Here, we report direct band gap transition for Gallium Phosphide (GaP) when alloyed with just 1?2 at% antimony (Sb) utilizing both density functional theory based computations and experiments. First principles density functional theory calculations of GaSbxP1?x alloys in a 216 atom supercell configuration indicate that an indirect to direct band gap transition occurs at x?=?0.0092 or higher Sb incorporation into GaSbxP1?x. Furthermore, these calculations indicate band edge straddling of the h...

  16. Living on the edge: roads and edge effects on small mammal populations. (United States)

    Fuentes-Montemayor, Elisa; Cuarón, Alfredo D; Vázquez-Domínguez, Ella; Benítez-Malvido, Julieta; Valenzuela-Galván, David; Andresen, Ellen


    1. Roads may affect wildlife populations through habitat loss and disturbances, as they create an abrupt linear edge, increasing the proportion of edge exposed to a different habitat. Three types of edge effects have been recognized: abiotic, direct biotic, and indirect biotic. 2. We explored the direct biotic edge effects of 3- to 4-m wide roads, and also a previously unrecognized type of edge effect: social. We live-trapped two threatened endemic rodents from Cozumel Island (Oryzomys couesi cozumelae and Reithrodontomys spectabilis) in 16 plots delimited by roads on two sides, to compare edge effects between two adjacent edges (corners), single-edge and interior forest, on life history and social variables. 3. No significant edge effects were observed on the life-history variables, with the exception of differences in body condition between males and females of O. c. cozumelae near edges. Both species showed significant and contrasting effects on their social variables. 4. O. c. cozumelae was distributed according to its age and sex: the proportion of adults and males was higher in interior than near edges, while juveniles and females were more abundant near edges. More nonreproductive females were present in corners than in single-edge and interior, while the opposite distribution was observed for nonreproductive males. 5. The distribution of R. spectabilis was related to its age and reproductive condition, but not to its sex. The proportion of adults was significantly higher in corners, while juveniles were only caught in single-edge and interior quadrants. The proportion of reproductive individuals was higher in edge than interior quadrants, while reproductive females were only present in edge quadrants. 6. We found significant differences between the quadrants with the greatest edge exposure in comparison with other quadrants. The social edge effects we identified complement the typology of edge effects recognized in ecological literature. Our study provides

  17. Edge effects on water droplet condensation. (United States)

    Medici, Marie-Gabrielle; Mongruel, Anne; Royon, Laurent; Beysens, Daniel


    In this study we investigate the effect of geometrical or thermal discontinuities on the growth of water droplets condensing on a cooled substrate. Edges, corners, and cooled and noncooled boundaries can have a strong effect on the vapor concentration profile and mass diffusion around the drops. In comparison to growth in a pattern where droplets have to compete to catch vapor, which results in a linear water concentration profile directed perpendicularly to the substrate, droplets near discontinuities can get more vapor (outer edges, corners), resulting in faster growth or less vapor (inner edges), giving lower growth. When the cooling heat flux limits growth instead of mass diffusion (substrate with low thermal conductivity, strong heat exchange with air), edge effects can be canceled. In certain cases, growth enhancement can reach nearly 500% on edges or corners.

  18. Edge separation using diffraction anomalous fine structure

    International Nuclear Information System (INIS)

    Ravel, B.; Bouldin, C.E.; Renevier, H.; Hodeau, J.L.; Berar, J.F.


    We exploit the crystallographic sensitivity of the Diffraction Anomalous Fine-Structure (DAFS) measurement to separate the fine structure contributions of different atomic species with closely spaced resonant energies. In BaTiO 3 the Ti K edge and Ba Lm edges are separated by 281 eV, or about 8.2 Angstrom -1 ), thus severely limiting the information content of the Ti K edge signal. Using the site selectivity of DAFS we can separate the two fine structure spectra using an iterative Kramers-Kronig method, thus extending the range of the Ti K edge spectrum. This technique has application to many rare earth/transition metal compounds, including many magnetic materials of technological significance for which K and L edges overlap in energy. (au)

  19. Dual-band infrared camera (United States)

    Vogel, H.; Schlemmer, H.


    Every year, numerous accidents happen on European roads due to bad visibility (fog, night, heavy rain). Similarly, the dramatic aviation accidents of year 2001 in Milan and Zurich have reminded us that aviation safety is equally affected by reduced visibility. A dual-band thermal imager was developed in order to raise human situation awareness under conditions of reduced visibility especially in the automotive and aeronautical context but also for all transportation or surveillance tasks. The chosen wavelength bands are the Short Wave Infrared SWIR and the Long Wave Infrared LWIR band which are less obscured by reduced visibility conditions than the visible band. Furthermore, our field tests clearly show that the two different spectral bands very often contain complementary information. Pyramidal fusion is used to integrate complementary and redundant features of the multi-spectral images into a fused image which can be displayed on a monitor to provide more and better information for the driver or pilot.

  20. Scaling laws and edge effects for polymer surface discharges (United States)

    Balmain, K. G.


    Specimens of Mylar sheet were exposed to a 20 kV electron beam. The resulting surface discharge arcs were photographed and the discharge current into a metal backing plate measured as a function of time. The area of the Mylar sheet was defined by a round aperture in a close-fitting metal mask, and the current pulse characteristics were plotted against area on log-log paper. The plots appear as straight lines (due to power-law behavior) with slopes of 0.50 for the peak current, 1.00 for the charge released, 1.49 for the energy and 0.55 for the pulse duration. Evidence is presented for the occurrence of banded charge distributions near grounded edges, on both Teflon and Mylar.

  1. Operation of transition-edge sensors with excess thermal noise

    International Nuclear Information System (INIS)

    Maasilta, I J; Kinnunen, K M; Nuottajaervi, A K; Leppaeniemi, J; Luukanen, A


    The superconducting transition-edge sensor (TES) is currently one of the most attractive choices for ultra-high resolution calorimetry in the keV x-ray band, and is being considered for future ESA and NASA missions. We have performed a study on the noise characteristics of Au/Ti bilayer TESs, at operating temperatures around ∼100 mK, with the SQUID readout at 1.5 K. Experimental results indicate that without modifications the back-action noise from the SQUID chip degrades the noise characteristics significantly. We present a simple and effective solution to the problem: by installing an extra shunt resistor which absorbs the excess radiation from the SQUID input, we have reduced the excess thermal (photon) noise power down by approximately a factor of five, allowing high resolution operation of the sensors

  2. Doping and bond length contributions to Mn K-edge shift in La1 ...

    Indian Academy of Sciences (India)

    of La1−xSrxMnO3 (x = 0–0.7) are compared with the band structure calculations using spin polarized density functional .... and electronic structure calculations that shift in Mn K-edge position on Sr doping in LaMnO3 corresponds to ... three directions for the tetrahedron integration were used to calculate the density of states.

  3. Elastically Deformable Side-Edge Link for Trailing-Edge Flap Aeroacoustic Noise Reduction (United States)

    Khorrami, Mehdi R. (Inventor); Lockard, David P. (Inventor); Moore, James B. (Inventor); Su, Ji (Inventor); Turner, Travis L. (Inventor); Lin, John C. (Inventor); Taminger, Karen M. (Inventor); Kahng, Seun K. (Inventor); Verden, Scott A. (Inventor)


    A system is provided for reducing aeroacoustic noise generated by an aircraft having wings equipped with trailing-edge flaps. The system includes a plurality of elastically deformable structures. Each structure is coupled to and along one of the side edges of one of the trailing-edge flaps, and is coupled to a portion of one of the wings that is adjacent to the one of the side edges. The structures elastically deform when the trailing-edge flaps are deployed away from the wings.

  4. Localized Edge Vibrations and Edge Reconstruction by Joule Heating in Graphene Nanostructures

    DEFF Research Database (Denmark)

    Engelund, Mads; Fürst, Joachim Alexander; Jauho, Antti-Pekka


    Control of the edge topology of graphene nanostructures is critical to graphene-based electronics. A means of producing atomically smooth zigzag edges using electronic current has recently been demonstrated in experiments [Jia et al., Science 323, 1701 (2009)]. We develop a microscopic theory...... for current-induced edge reconstruction using density functional theory. Our calculations provide evidence for localized vibrations at edge interfaces involving unpassivated armchair edges. We demonstrate that these vibrations couple to the current, estimate their excitation by Joule heating, and argue...

  5. Observation of topological edge states of acoustic metamaterials at subwavelength scale (United States)

    Dai, Hongqing; Jiao, Junrui; Xia, Baizhan; Liu, Tingting; Zheng, Shengjie; Yu, Dejie


    Topological states are of key importance for acoustic wave systems owing to their unique transport properties. In this study, we develop a hexagonal array of hexagonal columns with Helmholtz resonators to obtain subwavelength Dirac cones. Rotation operations are performed to open the Dirac cones and obtain acoustic valley vortex states. In addition, we calculate the angular-dependent frequencies for the band edges at the K-point. Through a topological phase transition, the topological phase of pattern A can change into that of pattern B. The calculations for the bulk dispersion curves show that the acoustic metamaterials exhibit BA-type and AB-type topological edge states. Experimental results demonstrate that a sound wave can transmit well along the topological path. This study could reveal a simple approach to create acoustic topological edge states at the subwavelength scale.

  6. Direct in situ observations of single Fe atom catalytic processes and anomalous diffusion at graphene edges (United States)

    Zhao, Jiong; Deng, Qingming; Avdoshenko, Stanislav M.; Fu, Lei; Eckert, Jürgen; Rümmeli, Mark H.


    Single-atom catalysts are of great interest because of their high efficiency. In the case of chemically deposited sp2 carbon, the implementation of a single transition metal atom for growth can provide crucial insight into the formation mechanisms of graphene and carbon nanotubes. This knowledge is particularly important if we are to overcome fabrication difficulties in these materials and fully take advantage of their distinct band structures and physical properties. In this work, we present atomically resolved transmission EM in situ investigations of single Fe atoms at graphene edges. Our in situ observations show individual iron atoms diffusing along an edge either removing or adding carbon atoms (viz., catalytic action). The experimental observations of the catalytic behavior of a single Fe atom are in excellent agreement with supporting theoretical studies. In addition, the kinetics of Fe atoms at graphene edges are shown to exhibit anomalous diffusion, which again, is in agreement with our theoretical investigations. PMID:25331874

  7. Interpretation of polarized Cu K x-ray absorption near-edge-structure spectra of CuO

    Czech Academy of Sciences Publication Activity Database

    Šipr, Ondřej; Šimůnek, Antonín


    Roč. 13, - (2001), s. 8519-8525 ISSN 0953-8984 Institutional research plan: CEZ:AV0Z1010914 Keywords : polarized Cu K-edge spectra * CuO * band-structure calculations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.611, year: 2001

  8. Partnership for Edge Physics Simulation

    Energy Technology Data Exchange (ETDEWEB)

    Kritz, Arnold H. [Lehigh Univ., Bethlehem, PA (United States). Dept. of Physics; Rafiq, Tariq [Lehigh Univ., Bethlehem, PA (United States). Dept. of Physics


    A major goal of our participation in the Edge Physics Simulation project has been to contribute to the understanding of the self-organization of tokamak turbulence fluctuations resulting in the formation of a staircase structure in the ion temperature. A second important goal is to demonstrate how small scale turbulence in plasmas self-organizes with dynamically driven quasi-stationary flow shear. These goals have been accomplished through the analyses of the statistical properties of XGC1 flux driven Gyrokinetic electrostatic ion temperature gradient (ITG) turbulence simulation data in which neutrals are included. The ITG turbulence data, and in particular fluctuation data, were obtained from a massively parallel flux-driven gyrokinetic full-f particle-in-cell simulation of a DIII-D like equilibrium. Below some the findings are summarized. It was observed that the emergence of staircase structure is related to the variations in the normalized temperature gradient length (R/LT) and the poloidal flow shear. Average turbulence intensity is found to be large in the vicinity of minima in R/LTi, where ITG growth is expected to be lower. The distributions of the occurrences of potential fluctuation are found to be Gaussian away from the staircase-step locations, but they are found to be non-Gaussian in the vicinity of staircase-step locations. The results of analytically derived expressions for the distribution of the occurrences of turbulence intensity and intensity flux were compared with the corresponding quantities computed using XGC1 simulation data and good agreement is found. The derived expressions predicts inward and outward propagation of turbulence intensity flux in an intermittent fashion. The outward propagation of turbulence intensity flux occurs at staircase-step locations and is related to the change in poloidal flow velocity shear and to the change in the ion temperature gradient. The standard deviation, skewness and kurtosis for turbulence quantities


    NARCIS (Netherlands)



    The relevance of different models, such as the one-band t-J model and the three-band Emery model, as a realistic description of the electronic structure of high-T(c) materials is discussed. Starting from a multiband approach using cluster calculations and an impurity approach, the following

  10. Influence of point defects on the near edge structure of hexagonal boron nitride (United States)

    McDougall, Nicholas L.; Partridge, Jim G.; Nicholls, Rebecca J.; Russo, Salvy P.; McCulloch, Dougal G.


    Hexagonal boron nitride (hBN) is a wide-band-gap semiconductor with applications including gate insulation layers in graphene transistors, far-ultraviolet light emitting devices and as hydrogen storage media. Due to its complex microstructure, defects in hBN are challenging to identify. Here, we combine x-ray absorption near edge structure (XANES) spectroscopy with ab initio theoretical modeling to identify energetically favorable defects. Following annealing of hBN samples in vacuum and oxygen, the B and N K edges exhibited angular-dependent peak modifications consistent with in-plane defects. Theoretical calculations showed that the energetically favorable defects all produce signature features in XANES. Comparing these calculations with experiments, the principle defects were attributed to substitutional oxygen at the nitrogen site, substitutional carbon at the boron site, and hydrogen passivated boron vacancies. Hydrogen passivation of defects was found to significantly affect the formation energies, electronic states, and XANES. In the B K edge, multiple peaks above the major 1 s to π* peak occur as a result of these defects and the hydrogen passivated boron vacancy produces the frequently observed doublet in the 1 s to σ* transition. While the N K edge is less sensitive to defects, features attributable to substitutional C at the B site were observed. This defect was also calculated to have mid-gap states in its band structure that may be responsible for the 4.1-eV ultraviolet emission frequently observed from this material.

  11. Deep Edge Guided Recurrent Residual Learning for Image Super-Resolution (United States)

    Yang, Wenhan; Feng, Jiashi; Yang, Jianchao; Zhao, Fang; Liu, Jiaying; Guo, Zongming; Yan, Shuicheng


    In this work, we consider the image super-resolution (SR) problem. The main challenge of image SR is to recover high-frequency details of a low-resolution (LR) image that are important for human perception. To address this essentially ill-posed problem, we introduce a Deep Edge Guided REcurrent rEsidual~(DEGREE) network to progressively recover the high-frequency details. Different from most of existing methods that aim at predicting high-resolution (HR) images directly, DEGREE investigates an alternative route to recover the difference between a pair of LR and HR images by recurrent residual learning. DEGREE further augments the SR process with edge-preserving capability, namely the LR image and its edge map can jointly infer the sharp edge details of the HR image during the recurrent recovery process. To speed up its training convergence rate, by-pass connections across multiple layers of DEGREE are constructed. In addition, we offer an understanding on DEGREE from the view-point of sub-band frequency decomposition on image signal and experimentally demonstrate how DEGREE can recover different frequency bands separately. Extensive experiments on three benchmark datasets clearly demonstrate the superiority of DEGREE over well-established baselines and DEGREE also provides new state-of-the-arts on these datasets.

  12. Electronic structures and edge effects of Ga2S2 nanoribbons (United States)

    Wang, Bao-Ji; Li, Xiao-Hua; Zhang, Li-Wei; Wang, Guo-Dong; Ke, San-Hang


    Ab initio density functional theory calculations are carried out to predict the electronic properties and relative stability of gallium sulfide nanoribbons (Ga2S2-NRs) with either zigzag- or armchair-terminated edges. It is found that the electronic properties of the nanoribbons are very sensitive to the edge structure. The zigzag nanoribbons (Ga2S2-ZNRs) are ferromagnetic (FM) metallic with spin-polarized edge states regardless of the H-passivation, whereas the bare armchair ones (Ga2S2-ANRs) are semiconducting with an indirect band gap. This band gap exhibits an oscillation behavior as the width increases and finally converges to a constant value. Similar behavior is also found in H-saturated Ga2S2-ANRs, although the band gap converges to a larger value. The relative stabilities of the bare ANRs and ZNRs are investigated by calculating their binding energies. It is found that for a similar width the ANRs are more stable than the ZNRs, and both are more stable than some Ga2S2 nanoclusters with stable configurations. Project supported by the National Natural Science Foundation of China (Grant Nos. 11174220 and 11374226), the Key Scientific Research Project of the Henan Institutions of Higher Learning (Grant No. 16A140009), the Program for Innovative Research Team of Henan Polytechnic University (Grant Nos. T2015-3 and T2016-2), and the Doctoral Foundation of Henan Polytechnic University (Grant No. B2015-46).

  13. gamma-induced modification on optical band gap of CR-39 SSNTD

    International Nuclear Information System (INIS)

    Zaki, M.F.


    effect of gamma irradiation on optical absorption of nuclear track detectors like CR-39 was studied at different absorbed doses using ultraviolet-visible (UV-VIS)spectroscopy. the existence of the peaks, their shifting and broadening as a result of gamma irradiation has been discussed. the width of the tail of localized states in the band gap (E u )was evaluated using the Urbach edge method. finally the indirect and direct band gap in pristine and gamma irradiated CR-39 have been determined. the values of indirect band gap have been found to be lower than the corresponding values of direct band gap. a decrease in the optical energy gap with increasing the gamma absorbed dose can be discussed on the basis of gamma-irradiation-induced defects in the CR-39. the correlation between optical band gap and the number of carbon atoms in a cluster with modified Tauc's equation has been discussed in case of CR-39.

  14. C3H2 : A wide-band-gap semiconductor with strong optical absorption (United States)

    Lu, Hong-Yan; Cuamba, Armindo S.; Geng, Lei; Hao, Lei; Qi, Yu-Min; Ting, C. S.


    Using first-principles calculations, we predict a new type of partially hydrogenated graphene system, C3H2 , which turns out to be a semiconductor with a band gap of 3.56 eV. The bands are rather flat at the band edges and thus lead to a large density of states, which further results in strong optical absorption between the valence band and the conduction band. Particularly, it shows strong optical absorption at about 4.5 eV for the light polarized along the lines connecting the nearest unhydrogenated carbon atoms. Thus, the predicted C3H2 system may have potential applications for a polarizer as well as other high-efficiency optical devices in the near ultraviolet region.

  15. Low-frequency band gap mechanism of torsional vibration of lightweight elastic metamaterial shafts (United States)

    Li, Lixia; Cai, Anjiang


    In this paper, the low-frequency band gap mechanism of torsional vibration is investigated for a kind of light elastic metamaterial (EM) shafts architecture comprised of a radial double-period element periodically as locally resonant oscillators with low frequency property. The dispersion relations are calculated by a method combining the transfer matrix and a lumped-mass method. The theoretical results agree well with finite method simulations, independent of the density of the hard material ring. The effects of the material parameters on the band gaps are further explored numerically. Our results show that in contrast to the traditional EM shaft, the weight of our proposed EM shaft can be reduced by 27% in the same band gap range while the vibration attenuation is kept unchanged, which is very convenient to instruct the potential engineering applications. Finally, the band edge frequencies of the lower band gaps for this light EM shaft are expressed analytically using physical heuristic models.

  16. Power deposition on misaligned edges in COMPASS

    Directory of Open Access Journals (Sweden)

    R. Dejarnac


    Full Text Available If the decision is made not to apply a toroidal chamfer to tungsten monoblocks at ITER divertor vertical targets, exposed leading edges will arise as a result of assembly tolerances between adjacent plasma-facing components. Then, the advantage of glancing magnetic field angles for spreading plasma heat flux on top surfaces is lost at the misaligned edges with an interaction occurring at near normal incidence, which can drive melting for the expected inter-ELM heat fluxes. A dedicated experiment has been performed on the COMPASS tokamak to thoroughly study power deposition on misaligned edges using inner-wall limited discharges on a special graphite tile presenting gaps and leading edges directly viewed by a high resolution infra-red camera. The parallel power flux deducted from the unperturbed measurement far from the gap is fully consistent with the observed temperature increase at the leading edge, respecting the power balance. All the power flowing into the gap is deposited at the leading edge and no mitigation factor is required to explain the thermal response. Particle-in-cell simulations show that the ion Larmor smoothing effect is weak and that the power deposition on misaligned edges is well described by the optical approximation because of an electron dominated regime associated with non-ambipolar parallel current flow.

  17. Topological Edge-State Manifestation of Interacting 2D Condensed Boson-Lattice Systems in a Harmonic Trap (United States)

    Galilo, Bogdan; Lee, Derek K. K.; Barnett, Ryan


    In this Letter, it is shown that interactions can facilitate the emergence of topological edge states of quantum-degenerate bosonic systems in the presence of a harmonic potential. This effect is demonstrated with the concrete model of a hexagonal lattice populated by spin-one bosons under a synthetic gauge field. In fermionic or noninteracting systems, the presence of a harmonic trap can obscure the observation of edge states. For our system with weakly interacting bosons in the Thomas-Fermi regime, we can clearly see a topological band structure with a band gap traversed by edge states. We also find that the number of edge states crossing the gap is increased in the presence of a harmonic trap, and the edge modes experience an energy shift while traversing the first Brillouin zone which is related to the topological properties of the system. We find an analytical expression for the edge-state energies and our comparison with numerical computation shows excellent agreement.

  18. Even–odd effect on the edge states for zigzag phosphorene nanoribbons under a perpendicular electric field

    International Nuclear Information System (INIS)

    Zhou, Benliang; Zhou, Guanghui; Zhou, Benhu; Zhou, Xiaoying


    We study the variation of electronic property for zigzag-edge phosphorene nanoribbons (ZPNRs) under a perpendicular electric field (PEF). Using the tight-binding Hamiltonian combined with the surface lattice Green’s function (GF) approach, we show that the response of edge states to PEF for a N -ZPNR with even- or odd- N (number of zigzag chains) is qualitatively different. The field opens a gap between two edge bands near the Fermi energy for even- N ribbons, but for odd- N ones where the two edge bands are always nearly degenerated. This difference is originally from that the Stark-effect-induced energies at the upper and lower edges for even- and odd- N ZPNRs are different due to the peculiar lattice structure of phosphorene. In consequence, the electronic densities are more localized at the edges driven by the field for even- N ZPNRs but not for odd- N ones. This even–odd effect is also reflected in conductance, which indicates that the odd- N ZPNRs may be more suitable for the usage of field-effect transistor. (paper)

  19. Topological Edge-State Manifestation of Interacting 2D Condensed Boson-Lattice Systems in a Harmonic Trap. (United States)

    Galilo, Bogdan; Lee, Derek K K; Barnett, Ryan


    In this Letter, it is shown that interactions can facilitate the emergence of topological edge states of quantum-degenerate bosonic systems in the presence of a harmonic potential. This effect is demonstrated with the concrete model of a hexagonal lattice populated by spin-one bosons under a synthetic gauge field. In fermionic or noninteracting systems, the presence of a harmonic trap can obscure the observation of edge states. For our system with weakly interacting bosons in the Thomas-Fermi regime, we can clearly see a topological band structure with a band gap traversed by edge states. We also find that the number of edge states crossing the gap is increased in the presence of a harmonic trap, and the edge modes experience an energy shift while traversing the first Brillouin zone which is related to the topological properties of the system. We find an analytical expression for the edge-state energies and our comparison with numerical computation shows excellent agreement.

  20. Band-notched ultrawide band antenna loaded with ferrite slab (United States)

    Wang, Hao; Zong, Weihua; Sun, Nian X.; Lin, Hwaider; Li, Shandong


    In this paper, a novel technique to design a band-notched UWB antenna by using Yttrium Iron Garnet (YIG) ferrite is proposed. A printed slot UWB antenna with size of 21mm×26 mm×0.8 mm is adopted as a basic antenna. A piece of ferrite slab with size of 5 mm×10 mm×2 mm is attached on the feeding layer of the antenna to achieve band-notched characteristics. The measured -10 dB bandwidth of the antenna without ferrite slab is 2.91-10.98 GHz. With loading of ferrite slab, the bandwidth turns to 2.73-5.12 and 5.87-10.78 GHz. A band notch of 5.12- 5.87 GHz is achieved to filter WLAN 5 GHz (5.15-5.825 GHz) band. The proposed technique has virtue of easy fabrication and keeping antenna miniaturization.

  1. Slip-band formation and dislocation kinetics in the stage I deformation of neutron-irradiated copper single crystals

    International Nuclear Information System (INIS)

    Kitajima, Sadakichi; Shinohara, Kazutoshi; Kutsuwada, Masanori


    The velocity of edge and screw dislocations moving in primary slip bands and the formation rate of primary slip bands were measured in stage I deformation of neutron-irradiated copper single crystals at different strain rates at room temperature using micro-cinematography and optical micrography. The average velocity of edge dislocations was larger at least by one order than that of screw ones, and that of screw dislocations did not depend so strongly on strain rate. The formation rate of primary slip bands was proportional to strain rate. From these results, it is concluded that (1) jogs produced on moving dislocations by cutting dislocation loops result in the difference in velocity between edge and screw dislocations and (2) the change in the density of mobile dislocations as well as velocity of dislocations is responsible for the change of plastic strain rate of a crystal. (author)

  2. Band-to-Band Tunneling Transistors: Scalability and Circuit Performance (United States)


    55* MEDICI ...3.2.1 Tunneling Theory 3.3 Simulation Methods 3.3.1 MEDICI 3.3.2 Sentaurus Local Tunneling 3.3.3 Sentaurus Nonlocal Tunneling 3.4 Sentaurus...tunneling current. 3.3.1 MEDICI MEDICI is a one and two-dimensional simulator created by Synopsys, Inc. [18]. It contains a band-to-band

  3. Cavitation on hydrofoils with sinusoidal leading edge (United States)

    Johari, H.


    Cavitation characteristics of hydrofoils with sinusoidal leading edge were examined experimentally at a Reynolds number of 7.2 × 105. The hydrofoils had an underlying NACA 634-021 profile and an aspect ratio of 4.3. The sinusoidal leading edge geometries included three amplitudes of 2.5%, 5%, and 12% and two wavelengths of 25% and 50% of the mean chord length. Results revealed that cavitation on the leading edge-modified hydrofoils existed in pockets behind the troughs whereas the baseline hydrofoil produced cavitation along its entire span. Moreover, cavitation on the modified hydrofoils appeared at consistently lower angles of attack than on the baseline hydrofoil.

  4. Adobe Edge Animate CC for dummies

    CERN Document Server

    Rohde, Michael


    The easy way to build HTML5 mobile and web apps using Adobe's new Edge Animate CC Edge Animate CC is an approachable WYSIWYG alternative for leveraging the power of languages like HTML5, CSS3, and JavaScript to design and develop for the web and mobile devices, even if you have no programming experience. Written by Michael Rohde, the book calls on this seasoned web developer's wealth of experience using Edge Animate CC, and a companion website includes all code from the book to help you apply what you learn as you go. Features an easy-to-use interface, with a propert


    Directory of Open Access Journals (Sweden)

    M. A. Gunen


    Full Text Available In this paper, a new method has been presented for the extraction of edge information by using Differential Search Optimization Algorithm. The proposed method is based on using a new heuristic image thresholding method for edge detection. The success of the proposed method has been examined on fusion of two remote sensed images. The applicability of the proposed method on edge detection and image fusion problems have been analysed in detail and the empirical results exposed that the proposed method is useful for solving the mentioned problems.

  6. Edge-Matching Problems with Rotations

    DEFF Research Database (Denmark)

    Ebbesen, Martin; Fischer, Paul; Witt, Carsten


    Edge-matching problems, also called puzzles, are abstractions of placement problems with neighborhood conditions. Pieces with colored edges have to be placed on a board such that adjacent edges have the same color. The problem has gained interest recently with the (now terminated) Eternity II...... puzzle, and new complexity results. In this paper we consider a number of settings which differ in size of the puzzles and the manipulations allowed on the pieces. We investigate the effect of allowing rotations of the pieces on the complexity of the problem, an aspect that is only marginally treated so...

  7. Edge-Disjoint Fibonacci Trees in Hypercube

    Directory of Open Access Journals (Sweden)

    Indhumathi Raman


    Full Text Available The Fibonacci tree is a rooted binary tree whose number of vertices admit a recursive definition similar to the Fibonacci numbers. In this paper, we prove that a hypercube of dimension h admits two edge-disjoint Fibonacci trees of height h, two edge-disjoint Fibonacci trees of height h-2, two edge-disjoint Fibonacci trees of height h-4 and so on, as subgraphs. The result shows that an algorithm with Fibonacci trees as underlying data structure can be implemented concurrently on a hypercube network with no communication latency.

  8. Selective Electroless Silver Deposition on Graphene Edges

    DEFF Research Database (Denmark)

    Durhuus, D.; Larsen, M. V.; Andryieuski, Andrei


    on silica substrate and thus potentially restoring electric connectivity with minimal influence on the overall graphene electrical and optical properties. The presented technique could find applications in graphene based transparent conductors as well as selective edge functionalization and can be extended......We demonstrate a method of electroless selective silver deposition on graphene edges or between graphene islands without covering the surface of graphene. Modifications of the deposition recipe allow for decoration of graphene edges with silver nanoparticles or filling holes in damaged graphene...

  9. Edge states in a honeycomb lattice: effects of anisotropic hopping and mixed edges

    Energy Technology Data Exchange (ETDEWEB)

    Dahal, Hari P [Los Alamos National Laboratory; Balatsky, Alexander V [Los Alamos National Laboratory; Sinistsyn, N A [Los Alamos National Laboratory; Hu, Zi - Xiang [ZHEJIANG UNIV; Yang, Kun [NHMFL/FSU


    We study the edge states in graphene in the presence of a magnetic field perpendicular to the plane of the lattice. Most of the work done so far discusses the edge states in either zigzag or armchair edge graphene considering an isotropic electron hopping. In practice, graphene can have a mixture of armchair and zigzag edges and the electron hopping can be anisotropic, which is the subject of this article. We predict that the mixed edges smear the enhanced local density of states (LDOS) at E=0 of the zigzag edge and, on the other hand, the anisotropic hopping gives rise to the enhanced LDOS at E=0 in the armchair edge. The behavior of the LDOS can be studied using scanning tunneling microscopy (STM) experiments. We suggest that care must be taken while interpreting the STM data, because the clear distinction between the zigzag edge (enhanced LDOS at E=0) and armchair edge (suppressed LDOS at E=0) can be lost if the hopping is not isotropic and if the edges are mixed.

  10. Cover Art: River's Edge: Downward, Outward, Upward

    Directory of Open Access Journals (Sweden)

    Jonee Kulman Brigham


    Full Text Available Artist's Statement for the cover art of IJPS volume 4, issue 3: River's Edge: Downward, Outward, Upward, 2015. Mixed Media: photograph, inkjet printed on presentation matte of colored pencil over photograph.

  11. Miniature Trailing Edge Effector for Aerodynamic Control (United States)

    Lee, Hak-Tae (Inventor); Bieniawski, Stefan R. (Inventor); Kroo, Ilan M. (Inventor)


    Improved miniature trailing edge effectors for aerodynamic control are provided. Three types of devices having aerodynamic housings integrated to the trailing edge of an aerodynamic shape are presented, which vary in details of how the control surface can move. A bucket type device has a control surface which is the back part of a C-shaped member having two arms connected by the back section. The C-shaped section is attached to a housing at the ends of the arms, and is rotatable about an axis parallel to the wing trailing edge to provide up, down and neutral states. A flip-up type device has a control surface which rotates about an axis parallel to the wing trailing edge to provide up, down, neutral and brake states. A rotating type device has a control surface which rotates about an axis parallel to the chord line to provide up, down and neutral states.

  12. Edge energies and shapes of nanoprecipitates.

    Energy Technology Data Exchange (ETDEWEB)

    Hamilton, John C.


    In this report we present a model to explain the size-dependent shapes of lead nano-precipitates in aluminum. Size-dependent shape transitions, frequently observed at nanolength scales, are commonly attributed to edge energy effects. This report resolves an ambiguity in the definition and calculation of edge energies and presents an atomistic calculation of edge energies for free clusters. We also present a theory for size-dependent shapes of Pb nanoprecipitates in Al, introducing the concept of ''magic-shapes'' defined as precipitate shapes having near zero elastic strains when inserted into similarly shaped voids in the Al matrix. An algorithm for constructing a complete set of magic-shapes is presented. The experimental observations are explained by elastic strain energies and interfacial energies; edge energies play a negligible role. We replicate the experimental observations by selecting precipitates having magic-shapes and interfacial energies less than a cutoff value.

  13. Thermal stability of the tokamak plasma edge

    International Nuclear Information System (INIS)

    Stacey, W.M.


    The general linear, fluid, thermal instability theory for the plasma edge has been extended. An analysis of a two-dimensional fluid model of the plasma edge has identified the importance of many previously unappreciated phenomena associated with parallel and gyroviscous forces in the presence of large radial gradients, with large radial or parallel flows, with the temperature dependence of transport coefficients, and with the coupling of temperature, flow and density perturbations. The radiative condensation effect is generalized to include a further destabilizing condensation effect associated with radial heat conduction. Representative plasma edge neutral and impurity densities are found to be capable of driving thermal instabilities in the edge transport barrier and radiative mantle, respectively. (author)

  14. Intensity formulas for triplet bands (United States)

    Budo, A.


    Previous work in this area is surveyed and the mathematics involved in determining the quantitative intensity measurements in triplet bands is presented. Explicit expressions for the intensity distribution in the branches of the 3 Sigma-3 Pi and 1 Sigma-3Pi bands valid for all values of the coupling constant Y of the 3 Pi terms are given. The intensity distribution calculated according to the formulas given is compared with measurements of PH, 3 Pi-3 Sigma. Good quantitative agreement is obtained.

  15. Edge and core dynamics in harness

    International Nuclear Information System (INIS)

    Ball, R.


    Resistive kink oscillations in tokamak plasmas are usually treated as core localized events, yet there there are several mechanisms by which they may interact with the edge dynamics. This suggests that we may regulate edge oscillatory behaviour, or ELMs, by harnessing the natural or contrived sawtooth period and amplitude. In this work I investigate core-edge oscillatory entrainment through direct propagation of heat pulses, inductive coupling, and global higher order resonance effects. In the core of auxiliary heated tokamak plasmas the ineluctable rhythm of slow buildup and rapid conversion of potential energy governs electron and heat radial transport. The growth phase of the sawtooth is accompanied by significant reconnection, then during the collapse the temperature and density in the core fall dramatically. There is evidence from experiments in reversed field pinch devices that ensuing energy fluxes can affect flow shear and confinement at the edge. The basis for this study is the dynamical (BDS) model for edge plasma behavior that was derived from electrostatic resistive MHD equations. The BDS model reflects the major qualitative features of edge dynamics that have been observed, such as L-H transitions and associated ELMs, hysteresis, and spontaneous reversal of poloidal shear flow. Under poorly dissipative conditions the transient behavior of the model can exhibit period-doubling, blue-sky, homoclinic, and other exotic bifurcations. Thus we might ask questions such as: Is it possible to mode-lock the edge dynamics to the core sawteeth? Can we induce, or prevent, a change in direction of shear flow? What about MHD effects? Is core-edge communication one way or is there some feedback? In the simplest prototype for coupled core-edge dynamics I model the sawtooth crash as a periodic power input to the edge potential energy reservoir. This is effected by coupling the BDS model to the dynamical system u = u(1 - u 2 - x 2 ) - ω s x, x = x(1-u 2 -x 2 ) + ω s u

  16. The effect of density-of-state tails on band-to-band tunneling: Theory and application to tunnel field effect transistors (United States)

    Sant, S.; Schenk, A.


    It is demonstrated how band tail states in the semiconductor influence the performance of a Tunnel Field Effect Transistor (TFET). As a consequence of the smoothened density of states (DOS) around the band edges, the energetic overlap of conduction and valence band states occurs gradually at the onset of band-to-band tunneling (BTBT), thus degrading the sub-threshold swing (SS) of the TFET. The effect of the band tail states on the current-voltage characteristics is modelled quantum-mechanically based on the idea of zero-phonon trap-assisted tunneling between band and tail states. The latter are assumed to arise from a 3-dimensional pseudo-delta potential proposed by Vinogradov [1]. This model potential allows the derivation of analytical expressions for the generation rate covering the whole range from very strong to very weak localization of the tail states. Comparison with direct BTBT in the one-band effective mass approximation reveals the essential features of tail-to-band tunneling. Furthermore, an analytical solution for the problem of tunneling from continuum states of the disturbed DOS to states in the opposite band is found, and the differences to direct BTBT are worked out. Based on the analytical expressions, a semi-classical model is implemented in a commercial device simulator which involves numerical integration along the tunnel paths. The impact of the tail states on the device performance is analyzed for a nanowire Gate-All-Around TFET. The simulations show that tail states notably impact the transfer characteristics of a TFET. It is found that exponentially decaying band tails result in a stronger degradation of the SS than tail states with a Gaussian decay of their density. The developed model allows more realistic simulations of TFETs including their non-idealities.

  17. Edge direction and the structure of networks


    Foster, Jacob G.; Foster, David V.; Grassberger, Peter; Paczuski, Maya


    Directed networks are ubiquitous and are necessary to represent complex systems with asymmetric interactions---from food webs to the World Wide Web. Despite the importance of edge direction for detecting local and community structure, it has been disregarded in studying a basic type of global diversity in networks: the tendency of nodes with similar numbers of edges to connect. This tendency, called assortativity, affects crucial structural and dynamic properties of real-world networks, such ...

  18. Applications of Hydrofoils with Leading Edge Protuberances (United States)


    APPLICATIONS OF HYDROFOILS WITH LEADING EDGE PROTUBERANCES Final Technical Report for Office of Naval Research contract...To) 03/30/2012 Final Technical Report 01-08-2008 to 31-12-2011 4. TITLE AND SUBTITLE Sa. CONTRACT NUMBER Applications of Hydrofoils with Leading...AVAILABILITY STATEMENT Approved for public release; distribution is unlimited. 13. SUPPLEMENTARY NOTES 14. ABSTRACT The leading edge modified hydrofoils

  19. Integrated core-edge-divertor modeling studies

    International Nuclear Information System (INIS)

    Stacey, W.M.


    An integrated calculation model for simulating the interaction of physics phenomena taking place in the plasma core, in the plasma edge and in the SOL and divertor of tokamaks has been developed and applied to study such interactions. The model synthesises a combination of numerical calculations (1) the power and particle balances for the core plasma, using empirical confinement scaling laws and taking into account radiation losses (2), the particle, momentum and power balances in the SOL and divertor, taking into account the effects of radiation and recycling neutrals, (3) the transport of feeling and recycling neutrals, explicitly representing divertor and pumping geometry, and (4) edge pedestal gradient scale lengths and widths, evaluation of theoretical predictions (5) confinement degradation due to thermal instabilities in the edge pedestals, (6) detachment and divertor MARFE onset, (7) core MARFE onsets leading to a H-L transition, and (8) radiative collapse leading to a disruption and evaluation of empirical fits (9) power thresholds for the L-H and H-L transitions and (10) the width of the edge pedestals. The various components of the calculation model are coupled and must be iterated to a self-consistent convergence. The model was developed over several years for the purpose of interpreting various edge phenomena observed in DIII-D experiments and thereby, to some extent, has been benchmarked against experiment. Because the model treats the interactions of various phenomena in the core, edge and divertor, yet is computationally efficient, it lends itself to the investigation of the effects of different choices of various edge plasma operating conditions on overall divertor and core plasma performance. Studies of the effect of feeling location and rate, divertor geometry, plasma shape, pumping and over 'edge parameters' on core plasma properties (line average density, confinement, density limit, etc.) have been performed for DIII-D model problems. A

  20. Edge Equilibrium Code (EEC) For Tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Li, Xujling


    The edge equilibrium code (EEC) described in this paper is developed for simulations of the near edge plasma using the finite element method. It solves the Grad-Shafranov equation in toroidal coordinate and uses adaptive grids aligned with magnetic field lines. Hermite finite elements are chosen for the numerical scheme. A fast Newton scheme which is the same as implemented in the equilibrium and stability code (ESC) is applied here to adjust the grids

  1. Presheath profiles in simulated tokamak edge plasmas

    International Nuclear Information System (INIS)

    LaBombard, B.; Conn, R.W.; Hirooka, Y.; Lehmer, R.; Leung, W.K.; Nygren, R.E.; Ra, Y.; Tynan, G.


    The PISCES plasma surface interaction facility at UCLA generates plasmas with characteristics similar to those found in the edge plasmas of tokamaks. Steady state magnetized plasmas produced by this device are used to study plasma-wall interaction phenomena which are relevant to tokamak devices. We report here progress on some detailed investigations of the presheath region that extends from a wall surface into these /open quotes/simulated tokamak/close quotes/ edge plasma discharges along magnetic field lines

  2. A numerical study of tokamak edge turbulence

    International Nuclear Information System (INIS)

    Hu Shuanghui; Huang Lin; Qiu Xiaoming


    The tokamak edge turbulence which contains resistivity and impurity gradients and impurity radiation driven sources is studied numerically. The effect of ohmic dissipation on the evolution and saturation of this turbulence is investigated. The ohmic effect drops the saturation levels of fluctuations efficiently in high density tokamaks (such as Alcator), indicating that the ohmic effect plays an important role in the evolution of tokamak edge turbulence in high density devices

  3. Interface band alignment in high-k gate stacks (United States)

    Eric, Bersch; Hartlieb, P.


    In order to successfully implement alternate high-K dielectric materials into MOS structures, the interface properties of MOS gate stacks must be better understood. Dipoles that may form at the metal/dielectric and dielectric/semiconductor interfaces make the band offsets difficult to predict. We have measured the conduction and valence band densities of states for a variety MOS stacks using in situ using inverse photoemission (IPE) and photoemission spectroscopy (PES), respectively. Results obtained from clean and metallized (with Ru or Al) HfO2/Si, SiO2/Si and mixed silicate films will be presented. IPE indicates a shift of the conduction band minimum (CBM) to higher energy (i.e. away from EF) with increasing SiO2. The effect of metallization on the location of band edges depends upon the metal species. The addition of N to the dielectrics shifts the CBM in a way that is thickness dependent. Possible mechanisms for these observed effects will be discussed.

  4. Band gap engineering via doping: A predictive approach

    Energy Technology Data Exchange (ETDEWEB)

    Andriotis, Antonis N., E-mail: [Institute of Electronic Structure and Laser, FORTH, P.O. Box 1527, 71110 Heraklio, Crete (Greece); Menon, Madhu, E-mail: [Department of Physics and Astronomy and Center for Computational Sciences, University of Kentucky, Lexington, Kentucky 40506 (United States)


    We employ an extension of Harrison's theory at the tight binding level of approximation to develop a predictive approach for band gap engineering involving isovalent doping of wide band gap semiconductors. Our results indicate that reasonably accurate predictions can be achieved at qualitative as well as quantitative levels. The predictive results were checked against ab initio ones obtained at the level of DFT/SGGA + U approximation. The minor disagreements between predicted and ab initio results can be attributed to the electronic processes not incorporated in Harrison's theory. These include processes such as the conduction band anticrossing [Shan et al., Phys. Rev. Lett. 82, 1221 (1999); Walukiewicz et al., Phys. Rev. Lett. 85, 1552 (2000)] and valence band anticrossing [Alberi et al., Phys. Rev. B 77, 073202 (2008); Appl. Phys. Lett. 92, 162105 (2008); Appl. Phys. Lett. 91, 051909 (2007); Phys. Rev. B 75, 045203 (2007)], as well as the multiorbital rehybridization. Another cause of disagreement between the results of our predictive approach and the ab initio ones is shown to be the result of the shift of Fermi energy within the impurity band formed at the edge of the valence band maximum due to rehybridization. The validity of our approach is demonstrated with example applications for the systems GaN{sub 1−x}Sb{sub x}, GaP{sub 1−x}Sb{sub x}, AlSb{sub 1−x}P{sub x}, AlP{sub 1−x}Sb{sub x}, and InP{sub 1−x}Sb{sub x}.

  5. What's happening at the edge of tokamaks

    International Nuclear Information System (INIS)

    Crandall, D.H.


    Handling the power deposition at the walls of a plasma fusion device and controlling the particle fueling of the plasma originated the interest in the edge of the plasma by magnetic fusion scientists. Recently this interest has intensified because of clear evidence that the quality of the central plasma confinement depends in unexpected ways on details of how the edge plasma is managed. Significant efforts are being pursued to understand and exploit the improved plasma confinement observed in the 'H-mode' obtained with divertors and in the 'super-shots' obtained with low neutral particle flux from the edge of TFTR limiter plasmas. The controls, that determine whether or not these well-confined plasmas are obtained, are applied in the edge plasma where a wealth of atomic and molecular processes occur. A qualitative overview of current research related to plasma edge and desirable features is presented to guide thoughts about atomic processes to be included in modeling and interpreting the plasma edge of tokamaks. (orig.)

  6. Edge effect correction using ion beam figuring. (United States)

    Yang, Bing; Xie, Xuhui; Li, Furen; Zhou, Lin


    The edge effect is regarded as one of the most difficult technical issues for fabricating large primary mirrors, as it can greatly reduce the key performance of the optical system. Ion beam figuring (IBF) has the advantage of no edge effect, so we can use it to remove high points on the edge and improve surface accuracy. The edge local correction method (ELCM) of IBF processes only the surface edge zone, and is very different from the current full caliber figuring method (FCFM). Therefore, it is necessary to study the ELCM of IBF. In this paper, the key factors of ELCM are analyzed, such as dwell time algorithm, edge data extension methods, and the outward dimension of the starting figuring point. At the same time, the distinctions between ELCM and FCFM are compared. Finally, a 142 mm diameter fused silica mirror is fabricated to verify the validity of the theoretical of ELCM. The experimental results indicate that the figuring precision and efficiency can be obviously improved by ELCM.

  7. Influence of a falling edge on high power microwave pulse combination (United States)

    Li, Jiawei; Huang, Wenhua; Zhu, Qi; Xiao, Renzhen; Shao, Hao


    This paper presents an explanation of the influence of a microwave falling edge on high-power microwave pulse combination. Through particle-in-cell simulations, we discover that the falling edge is the driving factor that limits the output power of the combined pulses. We demonstrate that the space charge field, which accumulates to become comparable to the E-field at the falling edge of the former pulse, will trap the electrons in the gas layer and decrease its energy to attain a high ionization rate. Hence, avalanche discharge, caused by trapped electrons, makes the plasma density to approach the critical density and cuts off the latter microwave pulse. An X-band combination experiment is conducted with different pulse intervals. This experiment confirms that the high density plasma induced by the falling edge can cut off the latter pulse, and that the time required for plasma recombination in the transmission channel is several microseconds. To ensure a high output power for combined pulses, the latter pulse should be moved ahead of the falling edge of the former one, and consequently, a beat wave with high peak power becomes the output by adding two pulses with normal amplitudes.

  8. Topologically protected edge states for out-of-plane and in-plane bulk elastic waves (United States)

    Huo, Shao-Yong; Chen, Jiu-Jiu; Huang, Hong-Bo


    Topological phononic insulators (TPnIs) show promise for application in the manipulation of acoustic waves for the design of low-loss transmission and perfectly integrated communication devices. Since solid phononic crystals exist as a transverse polarization mode and a mixed longitudinal-transverse polarization mode, the realization of topological edge states for both out-of-plane and in-plane bulk elastic waves is desirable to enhance the controllability of the edge waves in solid systems. In this paper, a two-dimensional (2D) solid/solid hexagonal-latticed phononic system that simultaneously supports the topologically protected edge states for out-of-plane and in-plane bulk elastic waves is investigated. Firstly, two pairs of two-fold Dirac cones, respectively corresponding to the out-of-plane and in-plane waves, are obtained at the same frequency by tuning the crystal parameters. Then, a strategy of zone folding is invoked to form double Dirac cones. By shrinking and expanding the steel scatterer, the lattice symmetry is broken, and band inversions induced, giving rise to an intriguing topological phase transition. Finally, the topologically protected edge states for both out-of-plane and in-plane bulk elastic waves, which can be simultaneously located at the frequency range from 1.223 to 1.251 MHz, are numerically observed. Robust pseudospin-dependent elastic edge wave propagation along arbitrary paths is further demonstrated. Our results will significantly broaden its practical application in the engineering field.

  9. Edge-Dependent Electronic and Magnetic Characteristics of Freestanding β 12-Borophene Nanoribbons (United States)

    Izadi Vishkayi, Sahar; Bagheri Tagani, Meysam


    This work presents an investigation of nanoribbons cut from β 12-borophene sheets by applying the density functional theory. In particular, the electronic and magnetic properties of borophene nanoribbons (BNR) are studied. It is found that all the ribbons considered in this work behave as metals, which is in good agreement with the recent experimental results. β 12-BNR has significant diversity due to the existence of five boron atoms in a unit cell of the sheet. The magnetic properties of the ribbons are strongly dependent on the cutting direction and edge profile. It is interesting that a ribbon with a specific width can behave as a normal or a ferromagnetic metal with magnetization at just one edge or two edges. Spin anisotropy is observed in some ribbons, and the magnetic moment is not found to be the same in both edges in an antiferromagnetic configuration. This effect stems from the edge asymmetry of the ribbons and results in the breaking of spin degeneracy in the band structure. Our findings show that β 12 BNRs are potential candidates for next-generation spintronic devices. [Figure not available: see fulltext.

  10. Edge subdivision and edge multisubdivision versus some domination related parameters in generalized corona graphs

    Directory of Open Access Journals (Sweden)

    Magda Dettlaff


    Full Text Available Given a graph \\(G=(V,E\\, the subdivision of an edge \\(e=uv\\in E(G\\ means the substitution of the edge \\(e\\ by a vertex \\(x\\ and the new edges \\(ux\\ and \\(xv\\. The domination subdivision number of a graph \\(G\\ is the minimum number of edges of \\(G\\ which must be subdivided (where each edge can be subdivided at most once in order to increase the domination number. Also, the domination multisubdivision number of \\(G\\ is the minimum number of subdivisions which must be done in one edge such that the domination number increases. Moreover, the concepts of paired domination and independent domination subdivision (respectively multisubdivision numbers are defined similarly. In this paper we study the domination, paired domination and independent domination (subdivision and multisubdivision numbers of the generalized corona graphs.

  11. Closed-edged bilayer phosphorene nanoribbons producing from collapsing armchair phosphorene nanotubes (United States)

    Liao, Xiangbiao; Xiao, Hang; Lu, Xiaobo; Chen, Youlong; Shi, Xiaoyang; Chen, Xi


    A new phosphorous allotrope, closed-edged bilayer phosphorene nanoribbon, is proposed via radially deforming armchair phosphorene nanotubes. Using molecular dynamics simulations, the transformation pathway from round PNTs falls into two types of collapsed structures: arc-like and sigmoidal bilayer nanoribbons, dependent on the number of phosphorene unit cells. The fabricated nanoribbions are energetically more stable than their parent nanotubes. It is also found via ab initio calculations that the band structure along tube axis substantially changes with the structural transformation. The direct-to-indirect transition of band gap is highlighted when collapsing into the arc-like nanoribbons but not the sigmoidal ones. Furthermore, the band gaps of these two types of nanoribbons show significant size-dependence of the nanoribbon width, indicative of wider tunability of their electrical properties.

  12. Valence-band splitting energies in wurtzite InP nanowires: Photoluminescence spectroscopy and ab initio calculations (United States)

    Gadret, E. G.; Dias, G. O.; Dacal, L. C. O.; de Lima, M. M., Jr.; Ruffo, C. V. R. S.; Iikawa, F.; Brasil, M. J. S. P.; Chiaramonte, T.; Cotta, M. A.; Tizei, L. H. G.; Ugarte, D.; Cantarero, A.


    We investigated experimentally and theoretically the valence-band structure of wurtzite InP nanowires. The wurtzite phase, which usually is not stable for III-V phosphide compounds, has been observed in InP nanowires. We present results on the electronic properties of these nanowires using the photoluminescence excitation technique. Spectra from an ensemble of nanowires show three clear absorption edges separated by 44 meV and 143 meV, respectively. The band edges are attributed to excitonic absorptions involving three distinct valence-bands labeled: A, B, and C. Theoretical results based on “ab initio” calculation gives corresponding valence-band energy separations of 50 meV and 200 meV, respectively, which are in good agreement with the experimental results.

  13. Evidence for Topological Edge States in a Large Energy Gap near the Step Edges on the Surface of ZrTe_{5}

    Directory of Open Access Journals (Sweden)

    R. Wu


    Full Text Available Two-dimensional topological insulators with a large bulk band gap are promising for experimental studies of quantum spin Hall effect and for spintronic device applications. Despite considerable theoretical efforts in predicting large-gap two-dimensional topological insulator candidates, none of them have been experimentally demonstrated to have a full gap, which is crucial for quantum spin Hall effect. Here, by combining scanning tunneling microscopy/spectroscopy and angle-resolved photoemission spectroscopy, we reveal that ZrTe_{5} crystal hosts a large full gap of ∼100  meV on the surface and a nearly constant density of states within the entire gap at the monolayer step edge. These features are well reproduced by our first-principles calculations, which point to the topologically nontrivial nature of the edge states.

  14. Losing your edge: climate change and the conservation value of range-edge populations. (United States)

    Rehm, Evan M; Olivas, Paulo; Stroud, James; Feeley, Kenneth J


    Populations occurring at species' range edges can be locally adapted to unique environmental conditions. From a species' perspective, range-edge environments generally have higher severity and frequency of extreme climatic events relative to the range core. Under future climates, extreme climatic events are predicted to become increasingly important in defining species' distributions. Therefore, range-edge genotypes that are better adapted to extreme climates relative to core populations may be essential to species' persistence during periods of rapid climate change. We use relatively simple conceptual models to highlight the importance of locally adapted range-edge populations (leading and trailing edges) for determining the ability of species to persist under future climates. Using trees as an example, we show how locally adapted populations at species' range edges may expand under future climate change and become more common relative to range-core populations. We also highlight how large-scale habitat destruction occurring in some geographic areas where many species range edge converge, such as biome boundaries and ecotones (e.g., the arc of deforestation along the rainforest-cerrado ecotone in the southern Amazonia), can have major implications for global biodiversity. As climate changes, range-edge populations will play key roles in helping species to maintain or expand their geographic distributions. The loss of these locally adapted range-edge populations through anthropogenic disturbance is therefore hypothesized to reduce the ability of species to persist in the face of rapid future climate change.

  15. Living on the Edge: Parasite Prevalence Changes Dramatically across a Range Edge in an Invasive Gecko. (United States)

    Coates, Andrew; Barnett, Louise K; Hoskin, Conrad; Phillips, Ben L


    Species interactions can determine range limits, and parasitism is the most intimate of such interactions. Intriguingly, the very conditions on range edges likely change host-parasite dynamics in nontrivial ways. Range edges are often associated with clines in host density and with environmental transitions, both of which may affect parasite transmission. On advancing range edges, founder events and fitness/dispersal costs of parasitism may also cause parasites to be lost on range edges. Here we examine the prevalence of three species of parasite across the range edge of an invasive gecko, Hemidactylus frenatus, in northeastern Australia. The gecko's range edge spans the urban-woodland interface at the edge of urban areas. Across this edge, gecko abundance shows a steep decline, being lower in the woodland. Two parasite species (a mite and a pentastome) are coevolved with H. frenatus, and these species become less prevalent as the geckos become less abundant. A third species of parasite (another pentastome) is native to Australia and has no coevolutionary history with H. frenatus. This species became more prevalent as the geckos become less abundant. These dramatic shifts in parasitism (occurring over 3.5 km) confirm that host-parasite dynamics can vary substantially across the range edge of this gecko host.

  16. Controllable Absorption and Dispersion Properties of an RF-driven Five-Level Atom in a Double-Band Photonic-Band-Gap Material

    International Nuclear Information System (INIS)

    Ding Chunling; Li Jiahua; Yang Xiaoxue


    The probe absorption-dispersion spectra of a radio-frequency (RF)-driven five-level atom embedded in a photonic crystal are investigated by considering the isotropic double-band photonic-band-gap (PBG) reservoir. In the model used, the two transitions are, respectively, coupled by the upper and lower bands in such a PBG material, thus leading to some curious phenomena. Numerical simulations are performed for the optical spectra. It is found that when one transition frequency is inside the band gap and the other is outside the gap, there emerge three peaks in the absorption spectra. However, for the case that two transition frequencies lie inside or outside the band gap, the spectra display four absorption profiles. Especially, there appear two sharp peaks in the spectra when both transition frequencies exist inside the band gap. The influences of the intensity and frequency of the RF-driven field on the absorptive and dispersive response are analyzed under different band-edge positions. It is found that a transparency window appears in the absorption spectra and is accompanied by a very steep variation of the dispersion profile by adjusting system parameters. These results show that the absorption-dispersion properties of the system depend strongly on the RF-induced quantum interference and the density of states (DOS) of the PBG reservoir. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

  17. Multidimensional EMD-based edge detection and the application to GPR imaging (United States)

    Jeng, Yih; Chen, Chih-Sung; Chen, Sung-Chih


    The edge detection is an effective approach in identifying object boundaries within a digital image. In recent years, it has been introduced to process geophysical data in the hope of enhancing the target boundary and improving the delineation of geological structures. However, most successful cases are applications to potential-field data. For GPR imaging, the edge detection is an emerging technique, and much effort is needed to make this method become an essential GPR data processing component. The major difficulty of applying edge detection to GPR data is that the GPR profile is orientation dependent, and a method successful in processing the digital image or potential-field data may not have the same achievement in GPR. Another concern for applying the edge detection is that the data must have acceptable signal-to-noise ratios, but the signal enhancement in GPR imaging has not been completely solved yet. In this study, we introduce a multidimensional EMD-based edge detection which can reduce the mentioned difficulties and improve the effect of edge detection. The proposed scheme suggests that the GPR data are pre-processed and reconstructed by using the multidimensional EMD to enhance the signal to noise ratio. This procedure is decisive because the adaptability of the EMD decomposition and the dyadic nature of the EMD components both allow the reconstructed data to have less noise and retain more signal than using conventional filters. In addition, the multidimensional EMD is efficient in identifying structure in different directions, which is suitable for processing orientation dependent data. Moreover, all the advantages gained in the multidimensional EMD do not rely on any prerequisite knowledge of the noise frequency band. After the multidimensional EMD process, we then apply the edge detection to the reconstructed data for the final interpretation. With the typical model study, the proposed scheme is also tested on the GPR data acquired in a buried hot

  18. William Band at Yenching University (United States)

    Hu, Danian


    William Band (1906-1993) has been widely remembered by his American colleagues and students as ``a fine physicist and teacher,'' who taught at Washington State University in Pullman between 1949 and 1971 and authored Introduction to Quantum Statistics (1954) and Introduction to Mathematical Physics (1959). Not many, however, knew much about Band's early career, which was very ``uncommon and eventful.'' Born in England, Band graduated from University of Liverpool in 1927 with an MsSc degree in physics. Instead of pursuing his Ph.D. at Cambridge, he chose to teach physics at Yenching University, a prestigious Christian university in Beijing, China. Arriving in 1929, Band established his career at Yenching, where he taught and researched the theory of relativity and quantum mechanics, pioneered the study on low-temperature superconductivity in China, founded the country's first graduate program in physics, and chaired the Physics Department for 10 years until he fled from Yenching upon hearing of the attack on Pearl Harbor. It took him two years to cross Japanese occupied areas under the escort of the Communist force; he left China in early 1945. This presentation will explore Band's motivation to work in China and his contributions to the Chinese physics research and education.

  19. Edge Modeling by Two Blur Parameters in Varying Contrasts. (United States)

    Seo, Suyoung


    This paper presents a method of modeling edge profiles with two blur parameters, and estimating and predicting those edge parameters with varying brightness combinations and camera-to-object distances (COD). First, the validity of the edge model is proven mathematically. Then, it is proven experimentally with edges from a set of images captured for specifically designed target sheets and with edges from natural images. Estimation of the two blur parameters for each observed edge profile is performed with a brute-force method to find parameters that produce global minimum errors. Then, using the estimated blur parameters, actual blur parameters of edges with arbitrary brightness combinations are predicted using a surface interpolation method (i.e., kriging). The predicted surfaces show that the two blur parameters of the proposed edge model depend on both dark-side edge brightness and light-side edge brightness following a certain global trend. This is similar across varying CODs. The proposed edge model is compared with a one-blur parameter edge model using experiments of the root mean squared error for fitting the edge models to each observed edge profile. The comparison results suggest that the proposed edge model has superiority over the one-blur parameter edge model in most cases where edges have varying brightness combinations.

  20. Band Structure Analysis of La0.7Sr0.3MnO3 Perovskite Manganite Using a Synchrotron

    Directory of Open Access Journals (Sweden)

    Hong-Sub Lee


    Full Text Available Oxide semiconductors and their application in next-generation devices have received a great deal of attention due to their various optical, electric, and magnetic properties. For various applications, an understanding of these properties and their mechanisms is also very important. Various characteristics of these oxides originate from the band structure. In this study, we introduce a band structure analysis technique using a soft X-ray energy source to study a La0.7Sr0.3MnO3 (LSMO oxide semiconductor. The band structure is formed by a valence band, conduction band, band gap, work function, and electron affinity. These can be determined from secondary electron cut-off, valence band spectrum, O 1s core electron, and O K-edge measurements using synchrotron radiation. A detailed analysis of the band structure of the LSMO perovskite manganite oxide semiconductor thin film was established using these techniques.

  1. Robust band gap and half-metallicity in graphene with triangular perforations

    DEFF Research Database (Denmark)

    Gregersen, Søren Schou; Power, Stephen; Jauho, Antti-Pekka


    . The inclusion of spin polarization within a mean-field Hubbard approach gives rise to a large overall magnetic moment at each antidot due to the sublattice imbalance imposed by the triangular geometry. Half-metallic behavior arises from the formation of spin-split dispersive states near the Fermi energy...... disorders. Here we study a rectangular array of triangular antidots with zigzag edge geometries and show that their band gap behavior qualitatively differs from the standard behavior which is exhibited, e.g., by rectangular arrays of armchair-edged triangles. In the spin unpolarized case, zigzag......, and furthermore, of exploiting the strong spin dependence of the system for spintronic applications....

  2. Acyclicity in edge-colored graphs

    DEFF Research Database (Denmark)

    Gutin, Gregory; Jones, Mark; Sheng, Bin


    A walk W in edge-colored graphs is called properly colored (PC) if every pair of consecutive edges in W is of different color. We introduce and study five types of PC acyclicity in edge-colored graphs such that graphs of PC acyclicity of type i is a proper superset of graphs of acyclicity of type i......+1, i=1,2,3,4. The first three types are equivalent to the absence of PC cycles, PC closed trails, and PC closed walks, respectively. While graphs of types 1, 2 and 3 can be recognized in polynomial time, the problem of recognizing graphs of type 4 is, somewhat surprisingly, NP-hard even for 2-edge-colored...... graphs (i.e., when only two colors are used). The same problem with respect to type 5 is polynomial-time solvable for all edge-colored graphs. Using the five types, we investigate the border between intractability and tractability for the problems of finding the maximum number of internally vertex...

  3. Trailing edge modifications for flatback airfoils.

    Energy Technology Data Exchange (ETDEWEB)

    Kahn, Daniel L. (University of California, Davis, CA); van Dam, C.P. (University of California, Davis, CA); Berg, Dale E.


    The adoption of blunt trailing edge airfoils (also called flatback airfoils) for the inboard region of large wind turbine blades has been proposed. Blunt trailing edge airfoils would not only provide a number of structural benefits, such as increased structural volume and ease of fabrication and handling, but they have also been found to improve the lift characteristics of thick airfoils. Therefore, the incorporation of blunt trailing edge airfoils would allow blade designers to more freely address the structural demands without having to sacrifice aerodynamic performance. These airfoils do have the disadvantage of generating high levels of drag as a result of the low-pressure steady or periodic flow in the near-wake of the blunt trailing edge. Although for rotors, the drag penalty appears secondary to the lift enhancement produced by the blunt trailing edge, high drag levels are of concern in terms of the negative effect on the torque and power generated by the rotor. Hence, devices are sought that mitigate the drag of these airfoils. This report summarizes the literature on bluff body vortex shedding and bluff body drag reduction devices and proposes four devices for further study in the wind tunnel.

  4. Photoionization bands of rubidium molecule (United States)

    Rakić, M.; Pichler, G.


    We studied the absorption spectrum of dense rubidium vapor generated in a T-type sapphire cell with a special emphasis on the structured photoionization continuum observed in the 200-300 nm spectral region. The photoionization spectrum has a continuous atomic contribution with a pronounced Seaton-Cooper minimum at about 250 nm and a molecular photoionization contribution with many broad bands. We discuss the possible origin of the photoionization bands as stemming from the absorption from the ground state of the Rb2 molecule to excited states of Rb2+* and to doubly excited autoionizing states of Rb2** molecule. All these photoionization bands are located above the Rb+ and Rb2+ ionization limits.

  5. Measured intrinsic defect density throughout the entire band gap at the Si/SiO2 interface (United States)

    Sands, D.; Brunson, K. M.; Tayarani-Najaran, M. H.


    Conductance-frequency measurements down to temperatures of 100 K have been performed on both p-type and n-type silicon oxidized in dry oxygen at 900 degrees C. The metal electrode capacitors used were not given a post-metallization anneal in forming gas. This has allowed measurements of the intrinsic density of states, capture cross section, and surface potential fluctuations to within 0.06 eV of the band edges. Two peaks in the defect density at energies of 0.3 eV and 0.85 eV above the valence band are clearly visible above an asymmetric background, which rises rapidly towards the conduction band edge. The capture cross section is near constant at approximately 1016 cm2 across the gap and independent of temperature. The surface potential fluctuations reveal a peak value of approximately 70 meV centred at 0.4 eV above the valence band superimposed on a constant background of approximately 40 meV. The authors attribute the peaks in the density of states to the amphoteric trivalent silicon Pb centres. The probable causes of the asymmetric background are either the tail of a defect peak centred around the conduction band edge, or states descending from the conduction band induced by stress within the oxide.

  6. Band-in-band segregation of multidisperse granular mixtures

    NARCIS (Netherlands)

    Newey, M.; Ozik, J.; van der Meer, S.M.


    Radial and axial segregation is investigated experimentally in polydisperse mixtures of granular materials rotated in a long, partly filled, horizontal cylinder. Radial segregation by size is observed in all polydisperse mixtures. Axial segregation, with smaller-size particles forming bands within

  7. Radiology of vertical banded gastroplasty

    International Nuclear Information System (INIS)

    Leekam, R.N.; Deitel, M.; Shankar, L.; Salsberg, B.


    Vertical banded gastroplasty is now the most common procedure for the surgical treatment of obesity. In the past 4 years 120 patients have been referred for radiologic examination. This exhibit describes the normal and abnormal findings in many of these patients. The authors divided radiologic abnormalities into three groups: abnormalities of the partition, abnormalities of the banded channel, and ulcers and extragastric leaks. The authors' examination technique has been adapted from those described by others, our important addition being the preliminary precontrast film, on which the staple lines can be examined. This has proved most effective in the detection of partition defects

  8. Understanding the shrinkage of optical absorption edges of nanostructured Cd-Zn sulphide films for photothermal applications

    Energy Technology Data Exchange (ETDEWEB)

    Hossain, Md. Sohrab [Department of Physics, Jahangirnagar University, Savar, Dhaka 1342 (Bangladesh); Kabir, Humayun [Department of Physics, Jahangirnagar University, Savar, Dhaka 1342 (Bangladesh); School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Rahman, M. Mahbubur, E-mail: [Department of Physics, Jahangirnagar University, Savar, Dhaka 1342 (Bangladesh); Surface Analysis and Materials Engineering Research Group, School of Engineering & Information Technology, Murdoch University, Perth, Western Australia 6150 (Australia); Hasan, Kamrul [Department of Chemistry, College of Sciences, University of Sharjah, P.O. Box 27272, Sharjah (United Arab Emirates); Bashar, Muhammad Shahriar; Rahman, Mashudur [Institute of Fuel and Research Development, Bangladesh Council for Scientific and Industrial Research, Dhanmondi, Dhaka (Bangladesh); Gafur, Md. Abdul [Pilot Plant and Process Development Center, Bangladesh Council for Scientific and Industrial Research, Dhanmondi, Dhaka (Bangladesh); Islam, Shariful [Department of Physics, Comilla University, Comilla (Bangladesh); Amri, Amun [Department of Chemical Engineering, Universitas Riau, Pekanbaru (Indonesia); Jiang, Zhong-Tao [Surface Analysis and Materials Engineering Research Group, School of Engineering & Information Technology, Murdoch University, Perth, Western Australia 6150 (Australia); Altarawneh, Mohammednoor; Dlugogorski, Bogdan Z. [School of Engineering & Information Technology, Murdoch University, Murdoch, WA 6150 (Australia)


    Highlights: • Cd-Zn sulphide films synthesized via chemical bath deposition technique. • Nanocrystalline phase of Cd-Zn sulphide films were seen in XRD studies. • Nanocrystalline structures of the films were also confirmed by the SEM. • The band gap of these films is a combination of composition and size. • E{sub U} and σ studies ascribed the shrinkage of absorption edges around the optical band-gaps. - Abstract: In this article Cd-Zn sulphide thin films deposited onto soda lime glass substrates via chemical bath deposition (CBD) technique were investigated for photovoltaic applications. The synthesized films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet visible (UV–vis) spectroscopic methodologies. A higher degree of crystallinity of the films was attained with the increase of film thicknesses. SEM micrographs exhibited a partial crystalline structure with a particulate appearance surrounded by the amorphous grain boundaries. The optical absorbance and absorption coefficient of the films were also enhanced significantly with the increase in film thicknesses. Optical band-gap analysis indicated a monotonic decrease in direct and indirect band-gaps with the increase of thicknesses of the films. The presence of direct and indirect transitional energies due to the exponential falling edges of the absorption curves may either be due to the lack of long-range order or to the existence of defects in the films. The declination of the optical absorption edges was also confirmed via Urbach energy and steepness parameters studies.

  9. Contrast edge colors under different natural illuminations. (United States)

    Nieves, Juan Luis; Nascimento, Sérgio M C; Romero, Javier


    Essential to sensory processing in the human visual system is natural illumination, which can vary considerably not only across space but also along the day depending on the atmospheric conditions and the sun's position in the sky. In this work, edges derived from the three postreceptoral Luminance, Red-Green, and Blue-Yellow signals were computed from hyperspectral images of natural scenes rendered with daylights of Correlated Color Temperatures (CCTs) from 2735 to 25,889 K; for low CCT, the same analysis was performed using Planckian illuminants up to 800 K. It was found that average luminance and chromatic edge contrasts were maximal for low correlated color temperatures and almost constants above 10,000 K. The magnitude of these contrast changes was, however, only about 2% across the tested daylights. Results suggest that the postreceptoral opponent and nonopponent color vision mechanisms produce almost constant responses for color edge detection under natural illumination. © 2012 Optical Society of America

  10. Edge effects in composites by moire interferometry (United States)

    Czarnek, R.; Post, D.; Herakovich, C.


    The very high sensitivity of moire interferometry has permitted the present edge effect experiments to be conducted at a low average stress and strain level, assuring linear and elastic behavior in the composite material samples tested. Sensitivity corresponding to 2450 line/mm moire was achieved with a 0.408 micron/fringe. Simultaneous observations of the specimen face and edge displacement fields showed good fringe definition despite the 1-mm thickness of the specimens and the high gradients, and it is noted that the use of a carrier pattern and optical filtering was effective in even these conditions. Edge effects and dramatic displacement gradients were confirmed in angle-ply composite laminates.

  11. Free edge effects in laminated composites (United States)

    Herakovich, C. T.


    The fundamental mechanics of free-edge effects in laminated fiber-reinforced composites is examined, reviewing the results of recent experimental and analytical investigations. The derivation of the governing equations for the basic problem is outlined, including the equilibrium and mismatch conditions and the elasticity formulation, and experimental data on axial displacement and shear strain in angle-ply laminates are summarized. Numerical predictions of free-edge deformation and interlaminar and through-thickness stress distributions are presented for cross-ply, angle-ply, and quasi-isotropic laminates, and the mechanisms of edge damage and failure in angle-ply laminates are briefly characterized. Extensive diagrams, drawings, graphs, and photographs are provided.

  12. Edge Detection in Landing Budgerigars (Melopsittacus undulatus) (United States)

    Bhagavatula, Partha; Claudianos, Charles; Ibbotson, Michael; Srinivasan, Mandyam


    Background While considerable scientific effort has been devoted to studying how birds navigate over long distances, relatively little is known about how targets are detected, obstacles are avoided and smooth landings are orchestrated. Here we examine how visual features in the environment, such as contrasting edges, determine where a bird will land. Methodology/Principal Findings Landing in budgerigars (Melopsittacus undulatus) was investigated by training them to fly from a perch to a feeder, and video-filming their landings. The feeder was placed on a grey disc that produced a contrasting edge against a uniformly blue background. We found that the birds tended to land primarily at the edge of the disc and walk to the feeder, even though the feeder was in the middle of the disc. This suggests that the birds were using the visual contrast at the boundary of the disc to target their landings. When the grey level of the disc was varied systematically, whilst keeping the blue background constant, there was one intermediate grey level at which the budgerigar's preference for the disc boundary disappeared. The budgerigars then landed randomly all over the test surface. Even though this disc is (for humans) clearly distinguishable from the blue background, it offers very little contrast against the background, in the red and green regions of the spectrum. Conclusions We conclude that budgerigars use visual edges to target and guide landings. Calculations of photoreceptor excitation reveal that edge detection in landing budgerigars is performed by a color-blind luminance channel that sums the signals from the red and green photoreceptors, or, alternatively, receives input from the red double-cones. This finding has close parallels to vision in honeybees and primates, where edge detection and motion perception are also largely color-blind. PMID:19809500

  13. Edge detection in landing budgerigars (Melopsittacus undulatus.

    Directory of Open Access Journals (Sweden)

    Partha Bhagavatula

    Full Text Available BACKGROUND: While considerable scientific effort has been devoted to studying how birds navigate over long distances, relatively little is known about how targets are detected, obstacles are avoided and smooth landings are orchestrated. Here we examine how visual features in the environment, such as contrasting edges, determine where a bird will land. METHODOLOGY/PRINCIPAL FINDINGS: Landing in budgerigars (Melopsittacus undulatus was investigated by training them to fly from a perch to a feeder, and video-filming their landings. The feeder was placed on a grey disc that produced a contrasting edge against a uniformly blue background. We found that the birds tended to land primarily at the edge of the disc and walk to the feeder, even though the feeder was in the middle of the disc. This suggests that the birds were using the visual contrast at the boundary of the disc to target their landings. When the grey level of the disc was varied systematically, whilst keeping the blue background constant, there was one intermediate grey level at which the budgerigar's preference for the disc boundary disappeared. The budgerigars then landed randomly all over the test surface. Even though this disc is (for humans clearly distinguishable from the blue background, it offers very little contrast against the background, in the red and green regions of the spectrum. CONCLUSIONS: We conclude that budgerigars use visual edges to target and guide landings. Calculations of photoreceptor excitation reveal that edge detection in landing budgerigars is performed by a color-blind luminance channel that sums the signals from the red and green photoreceptors, or, alternatively, receives input from the red double-cones. This finding has close parallels to vision in honeybees and primates, where edge detection and motion perception are also largely color-blind.

  14. Photoelectric interaction around the K edge

    International Nuclear Information System (INIS)

    Murty, V.R.K.; Rao, K.S.; Parthasaradhi, K.; Rao, J.R.; Lakshminarayana, V.


    Total photon cross sections are determined around the K edges of four elements Cu, Sn, Pb and U using a Ge(Li) detector, argon and krypton proportional counters on a 'good geometry' set-up. The total photoelectric cross sections are extracted by subtracting the small scattering contribution from the total photon cross sections. Total-to-K-shell photoelectric cross section ratios (K-jump ratios) are evaluated by extrapolating the total photon cross section data to the K edge. An analysis of the data is presented. (author)

  15. Plasma edge modelling with ICRF coupling

    Directory of Open Access Journals (Sweden)

    Zhang Wei


    Full Text Available The physics of Radio-Frequency (RF wave heating in the Ion Cyclotron Range of Frequencies (ICRF in the core plasmas of fusion devices are relatively well understood while those in the Scrape-Off Layer (SOL remain still unresolved. This paper is dedicated to study the ICRF interactions with the plasma edge, mainly from the theoretical and numerical point of view, in particular with the 3D edge plasma fluid and neutral transport code EMC3-EIRENE and various wave codes. Here emphasis is given to the improvement of ICRF coupling with local gas puffing and to the ICRF induced density convection in the SOL.

  16. Multi-scale Regions from Edge Fragments

    DEFF Research Database (Denmark)

    Kazmi, Wajahat; Andersen, Hans Jørgen


    In this article we introduce a novel method for detecting multi-scale salient regions around edges using a graph based image compression algorithm. Images are recursively decomposed into triangles arranged into a binary tree using linear interpolation. The entropy of any local region of the image...... to estimate regions. Salient regions are thus formed as stable regions around edges. Tree hierarchy is then used to generate multi-scale regions. We evaluate our detector by performing image retrieval tests on our building database which shows that combined with Spin Images (Lazebnik et al., 2003...

  17. AliEn - EDG Interoperability in ALICE


    Bagnasco, S.; Barbera, R.; Buncic, P.; Carminati, F.; Cerello, P.; Saiz, P.


    AliEn (ALICE Environment) is a GRID-like system for large scale job submission and distributed data management developed and used in the context of ALICE, the CERN LHC heavy-ion experiment. With the aim of exploiting upcoming Grid resources to run AliEn-managed jobs and store the produced data, the problem of AliEn-EDG interoperability was addressed and an in-terface was designed. One or more EDG (European Data Grid) User Interface machines run the AliEn software suite (Cluster Monitor, Stora...

  18. Correlations in a band insulator

    Czech Academy of Sciences Publication Activity Database

    Sentef, M.; Kuneš, Jan; Werner, P.; Kampf, A. P.


    Roč. 80, č. 15 (2009), 155116/1-155116/7 ISSN 1098-0121 Institutional research plan: CEZ:AV0Z10100521 Keywords : electronic correlations * dynamical mean-field theory * band insulator Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.475, year: 2009

  19. Metaphyseal bands in osteogenesis imperfecta

    Directory of Open Access Journals (Sweden)

    Suresh S


    Full Text Available An increasing number of patients with osteogenesis imperfecta are undergoing pamidronate therapy to prevent the incidence of fragility fractures. The authors herein report a child aged 3 years who received five cycles of pamidronate, resulting in metaphyseal bands, known as "zebra lines."

  20. Singing in the Band Rehearsal. (United States)

    Wolbers, Mark


    Explains how singing can be incorporated into the band rehearsal. Discusses how to improve student aural skills by including singing in the rehearsal and the benefits of having students sing. Describes how music teachers can use songs or chorales in the classroom. (CMK)

  1. The edge engineering of topological Bi(111) bilayer


    Li, Xiao; Liu, Hai-Wen; Jiang, Hua; Wang, Fa; Feng, Ji


    A topological insulator is a novel quantum state, characterized by symmetry-protected non-trivial edge/surface states. Our first-principle simulations show the significant effects of the chemical decoration on edge states of topological Bi(111) bilayer nanoribbon, which remove the trivial edge state and recover the Dirac linear dispersion of topological edge state. By comparing the edge states with and without chemical decoration, the Bi(111) bilayer nanoribbon offers a simple system for asse...

  2. [An object-oriented remote sensing image segmentation approach based on edge detection]. (United States)

    Tan, Yu-Min; Huai, Jian-Zhu; Tang, Zhong-Shi


    Satellite sensor technology endorsed better discrimination of various landscape objects. Image segmentation approaches to extracting conceptual objects and patterns hence have been explored and a wide variety of such algorithms abound. To this end, in order to effectively utilize edge and topological information in high resolution remote sensing imagery, an object-oriented algorithm combining edge detection and region merging is proposed. Susan edge filter is firstly applied to the panchromatic band of Quickbird imagery with spatial resolution of 0.61 m to obtain the edge map. Thanks to the resulting edge map, a two-phrase region-based segmentation method operates on the fusion image from panchromatic and multispectral Quickbird images to get the final partition result. In the first phase, a quad tree grid consisting of squares with sides parallel to the image left and top borders agglomerates the square subsets recursively where the uniform measure is satisfied to derive image object primitives. Before the merger of the second phrase, the contextual and spatial information, (e. g., neighbor relationship, boundary coding) of the resulting squares are retrieved efficiently by means of the quad tree structure. Then a region merging operation is performed with those primitives, during which the criterion for region merging integrates edge map and region-based features. This approach has been tested on the QuickBird images of some site in Sanxia area and the result is compared with those of ENVI Zoom Definiens. In addition, quantitative evaluation of the quality of segmentation results is also presented. Experiment results demonstrate stable convergence and efficiency.

  3. High Selectivity Dual-Band Bandpass Filter with Tunable Lower Passband

    Directory of Open Access Journals (Sweden)

    Wei-Qiang Pan


    Full Text Available This paper presents a novel method to design dual-band bandpass filters with tunable lower passband and fixed upper passband. It utilizes a trimode resonator with three controllable resonant modes. Discriminating coupling is used to suppress the unwanted mode to avoid the interference. Varactors are utilized to realize tunable responses. The bandwidth of the two bands can be controlled individually. Transmission zeros are generated near the passband edges, resulting in high selectivity. For demonstration, a tunable bandpass filter is implemented. Good agreement between the prediction and measurement validates the proposed method.

  4. Photonic band gap materials: design, synthesis, and applications

    International Nuclear Information System (INIS)

    John, S.


    Full text: Unlike semiconductors which facilitate the coherent propagation of electrons, photonic band gap (PBG) materials execute their novel functions through the coherent localization of photons. I review and discuss our recent synthesis of a large scale three-dimensional silicon photonic crystal with a complete photonic band gap near 1.5 microns. When a PBG material is doped with impurity atoms which have an electronic transition that lies within the gap, spontaneous emission of light from the atom is inhibited. Inside the gap, the photon forms a bound state to the atom. Outside the gap, radiative dynamics in the colored vacuum is highly non Markovian. I discuss the influence of these memory effects on laser action. When spontaneous emission is absent, the next order radiative effect (resonance dipole dipole interaction between atoms) must be incorporated leading to anomalous nonlinear optical effects which occur at a much lower threshold than in ordinary vacuum. I describe the collective switching of two-level atoms near a photonic band edge, by external laser field, from a passive state to one exhibiting population inversion. This effect is forbidden in ordinary vacuum. However, in the context of a PBG material, this effect may be utilized for an all-optical transistor. Finally, I discuss the prospects for a phase sensitive, single atom quantum memory device, onto which information may be written by an external laser pulse

  5. Design of Ka-band antipodal finline mixer and detector

    International Nuclear Information System (INIS)

    Yao Changfei; Xu Jinping; Chen Mo


    This paper mainly discusses the analysis and design of a finline single-ended mixer and detector. In the circuit, for the purpose of eliminating high-order resonant modes and improving transition loss, metallic via holes are implemented along the mounting edge of the substrate embedded in the split-block of the WG-finline-microstrip transition. Meanwhile, a Ka band slow-wave and bandstop filter, which represents a reactive termination, is designed for the utilization of idle frequencies and operation frequencies energy. Full-wave analysis is carried out to optimize the input matching network of the mixer and the detector circuit using lumped elements to model the nonlinear diode. The exported S-matrix of the optimized circuit is used for conversion loss and voltage sensitivity analysis. The lowest measured conversion loss is 3.52 dB at 32.2 GHz; the conversion loss is flat and less than 5.68 dB in the frequency band of 29-34 GHz. The highest measured zero-bias voltage sensitivity is 1450 mV/mW at 38.6 GHz, and the sensitivity is better than 1000 mV/mW in the frequency band of 38-40 GHz.

  6. An Edge-Sensing Predictor in Wavelet Lifting Structures for Lossless Image Coding

    Directory of Open Access Journals (Sweden)

    Ömer N. Gerek


    Full Text Available The introduction of lifting implementations for image wavelet decomposition generated possibilities of several applications and several adaptive decomposition variations. The prediction step of a lifting stage constitutes the interesting part of the decomposition since it aims to reduce the energy of one of the decomposition bands by making predictions using the other decomposition band. In that aspect, more successful predictions yield better efficiency in terms of reduced energy in the lower band. In this work, we present a prediction filter whose prediction domain pixels are selected adaptively according to the local edge characteristics of the image. By judicuously selecting the prediction domain from pixels that are expected to have closer relation to the estimated pixel, the prediction error signal energy is reduced. In order to keep the adaptation rule symmetric for the encoder and the decoder sides, lossless compression applications are examined. Experimental results show that the proposed algorithm provides good compression results. Furthermore, the edge calculation is computationally inexpensive and comparable to the famous Daubechies 5/3 lifting implementation.

  7. Tangential 2-D Edge Imaging for GPI and Edge/Impurity Modeling

    International Nuclear Information System (INIS)

    Maqueda, Ricardo; Levinton, Fred M.


    Nova Photonics, Inc. has a collaborative effort at the National Spherical Torus Experiment (NSTX). This collaboration, based on fast imaging of visible phenomena, has provided key insights on edge turbulence, intermittency, and edge phenomena such as edge localized modes (ELMs) and multi-faceted axisymmetric radiation from the edge (MARFE). Studies have been performed in all these areas. The edge turbulence/intermittency studies make use of the Gas Puff Imaging diagnostic developed by the Principal Investigator (Ricardo Maqueda) together with colleagues from PPPL. This effort is part of the International Tokamak Physics Activity (ITPA) edge, scrape-off layer and divertor group joint activity (DSOL-15: Inter-machine comparison of blob characteristics). The edge turbulence/blob study has been extended from the current location near the midplane of the device to the lower divertor region of NSTX. The goal of this effort was to study turbulence born blobs in the vicinity of the X-point region and their circuit closure on divertor sheaths or high density regions in the divertor. In the area of ELMs and MARFEs we have studied and characterized the mode structure and evolution of the ELM types observed in NSTX, as well as the study of the observed interaction between MARFEs and ELMs. This interaction could have substantial implications for future devices where radiative divertor regions are required to maintain detachment from the divertor plasma facing components.

  8. Edge control in CNC polishing, paper 2: simulation and validation of tool influence functions on edges. (United States)

    Li, Hongyu; Walker, David; Yu, Guoyu; Sayle, Andrew; Messelink, Wilhelmus; Evans, Rob; Beaucamp, Anthony


    Edge mis-figure is regarded as one of the most difficult technical issues for manufacturing the segments of extremely large telescopes, which can dominate key aspects of performance. A novel edge-control technique has been developed, based on 'Precessions' polishing technique and for which accurate and stable edge tool influence functions (TIFs) are crucial. In the first paper in this series [D. Walker Opt. Express 20, 19787-19798 (2012)], multiple parameters were experimentally optimized using an extended set of experiments. The first purpose of this new work is to 'short circuit' this procedure through modeling. This also gives the prospect of optimizing local (as distinct from global) polishing for edge mis-figure, now under separate development. This paper presents a model that can predict edge TIFs based on surface-speed profiles and pressure distributions over the polishing spot at the edge of the part, the latter calculated by finite element analysis and verified by direct force measurement. This paper also presents a hybrid-measurement method for edge TIFs to verify the simulation results. Experimental and simulation results show good agreement.

  9. On the Lipschitz continuity of spectral bands of Harper-like and magnetic Schrödinger operators

    DEFF Research Database (Denmark)

    Cornean, Horia


    We show for a large class of discrete Harper-like and continuous magnetic Schrödinger operators that their band edges are Lipschitz continuous with respect to the intensity of the external constant magnetic field. We generalize a result obtained by Bellissard (Commun Math Phys 160:599–613, 1994...

  10. Beam-Steerable Multi-Band Mm-Wave Bow-Tie Antenna Array for Mobile Terminals

    DEFF Research Database (Denmark)

    Rodriguez Cano, Rocio; Zhang, Shuai; Pedersen, Gert F.


    A multiple-band 5G end-fire antenna array is proposed to be placed on the upper and bottom edges of mobile terminals. The antenna element consists of two bow-tie radiators designed to resonate at 28 and 60 GHz. A sixteen-element beam-steerable array is presented in this paper, with overall dimens...

  11. Edge localized modes of cold neutrons in periodic condensed media (United States)

    Belyakov, V. A.


    It is found that for certain energies of discreet cold neutrons, quasi-stationary eigen solutions of the corresponding Schrodinger equation, which are localized in the layer of a periodic medium, exist. The localization time of these solutions is strongly dependent on the layer thickness, being finite for a finite layer thickness and increasing indefinitely upon a infinite growth of the layer thickness as the third power of the layer thickness. The problem has been solved in the two-wave approximation of the dynamic diffraction theory for the neutron propagation direction coinciding with the periodicity axes (normal incidence of the neutron beam on the layer). The expressions for neutron eigenwave functions in a periodic medium, the reflection and transmission coefficients, and the neutron wavefunction in the layer as a function of the neutron energy incident on the layer have been determined. It turns out that for the certain discrete neutron energies, the amplitudes of the neutron wavefunction in the layer reach sharp maxima. The corresponding energies are just outside of the neutron stop band (energies forbidden for neutron propagation in the layer) and determine the energies of neutron edge modes (NEMs) localized in the layer, which are direct analogs of the optical edge modes for photonic crystals. The dispersion equation for the localized neutron edge modes has been obtained and analytically solved for the case of thick layers. A rough estimate for the localization length L is L ( db N)-1, where b is the neutron scattering length, d is the crystal period, and N is the density of nuclei in the crystal. The estimates of the localized thermal neutron lifetime show that acheaving of a lifetime close to the free neutron lifetime seems nonrealistic due to absorption of thermal neutrons and requires a perfect large size crystal. Nevertheless, acheaving the localized neutron lifetime exceeding by 104 times the neutron time of flight through the layer appears as

  12. Acoustic streaming of a sharp edge. (United States)

    Ovchinnikov, Mikhail; Zhou, Jianbo; Yalamanchili, Satish


    Anomalous acoustic streaming is observed emanating from sharp edges of solid bodies that are vibrating in fluids. The streaming velocities can be orders of magnitude higher than expected from the Rayleigh streaming at similar amplitudes of vibration. Acoustic velocity of fluid relative to a solid body diverges at a sharp edge, giving rise to a localized time-independent body force acting on the fluid. This force results in a formation of a localized jet. Two-dimensional numerical simulations are performed to predict acoustic streaming for low amplitude vibration using two methods: (1) Steady-state solution utilizing perturbation theory and (2) direct transient solution of the Navier-Stokes equations. Both analyses agree with each other and correctly predict the streaming of a sharp-edged vibrating blade measured experimentally. The origin of the streaming can be attributed to the centrifugal force of the acoustic fluid flow around a sharp edge. The dependence of this acoustic streaming on frequency and velocity is examined using dimensional analysis. The dependence law is devised and confirmed by numerical simulations.

  13. Leading-Edge Vortex lifts swifts

    NARCIS (Netherlands)

    Videler, JJ; Stamhuis, EJ; Povel, GDE


    The current understanding of how birds fly must be revised, because birds use their hand-wings in an unconventional way to generate lift and drag. Physical models of a common swift wing in gliding posture with a 60degrees sweep of the sharp hand-wing leading edge were tested in a water tunnel.

  14. Edge analytics in the internet of things


    Satyanarayanan, Mahadev; Simoens, Pieter; Xiao, Yu; Pillai, Padmanabhan; Chen, Zhuo; Ha, Kiryong; Hu, Wenlu; Amos, Brandon


    High-data-rate sensors are becoming ubiquitous in the Internet of Things. GigaSight is an Internet-scale repository of crowd-sourced video content that enforces privacy preferences and access controls. The architecture is a federated system of VM-based cloudlets that perform video analytics at the edge of the Internet.

  15. Superconducting Metallic Glass Transition-Edge-Sensors (United States)

    Hays, Charles C. (Inventor)


    A superconducting metallic glass transition-edge sensor (MGTES) and a method for fabricating the MGTES are provided. A single-layer superconducting amorphous metal alloy is deposited on a substrate. The single-layer superconducting amorphous metal alloy is an absorber for the MGTES and is electrically connected to a circuit configured for readout and biasing to sense electromagnetic radiation.

  16. The SKED: speckle knife edge detector

    International Nuclear Information System (INIS)

    Sharpies, S D; Light, R A; Achamfuo-Yeboah, S O; Clark, M; Somekh, M G


    The knife edge detector—also known as optical beam deflection—is a simple and robust method of detecting ultrasonic waves using a laser. It is particularly suitable for detection of high frequency surface acoustic waves as the response is proportional to variation of the local tilt of the surface. In the case of a specular reflection of the incident laser beam from a smooth surface, any lateral movement of the reflected beam caused by the ultrasonic waves is easily detected by a pair of photodiodes. The major disadvantage of the knife edge detector is that it does not cope well with optically rough surfaces, those that give a speckled reflection. The optical speckles from a rough surface adversely affect the efficiency of the knife edge detector, because 'dark' speckles move synchronously with 'bright' speckles, and their contributions to the ultrasonic signal cancel each other out. We have developed a new self-adapting sensor which can cope with the optical speckles reflected from a rough surface. It is inelegantly called the SKED—speckle knife edge detector—and like its smooth surface namesake it is simple, cheap, compact, and robust. We describe the theory of its operation, and present preliminary experimental results validating the overall concept and the operation of the prototype device

  17. Anomalous transport in the tokamak edge

    International Nuclear Information System (INIS)

    Vayakis, G.


    The tokamak edge has been studied with arrays of Langmuir and magnetic probes on the DITE and COMPASS-C devices. Measurements of plasma parameters such as density, temperature and radial magnetic field were taken in order to elucidate the character, effect on transport and origin of edge fluctuations. The tokamak edge is a strongly-turbulent environment, with large electrostatic fluctuation levels and broad spectra. The observations, including direct correlation measurements, are consistent with a picture in which the observed magnetic field fluctuations are driven by the perturbations in electrostatic parameters. The propagation characteristics of the turbulence, investigated using digital spectral techniques, appear to be dominated by the variation of the radial electric field, both in limiter and divertor plasmas. A shear layer is formed, associated in each case with the last closed flux surface. In the shear layer, the electrostatic wavenumber spectra are significantly broader. The predictions of a drift wave model (DDGDT) and of a family of models evolving from the rippling mode (RGDT group), are compared with experimental results. RGDT, augmented by impurity radiation effects, is shown to be the most reasonable candidate to explain the nature of the edge turbulence, only failing in its estimate of the wavenumber range. (Author)

  18. Study Abroad: A Competitive Edge for Women? (United States)

    Opper, Susan


    Studies effects of study abroad among 172 female and 217 male graduates in the United Kingdom, France, and the Federal Republic of Germany between 1980 and 1984. Finds study abroad expedites obtaining job interviews but was of little advantage in securing employment for either sex. Finds degree credential provides a competitive edge. (NL)

  19. Zone edge effects with variable rate irrigation (United States)

    Variable rate irrigation (VRI) systems may offer solutions to enhance water use efficiency by addressing variability within a field. However, the design of VRI systems should be considered to maximize application uniformity within sprinkler zones, while minimizing edge effects between such zones alo...

  20. Evaluation of alternative snow plow cutting edges. (United States)


    With approximately 450 snow plow trucks, the Maine Department of Transportation (MaineDOT) uses in : excess of 10,000 linear feet of plow cutting edges each winter season. Using the 2008-2009 cost per linear : foot of $48.32, the Departments total co...

  1. Increased heat fluxes near a forest edge

    NARCIS (Netherlands)

    Klaassen, W; van Breugel, PB; Moors, EJ; Nieveen, JP


    Observations of sensible and latent heat flux above forest downwind of a forest edge show these fluxes to be larger than the available energy over the forest. The enhancement averages to 56 W m(-2), or 16% of the net radiation, at fetches less than 400 m, equivalent to fetch to height ratios less

  2. Increased heat fluxes near a forest edge

    NARCIS (Netherlands)

    Klaassen, W.; Breugel, van P.B.; Moors, E.J.; Nieveen, J.P.


    Observations of sensible and latent heat flux above forest downwind of a forest edge show these fluxes to be larger than the available energy over the forest. The enhancement averages to 56 W mm2, or 16 f the net radiation, at fetches less than 400 m, equivalent to fetch to height ratios less than


    African Journals Online (AJOL)

    This paper presented a modified edge fed Sierpinski carpet microstrip patch antenna for antenna miniaturization. The proposed design was etched as Sierpinski carpet to lower the antenna resonant frequency, which is used to reduce the conventional patch antenna size. After the Sierpinski carpet second iteration, the ...

  4. Edge diagnostics for tandem mirror machines

    International Nuclear Information System (INIS)

    Allen, S.L.


    The edge plasma in a tandem mirror machine shields the plasma core from cold neutral gas and impurities. A variety of diagnostics are used to measure the fueling, shielding, and confinement of the edge plasma in both the end plug and central cell regions. Fast ion gauges and residual gas analyzers measure the gas pressure and composition outside of the plasma. An array of Langmuir probes is used to measure the electron density and temperature. Extreme ultraviolet (euv) and visible spectroscopy are used to measure both the impurity and deuterium densities and to estimate the shielding factor for the core plasma. The linear geometry of a tandem mirror also allows direct measurements of the edge plasma by sampling the ions and electrons lost but the ends of the machine. Representative data obtained by these diagnostics during operation of the Tandem Mirror Experiment (TMX) and Tandem Mirror Experiment-Upgrade (TMX-U) experiments are presented. Diagnostics that are currently being developed to diagnose the edge plasma are also discussed

  5. Reading Edge. What Works Clearinghouse Intervention Report (United States)

    What Works Clearinghouse, 2012


    "Reading Edge" is a middle school literacy program that emphasizes cooperative learning, goal setting, feedback, classroom management techniques, and the use of metacognitive strategy, whereby students assess their own skills and learn to apply new ones. The program is a component of the "Success for All"[superscript 2]…

  6. Flow distortion at a dense forest edge

    DEFF Research Database (Denmark)

    Dellwik, Ebba; Bingöl, Ferhat; Mann, Jakob


    The flow near tall forest edges is complex, yet poorly described. A field experiment using two meteorological masts equipped with sonic anemometers and a horizontally staring lidar was performed upwind and downwind of the interface between an open flat farmland and a tall (hc = 24 m) beech forest...

  7. Edge maps: Representing flow with bounded error

    KAUST Repository

    Bhatia, Harsh


    Robust analysis of vector fields has been established as an important tool for deriving insights from the complex systems these fields model. Many analysis techniques rely on computing streamlines, a task often hampered by numerical instabilities. Approaches that ignore the resulting errors can lead to inconsistencies that may produce unreliable visualizations and ultimately prevent in-depth analysis. We propose a new representation for vector fields on surfaces that replaces numerical integration through triangles with linear maps defined on its boundary. This representation, called edge maps, is equivalent to computing all possible streamlines at a user defined error threshold. In spite of this error, all the streamlines computed using edge maps will be pairwise disjoint. Furthermore, our representation stores the error explicitly, and thus can be used to produce more informative visualizations. Given a piecewise-linear interpolated vector field, a recent result [15] shows that there are only 23 possible map classes for a triangle, permitting a concise description of flow behaviors. This work describes the details of computing edge maps, provides techniques to quantify and refine edge map error, and gives qualitative and visual comparisons to more traditional techniques. © 2011 IEEE.

  8. Conical shell edge disturbance : An engineer's derivation

    NARCIS (Netherlands)

    Blaauwendraad, J.; Hoefakker, JH


    Because a rigorous bending theory for thin shells of revolution is complicated, attempts have been made for reliable approximations of the edge disturbance problem under axisymmetric loading. A well-known one was published by Geckeler [1, 2], who obtained his approximation by mathematical

  9. Universality in edge-source diffusion dynamics

    DEFF Research Database (Denmark)

    Mortensen, Asger; Okkels, Fridolin; Bruus, Henrik


    We show that in edge-source diffusion dynamics the integrated concentration N(t) has a universal dependence with a characteristic time scale tau=(A/P)(2)pi/(4D), where D is the diffusion constant while A and P are the cross-sectional area and perimeter of the domain, respectively. For the short...

  10. The visibility of IQHE at sharp edges: experimental proposals based on interactions and edge electrostatics

    International Nuclear Information System (INIS)

    Erkarslan, U; Oylumluoglu, G; Grayson, M; Siddiki, A


    The influence of the incompressible strips on the integer quantized Hall effect (IQHE) is investigated, considering a cleaved-edge overgrown (CEO) sample as an experimentally realizable sharp edge system. We propose a set of experiments to clarify the distinction between the large-sample limit when bulk disorder defines the IQHE plateau width and the small-sample limit smaller than the disorder correlation length, when self-consistent edge electrostatics define the IQHE plateau width. The large-sample or bulk quantized Hall (QH) regime is described by the usual localization picture, whereas the small-sample or edge regime is discussed within the compressible/incompressible strips picture, known as the screening theory of QH edges. Utilizing the unusually sharp edge profiles of the CEO samples, a Hall bar design is proposed to manipulate the edge potential profile from smooth to extremely sharp. By making use of a side-gate perpendicular to the two-dimensional electron system, it is shown that the plateau widths can be changed or even eliminated altogether. Hence, the visibility of IQHE is strongly influenced when adjusting the edge potential profile and/or changing the dc current direction under high currents in the nonlinear transport regime. As a second investigation, we consider two different types of ohmic contacts, namely highly transmitting (ideal) and highly reflecting (non-ideal) contacts. We show that if the injection contacts are non-ideal, but still ohmic, it is possible to measure directly the non-quantized transport taking place at the bulk of the CEO samples. The results of the experiments we propose will clarify the influence of the edge potential profile and the quality of the contacts, under QH conditions. (paper)

  11. Effects of edge grinding and sealing on mechanical properties of machine damaged laminate composites (United States)

    Asmatulu, Ramazan; Yeoh, Jason; Alarifi, Ibrahim M.; Alharbi, Abdulaziz


    Fiber reinforced composites have been utilized for a number of different applications, including aircraft, wind turbine, automobile, construction, manufacturing, and many other industries. During the fabrication, machining (waterjet, diamond and band saws) and assembly of these laminate composites, various edge and hole delamination, fiber pullout and other micro and nanocracks can be formed on the composite panels. The present study mainly focuses on the edge grinding and sealing of the machine damaged fiber reinforced composites, such as fiberglass, plain weave carbon fiber and unidirectional carbon fiber. The MTS tensile test results confirmed that the composite coupons from the grinding process usually produced better and consistent mechanical properties compared to the waterjet cut samples only. In addition to these studies, different types of high strength adhesives, such as EPON 828 and Loctite were applied on the edges of the prepared composite coupons and cured under vacuum. The mechanical tests conducted on these coupons indicated that the overall mechanical properties of the composite coupons were further improved. These processes can lower the labor costs on the edge treatment of the composites and useful for different industrial applications of fiber reinforced composites.

  12. Detection of metal stress in boreal forest species using the 0.67-micron chlorophyll absorption band (United States)

    Singhroy, Vernon H.; Kruse, Fred A.


    Several recent studies have shown that a shift of the red-edge inflection near 0.70 micron in vegetation reflectance spectra is an indicator of metal stress, partially attributable to changes in chlorophyll concentration. This 'red-edge shift', however, is difficult to detect and has been reported both toward longer (red) and shorter (blue) wavelengths. Our work demonstrates that direct measurement of the depth and width of the chlorophyll absorption band at 0.67 micron using digital feature extraction and absorption band characterization procedures developed for the analysis of mineral spectra is a more consistent indicator of metal stress. Additionally, the magnitude of these parameters is generally greater than that of the red edge shift and thus should be more amenable to detection and mapping using field and aircraft spectrometers.

  13. Troposcatter at the KU Band (United States)


    edge of the common volume at about ten am . 2.4 Ducting Although ducting is a special case of clear turbulence, it is usually not considered as --jc...that power would also be very small. Neither of these charactensucs ame observed for any extended penod of ume on the path. 2.7 Aircraft Scatter The...where d is the location of the receiver relative to the trasmitter [Crane 1981 ]. The scatterng cross Secuons are as given in chapter 2. This equation

  14. Tunable plasmons in regular planar arrays of graphene nanoribbons with armchair and zigzag-shaped edges

    Directory of Open Access Journals (Sweden)

    Cristian Vacacela Gomez


    Full Text Available Recent experimental evidence for and the theoretical confirmation of tunable edge plasmons and surface plasmons in graphene nanoribbons have opened up new opportunities to scrutinize the main geometric and conformation factors, which can be used to modulate these collective modes in the infrared-to-terahertz frequency band. Here, we show how the extrinsic plasmon structure of regular planar arrays of graphene nanoribbons, with perfectly symmetric edges, is influenced by the width, chirality and unit-cell length of each ribbon, as well as the in-plane vacuum distance between two contiguous ribbons. Our predictions, based on time-dependent density functional theory, in the random phase approximation, are expected to be of immediate help for measurements of plasmonic features in nanoscale architectures of nanoribbon devices.

  15. Graphene nanoribbons as low band gap donor materials for organic photovoltaics: quantum chemical aided design. (United States)

    Osella, Silvio; Narita, Akimitsu; Schwab, Matthias Georg; Hernandez, Yenny; Feng, Xinliang; Müllen, Klaus; Beljonne, David


    Graphene nanoribbons (GNRs) are strips of graphene cut along a specific direction that feature peculiar electronic and optical properties owing to lateral confinement effects. We show here by means of (time-dependent) density functional theory calculations that GNRs with properly designed edge structures fulfill the requirements in terms of electronic level alignment with common acceptors (namely, C(60)), solar light harvesting, and singlet-triplet exchange energy to be used as low band gap semiconductors for organic photovoltaics.

  16. Layer-dependent band alignment and work function of few-layer phosphorene. (United States)

    Cai, Yongqing; Zhang, Gang; Zhang, Yong-Wei


    Using first-principles calculations, we study the electronic properties of few-layer phosphorene focusing on layer-dependent behavior of band gap, work function band alignment and carrier effective mass. It is found that few-layer phosphorene shows a robust direct band gap character, and its band gap decreases with the number of layers following a power law. The work function decreases rapidly from monolayer (5.16 eV) to trilayer (4.56 eV), and then slowly upon further increasing the layer number. Compared to monolayer phosphorene, there is a drastic decrease of hole effective mass along the ridge (zigzag) direction for bilayer phosphorene, indicating a strong interlayer coupling and screening effect. Our study suggests that 1). Few-layer phosphorene with a layer-dependent band gap and a robust direct band gap character is promising for efficient solar energy harvest. 2). Few-layer phosphorene outperforms monolayer counterpart in terms of a lighter carrier effective mass, a higher carrier density and a weaker scattering due to enhanced screening. 3). The layer-dependent band edges and work functions of few-layer phosphorene allow for modification of Schottky barrier with enhanced carrier injection efficiency. It is expected that few-layer phosphorene will present abundant opportunities for a plethora of new electronic applications.

  17. Linear methods in band theory

    DEFF Research Database (Denmark)

    Andersen, O. Krogh


    Two approximate methods for solving the band-structure problem in an efficient and physically transparent way are presented and discussed in detail. The variational principle for the one-electron Hamiltonian is used in both schemes, and the trial functions are linear combinations of energy......-independent augmented plane waves (APW) and muffin-tin orbitals (MTO), respectively. The secular equations are therefore eigenvalue equations, linear in energy. The trial functions are defined with respect to a muffin-tin (MT) potential and the energy bands depend on the potential in the spheres through potential...... parameters which describe the energy dependence of the logarithmic derivatives. Inside the spheres, the energy-independent APW is that linear combination of an exact solution, at the arbitrary but fixed energy Eν, and its energy derivative which matches continuously and differentiably onto the plane...

  18. NCenter wide band neutrino beam

    International Nuclear Information System (INIS)

    Stutte, L.G.


    This memo describes the physical properties of the currently operating N-Center wide band neutrino beam---commonly called the triplet train, following a past tradition of a triplet lens configuration. In reality, in order to gain a larger momentum acceptance and to minimize the angular divergence of the beam, a quadruplet beam (4 lenses) employing point-to-parallel optics at a central momentum of 300 GeV was built. 6 refs., 13 figs., 1 tab

  19. [Gastric band erosion: Alternative management]. (United States)

    Echaverry-Navarrete, Denis José; Maldonado-Vázquez, Angélica; Cortes-Romano, Pablo; Cabrera-Jardines, Ricardo; Mondragón-Pinzón, Erwin Eduardo; Castillo-González, Federico Armando


    Obesity is a public health problem, for which the prevalence has increased worldwide at an alarming rate, affecting 1.7 billion people in the world. To describe the technique employed in incomplete penetration of gastric band where endoscopic management and/or primary closure is not feasible. Laparoscopic removal of gastric band was performed in five patients with incomplete penetrance using Foley catheterization in the perforation site that could lead to the development of a gastro-cutaneous fistula. The cases presented include a leak that required surgical lavage with satisfactory outcome, and one patient developed stenosis 3 years after surgical management, which was resolved endoscopically. In all cases, the penetration site closed spontaneously. Gastric band erosion has been reported in 3.4% of cases. The reason for inserting a catheter is to create a controlled gastro-cutaneous fistula, allowing spontaneous closure. Various techniques have been described: the totally endoscopic, hybrid techniques (endoscopic/laparoscopic) and completely laparoscopic. A technique is described here that is useful and successful in cases where the above-described treatments are not viable. Copyright © 2015. Published by Masson Doyma México S.A.

  20. Edge-effect interactions in fragmented and patchy landscapes. (United States)

    Porensky, Lauren M; Young, Truman P


    Ecological edges are increasingly recognized as drivers of landscape patterns and ecosystem processes. In fragmented and patchy landscapes (e.g., a fragmented forest or a savanna with scattered termite mounds), edges can become so numerous that their effects pervade the entire landscape. Results of recent studies in such landscapes show that edge effects can be altered by the presence or proximity of other nearby edges. We considered the theoretical significance of edge-effect interactions, illustrated various landscape configurations that support them and reviewed existing research on this topic. Results of studies from a variety of locations and ecosystem types show that edge-effect interactions can have significant consequences for ecosystems and conservation, including higher tree mortality rates in tropical rainforest fragments, reduced bird densities in grassland fragments, and bush encroachment and reduced wildlife densities in a tropical savanna. To clarify this underappreciated concept and synthesize existing work, we devised a conceptual framework for edge-effect interactions. We first worked to reduce terminological confusion by clarifying differences among terms such as edge intersection and edge interaction. For cases in which nearby edge effects interact, we proposed three possible forms of interaction: strengthening (presence of a second edge causes stronger edge effects), weakening (presence of a second edge causes weaker edge effects), and emergent (edge effects change completely in the presence of a second edge). By clarifying terms and concepts, this framework enables more precise descriptions of edge-effect interactions and facilitates comparisons of results among disparate study systems and response variables. A better understanding of edge-effect interactions will pave the way for more appropriate modeling, conservation, and management in complex landscapes. © 2013 Society for Conservation Biology.

  1. Modified edge-to-edge technique for correction of congenital mitral regurgitation in infants and children. (United States)

    Zhang, Gang; Zhang, Fusheng; Zhu, Mei; Zhang, Wenlong; Fan, Quanxin; Zou, Chengwei; Wang, Anbiao


    Since 2008, 28 patients with congenital mitral regurgitation have undergone mitral valve repair with a modified edge-to-edge technique at our institution. The regurgitant mitral leaflet was sutured with a pledget-reinforced, horizontal mattress suture with No. 4-0 polypropylene on the ventricle side and a pledget-reinforced mattress suture with Gore-Tex sutures (W.L. Gore & Associates, Flagstaff, AZ) and Dacron pledgets (Chest, Shanghai) placed on the anterior and posterior annulus corresponding to the edge-to-edge suturing site. Early results are encouraging, but a longer follow-up is needed. Copyright © 2011 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.

  2. Evidence of type-II band alignment at the ordered GaInNP to GaAs heterointerface

    International Nuclear Information System (INIS)

    Hsu, H.P.; Huang, Y.N.; Huang, Y.S.; Sitarek, P.; Tiong, K.K.; Tu, C.W.


    Polarized piezoreflectance (PzR) and photoreflectance (PR) are employed to study band alignment in Ga 0.46 In 0.54 N y P 1-y /GaAs heterostructures grown by gas-source molecular-beam epitaxy. The features near the band edge of Ga 0.46 In 0.54 N y P 1-y show strong polarization dependence, indicating the existence of some degree of ordering of these samples. The PR spectra exhibit Franz-Keldysh Oscillations (FKOs) above the band edge of GaAs. The electric fields in the GaAs region are evaluated by analyzing the FKOs and found to decrease with increasing nitrogen content. The type-II band alignment at the Ga 0.46 In 0.54 N y P 1-y /GaAs interface is concluded for the alloys with nitrogen content y larger than 0.5% based on the appearance of additional features below band edge of GaAs. These features are attributed to the spatially indirect type-II transitions in the vicinity of interface region between Ga 0.46 In 0.54 N y P 1-y and GaAs. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Adsorption, intercalation and sensing of helium on yttrium functionalized open edge boron nitride: A first principle DFT and TDDFT study (United States)

    Taherpour, Avat (Arman); Shahri, Zahra; Rezaei, Omid; Jamshidi, Morteza; Fellowes, Thomas


    Open edge BN boron-nitride has a stable graphene-like structure, which could be doped by a range of impurities, so the band gap could be tuned. The optical, electrical, physicochemical properties, NBO and electron density of open edge BN that is doped by Yttrium was evaluated using DFT method as a sensor for He gas. Here, was applied HSE1PBE method exchange correlation and LANL2DZ. The density of states and natural bond orbital analysis calculated have depicted that the band gap of BN-Y flake after sensing He gas and it has shown change from 1.66 → 2.42 eV. The UV-Vis absorption in λmax area showed a significant red-shift that it is an appropriate parameter to recognize He molecule.

  4. Balancing the edge effects budget: bay scallop settlement and loss along a seagrass edge. (United States)

    Carroll, John M; Furman, Bradley T; Tettelbach, Stephen T; Peterson, Bradley J


    Edge effects are a dominant subject in landscape ecology literature, yet they are highly variable and poorly understood. Often, the literature suggests simple models for edge effects-positive (enhancement at the edge), negative (enhancement at the interior), or no effect (neutral)--on a variety of metrics, including abundance, diversity, and mortality. In the marine realm, much of this work has focused on fragmented seagrass habitats due to their importance for a variety of commercially important species. In this study, the settlement, recruitment, and survival of bay scallops was investigated across a variety of seagrass patch treatments. By simultaneously collecting settlers (those viable larvae available to settle and metamorphose) and recruits (those settlers that survive some period of time, in this case, 6 weeks) on the same collectors, we were able to demonstrate a "balance" between positive and negative edge effects, resulting in a net neutral effect. Scallop settlement was significantly enhanced along seagrass edges, regardless of patch type while survival was elevated within patch interiors. However, recruitment (the net result of settlement and post-settlement loss) did not vary significantly from edge to center, representing a neutral effect. Further, results suggest that post-settlement loss, most likely due to predation, appears to be the dominant mechanism structuring scallop abundance, not patterns in settlement. These data illustrate the complexity of edge effects, and suggest that the metric used to investigate the effect (be it abundance, survival, or other metrics) can often influence the magnitude and direction of the perceived effect. Traditionally, high predation along a habitat edge would have indicated an "ecological trap" for the species in question; however, this study demonstrates that, at the population level, an ecological trap may not exist.

  5. Urbanization Impacts on Mammals across Urban-Forest Edges and a Predictive Model of Edge Effects


    Villaseñor, Nélida R.; Driscoll, Don A.; Escobar, Martín A. H.; Gibbons, Philip; Lindenmayer, David B.


    With accelerating rates of urbanization worldwide, a better understanding of ecological processes at the wildland-urban interface is critical to conserve biodiversity. We explored the effects of high and low-density housing developments on forest-dwelling mammals. Based on habitat characteristics, we expected a gradual decline in species abundance across forest-urban edges and an increased decline rate in higher contrast edges. We surveyed arboreal mammals in sites of high and low housing den...

  6. Independent component analysis of edge information for face recognition

    CERN Document Server

    Karande, Kailash Jagannath


    The book presents research work on face recognition using edge information as features for face recognition with ICA algorithms. The independent components are extracted from edge information. These independent components are used with classifiers to match the facial images for recognition purpose. In their study, authors have explored Canny and LOG edge detectors as standard edge detection methods. Oriented Laplacian of Gaussian (OLOG) method is explored to extract the edge information with different orientations of Laplacian pyramid. Multiscale wavelet model for edge detection is also propos

  7. Band structure engineering of monolayer MoS₂ by surface ligand functionalization for enhanced photoelectrochemical hydrogen production activity. (United States)

    Pan, Jing; Wang, Zilu; Chen, Qian; Hu, Jingguo; Wang, Jinlan


    To achieve photoelectrochemical (PEC) activity of MoS2 for hydrogen production through water splitting, the band edges of MoS2 should match with the hydrogen and oxygen production levels. Our first-principles calculations show that the band edges of monolayer MoS2 can be effectively tuned by surface ligand functionalization, resulting from the intrinsic dipole of the ligand itself and the induced dipole at the ligand/MoS2 interface. We further explore the influence of ligand coverage, ligand functionalization and the substrate on the band structure of MoS2. The hybrid C6H5CH2NH2/MoS2/graphene structures may be compelling candidates as they satisfy the stringent requirements of PEC water splitting.

  8. Crystallographic study of grain refinement in aluminum alloys using the edge-to-edge matching model

    International Nuclear Information System (INIS)

    Zhang, M.-X.; Kelly, P.M.; Easton, M.A.; Taylor, J.A.


    The edge-to-edge matching model for describing the interfacial crystallographic characteristics between two phases that are related by reproducible orientation relationships has been applied to the typical grain refiners in aluminum alloys. Excellent atomic matching between Al 3 Ti nucleating substrates, known to be effective nucleation sites for primary Al, and the Al matrix in both close packed directions and close packed planes containing these directions have been identified. The crystallographic features of the grain refiner and the Al matrix are very consistent with the edge-to-edge matching model. For three other typical grain refiners for Al alloys, TiC (when a = 0.4328 nm), TiB 2 and AlB 2 , the matching only occurs between the close packed directions in both phases and between the second close packed plane of the Al matrix and the second close packed plane of the refiners. According to the model, it is predicted that Al 3 Ti is a more powerful nucleating substrate for Al alloy than TiC, TiB 2 and AlB 2 . This agrees with the previous experimental results. The present work shows that the edge-to-edge matching model has the potential to be a powerful tool in discovering new and more powerful grain refiners for Al alloys

  9. Tensile strain-induced magnetism transition in multilayer graphene with excess electrons: Stability of the edge-quantum well

    Directory of Open Access Journals (Sweden)

    Lei Yang


    Full Text Available The stability of edge-quantum well-induced strong magnetism of multilayer armchair graphene nanoribbon (AGNR with excess electrons was investigated under applied tensile strain by density functional theory (DFT calculations. The results indicated that: (1 The strain along the armchair edge direction led to a transition of the multilayer AGNRs from ferromagnetic state to nonmagnetic state when the strain increased to a critical value; (2 The strain induced bond length changes reduced the stability of the edge-quantum well in terms of the reduction of the electrons capturing capacity; and (3 The spin splitting of the energy bands near the Fermi level reduced with the increase of the strain, resulting in the decrease of the spin moment. This finding suggests that the magnetic properties of graphene have strong dependence on its strain states, which is crucial to the design of graphene-based magnetic devices.

  10. More on Estimation of Banded and Banded Toeplitz Covariance Matrices


    Berntsson, Fredrik; Ohlson, Martin


    In this paper we consider two different linear covariance structures, e.g., banded and bended Toeplitz, and how to estimate them using different methods, e.g., by minimizing different norms. One way to estimate the parameters in a linear covariance structure is to use tapering, which has been shown to be the solution to a universal least squares problem. We know that tapering not always guarantee the positive definite constraints on the estimated covariance matrix and may not be a suitable me...

  11. Effects of the edge shape and the width on the structural and electronic properties of silicene nanoribbons

    International Nuclear Information System (INIS)

    Song Yuling; Zhang Yan; Zhang Jianmin; Lu Daobang


    Under the generalized gradient approximation (GGA), the structural and electronic properties are studied for H-terminated silicene nanoribbons (SiNRs) with either zigzag edge (ZSiNRs) or armchair edge (ASiNRs) by using the first-principles projector-augmented wave potential within the density function theory (DFT) framework. The results show that the length of the Si-H bond is always 1.50 A, but the edge Si-Si bonds are shorter than the inner ones with identical orientation, implying a contraction relaxation of edge Si atoms. An edge state appears at the Fermi level E F in broader ZSiNRs, but does not appear in all ASiNRs due to their dimer Si-Si bond at edge. With increasing width of ASiNRs, the direct band gaps exhibit not only an oscillation behavior, but also a periodic feature of Δ 3n > Δ 3n+1 > Δ 3n+2 for a certain integer n. The charge density contours analysis shows that the Si-H bond is an ionic bond due to a relative larger electronegativity of H atom. However, all kinds of the Si-Si bonds display a typical covalent bonding feature, although their strength depends on not only the bond orientation but also the bond position. That is, the larger deviation of the Si-Si bond orientation from the nanoribbon axis as well as the closer of the Si-Si bond to the nanoribbon edge, the stronger strength of the Si-Si bond. Besides the contraction of the nanoribbon is mainly in its width direction especially near edge, the addition contribution from the terminated H atoms may be the other reason.

  12. X-ray absorption near-edge structure of GaN with high Mn concentration grown on SiC (United States)

    Sancho-Juan, O.; Cantarero, A.; Garro, N.; Cros, A.; Martínez-Criado, G.; Salomé, M.; Susini, J.; Olguín, D.; Dhar, S.


    By means of x-ray absorption near-edge structure (XANES) several Ga1-xMnxN (0.03edges. All samples studied present a similar Mn ionization state, very close to 2+, and tetrahedral coordination. In order to interpret the near-edge structure, we have performed ab initio calculations using the full potential linear augmented plane wave method as implemented in the Wien2k code. The calculations show the appearance of a Mn bonding \\mathrm {t_{2}}\\uparrow band localized in the gap region, and the corresponding anti-bonding state \\mathrm {t_{2}}\\downarrow , which seem to be responsible for the double structure which appears at the pre-edge absorption region. The shoulders and main absorption peak of the XANES spectra are attributed to transitions from the Mn(1s) band to the conduction bands, which are partially dipole allowed because of the Mn(4p) contribution to these bands.

  13. X-ray absorption near-edge structure of GaN with high Mn concentration grown on SiC

    Energy Technology Data Exchange (ETDEWEB)

    Sancho-Juan, O; Cantarero, A; Garro, N; Cros, A [Materials Science Institute, University of Valencia, PO Box 22085, E46071 Valencia (Spain); Martinez-Criado, G; Salome, M; Susini, J [European Synchrotron Radiation Facility, 6 rue Jules Horowitz, 38043 Grenoble (France); Olguin, D [Dept. de Fisica, CINVESTAV-IPN, 07300 Mexico D F (Mexico); Dhar, S [Experimentalphysik, Universitaet Duisburg-Essen, Lotharstrasse 1, 47057 Duisburg (Germany)


    By means of x-ray absorption near-edge structure (XANES) several Ga{sub 1-x}Mn{sub x}N (0.03edges. All samples studied present a similar Mn ionization state, very close to 2+, and tetrahedral coordination. In order to interpret the near-edge structure, we have performed ab initio calculations using the full potential linear augmented plane wave method as implemented in the Wien2k code. The calculations show the appearance of a Mn bonding t{sub 2}arrow up band localized in the gap region, and the corresponding anti-bonding state t{sub 2}arrow down, which seem to be responsible for the double structure which appears at the pre-edge absorption region. The shoulders and main absorption peak of the XANES spectra are attributed to transitions from the Mn(1s) band to the conduction bands, which are partially dipole allowed because of the Mn(4p) contribution to these bands.

  14. GSGG edge cladding development: Final technical report

    International Nuclear Information System (INIS)

    Izumitani, T.; Meissner, H.E.; Toratani, H.


    The objectives of this project have been: (1) Investigate the possibility of chemical etching of GSGG crystal slabs to obtain increased strength. (2) Design and construct a simplified mold assembly for casting cladding glass to the edges of crystal slabs of different dimensions. (3) Conduct casting experiments to evaluate the redesigned mold assembly and to determine stresses as function of thermal expansion coefficient of cladding glass. (4) Clad larger sizes of GGG slabs as they become available. These tasks have been achieved. Chemical etching of GSGG slabs does not appear possible with any other acid than H 3 PO 4 at temperatures above 300 0 C. A mold assembly has been constructed which allowed casting cladding glass around the edges of the largest GGG slabs available (10 x 20 x 160 mm) without causing breakage through the annealing step

  15. On thermal edge effects in composite laminates (United States)

    Herakovich, C. T.


    Results are presented for a finite-element investigation of the combined influence of edge effects due to mechanical and thermal mismatch in composite laminates with free edges. Laminates of unidirectional boron/epoxy symmetrically bonded to sheets of aluminum and titanium were studied. It is shown that interlaminar thermal stresses may be more significant than the interlaminar stresses due to loading only. In addition, the stresses due to thermal mismatch may be of the same sign as those due to Poisson's mismatch or they may be of opposite sign depending upon material properties, stacking sequence, and direction of loading. The paper concludes with a brief discussion of thermal stresses in all-composite laminates.

  16. Quantum nature of edge magnetism in graphene. (United States)

    Golor, Michael; Wessel, Stefan; Schmidt, Manuel J


    It is argued that the subtle crossover from decoherence-dominated classical magnetism to fluctuation-dominated quantum magnetism is experimentally accessible in graphene nanoribbons. We show that the width of a nanoribbon determines whether the edge magnetism is on the classical side, on the quantum side, or in between. In the classical regime, decoherence is dominant and leads to static spin polarizations at the ribbon edges, which are well described by mean-field theories. The quantum Zeno effect is identified as the basic mechanism which is responsible for the spin polarization and thereby enables the application of graphene in spintronics. On the quantum side, however, the spin polarization is destroyed by dynamical processes. The great tunability of graphene magnetism thus offers a viable route for the study of the quantum-classical crossover.

  17. Resource distribution influences positive edge effects in a seagrass fish. (United States)

    Macreadie, Peter I; Hindell, Jeremy S; Keough, Michael J; Jenkins, Gregory P; Connolly, Rod M


    According to conceptual models, the distribution of resources plays a critical role in determining how organisms distribute themselves near habitat edges. These models are frequently used to achieve a mechanistic understanding of edge effects, but because they are based predominantly on correlative studies, there is need for a demonstration of causality, which is best done through experimentation. Using artificial seagrass habitat as an experimental system, we determined a likely mechanism underpinning edge effects in a seagrass fish. To test for edge effects, we measured fish abundance at edges (0-0.5 m) and interiors (0.5-1 m) of two patch configurations: continuous (single, continuous 9-m2 patches) and patchy (four discrete 1-m2 patches within a 9-m2 area). In continuous configurations, pipefish (Stigmatopora argus) were three times more abundant at edges than interiors (positive edge effect), but in patchy configurations there was no difference. The lack of edge effect in patchy configurations might be because patchy seagrass consisted entirely of edge habitat. We then used two approaches to test whether observed edge effects in continuous configurations were caused by increased availability of food at edges. First, we estimated the abundance of the major prey of pipefish, small crustaceans, across continuous seagrass configurations. Crustacean abundances were highest at seagrass edges, where they were 16% greater than in patch interiors. Second, we supplemented interiors of continuous treatment patches with live crustaceans, while control patches were supplemented with seawater. After five hours of supplementation, numbers of pipefish were similar between edges and interiors of treatment patches, while the strong edge effects were maintained in controls. This indicated that fish were moving from patch edges to interiors in response to food supplementation. These approaches strongly suggest that a numerically dominant fish species is more abundant at seagrass

  18. Optimizing Transition Edge Sensors for High-Resolution X-ray Spectroscopy

    International Nuclear Information System (INIS)

    Saab, Tarek; Bandler, Simon R.; Boyce, Kevin; Chervenak, James A.; Figueroa-Feliciano, Enectali; Iyomoto, Naoko; Kelley, Richard L.; Kilbourne, Caroline A.; Porter, Frederick S.; Sadleir, John E.


    Transition Edge Sensors (TES) have found applications as astronomical detectors ranging from the microwave to the gamma ray energy bands. Each energy band, however, imposes a different set of requirements on the TES such as energy and timing resolution, focal plane coverage, and the mechanisms by which the signal is coupled to the detector. This paper focuses on the development of TESs optimized for the 0.1-10 keV energy range at the NASA Goddard Space Flight Center. Such detectors are suitable candidates for some of the upcoming X-ray observatories such as NeXT and Constellation-X. Ongoing efforts at producing, characterizing, and modeling such devices, as well as the latest results, are discussed

  19. The transition-edge microbolometer (TREMBOL)

    International Nuclear Information System (INIS)

    Wentworth, S.M.; Neikirk, D.P.


    The TREMBOL (transition-edge microbolometer) and the composite TREMBOL are introduced as detectors for FIR imaging arrays. The TREMBOL uses a superconductor's sharp change in resistance at the normal conduction to superconduction transition. The structure of the composite TREMBOL enables heating of the individual detectors in an array up to their transition temperature, and can thus be used in multiplexing, which would be very advantageous for two-dimensional arrays. 23 refs

  20. Edge-on View of Saturn's Rings (United States)


    TOP - This is a NASA Hubble Space Telescope snapshot of Saturn with its rings barely visible. Normally, astronomers see Saturn with its rings tilted. Earth was almost in the plane of Saturn's rings, thus the rings appear edge-on.In this view, Saturn's largest moon, Titan, is casting a shadow on Saturn. Titan's atmosphere is a dark brown haze. The other moons appear white because of their bright, icy surfaces. Four moons - from left to right, Mimas, Tethys, Janus, and Enceladus - are clustered around the edge of Saturn's rings on the right. Two other moons appear in front of the ring plane. Prometheus is on the right edge; Pandora, on the left. The rings also are casting a shadow on Saturn because the Sun was above the ring plane.BOTTOM - This photograph shows Saturn with its rings slightly tilted. The moon called Dione, on the lower right, is casting a long, thin shadow across the whole ring system due to the setting Sun on the ring plane. The moon on the upper left of Saturn is Tethys.Astronomers also are studying the unusual appearance of Saturn's rings. The bottom image displays a faint, narrow ring, the F-ring just outside the main ring, which normally is invisible from Earth. Close to the edge of Saturn's disk, the front section of rings seem brighter and more yellow than the back due to the additional lumination by yellowish Saturn.The color images were assembled from separate exposures taken August 6 (top) and November 17 (bottom), 1995 with the Wide Field Planetary Camera-2.The Wide Field/Planetary Camera 2 was developed by the Jet Propulsion Laboratory and managed by the Goddard Spaced Flight Center for NASA's Office of Space Science.This image and other images and data received from the Hubble Space Telescope are posted on the World Wide Web on the Space Telescope Science Institute home page at URL

  1. An edge extraction technique for noisy images

    International Nuclear Information System (INIS)

    Cios, K.J.; Sarieh, A.


    We present an algorithm for extracting edges from noisy images. Our method uses an unsupervised learning approach for local threshold computation by means of Pearson's method for mixture density identification. We tested the technique by applying it to computer-generated images corrupted with artificial noise and to an actual Thallium-201 heart image and it is shown that the technique has potential use for noisy images

  2. Electronic and magnetic properties of MoSe2 armchair nanoribbons controlled by the different edge structures (United States)

    Zhang, Hui; Zhao, Xu; Gao, Yonghui; Wang, Haiyang; Wang, Tianxing; Wei, Shuyi


    Tow-dimensional materials obviously have potential applications in next-generation nanodevices because of their extraordinary physical and chemical properties and the demands of the market. Using first-principle calculation based on density functional theory, we explore electronic and magnetic properties of the different nanoribbons with various edge structures, namely, with hydrogenation or not. In addition, we also calculate the binding energy to analyze the stability of the nanoribbon. Our calculations tell us that the passivated nanoribbons have the positive binding energies, which indicates the passivated nanoribbons are relative stable and hydrogenation can improve the stability of the bare nanoribbons due to the reduction of the dangling bonds. Among of them, full hydrogenation has the highest stability. We find all the nanoribbons with full and without hydrogenation are nonmagnetic semiconductors. It is worth mentioning that hydrogenation can induce the bare nanoribbons to transform gradually from indirect band gap semiconductor to direct band gap semiconductor, even to half-metal. In addition, the magnetic moment of the bare nanoribbon change bit by bit as the rate of hydrogenation increases. When the edge atoms are fully hydrogenated, the magnetic moment return to zero. What's more, our research results still confirm that electronic and magnetic properties of the nanorribons without and with different edge passivation are mainly contributed by the atoms at the edges. These studies about MoSe2 nanoribbons will shed light on the further development of the relevant nanodevices in versatile applications, such as spintronics and energy harvesting.

  3. Observation of valleylike edge states of sound at a momentum away from the high-symmetry points (United States)

    Xia, Bai-Zhan; Zheng, Sheng-Jie; Liu, Ting-Ting; Jiao, Jun-Rui; Chen, Ning; Dai, Hong-Qing; Yu, De-Jie; Liu, Jian


    In condensed matter physics, topologically protected edge transportation has drawn extensive attention over recent years. Thus far, the topological valley edge states have been produced near the Dirac cones fixed at the high-symmetry points of the Brillouin zone. In this paper, we demonstrate a unique valleylike phononic crystal (PnC) with the position-varying Dirac cones at the high-symmetry lines of the Brillouin zone boundary. The emergence of such Dirac cones, characterized by the vortex structure in a momentum space, is attributed to the unavoidable band crossing protected by the mirror symmetry. The Dirac cones can be unbuckled and a complete band gap can be induced through breaking the mirror symmetry. Interestingly, by simply rotating the square columns, we realize the valleylike vortex states and the band inversion effect which leads to the valley Hall phase transition. Along the valleylike PnC interfaces separating two distinct acoustic valley Hall phases, the valleylike protected edge transport of sound in domain walls is observed in both the simulations and the experiments. These results are promising for the exploration of alternative topological phenomena in the valleylike PnCs beyond the graphenelike lattice.

  4. Canny edge-based deformable image registration. (United States)

    Kearney, Vasant; Huang, Yihui; Mao, Weihua; Yuan, Baohong; Tang, Liping


    This work focuses on developing a 2D Canny edge-based deformable image registration (Canny DIR) algorithm to register in vivo white light images taken at various time points. This method uses a sparse interpolation deformation algorithm to sparsely register regions of the image with strong edge information. A stability criterion is enforced which removes regions of edges that do not deform in a smooth uniform manner. Using a synthetic mouse surface ground truth model, the accuracy of the Canny DIR algorithm was evaluated under axial rotation in the presence of deformation. The accuracy was also tested using fluorescent dye injections, which were then used for gamma analysis to establish a second ground truth. The results indicate that the Canny DIR algorithm performs better than rigid registration, intensity corrected Demons, and distinctive features for all evaluation matrices and ground truth scenarios. In conclusion Canny DIR performs well in the presence of the unique lighting and shading variations associated with white-light-based image registration.

  5. Edge direction and the structure of networks. (United States)

    Foster, Jacob G; Foster, David V; Grassberger, Peter; Paczuski, Maya


    Directed networks are ubiquitous and are necessary to represent complex systems with asymmetric interactions--from food webs to the World Wide Web. Despite the importance of edge direction for detecting local and community structure, it has been disregarded in studying a basic type of global diversity in networks: the tendency of nodes with similar numbers of edges to connect. This tendency, called assortativity, affects crucial structural and dynamic properties of real-world networks, such as error tolerance or epidemic spreading. Here we demonstrate that edge direction has profound effects on assortativity. We define a set of four directed assortativity measures and assign statistical significance by comparison to randomized networks. We apply these measures to three network classes--online/social networks, food webs, and word-adjacency networks. Our measures (i) reveal patterns common to each class, (ii) separate networks that have been previously classified together, and (iii) expose limitations of several existing theoretical models. We reject the standard classification of directed networks as purely assortative or disassortative. Many display a class-specific mixture, likely reflecting functional or historical constraints, contingencies, and forces guiding the system's evolution.

  6. Band Subset Selection for Hyperspectral Image Classification

    Directory of Open Access Journals (Sweden)

    Chunyan Yu


    Full Text Available This paper develops a new approach to band subset selection (BSS for hyperspectral image classification (HSIC which selects multiple bands simultaneously as a band subset, referred to as simultaneous multiple band selection (SMMBS, rather than one band at a time sequentially, referred to as sequential multiple band selection (SQMBS, as most traditional band selection methods do. In doing so, a criterion is particularly developed for BSS that can be used for HSIC. It is a linearly constrained minimum variance (LCMV derived from adaptive beamforming in array signal processing which can be used to model misclassification errors as the minimum variance. To avoid an exhaustive search for all possible band subsets, two numerical algorithms, referred to as sequential (SQ and successive (SC algorithms are also developed for LCMV-based SMMBS, called SQ LCMV-BSS and SC LCMV-BSS. Experimental results demonstrate that LCMV-based BSS has advantages over SQMBS.

  7. Band structure and optical properties of diglycine nitrate crystal

    International Nuclear Information System (INIS)

    Andriyevsky, Bohdan; Ciepluch-Trojanek, Wioleta; Romanyuk, Mykola; Patryn, Aleksy; Jaskolski, Marcin


    Experimental and theoretical investigations of the electron energy characteristics and optical spectra for diglycine nitrate crystal (DGN) (NH 2 CH 2 COOH) 2 .HNO 3 , in the paraelectric phase (T=295K) are presented. Spectral dispersion of light reflection R(E) have been measured in the range of 3-22eV and the optical functions n(E) and k(E) have been calculated using Kramers-Kronig relations. First principal calculations of the electron energy characteristic and optical spectra of DGN crystal have been performed in the frame of density functional theory using CASTEP code (CAmbridge Serial Total Energy Package). Optical transitions forming the low-energy edge of fundamental absorption are associated with the nitrate groups NO 3 . Peculiarities of the band structure and DOS projected onto glycine and NO 3 groups confirm the molecular character of DGN crystal

  8. Luminescence properties of KCl:Ag{sup -} crystals excited near the fundamental absorption edge

    Energy Technology Data Exchange (ETDEWEB)

    Kawai, Taketoshi, E-mail: [Department of Physical Science, Graduate School of Science, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku, Sakai, Osaka 599-8531 (Japan); Hirai, Takeshi [Department of Physical Science, Faculty of Science and Engineering, Ritsumeikan University, Noji Higashi 1-1-1, Kusatsu, Shiga 525-8577 (Japan)


    Luminescence properties of KCl single crystals doped with Ag{sup -} centers have been investigated under various excitation energies around the fundamental absorption edge at low temperatures. Under the excitation at 6.89 eV, which is lower than the intrinsic exciton energy by 0.87 eV, the A Prime luminescence band due to the intraionic transition in the Ag{sup -} ion is dominantly observed at 2.91 eV. On the other hand, the excitation at 6.66 eV induces a broad luminescence band at 2.60 eV in addition to the A Prime luminescence band. From the comparison with the localized excitons in KCl:I crystals, the 2.60 eV luminescence band is attributed to the two-center type localized exciton related with the Ag{sup -} ion. The adiabatic potential energy surfaces of the excited states in the Ag{sup -} center and the localized exciton in KCl:Ag{sup -} are discussed. - Highlights: Black-Right-Pointing-Pointer We study the luminescence properties of KCl single crystals doped with Ag{sup -} ions. Black-Right-Pointing-Pointer The excitation around the absorption edge induces a broad luminescence at 2.60 eV. Black-Right-Pointing-Pointer The 2.60 eV luminescence is attributed to the exciton localized at the Ag{sup -} ion. Black-Right-Pointing-Pointer The localized exciton has the two-center type configuration of the relaxed exciton.

  9. Research on reducing the edge effect in magnetorheological finishing. (United States)

    Hu, Hao; Dai, Yifan; Peng, Xiaoqiang; Wang, Jianmin


    The edge effect could not be avoided in most optical manufacturing methods based on the theory of computer controlled optical surfacing. The difference between the removal function at the workpiece edge and that inside it is also the primary cause for edge effect in magnetorheological finishing (MRF). The change of physical dimension and removal ratio of the removal function is investigated through experiments. The results demonstrate that the situation is different when MRF "spot" is at the leading edge or at the trailing edge. Two methods for reducing the edge effect are put into practice after analysis of the processing results. One is adopting a small removal function for dealing with the workpiece edge, and the other is utilizing the removal function compensation. The actual processing results show that these two ways are both effective on reducing the edge effect in MRF.

  10. Environmental Dataset Gateway (EDG) CS-W Interface (United States)

    U.S. Environmental Protection Agency — Use the Environmental Dataset Gateway (EDG) to find and access EPA's environmental resources. Many options are available for easily reusing EDG content in other...

  11. Urbanization Impacts on Mammals across Urban-Forest Edges and a Predictive Model of Edge Effects (United States)

    Villaseñor, Nélida R.; Driscoll, Don A.; Escobar, Martín A. H.; Gibbons, Philip; Lindenmayer, David B.


    With accelerating rates of urbanization worldwide, a better understanding of ecological processes at the wildland-urban interface is critical to conserve biodiversity. We explored the effects of high and low-density housing developments on forest-dwelling mammals. Based on habitat characteristics, we expected a gradual decline in species abundance across forest-urban edges and an increased decline rate in higher contrast edges. We surveyed arboreal mammals in sites of high and low housing density along 600 m transects that spanned urban areas and areas turn on adjacent native forest. We also surveyed forest controls to test whether edge effects extended beyond our edge transects. We fitted models describing richness, total abundance and individual species abundance. Low-density housing developments provided suitable habitat for most arboreal mammals. In contrast, high-density housing developments had lower species richness, total abundance and individual species abundance, but supported the highest abundances of an urban adapter (Trichosurus vulpecula). We did not find the predicted gradual decline in species abundance. Of four species analysed, three exhibited no response to the proximity of urban boundaries, but spilled over into adjacent urban habitat to differing extents. One species (Petaurus australis) had an extended negative response to urban boundaries, suggesting that urban development has impacts beyond 300 m into adjacent forest. Our empirical work demonstrates that high-density housing developments have negative effects on both community and species level responses, except for one urban adapter. We developed a new predictive model of edge effects based on our results and the literature. To predict animal responses across edges, our framework integrates for first time: (1) habitat quality/preference, (2) species response with the proximity to the adjacent habitat, and (3) spillover extent/sensitivity to adjacent habitat boundaries. This framework will

  12. Urbanization impacts on mammals across urban-forest edges and a predictive model of edge effects. (United States)

    Villaseñor, Nélida R; Driscoll, Don A; Escobar, Martín A H; Gibbons, Philip; Lindenmayer, David B


    With accelerating rates of urbanization worldwide, a better understanding of ecological processes at the wildland-urban interface is critical to conserve biodiversity. We explored the effects of high and low-density housing developments on forest-dwelling mammals. Based on habitat characteristics, we expected a gradual decline in species abundance across forest-urban edges and an increased decline rate in higher contrast edges. We surveyed arboreal mammals in sites of high and low housing density along 600 m transects that spanned urban areas and areas turn on adjacent native forest. We also surveyed forest controls to test whether edge effects extended beyond our edge transects. We fitted models describing richness, total abundance and individual species abundance. Low-density housing developments provided suitable habitat for most arboreal mammals. In contrast, high-density housing developments had lower species richness, total abundance and individual species abundance, but supported the highest abundances of an urban adapter (Trichosurus vulpecula). We did not find the predicted gradual decline in species abundance. Of four species analysed, three exhibited no response to the proximity of urban boundaries, but spilled over into adjacent urban habitat to differing extents. One species (Petaurus australis) had an extended negative response to urban boundaries, suggesting that urban development has impacts beyond 300 m into adjacent forest. Our empirical work demonstrates that high-density housing developments have negative effects on both community and species level responses, except for one urban adapter. We developed a new predictive model of edge effects based on our results and the literature. To predict animal responses across edges, our framework integrates for first time: (1) habitat quality/preference, (2) species response with the proximity to the adjacent habitat, and (3) spillover extent/sensitivity to adjacent habitat boundaries. This framework will

  13. Urbanization impacts on mammals across urban-forest edges and a predictive model of edge effects.

    Directory of Open Access Journals (Sweden)

    Nélida R Villaseñor

    Full Text Available With accelerating rates of urbanization worldwide, a better understanding of ecological processes at the wildland-urban interface is critical to conserve biodiversity. We explored the effects of high and low-density housing developments on forest-dwelling mammals. Based on habitat characteristics, we expected a gradual decline in species abundance across forest-urban edges and an increased decline rate in higher contrast edges. We surveyed arboreal mammals in sites of high and low housing density along 600 m transects that spanned urban areas and areas turn on adjacent native forest. We also surveyed forest controls to test whether edge effects extended beyond our edge transects. We fitted models describing richness, total abundance and individual species abundance. Low-density housing developments provided suitable habitat for most arboreal mammals. In contrast, high-density housing developments had lower species richness, total abundance and individual species abundance, but supported the highest abundances of an urban adapter (Trichosurus vulpecula. We did not find the predicted gradual decline in species abundance. Of four species analysed, three exhibited no response to the proximity of urban boundaries, but spilled over into adjacent urban habitat to differing extents. One species (Petaurus australis had an extended negative response to urban boundaries, suggesting that urban development has impacts beyond 300 m into adjacent forest. Our empirical work demonstrates that high-density housing developments have negative effects on both community and species level responses, except for one urban adapter. We developed a new predictive model of edge effects based on our results and the literature. To predict animal responses across edges, our framework integrates for first time: (1 habitat quality/preference, (2 species response with the proximity to the adjacent habitat, and (3 spillover extent/sensitivity to adjacent habitat boundaries. This


    DEFF Research Database (Denmark)


    An optical fibre having a periodicidal cladding structure provididing a photonic band gap structure with superior qualities. The periodical structure being one wherein high index areas are defined and wherein these are separated using a number of methods. One such method is the introduction...... of additional low index elements, another method is providing elongated elements deformed in relation to a circular cross section. Also described is a cladding structure comprising elongated elements of a material having an index of refraction higher than that of the material adjacent thereto. Using...

  15. Prenatal diagnosis of amniotic band syndrome

    Directory of Open Access Journals (Sweden)

    Laxmi Devi Padmanabhan


    Full Text Available Amniotic band can cause a broad spectrum of anomalies ranging from simple band constrictions to major craniofacial and visceral defects. It can cause significant neonatal morbidity. Accurate diagnosis will help in the management of the present pregnancy and in counseling with regard to future pregnancies. Here we report three cases of amniotic band syndrome detected in the prenatal period.

  16. Multi-band Modelling of Appearance

    DEFF Research Database (Denmark)

    Stegmann, Mikkel Bille; Larsen, Rasmus


    the appearance of both derived feature bands and an intensity band. As a special case of feature-band augmented appearance modelling we propose a dedicated representation with applications to face segmentation. The representation addresses a major problem within face recognition by lowering the sensitivity...

  17. Multi-band Modelling of Appearance

    DEFF Research Database (Denmark)

    Stegmann, Mikkel Bille; Larsen, Rasmus


    the appearance of both derived feature bands and an intensity band. As a special case of feature-band augmented appearance modelling we propose a dedicated representation with applications to face segmentation. The representation addresses a major problem within face recognition by lowering the sensitivity...

  18. Band engineering of GaSbN alloy for solar fuel applications (United States)

    Shi, Qing; Chen, Ying-Chih; Chowdhury, Faqrul A.; Mi, Zetian; Michaud-Rioux, Vincent; Guo, Hong


    III-nitride nanostructures possess ideal attributes for harvesting solar energy and generating solar fuel through natural water splitting. The most basic requirement of the latter is to engineer the band gap of the semiconductor to straddle the redox potential of water molecules. To this end, using first principles method we predict that GaN engineered with Sb doping at the dilute limit of 0.3% and/or slightly less is suitable for photochemical water splitting applications. The valence band edge is very significantly enhanced by dilute Sb doping while the conduction band edge is not. The microscopic physics behind the strong band bowing by such a small impurity concentration, not seen in other III-V semiconductors, is revealed by investigating the quantum interaction between Sb impurity states and the host GaN states. The dilute doping limit dictates very large systems to be calculated at the hybrid exchange-correlation level which is made possible by our newly developed first principles approach.

  19. Zigzag graphene nanoribbon edge reconstruction with Stone-Wales defects

    DEFF Research Database (Denmark)

    Rodrigues, J. N. B.; Gonçalves, P. A. D; Rodrigues, N. F. G.


    the edge; at the Dirac points one of these lengths diverges, whereas the other remains finite, of the order of the lattice parameter. We trace this curious effect to the doubling of the unit cell along the edge, brought about by the edge reconstruction. In the presence of a magnetic field, the zero......-energy Landau level is no longer degenerate with edge states as in the case of the pristine zigzag ribbon....

  20. Edge and line feature extraction based on covariance models

    NARCIS (Netherlands)

    van der Heijden, Ferdinand

    Image segmentation based on contour extraction usually involves three stages of image operations: feature extraction, edge detection and edge linking. This paper is devoted to the first stage: a method to design feature extractors used to detect edges from noisy and/or blurred images.

  1. The use of edge habitats by commuting and foraging bats

    NARCIS (Netherlands)

    Verboom, B.


    Travelling routes and foraging areas of many bat species are mainly along edge habitats, such as treelines, hedgerows, forest edges, and canal banks. This thesis deals with the effects of density, configuration, and structural features of edge habitats on the occurrence of bats. Four

  2. Atomic scale structures of interfaces between kaolinite edges and water

    NARCIS (Netherlands)

    Liu, X.; Lu, X.; Wang, R.; Meijer, E.J.; Zhou, H.; He, H.


    This paper reports the atomic scale structures of kaolinite edge surfaces in contact with water. The commonly occurring edge surfaces are investigated (i.e. (0 1 0) and (1 1 0)) by using first principles molecular dynamics (FPMD) technique. For (1 1 0)-type edge surface, there are two different

  3. South African Identities on the Edge: Lauren Beukes's Moxyland ...

    African Journals Online (AJOL)

    We follow the work of various critics and argue that the text presents identity as fractured, riven and characterized by sharp edges. The edges in question refer to the boundaries of personal, corporeal, national and corporate identity. These edges may be considered symptomatic of the individual and social demands placed ...

  4. Roads as edges: Effects on birds in forested landscapes (United States)

    Yvette K. Ortega; David E. Capen


    Numerous studies have documented that forest edges affect habitat use and reproductive success of forest birds, but few studies have considered edges created by narrow breaks in the forest canopy. We compared predation rates on artificial nests placed within forest habitat along edge transects, 10 m from unpaved roads, and along interior transects, 300 m from forest-...

  5. Education Confronts Changing Demographics. The Challenge to Edge Cities. (United States)

    Tushnet, Naida C.

    This monograph introduces a conference addressing the educational issues of the edge cities of the urban Pacific Southwest. Edge cities on the outside of urban cores (edge cities) are currently facing many of the problems formerly experienced only in urban areas. Of the 30 fastest-growing cities of over 100,000 residents in the country, 19 are…

  6. Bulk Versus Edge in the Quantum Hall Effect


    Kao, Y. -C.; Lee, D. -H.


    The manifestation of the bulk quantum Hall effect on edge is the chiral anomaly. The chiral anomaly {\\it is} the underlying principle of the ``edge approach'' of quantum Hall effect. In that approach, $\\sxy$ should not be taken as the conductance derived from the space-local current-current correlation function of the pure one-dimensional edge problem.

  7. The effect of defocus on edge contrast sensitivity

    NARCIS (Netherlands)

    Jansonius, NM; Kooijman, AC

    The effect of optical blur (defocus) on edge contrast sensitivity was studied. Edge contrast sensitivity detoriates with fairly small amounts of blur (similar to 0.5 D) and is roughly reduced by half for each dioptre of blur. The effect of blur on edge contrast sensitivity equals the effect of blur

  8. Magnetic edge states and magnetotransport in graphene antidot barriers

    DEFF Research Database (Denmark)

    Thomsen, M. R.; Power, Stephen; Jauho, Antti-Pekka


    in lattice configuration and antidot edge chirality. Moreover, we calculate the transmittance of disordered GABs and find that magnetic edge states survive a moderate degree of disorder. Due to the long phase-coherence length in graphene and the robustness of these states, we expect magnetic edge states...

  9. L-band brightness temperature disaggregation for use with S-band and C-band radiometer data for WCOM (United States)

    Yao, P.; Shi, J.; Zhao, T.; Cosh, M. H.; Bindlish, R.


    There are two passive microwave sensors onboard the Water Cycle Observation Mission (WCOM), which includes a synthetic aperture radiometer operating at L-S-C bands and a scanning microwave radiometer operating from C- to W-bands. It provides a unique opportunity to disaggregate L-band brightness temperature (soil moisture) with S-band C-bands radiometer data. In this study, passive-only downscaling methodologies are developed and evaluated. Based on the radiative transfer modeling, it was found that the TBs (brightness temperature) between the L-band and S-band exhibit a linear relationship, and there is an exponential relationship between L-band and C-band. We carried out the downscaling results by two methods: (1) downscaling with L-S-C band passive measurements with the same incidence angle from payload IMI; (2) downscaling with L-C band passive measurements with different incidence angle from payloads IMI and PMI. The downscaling method with L-S bands with the same incident angle was first evaluated using SMEX02 data. The RMSE are 2.69 K and 1.52 K for H and V polarization respectively. The downscaling method with L-C bands is developed with different incident angles using SMEX03 data. The RMSE are 2.97 K and 2.68 K for H and V polarization respectively. These results showed that high-resolution L-band brightness temperature and soil moisture products could be generated from the future WCOM passive-only observations.

  10. Reconfigurable L-Band Radar (United States)

    Rincon, Rafael F.


    The reconfigurable L-Band radar is an ongoing development at NASA/GSFC that exploits the capability inherently in phased array radar systems with a state-of-the-art data acquisition and real-time processor in order to enable multi-mode measurement techniques in a single radar architecture. The development leverages on the L-Band Imaging Scatterometer, a radar system designed for the development and testing of new radar techniques; and the custom-built DBSAR processor, a highly reconfigurable, high speed data acquisition and processing system. The radar modes currently implemented include scatterometer, synthetic aperture radar, and altimetry; and plans to add new modes such as radiometry and bi-static GNSS signals are being formulated. This development is aimed at enhancing the radar remote sensing capabilities for airborne and spaceborne applications in support of Earth Science and planetary exploration This paper describes the design of the radar and processor systems, explains the operational modes, and discusses preliminary measurements and future plans.

  11. Novel Compact and High Selectivity Dual-band BPF with Wide Stopband

    Directory of Open Access Journals (Sweden)

    L. Wang


    Full Text Available A novel type of compact and high selectivity dual-band bandpass filter (BPF incorporating a dual-mode defected ground structure resonator (DDGSR and a dual-mode open-stub loaded stepped impedance resonator (DOLSIR is proposed in this paper. Utilizing capacitive source-load coupling and the intrinsic characteristics of the two types of dual-mode resonators, compact dual-band BPF with multi transmission zeros near the passband edges as well as a wide stopband which can be used to achieve high selectivity is realized. An experimental dual-band BPF located at 2.4 and 3.2 GHz was designed and fabricated. The validity of the design approach is verified by good agreement between simulated and measurement results.

  12. Band structure engineering and vacancy induced metallicity at the GaAs-AlAs interface

    KAUST Repository

    Upadhyay Kahaly, M.


    We study the epitaxial GaAs-AlAs interface of wide gap materials by full-potential density functional theory. AlAsthin films on a GaAs substrate and GaAsthin films on an AlAs substrate show different trends for the electronic band gap with increasing film thickness. In both cases, we find an insulating state at the interface and a negligible charge transfer even after relaxation. Differences in the valence and conduction band edges suggest that the energy band discontinuities depend on the growth sequence. Introduction of As vacancies near the interface induces metallicity, which opens great potential for GaAs-AlAs heterostructures in modern electronics.

  13. Applying a rigid band model to the XYB{sub 14} crystal family

    Energy Technology Data Exchange (ETDEWEB)

    Wan Liwen F; Beckman, Scott P, E-mail: [Department of Material Science and Engineering, Iowa State University, Ames, IA 50011 (United States)


    The compounds AlMgB{sub 14}, AlLiB{sub 14} and MgMgB{sub 14} belong to the same space group, Imma, and share similar structural properties. It is predicted that the rigid band model accurately describes the electronic states of these orthorhombic borides. The position of the Fermi level within the states depends on the metal site constituency. In this work the electronic properties of each compound are studied in detail by ab initio methods. Loewdin population analysis is conducted to examine the local charge distribution, and the projected density of states is calculated. It is found that the valence band edge is strongly dominated by the 'B{sub inter}' and 'B{sub connector}' atoms. This indicates that moving the Fermi level into the valence band will result in changes to the local bonding between the icosahedra and the inter-icosahedra B atoms.

  14. Absolute band structure determination on naturally occurring rutile with complex chemistry: Implications for mineral photocatalysis on both Earth and Mars (United States)

    Li, Yan; Xu, Xiaoming; Li, Yanzhang; Ding, Cong; Wu, Jing; Lu, Anhuai; Ding, Hongrui; Qin, Shan; Wang, Changqiu


    Rutile is the most common and stable form of TiO2 that ubiquitously existing on Earth and other terrestrial planets like Mars. Semiconducting mineral such as rutile-based photoredox reactions have been considered to play important roles in geological times. However, due to the inherent complexity in chemistry, the precision determination on band structure of natural rutile and the theoretical explanation on its solar-driven photochemistry have been hardly seen yet. Considering the multiple minor and trace elements in natural rutile, we firstly obtained the single-crystal crystallography, mineralogical composition and defects characteristic of the rutile sample by using both powder and single crystal X-ray diffraction, electron microprobe analysis and X-ray photoelectron spectroscopy. Then, the band gap was accurately determined by synchrotron-based O K-edge X-ray absorption and emission spectra, which was firstly applied to natural rutile due to its robustness on compositions and defects. The absolute band edges of the rutile sample was calculated by considering the electronegativity of the atoms, band gap and point of zero charge. Besides, after detecting the defect energy levels by photoluminescence spectra, we drew the schematic band structure of natural rutile. The band gap (2.7 eV) of natural rutile was narrower than that of synthetic rutile (3.0 eV), and the conduction and valence band edges of natural rutile at pH = pHPZC were determined to be -0.04 V and 2.66 V (vs. NHE), respectively. The defect energy levels located at nearly the middle position of the forbidden band. Further, we used theoretical calculations to verify the isomorphous substitution of Fe and V for Ti gave rise to the distortion of TiO6 octahedron and created vacancy defects in natural rutile. Based on density functional theory, the narrowed band gap was interpreted to the contribution of Fe-3d and V-3d orbits, and the defect energy state was formed by hybridization of O-2p and Fe/V/Ti-3d

  15. Photonic Band Gap Accelerator Demonstration at Ku-Band.

    CERN Document Server

    Smirnova, Evgenya I; Edwards, Randall L; Kesar, Amit S; Mastovsky, Ivan; Shapiro, Michael A; Temkin, Richard J


    We report progress on the design and cold test of a metal Ku-band PBG accelerator structure. The 17.140 GHz 6-cell PBG accelerator structure with reduced long-range wakefields was designed for the experiment. The copper structure was electroformed and cold-tested. Tuning was performed through chemical etching of the rods. Final cold test measurements were found to be in very good agreement with the design. The structure will be installed on the beam line at the accelerator laboratory at Massachusetts Institute of Technology and will be powered with 3 MW of peak power from the Haimson 17.14 GHz klystron. Results of the design, fabrication, cold test and hot test on the Haimson accelerator will be presented.

  16. Dust bands in the asteroid belt

    International Nuclear Information System (INIS)

    Sykes, M.V.; Greenberg, R.; Dermott, S.F.; Nicholson, P.D.; Burns, J.A.


    This paper describes the original IRAS observations leading to the discovery of the three dust bands in the asteroid belt and the analysis of data. Special attention is given to an analytical model of the dust band torus and to theories concerning the origin of the dust bands, with special attention given to the collisional equilibrium (asteroid family), the nonequilibrium (random collision), and the comet hypotheses of dust-band origin. It is noted that neither the equilibrium nor nonequilibrium models, as currently formulated, present a complete picture of the IRAS dust-band observations. 32 refs

  17. Flat band in disorder-driven non-Hermitian Weyl semimetals (United States)

    Zyuzin, A. A.; Zyuzin, A. Yu.


    We study the interplay of disorder and band-structure topology in a Weyl semimetal with a tilted conical spectrum around the Weyl points. The spectrum of particles is given by the eigenvalues of a non-Hermitian matrix, which contains contributions from a Weyl Hamiltonian and complex self-energy due to electron elastic scattering on disorder. We find that the tilt-induced matrix structure of the self-energy gives rise to either a flat band or a nodal line segment at the interface of the electron and hole pockets in the bulk band structure of type-II Weyl semimetals depending on the Weyl cone inclination. For the tilt in a single direction in momentum space, each Weyl point expands into a flat band lying on the plane, which is transverse to the direction of the tilt. The spectrum of the flat band is fully imaginary and is separated from the in-plane dispersive part of the spectrum by the "exceptional nodal ring" where the matrix of the Green's function in momentum-frequency space is defective. The tilt in two directions might shrink a flat band into a nodal line segment with "exceptional edge points." We discuss the connection to the non-Hermitian topological theory.

  18. Three Band Indexes for Leaf Nitrogen Content estimation in Holm oak in a temporal scale (United States)

    Pacheco-Labrador, J.; González, M. R.; Martín, M. P.; Riaño, D.; Salas, J.


    Holm oak Leaf Nitrogen Content (LNC) has been estimated in a Mediterranean savanna ecosystem "dehesa" in the Iberian Peninsula using an ASD FieldSpec° FR3 spectroradiometer connected to a Plant Probe with Leaf Clip ( One of each ten bands between 400nm and 2500nm were selected, and two different Three Bands Indexes (TBI) with all the possible band combinations were built. Linear and logarithmic empirical relations with LNC were analyzed and the most correlated models were independently and inter-annually validated using the bootstrap technique. Data from two complete phenological years were used, the first one for calibration and the second for validation. The consideration of the temporal variation of both, optical responses and LNC resulted critical for the achievement of robust models, which showed high correlations (R2 max =0.81) and low errors (RMSE min = 8.74%). Nitrogen absorption bands were found in the selected indexes where non-correlated bands and usually the red edge region were also involved. Three Band Indexes may be sensible to physical responses of nitrogen bounds in the leaf molecules, though it is still necessary proving the influence of such absorptions in these relations.

  19. Edge responses are different in edges under natural versus anthropogenic influence: a meta-analysis using ground beetles. (United States)

    Magura, Tibor; Lövei, Gábor L; Tóthmérész, Béla


    Most edges are anthropogenic in origin, but are distinguishable by their maintaining processes (natural vs. continued anthropogenic interventions: forestry, agriculture, urbanization). We hypothesized that the dissimilar edge histories will be reflected in the diversity and assemblage composition of inhabitants. Testing this "history-based edge effect" hypothesis, we evaluated published information on a common insect group, ground beetles (Coleoptera: Carabidae) in forest edges. A meta-analysis showed that the diversity-enhancing properties of edges significantly differed according to their history. Forest edges maintained by natural processes had significantly higher species richness than their interiors, while edges with continued anthropogenic influence did not. The filter function of edges was also essentially different depending on their history. For forest specialist species, edges maintained by natural processes were penetrable, allowing these species to move right through the edges, while edges still under anthropogenic interventions were impenetrable, preventing the dispersal of forest specialists out of the forest. For species inhabiting the surrounding matrix (open-habitat and generalist species), edges created by forestry activities were penetrable, and such species also invaded the forest interior. However, natural forest edges constituted a barrier and prevented the invasion of matrix species into the forest interior. Preserving and protecting all edges maintained by natural processes, and preventing anthropogenic changes to their structure, composition, and characteristics are key factors to sustain biodiversity in forests. Moreover, the increasing presence of anthropogenic edges in a landscape is to be avoided, as they contribute to the loss of biodiversity. Simultaneously, edges under continued anthropogenic disturbance should be restored by increasing habitat heterogeneity.

  20. Edge-defect induced spin-dependent Seebeck effect and spin figure of merit in graphene nanoribbons. (United States)

    Liu, Qing-Bo; Wu, Dan-Dan; Fu, Hua-Hua


    By using the first-principle calculations combined with the non-equilibrium Green's function approach, we have studied spin caloritronic properties of graphene nanoribbons (GNRs) with different edge defects. The theoretical results show that the edge-defected GNRs with sawtooth shapes can exhibit spin-dependent currents with opposite flowing directions by applying temperature gradients, indicating the occurrence of the spin-dependent Seebeck effect (SDSE). The edge defects bring about two opposite effects on the thermal spin currents: the enhancement of the symmetry of thermal spin-dependent currents, which contributes to the realization of pure thermal spin currents, and the decreasing of the spin thermoelectric conversion efficiency of the devices. It is fortunate that applying a gate voltage is an efficient route to optimize these two opposite spin thermoelectric properties towards realistic device applications. Moreover, due to the existence of spin-splitting band gaps, the edge-defected GNRs can be designed as spin-dependent Seebeck diodes and rectifiers, indicating that the edge-defected GNRs are potential candidates for room-temperature spin caloritronic devices.

  1. Magnetic edge states and magnetotransport in graphene antidot barriers

    DEFF Research Database (Denmark)

    Thomsen, M. R.; Power, Stephen; Jauho, Antti-Pekka


    for antidots smaller than the magnetic length and demonstrate the presence of magnetic edge states, which are localized states on the periphery of the antidots due to successive reflections on the antidot edge in the presence of a magnetic field. We show that these states are robust against variations...... in lattice configuration and antidot edge chirality. Moreover, we calculate the transmittance of disordered GABs and find that magnetic edge states survive a moderate degree of disorder. Due to the long phase-coherence length in graphene and the robustness of these states, we expect magnetic edge states...

  2. Graph Edge Coloring Vizing's Theorem and Goldberg's Conjecture

    CERN Document Server

    Stiebitz, Michael; Toft, Bjarne; Favrholdt, Lene M


    Features recent advances and new applications in graph edge coloring Reviewing recent advances in the Edge Coloring Problem, Graph Edge Coloring: Vizing's Theorem and Goldberg's Conjecture provides an overview of the current state of the science, explaining the interconnections among the results obtained from important graph theory studies. The authors introduce many new improved proofs of known results to identify and point to possible solutions for open problems in edge coloring. The book begins with an introduction to graph theory and the concept of edge coloring. Subsequent chapters explor

  3. Three Dimensional Digital Image Processing using Edge Detectors

    Directory of Open Access Journals (Sweden)

    John Schmeelk


    Full Text Available This paper provides an introduction to three dimensional image edge detection and its relationship to partial derivatives, convolutions and wavelets. We are especially addressing the notion of edge detection because it has far reaching applications in all areas of research to include medical research. A patient can be diagnosed as having an aneurysm by studying an angiogram. An angiogram is the visual view of the blood vessels whereby the edges are highlighted through the implementation of edge detectors. This process is completed through convolution, wavelets and matrix techniques. Some illustrations included will be vertical, horizontal, Sobel and wavelet edge detectors.

  4. An image super-resolution method considering edge character

    International Nuclear Information System (INIS)

    Yuan, Wang Yuan; Yong, Liang; Ming, Zhang Cheng


    Maximum A Posteriori (MAP) estimation is an important image super-resolution method. However, a clear edge is difficult to maintain. To address this problem, we analyze the causes of poor edge stability. We also present a method for reducing the smoothness of the edge, maintaining the smoothness of the soft regional area, and reducing pseudo noise to improve connected edge retention. The improved method fixes the iteration number and smoothing factor of the MAP estimation by using Gauss-Laplacian image edge extraction. Finally, the validity of this method is verified by its application to feature information recognition in remote sensing images

  5. Two-Dimensional Edge Detection by Guided Mode Resonant Metasurface (United States)

    Saba, Amirhossein; Tavakol, Mohammad Reza; Karimi-Khoozani, Parisa; Khavasi, Amin


    In this letter, a new approach to perform edge detection is presented using an all-dielectric CMOS-compatible metasurface. The design is based on guided-mode resonance which provides a high quality factor resonance to make the edge detection experimentally realizable. The proposed structure that is easy to fabricate, can be exploited for detection of edges in two dimensions due to its symmetry. Also, the trade-off between gain and resolution of edge detection is discussed which can be adjusted by appropriate design parameters. The proposed edge detector has also the potential to be used in ultrafast analog computing and image processing.

  6. Orientations of infinite graphs with prescribed edge-connectivity

    DEFF Research Database (Denmark)

    Thomassen, Carsten


    We prove a decomposition result for locally finite graphs which can be used to extend results on edge-connectivity from finite to infinite graphs. It implies that every 4k-edge-connected graph G contains an immersion of some finite 2k-edge-connected Eulerian graph containing any prescribed vertex...... set (while planar graphs show that G need not containa subdivision of a simple finite graph of large edge-connectivity). Also, every 8k-edge connected infinite graph has a k-arc-connected orientation, as conjectured in 1989....

  7. Antichiral Edge States in a Modified Haldane Nanoribbon (United States)

    Colomés, E.; Franz, M.


    Topological phases of fermions in two dimensions are often characterized by chiral edge states. By definition, these propagate in opposite directions at the two parallel edges when the sample geometry is that of a rectangular strip. We introduce here a model which exhibits what we call "antichiral" edge modes. These propagate in the same direction at both parallel edges of the strip and are compensated by counterpropagating modes that reside in the bulk. General arguments and numerical simulations show that backscattering is suppressed even when strong disorder is present in the system. We propose a feasible experimental realization of a system showing such antichiral edge modes in transition metal dichalcogenide monolayers.

  8. Viscosity in the edge of tokamak plasmas

    International Nuclear Information System (INIS)

    Stacey, W.M.


    A fluid representation of viscosity has been incorporated into a set of fluid equations that are maximally ordered in the ''short-radial-gradient-scale-length'' (srgsl) ordering that is appropriate for the edge of tokamak plasmas. The srgsl ordering raises viscous drifts and other viscous terms to leading order and fundamentally alters the character of the fluid equations. A leasing order viscous drift is identified. Viscous-driven radial particle and energy fluxes in the scrape-off layer and divertor channel are estimated to have an order unity effect in reducing radial peaking of energy fluxes transported along the field lines to divertor collector plates

  9. Refining Nodes and Edges of State Machines

    DEFF Research Database (Denmark)

    Hallerstede, Stefan; Snook, Colin


    State machines are hierarchical automata that are widely used to structure complex behavioural specifications. We develop two notions of refinement of state machines, node refinement and edge refinement. We compare the two notions by means of examples and argue that, by adopting simple conventions...... refinement theory and UML-B state machine refinement influences the style of node refinement. Hence we propose a method with direct proof of state machine refinement avoiding the detour via Event-B that is needed by UML-B....

  10. Edge plasma fluctuations measurements in fusion experiments

    International Nuclear Information System (INIS)

    Schrittwieser, R.; Ionitha, C.; Balan, P.C.; Varandas, C.A.F.; Figueiredo, H.F.C.; Silva, C.; Stoeckel, J.; Adamek, J.; Hron, M.; Tichy, M.; Hidalgo, C.; Pedrosa, M.A.; Calderon, E.; Martines, E.; Van Oost, G.; Rasmussen, J.J.; Naulin, V.


    We report on investigations on electrostatic fluctuations in the edge plasma region which have been carried out during the last few years at several European fusion experiments. Various methods and probe arrangements have been used to determine fluctuations of the plasma potential, the electric field and the electron temperature. Investigations were under-taken in ISTTOK (Instituto Superior Tecnico TOKamak), Lisbon, Portugal, in CASTOR (Czech Academy of Science TORus), Prague, Czech Republic, and the TJ-II Flexible Heliac at CIEMAT in Madrid, Spain. (author)

  11. Near edge x-ray spectroscopy theory

    International Nuclear Information System (INIS)


    We propose to develop a quantitative theory of x-ray spectroscopies in the near edge region, within about 100 eV of threshold. These spectroscopies include XAFS (X-ray absorption fine structure), photoelectron diffraction (PD), and diffraction anomalous fine structure (DAFS), all of which are important tools for structural studies using synchrotron radiation x-ray sources. Of primary importance in these studies are many-body effects, such as the photoelectron self-energy, and inelastic losses. A better understanding of these quantities is needed to obtain theories without adjustable parameters. We propose both analytical and numerical calculations, the latter based on our x-ray spectroscopy codes FEFF

  12. Plasma Edge Control in Tore Supra

    International Nuclear Information System (INIS)

    Evans, T.E.; Mioduszewski, P.K.; Foster, C.; Haste, G.; Horton, L.; Grosman, A.; Ghendrih, P.; Chatelier, M.; Capes, H.; Michelis, C. De; Fall, T.; Geraud, A.; Grisolia, C.; Guilhem, D.; Hutter, T.


    TORE SUPRA is a large superconducting tokamak designed for sustaining long inductive pulses (t∼ 30 s). In particular, all the first wall components have been designed for steady-state heat and particle exhaust, particle injection, and additional heating. In addition to these technological assets, a strict control of the plasma-wall interactions is required. This has been done at low power: experiments with ohmic heating have been mainly devoted to the pump limiter, ergodic divertor and pellet injection experiments. Some specific problems arising in large tokamaks are encountered; the pump limiter and the ergodic divertor yield the expected effects on the plasma edge. The effects on the bulk are discussed

  13. Laser Surface Hardening of Groove Edges (United States)

    Hussain, A.; Hamdani, A. H.; Akhter, R.; Aslam, M.


    Surface hardening of groove-edges made of 3Cr13 Stainless Steel has been carried out using 500 W CO2 laser with a rectangular beam of 2.5×3 mm2. The processing speed was varied from 150-500 mm/min. It was seen that the hardened depth increases with increase in laser interaction time. A maximum hardened depth of around 1mm was achieved. The microhardness of the transformed zone was 2.5 times the hardness of base metal. The XRD's and microstructural analysis were also reported.

  14. Thermal physics of transition edge sensor arrays

    International Nuclear Information System (INIS)

    Hoevers, H.F.C.


    Thermal transport in transition edge sensor (TES)-based microcalorimeter arrays is reviewed. The fundamentals of thermal conductance in Si 3 N 4 membranes are discussed and the magnitude of the electron-phonon coupling and Kapitza coupling in practical devices is summarized. Next, the thermal transport in high-stopping power and low-heat capacity absorbers, required for arrays of TES microcalorimeters, is discussed in combination with a performance analysis of detectors with mushroom-absorbers. Finally, the phenomenology of unexplained excess noise, observed in both Mo- and Ti-based TESs, is briefly summarized and related with the coupling of the TES to the heat bath

  15. Band alignment of rutile and anatase TiO₂. (United States)

    Scanlon, David O; Dunnill, Charles W; Buckeridge, John; Shevlin, Stephen A; Logsdail, Andrew J; Woodley, Scott M; Catlow, C Richard A; Powell, Michael J; Palgrave, Robert G; Parkin, Ivan P; Watson, Graeme W; Keal, Thomas W; Sherwood, Paul; Walsh, Aron; Sokol, Alexey A


    The most widely used oxide for photocatalytic applications owing to its low cost and high activity is TiO₂. The discovery of the photolysis of water on the surface of TiO₂ in 1972 launched four decades of intensive research into the underlying chemical and physical processes involved. Despite much collected evidence, a thoroughly convincing explanation of why mixed-phase samples of anatase and rutile outperform the individual polymorphs has remained elusive. One long-standing controversy is the energetic alignment of the band edges of the rutile and anatase polymorphs of TiO₂ (ref. ). We demonstrate, through a combination of state-of-the-art materials simulation techniques and X-ray photoemission experiments, that a type-II, staggered, band alignment of ~ 0.4 eV exists between anatase and rutile with anatase possessing the higher electron affinity, or work function. Our results help to explain the robust separation of photoexcited charge carriers between the two phases and highlight a route to improved photocatalysts.

  16. Atomic scattering factor of the ASTRO-H (Hitomi) SXT reflector around the gold's L edges

    DEFF Research Database (Denmark)

    Kikuchi, Naomichi; Kurashima, Sho; Ishida, Manabu


    The atomic scattering factor in the energy range of 11.2-15.4 keV for the ASTRO-H Soft X-ray Telescope (SXT) is reported. The large effective area of the SXT makes use of photon spectra above 10 keV viable, unlike most other X-ray satellites with total-reflection mirror optics. Presence of gold's L-edges...... in the energy band is a major issue, as it complicates the function of the effective area. In order to model the area, the reflectivity measurements in the 11.2-15.4 keV band with the energy pitch of 0.4-0.7 eV were made in the synchrotron beamline Spring-8 BL01B1. We obtained atomic scattering factors f1 and f......2 by the curve fitting to the reflectivities of our witness sample. The edges associated with the L-I, II, and III transitions are identified, of which the depths are found to be roughly 60% shallower than those expected from the Henke's atomic scattering factor....

  17. Giemsa C-banding of Barley Chromosomes. I: Banding Pattern Polymorphism

    DEFF Research Database (Denmark)

    Linde-Laursen, Ib


    Twenty barley (Hordeum vulgare) lines studied had a common basic chromosome banding pattern. Most bands ranged from medium to very small in size. The most conspicuous banding occurred at or near the centromeres, in the proximal, intercalary parts of most chromosome arms and beside the secondary c...... 7. Seventeen differently banded karyotypes were found. Some banding pattern polymorphisms can be used in cytological and cytogenetic studies....

  18. Influence of edge on predator prey distribution and abundance (United States)

    Ferguson, Steven H.


    I investigated the effect of spatial configuration on distribution and abundance of invertebrate trophic groups by counting soil arthropods under boxes (21 × 9.5 cm) arranged in six different patterns that varied in the amount of edge (137-305 cm). I predicted fewer individuals from the consumer trophic group (Collembola) in box groups with greater amount of edge. This prediction was based on the assumption that predators (mites, ants, spiders, centipedes) select edge during foraging and thereby reduce abundance of the less mobile consumer group under box patterns with greater edge. Consumer abundance (Collembola) was not correlated with amount of edge. Among the predator groups, mite, ant and centipede abundance related to the amount of edge of box groups. However, in contrast to predictions, abundance of these predators was negatively correlated with amount of edge in box patterns. All Collembola predators, with the exception of ants, were less clumped in distribution than Collembola. The results are inconsistent with the view that predators used box edges to predate the less mobile consumer trophic group. Alternative explanations for the spatial patterns other than predator-prey relations include (1) a negative relationship between edge and moisture, (2) a positive relationship between edge and detritus decomposition (i.e. mycelium as food for the consumer group), and (3) a negative relationship between edge and the interstices between adjacent boxes. Landscape patterns likely affect microclimate, food, and predator-prey relations and, therefore, future experimental designs need to control these factors individually to distinguish among alternative hypotheses.

  19. Edge detection in gravity field of the Gheshm sedimentary basin

    Directory of Open Access Journals (Sweden)

    Ali Akbar Hosseini


    Full Text Available Edge detection and edge enhancement techniques play an essential role in interpreting potential field data. This paper describes the application of various edge detection techniques to gravity data in order to delineate the edges of subsurface structures. The edge detection methods comprise analytic signal, total horizontal derivative (THDR, theta angle, tilt angle, hyperbolic of tilt angle (HTA, normalised total horizontal gradient (TDX and normalised horizontal derivative (NTHD. The results showed that almost all filters delineated edges of anomalies successfully. However, the capability of these filters in edge detection decreased as the depth of sources increased. Of the edge enhancement filters, normalized standard deviation filter provided much better results in delineating deeper sources. The edge detection techniques were further applied on a real gravity data from the Gheshm sedimentary basin in the Persian Gulf in Iran. All filters specified a northeast-southwest structural trend. The THDR better outlined the structural morphology and trend. Moreover, it indicated the salt plugs much better than other filters. Analytic signal and THDR successfully enhanced the edges of the shorter wavelength residual structures. Normalized standard deviation (NSTD, TDX and hyperbolic of tilt angle (HTA filters highlighted the likely fault pattern and lineaments, with a dominant northeast-southwest structural trend. This case study shows that the edge detection techniques provides valuable information for geologists and petroleum engineers to outline the horizontal location of geological sources including salt plugs and stand out buried faults, contacts and other tectonic and geological features.

  20. Photonic band gap structure simulator (United States)

    Chen, Chiping; Shapiro, Michael A.; Smirnova, Evgenya I.; Temkin, Richard J.; Sirigiri, Jagadishwar R.


    A system and method for designing photonic band gap structures. The system and method provide a user with the capability to produce a model of a two-dimensional array of conductors corresponding to a unit cell. The model involves a linear equation. Boundary conditions representative of conditions at the boundary of the unit cell are applied to a solution of the Helmholtz equation defined for the unit cell. The linear equation can be approximated by a Hermitian matrix. An eigenvalue of the Helmholtz equation is calculated. One computation approach involves calculating finite differences. The model can include a symmetry element, such as a center of inversion, a rotation axis, and a mirror plane. A graphical user interface is provided for the user's convenience. A display is provided to display to a user the calculated eigenvalue, corresponding to a photonic energy level in the Brilloin zone of the unit cell.

  1. The fundamental absorption edge in MnIn{sub 2}Se{sub 4} layer semi-magnetic semiconductor

    Energy Technology Data Exchange (ETDEWEB)

    Rincón, C., E-mail: [Centro de Estudios de Semiconductores, Departamento de Física, Facultad de Ciencias, Universidad de Los Andes, Mérida (Venezuela, Bolivarian Republic of); Torrres, T.E. [Laboratorio de Magnetismo, Departamento de Física, Facultad de Ciencias, Universidad de Los Andes, Mérida (Venezuela, Bolivarian Republic of); Instituto de Nanociencia de Aragón, Laboratorio de Microscopías Avanzadas, Universidad de Zaragoza 50009, Zaragoza (Spain); Departamento de Física de la Materia Condensada, Facultad de Ciencias, Universidad de Zaragoza 50009, Zaragoza, Spain. (Spain); Sagredo, V. [Laboratorio de Magnetismo, Departamento de Física, Facultad de Ciencias, Universidad de Los Andes, Mérida (Venezuela, Bolivarian Republic of); Jiménez-Sandoval, Sergio J.; Mares-Jacinto, E. [CINVESTAV Querétaro, Libramiento Norponiente N° 2000, Frac. Real de Juriquilla, Querétaro, Qro. 76230 (Mexico)


    From the study of the optical absorption coefficient and photoluminescence spectra of the layer semi-magnetic semiconductor MnIn{sub 2}Se{sub 4} the nature of its fundamental absorption edge is established. It is found that the lowest-energy-gap of this compound is allowed-indirect between parabolic bands that vary from about 1.55–1.43 eV in the temperature range from 10 K to room temperature. In addition, two allowed direct band-to-band transitions beginning at 1.72 and 1.85 eV at 295 K, and at 1.82 and 1.96 eV at 10 K which are related to optical absorption processes between the uppermost Γ{sub 4}(z) and the middle Γ{sub 5}(x) valence bands and the conduction band respectively, are observed in the high energy range. It is also found that the crystal field splitting parameter (Δ{sub cf}) of MnIn{sub 2}Se{sub 4} is of about 0.15 eV nearly independent of the temperature. At energies around 2.2 eV a photoluminescence band related to internal transitions between d-excited levels of Mn{sup +2} ion to its {sup 6}A{sub 1} ground state is also observed in spectra.

  2. Slim edges in double-sided silicon 3D detectors

    International Nuclear Information System (INIS)

    Povoli, M; Dalla Betta, G-F; Bagolini, A; Boscardin, M; Giacomini, G; Vianello, E; Zorzi, N


    Minimization of the insensitive edge area is one of the key requirements for silicon radiation detectors to be used in future silicon trackers. In 3D detectors this goal can be achieved with the active edge, at the expense of a high fabrication process complexity. In the framework of the ATLAS 3D sensor collaboration, we produced modified 3D silicon sensors with a double-sided technology. While this approach is not suitable to obtain active edges, because it does not use a support wafer, it allows for a new type of edge termination, the slim edge. In this paper we report on the development of the slim edge, from numerical simulations to design and testing, proving that it works effectively without increasing the fabrication complexity of silicon 3D detectors, and that it could be further optimized to reduce the insensitive edge region to less than 100 μm.

  3. Aerodynamic Analysis of Trailing Edge Enlarged Wind Turbine Airfoils

    DEFF Research Database (Denmark)

    Xu, Haoran; Shen, Wen Zhong; Zhu, Wei Jun


    characteristics of blunt trailing edge airfoils are caused by blunt body vortices at low angles of attack, and by the combined effect of separation and blunt body vortices at large angles of attack. With the increase of thickness of blunt trailing edge, the vibration amplitudes of lift and drag curves increase......The aerodynamic performance of blunt trailing edge airfoils generated from the DU- 91-W2-250, DU-97-W-300 and DU-96-W-350 airfoils by enlarging the thickness of trailing edge symmetrically from the location of maximum thickness to chord to the trailing edge were analyzed by using CFD and RFOIL...... methods at a chord Reynolds number of 3 × 106. The goal of this study is to analyze the aerodynamic performance of blunt trailing edge airfoils with different thicknesses of trailing edge and maximum thicknesses to chord. The steady results calculated by the fully turbulent k-ω SST, transitional k-ω SST...

  4. Measuring the Edge Recombination Velocity of Monolayer Semiconductors. (United States)

    Zhao, Peida; Amani, Matin; Lien, Der-Hsien; Ahn, Geun Ho; Kiriya, Daisuke; Mastandrea, James P; Ager, Joel W; Yablonovitch, Eli; Chrzan, Daryl C; Javey, Ali


    Understanding edge effects and quantifying their impact on the carrier properties of two-dimensional (2D) semiconductors is an essential step toward utilizing this material for high performance electronic and optoelectronic devices. WS 2 monolayers patterned into disks of varying diameters are used to experimentally explore the influence of edges on the material's optical properties. Carrier lifetime measurements show a decrease in the effective lifetime, τ effective , as a function of decreasing diameter, suggesting that the edges are active sites for carrier recombination. Accordingly, we introduce a metric called edge recombination velocity (ERV) to characterize the impact of 2D material edges on nonradiative carrier recombination. The unpassivated WS 2 monolayer disks yield an ERV ∼ 4 × 10 4 cm/s. This work quantifies the nonradiative recombination edge effects in monolayer semiconductors, while simultaneously establishing a practical characterization approach that can be used to experimentally explore edge passivation methods for 2D materials.

  5. Edge states in quantum Hall effect in graphene

    International Nuclear Information System (INIS)

    Gusynin, V.P.; Miransky, V.A.; Sharapov, S.G.; Shovkovy, I.A.


    We review recent results concerning the spectrum of edge states in the quantum Hall effect in graphene. In particular, special attention is paid to the derivation of the conditions under which gapless edge states exist in the spectrum of graphene with 'zigzag' and 'armchair' edges. It is found that in the case of a half-plane or a ribbon with zigzag edges, there are gapless edge states only when a spin gap dominates over a Dirac mass gap. In the case of a half-plane with an armchair edge, the existence of the gapless edge states depends on the specific type of Dirac mass gaps. The implications of these results for the dynamics in the quantum Hall effect in graphene are discussed

  6. Broad-band beam buncher

    International Nuclear Information System (INIS)

    Goldberg, D.A.; Flood, W.S.; Arthur, A.A.; Voelker, F.


    This patent describes a broad-band beam buncher. This beam buncher consists of: a housing adapted to be eacuated, an electron gun in the housing for producing a beam of electrons, buncher means in the housing forming a buncher cavity which has an entrance opening for receiving the electron beam and an exit opening through which the electron beam passes out of the buncher cavity, a drift tube electrode in the buncher cavity and disposed between the entrance opening and the exit opening with first and second gaps between the drift tube electrode and the entrance and exit openings, the drift tube electrode which has a first drift space through which the electron beam passes in traveling between the entrance and exit openings, modulating means for supplying an ultrahigh frequeny modulating signal to the drift tube electrode for producing velocity modulation of the electrons in the electron beam as the electrons pass through the buncher cavity and the drift tube electrode between the entrance opening and the exit opening, drift space means in the housing forming a second drift space for receiving the velocity modulated electron beam from the exit opening, the velocity modulated electron beam being bunched as it passes along the second drift space, the drift space means has a discharge opening through which the electron beam is discharged from the second drift space after being bunched therein, the modulating means containing a signal source for producing an ultrahigh frequency signal, a transmission line connected between the signal source and the drift tube electrode, and terminating means connected to the drift tube electrode for terminating the transmission line in approximately its characteristic impedance to afford a broad response band with minimum 6 variations therein

  7. Effect of elastic strain on the band gaps, band alignment, and electronic structure of epitaxial ASnO3 (A = Ca, Sr, and Ba) films and heterostructures revealed through in situ photoemission, spectroscopic ellipsometry, and density functional theory (United States)

    Baniecki, John; Yamazaki, Takashi; Aso, Hiroyuki; Imanaka, Yoshihiko; Ricinschi, Dan

    The alkaline earth stannates ASnO3 (A = Ba, Sr, and Ca) are emerging as important materials. Band gaps in stannates are remarkably dependent on volumetric strain with a decrease in volumetric strain of 3 percent in SrSnO3 resulting in an increase in the band gap of 0.35 eV. However, little understanding of volumetric strain dependence on the valence band (VB) electronic structure and band alignments between stannates and other oxides exits. In this talk we will examine the effect of elastic strain on the band gaps, band alignment, and electronic structure of stannate films and heterostructures through in situ photoemission, spectroscopic ellipsometry, scanning transmission electron microscopy with geometric phase analysis, and density functional theory. CaSnO3 (CSO), SrSnO3 (SSO) and La-doped BaSnO3 (BLSO) thin films were grown by pulsed laser epitaxy with strain control via epitaxial buffer layers. While the VB electronic structure is strain dependent VB offsets do not vary significantly with strain, which resulted in ascribing most of the difference in band alignment to the conduction band (CB) edge. Significantly, strain-induced tuning of CB offset differences are as large as 0.6 eV for SSO and may provide a pathway to enhance stannate-based devices.

  8. Investigation of the sensitivity of visible continuum Zeff(0) to edge radiation

    International Nuclear Information System (INIS)

    Telesca, G.; Oost, G. Van; Ongena, J.; Leys, C.; Schoon, N.


    The determination of Z eff from visible continuum radiation is based on the assumption that the line-integrated continuum signal is mostly composed of bremsstrahlung radiation. In practice a wavelength window relatively free of spectral lines is selected, and the line-integrated continuum signal along different chords from the edge up to the central plasma is measured. The local emissivity ε(r) is then calculated using an Abel inversion procedure, and the Z eff profile can be obtained. Although theory and techniques are well established, in any experimental device there remains an uncertainty in the calculated value of Z eff due to the non-bremsstrahlung radiation from the cooler edge plasma (e.g. emission from recombination and molecular bands). As a consequence, the local bremsstrahlung emissivity in the outer region of the plasma cannot be determined and the signal measured along every chord through the plasma contains a spurious contribution. In this paper the error in the value of the central plasma emissivity (and Z eff ) due to edge radiation has been investigated. Qualitative analytical considerations have been complemented by a qualitative analysis, consisting of the comparison of test emissivity profiles with Abel-inverted profiles obtained from the integrals along central chords only. (author) 5 refs., 5 figs

  9. Impact of edge states on device performance of phosphorene heterojunction tunneling field effect transistors. (United States)

    Liu, Fei; Wang, Jian; Guo, Hong


    Black phosphorus (BP) tunneling field effect transistors (TFETs) using heterojunctions (Hes) are investigated by atomistic quantum transport simulations. It is observed that edge states have a great impact on the transport characteristics of BP He-TFETs, which results in the potential pinning effect and deterioration of gate control. However, the on-state current can be effectively enhanced by using hydrogen to saturate the edge dangling bonds in BP He-TFETs, by which means edge states are quenched. By extending layered BP with a smaller band gap to the channel region and modulating the BP thickness, the device performance of BP He-TFETs can be further optimized and can fulfil the requirements of the international technology road-map for semiconductors (ITRS) 2013 for low power applications. In 15 nm 3L-1L and 4L-1L BP He-TFETs along the armchair direction the on-state currents are over two times larger than the current required by ITRS 2013 and can reach above 10 3 μA μm -1 with the fixed off-state current of 10 pA μm -1 . It is also found that the ambipolar effect can be effectively suppressed in BP He-TFETs.

  10. Airborne Multi-Band SAR in the Arctic (United States)

    Gardner, J. M.; Brozena, J. M.; Liang, R.; Ball, D.; Holt, B.; Thomson, J.


    As one component of the Office of Naval Research supported Sea State Departmental Research Initiative during October of 2015 the Naval Research Laboratory flew an ultrawide-band, low-frequency, polarimetric SAR over the southward advancing sea ice in Beaufort Sea. The flights were coordinated with the research team aboard the R/V Sikuliaq working near and in the advancing pack ice. The majority of the SAR data were collected with the L-Band sensor (1000-1500 MHz) from an altitude of 10,000', providing a useful swath 6 km wide with 75o and 25 o angles of incidence at the inner and outer edge of the swath respectively. Some data were also collected with the P-Band SAR (215-915 MHz). The extremely large bandwidths allowed for formation of image pixels as small as 30 cm, however, we selected 60 cm pixel size to reduce image speckle. The separate polarimetric images are calibrated to one pixel to allow for calculations such as polarimetric decompositions that require the images to be well aligned. Both frequencies are useful particularly for the detection of ridges and areas of deformed ice. There are advantages and disadvantages to airborne SAR imagery compared to satellites. The chief advantages being the enormous allowable bandwidth leading to very fine range resolution, and the ability to fly arbitrary trajectories on demand. The latter permits specific areas to be imaged at a given time with a specified illumination direction. An area can even be illuminated from all directions by flying a circular trajectory around the target area. This captures ice features that are sensitive to illumination direction such as cracks, sastrugi orientation, and ridges. The disadvantages include variation of intensity across the swath with range and incidence angle. In addition to the SAR data, we collected photogrammetric imagery from a DSS-439, scanning lidar from a Riegl Q560 and surface brightness temperatures from a KT-19. However, since all of these sensors are nadir pointing

  11. The dynamics of a shear band (United States)

    Giarola, Diana; Capuani, Domenico; Bigoni, Davide


    A shear band of finite length, formed inside a ductile material at a certain stage of a continued homogeneous strain, provides a dynamic perturbation to an incident wave field, which strongly influences the dynamics of the material and affects its path to failure. The investigation of this perturbation is presented for a ductile metal, with reference to the incremental mechanics of a material obeying the J2-deformation theory of plasticity (a special form of prestressed, elastic, anisotropic, and incompressible solid). The treatment originates from the derivation of integral representations relating the incremental mechanical fields at every point of the medium to the incremental displacement jump across the shear band faces, generated by an impinging wave. The boundary integral equations (under the plane strain assumption) are numerically approached through a collocation technique, which keeps into account the singularity at the shear band tips and permits the analysis of an incident wave impinging a shear band. It is shown that the presence of the shear band induces a resonance, visible in the incremental displacement field and in the stress intensity factor at the shear band tips, which promotes shear band growth. Moreover, the waves scattered by the shear band are shown to generate a fine texture of vibrations, parallel to the shear band line and propagating at a long distance from it, but leaving a sort of conical shadow zone, which emanates from the tips of the shear band.

  12. Edge detection and texture classification by cuttlefish. (United States)

    Zylinski, Sarah; Osorio, Daniel; Shohet, Adam J


    Cephalopod mollusks including octopus and cuttlefish are adept at adaptive camouflage, varying their appearance to suit the surroundings. This behavior allows unique access into the vision of a non-human species because one can ask how these animals use spatial information to control their coloration pattern. There is particular interest in factors that affect the relative levels of expression of the Mottle and the Disruptive body patterns. Broadly speaking, the Mottle is displayed on continuous patterned surfaces whereas the Disruptive is used on discrete objects such as pebbles. Recent evidence from common cuttlefish, Sepia officinalis, suggests that multiple cues are relevant, including spatial scale, contrast, and depth. We analyze the body pattern responses of juvenile cuttlefish to a range of checkerboard stimuli. Our results suggest that the choice of camouflage pattern is consistent with a simple model of how cuttlefish classify visual textures, according to whether they are Uniform or patterned, and whether the pattern includes visual edges. In particular, cuttlefish appear to detect edges by sensing the relative spatial phases of two spatial frequency components (e.g., fundamental and the third harmonic Fourier component in a square wave). We discuss the relevance of these findings to vision and camouflage in aquatic environments.

  13. Inertial gravity currents from edge drainage (United States)

    Momen, Mostafa; Zheng, Zhong; Bou-Zeid, Elie; Stone, Howard


    Gravity currents are formed due to a density gradient in the horizontal direction between the current and an ambient fluid. In this work, we present theoretical, numerical, and experimental studies of the release of a finite volume of fluid instantaneously from the edge of a rectangular domain for high-Reynolds-number flows. The setup is relevant in geophysical and engineering applications such as open channels, and dam-break problems. For the cases we considered, the results indicate that about half of the initial volume exits during an early adjustment period. Then, the inertial gravity current reaches a self-similar phase during which about 40% of its volume drains and its height decreases as τ-2, where τ is a dimensionless time that is derived with the typical gravity wave speed and the horizontal length of the domain. Based on scaling arguments, we reduce the shallow-water PDEs into two nonlinear ODEs, which are then solved analytically. The new self-similar solutions are in good agreement with the performed experiments and direct numerical simulations for various geometries and fluid densities. This study provides new insights into the dynamical behavior of edge drainage flows, particularly during the inertial regime. The simulations were performed on the Della computer clusters of Princeton University.

  14. Converging social classes through humanized urban edges (United States)

    Abuan, M. V.; Galingan, Z. D.


    Urban open spaces are created to be used by people. It is a place of convergence and social activity. However, these places have transformed into places of divergence. When spaces become dehumanized, it separates social classes. As a result, underused spaces contribute to urban decay. Particularly an urban edge, the JP Rizal Makati Waterfront Area is the center of this paper. The JP Rizal Makati Waterfront Area is a waterfront development situated along the banks of one of Metro Manila’s major water thoroughfare --- Pasig River. The park and its physical form, urban design and landscape tend to deteriorate over time --- creating a further division of social convergence. Social hostility, crime, negligent maintenance and poor urban design are contributing factors to this sprawling decay in what used to be spaces of bringing people together. Amidst attempts to beautify and renew this portion of Makati City’s edge, the urban area still remains misspent.This paper attempts to re-humanize the waterfront development. It uses the responsive environment design principles to be able to achieve this goal.

  15. Characterizing the 21-cm Signal from Neutral Hydrogen in the IGM at Redshifts 27>z>6 with EDGES (United States)

    Monsalve, Raul A.; Rogers, Alan E. E.; Bowman, Judd D.; Mozdzen, Thomas J.; Mahesh, Nivedita


    Understanding the period when the first stars formed and ionized the InterGalactic Medium (IGM) during the Epoch of Reionization (EoR) represents one of the main objectives of modern cosmology. The Experiment to Detect the Global EoR Signature (EDGES) strives to characterize this period by measuring, for the first time, the all-sky spectrum of the 21-cm signal produced by neutral hydrogen in the IGM at redshifts 27>z>6. In this talk I will describe recent EDGES constraints for the 21-cm signal. Specifically, with measurements from the EDGES High-Band instrument in the range 90-190 MHz, we rule out traditional Tanh models for the epoch of reionization with durations of up to dz=1 over the redshift range 14>z>7. We also rule out a wide range of phenomenological and physically-motivated 21-cm models that contain a large absorption feature in this redshift range, produced by the complex interaction between UV and X-ray radiation from the first sources and the neutral hydrogen in the IGM. Finally, I will describe our efforts to detect the 21-cm signal in the range 27>z>13 with two Low-Band instruments that have observed over 50-100 MHz since 2015. These instruments implement refined calibration techniques and lessons learned from previous generations of EDGES, and have achieved a level of systematic uncertainty low enough to enable detection. I will present Low-Band analysis results, including a variety of cross-checks performed to discriminate between residual instrumental effects and spectral structure that is intrinsic to the sky. I will conclude by describing the preparation of the next observational campaign with upgraded instrumentation.

  16. Strength on cut edge and ground edge glass beams with the failure analysis method

    Directory of Open Access Journals (Sweden)

    Stefano Agnetti


    Full Text Available The aim of this work is the study of the effect of the finishing of the edge of glass when it has a structural function. Experimental investigations carried out for glass specimens are presented. Various series of annealed glass beam were tested, with cut edge and with ground edge. The glass specimens are tested in four-point bending performing flaw detection on the tested specimens after failure, in order to determine glass strength. As a result, bending strength values are obtained for each specimen. Determining some physical parameter as the depth of the flaw and the mirror radius of the fracture, after the failure of a glass element, it could be possible to calculate the failure strength of that.The experimental results were analyzed with the LEFM theory and the glass strength was analyzed with a statistical study using two-parameter Weibull distribution fitting quite well the failure stress data. The results obtained constitute a validation of the theoretical models and show the influence of the edge processing on the failure strength of the glass. Furthermore, series with different sizes were tested in order to evaluate the size effect.

  17. CHANG-ES X: Spatially Resolved Separation of Thermal Contribution from Radio Continuum Emission in Edge-on Galaxies (United States)

    Vargas, Carlos J.; Mora-Partiarroyo, Silvia Carolina; Schmidt, Philip; Rand, Richard J.; Stein, Yelena; Walterbos, René A. M.; Wang, Q. Daniel; Basu, Aritra; Patterson, Maria; Kepley, Amanda; Beck, Rainer; Irwin, Judith; Heald, George; Li, Jiangtao; Wiegert, Theresa


    We analyze the application of star formation rate calibrations using Hα and 22 μm infrared (IR) imaging data in predicting the thermal radio component for a test sample of three edge-on galaxies (NGC 891, NGC 3044, and NGC 4631) in the Continuum Halos in Nearby Galaxies—an EVLA Survey (CHANG-ES). We use a mixture of Hα and 24 μm calibration from Calzetti et al. and a linear 22 μm only calibration from Jarrett et al. on the test sample. We apply these relations on a pixel-to-pixel basis to create thermal prediction maps in the two CHANG-ES bands: L and C band (1.5 GHz and 6.0 GHz, respectively). We analyze the resulting nonthermal spectral index maps, and find a characteristic steepening of the nonthermal spectral index with vertical distance from the disk after application of all methods. We find possible evidence of extinction in the 22 μm data as compared to 70 μm Spitzer Multiband Imaging Photometer imaging in NGC 891. We analyze a larger sample of edge-on and face-on galaxy 25–100 μm flux ratios, and find that the ratios for edge-ons are systematically lower by a factor of 1.36, a result we attribute to excess extinction in the mid-IR in edge-ons. We introduce a new calibration for correcting the Hα luminosity for dust when galaxies are edge-on or very dusty.

  18. Effect of ZnO on the Physical Properties and Optical Band Gap of Soda Lime Silicate Glass (United States)

    Zaid, Mohd Hafiz Mohd; Matori, Khamirul Amin; Aziz, Sidek Hj. Abdul; Zakaria, Azmi; Ghazali, Mohd Sabri Mohd


    This manuscript reports on the physical properties and optical band gap of five samples of soda lime silicate (SLS) glass combined with zinc oxide (ZnO) that were prepared by a melting and quenching process. To understand the role of ZnO in this glass structure, the density, molar volume and optical band gaps were investigated. The density and absorption spectra in the Ultra-Violet-Visible (UV-Visible) region were recorded at room temperature. The results show that the densities of the glass samples increased as the ZnO weight percentage increased. The molar volume of the glasses shows the same trend as the density: the molar volume increased as the ZnO content increased. The optical band gaps were calculated from the absorption edge, and it was found that the optical band gap decreased from 3.20 to 2.32 eV as the ZnO concentration increased. PMID:22837711

  19. First-principles study of direct and narrow band gap semiconducting β-CuGaO2

    International Nuclear Information System (INIS)

    Nguyen, Manh Cuong; Zhao, Xin; Wang, Cai-Zhuang; Ho, Kai-Ming


    Semiconducting oxides have attracted much attention due to their great stability in air or water and the abundance of oxygen. Recent success in synthesizing a metastable phase of CuGaO 2 with direct narrow band gap opens up new applications of semiconducting oxides as absorber layer for photovoltaics. Using first-principles density functional theory calculations, we investigate the thermodynamic and mechanical stabilities as well as the structural and electronic properties of the β-CuGaO 2 phase. Our calculations show that the β-CuGaO 2 structure is dynamically and mechanically stable. The energy band gap is confirmed to be direct at the Γ point of Brillouin zone. The optical absorption occurs right at the band gap edge and the density of states near the valance band maximum is large, inducing an intense absorption of light as observed in experiment. (paper)

  20. Adaptive Confidence Bands for Nonparametric Regression Functions. (United States)

    Cai, T Tony; Low, Mark; Ma, Zongming


    A new formulation for the construction of adaptive confidence bands in non-parametric function estimation problems is proposed. Confidence bands are constructed which have size that adapts to the smoothness of the function while guaranteeing that both the relative excess mass of the function lying outside the band and the measure of the set of points where the function lies outside the band are small. It is shown that the bands adapt over a maximum range of Lipschitz classes. The adaptive confidence band can be easily implemented in standard statistical software with wavelet support. Numerical performance of the procedure is investigated using both simulated and real datasets. The numerical results agree well with the theoretical analysis. The procedure can be easily modified and used for other nonparametric function estimation models.