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1

Liquid Surface Wave Band Structure Instabilities  

Microsoft Academic Search

We study interfacial instabilities between two spatially periodically sheared ideal fluids. Bloch wave function decompositions of the surface deformation and fluid velocities result in a non-Hermitian secular matrix with an associated band structure that yields both linear oscillating and nonoscillating instabilities, enhanced near Bragg planes corresponding to the periodicity determined by converging or diverging surface flows. The instabilities persist even

Tom Chou

1997-01-01

2

Liquid Surface Wave Band Structure Instabilites  

Microsoft Academic Search

We study interfacial instabilities between two spatially periodically sheared ideal fluids. Bloch wavefunction decompositions of the surface deformation and fluid velocities result in a nonhermitian secular matrix with an associated band structure that yields both linear oscillating and nonoscillating instabilities, enhanced near Bragg planes corresponding to the periodicity determined by converging or diverging surface flows. The instabilities persist even when

Tom Chou

1998-01-01

3

Liquid Surface Wave Band Structure Instabilities  

E-print Network

We study interfacial instabilities between two spatially periodically sheared ideal fluids. Bloch wavefunction decompositions of the surface deformation and fluid velocities result in a nonhermitian secular matrix with an associated band structure that yields both linear oscillating and nonoscillating instabilities, enhanced near Bragg planes corresponding to the periodicity determined by converging or diverging surface flows. The instabilities persist even when the dynamical effects of the upper fluid are neglected, in contrast to the uniform shear Kelvin-Helmholtz (KH) instability. Periodic flows can also couple with uniform shear and suppress standard KH instabilities.

Tom Chou

1997-11-01

4

Band structures and band gaps of liquid surface waves propagating through an infinite array of cylinders  

Microsoft Academic Search

The multiple scattering method is applied to the calculations of band structures of liquid surface waves propagating through an infinite array of vertical cylinders. The influence of the filling fraction on the formation of band gaps is discussed. It is found that there exist complete band gaps for both the square and triangular arrays of cylinders.

Xinhua Hu; Yifeng Shen; Xiaohan Liu; Rongtang Fu; Jian Zi; Xunya Jiang; Songlin Feng

2003-01-01

5

Band structure and Fermi surface of atomically uniform lead films  

NASA Astrophysics Data System (ADS)

Atomically uniform lead films are prepared on Si(111)-(7×7) substrates by the molecular beam epitaxy method, and their electronic structures are investigated by high-resolution angle-resolved photoemission spectroscopy and first-principles density functional theory calculations. We have observed the six-fold symmetric Fermi surfaces of Pb/Si(111)-(7×7) films. Their topology and size are almost the same regardless of the difference of film thicknesses (17, 21, 24 and 25 monolayers). The comparison between the measured and calculated thin-film Fermi surfaces suggests that the as-prepared Pb/Si(111)-(7×7) films are dominated by the hexagonal-close-packed stacking films instead of the face-centered-cubic ones. The theoretical calculations also indicate that spin-orbit coupling plays an important role in the band structures and Fermi surface topologies of Pb films.

He, Shaolong; Zeng, Zhenhua; Arita, Masashi; Sawada, Masahiro; Shimada, Kenya; Qiao, Shan; Li, Guoling; Li, Wei-Xue; Zhang, Yan-Feng; Zhang, Yi; Ma, Xucun; Jia, Jinfeng; Xue, Qi-Kun; Namatame, Hirofumi; Taniguchi, Masaki

2010-11-01

6

Investigations of the Band Structure and Morphology of Nanostructured Surfaces  

NASA Astrophysics Data System (ADS)

In this dissertation, I examine the electronic structure of two very different types of two-dimensional systems: valence band electrons in single layer graphene and electronic states created at the vacuum interface of single crystal copper surfaces. The characteristics of both electronic systems depend intimately on the morphology of the surfaces they inhabit. Thus, in addition to discussing the respective band structures of these systems, a significant portion of this dissertation will be devoted to measurements of the surface morphology of these systems. Free-standing exfoliated monolayer graphene is an ultra-thin flexible membrane and, as such, is known to exhibit large out-of-plane deformation due to substrate and adsorbate interaction as well as thermal vibrations and, possibly, intrinsic buckling. Such crystal deformation is known to limit mobility and increase local chemical reactivity. Additionally, deformations present a measurement challenge to researchers wishing to determine the band structure by angle-resolved photoemission since they limit electron coherence in such measurements. In this dissertation, I present low energy electron microscopy and micro probe diffraction measurements, which are used to image and characterize corrugation in SiO2-supported and suspended exfoliated graphene at nanometer length scales. Diffraction line-shape analysis reveals quantitative differences in surface roughness on length scales below 20 nm which depend on film thickness and interaction with the substrate. Corrugation decreases with increasing film thickness, reflecting the increased stiffness of multilayer films. Specifically, single-layer graphene shows a markedly larger short range roughness than multilayer graphene. Due to the absence of interactions with the substrate, suspended graphene displays a smoother morphology and texture than supported graphene. A specific feature of suspended single-layer films is the dependence of corrugation on both adsorbate load and temperature, which is manifested by variations in the diffraction lineshape. The effects of both intrinsic and extrinsic corrugation factors will be discussed. Through a carefully coordinated study I show how these surface morphology measurements can be combined with angle resolved photoemission measurements to understand the role of surface corrugation in the ARPES measurement process. The measurements described here rely on the development of an analytical formulation for relating the crystal corrugation to the photoemission linewidth. I present ARPES measurements that show that, despite significant deviation from planarity of the crystal, the electronic structure of exfoliated suspended graphene is nearly that of ideal, undoped graphene; the Dirac point is measured to be within 25 meV of EF. Further, I show that suspended graphene behaves as a marginal Fermi-liquid, with a quasiparticle lifetime which scales as (E -- EF)--1 ; comparison with other graphene and graphite data is discussed. In contrast to graphene, which must be treated as a flexible membrane with continuous height variation, roughness in clean single crystal surfaces arises from lattice dislocations, which introduce discrete height variations. Such height variations can be exploited to generate a self assembled nano-structured surface. In particular, by making a vicinal cut on a single crystal surface, a nanoscale step array can be formed. A model system for such nanoscale self assembly is Cu(111). Cu(775) is formed by making an 8.5° viscinal cut of Cu(111) along the [112¯] axis. The electronic states formed on the surface of this system, with a nanoscale step array of 14 A terraces, shows markedly different behavior those formed on Cu(111). In this dissertation, I show that the tunability of a femtosecond optical parametric oscillator, combined with its high-repetition rate and short pulse length, provides a powerful tool for resonant band mapping of the sp surface and image states on flat and vicinal Cu(111)-Cu (775) surfaces, over the photon energy range from 3.9 to 5 eV. Since the tim

Knox, Kevin R.

7

Coplanar waveguide method for identifying the surface wave band-gap range of mushroom-like electromagnetic band-gap structure  

Microsoft Academic Search

In this paper, coplanar waveguide (CPW) method is proposed for identifying the surface wave band-gap of mushroom-like EBG structure. Two lines are cut off from the complete ground plane of the EBG structure and the defected ground plane can be viewed as a coplanar waveguide with characteristic impedance of 50 Ohm. The other layer of the EBG structure is not

Zhengheng Mi; Jiadong Xu; Fuguo Zhu; Gao Wei; Chong Zhang

2010-01-01

8

Polarization sensitive surface band structure of doped BaTiO3(001).  

PubMed

We present a spatial and wave-vector resolved study of the electronic structure of micron sized ferroelectric domains at the surface of a BaTiO(3)(001) single crystal. The n-type doping of the BaTiO(3) is controlled by in situ vacuum and oxygen annealing, providing experimental evidence of a surface paraelectric-ferroelectric transition below a critical doping level. Real space imaging of photoemission threshold, core level and valence band spectra show contrast due to domain polarization. Reciprocal space imaging of the electronic structure using linearly polarized light provides unambiguous evidence for the presence of both in- and out-of-plane polarization with two- and fourfold symmetry, respectively. The results agree well with first principles calculations. PMID:24093301

Rault, J E; Dionot, J; Mathieu, C; Feyer, V; Schneider, C M; Geneste, G; Barrett, N

2013-09-20

9

Role of surface band structures in the survival of anions scattered off plane and nano-stepped surfaces  

NASA Astrophysics Data System (ADS)

Resonant charge transfer between ions and metal surfaces is a valuable tool to explore the surface electronic structure. Using the Crank-Nicholson propagation [1] we solve the time-dependent Schroedinger equation to simulate the dynamic electron redistribution during the scattering of a hydrogen anion from plane and nano-stepped vicinal metal surfaces. The electronic evolution during the scattering and the final ion survival probability as a function of the projectile's incident angle are calculated. We find that the survival of the ion reflected from a plane surface is very sensitive to the component of the projectile speed perpendicular to the surface. For a host of simple metal surfaces, unique roles of the band gap and the image states are uncovered that enable a nearly universal energy-scaling of the ion-survival. For the stepped surfaces, conversely, the survival is found to depend critically on the ion speed parallel to the surface, resulting in rich structures in the survival probability.[4pt] [1] Chakraborty et al., Phys. Rev. A 70, 052903 (2004).

Schmitz, Andrew; Shaw, John; Chakraborty, Himadri; Thumm, Uwe

2009-11-01

10

Complexity of band structures: Semi-analytical finite element analysis of one-dimensional surface phononic crystals  

NASA Astrophysics Data System (ADS)

Band structures of surface phononic crystals with one-dimensional periodicity are investigated in this paper. Real and complex dispersion relations of surface acoustic waves are calculated by a semi-analytical finite element method in the frequency domain. The model applies 2D nine-noded elements in the periodic direction to discretize a unit cell with finite depth. Propagation perpendicular to the periodic direction is modeled by analytic functions. Two eigenproblems are obtained from the method which lead to real or to complex dispersion relations of the one-dimensional phononic crystal. The model results in a Lamb wave band structure where the surface modes are identified by their displacement and elastic energy distribution. The complex band structure includes imaginary and complex modes in addition to the real dispersion relation describing also standing and evanescent modes. Such evanescent waves not only include the folded surface waves, but it is also shown that an evanescent mode is present within the stop band.

Veres, Istvan A.; Berer, Thomas

2012-09-01

11

Influence of GaAs surface termination on GaSb/GaAs quantum dot structure and band offsets  

SciTech Connect

We have investigated the influence of GaAs surface termination on the nanoscale structure and band offsets of GaSb/GaAs quantum dots (QDs) grown by molecular-beam epitaxy. Transmission electron microscopy reveals both coherent and semi-coherent clusters, as well as misfit dislocations, independent of surface termination. Cross-sectional scanning tunneling microscopy and spectroscopy reveal clustered GaSb QDs with type I band offsets at the GaSb/GaAs interfaces. We discuss the relative influences of strain and QD clustering on the band offsets at GaSb/GaAs interfaces.

Zech, E. S.; Chang, A. S.; Martin, A. J.; Canniff, J. C.; Millunchick, J. M. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)] [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Lin, Y. H. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)] [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Goldman, R. S. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States) [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)

2013-08-19

12

Band structure engineering of monolayer MoS2 by surface ligand functionalization for enhanced photoelectrochemical hydrogen production activity.  

PubMed

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. PMID:25268589

Pan, Jing; Wang, Zilu; Chen, Qian; Hu, Jingguo; Wang, Jinlan

2014-10-24

13

Electric-field tuning of the surface band structure of topological insulator Sb2Te3 thin films.  

PubMed

We measured the response of the surface state spectrum of epitaxial Sb(2)Te(3) thin films to applied gate electric fields by low temperature scanning tunneling microscopy. The gate dependent shift of the Fermi level and the screening effect from bulk carriers vary as a function of film thickness. We observed a gap opening at the Dirac point for films thinner than four quintuple layers, due to the coupling of the top and bottom surfaces. Moreover, the top surface state band gap of the three quintuple layer films was found to be tunable by a back gate, indicating the possibility of observing a topological phase transition in this system. Our results are well explained by an effective model of 3D topological insulator thin films with structure inversion asymmetry, indicating that three quintuple layer Sb(2)Te(3) films are topologically nontrivial and belong to the quantum spin Hall insulator class. PMID:23952429

Zhang, Tong; Ha, Jeonghoon; Levy, Niv; Kuk, Young; Stroscio, Joseph

2013-08-01

14

Electric-Field Tuning of the Surface Band Structure of Topological Insulator Sb2Te3 Thin Films  

NASA Astrophysics Data System (ADS)

We measured the response of the surface state spectrum of epitaxial Sb2Te3 thin films to applied gate electric fields by low temperature scanning tunneling microscopy. The gate dependent shift of the Fermi level and the screening effect from bulk carriers vary as a function of film thickness. We observed a gap opening at the Dirac point for films thinner than four quintuple layers, due to the coupling of the top and bottom surfaces. Moreover, the top surface state band gap of the three quintuple layer films was found to be tunable by a back gate, indicating the possibility of observing a topological phase transition in this system. Our results are well explained by an effective model of 3D topological insulator thin films with structure inversion asymmetry, indicating that three quintuple layer Sb2Te3 films are topologically nontrivial and belong to the quantum spin Hall insulator class.

Zhang, Tong; Ha, Jeonghoon; Levy, Niv; Kuk, Young; Stroscio, Joseph

2013-08-01

15

Band-gap structures of surface-plasmon polaritons in a subwavelength metal slit filled with periodic dielectrics  

SciTech Connect

We propose a combination structure which consists of a subwavelength metal slit filled periodically with two different dielectrics to modulate slit plasmon polaritons (slit-PPs). The transmission spectra are simulated by the finite-difference time-domain method and the photonic band gaps are observed. The theoretical formula to calculate the band-gap structures is deduced and the calculation results agree satisfactorily with simulated results. This structure can be termed as slit-PP crystal.

Zhou Yunsong [Department of Physics, Capital Normal University, Beijing 100048 (China); Gu Benyuan [Institute of Physics, Chinese Academy of Sciences, Post Office Box 603, Beijing 100080 (China); Wang Huaiyu [Department of Physics, Tsinghua University, Beijing 100084 (China)

2010-01-15

16

Multi-band localized spoof plasmons with texturing closed surfaces  

NASA Astrophysics Data System (ADS)

We demonstrate that periodically textured closed surface with multiple groove depths can support multi-band spoof localized surface plasmons (LSPs). It is interesting to note that the spoof LSPs in each band resemble those generated by the textured closed surface of the same periodicity with the corresponding single groove depth. In this way, it paves the way for the generation and design of multi-band spoof LSPs. Moreover, multiple resonance band structures and devices, such as resonator, oscillator, and other band-notched structures in the microwave and terahertz regimes can be realized.

Li, Zhuo; Liu, Liangliang; Gu, Changqing; Ning, Pingping; Xu, Bingzheng; Niu, Zhenyi; Zhao, Yongjiu

2014-03-01

17

Band structures in 99Rh  

NASA Astrophysics Data System (ADS)

Excited states in the 99Rh nucleus were populated using the fusion-evaporation reaction 75As(28Si,2p2n) at {{E}_{lab}}=120\\;MeV and the de-excitations were investigated through in-beam ?-ray spectroscopic techniques using the INGA spectrometer consisting of 18 clover detectors. The observed band structures are discussed in the framework of tilted axis cranking shell-model calculations. Level structures at low energies are identified as resulting from the rotational bands based on the \\pi {{p}_{1/2}} and \\pi {{g}_{9/2}} configurations. The \\Delta I = 1 coupled bands are observed at higher excitation energies and have been interpreted as based on the \\pi {{g}_{9/2}}\\otimes \

Kumar, S.; Singh, V.; Singh, K.; Sihotra, S.; Singh, N.; Goswamy, J.; Malik, S. S.; Ragnarsson, I.; Trivedi, T.; Singh, R. P.; Muralithar, S.; Kumar, R.; Bhowmik, R. K.; Palit, R.; Bharti, A.; Mehta, D.

2014-10-01

18

Scattering of H^- by plane and nano-stepped surfaces: Role of the ion speed for probing the surface band structure  

NASA Astrophysics Data System (ADS)

Resonant charge transfer between ions and metal surfaces is a useful tool to explore the surface electronic structure. Using the Crank-Nicholson propagation method [1] we solve the time-dependent Schroedinger equation to simulate the dynamic electron redistribution during the scattering of a hydrogen anion from plane and nano-stepped metal surfaces. We calculate electronic evolution during the scattering and the final ion survival probability as a function of the projectile's incident angle. We find that the survival of the ion reflected off a plane surface is very sensitive to the component of the projectile speed perpendicular to the surface and analyze rich structure of the survival probability as a function of the perpendicular speed. For the stepped surfaces, conversely, the ion survival is found to depend critically on the ion speed parallel to the surface. [1] Chakraborty et al., Phys. Rev. A 70, 052903 (2004).

Chakraborty, Himadri; Thumm, Uwe

2009-05-01

19

Granular Banding - the Fine Structure  

NASA Astrophysics Data System (ADS)

Solid-liquid two-phase flow in a partially filled, horizontally rotating cylinder is studied experimentally. This system can display several different flow states. The rotation rate, the filling level and the fluid properties determine which state is adopted. In the phase plane different states are separated from each other by sharp transition boundaries. The influence of granular additives on these boundaries is investigated. Results for particles of different sizes, densities and shapes are presented. Under certain conditions the granular additives come out of suspension to form regularly spaced circumferential bands on the inner cylinder wall [1,2]. We report the observation of a new phenomenon by which these primary bands develop a fine structure. The fine structure is characterized by each primary band adopting a compound structure consisting of three narrower secondary rings [3]. References: [1] Boote & Thomas, Phys. Fluids vol. 11(8), p. 2020 (1999), [2] Tirumkudulu et al., Phys. Fluids vol. 12(6), p. 1615 (2000), [3] Thomas et al., Phys. Fluids vol. 13 (9), pages not yet known (2001)

Thomas, Peter J.; Riddell, Gareth D.; King, Gregory P.

2001-11-01

20

High-impedance electromagnetic surfaces with a forbidden frequency band  

Microsoft Academic Search

A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Although it is made of continuous metal, and conducts dc currents, it does not conduct ac currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves, and its image currents are not phase reversed.

Dan Sievenpiper; Lijun Zhang; Romulo F. Jimenez Broas; Nicolaos G. Alexopoulos; E. Yablonovitch

1999-01-01

21

Band structure of silicene on zirconium diboride (0001) thin-film surface: Convergence of experiment and calculations in the one-Si-atom Brillouin zone  

NASA Astrophysics Data System (ADS)

So far, it represents a challenging task to reproduce angle-resolved photoelectron (ARPES) spectra of epitaxial silicene by first-principles calculations. Here, we report on the resolution of the previously controversial issue related to the structural configuration of silicene on the ZrB2(0001) surface and its band structure. In particular, by representing the band structure in a large Brillouin zone associated with a single Si atom, it is found that the imaginary part of the one-particle Green's function follows the spectral weight observed in ARPES spectra. By additionally varying the in-plane lattice constant, the results of density functional theory calculations and ARPES data obtained in a wide energy range converge into the "planarlike" phase and provide the orbital character of electronic states in the vicinity of the Fermi level. It is anticipated that the choice of a smaller commensurate unit cell for the representation of the electronic structure will be useful for the study of epitaxial two-dimensional materials on various substrates in general.

Lee, Chi-Cheng; Fleurence, Antoine; Yamada-Takamura, Yukiko; Ozaki, Taisuke; Friedlein, Rainer

2014-08-01

22

Effect of the band structure of InGaN/GaN quantum well on the surface plasmon enhanced light-emitting diodes  

NASA Astrophysics Data System (ADS)

The spontaneous emission (SE) of InGaN/GaN quantum well (QW) structure with silver(Ag) coated on the n-GaN layer has been investigated by using six-by-six K-P method taking into account the electron-hole band structures, the photon density of states of surface plasmon polariton (SPP), and the evanescent fields of SPP. The SE into SPP mode can be remarkably enhanced due to the increase of electron-hole pairs near the Ag by modulating the InGaN/GaN QW structure or increasing the carrier injection. However, the ratio between the total SE rates into SPP mode and free space will approach to saturation or slightly decrease for the optimized structures with various distances between Ag film and QW layer at a high injection carrier density. Furthermore, the Ga-face QW structure has a higher SE rate than the N-face QW structure due to the overlap region of electron-hole pairs nearer to the Ag film.

Li, Yi; Zhang, Rong; Liu, Bin; Xie, Zili; Zhang, Guogang; Tao, Tao; Zhuang, Zhe; Zhi, Ting; Zheng, Youdou

2014-07-01

23

The electronic band structure of cobalt disulfide(100)  

NASA Astrophysics Data System (ADS)

The pyrite-type transition metal compound CoS2 is an itinerant electron ferromagnet and is predicted, in ground state band structure calculations to be close to half-metallic. The Curie temperature is about 120 K. Although some minority spin states are present at the Fermi level in bulk band structure, the system is predicted to be relatively highly spin polarized. The measured saturation magnetization is less than 1.0 microB/Co expected of ideal half-metallic CoS2, which is consistent with these calculations. The measured transport spin polarizations are 56 - 64 %, as determined from point-contact Andreev reflection. An accurate determination of the surface structure is essential for understanding electron spectroscopy studies, as well as providing a starting point for modeling the interface properties, essential for modeling any spintronics device applications. The success of this work was made possible by the cleavage of sufficiently large CoS2 (100) single crystals. LEED I(V) analysis, was used to determine surface structure. 1S-terminated model is favored, in which, the atoms in sublayer S and Co relax outward (toward the vacuum) and inward (toward the bulk), along the surface normal by approximately 0.03 and 0.11 A, respectively. This kind of surface relaxation of best-fit model is also confirmed by surface stability studies. Photon energy dependent and angle dependent photoemission spectra were taken in order to map out the bulk band structure (k?) along surface normal and surface band structure (k//) respectively. The agreement between experimental and theory calculation suggests that the CoS 2 bulk band structure near the Fermi level is sensitive to the S-S separation, and the half-metallic gap may be controlled by antibonding sulfur p states, rather than exchange splitting of Co d states. The calculated surface band structure for the (100) surface includes the corrections for the known surface relaxation. The comparison with the experimental k// indicates that the photoemission spectra are indeed dominated by surface weighted bands. The surface state and surface resonance band dispersions in theoretical and experimental band mappings are in general agreement. The spin polarized band structure calculations indicate a true surface state in the minority spin band structure.

Wu, Ning

24

Near-Surface Vortex Structure in a Tornado and in a Sub-Tornado-Strength Convective-Storm Vortex Observed by a Mobile, W-Band Radar during VORTEX2  

E-print Network

Near-Surface Vortex Structure in a Tornado and in a Sub-Tornado-Strength Convective-Storm Vortex Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) field campaign, a very high-resolution, mobile, W-band Doppler radar collected near-surface (#200 m AGL) observations in an EF-0 tornado near

Xue, Ming

25

Band structure and spontaneous polarization in tetragonal knbo3  

Microsoft Academic Search

The electronic energy band structure in ferroelectric tetragonal potassium niobate has been calculated using an X? exchange and a plane-wave gaussian basis set. The band gaps compared favorably with those measured by Kaifu and Wiesendanger. The spontaneous polarization Ps was then calculated by assuming that the boundaries of a molecule are given by minimum charge density surfaces. The value of

Kam-Shing Kam; John H. Henkel

1981-01-01

26

Evidence for hybrid surface metallic band in (4 × 4) silicene on Ag(111)  

NASA Astrophysics Data System (ADS)

The electronic band structure of monolayer (4 × 4) silicene on Ag(111) is imaged by angle resolved photoelectron spectroscopy. A dominant hybrid surface metallic band is observed to be located near the bulk Ag sp-band which is also faintly visible. The two-dimensional character of the hybrid band has been distinguished against the bulk character of the Ag(111) sp-band by means of photon energy dependence experiments. The surface band exhibits a steep linear dispersion around the K¯Ag point and has a saddle point near the M¯Ag point of Ag(111) resembling the ?-band dispersion in graphene.

Tsoutsou, D.; Xenogiannopoulou, E.; Golias, E.; Tsipas, P.; Dimoulas, A.

2013-12-01

27

Evidence for hybrid surface metallic band in (4?×?4) silicene on Ag(111)  

SciTech Connect

The electronic band structure of monolayer (4?×?4) silicene on Ag(111) is imaged by angle resolved photoelectron spectroscopy. A dominant hybrid surface metallic band is observed to be located near the bulk Ag sp-band which is also faintly visible. The two-dimensional character of the hybrid band has been distinguished against the bulk character of the Ag(111) sp-band by means of photon energy dependence experiments. The surface band exhibits a steep linear dispersion around the K{sup ¯}{sub Ag} point and has a saddle point near the M{sup ¯}{sub Ag} point of Ag(111) resembling the ?-band dispersion in graphene.

Tsoutsou, D., E-mail: dtsoutsou@ims.demokritos.gr; Xenogiannopoulou, E.; Golias, E.; Tsipas, P.; Dimoulas, A. [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece)] [National Center for Scientific Research “Demokritos,” 15310 Athens (Greece)

2013-12-02

28

Complete band gaps for liquid surface waves propagating over a periodically drilled bottom  

Microsoft Academic Search

A plane-wave expansion approach is developed to solve the mild-slope equation for liquid surface waves propagating over a bottom with periodic structures. Band structures are calculated for the bottom periodically drilled with the square or triangular lattice of holes. Complete band gaps are found for both lattices. Parameters that influence the formation of band gaps are discussed.

Xinhua Hu; Yifeng Shen; Xiaohan Liu; Rongtang Fu; Jian Zi

2003-01-01

29

Complete band gaps for liquid surface waves propagating over a periodically drilled bottom  

NASA Astrophysics Data System (ADS)

A plane-wave expansion approach is developed to solve the mild-slope equation for liquid surface waves propagating over a bottom with periodic structures. Band structures are calculated for the bottom periodically drilled with the square or triangular lattice of holes. Complete band gaps are found for both lattices. Parameters that influence the formation of band gaps are discussed.

Hu, Xinhua; Shen, Yifeng; Liu, Xiaohan; Fu, Rongtang; Zi, Jian

2003-12-01

30

An Evaluation of the ALOS PALSAR L-Band Backscatter—Above Ground Biomass Relationship Queensland, Australia: Impacts of Surface Moisture Condition and Vegetation Structure  

Microsoft Academic Search

Focusing on woody vegetation in Queensland, Australia, the study aimed to establish whether the relationship between Advanced Land Observing Satellite (ALOS) Phased Array L-band SAR (PALSAR) HH and HV backscattering coefficients and above ground biomass (AGB) was consistent within and between structural formations (forests, woodlands and open woodlands, including scrub). Across these formations, 2781 plot-based measurements (from 1139 sites) of

Richard Lucas; John Armston; Russell Fairfax; Rod Fensham; Arnon Accad; Joao Carreiras; Jack Kelley; Peter Bunting; Dan Clewley; Steven Bray; Dan Metcalfe; John Dwyer; M. Bowen; T. Eyre; M. Laidlaw; M. Shimada

2010-01-01

31

Band structure of W and Mo by empirical pseudopotential method  

NASA Technical Reports Server (NTRS)

The empirical pseudopotential method (EPM) is used to calculate the band structure of tungsten and molybdenum. Agreement between the calculated reflectivity, density of states, density of states at the Fermi surface and location of the Fermi surface from this study and experimental measurements and previous calculations is good. Also the charge distribution shows the proper topological distribution of charge for a bcc crystal.

Sridhar, C. G.; Whiting, E. E.

1977-01-01

32

Band structure of 235U  

NASA Astrophysics Data System (ADS)

Over a period of several years we have performed three separate experiments at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron in which 235U (thick target) was Coulomb-excited. The program involved stand-alone experiments with Gammmasphere and with the 8pi Spectrometer using 136Xe beams at 720 MeV, and a CHICO-Gammasphere experiment with a 40Ca beam at 184 MeV. In addition to extending the known negative-parity bands to high spin, we have assigned levels in some seven positive-parity bands which are in some cases (e.g., [631]1/2, [624]7/2, and [622]5/2) strongly populated by E3 excitation. The CHICO data have been analyzed to extract E2 and E3 matrix elements from the observed yields. Additionally, many M1 matrix elements could be extracted from the ?-ray branching ratios. A number of new features have emerged, including the unexpected attenuation of magnetic transitions between states of the same Nilsson multiplet, the breakdown of Coriolis staggering at high spin, and the effect of E3 collectivity on Coriolis interactions.

Ward, D.; Macchiavelli, A. O.; Clark, R. M.; Cline, D.; Cromaz, M.; Deleplanque, M. A.; Diamond, R. M.; Fallon, P.; Görgen, A.; Hayes, A. B.; Lane, G. J.; Lee, I.-Y.; Nakatsukasa, T.; Schmidt, G.; Stephens, F. S.; Svensson, C. E.; Teng, R.; Vetter, K.; Wu, C. Y.

2012-12-01

33

Photonic Band Gap Structures for Accelerator Applications  

NASA Astrophysics Data System (ADS)

A photonic band gap (PBG) structure is a one-, two- or three-dimensional periodic metallic and/or dielectric system, which acts like a filter, reflecting rf fields in some frequency range and allowing rf fields at other frequencies to transmit through. PBG structures have many promising applications in active and passive devices at millimeter wave and higher frequencies. Metal PBG structures can be employed at X and Ku-band accelerators to suppress wakefields. Dielectric PBG structures are attractive at terahertz frequencies for construction of high gradient laser-driven accelerators. For both applications two-dimensional (2D) PBG structures are of main interest, although planar and three-dimensional (3D) structures are also used. In this paper a review of theoretical studies and computer modeling of 2D metal and dielectric structures is presented, and current experimental efforts on constructing and testing metal and dielectric PBG accelerators are discussed.

Smirnova, E. I.

2004-12-01

34

Multiple band structures of {sup 131}Cs  

SciTech Connect

Excited states in {sup 131}Cs were investigated through in-beam {gamma}-ray spectroscopic techniques following its population in the {sup 124}Sn({sup 11}B, 4n) fusion-evaporation reaction at a beam energy of 46 MeV. The previously known level scheme has been substantially extended up to {approx}9 MeV excitation energy and 49/2({Dirac_h}/2{pi}) spin with the addition of seven new band structures. The present level scheme consisting of 15 bands exhibits a variety of collective features in this nucleus at intermediate spin. The excitation energies of the observed levels in different bands and the corresponding ratios of transition strengths, i.e., B(M1)/B(E2), have been compared with the results of projected deformed Hartree-Fock calculations based on various quasiparticle configurations. A strongly coupled band has been reassigned a high-K three-quasiparticle {pi}h{sub 11/2} x {nu}(h{sub 11/2}d{sub 3/2}) configuration based on the properties of this band and that of its new coupled side band. The configurations of these bands are also discussed in the framework of tilted-axis cranking model calculations and the systematics of the odd-A Cs isotopes. Additional three energetically closely placed coupled bands have been assigned different unpaired three-quasiparticle configurations. {gamma}-vibrational bands coupled to the {pi}h{sub 11/2} and {pi}g{sub 7/2} single-particle configurations have been reported in this nucleus. Observation of new E1 transitions linking the opposite-parity {pi}h{sub 11/2} and {pi}d{sub 5/2} bands provides fingerprints of possible octupole correlations.

Sihotra, S. [Department of Physics, Panjab University, Chandigarh-160014 (India); Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Mumbai-400005 (India); Department of Physics, Guru Nanak Dev University, Amritsar-143005 (India); Palit, R.; Naik, Z.; Joshi, P. K.; Deo, A. Y.; Jain, H. C. [Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Mumbai-400005 (India); Singh, K.; Goswamy, J.; Mehta, D.; Singh, N. [Department of Physics, Panjab University, Chandigarh-160014 (India); Malik, S. S. [Department of Physics, Guru Nanak Dev University, Amritsar-143005 (India); Praharaj, C. R. [Institute of Physics, Bhubaneswar-751005 (India)

2008-09-15

35

Evidence of surface acoustic wave band gaps in the phononic crystals created on thin plates  

E-print Network

Evidence of surface acoustic wave band gaps in the phononic crystals created on thin plates Xinya. However, few investigations have been performed on phononic structures in thin plates to form surface acoustic wave SAW band gaps. In this letter, we report a new type of phononic crystals manufactured

Deymier, Pierre

36

Band Structure and Electrical Conductivity in Semiconductors  

NSDL National Science Digital Library

In this experiment, we will, 1. understand how conductivity in semiconductors depends on carrier concentration and mobility, and how these depend on temperature, 2. distinguish between intrinsic and extrinsic temperature regimes and identify the applicable temperature range from an examination of measured data, 3. appreciate and utilize the advantages of the four-probe resistance measurement technique, 4. calculate the energy band gap for doped Si and pure Ge, 5. calculate the temperature dependent coefficient of the majority carriers, 6. through experimental realizations, appreciate a physical understanding of the band gap structure of semiconductors.

Khalid, Asma; Anwar, Muhammad S.; Zia, Wasif

2012-07-08

37

Shear horizontal guided wave band gaps in a homogenous plate with periodic tapered surface  

NASA Astrophysics Data System (ADS)

The shear horizontal (SH) guided wave band structures and transmission coefficients in a homogenous plate with periodic tapered surface, whose width is gradually decreases from the lower base to the upper base, are calculated based on the eigen-mode matching theory (EMMT) method. The finite element method (FEM) is also employed to calculate the band structures, which is in good agreement with the results by EMMT method. Numerical results show that the SH guided wave band structures in reduced frequency keep unchanged even if the whole homogenous plate with periodic tapered surface is filled with different materials. We also present the numerical investigations of the geometrical factors’ effect on the band structures, including the upper base width, the lower base width, the tapered surface thickness and the plate thickness. These properties of SH guided wave can potentially be utilized to design acoustic sensors, tune band gaps and generate filters.

Song, Guang-huang; Chen, Jiu-jiu; Han, Xu

2014-09-01

38

Wide band spectroscopy of liquid surface ripplon  

Microsoft Academic Search

A light scattering technique was developed to measure the propagation of liquid surface waves over a wide frequency range. Thermal fluctuation of liquid surface displacement excites a surface tension wave, called the ripplon, whose behavior gives information on dynamic properties of the liquid surface. A laser beam is scattered by the ripplon, and the power spectrum of the scattered light

K. Sakai; H. Tanaka; K. Takagi

1990-01-01

39

Investigation of surface oxides on aluminum alloys by valence band photoemission  

NASA Astrophysics Data System (ADS)

Core level and valence band x-ray photoelectron spectroscopy are used to study the chemical composition of the surface films on aluminum alloys. Certain alloying elements may preferentially migrate to the surface of an alloy, thereby altering the composition and consequently the chemistry of the surface. The behavior of a 6061 aluminum alloy is compared with that of pure aluminum. It is shown that the type of magnesium film formed at the alloy surface can be determined by comparing the valence band spectra of the aluminum alloy surface with that of known magnesium and aluminum compounds. The experimental valence band spectra of these compounds are supported by spectra generated from band structure calculations. The effect of boiling water on the surface film is discussed, with significant differences in surface chemistry being seen for the metal and the alloy. copyright 2002 American Vacuum Society.

Claycomb, Gregory D.; Sherwood, Peter M. A.

2002-07-01

40

Band bending and electrical transport at chemically modified silicon surfaces  

NASA Astrophysics Data System (ADS)

High resolution electron energy loss spectroscopy (HREELS) and electrical transport measurements have been used to investigate how various chemical modifications give rise to band bending and alter the conductivity of Si(111) surfaces. HREELS is a sensitive probe of band bending through observations of the low frequency free carrier plasmon mode. For hydrogen terminated surfaces, prepared by the standard etch in ammonium flouride, HREELS measurements on both n and n+ substrates are consistent with nearly flat bands. Chlorination of these surfaces results in substantial upward band bending due to the strong electron withdrawing nature of the chlorine, driving the surface into inversion. The presence of this inversion layer on high resistivity n-type samples is observed through a substantial enhancement of the surface conductivity (relative to the H-terminated surface), as well as through broadening of the quasi-elastic peak in the HREELS measurements. We have also begun to examine organically modified silicon surfaces, prepared by various wet chemical reactions with the H-terminated surface. Decyl modified Si(111) surfaces are seen to exhibit a small degree of band bending, attributed to extrinsic defect states cause by a small degree of oxidation accompanying the modification reaction. The prospects of using conductivity as an in-situ monitor of the rate of these reactions will be discussed.

Lopinski, Greg; Ward, Tim; Hul'Ko, Oleksa; Boukherroub, Rabah

2002-03-01

41

Ab initio probing of the electronic band structure and Fermi surface of fluorine-doped WO3 as a novel low- T C superconductor  

NASA Astrophysics Data System (ADS)

Ab initio calculations were performed to investigate the electronic structure and the Fermi surface of the newly discovered low-temperature superconductor: fluorine-doped WO3. We find that F doping provides the transition of the insulating tungsten trioxide into a metallic-like phase WO3 - x F x , where the near-Fermi states are formed mainly from W 5 d with admixture of O 2 p orbitals. The cooperative effect of fluorine additives in WO3 consists in change of electronic concentration as well as the lattice constant. At probing their influence on the near-Fermi states separately, the dominant role of the electronic factor for the transition of tungsten oxyfluoride into superconducting state was established. The volume of the Fermi surface gradually increases with the increase of the doping. In the sequence WO3 ? WO2.5F0.5 the effective atomic charges of W and O ions decrease, but much less, than it is predicted within the idealized ionic model—owing to presence of the covalent interactions W-O and W-F.

Shein, I. R.; Ivanovskii, A. L.

2012-03-01

42

Elucidating the stop bands of structurally colored systems through recursion  

NASA Astrophysics Data System (ADS)

Interference is the source of some of the spectacular colors of animals and plants in nature. In some of these systems, the physical structure consists of an ordered array of layers with alternating high and low refractive indices. This periodicity leads to an optical band structure that is analogous to the electronic band structure encountered in semiconductor physics: specific bands of wavelengths (the stop bands) are perfectly reflected. Here, we present a minimal model for optical band structure in a periodic multilayer structure and solve it using recursion relations. The stop bands emerge in the limit of an infinite number of layers by finding the fixed point of the recursion. We compare to experimental data for various beetles, whose optical structure resembles the proposed model. Thus, using only the phenomenon of interference and the idea of recursion, we are able to elucidate the concept of band structure in the context of the experimentally observed high reflectance and iridescent appearance of structurally colored beetles.

Amir, Ariel; Vukusic, Peter

2013-04-01

43

Effects of d-band shape on the surface reactivity of transition-metal alloys  

NASA Astrophysics Data System (ADS)

The d-band shape of a metal site, governed by the local geometry and composition of materials, plays an important role in determining trends of the surface reactivity of transition-metal alloys. We discuss this phenomenon using the chemisorption of various adsorbates such as C, N, O, and their hydrogenated species on Pd bimetallic alloys as an example. For many alloys, the d-band center, even with consideration of the d-band width and sp electrons, can not describe variations in reactivity from one surface to another. We investigate the effect of the d-band shape, represented by higher moments of the d band, on the local electronic structure of adsorbates, e.g., energy and filling of adsorbate-metal antibonding states. The upper d-band edge ?u, defined as the highest peak position of the Hilbert transform of the density of states projected onto d orbitals of an active metal site, is identified as an electronic descriptor for the surface reactivity of transition metals and their alloys, regardless of variations in the d-band shape. The utilization of the upper d-band edge with scaling relations enables a considerable reduction of the parameter space in search of improved alloy catalysts and further extends our understanding of the relationship between the electronic structure and chemical reactivity of metal surfaces.

Xin, Hongliang; Vojvodic, Aleksandra; Voss, Johannes; Nørskov, Jens K.; Abild-Pedersen, Frank

2014-03-01

44

Band structures in doubly odd Rh98  

NASA Astrophysics Data System (ADS)

Excited states in the transitional doubly odd Rh98 nucleus were populated in the As75(Si28,2p3n) fusion-evaporation reaction using the 120-MeV incident Si28 beam. The subsequent de-excitations were investigated through in-beam ?-ray spectroscopic techniques using an early implementation phase of the Indian National Gamma Array (INGA) spectrometer equipped with 18 clover Ge detectors. The level structures in Rh98 have been established up to excitation energy ?10 MeV and angular momentum ˜23?. The previously reported level schemes are considerably modified and extended substantially. Significant expansion of the level scheme at low excitation energies stipulates that the previously reported 842-726-994-980-265 keV ?-transition cascade in Rh98 is not directly based on the ground state (T1/2 = 8.7 min). Tilted-axis cranking (TAC) shell-model calculations have been used to put the present level scheme of Rh98 in perspective. Level structures have been interpreted in terms of the rotational bands based on the ?p1/2??h11/2 [triaxiality parameter (?) = 25?], and ?f5/2??h11/2 proton-neutron configurations having moderate quadrupole deformation (?2 ? 0.13) and the admixtures. Excited band structures are based on the ?p1/2/f5/2??(g9/2)2??h11/2 configuration and the fully stretched [?p1/2??(h11/2)2??d5/2]13- configuration.

Kumar, S.; Sihotra, S.; Singh, K.; Singh, V.; Sandeep, Goswamy, J.; Singh, N.; Mehta, D.; Malik, S. S.; Palit, R.; Kumar, R.; Singh, R. P.; Muralithar, S.; Bhowmik, R. K.

2014-03-01

45

Segmental structure in banded mongoose calls  

PubMed Central

In complex animal vocalizations, such as bird or whale song, a great variety of songs can be produced via rearrangements of a smaller set of 'syllables', known as 'phonological syntax' or 'phonocoding' However, food or alarm calls, which function as referential signals, were previously thought to lack such combinatorial structure. A new study of calls in the banded mongoose Mungos mungo provides the first evidence of phonocoding at the level of single calls. The first portion of the call provides cues to the identity of the caller, and the second part encodes its current activity. This provides the first example known in animals of something akin to the consonants and vowels of human speech. See research article http://www.biomedcentral.com/1741-7007/10/97 PMID:23206277

2012-01-01

46

The effect of surface stoichiometry on the band gap of the pyrite FeS2(100) surface  

NASA Astrophysics Data System (ADS)

Iron pyrite (FeS2) is experiencing a resurgence of interest for use in solar photovoltaic and photoelectrochemical cells. The main hurdle to the use of pyrite is the low open-circuit voltage of pyrite devices, which may result from gap states created by surface and bulk defects. Recently, systematic spin-polarized DFT calculations were performed for a series of pyrite FeS2(100) surfaces to clarify the effect of surface stoichiometry on stability, electronic structure, and band gap. It was found that while stoichiometric and S-poor FeS2(100) surfaces are semiconductors with band gaps of 0.56-0.72 eV, S-rich surfaces are small-gap semiconductors (Eg< 0.3 eV) or metals. The stoichiometric FeS2(100) surface is spin polarized in the topmost layer (2 ?B per Fe) and displays a band of Fe dz^2 gap states centered 0.2 eV above the valence band edge. Our calculations suggest that the low open-circuit voltage of pyrite solar cells may result from a narrowed surface band gap. S-poor surfaces may provide larger photovoltages than S-rich surfaces. The segregation process of sulfur vacancy under different surface conditions are also being studied, so as to provide useful guidelines for the design and fabrication of better pyrite photovoltaic materials and devices.

Zhang, Yanning; Hu, Jun; Law, Matt; Wu, Ruqian

2012-02-01

47

Band Structures of the Nucleus 129Cs  

NASA Astrophysics Data System (ADS)

High-spin states in 129Cs are populated via the 122Sn (11B, 4n) reaction at beam energies of 55 and 60 MeV. Two additional bands are placed in the level scheme and the previously known bands are extended to higher spins. The results are compared to the cranked shell model calculations and to the systematics of the adjacent Cs isotpoes. One of the new bands is interpreted as the ?-vibrational band built on the ?h11/2 orbital. The possible configuration for another new band is discussed. Upbend caused by (vh11/2)2 alignment is observed both in the favored and unfavored sequences of the ?h11/2 configuration. The band based on the ?g7/2 configuration at low spins forks around spin 17/2, and the two different S-bands are attributed to (vh11/2) and (?h11/2)2 rotational alignments, respectively.

Zhao, Yan-Xin; Ma, Ying-Jun; Zhou, Wen-Ping; Wang, Shou-Yu; Liu, Gong-Ye; Wu, Xiao-Guang; Zhu, Li-Hua; Hao, Xin; Liu, Ying; Li, Xue-Qin; Li, Ming-Fei

2009-09-01

48

Absence of X-point band overlap in divalent hexaborides and variability of the surface chemical potential  

SciTech Connect

Angle-resolved photoemission measurements of divalent hexaborides reveals a >1 eV X-point gap between the valence and conduction bands, in contradiction to the band overlap assumed in several models of their novel ferromagnetism. While the global ARPES band structure and gap size observed are consistent with the results of bulk-sensitive soft x-ray absorption and emission boron K-edge spectroscopy, the surface-sensitive photoemission measurements also show a variation with cation, surface and time of the position of the surface chemical potential in the band structure.

Denlinger, Jonathan D.; Gweon, Gey-Hong; Mo, Sung-Kwan; Allen, James W.; Sarrao, John L.; Bianchi, Adrian D.; Fisk, Zachary

2001-11-04

49

Theory of quasiparticle scattering in a two-dimensional system of helical Dirac fermions: Surface band structure of a three-dimensional topological insulator  

E-print Network

Theory of quasiparticle scattering in a two-dimensional system of helical Dirac fermions: Surface the quasiparticle interference QPI patterns caused by scattering off nonmagnetic, magnetic point impurities, which provide a lab- realizable condensed-matter analog of two-dimensional 2D , massless Dirac theory

Hu, Jiangping

50

Structure of ferroelectric surfaces  

Microsoft Academic Search

The structural characteristics of the surface layer of some of the well-known common ferroelectrics are examined in the light of recent experimental data obtained by a variety of analytical techniques, including Auger electron spectroscopy, UV and X-ray photoelectron spectroscopy, slow and fast electron diffraction analyses, and scanning electron microscopy. The discussion covers the electron and atomic structure, chemical composition, microstructure

Iu. Ia. Tomashpol'Skii

1987-01-01

51

Large spin splitting of metallic surface-state bands at adsorbate-modified gold/silicon surfaces  

PubMed Central

Finding appropriate systems with a large spin splitting of metallic surface-state band which can be fabricated on silicon using routine technique is an essential step in combining Rashba-effect based spintronics with silicon technology. We have found that originally poor structural and electronic properties of the surface can be substantially improved by adsorbing small amounts of suitable species (e.g., Tl, In, Na, Cs). The resultant surfaces exhibit a highly-ordered atomic structure and spin-split metallic surface-state band with a momentum splitting of up to 0.052 Å?1 and an energy splitting of up to 190?meV at the Fermi level. The family of adsorbate-modified surfaces, on the one hand, is thought to be a fascinating playground for exploring spin-splitting effects in the metal monolayers on a semiconductor and, on the other hand, expands greatly the list of material systems prospective for spintronics applications. PMID:23661151

Bondarenko, L. V.; Gruznev, D. V.; Yakovlev, A. A.; Tupchaya, A. Y.; Usachov, D.; Vilkov, O.; Fedorov, A.; Vyalikh, D. V.; Eremeev, S. V.; Chulkov, E. V.; Zotov, A. V.; Saranin, A. A.

2013-01-01

52

Engineering the Electronic Band Structure for Multiband Solar Cells  

SciTech Connect

Using the unique features of the electronic band structure of GaNxAs1-x alloys, we have designed, fabricated and tested a multiband photovoltaic device. The device demonstrates an optical activity of three energy bands that absorb, and convert into electrical current, the crucial part of the solar spectrum. The performance of the device and measurements of electroluminescence, quantum efficiency and photomodulated reflectivity are analyzed in terms of the Band Anticrossing model of the electronic structure of highly mismatched alloys. The results demonstrate the feasibility of using highly mismatched alloys to engineer the semiconductor energy band structure for specific device applications.

Lopez, N.; Reichertz, L.A.; Yu, K.M.; Campman, K.; Walukiewicz, W.

2010-07-12

53

Organosilane-functionalized wide band gap semiconductor surfaces  

NASA Astrophysics Data System (ADS)

Surface functionalization of wide band gap semiconductors, SiC, ZnO, and GaN, with organosilane is reported. Formation of self-assembled monolayers of mercaptopropyltrimethoxysilane is confirmed by x-ray photoelectron spectroscopy and atomic force microscopy. The molecules are adsorbed on the surfaces through the silane groups with the free thiol groups molecularly oriented away from the surface. Moreover, chemisorption via the thiolate is observed for the ZnO surface. Immobilization of a model biomolecule to the functionalized surface is demonstrated. An amino acid derivative, i.e., phosphotyrosine derived thiol, is linked on the functionalized ZnO and GaN surfaces via formation of disulfide bridges.

Petoral, R. M.; Yazdi, G. R.; Lloyd Spetz, A.; Yakimova, R.; Uvdal, K.

2007-05-01

54

Weak morphology dependent valence band structure of boron nitride  

NASA Astrophysics Data System (ADS)

We report a hard X-ray photoelectron spectroscopy (HX-PES) investigation on valence band structure of Boron Nitrides (BN) having different morphologies, including nanosheets, nanotubes, and micro-sized particles. Very weak morphology/valence band structure dependence was observed. For each case, the B-N ?-band overlapping with ?-band between 0 to -12.5 eV and the s-band below -15 eV were identified. No obvious morphology-induced band shifts and intensity variations were observed. First-principles calculations based on density functional theory were performed and the results were compared with the experimental data. This theoretical analysis well explains the weak morphology dependent valence band spectra of BN nanomaterials obtained during HX-PES measurements.

Zhi, Chunyi; Ueda, Shigenori; Zeng, Haibo; Wang, Xuebin; Tian, Wei; Wang, Xi; Bando, Yoshio; Golberg, Dmitri

2013-08-01

55

A dual-band flexible frequency selective surface with miniaturized elements and maximally flat (Butterworth) response  

NASA Astrophysics Data System (ADS)

A dual-band flexible frequency selective surface (FSS) with miniaturized elements and maximally flat (Butterworth) response is presented in this paper. It is composed of three metallic layers, which are fabricated on thin flexible polyimide substrates and bonded together using thin bonding films. The overall thickness of the proposed structure is only about 0.3 mm, making it an attractive choice for conformal FSS applications. All the three layers can constitute a miniaturized-element FSS (MEFSS) and produce the first pass-band with miniaturization property, while the up and bottom layers can constitute a symmetric biplanar FSS and produce the second pass-band with maximally flat (Butterworth) response. The two pass-bands are independent and there is a wide band spacing up to 30 GHz between them. The principles of operation, the simulated results by using the vector modal matching method, and the experimental values of the fabricated prototype are also presented and discussed.

Wang, Xiu-Zhi; Gao, Jin-Song; Xu, Nian-Xi; Liu, Hai

2014-04-01

56

Band gap creation using quasiordered structures based on sonic crystals  

Microsoft Academic Search

It is well known that sonic crystals are periodic structures that present acoustic band gaps attenuation centered at frequencies related with the lattice constant of the structure. We present an approach based on genetic algorithms to create band gaps in a predetermined range of frequencies. The mechanism used by genetic algorithms to achieve this objective is the creation of vacancies

V. Romero-García; E. Fuster; L. M. García-Raffi; E. A. Sánchez-Pérez; M. Sopena; J. Llinares; J. V. Sánchez-Pérez

2006-01-01

57

BAND STRUCTURE AND OPTICAL PROPERTIES OF MAGNESIUM FLUORIDE  

E-print Network

595 BAND STRUCTURE AND OPTICAL PROPERTIES OF MAGNESIUM FLUORIDE C. JOUANIN, J. P. ALBERT and C'autres transitions expéri- mentales. Abstract. 2014 The electronic band structure of magnesium fluoride is calculated, there is no precise theoretical information on the electronic states of the alkaline-earth fluorides. At the moment

Paris-Sud XI, Université de

58

Fractal FSS: a novel dual-band frequency selective surface  

Microsoft Academic Search

The multiband properties of self-similar fractals can be advantageously exploited to design multiband frequency selective surfaces (FSS). A Sierpinski dipole FSS has been analyzed and measured and the results show an interesting dual-band behavior. Furthermore a near-field measurement technique is applied to characterize the FSS response to different angles of incidence. Finally, it is shown that it is possible to

Jordi Romeu; Yahya Rahmat-Samii

2000-01-01

59

Tuning the electronic band structure of PCBM by electron irradiation  

PubMed Central

Tuning the electronic band structures such as band-edge position and bandgap of organic semiconductors is crucial to maximize the performance of organic photovoltaic devices. We present a simple yet effective electron irradiation approach to tune the band structure of [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM) that is the most widely used organic acceptor material. We have found that the lowest unoccupied molecular orbital (LUMO) level of PCBM up-shifts toward the vacuum energy level, while the highest occupied molecular orbital (HOMO) level down-shifts when PCBM is electron-irradiated. The shift of the HOMO and the LUMO levels increases as the irradiated electron fluence increases. Accordingly, the band-edge position and the bandgap of PCBM can be controlled by adjusting the electron fluence. Characterization of electron-irradiated PCBM reveals that the variation of the band structure is attributed to the molecular structural change of PCBM by electron irradiation. PMID:21970617

2011-01-01

60

Tuning the electronic band structure of PCBM by electron irradiation.  

PubMed

Tuning the electronic band structures such as band-edge position and bandgap of organic semiconductors is crucial to maximize the performance of organic photovoltaic devices. We present a simple yet effective electron irradiation approach to tune the band structure of [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM) that is the most widely used organic acceptor material. We have found that the lowest unoccupied molecular orbital (LUMO) level of PCBM up-shifts toward the vacuum energy level, while the highest occupied molecular orbital (HOMO) level down-shifts when PCBM is electron-irradiated. The shift of the HOMO and the LUMO levels increases as the irradiated electron fluence increases. Accordingly, the band-edge position and the bandgap of PCBM can be controlled by adjusting the electron fluence. Characterization of electron-irradiated PCBM reveals that the variation of the band structure is attributed to the molecular structural change of PCBM by electron irradiation. PMID:21970617

Yoo, Seung Hwa; Kum, Jong Min; Cho, Sung Oh

2011-01-01

61

Multi-band, highly absorbing, microwave metamaterial structures  

NASA Astrophysics Data System (ADS)

A further example of multi-band absorption using ultra-thin, polarization-insensitive, wide-angled metamaterial absorbers that operate in multi-frequency bands within the microwave regime is presented in this work. The basic structure geometry is utilised to create multi-band highly absorbing structures by incorporating the scalability property of the metamaterials. Simulation results verify the structure's ability for high absorption. The multi-band absorbers are promising candidates as absorbing elements in scientific and technical applications because of its multi-band absorption, polarization insensitivity, and wide-angle response. Finally, the current distributions for those structures are presented to gain a better insight into the physics behind the multiple absorption mechanism.

Kollatou, T. M.; Dimitriadis, A. I.; Assimonis, S. D.; Kantartzis, N. V.; Antonopoulos, C. S.

2014-05-01

62

Novel photonic band gap structures for accelerator applications  

E-print Network

In this thesis I present the design and experimental demonstration of the first photonic band gap (PBG) accelerator at 17.140 GHz. A photonic band gap structure is a one-, two- or three-dimensional periodic metallic and/or ...

Smirnova, Evgenya I

2005-01-01

63

Band Structure of SiGe: Coherent-Potential Approximation  

Microsoft Academic Search

The band structure of SiGe has been calculated using the coherent-potential approximation in conjunction with a realistic but local pseudopotential model. The effects of alloy disorder manifest themselves in complex band energies, each with an imaginary part inversely proportional to the electron lifetime. Spectral functions and the alloy denisty of states are also computed. The damping proves to be small,

D. Stroud; H. Ehrenreich

1970-01-01

64

Electronic structure and thermoelectric properties of narrow band gap chalcogenides  

Microsoft Academic Search

In recent years there have been a revival of interest in discovering and understanding the physical properties of novel thermoelectric (TE) systems with high figure of merit. These systems are primarily narrow band gap semiconductors. In this thesis, electronic structure calculations were carried out for several narrow band gap chalcogenide TE materials in order to understand their electronic and transport

Daniel Bilc

2005-01-01

65

Structure of ferroelectric surfaces  

NASA Astrophysics Data System (ADS)

The structural characteristics of the surface layer of some of the well-known common ferroelectrics are examined in the light of recent experimental data obtained by a variety of analytical techniques, including Auger electron spectroscopy, UV and X-ray photoelectron spectroscopy, slow and fast electron diffraction analyses, and scanning electron microscopy. The discussion covers the electron and atomic structure, chemical composition, microstructure and domains, and surface phase transitions of such ferroelectrics as BaTiO3, SrTiO3, PbTiO3, Bi4Ti3O12, Bi2Ti2O7, KNbO3, LiNbO3, and Pb5Ge3O11.

Tomashpol'Skii, Iu. Ia.

1987-12-01

66

Analysis of the sea clutter structure using temporal sequences of X-band marine radar images  

Microsoft Academic Search

This work analyses the spectral structure of the sea clutter obtained from temporal sequences of radar images of the sea surface. The images were acquired by ordinary marine radars, which work in X-band and horizontal polarization. The study analyses the different contributions to the sea clutter spectrum due to those phenomena, such as ocean waves, speckle due to sea surface

Jose C. Nieto-Borge; Ana M. Baquero-Martínez; David de la Mata-Moya; Jose L. Álvarez-Pérez

2008-01-01

67

Wide band gap photonic structures in dichromate gelatin emulsions  

NASA Astrophysics Data System (ADS)

The authors report the fabrication of wide band gap photonic crystals with planar structures in dichromate gelatin emulsions using a two-beam holographic method. By exploiting the differential swelling of the gelatin, planar structures with gradient spacing are fabricated. The crystals exhibit high efficiencies and wide band gaps in the visible range. The authors model the planar gelatin system by an effective medium approach and use transfer matrix to calculate the reflectance and transmittance. Good agreement is obtained between theory and experiment.

Ma, Rui; Xu, Jun; Tam, Wing Yim

2006-08-01

68

PhET Simulation: Band Structure  

NSDL National Science Digital Library

This webpage contains an interactive simulation that allows users to explore quantum bound states in multiple potential wells, and to see the formation of bands of energy levels. Users can interactively change features such as the number, width, spacing, and height of the wells, and see the changes to the energy levels and energy eigenstate wave functions continuously. Options also include using square and Coulomb shaped wells. Probability densities and wave functions can be shown using a variety of representations. This simulation is also contained within the Quantum Bound States simulation. Also included is a teacher's guide as well as sample learning goals for use with the simulation. This simulation is part of a large and growing collection. It has been designed using principles from physics education research and refined based on student interviews.

2006-10-20

69

Analysis and design of triple-band high-impedance surface absorber with periodic diversified impedance  

NASA Astrophysics Data System (ADS)

In this paper, a triple-band planar absorber with high-impedance surface (HIS) is designed and fabricated. The absorber structure is composed of polyurethane foam sandwiched between a lossy sheet of frequency selective surfaces (FSS) and a perfect electric conductor. The lossy FSS possesses different resistances in a periodic composite unit as compared with typical HIS absorber. Losses in the FSS are introduced by printing the periodic composite square ring pattern on blank stickers using various resistive inks. Physical mechanism of the HIS absorbers is analyzed by equivalent circuit model and electric field distribution studies. The proposed absorber with periodic composite units offers superimposed triple-band absorption as compared with that of the single units having single- or dual-band absorption characteristics. The reflection loss measurements show that the 90% absorption bandwidth of the HIS absorber is increased by 42% by the proposed composite periodic units.

Rui Zhang, Guo; Heng Zhou, Pei; Bin Zhang, Hui; Bo Zhang, Lin; Liang Xie, Jian; Jiang Deng, Long

2013-10-01

70

Active Narrow-Band Vibration Isolation of Large Engineering Structures  

NASA Technical Reports Server (NTRS)

We present a narrow-band tracking control method using a variant of the Least Mean Squares (LMS) algorithm to isolate slowly changing periodic disturbances from engineering structures. The advantage of the algorithm is that it has a simple architecture and is relatively easy to implement while it can isolate disturbances on the order of 40-50 dB over decades of frequency band. We also present the results of an experiment conducted on a flexible truss structure. The average disturbance rejection achieved is over 40 dB over the frequency band of 5 Hz to 50 Hz.

Rahman, Zahidul; Spanos, John

1994-01-01

71

Banded Electron Structure Formation in the Inner Magnetosphere  

NASA Technical Reports Server (NTRS)

Banded electron structures in energy-time spectrograms have been observed in the inner magnetosphere concurrent with a sudden relaxation of geomagnetic activity. In this study, the formation of these banded structures is considered with a global, bounce-averaged model of electron transport, and it is concluded that this structure is a natural occurrence when plasma sheet electrons are captured on closed drift paths near the Earth. These bands do not appear unless there is capture of plasma sheet electrons; convection along open drift paths making open pass around the Earth do not have time to develop this feature. The separation of high-energy bands from the injection population due to the preferential advection of the gradient-curvature drift creates spikes in the energy distribution, which overlap to form a series of bands in the energy spectrograms. The lowest band is the bulk of the injected population in the sub-key energy range. Using the Kp history for an observed banded structure event, a cloud of plasma sheet electrons is captured and the development of their distribution function is examined and discussed.

Liemohn, M. W.; Khazanov, G. V.

1997-01-01

72

Fragmentation of band and Fermi surface in stripe phase  

NASA Astrophysics Data System (ADS)

The mean-field study of the stripe phases of the t-t'-U Hubbard model confirms the formation of the in-gap subbands of states localized on the domain walls. For bond-aligned stripes it is shown that segments of Fermi surfaces in antinodal and nodal directions correspond to the in-gap band or to that delocalized over a whole antiferromagnet domain. This can explain the dichotomy between the corresponding quasiparticles in La2 - xSrxCuO4 (LSCO) and the suppression of spectral weight in the nodal direction in underdoped LSCO. The Fermi surface changes its topology with doping. It is confirmed also that diagonal stripes can provide an insulating state at nonzero doping.

Ovchinnikova, M. Ya.

2005-02-01

73

[Band electronic structures and crystal packing forces  

SciTech Connect

We investigated the electronic and structural properties of low-dimensional materials and explored the structure-property correlations governing their physical properties. Progress was made on how to interpret the scanning tunneling microscopy and atomic force microscopy images of layered materials and on how to account for charge density wave instabilities in 2-D metals. Materials studied included transition metal chalcogenides, transition metal halides, organic conducting salts, Mo bronzes, A[sub 2]PdH[sub 2], fullerenes, squarate tetrahydrate polymers Fe, Cu(C[sub 4]O[sub 4])4[center dot]H[sub 2]O, BEDT salts, etc.

Not Available

1993-01-01

74

Surface roughness of orthodontic band cements with different compositions  

PubMed Central

Objectives The present study evaluated comparatively the surface roughness of four orthodontic band cements after storage in various solutions. Material and Methods eight standardized cylinders were made from 4 materials: zinc phosphate cement (ZP), compomer (C), resin-modified glass ionomer cement (RMGIC) and resin cement (RC). Specimens were stored for 24 h in deionized water and immersed in saline (pH 7.0) or 0.1 M lactic acid solution (pH 4.0) for 15 days. Surface roughness readings were taken with a profilometer (Surfcorder SE1200) before and after the storage period. Data were analyzed by two-way ANOVA and Tukey's test (comparison among cements and storage solutions) or paired t-test (comparison before and after the storage period) at 5% significance level. Results The values for average surface roughness were statistically different (p<0.001) among cements at both baseline and after storage. The roughness values of cements in a decreasing order were ZP>RMGIC>C>R (p<0.001). After 15 days, immersion in lactic acid solution resulted in the highest surface roughness for all cements (p<0.05), except for the RC group (p>0.05). Compared to the current threshold (0.2 µm) related to biofilm accumulation, both RC and C remained below the threshold, even after acidic challenge by immersion in lactic acid solution. Conclusions Storage time and immersion in lactic acid solution increased the surface roughness of the majority of the tested cements. RC presented the smoothest surface and it was not influenced by storage conditions. PMID:21625737

van de SANDE, Françoise Hélène; da SILVA, Adriana Fernandes; MICHELON, Douver; PIVA, Evandro; CENCI, Maximiliano Sérgio; DEMARCO, Flávio Fernando

2011-01-01

75

Band structure of Charge Ordered Doped Antiferromagnets  

NASA Astrophysics Data System (ADS)

We study the distribution of electronic spectral weight in a doped antiferromagnet with various types of charge order and compare to angle resolved photoemission experiments on lightly doped La_2-xSr_xCuO4 and electron doped Nd_2-xCe_xCuO_4. Calculations on in-phase stripe and bubble phases for the electron doped system are both in good agreement with experiment including in particular the existence of in-gap spectral weight. In addition we find that for in-phase stripes, in contrast to anti-phase stripes, the chemical potential is likely to move with doping. For the hole doped system we find that ``staircase'' stripes which are globally diagonal but locally vertical or horizontal can reproduce the photoemission data whereas pure diagonal stripes cannot. We also calculate the structure factors of such staircase stripes and find that as the stripe separation is decreased with increased doping these evolve from diagonal to vertical separated by a coexistence region. The results suggest that the transition from horizontal to diagonal stripes seen in neutron scattering on underdoped LSCO may be a crossover between a regime where the typical length of straight stripe segments is longer than the inter-stripe spacing to one where it is shorter and that locally the stripes are always aligned with the Cu-O bonds.

Granath, Mats

2004-03-01

76

Bulk band structure of Bi2Te3  

NASA Astrophysics Data System (ADS)

The bulk band structure of Bi2Te3 has been determined by angle-resolved photoemission spectroscopy and compared to first-principles calculations. We have performed calculations using the local density approximation (LDA) of density functional theory and the one-shot GW approximation within the all-electron full-potential linearized augmented-plane-wave (FLAPW) formalism, fully taking into account spin-orbit coupling. Quasiparticle effects produce significant changes in the band structure of Bi2Te3 when compared to LDA. Experimental and calculated results are compared in the spectral regions where distinct differences between the LDA and GW results are present. Overall a superior agreement with GW is found, highlighting the importance of many-body effects in the band structure of this family of topological insulators.

Michiardi, Matteo; Aguilera, Irene; Bianchi, Marco; de Carvalho, Vagner Eustáquio; Ladeira, Luiz Orlando; Teixeira, Nayara Gomes; Soares, Edmar Avellar; Friedrich, Christoph; Blügel, Stefan; Hofmann, Philip

2014-08-01

77

Banded structures in collagen vitrigels for corneal injury repair.  

PubMed

There is a growing interest in using collagen vitrigels for corneal injury repair. We recently reported the synthesis and thermal denaturation behavior of these gels. In this paper, the banded structure in these vitrified gels is studied by small-angle X-ray scattering (SAXS) one-dimensional (1-D) correlation function analysis and transmission electron microscopy (TEM). Results demonstrate that the collagen vitrigel possess banded structures similar to those of the starting type I collagen, with an average D-spacing of 64nm (by SAXS) or 57nm (by TEM). A combination of SAXS 1-D correlation function analyses and TEM show that overlap and gap distances ranged from 30 to 33nm and from 23 to 25nm, respectively. Changing the vitrification condition does not impact on the banded structure significantly. PMID:24859294

Xia, Zhiyong; Calderón-Colón, Xiomara; McCally, Russell; Maranchi, Jeffrey; Rong, Lixia; Hsiao, Benjamin; Elisseeff, Jennifer; Trexler, Morgana

2014-08-01

78

Plasmon-polariton band structures of asymmetric T-shaped plasmonic gratings.  

PubMed

It is shown that asymmetric T-shaped plasmonic gratings can display plasmon-polariton band structures with wide range of band gaps and tunable group velocities. A structure gap is introduced in the post of Tshaped plasmonic gratings and it is found that the size of this gap plays an important role in controlling the plasmon-polariton band gap and group velocities. We obtained variation of energy band gap ranging from 0.4 eV to 0.0323 eV by changing the size of the structure gap from 0 to 250 nm. The plasmon-polariton band structures were obtained by using Rigorous Coupled Wave Analysis. We studied the difference between symmetric and asymmetric T-shaped gratings and found that the symmetric structure has a momentum gap in the photonic band structure, which can be avoided in the asymmetric structure. Furthermore, by varying the post and spacer (made of SiO2) thicknesses we can tune the energy band gap from 0.1 eV to 0.148 eV and from 0.183 eV to 0.19 eV, respectively. In this device, we obtain tunable group velocities ranging from one to several orders of magnitude smaller than the speed of light in the vacuum. This asymmetric T-shaped plasmonic grating is expected to have applications in surface plasmon polariton (SPP) based optical devices, such as filters, waveguides, splitters and lasers, especially for applications requiring large photonic band gap. PMID:20174078

Abbas, Mohammed Nadhim; Chang, Yia-Chung; Shih, M H

2010-02-01

79

FabryPerot effects in THz time-domain spectroscopy of plasmonic band-gap structures  

E-print Network

Fabry�Perot effects in THz time-domain spectroscopy of plasmonic band-gap structures J. W. Lee, M were reported in the tera- hertz THz region.13�16 We however note that Fabry�Perot resonance has never coupled surface plasmons in the optical and THz regions. In this letter, we explicitly show

Peinke, Joachim

80

Propagation of designer surface plasmons in structured conductor surfaces with  

E-print Network

-Vidal, "Highly confined guiding of terahertz surface plasmon polaritons on structured metal surfaces," NatPropagation of designer surface plasmons in structured conductor surfaces with parabolic gradient investigate the propagation of designer surface plasmons in planar perfect electric conductor structures

81

Tailoring band gaps of insulators by adsorption at surface defects: Benzoic acids on NaCl surfaces  

NASA Astrophysics Data System (ADS)

The adsorption of benzoic acid and its OH-substituted derivatives, namely, salicylic acid (SA) and parasalicylic acid on various NaCl surfaces has been investigated by density-functional theory with hybrid exchange-correlation functional. The ideal NaCl(100) surface is chemically inert as evidenced by the low binding energies. The molecular adsorption can be enhanced by both an anion vacancy and a surface step site. The bonding between the surface Na and the carboxylic O atom is of covalent character for all adsorption geometries. Our calculations show that the adsorption of SA has the largest binding energy of all three acids due to the additional interaction between Na and the phenolic O atom. Charge transfer between the molecule and the surface is generally very small, except in the presence of an anion vacancy where the unpaired electron is mostly transferred to the adsorbate. Surface defects generally have a strong influence on the electronic structure of the adsorbed molecules. Specifically, the adsorption of SA at [011]-oriented steps can significantly reduce the effective band gap to 1.6 eV due to the up shift of the Cl3p levels at the undercoordinated step edge. Implications of these results to the contact charging effect between wide-band-gap insulators will be discussed.

Chen, Wei; Tegenkamp, Christoph; Pfnür, Herbert; Bredow, Thomas

2009-06-01

82

Structure of the Red Fluorescence Band in Chloroplasts  

E-print Network

spectra for different concentra- tions of chloroplast fragments and measurements at 685 and 760 m# are pre spectra at -196�C are clearly different depending on whether an accessory pigment or chlorophyllStructure of the Red Fluorescence Band in Chloroplasts GOVINDJEE and LOUISA YANG From

Govindjee

83

Imaging Ripples on Phononic Crystals Reveals Acoustic Band Structure and Bloch Harmonics  

NASA Astrophysics Data System (ADS)

Broadband surface phonon wave packets on a phononic crystal made up of a microstructured line pattern are tracked in two dimensions and in real time with an ultrafast optical technique. The eigenmode distribution and the 2D acoustic band structure are obtained from spatiotemporal Fourier transforms of the data up to 1 GHz. We find stop bands at the zone boundaries for both leaky-longitudinal and Rayleigh waves, and show how the structure of individual acoustic eigenmodes in k space depends on Bloch harmonics and on mode coupling.

Profunser, Dieter M.; Wright, Oliver B.; Matsuda, Osamu

2006-08-01

84

Investigation of phononic band gap structures considering interface effects  

NASA Astrophysics Data System (ADS)

Interface imperfection has a significant effect on the wave's propagation behavior in the phononic crystals. To account for the interface imperfection, a numerical simulation based on the boundary element method has been proposed to investigate the propagation of in-plane waves in the phononic crystals with imperfect interfaces. The effects of interface spring stiffness, volume fractions, density ratio, and the shape of the scatters on the band gaps are analyzed. It can be concluded that slightly interface imperfection would not affect band structures too much. However, when the interface is relatively weak, the effect of interface imperfection cannot be neglected.

Zhu, Xingyi; Zhong, Sheng; Sun, Daquan; Ye, Anke; Deng, Fuwen

2014-10-01

85

Electronic band structure of magnetic bilayer graphene superlattices  

NASA Astrophysics Data System (ADS)

Electronic band structure of the bilayer graphene superlattices with ?-function magnetic barriers and zero average magnetic flux is studied within the four-band continuum model, using the transfer matrix method. The periodic magnetic potential effects on the zero-energy touching point between the lowest conduction and the highest valence minibands of pristine bilayer graphene are exactly analyzed. Magnetic potential is shown also to generate the finite-energy touching points between higher minibands at the edges of Brillouin zone. The positions of these points and the related dispersions are determined in the case of symmetric potentials.

Pham, C. Huy; Nguyen, T. Thuong; Nguyen, V. Lien

2014-09-01

86

Linear bands, zero-momentum Weyl semimetal, and topological transition in skutterudite-structure pnictides  

NASA Astrophysics Data System (ADS)

It was reported earlier [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.106.056401 106, 056401 (2011)] that the skutterudite structure compound CoSb3 displays a unique band structure with a topological transition versus a symmetry-preserving sublattice (Sb) displacement very near the structural ground state. The transition is through a massless Dirac-Weyl semimetal, point Fermi surface phase which is unique in that (1) it appears in a three-dimensional crystal, (2) the band critical point occurs at k=0, and (3) linear bands are degenerate with conventional (massive) bands at the critical point (before inclusion of spin-orbit coupling). Further interest arises because the critical point separates a conventional (trivial) phase from a topological phase. In the native cubic structure this is a zero-gap topological semimetal; we show how spin-orbit coupling and uniaxial strain converts the system to a topological insulator (TI). We also analyze the origin of the linear band in this class of materials, which is the characteristic that makes them potentially useful in thermoelectric applications or possibly as transparent conductors. We characterize the formal charge as Co+ d8, consistent with the gap, with its 3¯ site symmetry, and with its lack of moment. The Sb states are characterized as px (separately, py) ?-bonded Sb4 ring states occupied and the corresponding antibonding states empty. The remaining (locally) pz orbitals form molecular orbitals with definite parity centered on the empty 2a site in the skutterudite structure. Eight such orbitals must be occupied; the one giving the linear band is an odd orbital singlet A2u at the zone center. We observe that the provocative linearity of the band within the gap is a consequence of the aforementioned near-degeneracy, which is also responsible for the small band gap.

Pardo, V.; Smith, J. C.; Pickett, W. E.

2012-06-01

87

Inter-band optoelectronic properties in quantum dot structure of low band gap III-V semiconductors  

NASA Astrophysics Data System (ADS)

A generalized theory is developed to study inter-band optical absorption coefficient (IOAC) and material gain (MG) in quantum dot structures of narrow gap III-V compound semiconductor considering the wave-vector (k?) dependence of the optical transition matrix element. The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted for analysis of the IOAC and MG taking InAs, InSb, Hg1-xCdxTe, and In1-xGaxAsyP1-y lattice matched to InP, as example of III-V compound semiconductors, having varied split-off energy band compared to their bulk band gap energy. It has been found that magnitude of the IOAC for quantum dots increases with increasing incident photon energy and the lines of absorption are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of energy band parameters. The results show a significant deviation to the MG spectrum of narrow-gap materials having band nonparabolicity compared to the parabolic band model approximations. The results reflect the important role of valence band split-off energies in these narrow gap semiconductors.

Dey, Anup; Maiti, Biswajit; Chanda Sarkar, Debasree

2014-04-01

88

Structurally tunable resonant absorption bands in ultrathin broadband plasmonic absorbers.  

PubMed

Light absorption is a fundamental optical process playing significantly important role in wide variety of applications ranging from photovoltaics to photothermal therapy. Semiconductors have well-defined absorption bands with low-energy edge dictated by the band gap energy, therefore it is rather challenging to tune the absorption bandwidth of semiconductors. However, resonant absorbers based on plasmonic nanostructures and optical metamaterials emerged as alternative light absorbers due to spectrally selective absorption bands resulting from optical resonances. Recently, a broadband plasmonic absorber design was introduced by Aydin et al. with a reasonably high broadband absorption. Based on that design, here, structurally tunable, broadband absorbers with improved performance are demonstrated. This broadband absorber has a total thickness of 190 nm with 80% average measured absorption (90% simulated absorption) over the entire visible spectrum (400 - 700 nm). Moreover, the effect of the metal and the oxide thicknesses on the absorption spectra are investigated and results indicate that the shorter and the longer band-edge of broadband absorption can be structurally tuned with the metal and the oxide thicknesses, as well as with the resonator size. Detailed numerical simulations shed light on the type of optical resonances that contribute to the broadband absorption response and provide a design guideline for realizing plasmonic absorbers with structurally tunable bandwidths. PMID:25321029

Butun, Serkan; Aydin, Koray

2014-08-11

89

Mid-frequency Band Dynamics of Large Space Structures  

NASA Technical Reports Server (NTRS)

High and low intensity dynamic environments experienced by a spacecraft during launch and on-orbit operations, respectively, induce structural loads and motions, which are difficult to reliably predict. Structural dynamics in low- and mid-frequency bands are sensitive to component interface uncertainty and non-linearity as evidenced in laboratory testing and flight operations. Analytical tools for prediction of linear system response are not necessarily adequate for reliable prediction of mid-frequency band dynamics and analysis of measured laboratory and flight data. A new MATLAB toolbox, designed to address the key challenges of mid-frequency band dynamics, is introduced in this paper. Finite-element models of major subassemblies are defined following rational frequency-wavelength guidelines. For computational efficiency, these subassemblies are described as linear, component mode models. The complete structural system model is composed of component mode subassemblies and linear or non-linear joint descriptions. Computation and display of structural dynamic responses are accomplished employing well-established, stable numerical methods, modern signal processing procedures and descriptive graphical tools. Parametric sensitivity and Monte-Carlo based system identification tools are used to reconcile models with experimental data and investigate the effects of uncertainties. Models and dynamic responses are exported for employment in applications, such as detailed structural integrity and mechanical-optical-control performance analyses.

Coppolino, Robert N.; Adams, Douglas S.

2004-01-01

90

Band structure of polyethylene from many-body perturbation theory  

NASA Astrophysics Data System (ADS)

The electronic structure of polyethylene is an important benchmark and the infinite chain limit for the electronic properties of many molecules, monolayers, and oligomers. Therefore, the band structure of the ideal, one-dimensional polyethylene chain has been extensively researched, from both the experimental and the theoretical viewpoints. Despite this extensive effort, to the best of our knowledge agreement between theoretical calculations and the electronic structure obtained from photoelectron spectroscopy could only be obtained using artificial shifting and ``stretching'' of the computed data. Here, we present a quantitative quasi-particle band-structure for polyethylene using many-body perturbation theory. The approach is employed within the G0W0 approximation, based on a starting point calculated within the generalized gradient approximation to density functional theory. We compare our calculated band-structure to angle resolved photoemission spectroscopy measurements for various long saturated carbohydrates, demonstrate a much improved agreement with experiment, and discuss remaining discrepancies and their possible origins within both theory and experiment.

Biller, Ariel; Sharifzadeh, Sahar; Segev, Lior; Ismail-Beigi, Sohrab; Neaton, Jeffrey B.; Kronik, Leeor

2013-03-01

91

Unfolding of collapsed polymers in shear flow: Effects of colloid banding structures in confining channels  

NASA Astrophysics Data System (ADS)

Using hydrodynamic simulations, we demonstrate that confined colloidal suspensions can greatly enhance the unfolding of collapsed single polymers in flow. When colloids come in direct contact with the polymers due to the flow, the collapsed chains become flattened or elongated on the surface of the colloids, increasing the probability of forming large chain protrusions that the flow can pull out to unfold the polymers. This phenomenon may be suppressed if the colloid size is commensurate with the confining channels, where the colloids form well-defined banding structures. Here, we analyze the colloid banding structures in detail and their relation to the chain unfolding. We find that for colloid volume fractions up to 30%, the confined colloids form simple cubic (sc), hexagonal (hex), or a mixture of sc + hex structures. By directly changing the heights of the confining channels, we show that the collapsed polymers unfold the most in the mixed sc + hex structures. The diffuse (not well-defined) bands in the mixed sc + hex structures provide the highest collision probability for the colloids and the polymers, thus enhancing unfolding the most. Without colloidal suspensions, we show that the confining channels alone do not have an observable effect on the unfolding of collapsed polymers. The well-defined colloid bands also suppress the unfolding of noncollapsed polymers. In fact, the average size for noncollapsed chains is even smaller in the well-defined bands than in a channel without any colloids. The appearance of well-defined bands in this case also indicates that lift forces experienced by the polymers in confinement are negligible compared to those exerted by the colloidal band structures. Our results may be important for understanding the dynamics of mixed colloid polymer solutions.

Chen, Hsieh; Alexander-Katz, Alfredo

2014-03-01

92

Structured surfaces for hemocompatibility  

E-print Network

The rise of micro- and nano-technologies has brought to light intriguing examples of scale-driven performance in a diverse array of fields. The quest to create highly hydrophobic surfaces is one such field. The application ...

Schrauth, Anthony J

2005-01-01

93

Rectangular patch antennas over electromagnetic band gap structures  

NASA Astrophysics Data System (ADS)

In this paper, I propose a new design of a defected structure (DS) for use as an electromagnetic band gap (EBG) configuration to enhance the performance of low profile microstrip antennas. The proposed defected structure embodies a honeycomb lattice of cylindrical air holes. The proposed DS is applied to three different configurations using a dielectric substrate (dielectric constant 6 and thickness 1.5 mm); namely: a dielectric substrate backed by a defected ground plane, a defected dielectric substrate backed by a normal substrate and a defected dielectric substrate backed by a defected ground plane. The simulated values of the transmission coefficient S 21 for the last one show two well-defined stop bands around 8.5 and 9.5 GHz, respectively. The first band has been used to reduce mutual coupling in a microstrip array. On the other hand, the stop band defined around 9.5 GHz has been applied to enhance the characteristics of a rectangular patch antenna and improve the operational 10-dB bandwidth.

Areed, Nihal F. F.

2011-06-01

94

Tunable and sizable band gap in silicene by surface adsorption  

PubMed Central

Opening a sizable band gap without degrading its high carrier mobility is as vital for silicene as for graphene to its application as a high-performance field effect transistor (FET). Our density functional theory calculations predict that a band gap is opened in silicene by single-side adsorption of alkali atom as a result of sublattice or bond symmetry breaking. The band gap size is controllable by changing the adsorption coverage, with an impressive maximum band gap up to 0.50?eV. The ab initio quantum transport simulation of a bottom-gated FET based on a sodium-covered silicene reveals a transport gap, which is consistent with the band gap, and the resulting on/off current ratio is up to 108. Therefore, a way is paved for silicene as the channel of a high-performance FET. PMID:23152944

Quhe, Ruge; Fei, Ruixiang; Liu, Qihang; Zheng, Jiaxin; Li, Hong; Xu, Chengyong; Ni, Zeyuan; Wang, Yangyang; Yu, Dapeng; Gao, Zhengxiang; Lu, Jing

2012-01-01

95

Engineering Design of a Multipurpose X-band Accelerating Structure  

E-print Network

Both FEL projects, SwissFEL and Fermi-Elettra each require an X-band RF accelerating structure for optimal bunch compression at the respective injectors. As the CLIC project is pursuing a program for producing and testing the X-band high-gradient RF structures, a collaboration between PSI, Elettra and CERN has been established to build a multipurpose X-band accelerating structure. This paper focuses on its engineering design, which is based on the disked cells jointed together by diffusion bonding. Vacuum brazing and laser beam welding is used for auxiliary components. The accelerating structure consists of two coupler subassemblies, 73 disks and includes a wakefield monitor and diagnostic waveguides. The engineering study includes the external cooling system, consisting of two parallel cooling circuits and an RF tuning system, which allows phase advance tuning of the cell by deforming the outer wall. The engineering solution for the installation and sealing of the wake field monitor feed-through devices that...

Gudkov, Dmitry; Samoshkin, Alexander; Zennaro, Riccardo; Dehler, Micha; Raguin, Jean-Yves

2010-01-01

96

Quasiparticle band structure and density-functional theory: Single-particle excitations and band gaps in lattice models  

E-print Network

ARTICLES Quasiparticle band structure and density-functional theory: Single-particle excitations D.C. 20057 Received 31 August 1998 We compare the quasiparticle band structure for a model insulator-functional theory DFT and local- density approximation LDA . The discontinuity in the exchange-correlation potential

Hess, Daryl W.

97

Ultranarrow band absorbers based on surface lattice resonances in nanostructured metal surfaces.  

PubMed

Nanostructured metals have received a significant amount of attention in recent years due to their exciting plasmonic and photonic properties enabling strong field localization, light concentration, and strong absorption and scattering at their resonance frequencies. Resonant plasmonic and metamaterial absorbers are of particular interest for applications in a wide variety of technologies including photothermal therapy, thermophotovoltaics, heat-assisted magnetic recording, hot-electron collection, and biosensing. However, it is rather challenging to realize ultranarrow absorption bands using plasmonic materials due to large optical losses in metals that decrease the quality factor of optical resonators. Here, we theoretically and experimentally demonstrate an ultranarrow band absorber based on the surface lattice resonances (SLRs) in periodic nanowire and nanoring arrays on optically thick, reflecting metallic films. In experiments, we observed ultranarrow band resonant absorption peaks with a bandwidth of 12 nm and absorption amplitude exceeding 90% at visible frequencies. We demonstrate that the resonance absorption wavelength, amplitude of the absorption peak, and the bandwidth can be controlled by tuning the periodicity and the thickness of nanoring and nanowire arrays. Unlike conventional plasmonic absorbers utilizing common metal–insulator–metal stacks, our narrow band absorber consists solely of metals, facilitating stronger optical interaction between the SLR of periodic nanostructures and the highly reflective film. Moreover, by introducing asymmetry to the nanoring/nanowire hybrid system, we observe the spectral evolution of resonance splitting enabled by strong coupling between two individual SLRs arising from nanoring and nanowire arrays. Designing such all-metallic nanostructure arrays is a promising route for achieving ultranarrow band absorbers which can be used as absorption filters, narrow band thermal emitters in thermophotovoltaics, and plasmonic biosensors. PMID:25072803

Li, Zhongyang; Butun, Serkan; Aydin, Koray

2014-08-26

98

Calculation of band structure in (101)-biaxially strained Si  

NASA Astrophysics Data System (ADS)

The structure model used for calculation was defined according to Vegard’s rule and Hooke’s law. Calculations were performed on the electronic structures of (101)-biaxially strained Si on relaxed Si1- X Ge X alloy with Ge fraction ranging from X = 0 to 0.4 in steps of 0.1 by CASTEP approach. It was found that [±100] and [00±1] valleys (?4) splitting from the [0±10] valley (?2) constitute the conduction band (CB) edge, that valence band (VB) edge degeneracy is partially lifted and that the electron mass is unaltered under strain while the hole mass decreases in the [100] and [010] directions. In addition, the fitted dependences of CB splitting energy, VB splitting energy and indirect bandgap on X are all linear.

Song, Jianjun; Zhang, Heming; Hu, Huiyong; Fu, Qiang

2009-04-01

99

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

100

REVIEW ARTICLE: Wave interactions in photonic band structures: an overview  

NASA Astrophysics Data System (ADS)

An overview of the most relevant properties of photonic crystals is presented considering 1D, 2D and 3D structures. The emphasis is on nonlinear properties both of the second and third order. Different processes like second harmonic generation and parametric processes are considered. Nonlinearities of composite materials are also presented. Finally quantum effects and the control of spontaneous emission in PBG (photonic band gap) are discussed. Presented at the 2005 Erice Summer School on Nanophotonics.

Bertolotti, M.

2006-04-01

101

Structural, elastic, optical properties and quasiparticle band structure of solid cyanuric triazide  

NASA Astrophysics Data System (ADS)

In this Letter, we report the structural, elastic, and quasiparticle band structure of cynauric triazide. The structural properties using a dispersion corrected method to treat van der Waals (vdW) forces offers a significant improvement in the description of the ground state properties. The predicted bulk modulus from the equation of state and the elastic constants are consistent and the magnitude lies in the order of secondary explosives. Then, the G0W0 approximation is used to study the band structure and an indirect band gap of 6.33 eV is obtained. Finally, we have calculated the optical and detonation characteristics at ambient pressure.

Appalakondaiah, S.; Vaitheeswaran, G.; Lebègue, S.

2014-06-01

102

Bioinspired structured surfaces.  

PubMed

Nature has evolved objects with desired functionality using commonly found materials. Nature capitalizes on hierarchical structures to achieve functionality. The understanding of the functions provided by objects and processes found in nature can guide us to produce nanomaterials, nanodevices, and processes with desirable functionality. Various natural objects which provide functionality of commercial interest have been characterized to understand how a natural object provides functionality. We have modeled and fabricated structures in the lab using nature's route and developed optimum structures. Once it is understood how nature does it, optimum structures have been fabricated using smart materials and fabrication techniques. This feature article provides an overview of four topics: Lotus effect, rose petal effect, gecko feet, and shark skin. PMID:22233136

Bhushan, Bharat

2012-01-24

103

Gold bands as a suitable surface for enzyme immunoassays.  

PubMed

Gold bands sputtered over a polymeric material, Kapton, are employed for the development of enzyme immunoassays. The immunological interaction takes place between human IgM and alkaline phosphatase (AP) conjugated anti-IgM. The model analyte (IgM) could be determined following a non-competitive design in the range of 0.05-5 ppm, with a limit of detection of 50 ppb. After the interaction, gold bands are sequentially inserted in a flow system and the extension of the reaction is followed through the enzymatic hydrolysis of naphthylphosphate, AP substrate. The product, naphthol, is oxidised to naphtoquinone in the gold band of the flow cell that constitutes the detector. Parameters affecting the interaction are studied and calibration curves are performed. The reproducibility between different bands (RSD=4%, n=5) and possibilities of regeneration are also detailed. PMID:12191928

Abad-Villar, Eva M; Fernández-Abedul, M Teresa; Costa-García, Agustín

2002-09-01

104

Band gaps in the spectra of terahertz surface plasmons on metallic diffraction gratings  

Microsoft Academic Search

The effect of the appearance of band gaps in the energy spectra of terahertz surface plasmons has been experimentally observed and investigated. The band gaps are formed due to the interference interaction of the surface plasmons excited by pulsed terahertz radiation on metallic diffraction gratings. It has been shown that the experimental dispersion curves of terahertz plasmons are in good

A. V. Andreev; M. M. Nazarov; I. R. Prudnikov; A. P. Shkurinov

2009-01-01

105

Below-band-gap excitation of a terahertz surface plasmon-polariton  

Microsoft Academic Search

We analyze the excitation of a surface plasmon-polariton at terahertz frequencies by an optical pulse with tilted intensity front incident on a semiconductor surface. We show that one can achieve an order of magnitude increase in the generated terahertz power by using an optical pulse with frequencies below the band gap compared to the above-band-gap excitation.

M. I. Bakunov; A. V. Maslov; S. B. Bodrov

2006-01-01

106

Wireless Channel Characterization in the 5 GHz Microwave Landing System Extension Band for Airport Surface Areas  

NASA Technical Reports Server (NTRS)

In this project final report, entitled "Wireless Channel Characterization in the 5 GHz Microwave Landing System Extension Band for Airport Surface Areas," we provide a detailed description and model representation for the wireless channel in the airport surface environment in this band. In this executive summary, we review report contents, describe the achieved objectives and major findings, and highlight significant conclusions and recommendations.

Matolak, David W.

2007-01-01

107

Simultaneous Multi-band Detection of Low Surface Brightness Galaxies with Markovian Modeling  

NASA Astrophysics Data System (ADS)

We present to the astronomical community an algorithm for the detection of low surface brightness (LSB) galaxies in images, called MARSIAA (MARkovian Software for Image Analysis in Astronomy), which is based on multi-scale Markovian modeling. MARSIAA can be applied simultaneously to different bands. It segments an image into a user-defined number of classes, according to their surface brightness and surroundings—typically, one or two classes contain the LSB structures. We have developed an algorithm, called DetectLSB, which allows the efficient identification of LSB galaxies from among the candidate sources selected by MARSIAA. The application of the method to two and three bands simultaneously was tested on simulated images. Based on our tests, we are confident that we can detect LSB galaxies down to a central surface brightness level of only 1.5 times the standard deviation from the mean pixel value in the image background. To assess the robustness of our method, the method was applied to a set of 18 B- and I-band images (covering 1.3 deg2 in total) of the Virgo Cluster to which Sabatini et al. previously applied a matched-filter dwarf LSB galaxy search algorithm. We have detected all 20 objects from the Sabatini et al. catalog which we could classify by eye as bona fide LSB galaxies. Our method has also detected four additional Virgo Cluster LSB galaxy candidates undetected by Sabatini et al. To further assess the completeness of the results of our method, both MARSIAA, SExtractor, and DetectLSB were applied to search for (1) mock Virgo LSB galaxies inserted into a set of deep Next Generation Virgo Survey (NGVS) gri-band subimages and (2) Virgo LSB galaxies identified by eye in a full set of NGVS square degree gri images. MARSIAA/DetectLSB recovered ~20% more mock LSB galaxies and ~40% more LSB galaxies identified by eye than SExtractor/DetectLSB. With a 90% fraction of false positives from an entirely unsupervised pipeline, a completeness of 90% is reached for sources with r e > 3'' at a mean surface brightness level of ?g = 27.7 mag arcsec-2 and a central surface brightness of ?0 g = 26.7 mag arcsec-2. About 10% of the false positives are artifacts, the rest being background galaxies. We have found our proposed Markovian LSB galaxy detection method to be complementary to the application of matched filters and an optimized use of SExtractor, and to have the following advantages: it is scale free, can be applied simultaneously to several bands, and is well adapted for crowded regions on the sky. .

Vollmer, B.; Perret, B.; Petremand, M.; Lavigne, F.; Collet, Ch.; van Driel, W.; Bonnarel, F.; Louys, M.; Sabatini, S.; MacArthur, L. A.

2013-02-01

108

Tuning of a hypersonic surface phononic band gap using a nanoscale two-dimensional lattice of pillars  

NASA Astrophysics Data System (ADS)

We present experimental and theoretical evidence of a phononic band gap in a hypersonic range for thermally activated surface acoustic waves in two-dimensional (2D) phononic crystals. Surface Brillouin light scattering experiments were performed on the (001) surface of silicon, loaded with a 2D square lattice of 100- or 150-nm-high aluminum pillars with a spacing of 500nm. The surface Brillouin light scattering spectra revealed a different type of surface mode, related to the modulation of the lattice structure and the mechanical eigenmodes of the pillars. The experimental data were in excellent agreement with theoretical calculations performed using the finite-element method.

Graczykowski, B.; Mielcarek, S.; Trzaskowska, A.; Sarkar, J.; Hakonen, P.; Mroz, B.

2012-08-01

109

Microstrip antennas integrated with electromagnetic band-gap (EBG) structures: a low mutual coupling design for array applications  

Microsoft Academic Search

Utilization of electromagnetic band-gap (EBG) structures is becoming attractive in the electromagnetic and antenna community. In this paper, a mushroom-like EBG structure is analyzed using the finite-difference time-domain (FDTD) method. Its band-gap feature of surface-wave suppression is demonstrated by exhibiting the near field distributions of the electromagnetic waves. The mutual coupling of microstrip antennas is parametrically investigated, including both the

Fan Yang; Yahya Rahmat-Samii

2003-01-01

110

First direct observation of a nearly ideal graphene band structure  

SciTech Connect

Angle-resolved photoemission and x-ray diffraction experiments show that multilayer epitaxial graphene grown on the SiC(000{bar 1}) surface is a new form of carbon that is composed of effectively isolated graphene sheets. The unique rotational stacking of these films causes adjacent graphene layers to electronically decouple leading to a set of nearly independent linearly dispersing bands (Dirac cones) at the graphene K point. Each cone corresponds to an individual macroscale graphene sheet in a multilayer stack where AB-stacked sheets can be considered as low density faults.

Sprinkle, M.; Siegel, D.; Hu, Y.; Hicks, J.; Tejeda, A.; Taleb-Ibrahimi, A.; Le Fèvre, P.; Bertran, F.; Vizzini, S.; Enriquez, H.; Chiang, S.; Soukiassian, P.; Berger, C.; de Heer, W.A.; Lanzara, A.; Conrad, E.H.; (CNRS-UMR); (UCB); (CEAS); (SOLEIL); (GIT)

2009-12-10

111

First direct observation of a nearly ideal graphene band structure.  

PubMed

Angle-resolved photoemission and x-ray diffraction experiments show that multilayer epitaxial graphene grown on the SiC(0001) surface is a new form of carbon that is composed of effectively isolated graphene sheets. The unique rotational stacking of these films causes adjacent graphene layers to electronically decouple leading to a set of nearly independent linearly dispersing bands (Dirac cones) at the graphene K point. Each cone corresponds to an individual macroscale graphene sheet in a multilayer stack where AB-stacked sheets can be considered as low density faults. PMID:20366119

Sprinkle, M; Siegel, D; Hu, Y; Hicks, J; Tejeda, A; Taleb-Ibrahimi, A; Le Fèvre, P; Bertran, F; Vizzini, S; Enriquez, H; Chiang, S; Soukiassian, P; Berger, C; de Heer, W A; Lanzara, A; Conrad, E H

2009-11-27

112

Measurements of the energy band gap and valence band structure of AgSbTe2  

NASA Astrophysics Data System (ADS)

The de Haas-van Alphen effect, galvanomagnetic and thermomagnetic properties of high-quality crystals of AgSbTe2 are measured and analyzed. The transport properties reveal the material studied here to be a very narrow-gap semiconductor (Eg?7.6±3meV) with ˜5×1019cm-3 holes in a valence band with a high density of states and thermally excited ˜1017cm-3 high-mobility (2200cm2/Vs) electrons at 300 K. The quantum oscillations are measured with the magnetic field oriented along the ?111? axis. Taken together with the Fermi energy derived from the transport properties, the oscillations confirm the calculated valence band structure composed of 12 half-pockets located at the X -points of the Brillouin zone, six with a density-of-states effective mass mda??0.21me and six with mdb??0.55me , giving a total density-of-states effective mass, including Fermi pocket degeneracy, of md??1.7±0.2me ( me is the free electron mass). The lattice term dominates the thermal conductivity, and the electronic contribution in samples with both electrons and holes present is in turn dominated by the ambipolar term. The low thermal conductivity and very large hole mass of AgSbTe2 make it a most promising p -type thermoelectric material.

Jovovic, V.; Heremans, J. P.

2008-06-01

113

Orientation and shape effects on nanowire band structure  

NASA Astrophysics Data System (ADS)

The impact of wire-axis orientation and cross-sectional shape on the applicability of the Luttinger-Kohn and Burt-Foreman Hamiltonians to modeling the band structure of embedded nanowires is studied. Differences in the two theories at both zero and finite wave vector are derived. The magnitudes of the differences are accessed by carrying out calculations for 3 different wire directions ([001], [110], [111]), 3 different shapes (triangular, square, circular), and two different material systems (GaAs/AlAs, InGaAs/InP).

Lassen, Benny; Willatzen, Morten; Melnik, Roderick; Voon, Lok Lew Yan

2004-03-01

114

Band Structure Asymmetry of Bilayer Graphene Revealed by Infrared Spectroscopy  

SciTech Connect

We report on infrared spectroscopy of bilayer graphene integrated in gated structures. We observe a significant asymmetry in the optical conductivity upon electrostatic doping of electrons and holes. We show that this finding arises from a marked asymmetry between the valence and conduction bands, which is mainly due to the inequivalence of the two sublattices within the graphene layer and the next-nearest-neighbor interlayer coupling. From the conductivity data, the energy difference of the two sublattices and the interlayer coupling energy are directly determined.

Li, Z.Q.; Henriksen, E.A.; Jiang, Z.; Hao, Zhao; Martin, Michael C.; Kim, P.; Stormer, H.L.; Basov, Dimitri N.

2008-12-10

115

Electronic band structure of a type-II ‘W’ quantum well calculated by an eight-band k · p model  

NASA Astrophysics Data System (ADS)

In this paper, we present an investigation of type-II ‘W’ quantum wells for the InAs/Ga1-xInxSb/AlSb family, where ‘W’ denotes the conduction profile of the material. We focus our attention on using the eight-band k · p model to calculate the band structures within the framework of finite element method. For the sake of clarity, the simulation in this paper is simplified and based on only one period—AlSb/InAs/Ga1-xInxSb/InAs/AlSb. The obtained numerical results include the energy levels and wavefunctions of carriers. We discuss the variations of the electronic properties by changing several important parameters, such as the thickness of either InAs or Ga1-xInxSb layer and the alloy composition in Ga1-xInxSb separately. In the last part, in order to compare the eight-band k · p model, we recalculate the conduction bands of the ‘W’ structure using the one-band k · p model and then discuss the difference between the two results, showing that conduction bands are strongly coupled with valence bands in the narrow band gap structure. The in-plane energy dispersions, which illustrate the suppression of the Auger recombination process, are also obtained. Project supported by the National Natural Science Foundation of China (Grant No. 60636030).

Yu, Xiu; Gu, Yong-Xian; Wang, Qing; Wei, Xin; Chen, Liang-Hui

2011-03-01

116

Surface band bending and band alignment of plasma enhanced atomic layer deposited dielectrics on Ga- and N-face gallium nitride  

NASA Astrophysics Data System (ADS)

The effects of surface pretreatment, dielectric growth, and post deposition annealing on interface electronic structure and polarization charge compensation of Ga- and N-face bulk GaN were investigated. The cleaning process consisted of an ex-situ wet chemical NH4OH treatment and an in-situ elevated temperature NH3 plasma process to remove carbon contamination, reduce oxygen coverage, and potentially passivate N-vacancy related defects. After the cleaning process, carbon contamination decreased below the x-ray photoemission spectroscopy detection limit, and the oxygen coverage stabilized at ˜1 monolayer on both Ga- and N-face GaN. In addition, Ga- and N-face GaN had an upward band bending of 0.8 ± 0.1 eV and 0.6 ± 0.1 eV, respectively, which suggested the net charge of the surface states and polarization bound charge was similar on Ga- and N-face GaN. Furthermore, three dielectrics (HfO2, Al2O3, and SiO2) were prepared by plasma-enhanced atomic layer deposition on Ga- or N-face GaN and annealed in N2 ambient to investigate the effect of the polarization charge on the interface electronic structure and band offsets. The respective valence band offsets of HfO2, Al2O3, and SiO2 with respect to Ga- and N-face GaN were 1.4 ± 0.1, 2.0 ± 0.1, and 3.2 ± 0.1 eV, regardless of dielectric thickness. The corresponding conduction band offsets were 1.0 ± 0.1, 1.3 ± 0.1, and 2.3 ± 0.1 eV, respectively. Experimental band offset results were consistent with theoretical calculations based on the charge neutrality level model. The trend of band offsets for dielectric/GaN interfaces was related to the band gap and/or the electronic part of the dielectric constant. The effect of polarization charge on band offset was apparently screened by the dielectric-GaN interface states.

Yang, Jialing; Eller, Brianna S.; Nemanich, Robert J.

2014-09-01

117

Nutrient loss in leachate and surface runoff from surface-broadcast and subsurface-banded broiler litter.  

PubMed

Subsurface band application of poultry litter has been shown to reduce the transport of nutrients from fields in surface runoff compared with conventional surface broadcast application. Little research has been conducted to determine the effects of surface broadcast application and subsurface banding of litter on nutrients in leachate. Therefore, a field experiment was conducted to determine the effects of subsurface band application and surface broadcast application of poultry litter on nutrient losses in leachate. Zero-tension pan and passive capillary fiberglass wick lysimeters were installed in situ 50 cm beneath the soil surface of an established tall fescue ( Schreb.) pasture on a sandy loam soil. The treatments were surface broadcast and subsurface-banded poultry litter at 5 Mg ha and an unfertilized control. Results of the rainfall simulations showed that the concentrations of PO-P and total phosphorus (TP) in leachate were reduced by 96 and 37%, respectively, in subsurface-banded litter treatment compared with the surface-applied litter treatment. There was no significant difference in PO-P concentration between control and subsurface-banded litter treatment in leachate. The trend in the loading of nutrients in leachate was similar to the trend in concentration. Concentration and loading of the nutrients (TP, PO-P, NH-N, and NO-N) in runoff from the subsurface-banded treatment were significantly less than for the surface-applied treatment and were similar to those from control plots. These results show that, compared with conventional surface broadcast application of litter, subsurface band application of litter can greatly reduce loss of P in surface runoff and leachate. PMID:24216435

Lamba, Jasmeet; Srivastava, Puneet; Way, Thomas R; Sen, Sumit; Wood, C Wesley; Yoo, Kyung H

2013-09-01

118

Quasiparticle band structure of thirteen semiconductors and insulators  

SciTech Connect

By using a model dielectric matrix in electron self-energy evaluations the computational effort of a quasiparticle band-structure calculation for a semiconductor is greatly reduced. Applications to various systems with or without inversion symmetry, having narrow or wide band gaps, and semiconductor alloys demonstrate the reliability and accuracy of the method. Calculations have been performed for thirteen semiconducting or insulating materials: Si, LiCl, AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, and the Al{sub 0.5}Ga{sub 0.5}As and In{sub 0.53}Ga{sub 0.47}As alloys. Excellent agreement with experimental results is obtained for the quasiparticle energies for these materials. The only three exceptions, {ital E}({Gamma}{sub 1{ital c}}) of AlP, {ital E}({ital L}{sub 1{ital c}}) of AlAs, and {ital E}({ital L}{sub 1{ital c}}) of AlSb are discussed and attributed to various experimental uncertainties. Several other quasiparticle-excitation-related properties are also examined in this work. The many-body corrections to the eigenvalues of the valence-band-maximum states obtained from the local-density approximation are calculated for the zinc-blende-structure semiconductors, which are widely used in semiconductor-interface studies. In the present approach, the static screening of the Coulomb interaction between two electrons in a crystal is determined using a model that depends only on the local charge densities at these two points. Since a direct quantitative modeling of the electron self-energy operator has proven difficult, the successful application of the present model-dielectric-function scheme in self-energy calculations makes possible detailed studies of the quasiparticle properties of rather complex systems, which would be otherwise computationally too demanding.

Zhu, X.; Louie, S.G. (Department of Physics, University of California, Berkeley, California 94720 (US) Materials Science Division, Lawrence Berkeley Laboratory, Berkeley, California 94720)

1991-06-15

119

Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface  

PubMed Central

Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with two extinction bands to the structure with four bands is observed. This transition is shown to be caused by reorientation of the nematic director in the liquid crystal volume from the planar alignment to the homeotropic state with the pronounced radial configuration of nematic molecules on the surface. The observed textures are compared with different combinations of the volume LC orientations and the radial distribution of the director field and the disclination lines at the polycarbonate surface. PMID:23965955

Parshin, Alexander M.; Gunyakov, Vladimir A.; Zyryanov, Victor Y.; Shabanov, Vasily F.

2013-01-01

120

Quasiparticle semiconductor band structures including spin-orbit interactions.  

PubMed

We present first-principles calculations of the quasiparticle band structure of the group IV materials Si and Ge and the group III-V compound semiconductors AlP, AlAs, AlSb, InP, InAs, InSb, GaP, GaAs and GaSb. Calculations are performed using the plane wave pseudopotential method and the 'one-shot' GW method, i.e. G(0)W(0). Quasiparticle band structures, augmented with the effects of spin-orbit, are obtained via a Wannier interpolation of the obtained quasiparticle energies and calculated spin-orbit matrix. Our calculations explicitly treat the shallow semicore states of In and Ga, which are known to be important in the description of the electronic properties, as valence states in the quasiparticle calculation. Our calculated quasiparticle energies, combining both the ab initio evaluation of the electron self-energy and the vector part of the pseudopotential representing the spin-orbit effects, are in generally very good agreement with experimental values. These calculations illustrate the predictive power of the methodology as applied to group IV and III-V semiconductors. PMID:23396813

Malone, Brad D; Cohen, Marvin L

2013-03-13

121

Photonic band structure calculations using nonlinear eigenvalue techniques  

SciTech Connect

This paper considers the numerical computation of the photonic band structure of periodic materials such as photonic crystals. This calculation involves the solution of a Hermitian nonlinear eigenvalue problem. Numerical methods for nonlinear eigenvalue problems are usually based on Newton's method or are extensions of techniques for the standard eigenvalue problem. We present a new variation on existing methods which has its derivation in methods for bifurcation problems, where bordered matrices are used to compute critical points in singular systems. This new approach has several advantages over the current methods. First, in our numerical calculations the new variation is more robust than existing techniques, having a larger domain of convergence. Second, the linear systems remain Hermitian and are nonsingular as the method converges. Third, the approach provides an elegant and efficient way of both thinking about the problem and organising the computer solution so that only one linear system needs to be factorised at each stage in the solution process. Finally, first- and higher-order derivatives are calculated as a natural extension of the basic method, and this has advantages in the electromagnetic problem discussed here, where the band structure is plotted as a set of paths in the ({omega},k) plane.

Spence, Alastair [Department of Mathematical Sciences, University of Bath, Claverton Down, Bath BA2 7AY (United Kingdom); Poulton, Chris [High Frequency and Quantum Electronics Laboratory, University of Karlsruhe, Kaiserstrasse 12, Karlsruhe 76128 (Germany)]. E-mail: c.poulton@ihq.uni-karlsruhe.de

2005-03-20

122

Metal-induced gap states in ferroelectric capacitors and its relationship with complex band structures  

NASA Astrophysics Data System (ADS)

At metal-isulator interfaces, the metallic wave functions with an energy eigenvalue within the band gap decay exponentially inside the dielectric (metal-induced gap states, MIGS). These MIGS can be actually regarded as Bloch functions with an associated complex wave vector. Usually only real values of the wave vectors are discussed in text books, since infinite periodicity is assumed and, in that situation, wave functions growing exponentially in any direction would not be physically valid. However, localized wave functions with an exponential decay are indeed perfectly valid solution of the Schrodinger equation in the presence of defects, surfaces or interfaces. For this reason, properties of MIGS have been typically discussed in terms of the complex band structure of bulk materials. The probable dependence on the interface particulars has been rarely taken into account explicitly due to the difficulties to include them into the model or simulations. We aim to characterize from first-principles simulations the MIGS in realistic ferroelectric capacitors and their connection with the complex band structure of the ferroelectric material. We emphasize the influence of the real interface beyond the complex band structure of bulk materials.

Junquera, Javier; Aguado-Puente, Pablo

2013-03-01

123

Tunnel spectroscopy of electron sub-bands on Si surfaces  

Microsoft Academic Search

Reports tunnelling studies of quantised electron space-charge layers on (111) and (100) Si surfaces. Planar metal-SiO2-Si junctions were prepared on non-degenerate n- and p-type substrates. Metals of different work functions, lower than the Si electron affinity, were used as counter electrodes, yielding surface electron densities in the range (1-20)*1012 cm2. In samples on p-type substrates the surface density of the

U. Kunze

1984-01-01

124

Appearance of flat surface bands in three-dimensional topological insulators in a ferromagnetic exchange field  

NASA Astrophysics Data System (ADS)

We study the properties of the surface states in three-dimensional topological insulators in the presence of a ferromagnetic exchange field. We demonstrate that for layered materials like \\text{Bi}_2 \\text{Se}_3 the surface states on the top surface behave qualitatively different than the surface states at the side surfaces. We show that the group velocity of the surface states can be tuned by the direction and strength of the exchange field. If the exchange field becomes larger than the bulk gap of the material, a phase transition into a topologically nontrivial semimetallic state occurs. In particular, the material becomes a Weyl semimetal, if the exchange field possesses a nonzero component perpendicular to the layers. Associated with the Weyl semimetallic state we show that Fermi arcs appear at the surface. Under certain circumstances either one-dimensional or even two-dimensional surface flat bands can appear. We show that the appearance of these flat bands is related to chiral symmetries of the system and can be understood in terms of topological winding numbers. In contrast to previous systems that have been suggested to possess surface flat bands, the present system has a much larger energy scale, allowing the observation of surface flat bands at room temperature. The flat bands are tunable in the sense that they can be turned on or off by rotation of the ferromagnetic exchange field. Our findings are supported by both numerical results on a finite system as well as approximate analytical results.

Paananen, Tomi; Gerber, Henning; Götte, Matthias; Dahm, Thomas

2014-03-01

125

Coherent obliquity band and heterogeneous precession band responses in early Pleistocene tropical sea surface temperatures  

Microsoft Academic Search

The nature of the connection between high- and low-latitude climates during the early Pleistocene “41 kyr world” has important implications for our understanding of the feedbacks involved in translating insolation changes into global climate states. Here we focus on the tropical marine record, presenting alkenone-derived sea surface temperature (SST) and productivity records from the eastern equatorial Atlantic, eastern equatorial Pacific,

Laura C. Cleaveland; Timothy D. Herbert

2007-01-01

126

Unfolding the band structure of disordered solids: From bound states to high-mobility Kane fermions  

NASA Astrophysics Data System (ADS)

Supercells are often used in ab initio calculations to model compound alloys, surfaces, and defects. One of the main challenges of supercell electronic structure calculations is to recover the Bloch character of electronic eigenstates perturbed by disorder. Here we apply the spectral weight approach to unfolding the electronic structure of group III-V and II-VI semiconductor solid solutions. The illustrative examples include formation of donorlike states in dilute Ga(PN) and associated enhancement of its optical activity, direct observation of the valence band anticrossing in dilute GaAs:Bi, and a topological band crossover in ternary (HgCd)Te alloy accompanied by emergence of high-mobility Kane fermions. The analysis facilitates interpretation of optical and transport characteristics of alloys that are otherwise ambiguous in traditional first-principles supercell calculations.

Rubel, O.; Bokhanchuk, A.; Ahmed, S. J.; Assmann, E.

2014-09-01

127

Terahertz surface plasmon polaritons on a semiconductor surface structured with  

E-print Network

Terahertz surface plasmon polaritons on a semiconductor surface structured with periodic V: We demonstrate propagation of terahertz waves confined to a semiconductor surface-doped silicon surface, using anisotropic wet-etching of crystalline silicon, thereby forming a plasmonic

Murphy, Thomas E.

128

The reflection and transmission properties of a triple band dichroic surface  

NASA Technical Reports Server (NTRS)

The development of a triple-band dichroic surface design is detailed that is reflective in the Ka-band from 22.5 to 27.3 GHz and the Ku-band from 13.7 to 15.1 GHz, yet transparent in the S-band from 2.0 to 2.3 GHz, for all planes of incidence, and for all angles of incidence out to eta = 45 deg. The design is comprised of two gangbuster whole-surfaces separated by a distance, d, that is comparable to a fraction of a wavelength in S-band, and enhanced by the addition of a dielectric matching plate. The gangbuster array is comprised of tightly packed straight skewed dipole elements referred to as half-surfaces. Two of these half-surfaces are oriented orthogonal to each other and placed an array separation distance, s, apart to form the gangbuster whole-surface which allows any arbitrary plane of incidence. Results are given for the triple-band design with and without dielectric and conduction losses. The cross polarization properties of the dichroic surface was further investigated. It is shown that the reflection cross polarized component is dominated by the geometry of the front whole surface of the design (particularly the array separation s) and is never more than -22.5 dB in the frequency band 0 to 30 GHz. The transmission cross polarization component is dependent on both whole-surfaces and is never more than -30 dB in the same frequency band.

Schneider, S. W.; Munk, B. A.

1990-01-01

129

Band gaps in the spectra of terahertz surface plasmons on metallic diffraction gratings  

Microsoft Academic Search

The effect of the appearance of band gaps in the energy spectra of terahertz surface plasmons has been experimentally observed\\u000a and investigated. The band gaps are formed due to the interference interaction of the surface plasmons excited by pulsed terahertz\\u000a radiation on metallic diffraction gratings. It has been shown that the experimental dispersion curves of terahertz plasmons\\u000a are in good

A. V. Andreev; M. M. Nazarov; I. R. Prudnikov; A. P. Shkurinov

2009-01-01

130

Constraining CloudSat-based snowfall profiles using surface observations and C-band ground radar  

NASA Astrophysics Data System (ADS)

The CloudSat Precipitation Radar, launched in 2006, provides vertical profiles of W-band (94 GHz) reflectivity and is sensitive to falling snow through all but the most intense precipitating cloud structures. Precipitation retrievals of falling snow are affected by a wide diversity of factors describing the medium, such as snow particle shape, size, and composition, which in turn are controlled by ambient factors including the environmental temperature and humidity. Because satellite-based radiometric sounders such as the Microwave Humidity Sounder (MHS) operate without the benefit of coordinated space radar observations, microphysical descriptions of the snow particle medium derived from CloudSat or other radar observations are beneficial to passive microwave (PMW) radiometer-only snowfall retrieval methods. At the coarse scale of these PMW observations, the radiative signal due to the snow is relatively weak compared to the contributions from the atmosphere and the land surface emissivity. Using the C-band (5 GHz) polarization-agile King City radar (WKR) operated by Environment Canada, we examined the vertical structure of winter precipitation events from coordinated overpasses of CloudSat and NOAA 18 (MHS). Two-dimensional video disdrometer observations are used to limit (constrain) the range of the drop-size distribution parameters that are provided through a priori databases to dual-frequency (C/W-band) radar retrieval. Bayesian retrievals using the constrained database produce water content profiles that more closely replicate the observed radar reflectivity profiles and transition smoothly between the single-frequency (CloudSat only) and dual-frequency regions.

Turk, F. Joseph; Park, Kyung-Won; Haddad, Ziad S.; Rodriguez, Peter; Hudak, David R.

2011-12-01

131

Medium- and high-spin band structure of the chiral-candidate nucleus 134Pr  

NASA Astrophysics Data System (ADS)

Medium- and high-spin states of 134Pr were populated using the 116Cd(23Na,5n) reaction and studied with the GAMMASPHERE spectrometer. Several new bands have been found in this nucleus, one of them being linked to the previously observed chiral-candidate twin-band structure. The ground state of 134Pr could be determined through establishing a level structure that connects the two previously known long-lived isomeric states. Unambiguous spin-parity assignments for the excited states could be performed based on the known 2- spin-parity of the ground state combined with the present experimental data. Intrinsic single-particle configurations have been assigned to the newly observed bands on the basis of the measured B(M1)/B(E2) ratios, alignments, band-crossing frequencies, bandhead spins, the observed single-particle configurations in the neighboring nuclei, and taking into account the predictions of total Routhian surface and tilted-axis cranking calculations.

Timár, J.; Starosta, K.; Kuti, I.; Sohler, D.; Fossan, D. B.; Koike, T.; Paul, E. S.; Boston, A. J.; Chantler, H. J.; Descovich, M.; Clark, R. M.; Cromaz, M.; Fallon, P.; Lee, I. Y.; Macchiavelli, A. O.; Chiara, C. J.; Wadsworth, R.; Hecht, A. A.; Almehed, D.; Frauendorf, S.

2011-10-01

132

Survival of hydrogen anions near atomically flat metal surfaces: Band gap confinement and image state recapture effects  

NASA Astrophysics Data System (ADS)

Resonant charge transfer (RCT) between ions and surfaces is a key intermediate step in surface-chemical processes as well as in micro- and nano-fabrications on the surface. The RCT process in the collision of hydrogen anions with metal surfaces is described within a wave packet propagation methodology using Crank-Nicholson algorithm [1]. The ion-survival probability is found to strongly enhance at two different ion velocities perpendicular to the surface. The low velocity enhancement is induced from a dynamical confinement of the ion level inside the band gap, while the high velocity enhancement emerges owing to the recapture from transiently populated image states [2]. These structures are found to be somewhat sensitive to the ion's distance of closest approach to the surface and the choice of inter-atomic potentials between the ion and the surface atoms. [1] Chakraborty et al., Phys. Rev. A 70, 052903 (2004); [2] Schmitz et al., Phys. Rev. A (submitted).

Schmitz, Andrew; Shaw, John; Chakraborty, Himadri; Thumm, Uwe

2010-03-01

133

Analysis of frequency band structure in one-dimensional sonic crystal using Webster horn equation  

Microsoft Academic Search

Sound propagation through periodic arrangement of scatterers lead to formation of bands of frequencies, known as band gaps, where sound cannot propagate though the structure. We propose a method based on Webster horn equation, along with Floquet theorem, to predict the band gap of a one-dimensional periodic structure made of hard sound-scatterers. The method is further modified to obtain the

A. Gupta; K. M. Lim; C. H. Chew

2011-01-01

134

Role of interface band structure on hot electron transport  

NASA Astrophysics Data System (ADS)

Knowledge of electron transport through materials and interfaces is fundamentally and technologically important. For example, metal interconnects within integrated circuits suffer increasingly from electromigration and signal delay due to an increase in resistance from grain boundary and sidewall scattering since their dimensions are becoming shorter than the electron mean free path. Additionally, all semiconductor based devices require the transport of electrons through materials and interfaces where scattering and parallel momentum conservation are important. In this thesis, the inelastic and elastic scattering of hot electrons are studied in nanometer thick copper, silver and gold films deposited on silicon substrates. Hot electrons are electron with energy greater than kBT above the Fermi level (EF). This work was performed utilizing ballistic electron emission microscopy (BEEM) which is a three terminal scanning tunneling microscopy (STM) technique that measures the percentage of hot electrons transmitted across a Schottky barrier interface. Hot electron attenuation lengths of the metals were extracted by measuring the BEEM current as a function of metal overlayer thickness for both hot electron and hot hole injection at 80 K and under ultra high vacuum. The inelastic and elastic scattering lengths were extracted by fitting the energetic dependence of the measured attenuation lengths to a Fermi liquid based model. A sharp increase in the attenuation length is observed at low injection energies, just above the Schottky barrier height, only for metals on Si(001) substrates. In contrast, the attenuation length measured on Si(111) substrates shows a sharp decrease. These results indicate that interface band structure and parallel momentum conservation have significant impact upon the transport of hot electrons across non epitaxial metal-semiconductor interfaces. In addition, they help to separate effects upon hot electron transport that are inherent to the metal film from those associated with the interface and its band structure.

Garramone, John J.

135

Deriving surface albedo measurements from narrow band satellite data  

NASA Technical Reports Server (NTRS)

A target calibration procedure for obtaining surface albedo from satellite data is presented. The methodology addresses two key issues, the calibration of remotely-sensed, discrete wavelength, digital data and the derivation of an albedo measurement (defined over the solar short wave spectrum) from spectrally limited observations. Twenty-seven Landsat observations, calibrated with urban targets (building roof-tops and parking lots), are used to derive spatial and seasonal patterns of surface reflectance and albedo for four land cover types: city, suburb, farm and forest.

Brest, Christopher L.; Goward, Samuel N.

1987-01-01

136

FAST TRACK COMMUNICATION: Field modulation in bilayer graphene band structure  

Microsoft Academic Search

Using an external electric field, one can modulate the band gap of Bernal stacked bilayer graphene by breaking the A-\\\\tilde {\\\\mathrm {B}} symmetry. We analyze strain effects on the bilayer graphene using the extended Hückel theory and find that reduced interlayer distance results in higher band gap modulation, as expected. Furthermore, above about 2.5 Å interlayer distance, the band gap

Hassan Raza; Edwin C. Kan

2009-01-01

137

Electronic structures and transport properties of silicene on Ag surface  

NASA Astrophysics Data System (ADS)

It has been predicted from first-principle that ``silicene'', a two-dimensional buckled honeycomb structure of silicon, is thermally stable and has a graphene-like band structure. In experiments, epitaxial silicene were observed to form at hexagonal Ag(111) and ZrB2(0001) surfaces. However, electronic structure and transport properties related to silicene have not been thoroughly studied. In this work, we have studied band structures of silicene on top of Ag surface using density-functional theory. The effective band structure mapped onto 1x1 unit cell of monolayer silicene on Ag(111) surface could be compared directly with Angle-Resolved Photoemission Spectra (ARPES). We have also studied electronic transport property across monolayer and bilayer silicene sheets using the Non-Equilibrium Green's Function (NEGF) method. The transmission curve shows a maximum at Fermi energy for the monolayer silicene case, but shows a minimum for the bilayer silicene case, which can be explained by their band structures.

Wang, Yun-Peng; Cheng, Hai-Ping

2013-03-01

138

Nanoscale probing of electronic band gap and topography of VO2 thin film surfaces by scanning tunneling microscopy  

NASA Astrophysics Data System (ADS)

The metal-insulator transition (MIT) in vanadium dioxide in the vicinity of room temperature makes it one of the most interesting materials for novel switching device applications. It is therefore essential to have a fundamental understanding of the VO2 surface when it is incorporated into multilayer structures or nanodevices. This study focuses on the surface modification of VO2 in response to the thermal treatment during phase transition. Vacuum annealing at temperatures in the vicinity of the MIT triggers a partial reduction in the surface, and thus initiates a chemical phase transition. Scanning tunneling microscopy and spectroscopy are used to investigate the electronic properties and surface structure of the VO2 thin film on (0001) sapphire substrates. Band gap maps with a high spatial resolution and single point spectroscopy I-V curves are measured as the sample is cycled through the MIT, and thus provide a direct observation of the surface phase transition at the nanoscale. The VO2 surface exhibits a homogeneous insulating behavior with a typical band gap of ˜0.5 eV at room temperature, and the surface becomes more metallic and spatially inhomogeneous in conductivity during MIT, and wide range of surface oxides can be identified. The surface still remains partially metallic after cooling down from a long period anneal, and such irreversible surface electrical change is attributed to the loss of oxygen. The location of metallic islands after thermal cycling is strongly coupled to the topography of the film, and relaxation processes and continued modification of the spatial distribution of the metallic regions are recognized on a longer timescale. The impact of film morphology, strain, surface chemistry, and structural phase transition on the electronic characteristics of VO2 surfaces are discussed.

Yin, W.; Wolf, S.; Ko, C.; Ramanathan, S.; Reinke, P.

2011-01-01

139

Band-structure analysis from photoreflectance spectroscopy in (Ga,Mn)As  

SciTech Connect

Modulation photoreflectance spectroscopy has been applied to study the band-structure evolution in (Ga,Mn)As epitaxial layers with increasing Mn content. Structural and magnetic properties of the layers were characterized with high-resolution X-ray diffractometry and SQUID magnetometery, respectively. The revealed results of decrease in the band-gap-transition energy in the (Ga,Mn)As layers with increasing Mn content are interpreted in terms of a disordered valence band, extended within the band gap, formed, in highly Mn-doped (Ga,Mn)As, as a result of merging the Mn-related impurity band with the host GaAs valence band.

Yastrubchak, Oksana; Gluba, Lukasz; Zuk, Jerzy [Institute of Physics, Maria Curie-Sklodowska University, 20-031 Lublin (Poland); Wosinski, Tadeusz; Andrearczyk, Tomasz; Domagala, Jaroslaw Z. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Sadowski, Janusz [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland and MAX-Lab, Lund University, 22100 Lund (Sweden)

2013-12-04

140

SIMULTANEOUS MULTI-BAND DETECTION OF LOW SURFACE BRIGHTNESS GALAXIES WITH MARKOVIAN MODELING  

SciTech Connect

We present to the astronomical community an algorithm for the detection of low surface brightness (LSB) galaxies in images, called MARSIAA (MARkovian Software for Image Analysis in Astronomy), which is based on multi-scale Markovian modeling. MARSIAA can be applied simultaneously to different bands. It segments an image into a user-defined number of classes, according to their surface brightness and surroundings-typically, one or two classes contain the LSB structures. We have developed an algorithm, called DetectLSB, which allows the efficient identification of LSB galaxies from among the candidate sources selected by MARSIAA. The application of the method to two and three bands simultaneously was tested on simulated images. Based on our tests, we are confident that we can detect LSB galaxies down to a central surface brightness level of only 1.5 times the standard deviation from the mean pixel value in the image background. To assess the robustness of our method, the method was applied to a set of 18 B- and I-band images (covering 1.3 deg{sup 2} in total) of the Virgo Cluster to which Sabatini et al. previously applied a matched-filter dwarf LSB galaxy search algorithm. We have detected all 20 objects from the Sabatini et al. catalog which we could classify by eye as bona fide LSB galaxies. Our method has also detected four additional Virgo Cluster LSB galaxy candidates undetected by Sabatini et al. To further assess the completeness of the results of our method, both MARSIAA, SExtractor, and DetectLSB were applied to search for (1) mock Virgo LSB galaxies inserted into a set of deep Next Generation Virgo Survey (NGVS) gri-band subimages and (2) Virgo LSB galaxies identified by eye in a full set of NGVS square degree gri images. MARSIAA/DetectLSB recovered {approx}20% more mock LSB galaxies and {approx}40% more LSB galaxies identified by eye than SExtractor/DetectLSB. With a 90% fraction of false positives from an entirely unsupervised pipeline, a completeness of 90% is reached for sources with r{sub e} > 3'' at a mean surface brightness level of {mu}{sub g} = 27.7 mag arcsec{sup -2} and a central surface brightness of {mu}{sup 0}{sub g} = 26.7 mag arcsec{sup -2}. About 10% of the false positives are artifacts, the rest being background galaxies. We have found our proposed Markovian LSB galaxy detection method to be complementary to the application of matched filters and an optimized use of SExtractor, and to have the following advantages: it is scale free, can be applied simultaneously to several bands, and is well adapted for crowded regions on the sky.

Vollmer, B.; Bonnarel, F.; Louys, M. [CDS, Observatoire Astronomique, UMR 7550, 11 rue de l'universite, F-67000 Strasbourg (France); Perret, B.; Petremand, M.; Lavigne, F.; Collet, Ch. [LSIIT, Universite de Strasbourg, 7, Rue Rene Descartes, F-67084 Strasbourg (France); Van Driel, W. [GEPI, Observatoire de Paris, CNRS, Universite Paris Diderot, 5 place Jules Janssen, F-92190 Meudon (France); Sabatini, S. [INAF/IASF-Roma, via Fosso de Cavaliere 100, I-00133 Roma (Italy); MacArthur, L. A., E-mail: Bernd.Vollmer@astro.unistra.fr [Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, BC V9E 2E7 (Canada)

2013-02-01

141

Three-dimensional dynamic thermal imaging of structural flaws by dual-band infrared computed tomography  

SciTech Connect

We discuss three-dimensional (3D) dynamic thermal imaging of structure flaws using dual-band infrared (DBIR) computed tomography. Conventional thermography provides single-band infrared images which are difficult to interpret. Standard procedures yield imprecise (or qualitative) information about subsurface flaw sites which are typically masked by surface clutter. We use a DBIR imaging unique pioneered at LLNL to capture the time history of surface temperature difference for flash-heated targets. We relate these patterns to the location, size, shape and depth of subsurface flaws. We have demonstrated temperature accuracies of 0.2{degree}C, timing synchronizations of 3 ms (after onset of heat flash) and intervals of 42 ms, between images, during an 8 s cooling (and hearing) interval characterizing the front (and back) surface temperature-time history of an epoxy-glue disbond site in a flash-heated aluminum lap joint. This type of disbond played a significant role in causing damage to the Aloha Aircraft fuselage on the aged Boeing 737 jetliner. By ratioing DBIR images (near 5 and 10 micron), we located surface temperature patterns (generated by weak heat flow anomalies at subsurface flaw sites) and removed the emissivity mask (from surface roughness variations). We compared measurements with calculations from the three-dimensional, finite element computer code: TOPAZ3D. We combined infrared, ultrasound and x-ray imaging methods to characterize the lap joint disbond site spatial, bond quality, and material differences.

Del Grande, N.K.; Dolan, K.W.; Durbin, P.F.; Gorvad, M.R.; Kornblum, B.T.; Perkins, D.E.; Schneberk, D.J.; Shapiro, A.B.

1993-04-01

142

ANTIGENIC STRUCTURE OF CELL SURFACES  

PubMed Central

The representation of mouse alloantigens belonging to three systems, H-2, ? and TL, on the surface of cells from thymus, spleen, lymph nodes, and peritoneal cavity, was studied by electron microscopy with ferritin-labeled antibody. As expected from earlier serological data, TL was confined to thymocytes, ? was found on thymocytes and lymphocytes, and H-2 occurred to some extent on all cell types observed. On reticular cells, lymphocytes, plasma cells, and eosinophils, the majority of the cell surface was occupied by H-2; thymocytes had considerably less H-2, and erythrocytes and peritoneal macrophages least of all. In every instance the representation of antigen was discontinuous, the fraction of the cell surface covered being characteristic both of the antigen and of the type of cell. H-2 and ? provide a striking example of this; H-2 is present in far higher amounts on lymphocytes than on thymocytes, whereas the converse is true of ?. Within areas positive for H-2 or ?, protuberances of the surface membrane were often antigen-negative. A better definition of cell surface structure, gained from studies such as this, is necessary for further inquiry into how the cell surface is assembled, and into selective gene action in relation to cellular differentiation. PMID:5347699

Aoki, Tadao; Hammerling, Ulrich; de Harven, Etienne; Boyse, Edward A.; Old, Lloyd J.

1969-01-01

143

Elastic surface waves and the structure of liquid surfaces  

Microsoft Academic Search

The high-frequency elastic behavior of fluid surfaces is studied from first principles. The general dispersion equation for elastic surface waves thus obtained reveals the influence of the surface structure on Rayleigh's surface waves. New types of surface waves are also found. Their existence depends crucially on the presence of nonvanishing surface excess elastic moduli and hence these waves are inaccessible

C. F. Tejero; M. J. Rodriguez; M. Baus

1984-01-01

144

Surface impedance of HTSC single crystals in the microwave band  

Microsoft Academic Search

Currently available data on the real, Rs, and imaginary, Xs, parts of the microwave frequency surface impedance Zs = Rs + i Xs are presented for the high-quality singlecrystal high-temperature superconductors YBa2Cu3O6.95, Ba0.6K0.4BiO3, Tl2Ba2CaCu2O8-?, Tl2Ba2CuO6 + ?, and Bi2Sr2CaCu2O8. A high-precision technique for measuring the temperature dependences Rs(T) and Xs(T) in the range 4.2 ? T ? 150 K is

Mikhail R Trunin

1998-01-01

145

Determination of the surface band bending in InxGa1-xN films by hard x-ray photoemission spectroscopy  

NASA Astrophysics Data System (ADS)

Core-level and valence band spectra of InxGa1-xN films were measured using hard x-ray photoemission spectroscopy (HX-PES). Fine structure, caused by the coupling of the localized Ga 3d and In 4d with N 2s states, was experimentally observed in the films. Because of the large detection depth of HX-PES (˜20 nm), the spectra contain both surface and bulk information due to the surface band bending. The InxGa1-xN films (x = 0-0.21) exhibited upward surface band bending, and the valence band maximum was shifted to lower binding energy when the mole fraction of InN was increased. On the other hand, downward surface band bending was confirmed for an InN film with low carrier density despite its n-type conduction. Although the Fermi level (EF) near the surface of the InN film was detected inside the conduction band as reported previously, it can be concluded that EF in the bulk of the film must be located in the band gap below the conduction band minimum.

Lozac'h, Mickael; Ueda, Shigenori; Liu, Shitao; Yoshikawa, Hideki; Liwen, Sang; Wang, Xinqiang; Shen, Bo; Sakoda, Kazuaki; Kobayashi, Keisuke; Sumiya, Masatomo

2013-02-01

146

High Gradient Test of a Clamped, Molybdenum Iris, X-Band Accelerator Structure at NLCTA  

SciTech Connect

Inspired by the very high gradients (150-195 MV/m) achieved at CERN in 30 GHz accelerator structures made with tungsten and molybdenum irises and operated with short (16 ns) rf pulses [1], an X-band (11.4 GHz) version of this structure design was built at CERN and tested at SLAC. The goals of this experiment were to provide frequency scaling data on high gradient phenomena at similar pulse lengths, and to measure the structure performance at the longer pulse lengths available at SLAC (the CLIC test facility, CTF II, could provide only 16 ns pulses for high power operation and 32 ns pulses for medium power operation). Earlier high gradient tests of 21 GHz to 39 GHz standing-wave, single cells, indicated no significant frequency dependence of the maximum obtainable surface field [2]. The X-band scaling test would check if this was true for travelling-wave, multi-cell structures as well. For the experiment, the CLIC group at CERN built a 30 cell accelerating structure that consisted of copper cells and molybdenum irises that were clamped together. The structure was mounted in a vacuum tank and installed in the Next Linear Collider Test Accelerator (NLCTA) beam line at SLAC where it was operated at high power for more than 700 hours.

Doebert, S.

2004-11-08

147

Modifications in the Band Structure of a 2-Dimensional Kerr-Nonlinear Photonic Crystals  

NASA Astrophysics Data System (ADS)

Modifications in the band structure of a 2-dimensional photonic crystal composed of a square array of circular air holes drilled in a Kerr-type nonlinear dielectric material are investigated. Special attention is paid on the position and width of the overlap region of TE and TM band gaps. Angular frequencies of the modes in the whole band structure are found to redshift (blueshift) for a positive (negative) Kerr susceptibility. Although the observed shift in the midgap frequencies of the band gaps increases for higher angular frequencies, the lower edges of TE and TM band gaps appear to be more sensitive to nonlinearity than the upper edges. Broadening (contraction) of the band gaps is related to the relative shift of the band edges. Parameters for polarizing-device applications are discussed on the basis of band structure engineering.

Cicek, Ahmet; Ulug, Bulent

2007-04-01

148

Space-based detection of wetlands' surface water level changes from L-band SAR interferometry  

E-print Network

Space-based detection of wetlands' surface water level changes from L-band SAR interferometry�1996 reveals detectable surface changes in the Everglades wetlands. Although our study is limited to south Florida it has implication for other large-scale wetlands, because south Florida wetlands have diverse

Amelung, Falk

149

The band structure of carbonmonoxide on 2-D Au islands on graphene  

NASA Astrophysics Data System (ADS)

The dispersion of the occupied molecular orbitals of carbon monoxide adsorbed on Au 2D islands, vapor-deposited on graphene/Ru(0 0 0 1), is seen to be wave vector dependent, as revealed by angle-resolved photoemission. The band dispersion is similar to CO monolayers adsorbed on many single crystal metal surfaces. Thus not only are the adsorbed gold islands on graphene flat and crystalline, as evident in the dispersion of the Au d-states, but the CO molecular adlayer is both molecular and ordered as well. The experimental angle-resolved photoemission combined with model calculations of the occupied CO band structure, suggest that, in spite of being a very weakly bound adsorbate, the CO adlayer on Au 2D islands on graphene is strongly hybridized to the Au layer.

Katsiev, K.; Losovyj, Y.; Lozova, N.; Wang, Lu; Mei, Wai-Ning; Zheng, Jiaxin; Vescovo, E.; Liu, Li; Dowben, P. A.; Goodman, D. W.

2014-06-01

150

Mimicking Surface Plasmons with Structured Surfaces  

E-print Network

is an exception, but even such a material can be induced to support surface modes by drilling an array of holes a surface that is a perfect conductor pierced by an array of holes. For simplicity, we shall assume a square cross section a a for the holes and a square array of side d (Fig. 1). We sup- pose that the holes

Pendry, John

151

Global Kinetic Modeling of Banded Electron Structures in the Plasmasphere  

NASA Technical Reports Server (NTRS)

Significant fluxes of 10 eV to 30 keV electrons have been detected in the plasmasphere, appearing as banded structures in energy with broad spatial extents and slowly evolving over several days. It is thought that these populations are decaying plasma sheet electrons injected into the corotating region of near-Earth space. This capture can occur when the convective electric field drops rapidly and the Alfven boundary suddenly outward, trapping the inner edge of the plasma sheet along closed drift paths. Our bounce-averaged kinetic model of superthermal electron transport is able to simulate this capture and the subsequent drift, diffusion, and decay of the plasma cloud. Results of this simulation will be shown and discussed, from the initial injection during the elevated convection to the final loss of the particles. It is thought that not only Coulomb collisions but also wave-particle interactions play a significant role in altering the plasma cloud. Quasilinear diffusion is currently being incorporated into the model and the importance of this mechanism will be examined. Also, the high anisotropy of the trapped population could be unstable and generate plasma waves. These and other processes will be investigated to determine the final fate of the cloud and to quantify where, how, and when the energy of the plasma cloud is deposited. Comparisons with CRRES observations of these events are shown to verify the model and explain the data.

Liemohn, M. W.; Khazanov, G. V.

1997-01-01

152

Complex band structure of topologically protected edge states  

NASA Astrophysics Data System (ADS)

One of the great successes of modern condensed matter physics is the discovery of topological insulators (TIs). A thorough investigation of their properties could bring such materials from fundamental research to potential applications. Here, we report on theoretical investigations of the complex band structure (CBS) of two-dimensional (2D) TIs. We utilize the tight-binding form of the Bernevig, Hughes, and Zhang model as a prototype for a generic 2D TI. Based on this model, we outline the conditions that the CBS must satisfy in order to guarantee the presence of topologically protected edge states. Furthermore, we use the Green's function technique to show how these edge states are localized, highlighting the fact that the decay of the edge-state wave functions into the bulk of a TI is not necessarily monotonic and, in fact, can exhibit an oscillatory behavior that is consistent with the predicted CBS of the bulk TI. These results may have implications for electronic and spin transport across a TI when it is used as a tunnel barrier.

Dang, Xiaoqian; Burton, J. D.; Kalitsov, Alan; Velev, Julian P.; Tsymbal, Evgeny Y.

2014-10-01

153

Graphene band structure and its 2D Raman mode  

NASA Astrophysics Data System (ADS)

High-precision simulations are used to generate the 2D Raman mode of graphene under a range of screening conditions and laser energies EL. We reproduce the decreasing trend of the 2D mode FWHM vs EL and the nearly linearly increasing dispersion ??2D/?EL seen experimentally in freestanding (unscreened) graphene, and propose relations between these experimentally accessible quantities and the local, two-dimensional gradients |? | of the electronic and TO phonon bands. In light of state-of-the-art electronic structure calculations that acutely treat the long-range e-e interactions of isolated graphene and its experimentally observed 2D Raman mode, our calculations determine a 40% greater slope of the TO phonons about K than given by explicit phonon measurements performed in graphite or GW phonon calculations in graphene. We also deduce the variation of the broadening energy ? [EL] for freestanding graphene and find a nominal value ? ˜140 meV, showing a gradually increasing trend for the range of frequencies available experimentally.

Narula, Rohit; Reich, Stephanie

2014-08-01

154

Direct band gap structures on nanometer-scale, micromachined silicon tips J. R. Shealy,a)  

E-print Network

Direct band gap structures on nanometer-scale, micromachined silicon tips J. R. Shealy,a) N. C optical quality, direct band gap materials on the silicon nanostructures. We demonstrate using the organometallic vapor phase epitaxy of GaInP that the direct band gap semiconductor nucleates selectively

MacDonald, Noel C.

155

Viscoelastic surface waves and the surface structure of liquids  

Microsoft Academic Search

The dispersion relations for surface waves on a planar liquid surface are obtained from first principles. The high-frequency elastic, low-frequency hydrodynamic and intermediate viscoelastic regimes are investigated separately. It is shown that the structure of the liquid surface modifies the expression for Rayleigh's elastic surface waves and Kelvin's capillary waves and allows for the existence of new surface waves besides

C. F. Tejero; M. Baus

1985-01-01

156

Towards efficient band structure and effective mass calculations for III-V direct band-gap semiconductors  

Microsoft Academic Search

The band structures and effective masses of III-V semiconductors (InP, InAs, InSb, GaAs, and GaSb) are calculated using the GW method, the Heyd, Scuseria, and Ernzerhof hybrid functional, and modified Becke-Johnson combined with the local-density approximation (MBJLDA)---a local potential optimized for the description of the fundamental band gaps [F. Tran and P. Blaha, Phys. Rev. Lett. 102, 226401 (2009)10.1103\\/PhysRevLett.102.226401]. We

Yoon-Suk Kim; Martijn Marsman; Georg Kresse; Fabien Tran; Peter Blaha

2010-01-01

157

Effect of anisotropy on the photonic band gap and surface polaritons of a one-dimensional single-negative photonic crystal  

NASA Astrophysics Data System (ADS)

The effect of anisotropy on the photonic band structure and surface polaritons of a one-dimensional photonic crystal made of uniaxially anisotropic epsilon-negative (?<0,?>0) and mu-negative (?>0,?<0) metamaterials is theoretically investigated. Two different cases of uniaxially anisotropic epsilon-negative and mu-negative metamaterials are considered. It is found out that for one case of anisotropy, one-dimensional photonic crystal does not have any single-negative band gap. As a result, it can not support the surface polaritons. While, for another case, the structure shows single-negative band gaps. So, the surface polaritons can be excited at the interface of such a photonic crystal. However, these surface polaritons, unlike the isotropic case, are not omnidirectional and they are restricted to a limited rang of the propagation constant.

Roshan Entezar, S.; Madani, A.; Namdar, A.; Tajalli, H.

2012-05-01

158

Magnetoreflection study of the band structure of antimony  

Microsoft Academic Search

Direct energy band gaps of (0.101+or-0.002) eV and (0.149+or-0.003) eV have been observed in a new magnetoreflection study of binary faces of pure antimony in good agreement with the measurements of Dresselhaus and Mavroides (1966). The reduced cyclotron effective masses associated with the smaller band gap differ significantly from those previously reported. Line shape peculiarities, triplet splitting and a reciprocal

D. A. Huntley; M. J. Apps

1972-01-01

159

Infrared detectors and lasers operating in the 3-12 mum range using band-gap engineered structures with type II band-gap alignment  

Microsoft Academic Search

The Type II broken band-gap alignment in semiconductor structures wherein the conduction band minimum is in one semiconductor (e.g., InAs) and the valence band maximum is in another (e.g., GaInSb) offers certain unique advantages which can be utilized to realize band-gap engineered novel quantum electro-optic devices such as lasers and detectors. The advantages of the type II structures include reduced

Venkataraman Swaminathan; John W. Little; Richard L. Tober

2006-01-01

160

Infrared detectors and lasers operating in the 3-12 um range using band-gap engineered structures with Type II band-gap alignment  

Microsoft Academic Search

The Type II broken band-gap alignment in semiconductor structures wherein the conduction band minimum is in one semiconductor (e.g., InAs) and the valence band maximum is in another (e.g., GaInSb) offers certain unique advantages which can be utilized to realize band-gap engineered novel quantum electro-optic devices such as lasers and detectors. The advantages of the type II structures include reduced

Venkataraman Swaminathan; John W. Little; Richard L. Tober

161

Systematic design of phononic band-gap materials and structures by topology optimization.  

PubMed

Phononic band-gap materials prevent elastic waves in certain frequency ranges from propagating, and they may therefore be used to generate frequency filters, as beam splitters, as sound or vibration protection devices, or as waveguides. In this work we show how topology optimization can be used to design and optimize periodic materials and structures exhibiting phononic band gaps. Firstly, we optimize infinitely periodic band-gap materials by maximizing the relative size of the band gaps. Then, finite structures subjected to periodic loading are optimized in order to either minimize the structural response along boundaries (wave damping) or maximize the response at certain boundary locations (waveguiding). PMID:12804226

Sigmund, Ole; Jensen, Jakob Søndergaard

2003-05-15

162

Carrier Multiplication in Semiconductor Nanocrystals: Theoretical Screening of Candidate Materials Based on Band-Structure Effects  

SciTech Connect

Direct carrier multiplication (DCM) occurs when a highly excited electron-hole pair decays by transferring its excess energy to the electrons rather than to the lattice, possibly exciting additional electron-hole pairs. Atomistic electronic structure calculations have shown that DCM can be induced by electron-hole Coulomb interactions, in an impact-ionization-like process whose rate is proportional to the density of biexciton states {rho}{sub XX}. Here we introduce a DCM 'figure of merit' R{sub 2}(E) which is proportional to the ratio between the biexciton density of states {rho}{sub XX} and the single-exciton density of states {rho}{sub x}, restricted to single-exciton and biexciton states that are coupled by Coulomb interactions. Using R{sub 2}(E), we consider GaAs, InAs, InP, GaSb, InSb, CdSe, Ge, Si, and PbSe nanocrystals of different sizes. Although DCM can be affected by both quantum-confinement effects (reflecting the underly electronic structure of the confined dot-interior states) and surface effects, here we are interested to isolate the former. To this end the nanocrystal energy levels are obtained from the corresponding bulk band structure via the truncated crystal approximation. We find that PbSe, Si, GaAs, CdSe, and InP nanocrystals have larger DCM figure of merit than the other nanocrystals. Our calculations suggest that high DCM efficiency requires high degeneracy of the corresponding bulk band-edge states. Interestingly, by considering band structure effects we find that as the dot size increases the DCM critical energy E{sub 0} (the energy at which R{sub 2}(E) becomes {ge}1) is reduced, suggesting improved DCM. However, whether the normalized E{sub 0}/{var_epsilon}{sub g} increases or decreases as the dot size increases depends on dot material.

Luo, J. W.; Franceschetti, A.; Zunger, A.

2008-01-01

163

Band structure of the diluted magnetic semiconductor Mn x Cd 1? x GeAs 2  

Microsoft Academic Search

The electron-density-functional approach is used to calculate the band structure of the CdGeAs2 semiconductor and the diluted magnetic semiconductor MnxCd1?x\\u000a GeAs2, which has a ferromagnetic structure at x = 0.06. The results indicate that the incorporation of Mn increases the band gap at its center and leads to the formation\\u000a of a band derived from Mn levels, whose energy is

V. G. Yarzhemsky; S. V. Murashov; V. I. Nefedov; E. N. Murav’ev; A. V. Molchanov; A. A. Bagatur’yants; A. A. Knizhnik; V. A. Morozova

2006-01-01

164

Theoretical study on the band structure of Bi1?-x?Sbx? thin films  

E-print Network

The study on the electronic band structures of Bi1-xSbx thin films is a very interesting topic. Recall that in bulk Bi1-xSbx, the electronic band structure can be varied as a function of temperature T, pressure P and ...

Tang, Shuang, S.M. Massachusetts Institute of Technology

2012-01-01

165

Electronic band structure of black phosphorus studied by angle-resolved ultraviolet photoelectron spectroscopy  

Microsoft Academic Search

The electronic band structure of black phosphorus has been studied by angle-resolved ultraviolet photoelectron (ARUPS). The experimental valence band structure has been successfully obtained by the use of the He I and Ne I resonance lines. The binding energies of some special points with almost no interlayer energy dispersion have been experimentally determined and compared with the result of the

T. Takahashi; H. Tokailin; S. Suzuki; T. Sagawa; I. Shirotani

1985-01-01

166

B3LYP, BLYP and PBE DFT band structures of the nucleotide base stacks  

Microsoft Academic Search

DFT crystal orbital (band structure) calculations have been performed for the nucleotide base stacks of cytosine, thymine, adenine, and guanine arranged in DNA B geometry. The band structures obtained with PBE, BLYP, and B3LYP functionals are presented and compared to other related experimental and theoretical results. The influence of the quality of the basis set on the fundamental gap values

Zs Szekeres; F. Bogár; J. Ladik

2005-01-01

167

Acoustic band-gap engineering using finite-size layered structures of multiple periodicity  

E-print Network

Acoustic band-gap engineering using finite-size layered structures of multiple periodicity Mingrong and also measured as a function of frequency. It was found that acoustic band gaps can be created using structure, very sharp passbands and very broad stopbands can be engineered for acoustic waves. Such acoustic

Cao, Wenwu

168

Thin frequency selective surface (FSS) superstrate with different periodicities for dual-band directivity enhancement  

Microsoft Academic Search

In this paper we present a novel design of a high directivity resonator antenna that utilizes a two-layered frequency selective surface (FSS) superstrate with different periodicities - as an alternative to a conventional FSS superstrate - for dual band directivity enhancement to reduce its height. Two strip dipole arrays with different periodicities are placed above and below a dielectric layer.

Young Ju Lee; Junho Yeo; R. Mittra; Wee Sang Park

2005-01-01

169

Optical band gap of nitrogenated amorphous carbon thin films synthesized by microwave surface wave plasma CVD  

Microsoft Academic Search

Nitrogenated amorphous carbon (a-C:N) thin films were prepared on silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition system, aiming to control optical band gap (Eg) of the films for photovoltaic solar cells application. For films deposition, we used argon as carrier gas, nitrogen as dopant and hydrocarbon source gases, such as camphor dissolved with ethyl alcohol

Sudip Adhikari; Hare Ram Aryal; Dilip Chandra Ghimire; Golap Kalita; Masayoshi Umeno

2008-01-01

170

The Band Structure of Polymers: Its Calculation and Interpretation. Part 3. Interpretation.  

ERIC Educational Resources Information Center

In this article, the third part of a series, the results of ab initio polymer calculations presented in part 2 are discussed. The electronic structure of polymers, symmetry properties of band structure, and generalizations are presented. (CW)

Duke, B. J.; O'Leary, Brian

1988-01-01

171

3D spherical layer photonic band-gap structures in dichromate gelatin.  

E-print Network

??Three-dimensional spherical layer photonic band-gap structures were fabricated in dichromate gelatin (DCG) holographic emulsions by a holographic lithography technique. Five spherical layer structures with different… (more)

Hung, Jenny

2008-01-01

172

Detecting forest structure and biomass with C-band multipolarization radar - Physical model and field tests  

NASA Technical Reports Server (NTRS)

The ability of C-band radar (4.75 GHz) to discriminate features of forest structure, including biomass, is tested using a truck-mounted scatterometer for field tests on a 1.5-3.0 m pygmy forest of cypress (Cupressus pygmaea) and pine (Pinus contorta ssp, Bolanderi) near Mendocino, CA. In all, 31 structural variables of the forest are quantified at seven sites. Also measured was the backscatter from a life-sized physical model of the pygmy forest, composed of nine wooden trees with 'leafy branches' of sponge-wrapped dowels. This model enabled independent testing of the effects of stem, branch, and leafy branch biomass, branch angle, and moisture content on radar backscatter. Field results suggested that surface area of leaves played a greater role in leaf scattering properties than leaf biomass per se. Tree leaf area index was strongly correlated with vertically polarized power backscatter (r = 0.94; P less than 0.01). Field results suggested that the scattering role of leaf water is enhanced as leaf surface area per unit leaf mass increases; i.e., as the moist scattering surfaces become more dispersed. Fog condensate caused a measurable rise in forest backscatter, both from surface and internal rises in water content. Tree branch mass per unit area was highly correlated with cross-polarized backscatter in the field (r = 0.93; P less than 0.01), a result also seen in the physical model.

Westman, Walter E.; Paris, Jack F.

1987-01-01

173

Topological equivalence of crystal and quasicrystal band structures  

NASA Astrophysics Data System (ADS)

A number of recent articles have reported the existence of topologically nontrivial states and associated end states in one-dimensional incommensurate lattice models that would usually only be expected in higher dimensions. Using an explicit construction, we here argue that the end states have precisely the same origin as their counterparts in commensurate models and that incommensurability does not in fact provide a meaningful connection to the topological classification of systems in higher dimensions. In particular, we show that it is possible to smoothly interpolate between states with commensurate and incommensurate modulation parameters without closing the band gap and without states crossing the band gap.

Madsen, Kevin A.; Bergholtz, Emil J.; Brouwer, Piet W.

2013-09-01

174

SMOS satellite L-band radiometer: A new capability for ocean surface remote sensing in hurricanes  

NASA Astrophysics Data System (ADS)

The Soil Moisture and Ocean Salinity (SMOS) mission currently provides multiangular L-band (1.4 GHz) brightness temperature images of the Earth. Because upwelling radiation at 1.4 GHz is significantly less affected by rain and atmospheric effects than at higher microwave frequencies, these new SMOS measurements offer unique opportunities to complement existing ocean satellite high wind observations that are often contaminated by heavy rain and clouds. To illustrate this new capability, we present SMOS data over hurricane Igor, a tropical storm that developed to a Saffir-Simpson category 4 hurricane from 11 to 19 September 2010. Thanks to its large spatial swath and frequent revisit time, SMOS observations intercepted the hurricane 9 times during this period. Without correcting for rain effects, L-band wind-induced ocean surface brightness temperatures (TB) were co-located and compared to H*Wind analysis. We find the L-band ocean emissivity dependence with wind speed appears less sensitive to roughness and foam changes than at the higher C-band microwave frequencies. The first Stokes parameter on a ˜50 km spatial scale nevertheless increases quasi-linearly with increasing surface wind speed at a rate of 0.3 K/m s-1 and 0.7 K/m s-1 below and above the hurricane-force wind speed threshold (˜32 m s-1), respectively. Surface wind speeds estimated from SMOS brightness temperature images agree well with the observed and modeled surface wind speed features. In particular, the evolution of the maximum surface wind speed and the radii of 34, 50 and 64 knots surface wind speeds are consistent with GFDL hurricane model solutions and H*Wind analyses. The SMOS sensor is thus closer to a true all-weather satellite ocean wind sensor with the capability to provide quantitative and complementary surface wind information of interest for operational Hurricane intensity forecasts.

Reul, Nicolas; Tenerelli, Joseph; Chapron, Bertrand; Vandemark, Doug; Quilfen, Yves; Kerr, Yann

2012-02-01

175

High spin band structure of 3885Sr47  

NASA Astrophysics Data System (ADS)

High spin states in the Sr85 nucleus were populated in the reaction Ge76(13C,4n) at a beam energy of 45 MeV. The ?-? and ?-?-? coincidence measurements have been utilized to establish the level scheme of Sr85 up to I?=35/2-. Nearly 50 new ? rays and about 25 new levels were identified and most of the previously known levels confirmed. The spin-parity assignment of the levels was made by using the directional correlations of the oriented nuclei ratios and polarization asymmetry measurements. The shell-model calculations have been performed by using two recent interactions, JUN45 and jj44b, for a detailed comparison between theoretical results and the experimental data obtained in the present work. The shell-model results are in good agreements with the experimental data and are able to explain the various features such as the odd-even staggering well. Tilted axis cranking calculations were also performed to understand the magnetic rotation (MR) phenomenon at higher spins. One of the positive-parity ?I =1 bands has been assigned a three-quasiparticle (3qp) configuration, which appears to behave like a MR band. A negative-parity band populated up to I?=35/2- was also assigned a 3qp configuration at low spin and a five-quasiparticle configuration at high spin; however, it does not exhibit the expected MR features, in contrast to a similar band in the Kr83 nucleus.

Kumar, S.; Kumar, Naveen; Mandal, S.; Pancholi, S. C.; Srivastava, P. C.; Jain, A. K.; Palit, R.; Saha, S.; Sethi, J.; Naidu, B. S.; Donthi, R.; Joshi, P. K.; Trivedi, T.; Muralithar, S.; Singh, R. P.; Kumar, R.; Dhal, A.; Bhowmik, R. K.

2014-08-01

176

Novel band structures in silicene on monolayer zinc sulfide substrate  

NASA Astrophysics Data System (ADS)

Opening a sizable band gap in the zero-gap silicene without lowering the carrier mobility is a key issue for its application in nanoelectronics. Based on ?rst-principles calculations, we find that the interaction energies are in the range of -0.09?0.3?eV?per Si atom, indicating a weak interaction between silicene and ZnS monolayer and the ABZn stacking is the most stable pattern. The band gap of silicene can be effectively tuned ranging from 0.025 to 1.05?eV in silicene and ZnS heterobilayer (Si/ZnS HBL). An unexpected indirect-direct band gap crossover is also observed in HBLs, dependent on the stacking pattern, interlayer spacing and external strain effects on silicene. Interestingly, the characteristics of Dirac cone with a nearly linear band dispersion relation of silicene can be preserved in the ABS pattern which is a metastable state, accompanied by a small electron effective mass and thus the carrier mobility is expected not to degrade much. These provide a possible way to design effective FETs out of silicene on a ZnS monolayer.

Li, Sheng-shi; Zhang, Chang-wen; Yan, Shi-shen; Hu, Shu-jun; Ji, Wei-xiao; Wang, Pei-ji; Li, Ping

2014-10-01

177

Doping mode, band structure and photocatalytic mechanism of B-N-codoped TiO 2  

NASA Astrophysics Data System (ADS)

The photocatalyst B and N codoped TiO 2 (B-N-TiO 2) was prepared via the sol-gel method by using boric acid and ammonia as B and N precursors. The doping mode, band structure and photocatalytic mechanism of B-N-TiO 2 were investigated well and elucidated in detail. B-N-TiO 2 showed the narrowed band gap and thus extended the optical absorption due to interstitial N and [NOB] species in the TiO 2 crystal lattice. The coexistence of interstitial N and [NOB] species in the TiO 2 crystal lattice and surface NO x species allowed the more efficient utilization of visible light. Simultaneously, interstitial [NOB] and N species and surface B 2O 3 and NO x species facilitated the separation of photo generated electrons and holes and suppress their recombination effectively. Hence, B-N-TiO 2 showed a higher photocatalytic activity than pure TiO 2, N-doped TiO 2 (N-TiO 2) and B-doped TiO 2 (B-TiO 2) under both UV and visible light irradiation.

Yuan, Jixiang; Wang, Enjun; Chen, Yongmei; Yang, Wensheng; Yao, Jianghong; Cao, Yaan

2011-06-01

178

Dual-band tunable negative refractive index metamaterial with F-Shape structure  

NASA Astrophysics Data System (ADS)

This paper presents a negative refractive index tunable metamaterial based on F-Shape structure which is capable of achieving dual-band negative permeability and permittivity, thus dual-band negative refractive index. An electromagnetic simulation was performed and effective media parameters were retrieved. Numerical investigations show clear existence of two frequency bands in which permeability and permittivity both are negative. The two negative refractive index bandwidths are from 23.8 GHz to 24.1 GHz and from 28.3 GHz to 34.9 GHz, respectively. The geometry of the structure is simple so it can easily be fabricated. The proposed structure can be used in multiband and broad band devices, as the band range in second negative refractive index region is 7 GHz, for potential applications instead of using complex geometric structures and easily tuned by varying the separation between the horizontal wires.

Rizwan, Muhammad; Jin, Hai-Bo; Rehman, Fida; Hou, Zhi-Ling; Li, Jing-Bo; Butt, Faheem K.; Ali, Zulfiqar

2014-08-01

179

Presence of gapped silicene-derived band in the prototypical (3 × 3) silicene phase on silver (111) surfaces  

NASA Astrophysics Data System (ADS)

By mapping the low-energy electronic dynamics using angle resolved photoemission spectroscopy (ARPES), we have shed light on essential electronic characteristics of the (3 × 3) silicene phase on Ag(111) surfaces. In particular, our results show a silicene-derived band with a clear gap and linear energy-momentum dispersion near the Fermi level at the ? symmetry point of the (3 × 3) phase at several distinctive Brillouin zones. Moreover, we have confirmed that the large buckling of ˜0.7 Å of this silicene structure induces the opening of a gap close to the Fermi level higher than at least 0.3 eV, in agreement with recent reported photoemission results. The two-dimensional character of the charge carriers has also been revealed by the photon energy invariance of the gapped silicene band, suggesting a limited silicene-silver hybridization, in disagreement with recent density-functional theory (DFT) predictions.

Avila, J.; De Padova, P.; Cho, S.; Colambo, I.; Lorcy, S.; Quaresima, C.; Vogt, P.; Resta, A.; Le Lay, G.; Asensio, M. C.

2013-07-01

180

LOCALLY HOMOGENEOUS RIGID GEOMETRIC STRUCTURES ON SURFACES  

E-print Network

LOCALLY HOMOGENEOUS RIGID GEOMETRIC STRUCTURES ON SURFACES SORIN DUMITRESCU Abstract. We study locally homogeneous rigid geometric structures on surfaces. We show that a locally homogeneous projective connection on a compact surface is flat. We also show that a locally homogeneous unimodular affine connection

Boyer, Edmond

181

Band structure and CK ? emission of ultrathin nanotubes  

Microsoft Academic Search

An attempt is made to calculate the energy bands and spectra of the characteristic CK\\u000a ? emission of small-diameter carbon nanotubes. The calculated spectra for the nanotubes are compared with similar spectra for\\u000a graphite monolayers used as a test object and with known experimental results for nanotubes. It is concluded that the x-ray\\u000a emission spectra can be used to identify

M. M. Brzhezinskaya; E. M. Baitinger; V. I. Kormilets

2000-01-01

182

A DFT study on structural, vibrational properties, and quasiparticle band structure of solid nitromethane.  

PubMed

We report a detailed theoretical study of the structural and vibrational properties of solid nitromethane using first principles density functional calculations. The ground state properties were calculated using a plane wave pseudopotential code with either the local density approximation, the generalized gradient approximation, or with a correction to include van der Waals interactions. Our calculated equilibrium lattice parameters and volume using a dispersion correction are found to be in reasonable agreement with the experimental results. Also, our calculations reproduce the experimental trends in the structural properties at high pressure. We found a discontinuity in the bond length, bond angles, and also a weakening of hydrogen bond strength in the pressure range from 10 to 12 GPa, picturing the structural transition from phase I to phase II. Moreover, we predict the elastic constants of solid nitromethane and find that the corresponding bulk modulus is in good agreement with experiments. The calculated elastic constants show an order of C11> C22 > C33, indicating that the material is more compressible along the c-axis. We also calculated the zone center vibrational frequencies and discuss the internal and external modes of this material under pressure. From this, we found the softening of lattice modes around 8-11 GPa. We have also attempted the quasiparticle band structure of solid nitromethane with the G0W0 approximation and found that nitromethane is an indirect band gap insulator with a value of the band gap of about 7.8 eV with G0W0 approximation. Finally, the optical properties of this material, namely the absorptive and dispersive part of the dielectric function, and the refractive index and absorption spectra are calculated and the contribution of different transition peaks of the absorption spectra are analyzed. The static dielectric constant and refractive indices along the three inequivalent crystallographic directions indicate that this material has a considerable optical anisotropy. PMID:23676062

Appalakondaiah, S; Vaitheeswaran, G; Lebègue, S

2013-05-14

183

Quasiparticle band structures and optical properties of magnesium fluoride.  

PubMed

The quasiparticle and optical properties of magnesium fluoride (MgF(2)) are computed within the GW approximation based on many-body perturbation theory (MBPT). The many-body effects appearing in self-energy and electron-hole interactions have an important influence on the electronic and optical properties. The DFT-LDA calculation shows a 6.78 eV band gap. Two methods are employed to evaluate the self-energy within the GW approximation in the present work. The generalized plasmon pole model (GPP) provides a band gap of 12.17 eV, which agrees well with the experimental value of 12.4 eV (Thomas et al 1973 Phys. Status Solidi b 56 163). Another band gap value of 11.30 eV is obtained by using a full frequency-dependent self-energy, which is also not far from the experimental value and is much better than the result from the LDA calculation. The calculated optical spectrum within DFT is significantly different from the experiment. Although the calculated optical absorption threshold within the GW method is close to the experiment, the overall shape of the spectrum is still similar to the case of DFT. However, the overall shape of the spectrum via the Bethe-Salpeter equation (BSE) method agrees well with the experiment. PMID:22277330

Yi, Zhijun; Jia, Ran

2012-02-29

184

Computing Surface Hyperbolic Structure and Real Projective Structures  

E-print Network

Computing Surface Hyperbolic Structure and Real Projective Structures Miao Jin1 Feng Luo2 Xianfeng and Real Projective Structures #12;Geometries M.C.Esher's art works: Angels and Devils Regular divisin (David) Gu Hyperbolic and Real Projective Structures #12;Geometries defined on surfaces Miao Jin, Feng

185

Broad-band Measurement and Inversion of Interstation Surface-Wave Dispersion  

NASA Astrophysics Data System (ADS)

We present a novel combination of waveform analysis techniques for accurate, broad-band interstation measurement of surface-wave phase velocities. We first measure the fundamental-mode dispersion between a pair of stations by cross-correlating seismograms from the stations (Meier et al. GJI 2004). Waveforms observed at short periods (10-20 s) are complex, distorted by diffraction. It turns out, however, that patterns of waveform complexity often change little as seismic waves propagate from one station to another nearby; cross-correlation can extract accurate measurements even from signals that appear prohibitively complex. We then measure average phase velocities between sources and stations by means of the Automated Multimode Inversion (AMI) of surface- and S-wave forms (Lebedev et al. GJI 2005), and calculate interstation dispersion from each pair of measurements (same event, both stations). AMI synthesizes complete seismograms, and fundamental-mode dispersion can be measured even when the mode interferes with energetic S waves. The cross-correlation technique thus provides short-period measurements and the multimode-waveform technique yields more longest-period measurements, especially for Love waves. Robust dispersion curves with error estimates are derived by averaging over tens or hundreds of smooth curves measured using different events. Any one-event measurement can be biased due to diffraction. Selection of only smooth portions of the curves, removal of outliers, and averaging over many curves obtained with earthquake signals from different regions and from different directions combine to enhance the accuracy of the measured dispersion. Applications of the method to permanent-station data produced measurements in period ranges 10-300 s and broader, with resolving power for isotropic and anisotropic structure from the upper crust to deep upper mantle. S-velocity profiles can be computed from the data by solving small, well-determined inverse problems. Using series of target tests, we can also explore the model spaces of the inverse problems and derive robust ranges of seismic structure parameters consistent with the data. We present results of measurements and inversions for stable and active continental regions, with inferences on structure and dynamics of the lithosphere and asthenosphere.

Lebedev, S.; Meier, T.

2007-12-01

186

Band structures of bilayer radial phononic crystal plate with crystal gliding  

NASA Astrophysics Data System (ADS)

Lamb wave propagation in bilayer radial phononic crystal plate with crystal gliding is investigated. Axial symmetric model in cylindrical coordinate is applied to the bilayer radial phononic crystal plate for band structure calculation and transmission spectra. Gliding in radial direction and direction vertical to plate thickness is analyzed to modulate band gaps. Physical mechanism of gliding effects on radial phononic crystal plate is also studied with displacement fields of super cells. Numerical results show that crystal gliding both in radial direction and direction vertical to plate thickness can significantly tune omnidirectional band gaps. New lower band gaps occur and attenuation areas in transmission spectra are in good agreement with gaps of band structure calculation. Band structure evolution together with eigenmodes indicate that gliding effect converts lamb wave modes resulting in separations or interactions of adjacent bands to open new gaps or close the original ones. In addition, band gaps' sensitivity to crystal gliding is also investigated. Higher gaps are more sensitive to crystal gliding in thickness direction, and lowest gap extends in the map. Crystal gliding in radial direction can open new lowest order gap and open or close another two higher gaps, while the fourth gap is insensitive to it. The omnidirectional band gaps properties have potential application in acoustic device with isotropic gap characters.

Ma, Ting; Chen, Tianning; Wang, Xiaopeng; Li, Yinggang; Wang, Peng

2014-09-01

187

C-Band Airport Surface Communications System Standards Development, Phase I  

NASA Technical Reports Server (NTRS)

This document is being provided as part of ITT's NASA Glenn Research Center Aerospace Communication Systems Technical Support (ACSTS) contract NNC05CA85C, Task 7: "New ATM Requirements--Future Communications, C-Band and L-Band Communications Standard Development." The proposed future C-band (5091- to 5150-MHz) airport surface communication system, referred to as the Aeronautical Mobile Airport Communications System (AeroMACS), is anticipated to increase overall air-to-ground data communications systems capacity by using a new spectrum (i.e., not very high frequency (VHF)). Although some critical services could be supported, AeroMACS will also target noncritical services, such as weather advisory and aeronautical information services as part of an airborne System Wide Information Management (SWIM) program. AeroMACS is to be designed and implemented in a manner that will not disrupt other services operating in the C-band. This report defines the AeroMACS concepts of use, high-level system requirements, and architecture; the performance of supporting system analyses; the development of AeroMACS test and demonstration plans; and the establishment of an operational AeroMACS capability in support of C-band aeronautical data communications standards to be advanced in both international (International Civil Aviation Organization, ICAO) and national (RTCA) forums. This includes the development of system parameter profile recommendations for AeroMACS based on existing Institute of Electrical and Electronics Engineering (IEEE) 802.16e- 2009 standards

Hall, Edward; Isaacs, James; Zelkin, Natalie; Henriksen. Steve

2010-01-01

188

Chemical changes at the surface of RTV silicone rubber coatings on insulators during dry-band arcing  

Microsoft Academic Search

Under wet and contaminated conditions dry band arcing occurs on the surface of HV outdoor insulators coated with room temperature vulcanizing (RTV) silicone rubber. The thermal impact of the arcing on the surface of the RTV causes chemical changes. The gradual loss of hydrophobicity due to dry band arcing is of considerable concern because it results in a reduction of

Seog-Hyeon Kim; Edward A. Cherney; Reuben Hackam; Kenneth G. Rutherford

1994-01-01

189

Compact Electromagnetic Bandgap Structures for Notch Band in Ultra-Wideband Applications  

PubMed Central

This paper introduces a novel approach to create notch band filters in the front-end of ultra-wideband (UWB) communication systems based on electromagnetic bandgap (EBG) structures. The concept presented here can be implemented in any structure that has a microstrip in its configuration. The EBG structure is first analyzed using a full wave electromagnetic solver and then optimized to work at WLAN band (5.15–5.825 GHz). Two UWB passband filters are used to demonstrate the applicability and effectiveness of the novel EBG notch band feature. Simulation results are provided for two cases studied. PMID:22163430

Rotaru, Mihai; Sykulski, Jan

2010-01-01

190

Finite Element Analysis of Valence Band Structure of Square Quantum Well Under the Electric Field  

NASA Astrophysics Data System (ADS)

Valence band structure with spin-orbit (SO) coupling of GaAs/Ga1-xAlxAs square quantum well (SQW) under the electric field by a calculation procedure based on a finite element method (FEM) is investigated using the multiband effective mass theory (?c {k}?ot ?c {p} method). The validity of the method is confirmed with the results of D. Ahn, S. L. Chuang and Y. C. Chang (J. Appl. Phys. 64 (1998) 4056), who calculated valence band structure, using axial approximation for Luttinger-Kohn Hamiltonian and finite difference method. Our results demonstrated that SO coupling and electric field have significant effects on the valence band structure.

Gunes, M.; Kasapoglu, E.; Sari, H.; Akgungor, K.; Sökmen, I.

191

Photonic band structures of colloidal crystals measured with angle-resolved reflection spectroscopy.  

PubMed

We acquired angle- and polarization-resolved reflection spectra from a colloidal crystal made of polystyrene spheres along the two perpendicular directions corresponding to the LU and LW directions in the first Brillouin zone of an fcc lattice. Dispersion relations between the reflection peak positions and the wave vectors of the incident light were obtained from the measured spectra and compared with calculated photonic band structures. For the first stop band region in the spectra, the behavior of the reflection peak due to Bragg diffraction agreed with the calculated band structure and revealed some differences induced by the polarization and crystalline orientations. The spectral features observed in the higher energy regions also revealed these differences. In addition, dispersion relationships between the peak positions and the wave vectors were obtained from the results of fitting each spectrum with several Gaussian curves, compared with the calculated photonic band structures. The relationships obtained for the LU direction almost matched the calculated band structure, while the relationships obtained for the LW direction revealed the features of the mixed band structure calculated for the two perpendicular directions. These results indicate that angle- and polarization-resolved reflection spectroscopy has the potential to experimentally analyze the photonic band structures of actual photonic crystals. PMID:17258899

Ishii, Masahiko; Harada, Masashi; Tsukigase, Azusa; Nakamura, Hiroshi

2007-04-15

192

Mapping the band structure of three-dimensional topological insulator Bi2Se3 in two-dimensional limit  

Microsoft Academic Search

In this work, with in situ angle-resolved photoemission spectroscopy, we have investigated the thickness dependent band structure of molecular beam epitaxy grown Bi2Se3, a typical three-dimensional insulator, from 1 quintuple layer (QL) up to 200QL. An energy gap is observed in the topologically protected metallic surface states of bulk Bi2Se3 below the thickness of 6QL, due to the coupling between

Ke He; Yi Zhang; Cui-Zu Chang; Can-Li Song; Li-Li Wang; Xu-Cun Ma; Zhong Fang; Xi Dai; Wen-Yu Shan; Shun-Qing Shen; Qian Niu; Xiao-Liang Qi; Shou-Cheng Zhang; Xi Chen; Jin-Feng Jia; Qi-Kun Xue

2010-01-01

193

Modeling of graphene nano-ribbon Schottky diodes in the parabolic band structure limit  

NASA Astrophysics Data System (ADS)

In this paper we investigate the band structure of graphene nano-ribbons and the current density. A square root approximation shows that the band energy is parabolic in the low energy limit. In this parabolic region charge transport is controlled by the saturation velocity.

Moghaddam, N. S.; Ahmadi, M. T.; Webb, J. F.; Rahmani, M.; Sadegi, H.; Musavi, M.; Ismail, R.

2012-11-01

194

Optically decomposed near-band-edge structure and excitonic transitions in Ga2S3  

NASA Astrophysics Data System (ADS)

The band-edge structure and band gap are key parameters for a functional chalcogenide semiconductor to its applications in optoelectronics, nanoelectronics, and photonics devices. Here, we firstly demonstrate the complete study of experimental band-edge structure and excitonic transitions of monoclinic digallium trisulfide (Ga2S3) using photoluminescence (PL), thermoreflectance (TR), and optical absorption measurements at low and room temperatures. According to the experimental results of optical measurements, three band-edge transitions of EA = 3.052 eV, EB = 3.240 eV, and EC = 3.328 eV are respectively determined and they are proven to construct the main band-edge structure of Ga2S3. Distinctly optical-anisotropic behaviors by orientation- and polarization-dependent TR measurements are, respectively, relevant to distinguish the origins of the EA, EB, and EC transitions. The results indicated that the three band-edge transitions are coming from different origins. Low-temperature PL results show defect emissions, bound-exciton and free-exciton luminescences in the radiation spectra of Ga2S3. The below-band-edge transitions are respectively characterized. On the basis of experimental analyses, the optical property of near-band-edge structure and excitonic transitions in the monoclinic Ga2S3 crystal is revealed.

Ho, Ching-Hwa; Chen, Hsin-Hung

2014-08-01

195

Band structures tunability of bulk 2D phononic crystals made of magneto-elastic materials  

E-print Network

(2011) Evanescent waves and deaf bands in sonic crystals AIP Advances 1, 041601 (2011) AdditionalBand structures tunability of bulk 2D phononic crystals made of magneto-elastic materials J. O phononic crystal slabs using a hybrid lattice dynamics-continuum mechanics technique AIP Advances 1, 041403

Deymier, Pierre

196

Ab initio electronic structure calculations for metallic intermediate band formation in photovoltaic materials  

NASA Astrophysics Data System (ADS)

A metallic isolated band in the middle of the band gap of several III-V semiconductors has been predicted as photovoltaic materials with the possibility of providing substantially enhanced efficiencies. We have investigated the electronic band structures and lattice constants of GanAsmM and GanPmM with M=Sc, Ti, V, and Cr, to identify whether this isolated band is likely to exist by means of accurate calculations. For this task, we use the SIESTA program, an ab initio periodic density-functional method, fully self consistent in the local-density approximation. Norm-conserving, nonlocal pseudopotentials and confined linear combination of atomic orbitals have been used. We have carried out a case study of GanAsmTi and GanPmTi energy-band structure including analyses of the effect of the basis set, fine k-point mesh to ensure numerical convergence, structural parameters, and generalized gradient approximation for exchange and correlation corrections. We find the isolated intermediate band when one Ti atom replaces the position of one As (or P) atom in the crystal structure. For this kind of compound we show that the intermediate band relative position inside the band gap and width are sensitive to the dynamic relaxation of the crystal and the size of the basis set.

Wahnón, P.; Tablero, C.

2002-04-01

197

High power breakdown testing of a photonic band-gap accelerator structure with elliptical rods  

E-print Network

An improved single-cell photonic band-gap (PBG) structure with an inner row of elliptical rods (PBG-E) was tested with high power at a 60 Hz repetition rate at X-band (11.424 GHz), achieving a gradient of 128??MV/m at a ...

Munroe, Brian James

198

Electronic structure of QD arrays: Application to intermediate-band solar cells  

E-print Network

NUSOD 2007 Electronic structure of QD arrays: Application to intermediate-band solar cells S)Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK Abstract-Intermediate band solar cells (IBSC) have. Quantum nanostructures, such as quantum dots (QD), arranged in super-lattice arrays produce a mini

199

Band gap widening by photonic crystal heterostructures composed of two dimensional holes and diamond structure  

NASA Astrophysics Data System (ADS)

A new kind of heterostructures containing 3D diamond and 2D holes structures, and diamond-structure photonic crystals and 2D holes-structure photonic crystals fabricated by stereolithography and gel-casting with alumina were studied at microwave range, respectively. The heterostructures were designed by 2D holes structure embedded in 3D diamond structure, in which the lattice of three kinds of structures was equivalent. It was found that the band gaps of photonic crystal heterostructure were broadened by 124.6% and 150% comparing to that of diamond-structure crystal and 2D aerial holes structure. Experimental results showed the band gap broadened was not connected with a linear superposition of the band gap of 2D and 3D photonic crystals, which was the superposition of partial overlap.

Chen, Shibin; Li, Dichen; Zhi-Hui, Yuan

2013-06-01

200

Surface photovoltage spectroscopy of semiconductor structures: at the crossroads of physics, chemistry and electrical engineering  

Microsoft Academic Search

The possibility of obtaining a detailed picture of the electronic structure makes surface photovoltage spectroscopy (SPS) eminently suitable for bridging the gap between the chemical, physical, optical and electrical properties of semiconductors. In SPS, changes in band bending (both at the free semiconductor surface and at buried interfaces) are monitored as a function of external illumination. Surface photovoltage spectroscopy can

Leeor Kronik; Yoram Shapira

2001-01-01

201

Quasiparticle band structure and tight-binding model for single- and bilayer black phosphorus  

NASA Astrophysics Data System (ADS)

By performing ab initio calculations for one- to four-layer black phosphorus within the GW approximation, we obtain a significant difference in the band gap (˜1.5 eV), which is in line with recent experimental data. The results are analyzed in terms of the constructed four-band tight-binding model, which gives accurate descriptions of the mono- and bilayer band structure near the band gap, and reveal an important role of the interlayer hoppings, which are largely responsible for the obtained gap difference.

Rudenko, A. N.; Katsnelson, M. I.

2014-05-01

202

Band structure and related electronic properties of YxIn1-xN ternary system  

NASA Astrophysics Data System (ADS)

Based on a pseudopotential formalism under the virtual crystal approximation, a theoretical study is carried out on the electronic band structure and derived properties of YxIn1-xN ternary system for the hypothetical zinc-blende phase. Features such as direct and indirect energy band gaps and electron effective mass have been calculated. Besides, the ionicity of the alloy system under load has been discussed in terms of the antisymmetric band gap. Generally, our results agree well with the available experimental and previously published theoretical data. The alloy composition dependence of the band parameters of interest has been examined.

Benyounes, N.; Boucenna, M.

2014-11-01

203

Features of the band structure for semiconducting iron, ruthenium, and osmium monosilicides  

SciTech Connect

The pseudopotential method has been used to optimize the crystal lattice and calculate the energy band spectra for iron, ruthenium and, osmium monosilicides. It is found that all these compounds are indirect-gap semiconductors with band gaps of 0.17, 0.22, and 0.50 eV (FeSi, RuSi, and OsSi, respectively). A distinctive feature of their band structure is the 'loop of extrema' both in the valence and conduction bands near the center of the cubic Brillouin zone.

Shaposhnikov, V. L., E-mail: shaposhnikov@nano.bsuir.edu.by; Migas, D. B.; Borisenko, V. E. [Belarussian State University of Informatics and Radioelectronics (Belarus); Dorozhkin, N. N. [Belarussian State University (Belarus)

2009-02-15

204

The L-band PBMR measurements of surface soil moisture in FIFE  

Microsoft Academic Search

The NASA Langley Research Center's L-band pushbroom microwave radiometer (PBMR) aboard the NASA C-130 aircraft was used to map surface soil moisture at and around the Konza Prairie Natural Research Area in Kansas during the four intensive field campaigns of FIFE in May-October 1987. A total of 11 measurements were made when soils were known to be saturated. This measurement

J. R. Wang; J. C. Shiue; T. J. Schmugge; E. T. Engman

1990-01-01

205

Space-based detection of wetlands' surface water level changes from L-band SAR interferometry  

Microsoft Academic Search

Interferometric processing of JERS-1 L-band Synthetic Aperture Radar (SAR) data acquired over south Florida during 1993–1996 reveals detectable surface changes in the Everglades wetlands. Although our study is limited to south Florida it has implication for other large-scale wetlands, because south Florida wetlands have diverse vegetation types and both managed and natural flow environments. Our analysis reveals that interferometric coherence

Shimon Wdowinski; Sang-Wan Kim; Falk Amelung; Timothy H. Dixon; Fernando Miralles-Wilhelm; Roy Sonenshein

2008-01-01

206

Electronic band structure effects in monolayer, bilayer, and hybrid graphene structures  

NASA Astrophysics Data System (ADS)

Since its discovery in 2005, graphene has been the focus of intense theoretical and experimental study owing to its unique two-dimensional band structure and related electronic properties. In this thesis, we explore the electronic properties of graphene structures from several perspectives including the magnetoelectrical transport properties of monolayer graphene, gap engineering and measurements in bilayer graphene, and anomalous quantum oscillation in the monolayer-bilayer graphene hybrids. We also explored the device implications of our findings, and the application of some experimental techniques developed for the graphene work to the study of a complex oxide, Ca3Ru2O7, exhibiting properties of strongly correlated electrons. Graphene's high mobility and ballistic transport over device length scales, make it suitable for numerous applications. However, two big challenges remain in the way: maintaining high mobility in fabricated devices, and engineering a band gap to make graphene compatible with logical electronics and various optical devices. We address the first challenge by experimentally evaluating mobilities in scalable monolayer graphene-based field effect transistors (FETs) and dielectric-covered Hall bars. We find that the mobility is limited in these devices, and is roughly inversely proportional to doping. By considering interaction of graphene's Dirac fermions with local charged impurities at the interface between graphene and the top-gate dielectric, we find that Coulomb scattering is responsible for degraded mobility. Even in the cleanest devices, a band gap is still desirable for electronic applications of graphene. We address this challenge by probing the band structure of bilayer graphene, in which a field-tunable energy band gap has been theoretically proposed. We use planar tunneling spectroscopy of exfoliated bilayer graphene flakes demonstrate both measurement and control of the energy band gap. We find that both the Fermi level and electronic structure are highly sensitive to tunnel bias-induced charging in these devices, an effect that is traditionally neglected in other materials. However, careful consideration of both these effects and non-ideal tunneling processes allows extraction of valuable information from the tunneling spectra. We compare the tunable insulating state to our transport studies of bi-layer graphene-based FETs with similar dielectric environments. This work, as well as our work on top-gated monolayer-based devices, identifies the integration of graphene and a gate dielectric as being the next great challenge towards the realization of graphene-based electronics. We also report the discovery of anomalous quantum oscillations in magnetotransport measurements of monolayer and bilayer graphene hybrids. In these graphene hybrid structures, the Fermi levels of either portion lock at their interface, and the greatly different energy scales of emergent Landau levels support strong charge imbalance. The nature the interface states are yet to be clarified. Finally, we extend the techniques of device fabrication and measurement to exfoliated flakes of a layered material, Ca3Ru2O 7. This strongly correlated electronic system hosts a variety of exotic phenomena at low temperatures, which have been suggested to result from complex d-orbital interactions. We compare transport measurements of flakes to previous studies in bulk crystals, and explore the effects of tuning charge carrier density using an ionic liquid gate to induce densities several orders of magnitude greater than is possible with conventional dielectrics.

Puls, Conor

207

Experimental study of X-band dielectric-loaded accelerating structures  

NASA Astrophysics Data System (ADS)

A joint Argonne National Laboratory (ANL)/Naval Research Laboratory (NRL) program is under way to investigate X-band dielectric-loaded accelerating (DLA) structures, using high-power 11.424GHz radiation from the NRL Magnicon facility. As an advanced accelerator concepts, the dielectric-loaded accelerator offers the potential for a simple, inexpensive alternative to high-gradient RF linear accelerators. In this thesis, a comprehensive account of X-band DLA structure design, including theoretical calculation, numerical simulation, fabrication and testing, is presented in detail. Two types of loading dielectrics, alumina and MgxCa1-xTiO 3 (MCT), are investigated. For alumina (with dielectric constant 9.4), no RF breakdown has been observed up to 5 MW of drive power (equivalent to 8MV/m accelerating gradient) in the high power RF testing at NRL, but multipactor was observed to absorb a large fraction of the incident microwave power. Experimental results on suppression of multipactor using TiN coating on the inner surface of the dielectric are also reported. For MCT (with dielectric constant 20), although we did not observe dielectric breakdown in the structures, breakdown did occur at the ceramic joint, where the electric field is greatly enhanced (estimated to be around 100MV/m) due to the micro-scale vacuum gap. In addition, the MCT structure showed significantly less multipactor for the same level of RF field. The thesis also introduced a new design, a multilayered dielectric-loaded accelerating structure, to improve the performance over the conventional one layer DLA structure. Results of analysis for the case of a four layered DLA structure indicate a large reduction of RF power attenuation and an increase of shunt impedance for the structure. Beyond the main contents, the appendices of the thesis present two individual projects prompted by the experimental study of the dielectric-loaded accelerating structure. Appendix A shows a resonant loop technique that can be used in the bead-pull experiment on any cavity resonator. In appendix B, a direct wakefield measurement of the dielectric-loaded waveguide on the Argonne Wakefield Accelerator beamline is described.

Jing, Chunguang

208

Quasiparticle band structure of rocksalt-CdO determined using maximally localized Wannier functions.  

PubMed

CdO in the rocksalt structure is an indirect band gap semiconductor. Thus, in order to determine its band gap one needs to calculate the complete band structure. However, in practice, the exact evaluation of the quasiparticle band structure for the large number of k-points which constitute the different symmetry lines in the Brillouin zone can be an extremely demanding task compared to the standard density functional theory (DFT) calculation. In this paper we report the full quasiparticle band structure of CdO using a plane-wave pseudopotential approach. In order to reduce the computational effort and time, we make use of maximally localized Wannier functions (MLWFs). The MLWFs offer a highly accurate method for interpolation of the DFT or GW band structure from a coarse k-point mesh in the irreducible Brillouin zone, resulting in a much reduced computational effort. The present paper discusses the technical details of the scheme along with the results obtained for the quasiparticle band gap and the electron effective mass. PMID:23235114

Dixit, H; Lamoen, D; Partoens, B

2013-01-23

209

Ultraviolet surface-enhanced Raman scattering at the plasmonic band edge of a metallic grating.  

PubMed

Surface-enhanced Raman Scattering (SERS) is studied in sub-wavelength metallic gratings on a substrate using a rigorous electromagnetic approach. In the ultraviolet SERS is limited by the metallic dampening, yet enhancements as large as 10(5) are predicted. It is shown that these enhancements are directly linked to the spectral position of the plasmonic band edge of the metal/substrate surface plasmon. A simple methodology is presented for selecting the grating pitch to produce optimal enhancement for a given laser frequency. PMID:22274532

Mattiucci, Nadia; D'Aguanno, Giuseppe; Everitt, Henry O; Foreman, John V; Callahan, John M; Buncick, Milan C; Bloemer, Mark J

2012-01-16

210

Calculation of wakefields in a 17 GHz beam-driven photonic band-gap accelerator structure  

E-print Network

We present the theoretical analysis and computer simulation of the wakefields in a 17 GHz photonic band-gap (PBG) structure for accelerator applications. Using the commercial code CST Particle Studio, the fundamental ...

Hu, Min

211

Remote laser generation of narrow-band surface waves through optical fibers.  

PubMed

This paper demonstrates the use of a fiberoptic bundle for flexible, compact, remote, and noncontact laser generation of surface ultrasonic waves in materials. The bundle is able to deliver Nd:YAG pulsed light with a 60% delivery efficiency up to an average energy of 55 mJ/pulse for a pulse duration on the order of 10 ns and a pulse repetition rate of 20 Hz without signs of fiber damage. Details of the bundle construction and surface preparation are given, and pulsed light delivery tests performed with single tapered fibers are discussed. The high-power light delivery capabilities of the bundle are demonstrated for the generation of narrow-band surface waves in a Carbon/PEEK composite laminate by a spatial modulation technique that employs a periodic transmission mask. Single laser pulse ultrasonic tonebursts are clearly detectable using a small aperture piezoelectric transducer while ensuring thermoelastic generation conditions. The theory of narrow-band generation of surface acoustic waves is improved by accounting for the strength nonuniformity of the illumination sources. In addition, the effect of the number of illumination sources on the bandwidth of the generated surface wave is assessed experimentally, and excellent agreement is shown with the theoretical results predicted by the improved model. PMID:18244353

Di Scalea, F L; Berndt, T P; Spicer, J B; Djordjevic, B B

1999-01-01

212

Near-infrared observations of galaxies in Pisces-Perseus. I. vec H-band surface photometry of 174 spiral  

NASA Astrophysics Data System (ADS)

We present near-infrared, H-band (1.65 $() ?m), surface photometry of 174 spiral galaxies in the area of the Pisces-Perseus supercluster. The images, acquired with the ARNICA camera mounted on various telescopes, are used to derive radial profiles of surface brightness, ellipticities, and position angles, together with global parameters such as H-band magnitudes and diameters Radial profiles in tabular form and images FITS files are also available upon request from gmorio@arcetri.astro.it.}. The mean relation between H-band isophotal diameter D_{21.5} and the B-band D25 implies a B-H color of the outer disk bluer than 3.5; moreover, D_{21.5}/D25 depends on (global) color and absolute luminosity. The correlations among the various photometric parameters suggest a ratio between isophotal radius D_{21.5}/2 and disk scale length of ~ m3.5 and a mean disk central brightness ~ meq 17.5 H-mag arcsec^{-2}. We confirm the trend of the concentration index C31$ with absolute luminosity and, to a lesser degree, with morphological type. We also assess the influence of non-axisymmetric structures on the radial profiles and on the derived parameters. Based on observations at the TIRGO, NOT, and VATT telescopes. TIRGO (Gornergrat, CH) is operated by CAISMI-CNR, Arcetri, Firenze. NOT (La Palma, Canary Islands) is operated by NOTSA, the Nordic Observatory Scientific Association. VATT (Mt. Graham, Az) is operated by VORG, the Vatican Observatory Research Group Table 3 and Fig. 4 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html.

Moriondo, G.; Baffa, C.; Casertano, S.; Chincarini, G.; Gavazzi, G.; Giovanardi, C.; Hunt, L. K.; Pierini, D.; Sperandio, M.; Trinchieri, G.

1999-05-01

213

Valence Band Structure of Highly Efficient p-type Thermoelectric PbTe-PbS Alloys  

SciTech Connect

New experimental evidence is given relevant to the temperature-dependence of valence band structure of PbTe and PbTe1-xSx alloys (0.04 x 0.12), and its effect on the thermoelectric figure of merit zT. The x = 0.08 sample has zT ~ 1.55 at 773K. The magnetic field dependence of the high-temperature Hall resistivity of heavily p-type (> 1019 cm-3) Na-doped PbTe1-xSx reveals the presence of high-mobility electrons. This put in question prior analyses of the Hall coefficient and the conclusion that PbTe would be an indirect gap semiconductor at temperatures where its zT is optimal. Possible origins for these electrons are discussed: they can be induced by photoconductivity, or by the topology of the Fermi surface when the L and -bands merge. Negative values for the low-temperature thermopower are also observed. Our data show that PbTe continues to be a direct gap semiconductor at temperatures where the zT and S2 of p-type PbTe are optimal e.g. 700-900K. The previously suggested temperature induced rapid rise in energy of the heavy hole LVB relative to the light hole UVB is not supported by the experimental data.

Jaworski, C. M. [Ohio State University; Nielsen, Mechele [Ohio State University; Wang, Hsin [ORNL; Girard, Steven N. [Northwestern University, Evanston; Cai, Wei [ORNL; Porter, Wallace D [ORNL; Kanatzidis, Mercouri G. [Northwestern University, Evanston; Heremans, J. P. [Ohio State University

2013-01-01

214

Magnon band structure and magnon density in one-dimensional magnonic crystals  

NASA Astrophysics Data System (ADS)

By using Callen's Green's function method and the Tyablikov and Anderson-Callen decoupling approximations, we systematically study the magnon band structure and magnon density perpendicular to the superlattice plane of one-dimensional magnonic crystals, with a superlattice consisting of two magnetic layers with ferromagnetic (FM) or antiferromagnetic (AFM) interlayer exchange coupling. The effects of temperature, interlayer coupling, anisotropy and external magnetic field on the magnon-energy band and magnon density in the Kx-direction are investigated in three situations: a) the magnon band of magnetic superlattices with FM interlayer coupling, b) separate and c) overlapping magnon bands of magnetic superlattices with AFM interlayer coupling. In the present work, a quantum approach is developed to study the magnon band structure and magnon density of magnonic crystals and the results are beneficial for the design of magnonic-crystal waveguides or gigahertz-range spin-wave filters.

Qiu, Rong-ke; Huang, Te; Zhang, Zhi-dong

2014-11-01

215

Computing surface hyperbolic structure and real projective structure  

Microsoft Academic Search

e disk with the hyperbolic uniformization metric; the isometric embedding in the Klein disk which induces the real projective structure; the isometric embedding in the Poincar´ e disk, where the boundaries of fundamental domains are straightened to hyperbolic lines. Abstract Geometric structures are natural structures of surfaces, which enable different geometries to be defined on the surfaces. Al- gorithms designed

Miao Jin; Feng Luo; Xianfeng Gu

2006-01-01

216

Observation of interface band structure by ballistic-electron-emission microscopy  

NASA Technical Reports Server (NTRS)

The paper reports an advanced ballistic electron spectroscopy technique that was used to directly measure semiconductor band structure properties at a subsurface interface. Two interface systems having contrasting band structures were investigated by this method: Au-Si and Au-GaAs. It is concluded that the proposed method, based on scanning tunneling microscopy, enables the spatially resolved carrier-transport spectroscopy of interfaces.

Bell, L. D.; Kaiser, W. J.

1988-01-01

217

Space-based detection of wetlands' surface water level changes from L-band SAR interferometry  

USGS Publications Warehouse

Interferometric processing of JERS-1 L-band Synthetic Aperture Radar (SAR) data acquired over south Florida during 1993-1996 reveals detectable surface changes in the Everglades wetlands. Although our study is limited to south Florida it has implication for other large-scale wetlands, because south Florida wetlands have diverse vegetation types and both managed and natural flow environments. Our analysis reveals that interferometric coherence level is sensitive to wetland vegetation type and to the interferogram time span. Interferograms with time spans less than six months maintain phase observations for all wetland types, allowing characterization of water level changes in different wetland environments. The most noticeable changes occur between the managed and the natural flow wetlands. In the managed wetlands, fringes are organized, follow patterns related to some of the managed water control structures and have high fringe-rate. In the natural flow areas, fringes are irregular and have a low fringe-rate. The high fringe rate in managed areas reflects dynamic water topography caused by high flow rate due to gate operation. Although this organized fringe pattern is not characteristic of most large-scale wetlands, the high level of water level change enables accurate estimation of the wetland InSAR technique, which lies in the range of 5-10??cm. The irregular and low rate fringe pattern in the natural flow area reflects uninterrupted flow that diffuses water efficiently and evenly. Most of the interferograms in the natural flow area show an elongated fringe located along the transitional zone between salt- and fresh-water wetlands, reflecting water level changes due to ocean tides. ?? 2007 Elsevier Inc. All rights reserved.

Wdowinski, S.; Kim, S. -W.; Amelung, F.; Dixon, T. H.; Miralles-Wilhelm, F.; Sonenshein, R.

2008-01-01

218

Band structures of phononic-crystal plates in the form of a sandwich-layered structure.  

PubMed

This study investigates the propagation of Lamb waves in phononic-crystal plates in the form of a sandwich-layered structure. The composite plates are composed of periodic layers bilaterally deposited on both sides of the homogeneous core layer. Using the analyses of the band structures and the transmission spectra, it is revealed that the core layer may induce significant modulations to the lower-order Lamb modes. The modulations are ascribed to the reshaped particle displacement fields of the eigenmodes. Prominently, the core layer made of soft material (rubber) combines the identical eigenmodes of the periodic layers into a pair of asymmetric and symmetric modes in which case the periodic layers vibrate independently. However, the core layer made of hard material (tungsten) or medium hardness material (silicon) couples the periodic layers tightly, in which case the composites vibrate as a whole. In addition, it is found that the phononic band gaps are very sensitive to the thickness of the core layer; this could be indispensable to practical applications such as bandgap tuning. PMID:22087902

Cheng, Y; Liu, X J; Wu, D J

2011-11-01

219

Ammonia volatilization from surface-banded and broadcast application of liquid dairy manure on grass forage.  

PubMed

Manure can provide valuable nutrients, especially N, for grass forage, but high NH, volatilization losses from standard surface-broadcast application limits N availability and raises environmental concerns. Eight field trials were conducted to evaluate the emission of NH, from liquid dairy manure, either surface broadcast or applied in narrow surface bands with a trailing-foot implement. Manure was applied using both techniques at rates of approximately 25 and 50 m3 ha(-1) on either orchardgrass (Dactylis glomerata L.) on a well-drained silt loam or reed canarygrass (Phalaris arundinacea L.) on a somewhat poorly drained clay soil. Ammonia emission was measured with a dynamic chamber/equilibrium concentration technique. High NH3 emission rates in broadcast treatments, especially at the high rate (2 to 13 kg ha(-1) h(-1)), occurred during the first few hours after spreading, followed by a rapid reduction to low levels (<0.5 kg ha(-1) h(-1) in most cases) by 24 h after spreading and in subsequent days. Band treatments often followed the same pattern but with initial rates substantially lower and with a less dramatic decrease over time. Total estimated NH3 losses from broadcast application, as a percent of total ammoniacal N (TAN) applied, averaged 39% (range of 20 to 59%) from the high manure rate and 25% (range of 9 to 52%) from the low rate. Band spreading reduced total NH3 losses by an average of 52 and 29% for the high and low manure rates, respectively. Results show that the trailing-foot band application method can reduce NH3 losses and conserve N for perennial forage production. PMID:21520744

Pfluke, Paul D; Jokela, William E; Bosworth, Sidney C

2011-01-01

220

Analysis of frequency band structure in one-dimensional sonic crystal using Webster horn equation  

NASA Astrophysics Data System (ADS)

Sound propagation through periodic arrangement of scatterers lead to formation of bands of frequencies, known as band gaps, where sound cannot propagate though the structure. We propose a method based on Webster horn equation, along with Floquet theorem, to predict the band gap of a one-dimensional periodic structure made of hard sound-scatterers. The method is further modified to obtain the complex wave numbers, which give the decay constants. The decay constant is used to predict the sound attenuation of the evanescent wave in the finite sonic crystal. The theoretical prediction is verified with experimental measurements.

Gupta, A.; Lim, K. M.; Chew, C. H.

2011-05-01

221

ULTRA-HIGH GRADIENT COMPACT S-BAND ACCELERATING STRUCTURE*  

E-print Network

Abstract In this paper, we present the radio-frequency design of the DECA (Doubled Energy Compact are commonly available. The development of the DECA structure will offer an ultra-compact drop-in replacement. The thermal-stress analysis of the DECA structure is also presented. The machining of the first DECA cell has

Brookhaven National Laboratory

222

Structure and properties of solid surfaces  

NASA Technical Reports Server (NTRS)

Difficulties in experimental studies of crystalline surfaces are related to the fact that surface atoms have an intrinsic tendency to react with their environment. A second problem is connected with the effective thickness of surfaces, which ranges from one to several atom layers. The phenomenology of surface interactions with gases are considered, taking into account physical adsorption, chemisorption, and the oxidation of surfaces. Studies of the surface structure are discussed, giving attention to field emission microscopy, field-ion microscopy, electron diffraction techniques, Auger spectroscopy, scanning electron microscopy, electron probe microanalysis, ion microprobe methods, and low-energy backscattering spectroscopy. Investigations of semiconductor surfaces are also described.

Gatos, H. C.

1974-01-01

223

Vacancy clusters at domain boundaries and band bending at the SrTiO3(110) surface  

NASA Astrophysics Data System (ADS)

Antiphase domain boundaries (APDBs) in the (n×1)(n =4,5) reconstructions of the SrTiO3(110) surface were studied with scanning tunneling microscopy, x-ray photoemission spectroscopy, and density functional theory (DFT) calculations. Two types of APDBs form on each reconstruction; they consist of TixOy vacancy clusters with a specific stoichiometry. The presence of these clusters is controlled by the oxygen pressure during annealing. The structural models of the vacancy clusters are resolved with DFT, which also shows that their relative stability depends on the chemical potential of oxygen. The surface band bending can be tuned by controlling the vacancy clusters at the domain boundaries.

Wang, Zhiming; Hao, Xianfeng; Gerhold, Stefan; Schmid, Michael; Franchini, Cesare; Diebold, Ulrike

2014-07-01

224

Tuning Band Gap Energies in Pb3(C6X6) Extended Solid-State Structures  

SciTech Connect

A detailed plane-wave density functional theory investigation of the solid-state properties of the extended organometallic system Pb{sub 3}C{sub 6}X{sub 6} for X = O, S, Se, and Te has been performed. Initial geometry parameters for the Pb-X and C-X bond distances were obtained from optimized calculations on molecular fragment models. The Pb{sub 3}C{sub 6}X{sub 6} extended solid molecular structures were constructed in the space group P6/mmm on the basis of the known structure for X = S. Ground-state geometries, band gap energies, densities of states, and charge densities were calculated with the PBE-generalized gradient exchange-correlation functional and the HSE06 hybrid exchange-correlation functional. The PBE band gap energies were found to be lower than the HSE06 values by >0.7 eV. The band energies at points of high symmetry along the first Brillouin zone in the crystal were larger than the overall band gap of the system. Pb{sub 3}C{sub 6}O{sub 6} was predicted to be a direct semiconductor ({Lambda} point) with a PBE band gap of 0.28 eV and an HSE06 band gap of 1.06 eV. Pb{sub 3}C{sub 6}S{sub 6} and Pb{sub 3}C{sub 6}Se{sub 6} were predicted to have indirect band gaps. The PBE band gap for Pb{sub 3}C{sub 6}S{sub 6} was 0.98 eV, and the HSE06 band gap was 1.91 eV. The HSE06 value is in good agreement with the experimentally observed band gap of 1.7 eV. Pb{sub 3}C{sub 6}Se{sub 6} has a PBE band gap of 0.56 eV and a HSE06 band gap of 1.41 eV. Pb{sub 3}C{sub 6}Te{sub 6} was predicted to be metallic with both of the PBE and HSE06 functionals. A detailed analysis of the PBE band structure and partial density of states at two points before and after the metallic behavior reveals a change in orbital character indicative of band crossing in Pb{sub 3}C{sub 6}Te{sub 6}. These results show that the band gap energies can be fine-tuned by changing the substituent X atom.

Stott, Amanda C.; Vaid, Thomas P.; Bylaska, Eric J.; Dixon, David A.

2012-04-19

225

Evidence for water structuring forces between surfaces  

SciTech Connect

Structured water on apposing surfaces can generate significant energies due to reorganization and displacement as the surfaces encounter each other. Force measurements on a multitude of biological structures using the osmotic stress technique have elucidated commonalities that point toward an underlying hydration force. In this review, the forces of two contrasting systems are considered in detail: highly charged DNA and nonpolar, uncharged hydroxypropyl cellulose. Conditions for both net repulsion and attraction, along with the measured exclusion of chemically different solutes from these macromolecular surfaces, are explored and demonstrate features consistent with a hydration force origin. Specifically, the observed interaction forces can be reduced to the effects of perturbing structured surface water.

Stanley, Christopher B [ORNL; Rau, Dr. Donald [National Institutes of Health

2011-01-01

226

Estimating Sea Surface Salinity and Wind Using Combined Passive and Active L-Band Microwave Observations  

NASA Technical Reports Server (NTRS)

Several L-band microwave radiometer and radar missions have been, or will be, operating in space for land and ocean observations. These include the NASA Aquarius mission and the Soil Moisture Active Passive (SMAP) mission, both of which use combined passive/ active L-band instruments. Aquarius s passive/active L-band microwave sensor has been designed to map the salinity field at the surface of the ocean from space. SMAP s primary objectives are for soil moisture and freeze/thaw detection, but it will operate continuously over the ocean, and hence will have significant potential for ocean surface research. In this innovation, an algorithm has been developed to retrieve simultaneously ocean surface salinity and wind from combined passive/active L-band microwave observations of sea surfaces. The algorithm takes advantage of the differing response of brightness temperatures and radar backscatter to salinity, wind speed, and direction, thus minimizing the least squares error (LSE) measure, which signifies the difference between measurements and model functions of brightness temperatures and radar backscatter. The algorithm uses the conjugate gradient method to search for the local minima of the LSE. Three LSE measures with different measurement combinations have been tested. The first LSE measure uses passive microwave data only with retrieval errors reaching 1 to 2 psu (practical salinity units) for salinity, and 1 to 2 m/s for wind speed. The second LSE measure uses both passive and active microwave data for vertical and horizontal polarizations. The addition of active microwave data significantly improves the retrieval accuracy by about a factor of five. To mitigate the impact of Faraday rotation on satellite observations, the third LSE measure uses measurement combinations invariant under the Faraday rotation. For Aquarius, the expected RMS SSS (sea surface salinity) error will be less than about 0.2 psu for low winds, and increases to 0.3 psu at 25 m/s wind speed for warm waters (25 C). To achieve the required 0.2 psu accuracy, the impact of sea surface roughness (e.g. wind-generated ripples) on the observed brightness temperature has to be corrected to better than one tenth of a degree Kelvin. With this algorithm, the accuracy of retrieved wind speed will be high, varying from a few tenths to 0.6 m/s. The expected direction accuracy is also excellent (less than 10 ) for mid to high winds, but degrades for lower speeds (less than 7 m/s).

Yueh, Simon H.; Chaubell, Mario J.

2012-01-01

227

Electronic structure of Pt based topological Heusler compounds with C1{sub b} structure and 'zero band gap'  

SciTech Connect

Besides of their well-known wide range of properties it was recently shown that many of the heavy Heusler semiconductors with 1:1:1 composition and C1{sub b} structure exhibit a zero band gap behavior and are topological insulators induced by their inverted band structure. In the present study, the electronic structure of the Heusler compounds PtYSb and PtLaBi was investigated by bulk sensitive hard x-ray photoelectron spectroscopy. The measured valence band spectra are clearly resolved and in well agreement to the first-principles calculations of the electronic structure of the compounds. The experimental results give clear evidence for the zero band gap state.

Ouardi, Siham; Shekhar, Chandra; Fecher, Gerhard H.; Kozina, Xeniya; Stryganyuk, Gregory; Felser, Claudia [Institut fuer Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universitaet, D-55099 Mainz (Germany); Ueda, Shigenori; Kobayashi, Keisuke [NIMS Beamline Station at SPring-8, National Institute for Materials Science, Hyogo 679-5148 (Japan)

2011-05-23

228

Fine structure of the red luminescence band in undoped GaN  

NASA Astrophysics Data System (ADS)

Many point defects in GaN responsible for broad photoluminescence (PL) bands remain unidentified. Their presence in thick GaN layers grown by hydride vapor phase epitaxy (HVPE) detrimentally affects the material quality and may hinder the use of GaN in high-power electronic devices. One of the main PL bands in HVPE-grown GaN is the red luminescence (RL) band with a maximum at 1.8 eV. We observed the fine structure of this band with a zero-phonon line (ZPL) at 2.36 eV, which may help to identify the related defect. The shift of the ZPL with excitation intensity and the temperature-related transformation of the RL band fine structure indicate that the RL band is caused by transitions from a shallow donor (at low temperature) or from the conduction band (above 50 K) to an unknown deep acceptor having an energy level 1.130 eV above the valence band.

Reshchikov, M. A.; Usikov, A.; Helava, H.; Makarov, Yu.

2014-01-01

229

Functional topography of band 3: specific structural alteration linked to functional aberrations in human erythrocytes.  

PubMed Central

Band 3 is the major anion transport polypeptide of erythrocytes. It appears to be the binding site of several glycolytic enzymes. Structurally, band 3 is the major protein spanning the erythrocyte membrane and connects the plasma membrane to band 2.1, which binds to the cytoskeleton. In the present study, we report an alteration of band 3 molecule that is associated with the following changes: erythrocyte shape change from discoid to "thorny cells" (acanthocytes), restriction of rotational diffusion of band 3 in the membrane, increase in anion transport, and decrease in the number of high-affinity ankyrin-binding sites. Changes in erythrocyte IgG binding, glyceraldehyde-3-phosphate dehydrogenase, fluorescence polarization (indicative of membrane fluidity), and other membrane proteins as determined by polyacrylamide gel electrophoresis were not detected. Cells containing the altered band 3 polypeptide were obtained from individuals with abnormal erythrocyte morphology. Two-dimensional peptide maps revealed differences in the Mr 17,000 anion transport segment of band 3 consistent with additions of tyrosines or tyrosine-containing peptides. The data suggest that (i) this alteration of band 3 does not result in accelerated aging as does cleavage and (ii) structural changes in the anion transport region result in alterations in anion transport. Images PMID:2829189

Kay, M M; Bosman, G J; Lawrence, C

1988-01-01

230

Experimental study of photonic band gap accelerator structures  

E-print Network

This thesis reports theoretical and experimental research on a novel accelerator concept using a photonic bandgap (PBG) structure. Major advances in higher order mode (HOM) damping are required for the next generation of ...

Marsh, Roark A

2009-01-01

231

Structure and evolution of a convective band MCS  

E-print Network

of the structure and evolution of the already known structures of MCSs (e. g. , squall lines and rainbands), but also the discovery and analysis of new features within MCSs, like mesovortices. Zhang and Fritsch (1987) defined mesovortices as significant... of convection (Johnston 1981; Bosart and Sanders 1981; Zhang and Fritsch 1987; Menard and Fritsch 1989; Verlinde and Cotton 1990; and Bartels and Maddox 1991). Mesovortlces in squall line systems Using satellite imagery and a single Doppler radar, Smull...

Valdes-Manzanilla, Arturo

2012-06-07

232

Fine structure of granular banding in two-phase rimming flow  

NASA Astrophysics Data System (ADS)

Solid-liquid two-phase flow inside a partially filled horizontally rotating cylinder is investigated. We document the observation of a new, secondary banding pattern developing in the flow when the solid phase comes out of suspension to accumulate as regularly spaced, circumferential bands on the inner cylinder wall. This secondary pattern, the fine structure, is superposed on the primary pattern which we previously described [O. A. M. Boote and P. J. Thomas, Phys. Fluids 11, 2020 (1999)]. The fine structure is characterized by each of the primary bands adopting a compound structure consisting of three individual, narrower secondary bands. New results on the influence of the physical properties of the solid phase on transitions between characteristic flow states are briefly discussed. It is reported that state-transition boundaries in the phase plane and the wavelength of the primary instability are insensitive to particle size and shape while there exist influences due to the particle density.

Thomas, P. J.; Riddell, G. D.; Kooner, S.; King, G. P.

2001-09-01

233

First-Principles Study of the Band Gap Structure of Oxygen-Passivated Silicon Nanonets  

PubMed Central

A net-like nanostructure of silicon named silicon nanonet was designed and oxygen atoms were used to passivate the dangling bonds. First-principles calculation based on density functional theory with the generalized gradient approximation (GGA) were carried out to investigate the energy band gap structure of this special structure. The calculation results show that the indirect–direct band gap transition occurs when the nanonets are properly designed. This band gap transition is dominated by the passivation bonds, porosities as well as pore array distributions. It is also proved that Si–O–Si is an effective passivation bond which can change the band gap structure of the nanonets. These results provide another way to achieve a practical silicon-based light source. PMID:20596312

2009-01-01

234

High-spin structure and Band Termination in $^{103}$Cd  

E-print Network

Excited states of the neutron deficient $^{103}$Cd nucleus have been investigated via the $^{72}$Ge($^{35}$Cl, p3n) reaction at beam energy of 135 MeV by use of in-beam spectroscopic methods. Gamma rays depopulating the excited states were detected using the Gammasphere spectrometer with high-fold $\\gamma$-ray coincidences. A quadrupole $\\gamma$-ray coincidence analysis ($\\gamma^{4}$) has been used to extend the known level scheme. The positive parity levels have been established up to $J = 35/2\\hbar$ and $E_{x} = 7.071$ MeV. In addition to the observation of highly-fragmented level scheme belonging to the positive-parity sequences at E$_{x}\\sim$ 5 MeV, the termination of a negative-parity sequence connected by $E2$ transitions has been established at $J = 47/2 \\hbar$ and $E_{x} = 11.877$ MeV. The experimental results corresponding to both the positive- and negative-parity sequences have been theoretically interpreted in the framework of the core particle coupling model. Evidence is presented for a shape change from collective prolate to non-collective oblate above the $J^{\\pi} = 39/2^{-}$ (8011 keV) level and for a smooth termination of the negative-parity band.

A. Chakraborty; Krishichayan; S. Mukhopadhyay; S. Ray; S. N. Chintalapudi; S. S. Ghugre; N. S. Pattabiraman; A. K. Sinha; S. Sarkar; U. Garg; S. Zhu; M. Saha Sarkar

2007-09-11

235

Potential energy surface and vibrational band origins of the triatomic lithium cation  

NASA Astrophysics Data System (ADS)

The 104 point CISD Li +3 potential energy surface and its analytical representation is reported. The calculations predict the minimum energy geometry to be an equilateral triangle of side RLi?Li = 3.0 Å and of energy - 22.20506 E h. A fifth-order Morse—Dunham type analytical force field is used in the Carney—Porter normal co-ordinate vibrational Hamiltonian, the corresponding eigenvalue problem being solved variationally using a 560 configurational finite-element basis set. The predicted assignment of the vibrational band origins is in accord with that reported for H +3. Moreover, for 6Li +3 and 7Li +3 the lowest i.r. accessible band origin is the overline?0,1,±1 predicted to be at 243.6 and 226.0 cm -1 respectively.

Searles, Debra J.; Dunne, Simon J.; von Nagy-Felsobuki, Ellak I.

236

Shape Dependence of Band-Edge Exciton Fine Structure in CdSe Nanocrystals  

SciTech Connect

The band-edge exciton fine structure of wurtzite CdSe nanocrystals is investigated by a plane-wave pseudopotential method that includes spin-orbit coupling, screened electron-hole Coulomb interactions, and exchange interactions. Large-scale, systematic simulations have been carried out on quantum dots, nanorods, nanowires, and nanodisks. The size and shape dependence of the exciton fine structure is explored over the whole diameter-length configuration space and is explained by the interplay of quantum confinement, intrinsic crystal-field splitting, and electron-hole exchange interactions. Our results show that the band-edge exciton fine structure of CdSe nanocrystals is determined by the origin of their valence-band single-particle wave functions. Nanocrystals where the valence-band maximum originates from the bulk A band have a 'dark' ground-state exciton. Nanocrystals where the valence-band maximum is derived from the bulk B band have a 'quasi-bright' ground-state exciton. Thus, the diameter-length configuration map can be divided into two regions, corresponding to dark and quasi-bright ground-state excitons. We find that the dark/quasi-bright ground-state exciton crossover is not only diameter-dependent but also length-dependent, and it is characterized by a curve in the two-parameter space of diameter and length.

Zhao, Q.; Graf, P. A.; Jones, W. B.; Franceschetti, A.; Li, J.; Wang, L. W.; Kim, K.

2007-01-01

237

Shape dependence of band-edge exciton fine structure in CdSe nanocrystals.  

PubMed

The band-edge exciton fine structure of wurtzite CdSe nanocrystals is investigated by a plane-wave pseudopotential method that includes spin-orbit coupling, screened electron-hole Coulomb interactions, and exchange interactions. Large-scale, systematic simulations have been carried out on quantum dots, nanorods, nanowires, and nanodisks. The size and shape dependence of the exciton fine structure is explored over the whole diameter-length configuration space and is explained by the interplay of quantum confinement, intrinsic crystal-field splitting, and electron-hole exchange interactions. Our results show that the band-edge exciton fine structure of CdSe nanocrystals is determined by the origin of their valence-band single-particle wave functions. Nanocrystals where the valence-band maximum originates from the bulk A band have a "dark" ground-state exciton. Nanocrystals where the valence-band maximum is derived from the bulk B band have a "quasi-bright" ground-state exciton. Thus, the diameter-length configuration map can be divided into two regions, corresponding to dark and quasi-bright ground-state excitons. We find that the dark/quasi-bright ground-state exciton crossover is not only diameter-dependent but also length-dependent, and it is characterized by a curve in the two-parameter space of diameter and length. PMID:17900160

Zhao, Qingzhong; Graf, Peter A; Jones, Wesley B; Franceschetti, Alberto; Li, Jingbo; Wang, Lin-Wang; Kim, Kwiseon

2007-11-01

238

Investigation of the vertical structure of clouds over the Western Ghats, India using X-band and Ka-band Doppler radar observations  

NASA Astrophysics Data System (ADS)

Investigation of the vertical structure of clouds over the Western Ghats, India using X-band and Ka-band Doppler radar observations Subrata Kumar Das*, S. M. Deshpande, K. Chakravarty and M. C. R. Kalapureddy Indian Institute of Tropical Meteorology, Pune, India ABSTRACT The Western Ghats (WGs) located parallel to the west coast of India receives a huge amount of rainfall during the Indian summer monsoon (ISM) in which topography plays a huge role in it. To understand the dynamics and microphysics of monsoon precipitating clouds over the WGs, a High Altitude Cloud Physics Laboratory (HACPL) has been setup at Mahabaleshwar (17.92 oN, 73.6 oE, ~1.4 km AMSL) in 2012. As part of this laboratory, a mobile X-band (9.5 GHz) and Ka-band (35.29 GHz) dual-polarization Doppler weather radar system is installed at Mandhardev (18.04 oN, 73.87 oE, ~1.3 km AMSL, at 26 km radial distance from the HACPL). The X-band radar shows the dominant cloud movement is from the western side of the WGs to the eastern side, crossing the HACPL and the radar site. The cloud occurrence statistics show a sudden reduction within a distance of ~30 km on the eastern side of WGs indicates the possibility of a rain shadow area. Further, we investigate the vertical structure of cloud over the HACPL, and identified four cloud modes viz., shallow cumulus mode, congestus mode, deep convective mode, and overshooting convection mode. The frequency distribution of cloud-cell base height (CBH) and cloud-cell top height (CTH) shows most of the clouds with base below 2.5 km and tops usually not exceeding 9 km. This indicates the dominance of warm-rain process in the WGs region. The positive relationships between surface rainfall rates and CTH and 0oC isotherm level have observed. Details will be presented in the upcoming symposium.

Das, Subrata Kumar

239

Surface and Bulk Electronic Structure of Wurtzite GaN  

NASA Astrophysics Data System (ADS)

The electronic structure of thin film wurtzite GaN and Al_xGa_1-xN has been studied using angle resolved photoemission, inverse photoemission, soft x-ray absorption and soft x-ray emission. These complimentary spectroscopies allow us to measure the partial density of states (PDOS) of the occupied and unoccupied valence states, and the band dispersion of occupied and unoccupied surface and bulk states. The GaN(0001) thin films used in our experiments were grown using molecular beam epitaxy on sapphire substrates, and were Si doped n-type. Soft x-ray absorption (SXA) and soft x-ray emission (SXE) measurements were performed at the HASYLAB synchrotron, Hamburg, and at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory. Angle resolved photoemission (ARP) and momentum resolved inverse photoemission (IP) spectra were performed at Brookhaven. Clean surfaces were prepared by repeated cycles of sputtering with N2 ions and annealing in ultra-high vacuum at 900 C. Low energy electron diffraction from the clean surface displays a sharp hexagonal pattern with no evidence of surface reconstruction. ARP measurements for GaN show bulk bands that agree well with theoretical predictions,(A. Rubio, J.L. Corkhill, M.L. Cohen, E.L. Shirley, and S.G. Louie, Phys. Rev. B 48, 11810, (1993)) but also show the existence of a well defined surface state.(S.S. Dhesi, C.B. Stagarescu, K.E. Smith, D. Doppalapudi, R. Singh and T.D. Moustakas, Phys. Rev. B 56, 10271 (1997)) This state is occupied, and lies below the valence band maximum in a projected bulk band gap. It has spz character, consistent with a dangling bond state, and is sensitive to contamination of the surface by O2 or H_2. IP spectroscopy was used to measure the dispersion of the unoccupied GaN conduction band states, and no unoccupied surface states were observed. SXE and SXA were used to measure the bulk valence and conduction band partial density of states and band gap behavior for GaN (C. Stagarescu, L.C. Duda, K.E. Smith, J.H. Guo, J. Nordgren, R. Singh and T.D. Moustakas, Phys. Rev. B 54, 17,335 (1996)) and Al_xGa_1-xN. Given the strong dipole selection rules that govern SXE, and the sensitivity of our spectrometer, we are able to directly observe the hybrid states in these nitrides. Specifically, we find a weak feature in the N K-emission at approximately 19.5 eV below the valence band maximum that arises from hybridization between N 2p and Ga 3d states. We also directly observe hybridization between Ga 4s- and N 2p-states extending to the valence band maximum. X-ray absorption spectra show that the bottom of the conduction band is a mixture of Ga 4s and N 2p states.

Smith, Kevin E.

1998-03-01

240

The optical band gap and surface free energy of polyethylene modified by electron beam irradiations  

NASA Astrophysics Data System (ADS)

In this study, investigations have been carried out on electron beam irradiated ultra high molecular weight polyethylene (UHMWPE). Polyethylene samples were irradiated with 1.5 MeV electron beam at doses ranging from 50 to 500 kGy. Modifications in optical properties and photoluminescence behavior of the polymer were evaluated by UV-vis and photoluminescence techniques. Changes of surface layer composition of UHMWPE produced by electron irradiations were studied by Rutherford back scattering spectrometry (RBS). The change in wettability and surface free energy induced by irradiations was also investigated. The optical absorption studies reveal that both optical band gap and Urbach's energy decreases with increasing electron dose. A correlation between energy gap and the number of carbon atoms in clusters is discussed. Photoluminescence spectra were reveal remarkable decrease in the integrated luminescence intensity with increasing irradiation dose. Contact angle measurements showed that wettability and surface free energy increases with increasing the irradiation dose.

Abdul-Kader, A. M.

2013-04-01

241

A surface measure for probabilistic structural computations.  

PubMed

Computing three-dimensional structures from sparse experimental constraints requires method for combining heterogeneous sources of information, such as distances, angles, and measures of total volume, shape, and surface. For some types of information, such as distances between atoms, numerous methods are available for computing structures that satisfy the provided constraints. It is more difficult, however, to use information about the degree to which an atom is on the surface or buried as a useful constraint during structure computations. Surface measures have been used as accept/reject criteria for previously computed structures, but this is not an efficient strategy. In this paper, we investigate the efficacy of applying a surface measure in the computation of molecular structure, using a method of probabilistic least square computations which facilitates the introduction of multiple, noisy, heterogeneous data sources. For this purpose, we introduce a simple purely geometrical measure of surface proximity called maximal conic view (MCV). MCV is efficiently computable and differentiable, and is hence well suited to driving a structural optimization method based, in part, on surface data. As an initial validation, we show that MCV correlates well with known measures for total exposed surface area. We use this measure in our experiments to show that information about surface proximity (derived from theory or experiment, for example) can be added to a set of distance measurements to increase significantly the quality of the computed structure. In particular, when 30 to 50 percent of all possible short-range distances are provided, the addition of surface information improves the quality of the computed structure (as measured by RMS fit) by as much as 80 percent. Our results demonstrate that knowledge of which atoms are on the surface and which are buried can be used as a powerful constraint in estimating molecular structure. PMID:9783220

Schmidt, J P; Chen, C C; Cooper, J L; Altman, R B

1998-01-01

242

Shear band structure in ballistically tested bainitic steels  

E-print Network

’, Acta Metall., 1987, 35, 301–306. 5. W. J. Davies: ‘Surface fatigue in ball bearings, roller bearings, and gears in aircraft engines’, In: Fatigue in Rolling Contact. London, U.K.: Institution of Mechanical Engineers, 1963:23–40. 6. H. Schlicht: ‘About... are typically 10-100µm in width [2]. The phenomenon is therefore associated with high strain-rate deformation (for example during machining, or ballistic impact [3, 4]) and has been speculated to be the reason for damage accumulation in bearings [5, 6] although...

Fielding, L. C. D.; Bhadeshia, H. K. D. H.

243

Electronic absorption band broadening and surface roughening of phthalocyanine double layers by saturated solvent vapor treatment  

SciTech Connect

Variations in the electronic absorption (EA) and surface morphology of three types of phthalocyanine (Pc) thin film systems, i.e. copper phthalocyanine (CuPc) single layer, zinc phthalocyanine (ZnPc) single layer, and ZnPc on CuPc (CuPc/ZnPc) double layer film, treated with saturated acetone vapor were investigated. For the treated CuPc single layer film, the surface roughness slightly increased and bundles of nanorods were formed, while the EA varied little. In contrast, for the ZnPc single layer film, the relatively high solubility of ZnPc led to a considerable shift in the absorption bands as well as a large increase in the surface roughness and formation of long and wide nano-beams, indicating a part of the ZnPc molecules dissolved in acetone, which altered their molecular stacking. For the CuPc/ZnPc film, the saturated acetone vapor treatment resulted in morphological changes in mainly the upper ZnPc layer due to the significantly low solubility of the underlying CuPc layer. The treatment also broadened the EA band, which involved a combination of unchanged CuPc and changed ZnPc absorption.

Kim, Jinhyun [Department of Chemistry, Kookmin University, Seoul 136-702 (Korea, Republic of)] [Department of Chemistry, Kookmin University, Seoul 136-702 (Korea, Republic of); Yim, Sanggyu, E-mail: sgyim@kookmin.ac.kr [Department of Chemistry, Kookmin University, Seoul 136-702 (Korea, Republic of)] [Department of Chemistry, Kookmin University, Seoul 136-702 (Korea, Republic of)

2012-10-15

244

Design of a frequency selective surface (FSS) type superstrate for dual-band directivity enhancement of microstrip patch antennas  

Microsoft Academic Search

A novel design of a high-directivity resonator antenna that utilizes a two-layered frequency selective surface (FSS) superstrate - as an alternative to a dielectric electromagnetic band gap (EBG) superstrate - for dual band directivity enhancement and reduction in height is presented in this paper.

Young Ju Lee; Junho Yeo; R. Mittra; Wee Sang Park

2005-01-01

245

Superlattice band structure: New and simple energy quantification condition  

NASA Astrophysics Data System (ADS)

Assuming an approximated effective mass and using Bastard's boundary conditions, a simple method is used to calculate the subband structure for periodic semiconducting heterostructures. Our method consists to derive and solve the energy quantification condition (EQC), this is a simple real equation, composed of trigonometric and hyperbolic functions, and does not need any programming effort or sophistic machine to solve it. For less than ten wells heterostructures, we have derived and simplified the energy quantification conditions. The subband is build point by point; each point presents an energy level. Our simple energy quantification condition is used to calculate the subband structure of the GaAs/Ga0.5Al0.5As heterostructures, and build its subband point by point for 4 and 20 wells. Our finding shows a good agreement with previously published results.

Maiz, F.

2014-10-01

246

Surface orientation dependent band alignment for CuInSe2-ZnSe-ZnO  

NASA Astrophysics Data System (ADS)

The interface formation and band-lineup between ZnO and epitaxial CuInSe2 substrates is investigated with photoelectron spectroscopy. ZnO films prepared by a metal-organic molecular beam epitaxy process lead to the formation of an intrinsic ZnSe buffer layer. The effect of substrate orientation on the band alignment is studied for the orientations (112) and (001). We found a weak dependence of the interfacial dipole on orientation. Together with our findings for CuInS2 films, we suggest a ubiquitous CuInX2-ZnX-ZnO (X=Se, S) structure with an ultra-thin ZnX buffer layer for ZnO growth on chalcopyrites at elevated temperatures.

Hofmann, Andreas; Pettenkofer, Christian

2011-03-01

247

Electronic structure and band alignment at an epitaxial spinel/perovskite heterojunction.  

PubMed

The electronic properties of solid-solid interfaces play critical roles in a variety of technological applications. Recent advances of film epitaxy and characterization techniques have demonstrated a wealth of exotic phenomena at interfaces of oxide materials, which are critically dependent on the alignment of their energy bands across the interface. Here we report a combined photoemission and electrical investigation of the electronic structures across a prototypical spinel/perovskite heterojunction. Energy-level band alignment at an epitaxial Co3O4/SrTiO3(001) heterointerface indicates a chemically abrupt, type I heterojunction without detectable band bending at both the film and substrate. The unexpected band alignment for this typical p-type semiconductor on SrTiO3 is attributed to its intrinsic d-d interband excitation, which significantly narrows the fundamental band gap between the top of the valence band and the bottom of the conduction band. The formation of the type I heterojunction with a flat-band state results in a simultaneous confinement of both electrons and holes inside the Co3O4 layer, thus rendering the epitaxial Co3O4/SrTiO3(001) heterostructure to be a very promising material for high-efficiency luminescence and optoelectronic device applications. PMID:25075939

Qiao, Liang; Li, Wei; Xiao, Haiyan; Meyer, Harry M; Liang, Xuelei; Nguyen, N V; Weber, William J; Biegalski, Michael D

2014-08-27

248

Electronic- and band-structure evolution in low-doped (Ga,Mn)As  

SciTech Connect

Modulation photoreflectance spectroscopy and Raman spectroscopy have been applied to study the electronic- and band-structure evolution in (Ga,Mn)As epitaxial layers with increasing Mn doping in the range of low Mn content, up to 1.2%. Structural and magnetic properties of the layers were characterized with high-resolution X-ray diffractometry and SQUID magnetometery, respectively. The revealed results of decrease in the band-gap-transition energy with increasing Mn content in very low-doped (Ga,Mn)As layers with n-type conductivity are interpreted as a result of merging the Mn-related impurity band with the host GaAs valence band. On the other hand, an increase in the band-gap-transition energy with increasing Mn content in (Ga,Mn)As layers with higher Mn content and p-type conductivity indicates the Moss-Burstein shift of the absorption edge due to the Fermi level location within the valence band, determined by the free-hole concentration. The experimental results are consistent with the valence-band origin of mobile holes mediating ferromagnetic ordering in the (Ga,Mn)As diluted ferromagnetic semiconductor.

Yastrubchak, O.; Gluba, L.; ?uk, J. [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland)] [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland); Sadowski, J. [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland) [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland); MAX-Lab, Lund University, 22100 Lund (Sweden); Krzy?anowska, H. [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland) [Institute of Physics, UMCS, Pl. Marii Curie-Sk?odowskiej 1, 20-031 Lublin (Poland); Department of Physics and Astronomy, Vanderbilt University, 6506 Stevenson Center, Nashville, Tennessee 37325 (United States); Domagala, J. Z.; Andrearczyk, T.; Wosinski, T. [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland)] [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland)

2013-08-07

249

Theoretical analysis of overmoded dielectric photonic band gap structures for accelerator applications  

Microsoft Academic Search

An overmoded accelerator structure is proposed based on a dielectric photonic-band-gap (PBG) disk-loaded structure. The structure consists of dielectric rods and metal disks with irises. It is advantageous for application in high frequency (17 GHz and higher) linacs because of the large dimensions of the structure. The operating mode is a higher-order TM02 mode. One unique feature is that the

M. A. Shapiro; E. I. Smirnova; C. Chen; R. J. Temkin

2003-01-01

250

Two-zone heterogeneous structure within shear bands of a bulk metallic glass  

NASA Astrophysics Data System (ADS)

Shear bands, the main plastic strain carrier in metallic glasses, are severely deformed regions often considered as disordered and featureless. Here we report the observations of a sandwich-like heterogeneous structure inside shear bands in Pd40.5Ni40.5P19 metallic glass sample after plastic deformation by high-resolution transmission electron microscopy. The experimental results suggest a two-step plastic deformation mechanism with corresponding microstructure evolution at atomic scale, which may intimately connected to the stability of the shear band propagation and the overall plastic deformability.

Shao, Yang; Yao, Kefu; Li, Mo; Liu, Xue

2013-10-01

251

NUCLEAR AND HEAVY ION PHYSICS: Structural evolution of the intruder band in 118Sn  

NASA Astrophysics Data System (ADS)

Excited states of the positive-parity intruder band in 118Sn have been studied via the 116Cd(7Li, 1p4n) reaction at 7Li energy of 48 MeV using techniques of in-beam ?-ray spectroscopy. This intruder band has been observed up to 7187 keV with spin (16+). The structural evolution of this intruder band with increasing angular momentum has been discussed in terms of the aligned angular momentum and the ratio of the E-Gamma Over Spin (E-GOS) curve.

Wang, Shou-Yu; Duan, Bo-Tao; Zhu, Xin-Xin; Ren, Xiu-Lei; Yang, Xiao-Ling; Xi, Juan; Lü, Feng-Zheng; Sun, Da-Peng; Lü, Ying-Bo; Liu, Xi-Ju; Hua, Hui; Li, Zhong-Yu; Zhang, Shuang-Quan; Qi, Bin; Yao, Jiang-Ming; Zhu, Li-Hua; Wu, Xiao-Guang; Li, Guang-Sheng; Liu, Ying; Li, Xue-Qin; Zheng, Yun; Wang, Lie-Lin; Wang, Lei

2009-10-01

252

Two-zone heterogeneous structure within shear bands of a bulk metallic glass  

SciTech Connect

Shear bands, the main plastic strain carrier in metallic glasses, are severely deformed regions often considered as disordered and featureless. Here we report the observations of a sandwich-like heterogeneous structure inside shear bands in Pd{sub 40.5}Ni{sub 40.5}P{sub 19} metallic glass sample after plastic deformation by high-resolution transmission electron microscopy. The experimental results suggest a two-step plastic deformation mechanism with corresponding microstructure evolution at atomic scale, which may intimately connected to the stability of the shear band propagation and the overall plastic deformability.

Shao, Yang; Yao, Kefu; Liu, Xue [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China)] [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Li, Mo [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China) [School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245 (United States)

2013-10-21

253

Photonic band gaps of two-dimensional photonic lattices: the face-centered graphite structures  

NASA Astrophysics Data System (ADS)

We describe the calculation of photonic band structures of two-dimensional lattices made of more than one dielectric array. In particular, we study a face-centered graphite (fcg) structure obtained by an arrangement of two sets of cylindrical rods, one located at the vertices of regular hexagons (graphite sublattice) and another in the center of the hexagons (triangle sublattice). Changing the diameter of the centered rods, different patterns are produced including both triangle and graphite structures. We evaluate their relationships in terms of the existence of absolute photonic band gaps common to E and H polarized waves.

Chen, Y.

1997-07-01

254

Study on band gap structure of Fibonacci quantum superlattices by using the transfer matrix method  

NASA Astrophysics Data System (ADS)

The scattering properties of particles in a one-dimensional Fibonacci sequence based potential have been analyzed by means of the Transfer Matrix Method. The electronic band gaps are examined comparatively with those obtained using the corresponding periodic potentials. The reflection coefficient shows self-similar properties for the Fibonacci superlattices. Moreover, by using the generalized Bragg's condition, the band gaps positions are derived from the golden mean involved in the design of the superlattice structure.

Ferrando, V.; Castro-Palacio, J. C.; Marí, B.; Monsoriu, J. A.

2014-02-01

255

Interferometric technique for the measurement of photonic band structure in colloidal crystals  

NASA Astrophysics Data System (ADS)

Under suitable conditions polystyrene microsphere colloids form photonic crystals capable of diffracting visible light, analogous to x-ray diffraction from atomic crystal planes. The lattice spacings of these crystals can be tailored to satisfy the Bragg condition along a certain direction for a particular desired wavelength. A modified Mach-Zehnder interferometer has been developed for accurately measuring relative phase shifts of light propagating in photonic crystals to determine the dispersion resulting from photonic band structure near the band edges.

Tarhan, I. Inanc; Zinkin, Martin P.; Watson, George H.

1995-07-01

256

Nitride band-structure model in a quantum well laser simulator  

Microsoft Academic Search

The two-dimensional quantum well laser simulator Visible Laser Simulator (VLS) has been extended to simulate III–V nitride\\u000a based lasers. In this paper, we present details about the laser simulator and focus on the six band k.p solver used to calculate\\u000a the electronic band structure. The effect of strain on bulk and quantum well electronic dispersion is analyzed, and the influence

Anusha Venkatachalam; P. D. Yoder; Benjamin Klein; Aditya Kulkarni

2008-01-01

257

Estimation of Bare Surface Soil Moisture and Surface Roughness Parameter Using L-Band SAR Image Data  

NASA Technical Reports Server (NTRS)

An algorithm based on a fit of the single-scattering Integral Equation Method (IEM) was developed to provide estimation of soil moisture and surface roughness parameter (a combination of rms roughness height and surface power spectrum) from quad-polarized synthetic aperture radar (SAR) measurements. This algorithm was applied to a series of measurements acquired at L-band (1.25 GHz) from both AIRSAR (Airborne Synthetic Aperture Radar operated by the Jet Propulsion Laboratory) and SIR-C (Spaceborne Imaging Radar-C) over a well- managed watershed in southwest Oklahoma. Prior to its application for soil moisture inversion, a good agreement was found between the single-scattering IEM simulations and the L band measurements of SIR-C and AIRSAR over a wide range of soil moisture and surface roughness conditions. The sensitivity of soil moisture variation to the co-polarized signals were then examined under the consideration of the calibration accuracy of various components of SAR measurements. It was found that the two co-polarized backscattering coefficients and their combinations would provide the best input to the algorithm for estimation of soil moisture and roughness parameter. Application of the inversion algorithm to the co-polarized measurements of both AIRSAR and SIR-C resulted in estimated values of soil moisture and roughness parameter for bare and short-vegetated fields that compared favorably with those sampled on the ground. The root-mean-square (rms) errors of the comparison were found to be 3.4% and 1.9 dB for soil moisture and surface roughness parameter, respectively.

Shi, Jian-Cheng; Wang, James; Hsu, Ann Y.; ONeill, Peggy E.; Engman, Edwin T.

1997-01-01

258

Erbium emission from porous silicon one-dimensional photonic band gap structures  

Microsoft Academic Search

We report tunable, narrow, directional, and enhanced erbium emission from one-dimensional photonic band gap structures. The structures are prepared by anodic etching of crystalline silicon and consist of two highly reflecting porous silicon Bragg reflectors sandwiching an active layer. The cavities are doped by cathodic electromigration of the erbium ions into the porous silicon matrix, followed by high temperature oxidation.

Herman A. Lopez; Philippe M. Fauchet

2000-01-01

259

International X-Band Linear Collider Accelerator Structure R&D  

SciTech Connect

For more than fifteen years before the International Technology Recommendation Panel (ITRP) decision in August, 2004, there were intensive R&D activities and broad international collaboration among the groups at SLAC, KEK, FNAL, LLNL and other labs for the room temperature X-Band accelerator structures. The goal was to provide an optimized design of the main linac structure for the NLC (Next Linear Collider) or GLC (Global Linear Collider). There have been two major challenges in developing X-band accelerator structures for the linear colliders. The first is to demonstrate stable, long-term operation at the high gradient (65 MV/m) that is required to optimize the machine cost. The second is to strongly suppress the beam induced long-range wakefields, which is required to achieve high luminosity. More than thirty X-band accelerator structures with various RF parameters, cavity shapes and coupler types have been fabricated and tested since 1989. A summary of the main achievements and experiences are presented in this talk including the structure design, manufacturing techniques, high power performance, and other structure related issues. Also, the new progress in collaborating with the CLIC, high gradient structures and X-Band structure applications for RF deflectors and others are briefly introduced.

Wang, J.W.; /SLAC

2009-03-04

260

Structure of Liquid Surface and Mechanics of Surface Tension  

Microsoft Academic Search

The structure of the surface of a liquid is described by introducing a super-liquid covering the whole surface. Using this condition together with the conditions that the Gibbs-Helmholtz equation applies and that the entropy sum is constant, the thicknesses of the layer of super-liquid and the tension layer have been calculated. In the case of water, the thickness of the

Ryoji Takahashi

1983-01-01

261

Band structure of charge-ordered doped antiferromagnets  

NASA Astrophysics Data System (ADS)

We study the distribution of electronic spectral weight in a doped antiferromagnet with various types of charge order, and compare to angle resolved photoemission experiments on lightly doped La2-x Srx CuO4 (LSCO) and electron-doped Nd2-x Cex CuO4±? . Calculations on in-phase stripe and bubble phases for the electron-doped system are both in good agreement with the experiment, including, in particular, the existence of in-gap spectral weight. In addition we find that for in-phase stripes, in contrast to antiphase stripes, the chemical potential is likely to move with doping. For the hole-doped system we find that “staircase” stripes, which are globally diagonal but locally vertical or horizontal, can reproduce the photoemission data with the characteristic “Fermi arcs,” whereas pure diagonal stripes cannot. We also calculate the magnetic structure factors of such staircase stripes and find that as the stripe separation is decreased with increased doping, these evolve from diagonal to vertical, separated by a coexistence region. The results suggest that the transition from horizontal to diagonal stripes seen in neutron scattering on underdoped LSCO may be a crossover between a regime where the typical length of straight stripe segments is longer than the interstripe spacing, to one where it is shorter and that, locally, the stripes are always aligned with the Cu-O bonds.

Granath, Mats

2004-06-01

262

Microscopic surface structure of liquid alkali metals  

SciTech Connect

We report an x-ray scattering study of the microscopic structure of the surface of a liquid alkali metal. The bulk liquid structure factor of the eutectic K{sub 67}Na{sub 33} alloy is characteristic of an ideal mixture, and so shares the properties of an elemental liquid alkali metal. Analysis of off-specular diffuse scattering and specular x-ray reflectivity shows that the surface roughness of the K-Na alloy follows simple capillary wave behavior with a surface structure factor indicative of surface-induced layering. Comparison of the low-angle tail of the K{sub 67}Na{sub 33} surface structure factor with the one measured for liquid Ga and In previously suggests that layering is less pronounced in alkali metals. Controlled exposure of the liquid to H{sub 2} and O{sub 2} gas does not affect the surface structure, indicating that oxide and hydride are not stable at the liquid surface under these experimental conditions. (c) 2000 The American Physical Society.

Tostmann, H. [Division of Applied Sciences and Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States)] [Division of Applied Sciences and Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); DiMasi, E. [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States)] [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States); Pershan, P. S. [Division of Applied Sciences and Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States)] [Division of Applied Sciences and Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Ocko, B. M. [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States)] [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States); Shpyrko, O. G. [Division of Applied Sciences and Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States)] [Division of Applied Sciences and Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Deutsch, M. [Department of Physics, Bar-Ilan University, Ramat-Gan 52100, (Israel)] [Department of Physics, Bar-Ilan University, Ramat-Gan 52100, (Israel)

2000-03-15

263

UWB Band-notched Adjustable Antenna Using Concentric Split-ring Slots Structure  

NASA Astrophysics Data System (ADS)

In this paper, a kind of concentric split-ring slots structure is utilized to design a novel triple-band-notched UWB antenna. Firstly, a concentric split-ring slots structure that has a higher VSWR than that of a single slot at notch frequency is presented. What's more, the structure is very simple and feasible to obtain notched-band at different frequency by adjustment of the length of slot. Secondly, a triple-band-notched antenna, whose notched bands are at 3.52-3.81 GHz for WiMAX and 5.03-5.42 GHz and 5.73-56.17 GHz for WLAN, is designed by using this structure. At last, a compact size of 24 × 30 mm2 of the proposed antenna has been fabricated and measured and it is shown that the proposed antenna has a broadband matched impedance (3.05-14 GHz, VSWR < 2), relatively stable gain and good omnidirectional radiation patterns at low bands.

Yin, Y.; Hong, J. S.

2014-09-01

264

Photonic band structures of 1-D plasma photonic crystal with time-variation plasma density  

NASA Astrophysics Data System (ADS)

The photonic band structures of one-dimensional plasma photonic crystal (1-D PPC) with time-variation plasma density are studied by using differential transfer matrix method. Taking an exponential functional form of time as an illustration of the time-varying plasma density, we examine the photonic band structures of the 1-D PPC. The results show that the photonic band structures can be tuned correspondingly by changing the time which modifies the plasma dielectric constant in different frequency regions, especially in the range of 0

Guo, B.; Xie, M. Q.; Qiu, X. M.; Peng, L.

2012-04-01

265

Lateral energy band profile modulation in tunnel field effect transistors based on gate structure engineering  

NASA Astrophysics Data System (ADS)

Choosing novel materials and structures is important for enhancing the on-state current in tunnel field-effect transistors (TFETs). In this paper, we reveal that the on-state performance of TFETs is mainly determined by the energy band profile of the channel. According to this interpretation, we present a new concept of energy band profile modulation (BPM) achieved with gate structure engineering. It is believed that this approach can be used to suppress the ambipolar effect. Based on this method, a Si TFET device with a symmetrical tri-material-gate (TMG) structure is proposed. Two-dimensional numerical simulations demonstrated that the special band profile in this device can boost on-state performance, and it also suppresses the off-state current induced by the ambipolar effect. These unique advantages are maintained over a wide range of gate lengths and supply voltages. The BPM concept can serve as a guideline for improving the performance of nanoscale TFET devices.

Cui, Ning; Liang, Renrong; Wang, Jing; Xu, Jun

2012-06-01

266

Geometric and Electronic Structure of Reconstructed Semiconductor Surfaces  

NASA Astrophysics Data System (ADS)

The combination of high-resolution photoemission spectroscopy (PES) using synchrotron radiation, and reflection high-energy electron diffraction (RHEED), along with other techniques, have been used to examine the atomic-scale geometric and electronic properties of clean and adsorbate -covered semiconductor surfaces. The surfaces studied have been probed via core-level, valence band, and angle-resolved photoemission spectroscopy, and with the extended photoemission fine structure technique. The surface core-levels and surface states on the Si(111)-(7 x 7) surface have been used to examine submonolayer deposits of Ge onto this surface. Knowledge of the initial stages of interface formation in these systems is important due to their application in heterostructure device physics. The decomposed Si-2p and Ge-3d core levels and angle-integrated valence band spectra have been analyzed as a function of Ge coverage and annealing temperature. The results support the assignment of the lower binding energy component in both the Si-2p and Ge-3d cores to adatom emission. The implications with respect to adatom-to-rest-atom charge transfer are discussed. Lead adlayers on the (111) surfaces of Si and Ge have been examined as well. The surface phase diagram of Pb on these substrates exhibits interesting properties which arise in part due to the differing degrees of lattice matching (~4% for Pb/Si, < 1% for Pb/Ge) and the nature of the clean surface reconstructions ((7 x 7) vs. c(2 x 8)). Atomically abrupt interfaces are insured for these systems since Pb is insoluble in these surfaces even for temperatures well beyond the Pb melting point (340^circC). Thus, they are considered ideal systems to study with regard to metal-semiconductor interface formation and interface -dependent Schottky barrier studies, in contrast to reactive systems where intermixing usually occurs. This lack of interdiffusion has also allowed studies of the 2D melting of the Pb overlayers. The growth, desorption, Schottky -barrier heights, and atomic structure of the Pb-induced phases on Si and Ge are investigated via synchrotron radiation photoemission spectroscopy, along with other techniques such as reflection high-energy electron diffraction and Auger electron spectroscopy (AES). Examining the differences between these closely related systems nicely illustrates the complex interrelationship between the atomic and electronic structure of reconstructed surfaces.

Carlisle, John Arthur

267

Pseudo-atomic-orbital band theory applied to electron-energy-loss near-edge structures  

Microsoft Academic Search

The near-edge structure in inner-shell spectroscopy is a product of the slowly varying matrix element and the appropriate projected density of states. We have made use of the self-consistent pseudo-atomic-orbital band-structure-calculation method to produce accurate projected density of states. Our calculation is in good agreement with the K near-edge structure of diamond, silicon, cubic SiC, and Be2C, and the L

Xudong Weng; Peter Rez; O. F. Sankey

1989-01-01

268

Ab initio determination of potential energy surfaces for the first two UV absorption bands of SO2  

NASA Astrophysics Data System (ADS)

Three-dimensional potential energy surfaces for the two lowest singlet (A~1B1 and B~1A2) and two lowest triplet (a~3B1 and b~3A2) states of SO2 have been determined at the Davidson corrected internally contracted multi-reference configuration interaction level with the augmented correlation-consistent polarized triple-zeta basis set (icMRCI+Q/AVTZ). The non-adiabatically coupled singlet states, which are responsible for the complex Clements bands of the B band, are expressed in a 2 × 2 quasi-diabatic representation. The triplet state potential energy surfaces, which are responsible for the weak A band, were constructed in the adiabatic representation. The absorption spectrum spanning both the A and B bands, which is calculated with a three-state non-adiabatic coupled Hamiltonian, is in good agreement with experiment, thus validating the potential energy surfaces and their couplings.

Xie, Changjian; Hu, Xixi; Zhou, Linsen; Xie, Daiqian; Guo, Hua

2013-07-01

269

Theoretical determinations of semiconductor band structures and optical properties, and applications to TPV devices  

SciTech Connect

Electron band structures have been calculated from first principles using the Full Potential Linearized Augmented Plane Wave (FLAPW) computational code (1), including nonlocal screened exchange (sX-LDA) and spin-orbit effects (2, 3) for representative elemental, binary III-V and II-VI semiconductors, and configurationally optimized In{sub x}Ga{sub 1{minus}x}As. Predicted band gaps for narrow gap semiconductors (Ge, InAs, In{sub x}Ga{sub 1{minus}x}As and InSb) are all within 20{percent} of experimental values, compared with errors of over 100{percent} (negative band gaps) obtained with previous calculations based on the Local Density Approximation. Effects of In{sub x}Ga{sub 1{minus}x}As conduction band dispersion on TPV device quantum efficiency are illustrated. {copyright} {ital 1999 American Institute of Physics.}

Geller, G.B.; Blazeck, T.S. [Bettis Atomic Power Laboratory, West Miffin, Pennsylvania 15122-0079 (United States)] Wolf, W. [c/o Molecular Simulations Inc., San Diego, California 92121-3752 (United States)] Mannstadt, W. [Northwestern University, Evanston, Illinois 60208-3112 (United States)

1999-03-01

270

Valence-band density of states and surface electron accumulation in epitaxial SnO2 films  

NASA Astrophysics Data System (ADS)

The surface band bending and electronic properties of SnO2(101) films grown on r-sapphire by plasma-assisted molecular beam epitaxy have been studied by Fourier-transform infrared spectroscopy (FTIR), x-ray photoemission spectroscopy (XPS), Hall effect, and electrochemical capacitance-voltage measurements. The XPS results were correlated with density functional theory calculation of the partial density of states in the valence-band and semicore levels. Good agreement was found between theory and experiment with a small offset of the Sn 4d levels. Homogeneous Sb-doped SnO2 films allowed for the calculation of the bulk Fermi level with respect to the conduction-band minimum within the k .p carrier statistics model. The band bending and carrier concentration as a function of depth were obtained from the capacitance-voltage characteristics and model space charge calculations of the Mott-Schottky plots at the surface of Sb-doped SnO2 films. It was quantitatively demonstrated that SnO2 films have downward band bending and surface electron accumulation. The surface band bending, unoccupied donor surface-state density, and width of the accumulation region all decrease with increasing Sb concentration.

Vasheghani Farahani, S. K.; Veal, T. D.; Mudd, J. J.; Scanlon, D. O.; Watson, G. W.; Bierwagen, O.; White, M. E.; Speck, J. S.; McConville, C. F.

2014-10-01

271

Band structure and broadband compensation of absorption by amplification in layered optical metamaterials  

SciTech Connect

The frequency dependence of the gain required to compensate for absorption is determined for a layered structure consisting of alternating absorbing and amplifying layers. It is shown that the fulfillment of the same conditions is required for the existence of a band structure consisting of alternating bands allowed and forbidden for optical radiation propagation in the frequency-wave vector parametric region. Conditions are found under which the gain required for compensation is smaller than thresholds for absolute (parasitic lasing) and convective (waveguide amplification of radiation) instabilities.

Rozanov, N. N., E-mail: nrosanov@yahoo.com; Fedorov, S. V.; Savel'ev, R. S.; Sukhorukov, A. A.; Kivshar, Yu. S. [St. Petersburg State University of Information Technologies, Mechanics and Optics (Russian Federation)

2012-05-15

272

Low frequency phononic band structures in two-dimensional arc-shaped phononic crystals  

NASA Astrophysics Data System (ADS)

The low frequency phononic band structures of two-dimensional arc-shaped phononic crystals (APCs) were studied by the transfer matrix method in cylindrical coordinates. The results showed the first phononic band gaps (PBGs) of APCs from zero Hz with low modes. Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials. These properties can be efficiently used in a structure for low frequencies that are forbidden, or in a device that permits a narrow window of frequencies.

Xu, Zhenlong; Wu, Fugen; Guo, Zhongning

2012-07-01

273

Band Structure of Carbon Nanotubes in a Perpendicular Electric Field 2.0  

NSDL National Science Digital Library

The NanoEd Resource Portal, a âÂÂdynamic repository for information dissemination, research and collaborations among the community of nanoscale science and engineering education (NSEE) learners, teachers and researchers,â provides this interactive simulator. Contributed by Professor Umberto Ravaioli from the University of Illinois at Urbana-Champaign, this simulator performs "band structure calculations for zigzag and armchair type carbon nanotubes (CNT)." This band structure calculator could prove useful for both students and instructors in the field, and could prove valuable in the classroom as well.

Ravaioli, Umberto

2012-04-23

274

Longitudinal surface structures (flowstripes) on Antarctic glaciers  

NASA Astrophysics Data System (ADS)

Longitudinal surface structures (''flowstripes'') are common on many glaciers but their origin and significance are poorly understood. In this paper we present observations of the development of these longitudinal structures from four different Antarctic glacier systems (the Lambert Glacier/Amery Ice Shelf area, outlet glaciers in the Ross Sea sector, ice-shelf tributary glaciers on the Antarctic Peninsula, and the onset zone of a tributary to the Recovery Glacier Ice Stream in the Filchner Ice Shelf area). Mapping from optical satellite images demonstrates that longitudinal surface structures develop in two main situations: (1) as relatively wide flow stripes within glacier flow units and (2) as relatively narrow flow stripes where there is convergent flow around nunataks or at glacier confluence zones. Our observations indicate that the confluence features are narrower, sharper, and more clearly defined features. They are characterised by linear troughs or depressions on the ice surface and are much more common than the former type. Longitudinal surface structures within glacier flow units have previously been explained as the surface expression of localised bed perturbations but a universal explanation for those forming at glacier confluences is lacking. Here we propose that these features are formed at zones of ice acceleration and extensional flow at glacier confluences. We provide a schematic model for the development of longitudinal surface structures based on extensional flow that can explain their ridge and trough morphology as well as their down-ice persistence.

Glasser, N. F.; Gudmundsson, G. H.

2011-11-01

275

Longitudinal surface structures (flowstripes) on Antarctic glaciers  

NASA Astrophysics Data System (ADS)

Longitudinal surface structures ("flowstripes") are common on many glaciers but their origin and significance are poorly understood. In this paper we present observations of the development of these longitudinal structures from four different Antarctic glacier systems; the Lambert Glacier/Amery Ice Shelf area, the Taylor and Ferrar Glaciers in the Ross Sea sector, Crane and Jorum Glaciers (ice-shelf tributary glaciers) on the Antarctic Peninsula, and the onset zone of a tributary to the Recovery Glacier Ice Stream in the Filchner Ice Shelf area. Mapping from optical satellite images demonstrates that longitudinal surface structures develop in two main situations: (1) as relatively wide flow stripes within glacier flow units and (2) as relatively narrow flow stripes where there is convergent flow around nunataks or at glacier confluence zones. Our observations indicate that the confluence features are narrower, sharper, and more clearly defined features. They are characterised by linear troughs or depressions on the ice surface and are much more common than the former type. Longitudinal surface structures within glacier flow units have previously been explained as the surface expression of localised bed perturbations but a universal explanation for those forming at glacier confluences is lacking. Here we propose that these features are formed at zones of ice acceleration and extensional flow at glacier confluences. We provide a schematic model for the development of longitudinal surface structures based on extensional flow that can explain their ridge and trough morphology as well as their down-ice persistence.

Glasser, N. F.; Gudmundsson, G. H.

2012-03-01

276

Colloids with high-definition surface structures  

PubMed Central

Compared with the well equipped arsenal of surface modification methods for flat surfaces, techniques that are applicable to curved, colloidal surfaces are still in their infancy. This technological gap exists because spin-coating techniques used in traditional photolithographic processes are not applicable to the curved surfaces of spherical objects. By replacing spin-coated photoresist with a vapor-deposited, photodefinable polymer coating, we have now fabricated microstructured colloids with a wide range of surface patterns, including asymmetric and chiral surface structures, that so far were typically reserved for flat substrates. This high-throughput method can yield surface-structured colloidal particles at a rate of ?107 to 108 particles per operator per day. Equipped with spatially defined binding pockets, microstructured colloids can engage in programmable interactions, which can lead to directed self-assembly. The ability to create a wide range of colloids with both simple and complex surface patterns may contribute to the genesis of previously unknown colloidal structures and may have important technological implications in a range of different applications, including photonic and phononic materials or chemical sensors. PMID:17592149

Chen, Hsien-Yeh; Rouillard, Jean-Marie; Gulari, Erdogan; Lahann, Joerg

2007-01-01

277

Estimation of Bare Surface Soil Moisture and Surface Roughness Parameter Using L-Band SAR Image Data  

NASA Technical Reports Server (NTRS)

An algorithm based on a fit of the single-scattering Integral Equation Method (IEM) was developed to provide estimation of soil moisture and surface roughness parameter (a combination of rms roughness height and surface power spectrum) from quasi-polarized synthetic aperture radar (SAR) measurements. This algorithm was applied to a series of measurements acquired at L-band (1.25 GHz) from both AIRSAR (Airborne Synthetic Aperture Radar operated by Jet Propulsion Laboratory) and SIR-C (Spaceborne Imaging Radar-C) over a well-managed watershed in southwest Oklahoma. It was found that the two co-polarized backscattering coefficients and their combinations would provide the best input to the algorithm for estimation of soil moisture and roughness parameter. Application of the inversion algorithm to the co-polarized measurements of both AIRSAR and SIR-C resulted in estimated values of soil moisture and roughness parameter for bare and short-vegetated fields that compared favorably with those sampled on the ground. The root-mean-square (rms) errors of the comparison were found to be 3.4% and 1.9 dB for soil moisture and surface roughness parameter, respectively.

Shi, Jian-Cheng; Wang, James; Hsu, Ann; ONeill, Peggy; Engman, Edwin T.

1997-01-01

278

The optimal structure of two dimensional photonic crystals with the large absolute band gap.  

PubMed

This paper reports a new designed square lattice GaAs structure of two-dimensional photonic crystals with absolute band gap approach to 0.1623 (2?c/a), where a is the period of the square lattice. The optimal structure is obtained by combining the Geometry Projection Method and Finite Element Method. Both gradient information and symmetric control points are introduced to reduce the calculation cost. For benefit to the fabrication in reality, the structure is simplified by the combination of triangle and rectangular geometry. Through parameter optimization, the absolute band gap of the new structure is improved to 0.1735 (2?c/a), which is much larger than those reported before. The new PC structure is convenient and stab for fabrication, and may be found applications in the future optical devices. PMID:21996875

Wang, Donglin; Yu, Zhongyuan; Liu, Yumin; Lu, Pengfei; Han, Lihong; Feng, Hao; Guo, Xiaotao; Ye, Han

2011-09-26

279

Pseudopotential band structure of Al1-x-yGaxInyAs  

NASA Astrophysics Data System (ADS)

The fundamental energy gaps ?15v-?1c, ?15v-L1c, ?15v-X1c, of the quaternary solid solutions Al1-x-yGaxInyAs have been studied for a grid of values of the compositional parameters x and y, with the use of a model version of the coherent-potential approximation (CPA). The pseudopotential of Aymerich, Meloni, and Mula has been applied to the limiting ternary alloys by taking the charge transfer, between anionic and cationic sites, and the core repulsive part of the potential as adjustable parameters to fit the experimental bowing coefficients of the fundamental optical transitions. The values of the energy surfaces Ei(x, y) of quaternary solutions have been then obtained from the usual pseudopotential band-structure calculations with the use of, for each composition, geometrically interpolated values of the model potential parameters both for the virtual-crystal approximation term and for the CPA correction. The comparison of theoretical results to the energy-transition values obtained from the direct interpolation of the corresponding values of ternary alloys and to experimental measurements should allow us to clarify the law of combination of the nonlinear coefficients in multinary solid solutions of increasing complexity.

Aymerich, F.

1982-08-01

280

Nature inspired structured surfaces for biomedical applications.  

PubMed

Nature has created an array of superhydrophobic surfaces that possess water-repellent, self-cleaning and anti-icing properties. These surfaces have a number of potential applications in the biomedical industry, as they have the potential to control protein adsorption and cell adhesion. Natural superhydrophobic surfaces are typically composed of materials with a low intrinsic surface free-energy (e.g the cuticular waxes of lotus leaves and insect wings) with a hierarchical structural configuration. This hierarchical surface topography acts to decrease the contact area of water droplets in contact with the surface, thereby increasing the extent of the air/water interface, resulting in water contact angles greater than 150º. In order to employ these surfaces in biotechnological applications, fabrication techniques must be developed so that these multi-scale surface roughness characteristics can be reproduced. Additionally, these fabrication techniques must also be able to be applied to the material required for the intended application. An overview of some of the superhydrophobic surfaces that exist in nature is presented, together with an explanation of the theories of their wettability. Also included is a description of some of the biomedical applications of superhydrophobic surfaces and fabrication techniques that can be used to mimic superhydrophobic surfaces found in nature. PMID:21728964

Webb, H K; Hasan, J; Truong, V K; Crawford, R J; Ivanova, E P

2011-01-01

281

Effects of Electronic and Lattice Polarization on the Band Structure of Delafossite Transparent Conductive Oxides  

NASA Astrophysics Data System (ADS)

We use hybrid functionals and restricted self-consistent GW, state-of-the-art theoretical approaches for quasiparticle band structures, to study the electronic states of delafossite Cu(Al,In)O2, the first p-type and bipolar transparent conductive oxides. We show that a self-consistent GW approximation gives remarkably wider band gaps than all the other approaches used so far. Accounting for polaronic effects in the GW scheme we recover a very nice agreement with experiments. Furthermore, the modifications with respect to the Kohn-Sham bands are strongly k dependent, which makes questionable the common practice of using a scissor operator. Finally, our results support the view that the low energy structures found in optical experiments, and initially attributed to an indirect transition, are due to intrinsic defects in the samples.

Vidal, Julien; Trani, Fabio; Bruneval, Fabien; Marques, Miguel A. L.; Botti, Silvana

2010-04-01

282

Effect of gadolinium doping on the electronic band structure of europium oxide  

NASA Astrophysics Data System (ADS)

High quality films of EuO and Eu0.96Gd0.04O were grown on p-type Si(100) via pulsed laser deposition. X-ray-diffraction results show that the addition of Gd changes the growth texture from [001] to [111]. Angular-resolved photoemission spectroscopy reveals electron pockets around the X points in Gd-doped EuO, indicating that the band gap in EuO is indirect. Combined photoemission and inverse photoemission measurements show an apparent transition from n-type to p-type behavior, which is likely due to band bending near the polar (111) surface.

Colón Santana, Juan A.; An, Joonhee M.; Wu, Ning; Belashchenko, Kirill D.; Wang, Xianjie; Liu, Pan; Tang, Jinke; Losovyj, Yaroslav; Yakovkin, I. N.; Dowben, P. A.

2012-01-01

283

Correlation between surface chemistry, density and band gap in nanocrystalline WO3 thin films  

SciTech Connect

Nanocrystalline WO3 thin films were produced by sputter-deposition by varying the ratio of argon to oxygen in the reactive gas mixture during deposition. The surface chemistry, physical characteristics, and optical properties of nanocrystalline WO3 films were evaluated using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray reflectivity (XRR), and spectrophotometric measurements. The effect of ultra-microstructure was significant on the optical properties of WO3 films. The XPS analyses indicate the formation of stoichiometric WO3 with tungsten existing in fully oxidized valence state (W6+). However, WO3 films grown at high oxygen concentration (>60%) in the sputtering gas mixture were over stoichiometric with excess oxygen. XRR simulations, which are based on isotropic WO3 film - SiO2 interface - Si substrate model, indicate that the density of WO3 films is sensitive to the oxygen content in the sputtering gas. The spectral transmission of the films increased with the increasing oxygen. The band gap of these films increases from 2.78 eV to 3.25 eV with increasing oxygen. A direct correlation between the film-density and band gap in nanocrystalline WO3 films is established based on the observed results.

Vemuri, Venkata Rama Ses; Engelhard, Mark H.; Ramana, C.V.

2012-03-01

284

Real-space finite-difference calculation method of generalized Bloch wave functions and complex band structures with reduced computational cost  

NASA Astrophysics Data System (ADS)

Generalized Bloch wave functions of bulk structures, which are composed of not only propagating waves but also decaying and growing evanescent waves, are known to be essential for defining the open boundary conditions in the calculations of the electronic surface states and scattering wave functions of surface and junction structures. Electronic complex band structures being derived from the generalized Bloch wave functions are also essential for studying bound states of the surface and junction structures, which do not appear in conventional band structures. We present a novel calculation method to obtain the generalized Bloch wave functions of periodic bulk structures by solving a generalized eigenvalue problem, whose dimension is drastically reduced in comparison with the conventional generalized eigenvalue problem derived by Fujimoto and Hirose [Phys. Rev. B 67, 195315 (2003)], 10.1103/PhysRevB.67.195315. The generalized eigenvalue problem derived in this work is even mathematically equivalent to the conventional one, and, thus, we reduce computational cost for solving the eigenvalue problem considerably without any approximation and losing the strictness of the formulations. To exhibit the performance of the present method, we demonstrate practical calculations of electronic complex band structures and electron transport properties of Al and Cu nanoscale systems. Moreover, employing atom-structured electrodes and jellium-approximated ones for both of the Al and Si monatomic chains, we investigate how much the electron transport properties are unphysically affected by the jellium parts.

Tsukamoto, Shigeru; Hirose, Kikuji; Blügel, Stefan

2014-07-01

285

New band structures and an unpaired crossing in {sup 78}Kr  

SciTech Connect

High-spin states in {sup 78}Kr were studied using the {sup 58}Ni({sup 23}Na,3p) reaction at 70 MeV and the {sup 58}Ni({sup 28}Si,{alpha}4p) reaction at 130 MeV. Prompt {gamma}-{gamma} coincidences were measured using the Pitt-FSU detector array and the GAMMASPHERE-MICROBALL array. Results from these experiments have led to 26 new excitation levels, some of which have been grouped into 3 new bands. Spins were assigned based on directional correlations of oriented nuclei. Two of the new negative-parity bands appear to form a signature-partner pair based on a two-quasineutron structure, in contrast to the previously known two-quasiproton negative-parity bands. A forking has been observed at the 24{sup +} state in the yrast band, which calculations suggest may result from an unpaired crossing. The available evidence suggests oblate shapes in the yrast band coexist with prolate shapes in the negative-parity bands. {copyright} {ital 1999} {ital The American Physical Society}

Sun, H.; Doering, J.; Johns, G.D.; Kaye, R.A.; Solomon, G.Z.; Tabor, S.L. [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States)] [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States); Doering, J. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)] [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Devlin, M.; LaFosse, D.R.; Lerma, F.; Sarantites, D.G. [Department of Chemistry, Washington University, St. Louis, Missouri 63130 (United States)] [Department of Chemistry, Washington University, St. Louis, Missouri 63130 (United States); Baktash, C.; Rudolph, D.; Yu, C. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)] [Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Lee, I.Y.; Macchiavelli, A.O. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)] [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Birriel, I.; Saladin, J.X.; Winchell, D.F.; Wood, V.Q. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)] [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Ragnarsson, I. [Department of Mathematical Physics, Lund Institute of Technology, S-22100 Lund (Sweden)] [Department of Mathematical Physics, Lund Institute of Technology, S-22100 Lund (Sweden)

1999-02-01

286

New band structures and an unpaired crossing in {sup 78}Kr  

SciTech Connect

High-spin states in {sup 78}Kr were studied using the {sup 58}Ni({sup 23}Na,3p) reaction at 70 MeV and the {sup 58}Ni({sup 28}Si,{alpha}4p) reaction at 130 MeV. Prompt {gamma}-{gamma} coincidences were measured using the Pitt-FSU detector array and the GAMMASPHERE-MICROBALL array. Results from these experiments have led to 26 new excitation levels, some of which have been grouped into 3 new bands. Spins were assigned based on directional correlations of oriented nuclei. Two of the new negative-parity bands appear to form a signature-partner pair based on a two-quasineutron structure, in contrast to the previously known two-quasiproton negative-parity bands. A forking has been observed at the 24{sup +} state in the yrast band, which calculations suggest may result from an unpaired crossing. The available evidence suggests oblate shapes in the yrast band coexist with prolate shapes in the negative-parity bands.

Sun, H.; Doring, J.; Johns, R.A.; Solomon, G.; Tabor, S.; Devlin, M.; LaFosse, D.; Lerma, F.; Sarantites, D.; Baktash, C.; Rudolph, D.; Yu, C.H.; Lee, I.Y.; Macchiavelli, A.; Birriel, I.; Saladin, J.; Winchell, D.; Wood, V.Q.; Ragnarsson, I.

1998-07-06

287

C-band measurement of radar backscatter from the ocean surface during SWADE  

NASA Technical Reports Server (NTRS)

A preliminary analysis of backscatter measurements collected during the joint NASA/ONR Surface Wave Dynamics Experiment (SWADE) by a C-band scatterometer (C-SCAT) is presented. Data were collected during a total of ten flights on board the NASA/Ames C-130B off the coast of Virginia. These backscatter measurements are vertically polarized, and were obtained over a full 360* in azimuth, at incidence angles ranging from 20 to 50 . The data set is now in a state where it can provide a unique test bed for normalized radar cross section (NRCS) model functions because of the variety of phenomena encountered, and the quantity and quality of the measurements.

Carson, S. C.; Mcintosh, R. E.; Paylor, A. W.; Li, F.; Neumann, G.; Mclaughlin, D. J.

1992-01-01

288

A terahertz band-pass resonator based on enhanced reflectivity using spoof surface plasmons  

NASA Astrophysics Data System (ADS)

We demonstrate a band-pass resonator in the terahertz (THz) range, based on a frequency-selective designer reflector. The resonator consists of a parallel-plate waveguide, a designed groove pattern cut into the output facet of each plate, and a reflecting mirror. The patterned facet supports a spoof surface plasmon mode, which modifies the reflectivity at the waveguide output facet by interacting with the waveguide mode. By tuning the geometrical parameters of the groove pattern, the reflectivity at the patterned output facet can be increased up to ?100% for a selected frequency. Broadband THz waves are quasi-optically coupled into this resonator and reflected multiple times from the patterned facet. This leads to a narrowing of the spectrum at the selected frequency. The Q value of the resonator increases as the number of reflections on the patterned facet increases, reaching ?25 when the THz wave has experienced 12 reflections.

Liu, Jingbo; Mendis, Rajind; Mittleman, Daniel M.

2013-05-01

289

Identification of the Au Coverage and Structure of the Au /Si(111)-(5×2) Surface  

NASA Astrophysics Data System (ADS)

We identify the atomic structure of the Au /Si(111)-(5×2) surface by using density functional theory calculations. With seven Au atoms per unit cell, our model forms a bona fide (5×2) atomic structure, which is energetically favored over the leading model of Erwin et al. [Phys. Rev. B 80, 155409 (2009), 10.1103/PhysRevB.80.155409], and well reproduces the Y-shaped and V-shaped (5×2) STM images. This surface is metallic with a prominent half filled band of surface states, mostly localized around the Au-chain area. The correct identification of the atomic and band structure of the clean surface further clarifies the adsorption structure of Si adatoms and the physical origin of the intriguing metal-to-insulator transition driven by Si adatoms.

Kwon, Se Gab; Kang, Myung Ho

2014-08-01

290

PHYSICAL REVIEW B 85, 195405 (2012) Graphene on Ru(0001): Evidence for two graphene band structures  

E-print Network

grown on single-crystal substrates such as Ru(0001) is extremely ordered,1­10 but characterized by two for the "split" valence-band structure of graphene on Ru(0001) (Ref. 25) and SiC.26 The moir´e resulting from

Goodman, Wayne

291

Inuence of band 3 protein absence and skeletal structures on amphiphile-and Ca2  

E-print Network

In£uence of band 3 protein absence and skeletal structures on amphiphile- and Ca2 -induced shape Amphiphiles which induce either spiculated (echinocytic) or invaginated (stomatocytic) shapes in human. Both qualitative and quantitative differences were found. Amphiphiles induced no gross morphological

Iglic, Ales

292

Photonic band structures of two-dimensional systems containing metallic components  

Microsoft Academic Search

By use of the plane-wave method, we calculate the photonic band structure for electromagnetic waves of E and H polarization propagating in a system consisting of an infinite array of identical, infinitely long, parallel, metal cylinders of circular cross section, embedded in vacuum, whose intersection with a perpendicular plane forms a simple square or triangular lattice. The dielectric function of

V. Kuzmiak; A. A. Maradudin; F. Pincemin

1994-01-01

293

Calculations of strain-modified anatase TiO2 band structures  

Microsoft Academic Search

In order to theoretically quantify a strain-inducing method that we use to engineer the material properties of anatase titania, we studied its electronic band structure over a range of biaxial strain by utilizing both the density functional theory within the generalized gradient approximation (GGA) and quasiparticle theory calculations within the GW approximation. This strain-modified material is suitable for use as

Lukas Thulin; John Guerra

2008-01-01

294

A Band of Unusual Structure Probably Due to a Highly Unstable Calcium Hydride Molecule  

Microsoft Academic Search

In the spectrum of the calcium are in hydrogen at low pressure (best 3-20 mm) an isolated band occurs in association with the lines of neutral calcium. The wide spacing of the lines and the absence of appreciable isotope effect practically assure its hydride origin. The simple structure indicates a diatomic molecule. Reproductions and measurements of the lines are given.

Robert S. Mulliken

1925-01-01

295

Observation of 'Band' Structures in Spacecraft Observations of Inner Magnetosphere Plasma Ions  

NASA Astrophysics Data System (ADS)

In previous studies, several authors have reported inner magnetosphere observations of proton distributions confined to narrow energy bands in the range of 1-25 keV (Smith and Hoffman (1974), etc). These structures have been described as "nose structures", with reference to their appearance in energy-time spectrograms and are also known as "bands" if they occur for extended periods of time. Statistical surveys (Buzulukova et al. (2003); Vallat et al. (2007)) of these features in Interball and Cluster data highlight the presence of single nose in nightside sectors and multi-nose strutures in the dayside sectors. We examine Double-Star TC1 HIA data mainly recorded in the equatorial plane of the inner magnetosphere (L<15) to see how observations of "multi-banded structures" compare to the observations from more inclined orbits of Cluster and Interball. We investigate the properties of these multi-banded structures and carry out a statistical survey analysing them as a function of geomagnetic activity. This is a comparison study to a similar study conducted using DoubleStar TC-1 PEACE electron data.

Mohan, Kirthika; Fazakerley, Andrew; Grimald, Sandrine; Dandouras, Iannis; Owen, Chris

2014-05-01

296

Removing solids improves response of grass to surface-banded dairy manure slurry: a multiyear study.  

PubMed

Removing solids from slurry manure helps balance nutrients to plant needs and may increase soil infiltration rate toreduce loss of ammonia. The long-term effects of applying the separated liquid fraction (SLF) of dairy slurry with surface banding applicators are not well known. This 6-yr study compared the yield, N recovery, and stand persistence of tall fescue (Festuca arundinacea Schreb.) receiving SLF at 300 (SLF300) and 400 (SLF400) kg ha(-1) yr(-1) of total ammoniacal N (TAN); whole dairy slurry (WS) at 200 (WS200), 300 (WS300), and 400 (WS400) kg TAN ha(-1) yr(-1); and mineral fertilizerat 300 kg N ha(-1) yr(-1). The slurries were applied four times per year by surface banding, a technique that reduces ammonia emission and canopy contamination. Grass yield and N uptake were significantly higher for SLF300 than WS300 atequivalent rates of TAN. At similar total N, yield and N uptake were much greater for SLF than WS (2 Mg DM ha(-1) and 75 kg N ha(-1), respectively). Apparent total N recoverywas 63% greater for SLF300 than WS300 due to less ammonia loss and less immobile N. The apparent recovery of total N was 31% higher for Fert300 than for SLF300. Yield and N uptake for SLF300 and WS300 were similar in Harvests 1 and4, but SLF had higher values under hot and dry conditions in Harvests 2 and 3. Using SLF rather than WS will increase crop yield and allow higher application volumes near barns, whichwill reduce hauling costs. PMID:21520746

Bittman, S; Hunt, D E; Kowalenko, C G; Chantigny, M; Buckley, K; Bounaix, F

2011-01-01

297

Structure and Evolution of Convection Band Occurred over the Korean Peninsula  

NASA Astrophysics Data System (ADS)

A significant portion of the annual precipitation on the Korean peninsula is produced by heavy precipitation systems (HPSs) during summer. HPSs over the Korean peninsula could be classified into four major types (convection bands, cloud clusters, isolated thunderstorms, and squall lines) by phenomenological analysis. Among four major types of HPSs, convection bands (CBs) tend to concentrate a large amount of rainfall over limited area due to their quasi-stationary behavior for several hours. Convective cells embedded in CB move along the band and new cells are continuously formed in the upstream of the band. In this study, the structure and evolution of CB have been investigated using NCEP Climate Forecast System Reanalysis (CFSR) data and Weather Research and Forecasting (WRF) model. Thirty CB cases occurred during 2000-2010 were selected to conduct composite analysis. We obtained several profiles which represent northern area (NA), southern area (SA), and upstream area (UA) of CB by composite analysis. Modest band-perpendicular wind component (5 m s-1) is found in the level of 925-1000 hPa in SA, while band-perpendicular wind component of NA is nearly zero. Additionally, equivalent potential temperature in the lower-troposphere of SA is about 10 K larger than that of NA. Low-level band-perpendicular wind component of SA seems to play an important role in the development of CB by providing the environment for large-scale convergence and transporting warm and moist air from southern area of CB. Band-parallel wind component is predominant in the middle- and lower-troposphere. On the basis of the results of composite analysis, ideal simulation for the evolution of CB was set up. The analysis for the evolution of CB is in progress.

Kim, W.; Lee, T.

2011-12-01

298

Investigations on crystalline structure and optical band gap of nearly stoichiometric LiNbO3 nanoparticles  

NASA Astrophysics Data System (ADS)

The structural and optical characteristics of nearly stoichiometric lithium niobate, LiNbO3 nanoparticles have been studied. The results are very different compared to the bulk LiNbO3 single crystals. The nanoparticles were synthesized by citrate gel method and the phase was confirmed by powder X-ray diffraction. The size and size distribution of the nanoparticles were obtained by XRD, SEM, TEM and DLS experiments. The particles were in the range of 50-200 nm and most of the particles are about 100 nm of size. The lattice parameters obtained from selected area electron diffraction are aH = 5.213 Å and cH = 14.026 Å for hexagonal system which are slightly larger than the other reported values (JCPDS). The optical properties were obtained from optical absorption spectroscopy in UV-vis.-NIR and IR (FTIR) range, the electronic band gap structure were determined from the fundamental absorption edge in the UV region. The indirect band gap was of 4.78 eV where as the direct gap was of 6.0 eV which are much larger than the other experimental values. The absorption features in the UV range indicate the discrete nature of conduction band and the allowed energy levels in the forbidden gap appeared due to surface defects.

Debnath, C.; Kar, S.; Verma, S.; Bartwal, K. S.

2014-11-01

299

Narrow band filter using 1D periodic structure with defects for DWDM systems  

NASA Astrophysics Data System (ADS)

A 1D binary periodic structure with defect has been analysed using Transfer Matrix Method. For a particular nine layered structure of SiO2 and InP, a number of full stop bands (in other words, zero passbands or forbidden bands) at different regions of the spectrum under investigation are observed. Introducing a central spatial defect in the system by adjusting the layer width, it is possible to achieve an extremely narrow passband centred on 1554.9 nm in the 7th forbidden band. Moreover by varying the defect width, the number of passbands can be increased. These passbands have flat and 100% stopband and hence can be better candidate to drop single or multiple frequencies in WDM systems. It is further observed that with increase in the number of layers and/or defect width, the number of mini pass bands outside the original forbidden band also increases. Also by FDTD simulation it is seen that the field is localised within the defect for the passband frequency.

Ghosh, R.; Ghosh, K. K.; Chakraborty, R.

2013-02-01

300

Design of UWB monopole antenna with dual notched bands using one modified electromagnetic-bandgap structure.  

PubMed

A modified electromagnetic-bandgap (M-EBG) structure and its application to planar monopole ultra-wideband (UWB) antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR < 2 over UWB 3.1-10.6?GHz, except for the rejected bands of the world interoperability for microwave access (WiMAX) and the wireless local area network (WLAN) at 3.5?GHz and 5.5?GHz, respectively. PMID:24170984

Liu, Hao; Xu, Ziqiang

2013-01-01

301

Design of UWB Monopole Antenna with Dual Notched Bands Using One Modified Electromagnetic-Bandgap Structure  

PubMed Central

A modified electromagnetic-bandgap (M-EBG) structure and its application to planar monopole ultra-wideband (UWB) antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR < 2 over UWB 3.1–10.6?GHz, except for the rejected bands of the world interoperability for microwave access (WiMAX) and the wireless local area network (WLAN) at 3.5?GHz and 5.5?GHz, respectively. PMID:24170984

Xu, Ziqiang

2013-01-01

302

Effects of strain on the band structure of group-III nitrides  

NASA Astrophysics Data System (ADS)

We present a systematic study of strain effects on the electronic band structure of the group-III-nitrides (AlN, GaN and InN) in the wurtzite phase. The calculations are based on density functional theory with band-gap-corrected approaches including the Heyd-Scuseria-Ernzerhof hybrid functional (HSE) and quasiparticle G0W0 methods. We study strain effects under realistic strain conditions, hydrostatic pressure, and biaxial stress. The strain-induced modification of the band structures is found to be nonlinear; transition energies and crystal-field splittings show a strong nonlinear behavior under biaxial stress. For the linear regime around the experimental lattice parameters, we present a complete set of deformation potentials (acz, act, D1, D2, D3, D4, D5, D6) that allows us to predict the band positions of group-III nitrides and their alloys (InGaN and AlGaN) under realistic strain conditions. The benchmarking G0W0 results for GaN agree well with the HSE data and indicate that HSE provides an appropriate description for the band structures of nitrides. We present a systematic study of strain effects on the electronic band structure of the group-III nitrides (AlN, GaN, and InN). We quantify the nonlinearity of strain effects by introducing a set of bowing parameters. We apply the calculated deformation potentials to the prediction of strain effects on transition energies and valence-band structures of InGaN alloys and quantum wells (QWs) grown on GaN, in various orientations (including c-plane, m-plane, and semipolar). The calculated band gap bowing parameters, including the strain effect for c-plane InGaN, agree well with the results obtained by hybrid functional alloy calculations. For semipolar InGaN QWs grown in (202¯1), (303¯1), and (303¯1¯) orientations, our calculated deformation potentials have provided results for polarization ratios in good agreement with the experimental observations, providing further confidence in the accuracy of our values.

Yan, Qimin; Rinke, Patrick; Janotti, Anderson; Scheffler, Matthias; Van de Walle, Chris G.

2014-09-01

303

Simulation of pulsed optical logic gates based on photonic band gap structures  

Microsoft Academic Search

The change in the refractive index of GaAs due to the light-induced generation of nonequilibrium charge carriers is shown to substantially change the transmission of a one-dimensional GaAs\\/GaAlAs photonic band-gap structure, allowing low-threshold photonic-crystal optical logic gates to be created. Elementary logic operations of the Boolean algebra performed with nonlinear PBG structures, including the biconditional implication, modulo-two addition, Peirce's arrow,

Igor Nefedov; Yurii Morozov; Viktor Gusyatnikov; Aleksei Zheltikov

2001-01-01

304

Band Structure Calculations for Two-Dimensional Plasma Photonic Crystals in Honeycomb Lattice Arrangement  

Microsoft Academic Search

We propose an approach originating from plane wave expansion method to calculate band structure for two types of honeycomb lattice two-dimensional plasma photonic crystals. The eigenvalue equations of E-polarization for two types of structures, which depend on the honeycomb lattice realization(plasma rods immersed in dielectric background or vice versa), are derived respectively. A standard linearization technique which solves the general

Xiang-Kun Kong; Shao-Bin Liu; Hai-Feng Zhang; Liang Zhou; Chun-Zao Li

2011-01-01

305

Photonic Crystal and Photonic BandGap Structures for Light Extraction and Emission Control  

Microsoft Academic Search

Research into photonic crystal (PhC) and photonic band-gap (PBG) structures has been motivated, from the start, by their possible\\u000a use in controlling, modifying and enhancing the light emission process from high refractive index solid materials. This chapter\\u000a considers the possible role of such structures when incorporated into semiconductor diode based light-emitting devices. Both\\u000a light-emitting diodes (LEDs) and lasers will be

Richard M. De La Rue

306

Electronic structure of point defectson insulator surfaces  

Microsoft Academic Search

A review is presented of recent theoretical and experimental work dealing with the electronic structure of point-defects on the surfaces of dielectric materials. The term ``point-defect'' is taken to include, for example, color centers in alkali halides, alkaline-earth oxides and Si02 and partially-reduced metal ions on the surfaces of transition-metal compounds (e.g., Ti+3 on TiO2). The second section is a

Victor M. Bermudez

1981-01-01

307

Fourier transform infrared analysis of amide III bands of proteins for the secondary structure estimation  

NASA Astrophysics Data System (ADS)

Protein secondary structure has been analyzed using a Fourier transform infrared spectroscopic method in the amide III region. Although extensive work has been done on protein secondary structure using the amide I region (1700 - 1600 cm-1), the amide III region has not been utilized in the past for its potential in protein structural analysis. One of the major reasons for non-use of the amide III vibrations is perhaps the very weak signal in the amide III frequency region (1200 - 1350 cm-1). However, benefits of using the amide III region are substantial. For example, water vibrations do not interfere with the protein spectrum unlike in the amide I region. In the amide III region, the protein spectrum is better resolved into individual bands than in the amide I region. This feature allows for a greater ease in peak definement of the protein spectra. In the amide III region, the bands for the individual secondary structures ((alpha) -helix, (beta) -sheet and random coils) do not overlap as much as they do in the amide I region. This lack of overlapping allows for easier and a more reliable means of peak assignment, and secondary structure band positions are easier to determine. Amide III region of protein IR spectra appears to be a valuable tool in estimating the amount of secondary structure present in proteins.

Singh, Bal R.; DeOliveira, Daniel B.; Fu, Fen-Ni; Fuller, Michael P.

1993-05-01

308

Using Superlattice Ordering to Reduce the Band Gap of Random (In,Ga)As/InP Alloys to a Target Value Via the Inverse Band Structure Approach  

SciTech Connect

Thermophotovoltaic (TPV) devices are intended to absorb photons from hot blackbody radiating objects, often requiring semiconductor absorbers with band gap of {approx_equal} 0.6 eV. The random In{sub x}Ga{sub 1-x}As alloy lattice matched (x{sub In}=0.53) to a (001) InP substrate has a low-temperature band gap of 0.8 eV, about 0.2 eV too high for a TPV absorber. Bringing the band gap down by raising the In concentration induces strain with the substrate, leading to a two-dimensional (2D) {yields} three-dimensional (3D) morphological transition occurring before band gaps suitable for TPV applications are achieved. We use the inverse band structure approach, based on a genetic algorithm and empirical pseudopotential calculations, to search for lattice-matched InAs/GaAs multiple-repeat unit structures with individual layer thicknesses lower than the critical thickness for a 2D {yields} 3D transition. Despite the fact that quantum confinement usually increases band gaps, we find a quantum superlattice structure with the required reduced gap (and a significant optical transition) that matches all target requirements. This is explained by the predominance of (potential-energy) level anticrossing effects over (kinetic) quantum confinement effects.

Piquini, P.; Zunger, A.

2008-10-01

309

A compact broadband microstrip patch antenna with defective ground structure for C-Band applications  

NASA Astrophysics Data System (ADS)

A novel design of a circular patch antenna having defected ground structure is presented in this communication. The antenna is designed for C-band applications. A wide bandwidth of 60.3% (4.04-7.28) GHz is obtained in the C-band frequency range 4-8 GHz. It is also found through parametric analysis that shape and dimensions of the finite ground plane and slots in the patch are the key factors in improving the bandwidth of the proposed geometry. The antenna is fabricated using FR-4 substrate and parameters like return loss, VSWR and input impedance are measured experimentally.

Rawat, Sanyog; Sharma, K. K.

2014-09-01

310

Multi-use applications of dual-band infrared (DBIR) thermal imaging for detecting obscured structural defects  

SciTech Connect

Precise dual-band infrared (DBIR) thermal imaging provides a useful diagnostic tool for wide-area detection of defects from corrosion damage in metal airframes, heat damage in composite structures and structural damage in concrete bridge decks. We use DBIR image ratios to enhance surface temperature contrast, remove surface emissivity noise and increase signal-to-clutter ratios. We clarify interpretation of hidden defect sites by distinguishing temperature differences at defect sites from emissivity differences at clutter sites. This reduces the probability of false calls associated with misinterpreted image data. For airframe inspections, we map flash-heated defects in metal structures. The surface temperature rise above ambient at corrosion-thinned sites correlates with the percentage of material loss from corrosion thinning. For flash-heated composite structures, we measure the temperature-time history which relates to the depth and extent of heat damage. In preparation for bridge deck inspections, we map the natural day and night temperature variations at known concrete slab delamination sites which heat and coot at different rates than their surroundings. The above-ambient daytime and below-ambient nightime delamination site temperature differences correlate with the volume of replaced concrete at the delamination sites.

Del Grande, N.K.; Durbin, P.F.

1994-05-01

311

The dependence of S-band sea surface brightness and temperature on wind vector at normal incidence  

SciTech Connect

Aircraft measurements of the S-band sea surface brightness temperature at nadir as a function of wind speed and wind direction were carried out in various regions in 1985--1989. Data set of 65 circular flights was analyzed. It is shown that for water temperature recovering the wind direction is to be taken into account. This paper considers the relationship between S-band sea surface brightness temperature at nadir view angle and near surface wind speed as well as wind direction. The information of radiometer and scatterometer aircraft data set (RSAD) obtained at Space Research Institute was used. The 1985--1989 aircraft experiments in Pacific Ocean near Kamchatka peninsula and in Barents Sea were analyzed. The S-band radiometer data were used for the investigation due to their potential application of water temperature recovering and in this case the precise knowledge of wind speed dependence is very important.

Trokhimovski, Y.G. [NOAA/ERL/ETL/ET5, Boulder, CO (United States)] [NOAA/ERL/ETL/ET5, Boulder, CO (United States); Bolotnikova, G.A.; Grechko, S.I.; Kuzmin, A.V. [IKI RAN, Moscow (Russian Federation)] [IKI RAN, Moscow (Russian Federation); Etkin, V.S.

1995-07-01

312

Spin filtering with EuO: Insight from the complex band structure  

NASA Astrophysics Data System (ADS)

Spin-filter tunneling is a promising way to create highly-spin-polarized currents. So far the understanding of the spin-filtering effect has been limited to a free-electron description based on the spin-dependent tunneling barrier height. In this work we explore the complex of EuO as a representative ferromagnetic insulator used in spin-filter tunneling experiments and show that the mechanism of spin filtering is more intricate than it has been previously thought. We demonstrate the importance of the multiorbital band structure with an indirect band gap for spin-filter tunneling. By analyzing the symmetry of the complex bands and the decay rates for different wave vectors and energies we draw conclusions about spin-filter efficiency of EuO. Our results provide guidelines for the design of spin-filter tunnel junctions with enhanced spin polarization.

Lukashev, Pavel V.; Wysocki, Aleksander L.; Velev, Julian P.; van Schilfgaarde, Mark; Jaswal, Sitaram S.; Belashchenko, Kirill D.; Tsymbal, Evgeny Y.

2012-06-01

313

G0W0 band structure of CdWO4.  

PubMed

The full quasiparticle band structure of CdWO4 is calculated within the single-shot GW (G0W0) approximation using maximally localized Wannier functions, which allows one to assess the validity of the commonly used scissor operator. Calculations are performed using the Godby-Needs plasmon pole model and the accurate contour deformation technique. It is shown that while the two methods yield identical band gap energies, the low-lying states are given inaccurately by the plasmon pole model. We report a band gap energy of 4.94 eV, including spin-orbit interaction at the DFT-LDA (density functional theory-local density approximation) level. Quasiparticle renormalization in CdWO4 is shown to be correlated with localization distance. Electron and hole effective masses are calculated at the DFT and G0W0 levels. PMID:24599225

Laasner, Raul

2014-03-26

314

Quasiparticle excitations in valence-fluctuation materials: effects of band structure and crystal fields  

SciTech Connect

Evidence is now quite strong that the elementary hybridization model is the correct way to understand the lattice-coherent Fermi liquid regime at very low temperatures. Many-body theory leads to significant renormalizations of the input parameters, and many of the band-theoretic channels for hybridization are suppressed by the combined effects of Hund's-rule coupling, crystal-field splitting, and the f-f Coulomb repulsion U. Some exploratory calculations based on this picture are described, and some inferences are drawn about the band structures of several heavy-fermion materials. These inferences can and should be tested by suitably modified band-theoretic calculations. We find evidence for a significant Baber-scattering contribution in the very-low-temperature resistivity. A new mechanism is proposed for crossover from the coherent Fermi-liquid regime to the incoherent dense-Kondo regime. 28 refs.

Brandow, B.H.

1985-01-01

315

Calculating the Energy Band Structure Using Sampling and Greens Function Techniques  

E-print Network

In this paper, a new method based on Greens function theory and Fourier transform analysis has been proposed for calculating band structure with high accuracy and low processing time. This method utilizes sampling of potential energy in some points of crystals unit cell with Dirac delta functions, then through lattice Fourier transform gives us a simple and applicable formula for most of nanostructures. Sampling of potential in a crystal lattice of any kind contains accurate approximation of actual potential energy of atoms in the crystal. The step forward regarding the method concentrated on two novel ideas, Firstly, the potential was sampled and approximated by delta functions spread over the unit cell. Secondly, the principal equation of lattice is translated into reciprocal lattice and resulted in a huge reduction of calculations. By this method, it is possible to extract the band structure of any one, two or three dimensional crystalline structure.

Khoshnegar, Milad; Arjmandi, Nima; Khorasani, Sina

2012-01-01

316

Structural, photonic band-gap, and luminescence properties of the opal-erbium composite  

Microsoft Academic Search

Erbium oxide and silicates were embedded in the pores of synthetic opal by using the chemical bath deposition technique. Electron-microscopic\\u000a images showed the synthesized compounds to be deposited predominantly in a thin uniform layer on the inner surface of the\\u000a pores. An analysis of the transmittance spectra suggested that the opal-erbium composite thus obtained retained the photonic\\u000a band-gap properties of

G. N. Aliev; V. G. Golubev; A. A. Dukin; D. A. Kurdyukov; A. V. Medvedev; A. B. Pevtsov; L. M. Sorokin; J. L. Hutchison

2002-01-01

317

Determination of the valence band structure of an alkali phosphorus oxynitride glass: A synchrotron XPS study on LiPON  

NASA Astrophysics Data System (ADS)

Lithium phosphorus oxynitride (LiPON) is a solid state electrolyte commonly used in thin film batteries (TFBs). Advanced TFBs face the issue of detrimental electrode-electrolyte interlayer formation, related to the electronic structure of the interface. In this contribution, we study the valence band structure of LiPON using resonant photoemission and synchrotron photoemission with variable excitation energies. The identification of different valence band features is done according to the known valence band features of meta- and orthophosphates. Additionally we compare our results with partial density of states simulations from literature. We find that the valence band structure is similar to the known metaphosphates with an additional contribution of nitrogen states at the top of the valence band. From the results we conclude that synchrotron X-ray photoemission (XPS) is a useful tool to study the valence band structure of nitridated alkali phosphate glasses.

Schwöbel, André; Precht, Ruben; Motzko, Markus; Carrillo Solano, Mercedes A.; Calvet, Wolfram; Hausbrand, René; Jaegermann, Wolfram

2014-12-01

318

Structure of the doublet bands in doubly odd nuclei: The case of {sup 128}Cs  

SciTech Connect

The structure of the {Delta}J=1 doublet bands in {sup 128}Cs is investigated within the framework of the interacting vector boson-fermion model. A new, purely collective interpretation of these bands is given on the basis of the used boson-fermion dynamical symmetry of the model. The energy levels of the doublet bands as well as the absolute B(E2) and B(M1) transition probabilities between the states of both yrast and yrare bands are described quite well. The observed odd-even staggering of both B(M1) and B(E2) values is reproduced by the introduction of an appropriate interaction term of quadrupole type, which produces such a staggering effect in the transition strengths. The calculations show that the appearance of doublet bands in certain odd-odd nuclei could be a consequence of the realization of a larger dynamical symmetry based on the noncompact supersymmetry group OSp(2{Omega}/12,R).

Ganev, H. G. [Institute of Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Sofia 1784 (Bulgaria); Brant, S. [Department of Physics, Faculty of Science, University of Zagreb, 10000 Zagreb (Croatia)

2010-09-15

319

Structure of InSb(001) surface.  

PubMed

The InSb(001) surface has been studied experimentally, using room temperature scanning tunnelling microscopy (RT STM), and theoretically, using ab initio density functional theory (DFT) calculations. RT experimental STM images show bright lines running along the bulk crystal [110] direction. Resolved features between the bright lines whose appearance depends on the applied bias voltage confirm clearly the c(8×2) reconstruction of this surface. Our calculations, which are reported for this surface for the first time, include the reconstructed 4×2 and c(8×2) surfaces, the latter according to the so-called ?-model proposed previously by Lee et al and Kumpf et al. A 'defective' structure proposed previously by Kumpf et al, which contains an extra In atom within a top bilayer is also considered. In all cases, we obtained stable structures. Calculated STM images for the c(8×2) reconstruction obtained using the Tersoff-Hamann approximation compare extremely well with the experimental ones. We also find that the defect structure may not be clearly visible in the STM images. Finally, a brief discussion is given on the other, although closely related, phase of the same surface observed previously in low temperature (LT) experimental STM images (Goryl et al 2007 Surf. Sci. 601 3605). PMID:21386467

Toton, Dawid; He, Jiangping; Goryl, Grzegorz; Kolodziej, Jacek J; Godlewski, Szymon; Kantorovich, Lev; Szymonski, Marek

2010-07-01

320

Electronic band structures and x-ray photoelectron spectra of ZrC, HfC, and TaC  

Microsoft Academic Search

The band structures and densities of states (DOSs) of ZrC, HfC, and TaC were calculated by the augmented-plane-wave method, and the x-ray photoelectron spectra of valence bands of these compounds were observed. The theoretical energy distribution curves (EDCs) were in good agreement with the experimental EDCs. These band structures resemble each other and also those of TiC obtained by our

Hideo Ihara; Masayuki Hirabayashi; Hiroshi Nakagawa

1976-01-01

321

Structural vs electronic origin of renormalized band widths in TTF-TCNQ: An angular dependent NEXAFS study  

NASA Astrophysics Data System (ADS)

We have performed angle-dependent near-edge x-ray absorption fine structure measurements in the Auger electron yield mode on the correlated quasi-one-dimensional organic conductor tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) in order to determine the orientation of the molecules in the topmost surface layer. We find that the tilt angles of the molecules with respect to the one-dimensional axis are essentially the same as in the bulk. Thus, we can rule out surface relaxation as the origin of the renormalized band widths which were inferred from the analysis of photoemission data within the one-dimensional Hubbard model. Thereby, recent theoretical results are corroborated which invoke long-range Coulomb repulsion as alternative explanation to understand the spectral dispersions of TTF-TCNQ quantitatively within an extended Hubbard model.

Sing, M.; Meyer, J.; Hoinkis, M.; Glawion, S.; Blaha, P.; Gavrila, G.; Jacobsen, C. S.; Claessen, R.

2007-12-01

322

Triaxial projected shell model description of high-spin band-structures in 103,105Rh isotopes  

NASA Astrophysics Data System (ADS)

High-spin band structures in odd-proton 103,105Rh are investigated using the microscopic triaxial projected shell model approach. It is demonstrated that the observed band structures built on one- and three-quasiparticle states are reproduced reasonably well in the present work. Further, it is evident from the analysis of the projected wavefunctions that side-band in the low-spin regime is the normal ?-band built on the ground-state configuration. However, in the high-spin regime, the side band is shown to be highly mixed and ceases to be a ?-band. We provide a complete set of electromagnetic transition probabilities for the two bands and the experimental measurements are desirable to test the predictions of the present work.

Bhat, G. H.; Sheikh, J. A.; Dar, W. A.; Jehangir, S.; Palit, R.; Ganai, P. A.

2014-11-01

323

The Glacier and Ice Surface Topography Interferometer: UAVSAR's Single-pass Ka-Band Interferometer  

NASA Astrophysics Data System (ADS)

In May 2009 a new radar technique for mapping ice surface topography was demonstrated in a Greenland campaign as part of the NASA International Polar Year (IPY) activities. This was achieved with the airborne Glacier and Ice Surface Topography Interferometer (GLISTIN-A): a 35.6 GHz single-pass interferometer. Although the technique of using radar interferometry for mapping terrain has been demonstrated before, this is the first such application at millimeter-wave frequencies. The proof-of-concept demonstration was achieved by interfacing Ka-band RF and antenna hardware with the Uninhabited Airborne Vehicle Synthetic Aperture Radar (UAVSAR). The GLISTIN-A was implemented as a custom installation of the NASA Dryden Flight Research Center Gulfstream III. Instrument performance indicates swath widths over the ice between 5-7km, with height precisions ranging from 30cm-3m at a posting of 3m x 3m. Processing challenges were encountered in achieving the accuracy requirements on several fronts including, aircraft motion sensitivity, multipath and systematic drifts. However, through a combination of processor optimization, a modified phase-screen and motion-compensation implementations were able to minimize the impact of these systematic error sources. We will present results from the IPY data collections including system performance evaluations and imagery. This includes a large area digital elevation model (DEM) collected over Jakobshavn glacier as an illustrative science data product. Further, by intercomparison with the NASA Wallops Airborne Topographic Mapper (ATM) and calibration targets we quantify the interferometric penetration bias of the Ka-band returns into the snow cover. Following the success of the IPY campaign, we are funded under the Earth Science Techonology Office (ESTO) Airborne Innovative Technology Transition (AITT) program to transition GLISTIN-A to a permanently-available pod-only system compatible with unpressurized operation. In addition fundamental system upgrades will greatly enhance the performance and make wider-swath and higher altitude operation possible. We will show results from first flights of GLISTIN-A and summarize the plans for the near future including GLISTIN-H: GLISTIN on the NASA Global Hawk Spring 2013.

Moller, D.; Hensley, S.; Sadowy, G.; Wu, X.; Carswell, J.; Fisher, C.; Michel, T.; Lou, Y.

2012-12-01

324

Surface atomic geometry and electronic structure of II--VI cleavage faces  

SciTech Connect

Recent models of the electronic structure and surface atomic geometries on wurtzite-structure CdS and CdSe have been extended to encompass zinc-blende structure CdTe. The driving force for the surface reconstruction of the cleavage faces of all these materials is the lowering in energy of a band of anion dangling bond surface states accompanied by their acquisition of back-bonding character. The resulting reconstructed surface is characterized by the eigenvalue spectrum associated with this band of states as well as the atomic geometries. The predicted geometries for CdTe(110), CdSe(101-bar0), and CdSe(112-bar0) are in good correspondence with low-energy electron diffraction (LEED) and low-energy positron diffraction intensity analyses. The calculated surface state eigenvalue spectra are compared with recent angle-resolved photoemission spectra (ARPES) for CdTe(110) and CdSe(101-bar0). The main features of the ARPES measurements are reproduced by the calculated eigenvalue spectra. The predicted atomic geometry for CdTe(110) corresponds well both with prior predictions for ZnSe(110) and ZnS(110), and with LEED experimental surface structures indicating that these surfaces exhibit a universal structure in which the independent surface structural parameters scale linearly with the bulk lattice constant.

Duke, C.B.; Wang, Y.R.

1989-05-01

325

Structural phase transition in IrTe2: A combined study of optical spectroscopy and band structure calculations  

PubMed Central

Ir1?xPtxTe2 is an interesting system showing competing phenomenon between structural instability and superconductivity. Due to the large atomic numbers of Ir and Te, the spin-orbital coupling is expected to be strong in the system which may lead to nonconventional superconductivity. We grew single crystal samples of this system and investigated their electronic properties. In particular, we performed optical spectroscopic measurements, in combination with density function calculations, on the undoped compound IrTe2 in an effort to elucidate the origin of the structural phase transition at 280?K. The measurement revealed a dramatic reconstruction of band structure and a significant reduction of conducting carriers below the phase transition. We elaborate that the transition is not driven by the density wave type instability but caused by the crystal field effect which further splits/separates the energy levels of Te (px, py) and Te pz bands. PMID:23362455

Fang, A. F.; Xu, G.; Dong, T.; Zheng, P.; Wang, N. L.

2013-01-01

326

Band-edge engineering of Silicon by Surface Functionalization: a Combined Ab-initio and Photoemission Study  

NASA Astrophysics Data System (ADS)

The electrode material choice is limited in solar to fuel formation devices because of the requirement of band-edge matching to the fixed fuel formation potential. This limitation can be relieved via band-edge engineering. The changes of band-edge positions of Si electrodes induced by the adsorption of H-, Cl-, Br- and short-chain alkyl groups were investigated by combining density functional (DFT), many-body perturbation theory (MBPT), and ultraviolet photoelectron spectroscopy. The band edge shifts are related to the formation of surface dipole moments, and determine the barrier height of electrons and holes in doped silicon surfaces. We find that the trends of the sign and magnitude of the computed surface dipoles as a function of the adsorbate may be explained by simple electronegative rules. We show that quasi-particle energies obtained within MBPT are in good agreement with experiment, while DFT values may exhibit substantial errors. However computed band edge differences are in good agreement with spectroscopic and electrical measurements even at the DFT level of theory. [1] Y. Li and G. Galli, Phys. Rev. B 82, 045321 (2010). [2] Y. Li, L. O'Leary, N. Lewis and G. Galli, to be submitted.

Li, Yan; O'Leary, Leslie; Lewis, Nathan; Galli, Giulia

2012-02-01

327

Photonic band gap structures of obliquely incident electromagnetic wave propagation in a one-dimension absorptive plasma photonic crystal  

SciTech Connect

The photonic band gap structures of obliquely incident electromagnetic waves propagating in a one-dimension plasma photonic crystal with collision have been studied on the basis of electromagnetic theory and transfer matrix approach. The dispersion relations for both the transverse electric wave case and the transverse magnetic wave case are deduced. And the photonic band gap structures, with their function dependence on the microplasma layer density, microplasma width, collision frequency, background material dielectric constant, and incident angle, are computed. The results show that there exist two photonic band gap structures in an adsorptive plasma photonic crystal: one is a normal photonic band gap structure and the other is an absorption photonic band gap structure. Parameter dependence of the effects is calculated and discussed.

Guo Bin [Department of Physical Science and Technology, Wuhan University of Technology, Wuhan 430070 (China)

2009-04-15

328

Dual structure infrared surface combustion burner  

SciTech Connect

This patent describes an improvement in a surface combustion radiant heat burner comprising an inlet plenum for receiving fuel and oxidant gas mixtures from at least one supply inlet and a burner body secured in communication with the inlet plenum. The burner body having an inlet side facing the plenum and an outlet side defining a radiating surface. It comprises: the burner body comprising a first layer of porous ceramic material adjacent the inlet side and a second layer of porous ceramic material adjacent the outlet side defining the radiating surface, the first layer of porous ceramic material having a thickness of at least about 0.90:01 inch and a fine interconnected porous structure with a mean pore diameter ranging from 0.00004 inch to 0.10 inch, the second layer of porous ceramic material having a thickness of at least about 0.05 inch and a coarse interconnected porous structure with a mean diameter ranging from 0.05 to 0.40 inch, and at least the outer surfaces of the first porous layer and substantially all surfaces of the second porous layer being provided with a fully dense ceramic coating.

Morris, J.R.; Burlingame, N.H.

1989-12-26

329

Band gap and chemically ordered domain structure of a graphene analogue BCN  

NASA Astrophysics Data System (ADS)

Chemically synthesized few layer graphene analogues of B xC yN z are characterized by aberration corrected transmission electron microscopy and high resolution electron energy loss spectroscopy (HREELS) to determine the local phase, electronic structure and band gap. HREELS band gap studies of a B xC yN z composition reveal absorption edges at 2.08, 3.43 and 6.01 eV, indicating that the B xC yN z structure may consist of domains of different compositions. The K-absorption edge energy position of the individual elements in B xC yN z is determined and compared with h-BN and graphite. An understanding of these experimental findings is developed with complementary first-principles based calculations of the various ordered configurations of B xC yN z.

Venu, K.; Kanuri, S.; Raidongia, K.; Hembram, K. P. S. S.; Waghmare, U. V.; Datta, R.

2010-12-01

330

Influence of structural parameters on tunable photonic band gaps modulated by liquid crystals  

NASA Astrophysics Data System (ADS)

Tunable photonic crystals (PCs), which are infiltrated with nematic liquid crystals (LCs), tune photonic band gap (PBG) by rotating directors of LCs when applied with the external electrical field. Using the plane wave expansion method, we simulated the PBG structure of two-dimensional tunable PCs with a triangular lattice of circular column, square column and hexagon column, respectively. When PCs are composed of LCs and different substrate materials such as germanium (Ge) and silicon (Si), the influence of structural parameters including column shape and packing ration on PBG is discussed separately. Numerical simulations show that absolute PBG can't be found at any conditions, however large tuning range of polarized wave can be achieved by rotating directors of LCs. The simulation results provide theoretical guidance for the fabrication of field-sensitive polarizer with big tunable band range.

Huang, Aiqin; Zheng, Jihong; Jiang, Yanmeng; Zhou, Zengjun; Tang, Pingyu; Zhuang, Songlin

2011-10-01

331

Observation of wakefields in a beam-driven photonic band gap accelerating structure.  

SciTech Connect

Wakefield excitation has been experimentally studied in a three-cell X-band standing wave photonic band gap (PBG) accelerating structure. Major monopole (TM{sub 01}- and TM{sub 02}-like) and dipole (TM{sub 11}- and TM{sub 12}-like) modes were identified and characterized by precisely controlling the position of beam injection. The quality factor Q of the dipole modes was measured to be {approx}10 times smaller than that of the accelerating mode. A charge sweep, up to 80 nC, has been performed, equivalent to {approx} 30 MV/m accelerating field on axis. A variable delay low charge witness bunch following a high charge drive bunch was used to calibrate the gradient in the PBG structure by measuring its maximum energy gain and loss. Experimental results agree well with numerical simulations.

Conde, M.; Yusof, Z.; Power, J. G.; Jing, C.; Gao, F.; Antipov, S.; Xu, P.; Zheng, S.; Chen, H.; Tang, C.; Gai, W.; High Energy Physics; Euclid Techlabs LLC; Tsinghua Univ.

2009-12-01

332

Efficient quasiparticle band-structure calculations for cubic and noncubic crystals  

SciTech Connect

An efficient method developed for the calculation of quasiparticle corrections to density-functional-theory--local-density-approximation (DFT-LDA) band structures of diamond and zinc-blende materials is generalized for crystals with other cubic, hexagonal, tetragonal, and orthorhombic Bravais lattices. Local-field effects are considered in the framework of a LDA-like approximation. The dynamical screening is treated by expanding the self-energy linearly in energy. The anisotropy of the inverse dielectric matrix is taken into account. The singularity of the Coulomb potential in the screened-exchange part of the electronic self-energy is treated using auxiliary functions of the appropriate symmetry. An application to the electronic quasiparticle band structure of wurtzite 2{ital H}-SiC is presented within the approach of norm-conserving, nonlocal, fully separable pseudopotentials and a plane-wave expansion of the wave functions for the underlying DFT-LDA.

Wenzien, B. [Institut fuer Festkoerpertheorie und Theoretische Optik, Friedrich-Schiller-Universitaet Jena, Max-Wien-Platz 1, D-07743 Jena (Germany)] [Institut fuer Festkoerpertheorie und Theoretische Optik, Friedrich-Schiller-Universitaet Jena, Max-Wien-Platz 1, D-07743 Jena (Germany); Cappellini, G. [Istituto Di Fisica, Facolta di Medicina e Chirurgia, Universita di Cagliari, Via della Pineta 77, I-09125 Cagliari (Italy)] [Istituto Di Fisica, Facolta di Medicina e Chirurgia, Universita di Cagliari, Via della Pineta 77, I-09125 Cagliari (Italy); Bechstedt, F. [Institut fuer Festkoerpertheorie und Theoretische Optik, Friedrich-Schiller-Universitaet Jena, Max-Wien-Platz 1, D-07743 Jena (Germany)] [Institut fuer Festkoerpertheorie und Theoretische Optik, Friedrich-Schiller-Universitaet Jena, Max-Wien-Platz 1, D-07743 Jena (Germany)

1995-05-15

333

Electronic Properties of ZnO: Band Structure and Directional Compton Profiles  

NASA Astrophysics Data System (ADS)

The electronic band structure and directional Compton profiles (DCPs) of ZnO are studied in this work. Calculations are performed considering a set of three schemes based on density functional theory (DFT), the Hartree-Fock (HF) method, and a hybrid scheme. All band structures predict direct bandgaps. The best agreement with experiment is, however, shown by the hybrid scheme. The three schemes are also applied to compute DCPs along [100], [110], and [001] directions. These are compared with measurements made on single crystals of ZnO employing a 59.54 keV gamma-ray Compton spectrometer. Calculations overestimate the momentum density in the low-momentum region while underestimate the anisotropies. Positions of extremes in anisotropies deduced from calculations are well reproduced by the measured anisotropies in some cases. Within the experimental limits, the DCPs from the HF method are in better agreement with the measurements compared with DFT.

Sharma, G.; Mishra, M. C.; Dhaka, M. S.; Kothari, R. K.; Joshi, K. B.; Sharma, B. K.

2013-12-01

334

Upper mantle structure beneath the Caribbean-South American plate boundary from surface wave tomography  

E-print Network

by analysis of fundamental mode Rayleigh waves in the 20- to 100-s period band recorded at the BOLIVARUpper mantle structure beneath the Caribbean-South American plate boundary from surface wave 23 June 2008; accepted 9 October 2008; published 24 January 2009. [1] We have measured shear wave

Niu, Fenglin

335

Generation of narrow-band terahertz coherent Cherenkov radiation in a dielectric wakefield structure  

Microsoft Academic Search

This study explores the use of a dielectric-lined waveguide structure as a means of producing narrow-band terahertz radiation in the form of electron-beam-driven coherent Cherenkov radiation wakefields. This concept builds on previously studied scenarios such as the Cherenkov maser and the Cherenkov free-electron laser. It is distinct in that it relies solely on coherent wakefield excitation instead of a microbunching

Alan Matthew Cook

2009-01-01

336

Band structures tunability of bulk 2D phononic crystals made of magneto-elastic materials  

NASA Astrophysics Data System (ADS)

The feasibility of contactless tunability of the band structure of two-dimensional phononic crystals is demonstrated by employing magnetostrictive materials and applying an external magnetic field. The influence of the amplitude and of the orientation with respect to the inclusion axis of the applied magnetic field are studied in details. Applications to tunable selective frequency filters with switching functionnality and to reconfigurable wave-guides and demultiplexing devices are then discussed.

Vasseur, J. O.; Matar, O. Bou; Robillard, J. F.; Hladky-Hennion, A.-C.; Deymier, P. A.

2011-12-01

337

The Search for Velocity Structure in the Diffuse Interstellar Bands toward Herschel 36  

Microsoft Academic Search

We present results from a search for velocity structure in the Diffuse Interstellar Bands (DIBs) toward the star Herschel 36. This study utilizes high S\\/N data taken as part of a larger DIB survey using the echelle spectrograph at the Apache Point Observatory 3.5-m telescope. Herschel 36 is a young 07.5 star located in M8 (The Lagoon Nebula), and the

M. M. Drosback; T. P. Snow; J. A. Thorburn; S. D. Friedman; L. M. Hobbs; B. J. McCall; B. L. Rachford; P. Sonnentrucker; D. E. Welty; D. G. York

2004-01-01

338

Theoretical and photoemission studies of the band structure of CdI2  

Microsoft Academic Search

The band structure of CdI2 has been calculated using a modified semi-empirical tight-binding method and the results obtained have been compared with both angularly averaged and angularly resolved photoemission spectra. The theoretically computed density of states distribution is in excellent agreement with angularly averaged results and all the main features observed experimentally are reproduced in the theory. Angularly resolved spectra

J. V. McCanny; R. H. Williams; R. B. Murray; P. C. Kemeny

1977-01-01

339

The `muffin-tin' approximation in the calculation of electronic band structure  

Microsoft Academic Search

Several standard techniques for the calculation of electronic band structures in solids seem to require the crystal potential to be of `muffin-tin' form, but an elementary calculation shows that contributions from variations of the potential in the interstitial region may easily be included in the secular determinants of the augmented plane wave and Korringa-Kohn-Rostoker-Ziman methods. The corrections in the Korringa-Kohn-Rostoker

F. Beleznay; M. J. Lawrence

1968-01-01

340

Phys. 617, 10-8-2012 Effective Masses, and Common Semiconductor Properties Silicon band structure  

E-print Network

Phys. 617, 10-8-2012 ­ Effective Masses, and Common Semiconductor Properties Silicon band structure., Phys Rev B 66, 125204 2002 Group IV III-V II-VI Material Si Ge C AlAs GaAs InAs InP GaSb InSb GaN Hg produce traditional red laser-pointer color. InSb has particularly large mobility due to very small gap

Ross, Joseph

341

Dust detection over desert surfaces with thermal infrared bands using dynamic reference brightness temperature differences  

NASA Astrophysics Data System (ADS)

The brightness temperature difference (BTD) between two thermal infrared bands is a common index for dust detection. However, the BTD is sensitive to the observed temperature, which hinders its use in automatic dust detection, especially over desert land surfaces. In this paper, a dynamic reference brightness temperature differences (DRBTD) algorithm was developed to detect dust by removing the influence of the observed temperature on the BTD. Using long-term MODIS observations, the algorithm establishes the clear-sky linear relationships pixel by pixel between the brightness temperatures (BTs) at 12 and 11 µm channels and the relationships between the BTs at 8.6 and 11 µm channels. From these relationships, the reference BTDs are dynamically generated according to the observed brightness temperatures. Next, the DRBTDI, which is the difference of the observed BTD and the reference BTD, is created and used to separate the dust from other observed objects. This algorithm is applied to MODIS observations to detect several dust events during the daytime and the nighttime over Mongolia and northwestern and northern China. The results are compared with Ozone Monitoring Instrument aerosol index (OMI AI), MODIS Deep Blue aerosol optical depth (AOD), and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations. The comparisons indicate that the DRBTD algorithm can effectively distinguish dust from clouds and land surface. During the daytime, the DRBTDI is correlated with the OMI AI and MODIS AOD with a correlation coefficient of Pearson (r) of 0.79 and 0.77, respectively. At night, the DRBTDI is correlated with the CALIOP dust AOD with an r of 0.78.

Liu, Yang; Liu, Ronggao; Cheng, Xiao

2013-08-01

342

Robust topology optimization of three-dimensional photonic-crystal band-gap structures.  

PubMed

We perform full 3D topology optimization (in which "every voxel" of the unit cell is a degree of freedom) of photonic-crystal structures in order to find optimal omnidirectional band gaps for various symmetry groups, including fcc (including diamond), bcc, and simple-cubic lattices. Even without imposing the constraints of any fabrication process, the resulting optimal gaps are only slightly larger than previous hand designs, suggesting that current photonic crystals are nearly optimal in this respect. However, optimization can discover new structures, e.g. a new fcc structure with the same symmetry but slightly larger gap than the well known inverse opal, which may offer new degrees of freedom to future fabrication technologies. Furthermore, our band-gap optimization is an illustration of a computational approach to 3D dispersion engineering which is applicable to many other problems in optics, based on a novel semidefinite-program formulation for nonconvex eigenvalue optimization combined with other techniques such as a simple approach to impose symmetry constraints. We also demonstrate a technique for robust topology optimization, in which some uncertainty is included in each voxel and we optimize the worst-case gap, and we show that the resulting band gaps have increased robustness to systematic fabrication errors. PMID:25321732

Men, H; Lee, K Y K; Freund, R M; Peraire, J; Johnson, S G

2014-09-22

343

The Search for Velocity Structure in the Diffuse Interstellar Bands toward Herschel 36  

NASA Astrophysics Data System (ADS)

We present results from a search for velocity structure in the Diffuse Interstellar Bands (DIBs) toward the star Herschel 36. This study utilizes high S/N data taken as part of a larger DIB survey using the echelle spectrograph at the Apache Point Observatory 3.5-m telescope. Herschel 36 is a young 07.5 star located in M8 (The Lagoon Nebula), and the line of sight has a large ratio of total to selective extinction indicating the presence of larger than average interstellar dust grains. The atomic sodium and potassium lines in the spectrum indicate the presence of two major absorbing components in the line of sight, separated in velocity by nearly 60 km/s. Using this known velocity separation, we are studying the DIBs present in the spectrum to look for evidence of the same velocity structure in these unidentified, weak absorption bands. If separate velocity components can be seen in the DIBs toward this star, it may be possible to use known physical conditions in the line of sight to place constraints on the nature of some of the diffuse band carriers. We will incoporate into the discussion new FUSE results on the velocity structure of the molecular hydrogen in the line of sight as well.

Drosback, M. M.; Snow, T. P.; Thorburn, J. A.; Friedman, S. D.; Hobbs, L. M.; McCall, B. J.; Rachford, B. L.; Sonnentrucker, P.; Welty, D. E.; York, D. G.

2004-12-01

344

Robust topology optimization of three-dimensional photonic-crystal band-gap structures  

NASA Astrophysics Data System (ADS)

We perform full 3D topology optimization (in which "every voxel" of the unit cell is a degree of freedom) of photonic-crystal structures in order to find optimal omnidirectional band gaps for various symmetry groups, including fcc (including diamond), bcc, and simple-cubic lattices. Even without imposing the constraints of any fabrication process, the resulting optimal gaps are only slightly larger than previous hand designs, suggesting that current photonic crystals are nearly optimal in this respect. However, optimization can discover new structures, e.g. a new fcc structure with the same symmetry but slightly larger gap than the well known inverse opal, which may offer new degrees of freedom to future fabrication technologies. Furthermore, our band-gap optimization is an illustration of a computational approach to 3D dispersion engineering which is applicable to many other problems in optics, based on a novel semidefinite-program formulation for nonconvex eigenvalue optimization combined with other techniques such as a simple approach to impose symmetry constraints. We also demonstrate a technique for \\emph{robust} topology optimization, in which some uncertainty is included in each voxel and we optimize the worst-case gap, and we show that the resulting band gaps have increased robustness to systematic fabrication errors.

Men, H.; Lee, K. Y. K.; Freund, R. M.; Peraire, J.; Johnson, S. G.

2014-09-01

345

Inferring Land Surface Model Parameters for the Assimilation of Satellite-Based L-Band Brightness Temperature Observations into a Soil Moisture Analysis System  

NASA Technical Reports Server (NTRS)

The Soil Moisture and Ocean Salinity (SMOS) satellite mission provides global measurements of L-band brightness temperatures at horizontal and vertical polarization and a variety of incidence angles that are sensitive to moisture and temperature conditions in the top few centimeters of the soil. These L-band observations can therefore be assimilated into a land surface model to obtain surface and root zone soil moisture estimates. As part of the observation operator, such an assimilation system requires a radiative transfer model (RTM) that converts geophysical fields (including soil moisture and soil temperature) into modeled L-band brightness temperatures. At the global scale, the RTM parameters and the climatological soil moisture conditions are still poorly known. Using look-up tables from the literature to estimate the RTM parameters usually results in modeled L-band brightness temperatures that are strongly biased against the SMOS observations, with biases varying regionally and seasonally. Such biases must be addressed within the land data assimilation system. In this presentation, the estimation of the RTM parameters is discussed for the NASA GEOS-5 land data assimilation system, which is based on the ensemble Kalman filter (EnKF) and the Catchment land surface model. In the GEOS-5 land data assimilation system, soil moisture and brightness temperature biases are addressed in three stages. First, the global soil properties and soil hydraulic parameters that are used in the Catchment model were revised to minimize the bias in the modeled soil moisture, as verified against available in situ soil moisture measurements. Second, key parameters of the "tau-omega" RTM were calibrated prior to data assimilation using an objective function that minimizes the climatological differences between the modeled L-band brightness temperatures and the corresponding SMOS observations. Calibrated parameters include soil roughness parameters, vegetation structure parameters, and the single scattering albedo. After this climatological calibration, the modeling system can provide L-band brightness temperatures with a global mean absolute bias of less than 10K against SMOS observations, across multiple incidence angles and for horizontal and vertical polarization. Third, seasonal and regional variations in the residual biases are addressed by estimating the vegetation optical depth through state augmentation during the assimilation of the L-band brightness temperatures. This strategy, tested here with SMOS data, is part of the baseline approach for the Level 4 Surface and Root Zone Soil Moisture data product from the planned Soil Moisture Active Passive (SMAP) satellite mission.

Reichle, Rolf H.; De Lannoy, Gabrielle J. M.

2012-01-01

346

Photoemission measurements of quantum states in accumulation layers at narrow band gap III–V semiconductor surfaces  

Microsoft Academic Search

Tiny amounts of cesium adsorbed on cleaved InSb(110) surfaces result in a strong downward band bending (BB) and creates a two-dimensional (2D) electron channel in the sub-surface region. For the first time, electron emission arising from this channel was observed for this material. We compare it to the similar situation met previously with InAs(110). In this last case, new high-resolution

V. Yu. Aristov; V. M. Zhilin; C. Grupp; A. Taleb-Ibrahimi; H. J. Kim; P. S. Mangat; P. Soukiassian; G. Le Lay

2000-01-01

347

Design of dual-band low profile high directive EBG resonator antenna, using single layer frequency selective surface (FSS) superstrate  

Microsoft Academic Search

In this paper, we present a novel design of a dual-band high directive EBG resonator antenna that utilizes a single layer frequency selective surfaces (FSS) as a superstrate. In this study we use a special configuration of square loop-array to design the FSS superstrate layer. We obtain the different operating frequencies by adjusting the distance of FSS from printed patch

A. Pirhadi; F. Keshmiri; M. Hakkak

2006-01-01

348

Polarization Effects of GaN and AlGaN: Polarization Bound Charge, Band Bending, and Electronic Surface States  

NASA Astrophysics Data System (ADS)

GaN-based devices are currently limited by reliability issues such as gate leakage and current collapse, where the mechanisms responsible for degradation are closely related to the electronic surface state configuration. Therefore, understanding the electronic surface state configuration of GaN-based materials will help improve device performance. Since GaN has an inherent polarization, these materials are also subject to a bound polarization charge, which influences the electronic state configuration. In this study, the surface band bending of N-face GaN, Ga-face GaN, and Ga-face AlGaN was measured with x-ray photoemission spectroscopy after various cleaning steps to investigate the effects of the polarization. Despite the different surface bound charge on these materials, similar band bending was observed regardless of the magnitude or direction of the charge. Specifically, the band bending varied from -0.1 eV to 0.9 eV on these samples, which supported the models of a Fermi level pinning state at ˜0.4 eV to 0.8 eV below the conduction band. Based on available literature, we suggest this pinning state is indirectly evident of a nitrogen vacancy or gallium-dangling bond.

Eller, Brianna S.; Yang, Jialing; Nemanich, Robert J.

2014-09-01

349

Band structure of the odd-even {sup 125}La, {sup 127}La nuclei  

SciTech Connect

Excited states of the {sup 125}La and {sup 127}La nuclei were populated following {sup 112}Sn({sup 16}O,{ital p}2{ital n}) and {sup 112}Cd({sup 19}F,4{ital n}) fusion-evaporation reactions, respectively, and investigated using methods of in-beam {gamma}-ray spectroscopy. Five collective bands in {sup 125}La, and eleven collective bands in {sup 127}La were observed. The spin and/or parity assignments of excited states in these nuclei were based on angular-correlation and linear-polarization measurements. The experimental data are discussed and compared to the results of self-consistent total-Routhian-surface calculations including quadrupole pairing. {copyright} {ital 1996 The American Physical Society.}

Starosta, K.; Droste, C.; Morek, T.; Srebrny, J. [Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland)] [Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Fossan, D.B.; LaFosse, D.R.; Schnare, H.; Thorslund, I.; Vaska, P.; Waring, M.P. [Department of Physics, State University of New York at Stony Brook, Stony Brook, New York 11794 (United States)] [Department of Physics, State University of New York at Stony Brook, Stony Brook, New York 11794 (United States); Satul/a, W.; Rohozinski, S.G. [Institute of Theoretical Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland)] [Institute of Theoretical Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Wyss, R. [The Royal Institute of Technology, Physics Department, Frescati, Frescativaegen 24, S-104 05 Stockholm (Sweden)] [The Royal Institute of Technology, Physics Department, Frescati, Frescativaegen 24, S-104 05 Stockholm (Sweden); Hibbert, I.M.; Wadsworth, R.; Hauschild, K. [Department of Physics, University of York, Heslington, York Y01 5DD (United Kingdom)] [Department of Physics, University of York, Heslington, York Y01 5DD (United Kingdom); Beausang, C.W.; Forbes, S.A.; Nolan, P.J.; Paul, E.S. [Oliver Lodge Laboratory, University of Liverpool, P.O. Box 147, Liverpool L69 3BX (United Kingdom)] [Oliver Lodge Laboratory, University of Liverpool, P.O. Box 147, Liverpool L69 3BX (United Kingdom)

1996-01-01

350

Spin filtering with EuO: Insight from a complex band structure  

NASA Astrophysics Data System (ADS)

Spin-filter tunneling is a promising way to create highly-spin-polarized currents. So far the understanding of the spin-filtering effect has been limited to a free-electron description based on the spin-dependent tunneling barrier height. In this work we employ density-functional calculations to explore the complex bands of EuO as a representative ferromagnetic insulator used in spin-filter tunneling experiments and show that the mechanism of spin filtering deviates significantly from the standard free-electron picture and involves effects associated with the symmetry of spin-dependent evanescent states and the dependence of the decay constant on the transverse wave vector. We demonstrate the importance of the multiorbital band structure with an indirect band gap for spin-filter tunneling. By analyzing the symmetry of the complex bands and the decay rates for different wave vectors and energies we draw conclusions about spin-filter efficiency of EuO. Our results provide a new insight into spin-filter tunneling and may help to design tunnel junctions with enhanced spin polarization.

Lukashev, Pavel; Wysocki, Aleksander; Velev, Julian; van Schilfgaarde, Mark; Jaswal, Sitaram; Belashchenko, Kirill; Tsymbal, Evgeny

2013-03-01

351

Peculiarities of the band structure of multi-component photonic crystals with different dimensions.  

PubMed

In this work we offer a simple analytical method which allows us to determine and study the effects of the selective switching of photonic stop-bands in multi-component photonic crystals (Mc-PhCs) of any dimensionality. The calculations for Mc-PhCs with low dielectric contrast have been performed in the framework of the model based on the scattering form factor analysis. It has been shown that the effects of selective switching of photonic stop-bands predicted theoretically and found experimentally before in three-dimensional (3D) Mc-PhC have a general character and may be observed also in one-dimensional (1D) and two-dimensional (2D) Mc-PhCs. It is found that 1D, 2D and 3D Mc-PhCs demonstrate unexpectedly similar quasi-periodic behaviour of photonic stop-bands as a function of the reciprocal lattice vector. A proper choice of the structural and dielectric parameters can create a resonance photonic stop-band determining the Bragg wavelengths, to which a photonic crystal can never be transparent. PMID:21389463

Samusev, A K; Samusev, K B; Rybin, M V; Limonov, M F

2010-03-24

352

Janus kinases and focal adhesion kinases play in the 4.1 band: a superfamily of band 4.1 domains important for cell structure and signal transduction.  

PubMed Central

The band 4.1 domain was first identified in the red blood cell protein band 4.1, and subsequently in ezrin, radixin, and moesin (ERM proteins) and other proteins, including tumor suppressor merlin/schwannomin, talin, unconventional myosins VIIa and X, and protein tyrosine phosphatases. Recently, the presence of a structurally related domain has been demonstrated in the N-terminal region of two groups of tyrosine kinases: the focal adhesion kinases (FAK) and the Janus kinases (JAK). Additional proteins containing the 4.1/JEF (JAK, ERM, FAK) domain include plant kinesin-like calmodulin-binding proteins (KCBP) and a number of uncharacterized open reading frames identified by systematic DNA sequencing. Phylogenetic analysis of amino acid sequences suggests that band 4.1/JEF domains can be grouped in several families that have probably diverged early during evolution. Hydrophobic cluster analysis indicates that the band 4.1/JEF domains might consist of a duplicated module of approximately 140 residues and a central hinge region. A conserved property of the domain is its capacity to bind to the membrane-proximal region of the C-terminal cytoplasmic tail of proteins with a single transmembrane segment. Many proteins with band 4.1/JEF domains undergo regulated intra- or intermolecular homotypic interactions. Additional properties common to band 4.1/JEF domains of several proteins are binding of phosphoinositides and regulation by GTPases of the Rho family. Many proteins with band 4. 1/JEF domains are associated with the actin-based cytoskeleton and are enriched at points of contact with other cells or the extracellular matrix, from which they can exert control over cell growth. Thus, proteins with band 4.1/JEF domain are at the crossroads between cytoskeletal organization and signal transduction in multicellular organisms. Their importance is underlined by the variety of diseases that can result from their mutations. Images Fig. 1 Fig. 2 Fig. 4 Fig. 5 PMID:9990861

Girault, J. A.; Labesse, G.; Mornon, J. P.; Callebaut, I.

1998-01-01

353

Synthesis and band gap of ZnO particles with hexagonal bilayer structure  

NASA Astrophysics Data System (ADS)

The unique water/PVP (polyvinylpyrrolidone)/n-pentanol interface has been developed to prepare the ZnO particles with hexagonal bilayer structure. By modifying the interface through varying the amount of PVP and water, one can readily tune the particle size and change the particle shape from hexagonal bilayer to capped potlike to hemispherical features. The study of the growth dynamics and extinction spectra suggests that the bilayer structure arises from the selective adsorption of PVP on the ZnO crystallographic planes. Both the photoluminescence and extinction spectra show that the band gap of the hexagonal bilayer ZnO particles shrinks with increasing particle size.

Zhang, Jianhui; Liu, Huaiyong; Wang, Zhenlin; Ming, Naiben

2007-03-01

354

The Glacier and Ice Surface Topography Interferometer: UAVSAR's Single-pass Ka-Band Interferometer  

NASA Astrophysics Data System (ADS)

In May 2009 a new radar technique for mapping ice surface topography was demonstrated in a Greenland campaign as part of the NASA International Polar Year (IPY) activities. This was achieved with the airborne Glacier and Ice Surface Topography Interferometer (GLISTIN-A): a 35.6 GHz single-pass interferometer. The proof-of-concept demonstration was achieved by interfacing Ka-band RF and antenna hardware with the Uninhabited Airborne Vehicle Synthetic Aperture Radar (UAVSAR). The GLISTIN-A was implemented as a custom installation of the NASA Dryden Flight Research Center Gulfstream III. Instrument performance indicated swath widths over the ice between 5-7km, with height precisions ranging from 30cm-3m at a posting of 3m x 3m. Following the success of the IPY campaign, the Earth Science Techonology Office (ESTO) Airborne Innovative Technology Transition (AITT) program funded the upgrade of GLISTIN-A to a permanently-available pod-only system compatible with unpressurized operation. The AITT made three fundamental upgrades to improve system performance: 1. State-of-the-art solid-state power amplifiers (80W peak) were integrated directly on the antenna panel reducing front-end losses; 2. A ping-pong capability was incorporated to effectively double the baseline thereby improving height measurement precision by a factor of two; and 3. A high-fidelity calibration loop was implemented which is critical for routine processing. Upon completion of our engineering flights in February 2013, GLISTIN-A flew a brief campaign to Alaska (4/24-4/27/13). The purpose was to fully demonstrate GLISTIN-A's ability to generate high-precision, high resolution maps of ice surface topography with swaths in excess of 10km. Furthermore, the question of the utility of GLISTIN-A for sea-ice mapping, tracking and inventory has received a great deal of interest. To address this GLISTIN-A collected data over sea-ice in the Beaufort sea including an underflight of CryoSAT II. Note that there are ongoing activities to stage GLISTIN on the Global Hawk (GLISTIN-H) for which sea ice-mapping is a primary driver. Analysis of the data will focus on assessment of performance and interpretation over ice to include: 1. intercomparison of GLISTIN-A glacier height maps with lidar data and heritage SRTM DEM's for performance validation of GLISTIN-A over ice, 2. quantitative evaluation of mass change over the Columbia glacier via repeat observations made by GLISTIN-A with a 3 day separation, 3. assessment of GLISTIN-A's ability map sea ice extent, dynamics and possibly to measure freeboard.

Moller, D.; Hensley, S.; Wu, X.; Michel, T.; Muellerschoen, R.; Carswell, J.; Fisher, C.; Miller, T.; Milligan, L.; Sadowy, G.; Sanchez-Barbetty, M.; Lou, Y.

2013-12-01

355

Surface wear of incoloy and darvic bands on Atlantic Puffin adults and chicks  

Microsoft Academic Search

Bands are a common marking method in bird studies and capture-mark-reencounter (CMR) models are often used to analyze banding data. Common to this family of models are two assumptions: marks do not fall off or become unreadable and individuals within groups remain equally detectable. When data fail to meet these assumptions, results of CMR analyses may be biased. In studies

Andre R. Breton; Antony W. Diamond; Stephen W. Kress

2006-01-01

356

Alloy composition and electronic structure of Cd1-xZnxTe by surface photovoltage spectroscopy  

NASA Astrophysics Data System (ADS)

The alloy composition of a Cd1-xZnxTe(111) sample and its spatial homogeneity have been determined by surface photovoltage spectroscopy (SPS) and compared to conventional energy dispersive x-ray spectroscopy measurements. Experimental improvements of the former technique yield a contactless, surface sensitive, and highly accurate spectral resolution of the band gap (error<4 meV) and consequently of the Zn concentration (error<0.6% in comparison with the latter technique). In addition, SPS is capable of determining the face and type of the Cd1-xZnxTe as well as identifying gap states at its surface. The electronic structure has been investigated in comparison with n-CdTe(111), before and after various surface chemical treatments. An acceptor surface state has been observed at 1.21 eV below the conduction band edge and attributed to TeO2. A donor surface state (with a lower concentration relative to the corresponding state in CdTe) associated with Cd atom displacement has been found at 1.42 eV above the valence band maximum. A chemically induced surface state at 0.72 eV below the conduction band edge may be due to Zn vacancies, as supported by x-ray photoelectron spectroscopy measurements.

Yang, Jihua; Zidon, Y.; Shapira, Yoram

2002-01-01

357

Measurement of surface scratches on aircraft structures  

NASA Astrophysics Data System (ADS)

In assuring the quality of aircraft, the skin quality must be free of surface imperfections. Surface imperfections such as scratches are unacceptable for cosmetic and structural reasons. Scratches beyond a certain depth are not repairable, resulting in costly replacement of an aircraft's part. Measurements of aircraft exterior surfaces require a ladder or cherry picker for positioning the inspector. Commercially-available computer vision systems are not portable, easy to use, or ergonomic. The machine vision system must be designed with these criteria in mind. The scratch measurement system (SMS) uses computer vision, digital signal processing, and automated inspection methods. The system is portable and battery powered. It is certified for measuring the depth and width of the anomaly. The SMS provides a comprehensive, analytical, and accurate reading. A hardcopy output provides a permanent record of the analysis. The graphical data shows the surface profile and provides substantial information of the surface anomaly. The factory and flight line use the SMS at different stages of aircraft production. Six systems have been built for use within Boeing. A patent was issued for the SMS in February 1994.

Sarr, Dennis P.

1996-01-01

358

Search for localized Wannier functions of topological band structures via compressed sensing  

NASA Astrophysics Data System (ADS)

We investigate the interplay of band structure topology and localization properties of Wannier functions. To this end, we extend a recently proposed compressed sensing based paradigm for the search for maximally localized Wannier functions [Ozolins et al., Proc. Natl. Acad. Sci. USA 110, 18368 (2013), 10.1073/pnas.1318679110]. We develop a practical toolbox that enables the search for maximally localized Wannier functions which exactly obey the underlying physical symmetries of a translationally invariant quantum lattice system under investigation. Most saliently, this allows us to systematically identify the most localized representative of a topological equivalence class of band structures, i.e., the most localized set of Wannier functions that is adiabatically connected to a generic initial representative. We also elaborate on the compressed sensing scheme and find a particularly simple and efficient implementation in which each step of the iteration is an O (NlogN) algorithm in the number of lattice sites N. We present benchmark results on one-dimensional topological superconductors demonstrating the power of these tools. Furthermore, we employ our method to address the open question of whether compact Wannier functions can exist for symmetry-protected topological states such as topological insulators in two dimensions. The existence of such functions would imply exact flat-band models with finite range hopping. Here, we find numerical evidence for the absence of such functions. We briefly discuss applications in dissipative-state preparation and in devising variational sets of states for tensor network methods.

Budich, J. C.; Eisert, J.; Bergholtz, E. J.; Diehl, S.; Zoller, P.

2014-09-01

359

Crustal Structure Beneath Taiwan Using Frequency-band Inversion of Receiver Function Waveforms  

NASA Astrophysics Data System (ADS)

Receiver function analysis is used to determine local crustal structure beneath Taiwan. We have performed preliminary data processing and polarization analysis for the selection of stations and events and to increase overall data quality. Receiver function analysis is then applied to data from the Taiwan Seismic Network to obtain radial and transverse receiver functions. Due to the limited azimuthal coverage, only the radial receiver functions are analyzed in terms of horizontally layered crustal structure for each station. In order to improve convergence of the receiver function inversion, frequency-band inversion (FBI) is implemented, in which an iterative inversion procedure with sequentially higher low-pass corner frequencies is used to stabilize the waveform inversion. Frequency-band inversion is applied to receiver functions at six stations of the Taiwan Seismic Network. Initial 20-layer crustal models are inverted for using prior tomographic results for the initial models. The resulting 20-1ayer models are then simplified to 4 to 5 layer models and input into an alternating depth and velocity frequency-band inversion. For the six stations investigated, the resulting simplified models provide an average estimate of 38 km for the Moho thickness surrounding the Central Range of Taiwan. Also, the individual station estimates compare well with the recent tomographic model of and the refraction results of Rau and Wu (1995) and the refraction results of Ma and Song (1997).

Tomfohrde, D. A.; Nowack, R. L.

360

High-order modes of spoof surface plasmonic wave transmission on thin metal film structure.  

PubMed

Recently, conformal surface plasmon (CSP) structure has been successfully proposed that could support spoof surface plasmon polaritons (SPPs) on corrugated metallic strip with ultrathin thickness [Proc. Natl. Acad. Sci. U.S.A. 110, 40-45 (2013)]. Such concept provides a flexible, conformal, and ultrathin wave-guiding element, very promising for application of plasmonic devices, and circuits in the frequency ranging from microwave to mid-infrared. In this work, we investigated the dispersions and field patterns of high-order modes of spoof SPPs along CSP structure of thin metal film with corrugated edge of periodic array of grooves, and carried out direct measurement on the transmission spectrum of multi-band of surface wave propagation at microwave frequency. It is found that the mode number and mode bands are mainly determined by the depth of the grooves, providing a way to control the multi-band transmission spectrum. We have also experimentally verified the high-order mode spoof SPPs propagation on curved CSP structure with acceptable bending loss. The multi-band propagation of spoof surface wave is believed to be applicable for further design of novel planar devices such as filters, resonators, and couplers, and the concept can be extended to terahertz frequency range. PMID:24514689

Liu, Xiaoyong; Feng, Yijun; Zhu, Bo; Zhao, Junming; Jiang, Tian

2013-12-16

361

Selective Intermixing of InAs\\/InGaAs\\/InP Quantum Dot Structure With Large Energy Band Gap Tuning  

Microsoft Academic Search

Selective postgrowth band gap tuning of self-assembled InAs\\/InGaAs\\/InP quantum dot (QD) structures has been investigated. Very large band gap blueshift of over 158 meV of the InAs QD structure has been received through the intermixing by exposing the sample under argon plasma and followed by thermal annealing at 780 degC. Selective intermixing of the InAs QD structure has been studied

Tang Xiaohong; Yin Zongyou; Teng Jinghua; Du Anyan; Chin Mee Koy

2008-01-01

362

Strain-tunable band parameters of ZnO monolayer in graphene-like honeycomb structure  

NASA Astrophysics Data System (ADS)

We present ab initio calculations which show that the direct-band-gap, effective masses and Fermi velocities of charge carriers in ZnO monolayer (ML-ZnO) in graphene-like honeycomb structure are all tunable by application of in-plane homogeneous biaxial strain. Within our simulated strain limit of ±10%, the band gap remains direct and shows a strong non-linear variation with strain. Moreover, the average Fermi velocity of electrons in unstrained ML-ZnO is of the same order of magnitude as that in graphene. The results promise potential applications of ML-ZnO in mechatronics/straintronics and other nano-devices such as the nano-electromechanical systems (NEMS) and nano-optomechanical systems (NOMS).

Behera, Harihar; Mukhopadhyay, Gautam

2012-10-01

363

Periodic dielectric structure for production of photonic band gap and method for fabricating the same  

DOEpatents

A method for fabricating a periodic dielectric structure which exhibits a photonic band gap. Alignment holes are formed in a wafer of dielectric material having a given crystal orientation. A planar layer of elongate rods is then formed in a section of the wafer. The formation of the rods includes the step of selectively removing the dielectric material of the wafer between the rods. The formation of alignment holes and layers of elongate rods and wafers is then repeated to form a plurality of patterned wafers. A stack of patterned wafers is then formed by rotating each successive wafer with respect to the next-previous wafer, and then placing the successive wafer on the stack. This stacking results in a stack of patterned wafers having a four-layer periodicity exhibiting a photonic band gap.

Ozbay, Ekmel (Ames, IA); Tuttle, Gary (Ames, IA); Michel, Erick (Ames, IA); Ho, Kai-Ming (Ames, IA); Biswas, Rana (Ames, IA); Chan, Che-Ting (Ames, IA); Soukoulis, Costas (Ames, IA)

1995-01-01

364

Tunable double negative band structure from non-magnetic coated rods  

NASA Astrophysics Data System (ADS)

A system of periodic poly-disperse-coated nano-rods is considered. Both the coated nano-rods and the host material are non-magnetic. The exterior nano-coating has a frequency-dependent dielectric constant and the rod has a high dielectric constant. A negative effective magnetic permeability is generated near the Mie resonances of the rods, while the coating generates a negative permittivity through a field resonance controlled by the plasma frequency of the coating and the geometry of the crystal. The explicit band structure for the system is calculated in the subwavelength limit. Tunable pass bands exhibiting negative group velocity are generated and correspond to simultaneously negative effective dielectric permittivity and magnetic permeability. These can be explicitly controlled by adjusting the distance between the rods, the coating thickness and the rod diameters.

Chen, Yue; Lipton, Robert

2010-08-01

365

Opening of simultaneous photonic and phononic band gap in two-dimensional square lattice periodic structure  

NASA Astrophysics Data System (ADS)

We discuss two points related to the simultaneous existence of phononic and photonic band gaps in a two-dimensional crystal constituted by a square array of holes drilled in a matrix. In a first part, using the case of a sapphire sample in the microwave range, we show that in addition to the phononic gap, an absolute photonic gap may be obtained making use of the high values as well as the anisotropy of the dielectric matrix elements in the microwave regime. In a second part, using the case of silicon in the telecom frequency range, we demonstrate that absolute photonic and phononic gaps may be obtained by making a combination of two crystals having slightly different filling factors. The calculations of the band structures and transmission coefficients were mainly computed using the finite difference time domain method.

Bria, D.; Assouar, M. B.; Oudich, M.; Pennec, Y.; Vasseur, J.; Djafari-Rouhani, B.

2011-01-01

366

Periodic dielectric structure for production of photonic band gap and method for fabricating the same  

DOEpatents

A method is disclosed for fabricating a periodic dielectric structure which exhibits a photonic band gap. Alignment holes are formed in a wafer of dielectric material having a given crystal orientation. A planar layer of elongate rods is then formed in a section of the wafer. The formation of the rods includes the step of selectively removing the dielectric material of the wafer between the rods. The formation of alignment holes and layers of elongate rods and wafers is then repeated to form a plurality of patterned wafers. A stack of patterned wafers is then formed by rotating each successive wafer with respect to the next-previous wafer, and then placing the successive wafer on the stack. This stacking results in a stack of patterned wafers having a four-layer periodicity exhibiting a photonic band gap. 42 figures.

Ozbay, E.; Tuttle, G.; Michel, E.; Ho, K.M.; Biswas, R.; Chan, C.T.; Soukoulis, C.

1995-04-11

367

Enhanced modeling of band nonparabolicity with application to a mid-IR quantum cascade laser structure  

NASA Astrophysics Data System (ADS)

We analyze the influence of conduction-band nonparabolicity on bound electronic states in the active region of a quantum cascade laser (QCL). Our model assumes expansion of the conduction-band dispersion relation up to a fourth order in wavevector and use of a suitable second boundary condition at the interface of two III-V semiconductor layers. Numerical results, obtained by the transfer matrix method, are presented for two mid-infrared GaAs/Al0.33Ga0.67As QCL active regions, and they are in very good agreement with experimental data found in the literature. Comparison with a different nonparabolicity model is presented for the example of a GaAs/Al0.38Ga0.62As-based mid-IR QCL. Calculations have also been carried out for one THz QCL structure to illustrate the possible application of the model in the terahertz part of the spectrum.

Vukovic, N.; Radovanovic, J.; Milanovic, V.

2014-09-01

368

Touching points in the energy band structure of bilayer graphene superlattices  

NASA Astrophysics Data System (ADS)

The energy band structure of the bilayer graphene superlattices with zero-averaged periodic δ-function potentials are studied within the four-band continuum model. Using the transfer matrix method, the study is mainly focused on examining the touching points between adjacent minibands. For the zero-energy touching points the dispersion relation derived shows a Dirac-like double-cone shape with the group velocity which is periodic in the potential strength P with the period of π and becomes anisotropic at relatively large P. From the finite-energy touching points we have identified those located at zero wave-number. It was shown that for these finite-energy touching points the dispersion is direction-dependent in the sense that it is linear or parabolic in the direction parallel or perpendicular to the superlattice direction, respectively. We have also calculated the density of states and the conductivity which demonstrates a manifestation of the touching points examined.

Pham, C. Huy; Nguyen, V. Lien

2014-10-01

369

Finite difference method for analyzing band structure in semiconductor heterostructures without spurious solutions  

NASA Astrophysics Data System (ADS)

To stably employ multiband k.p model for analyzing the band structure in semiconductor heterostructures without spurious solutions (SSs), the Hermitian forward and backward difference (HFBD) scheme for finite difference method (FDM) is presented. The HFBD is the discretization scheme that eliminates the difference instability and employs the Burt-Foreman Hermitian operator ordering without geometric asymmetry. The difference instability arises from employing Foreman's strategy (FS). FS removes SSs caused by unphysical bowing in bulk dispersion curve meanwhile the HFBD is the only difference scheme that can accurately adapt for it. In comparison with other recent strategies, the proposed method in this paper is as accurate and reliable as FS, along with preserving the rapidness and simplicity of FDM. This difference scheme shows stable convergence without any SSs under variable grid size. Therefore, a wide range of experiment-determined band parameters can be applied to large-scale stable simulation with this method regardless of the SSs they originally generate.

Jiang, Yu; Ma, Xunpeng; Xu, Yun; Song, Guofeng

2014-11-01

370

Dual-band infrared imaging to detect corrosion damage within airframes and concrete structures  

SciTech Connect

We are developing dual-band infrared (DBIR) imaging and detection techniques to inspect air frames and concrete bridge decks for hidden corrosion damage. Using selective DBIR image ratios,, we enhanced surface temperature contrast and removed surface emissivity noise associated with clutter. Our surface temperature maps depicted defect sites, which heat and cool at different rates than their surroundings. Our emissivity-ratio maps tagged and removed the masking effects of surface clutter. For airframe inspections, we used time-resolved DBIR temperature, emissivity-ratio and composite thermal inertia maps to locate corrosion-thinning effects within a flash-heated Boeing 737 airframe. Emissivity-ratio maps tagged and removed clutter sites from uneven paint, dirt and surface markers. Temperature and thermal inertia maps characterized defect sites, types, sizes, thicknesses, thermal properties and material-loss effects from air frame corrosion. For concrete inspections, we mapped DBIR temperature and emissivity-ratio patterns to better interpret surrogate delamination sites within naturally-heated, concrete slabs and remove the clutter mask from sand pile-up, grease stains, rocks and other surface objects.

Del Grande, N.K.; Durbin, P.F.

1994-01-01

371

Ultra-thin quadri-band metamaterial absorber based on spiral structure  

NASA Astrophysics Data System (ADS)

We introduce a design of the metamaterial absorber (MA) consisting of spiral artificial inclusions printed on an ultra-thin dielectric layer backed by a metal plate. Both simulations and experiments show that the MA can achieve absorptions up to 96.49, 94.25, 98.94 and 92.04 % at 6.69, 8.70, 11.90 and 15.14 GHz, respectively. The surface current and power loss density of each absorption frequency were discussed to reveal the physical mechanism. Moreover, the proposed quadri-band MA possesses the advantages of being ultra-thin and polarization-insensitive and thus may find potential applications.

Wang, Wenjie; Yan, Mingbao; Pang, Yongqiang; Wang, Jiafu; Ma, Hua; Qua, Shaobo; Chen, Hongya; Xu, Cuilian; Feng, Mingde

2014-09-01

372

Cohesive band structure of carbon nanotubes for applications in quantum transport  

NASA Astrophysics Data System (ADS)

An integrated cohesive band structure of carbon nanotubes (CNTs) applicable to all chirality directions (n, m), starting from the Dirac cone of a graphene nanolayer in k-space, is demarcated, in direct contrast to dissimilar chiral and achiral versions in the published literature. The electron wave state of a CNT is quantized into one-dimensional (1-D) nanostructure with a wrapping mode, satisfying the boundary conditions from one Dirac K-point to an equivalent neighboring one with an identical phase and returning to the same K point. The repetitive rotation for an identical configuration with added band index (n - m)mod3, yields one metallic (M) with zero bandgap corresponding to (n - m)mod3 = 0, semiconducting state SC1 with (n - m)mod3 = 1 and SC2 with (n - m)mod3 = 2. The band gap and effective mass of SC2 state are twice as large as those of SC1 state. A broad-spectrum expression signifying the linear dependence of the effective mass on the bandgap is obtained. Both the Fermi energy and the intrinsic velocity limiting the current to the saturation level is calculated as a function of the carrier concentration. Limitations of the parabolic approximation are pointed out. Several new features of the band structure are acquired in a seamlessly unified mode for all CNTs, making it suitable for all-encompassing applications. Applications of the theory to high-field transport are advocated with an example of a metallic CNT, in agreement with experimental observations. The mechanism behind the breakdown of the linear current-voltage relation of Ohm's law and the associated surge in resistance are explained on the basis of the nonequilibrium Arora's distribution function (NEADF). These results are important for the performance evaluation and characterization of a variety of applications on CNT in modern nanoscale circuits and devices.

Arora, Vijay K.; Bhattacharyya, Arkaprava

2013-10-01

373

Comment on ``Photonic bands in two-dimensional microplasma array. I. Theoretical derivation of band structures of electromagnetic waves'' [J. Appl. Phys. 101, 073304 (2007)  

NASA Astrophysics Data System (ADS)

Recently, theoretical derivation of band structures of electromagnetic waves in two-dimensional microplasma array has been induced by Osamu Sakai et al. [J. Appl. Phys. 101, 073304 (2007)] using a modified plane wave expansion (PWE) method and a frequency-dependent finite difference time-domain (FDTD) method. This report reveals band diagrams with the effects of plasma electron collision frequency, especially focuses on the TE wave by nonmagnetized plasma. Although the band diagrams of TE wave and formulas of calculation look correct at first glance, there are some mistakes in the report which are unfortunately ignored by the authors. The correct formulas of the modified PWE method and FDTD method will be proposed.

Zhang, Hai-feng; Liu, Shao-bin; Kong, Xiang-kun; Zhou, Liang; Li, Chun-zao; Bian, Bo-rui

2011-07-01

374

Effects of the Antenna Aperture on Remote Sensing of Sea Surface Salinity at L-Band  

NASA Technical Reports Server (NTRS)

Remote sensing of sea surface salinity with sufficient accuracy to meet the needs of global oceanography is a challenging task. The global variability of the salinity signal in the open ocean is only a few Kelvin even at L-band and an accuracy on the order of 0.1K is desired to study the influence of salinity on ocean circulation and energy exchange with the atmosphere. On the other hand, resolution is not an issue for understanding the dynamics of the open ocean where scales of hundreds of km are not uncommon. This permits remote sensing with large antenna footprints and spatial averaging to reduce noise. However, antennas with large footprints introduce other problems. For example, the angle of incidence and hence the brightness temperature varies over the footprint. Similarly, the polarization of brightness temperature relative to the antenna ports changes. Studies have been conducted using antenna patterns representative of the antenna that will be flown on the Aquarius mission to examine these effects. Aquarius is a pushbroom style radiometer with three beams looking across track away from the sun. The beams are at incidences angles (at the spacecraft) of about 26.5, 34 and 40 degrees each with a half-power beam width of about 5.8 degrees. It is shown that the measured brightness temperature is biased relative to the value at boresight because of changes across the field of view. The bias can be as much as 4K and positive or negative depending on polarization. Polarization mixing because of the variations of the local plane of incidence across the footprint also occur and can result in biased polarimetric measurements. A bias in the third Stokes parameter of as much as 0.4K is possible. Such effects may affect algorithms that use the third Stokes parameter to correct for Faraday rotation. Another issue associated with the antenna is sun glint. This is an issue determined by surface roughness and antenna sidelobes. Examples will be given for the random component (glint) for the case of the Aquarius antenna beams. Fortunately, the Aquarius beams mostly look to the dark side of the day-night termination, but during some portions of the year they will see sun-lighted ocean. In this case, glint could be an issue for the inner-most beam.

Dinnat, Emmanuel P.; LeVine, David M.

2006-01-01

375

$^{16}$O + $^{16}$O molecular structures of positive- and negative-parity superdeformed bands in $^{34}$S  

E-print Network

The structures of excited states in $^{34}$S are investigated using the antisymmetrized molecular dynamics and generator coordinate method (GCM). The GCM basis wave functions are calculated via energy variation with a constraint on the quadrupole deformation parameter $\\beta$. By applying the GCM after parity and angular momentum projections, the coexistence of two positive- and one negative-parity superdeformed (SD) bands are predicted, and low-lying states and other deformed bands are obtained. The SD bands have structures of $^{16}$O + $^{16}$O + two valence neutrons in molecular orbitals around the two $^{16}$O cores in a cluster picture. The configurations of the two valence neutrons are $\\delta^2$ and $\\pi^2$ for the positive-parity SD bands and $\\pi^1\\delta^1$ for the negative-parity SD band. The structural changes of the yrast states are also discussed.

Yasutaka Taniguchi

2014-08-09

376

Electronic structure of InN studied using soft x-ray emission, soft x-ray absorption, and quasiparticle band structure calculations  

E-print Network

, and quasiparticle band structure calculations L. F. J. Piper,* Leyla Colakerol, Timothy Learmonth, Per-Anders Glans within the GW framework of many body perturbation theory. Good agreement between the experimental spectra theory DFT calculations of the valence band structure of single crystalline wurtzite InN have been

377

Bioinspired, dynamic, structured surfaces for biofilm prevention  

NASA Astrophysics Data System (ADS)

Bacteria primarily exist in robust, surface-associated communities known as biofilms, ubiquitous in both natural and anthropogenic environments. Mature biofilms resist a wide range of biocidal treatments and pose persistent pathogenic threats. Treatment of adherent biofilm is difficult, costly, and, in medical systems such as catheters, frequently impossible. Adding to the challenge, we have discovered that biofilm can be both impenetrable to vapors and extremely nonwetting, repelling even low surface tension commercial antimicrobials. Our study shows multiple contributing factors, including biochemical components and multiscale reentrant topography. Reliant on surface chemistry, conventional strategies for preventing biofilm only transiently affect attachment and/or are environmentally toxic. In this work, we look to Nature's antifouling solutions, such as the dynamic spiny skin of the echinoderm, and we develop a versatile surface nanofabrication platform. Our benchtop approach unites soft lithography, electrodeposition, mold deformation, and material selection to enable many degrees of freedom—material, geometric, mechanical, dynamic—that can be programmed starting from a single master structure. The mechanical properties of the bio-inspired nanostructures, verified by AFM, are precisely and rationally tunable. We examine how synthetic dynamic nanostructured surfaces control the attachment of pathogenic biofilms. The parameters governing long-range patterning of bacteria on high-aspect-ratio (HAR) nanoarrays are combinatorially elucidated, and we discover that sufficiently low effective stiffness of these HAR arrays mechanoselectively inhibits ˜40% of Pseudomonas aeruginosa biofilm attachment. Inspired by the active echinoderm skin, we design and fabricate externally actuated dynamic elastomer surfaces with active surface microtopography. We extract from a large parameter space the critical topographic length scales and actuation time scales for achieving nearly ˜80% attachment reduction. We furthermore investigate an atomically mobile, slippery liquid infused porous surface (SLIPS) inspired by the pitcher plant. We show up to 99.6% reduction of multiple pathogenic biofilms over a 7-day period under both static and physiologically realistic flow conditions—a ˜35x improvement over state-of-the-art surface chemistry, and over a far longer timeframe. Moreover, SLIPS is shown to be nontoxic: bacteria simply cannot attach to the smooth liquid interface. These bio-inspired strategies significantly advance biofilm attachment prevention and promise a tremendous range of industrial, clinical, and consumer applications.

Epstein, Alexander K.

378

Surface electronic structure of p-InP using temperature-controlled surface photovoltage spectroscopy  

E-print Network

Surface electronic structure of p-InP using temperature-controlled surface photovoltage have been investigated using temperature-controlled surface photovoltage spectros- copy T induced by temperature-controlled surface photovoltage spectroscopy T-SPS measurements. Another goal

Shapira, Yoram

379

Band structure, optical and transport properties of KTaO3, KNbO3 and BaTiO3 in the paraelectric phase  

Microsoft Academic Search

The electronic structure of ABO3 cubic perovskite-type oxides are determined by a modified tight-binding method. The imaginary part of the dielectric constant ?2 and the moments of ?2 provide a quantitative interpretation of optical data. Constant energy surfaces near the conduction band minimum are warped spheres. The conductivity and density of states effective mass are related to conductivity, Hall and

F. M. Michel-calendini; L. Castet

1976-01-01

380

Physica E 32 (2006) 484487 Nonlinear tuning of 3D photonic band-gap structures for single-photon  

E-print Network

Physica E 32 (2006) 484­487 Nonlinear tuning of 3D photonic band-gap structures for single-photon-deterministic photon gun based on the stimulated Raman adiabatic passage pumping and the nonlinear tuning of the photonic density of states in a photonic band-gap material. We show that this device allows deterministic

Dowling, Jonathan P.

381

Structure and Function of RSV Surface Glycoproteins  

PubMed Central

The two major glycoproteins on the surface of the RSV virion, the attachment glycoprotein (G) and the fusion (F) glycoprotein, control the initial phases of infection. G targets the ciliated cells of the airways, and F causes the virion membrane to fuse with a target cell membrane. The F protein is the major target for antiviral drug development, and both G and F glycoproteins are the antigens targeted by neutralizing antibodies induced by infection. In this chapter we review the structure and function of the RSV surface glycoproteins, including recent X-ray crystallographic data of the F glycoprotein in its pre- and postfusion conformations, and discuss how this information informs antigen selection and vaccine development. PMID:24362685

McLellan, Jason S.; Ray, William C.; Peeples, Mark E.

2014-01-01

382

Finding structures with specific properties in complex configurational spaces using multi-target inverse band structure approach  

NASA Astrophysics Data System (ADS)

The conventional strategy to look for materials with desired properties is to use physical intuition to select some candidates among an enormous number of possibilities.Apart the very special cases, the solutions to these search problems are far from obvious. The inverse band structure (IBS) approach, on the other hand, search for the desired electronic structures (instead of atomic configurations) from the beginning. Here we illustrate the power of this inverse approach by applying it to the simultaneous engineering of multi-target problems, which encompass huge configurational spaces: (i) the search of a specific band gap in the quaternary (In,Ga)(As,Sb) semiconductors(a) lattice-matched to InP and, (ii) the stacking sequence of (In,Ga)As/InP superlattices leading to band gaps and strains within the range suitable for thermophotovoltaic applications(b). [3pt] (a) P. Piquini, P.A. Graf, and A. Zunger, Phys. Rev. Lett. 100, 186403 (2008); [0pt] (b) P. Piquini and A. Zunger, Phys. Rev. B 78, 161302 (2008)

Piquini, Paulo; Zunger, Alex

2009-03-01

383

Structural evaluation of Marman V-band coupling and flange with conoseal gasket  

NASA Technical Reports Server (NTRS)

Results are described of a development test program directed at evaluating the structural capabilities of the Marman V-band coupling and flange with conoseal gasket. The intended end use was for the 75K NERVA flight engine propellant lines. Of major importance in the structural evaluation was the ability to predict stresses throughout the assembly for a variety of loading conditions. Computer finite element analysis was used to predict these stresses but, for the subject configuration, large uncertainties were introduced in modeling the complex geometry and boundary conditions. The purpose of the structural tests was to obtain actual stresses and deflections for correlation with, and updating of the finite element model. Results of the incomplete test program are inconclusive with respect to determining suitability for use on the NERVA engine.

Oates, J. H.

1972-01-01

384

[Band electronic structures and crystal packing forces: Progress report, July 1, 1989--December 13, 1991  

SciTech Connect

This report briefly summaries our research accomplishments made during the period of July 1, 1989 to December 13, 1991. A number of significant progresses were achieved in our studies of several different classes of low-dimensional solid state materials. On the basis of tight-binding band electronic structure calculations, we investigated the electronic properties of various organic conducting salts, cuprate superconductors, and transition-metal oxide and chalcogenide metals to find structure-property correlations governing of the physical properties of these low-dimensional materials. By employing a number of different quality basis sets, we also carried out extensive ab initio SCF-MO/MP2 calculations on model molecular systems to accurately describe the weak intermolecular contact interactions governing the structures of organic donor slats and molecular crystals. Our research efforts led to about 80 publications and two important computer programs.

Not Available

1991-12-31

385

(Band electronic structures and crystal packing forces: Progress report, July 1, 1989--December 13, 1991)  

SciTech Connect

This report briefly summaries our research accomplishments made during the period of July 1, 1989 to December 13, 1991. A number of significant progresses were achieved in our studies of several different classes of low-dimensional solid state materials. On the basis of tight-binding band electronic structure calculations, we investigated the electronic properties of various organic conducting salts, cuprate superconductors, and transition-metal oxide and chalcogenide metals to find structure-property correlations governing of the physical properties of these low-dimensional materials. By employing a number of different quality basis sets, we also carried out extensive ab initio SCF-MO/MP2 calculations on model molecular systems to accurately describe the weak intermolecular contact interactions governing the structures of organic donor slats and molecular crystals. Our research efforts led to about 80 publications and two important computer programs.

Not Available

1991-01-01

386

Carbon Nanotube Band Structure Effect on Carbon Nanotube Field Effect Transistor  

NASA Astrophysics Data System (ADS)

The band structure of a carbon nanotube (CNT) near to the minimum band energy is parabolic. However it is not parabolic in other parts of the band energy. In the parabolic part, based on the confinement effect, we present an analytical model that captures the essence of the physical processes relevant to the operation of a carbon nanotube field effect transistor (CNTFET). The model covers seamlessly the whole range of transport from drift-diffusion to ballistic. It has been clarified that the intrinsic speed of CNTs is governed by the transit time of electrons. Although the transit time is more dependent on the saturation velocity than on the weak-field mobility, the feature of high-electron mobility is beneficial in the sense that the drift velocity is always maintained closer to the saturation velocity, at least at the drain end of the transistor where the electric field is necessarily high and controls the saturation current. The results obtained are applied to the modeling of the current-voltage characteristics of a CNTFET. The channel-length modulation is shown to arise from the drain velocity becoming closer to the ultimate saturation velocity as the drain voltage is increased.

Ahamdi, M. T.; Johari, Z.; Ismail, R.; Webb, J. F.

2010-06-01

387

Ab initio quasiparticle band structure of ABA and ABC-stacked graphene trilayers  

NASA Astrophysics Data System (ADS)

We obtain the quasiparticle band structure of ABA and ABC-stacked graphene trilayers through ab initio density-functional theory (DFT) and many-body quasiparticle calculations within the GW approximation. To interpret our results, we fit the DFT and GW ? bands to a low-energy tight-binding model, which is found to reproduce very well the observed features near the K point. The values of the extracted hopping parameters are reported and compared with available theoretical and experimental data. For both stackings, the self-energy corrections lead to a renormalization of the Fermi velocity, an effect also observed in previous calculations on monolayer graphene. They also increase the separation between the higher-energy bands, which is proportional to the nearest-neighbor interlayer hopping parameter ?1. Both features are brought to closer agreement with experiment through the self-energy corrections. Finally, other effects, such as trigonal warping, electron-hole asymmetry, and energy gaps, are discussed in terms of the associated parameters.

Menezes, Marcos G.; Capaz, Rodrigo B.; Louie, Steven G.

2014-01-01

388

Emittance, surface structure, and electron emission  

NASA Astrophysics Data System (ADS)

The emittance of high brightness electron sources, particularly field emitters and photocathodes but also thermionic sources, is increased by surface roughness on the emitter. Such structure causes local field enhancement and complicates both the prediction of emittance and the underlying emission models on which such predictions depend. In the present work, a method to find the emission trajectories near regions of high field enhancement is given and applied to emittance predictions for field, photo, and thermal emission for an analytically tractable hemispherical model. The dependence of the emittance on current density, spatial variation, and acceleration close to the emission site is identified and the impact of space charge discussed. The methodology is extensible to field emission from close-spaced wirelike structures, in particular, and extensions to that configuration are discussed. The models have application to electron sources for high frequency vacuum electronics, high power microwave devices, and free-electron lasers.

Jensen, Kevin L.; Shiffler, Donald A.; Petillo, John J.; Pan, Zhigang; Luginsland, John W.

2014-04-01

389

Complex band structure under plane-wave nonlocal pseudopotential Hamiltonian of metallic wires and electrodes  

SciTech Connect

We present a practical approach to calculate the complex band structure of an electrode for quantum transport calculations. This method is designed for plane wave based Hamiltonian with nonlocal pseudopotentials and the auxiliary periodic boundary condition transport calculation approach. Currently there is no direct method to calculate all the evanescent states for a given energy for systems with nonlocal pseudopotentials. On the other hand, in the auxiliary periodic boundary condition transport calculation, there is no need for all the evanescent states at a given energy. The current method fills this niche. The method has been used to study copper and gold nanowires and bulk electrodes.

Yang, Chao

2009-07-17

390

Staggering of the B(M1) value as a fingerprint of specific chiral bands structure  

E-print Network

Nuclear chirality has been intensively studdied for the last several years in the context of experimental as well as theoretical approach. Characteristic gamma selection rules have been predicted for the strong chiral symmetry breaking limit that has been observed in Cs isotopes. The presented analysis shows that the gamma selection rules cannot be attributed only to chiral symmetry breaking. The selection rules relate to structural composition of the chiral rotational bands, i.e. to odd particle configuration and the deformation of the core.

Ernest Grodner

2011-01-31

391

Calculation of wakefields in a 17 GHz beam-driven photonic band-gap accelerator structure  

NASA Astrophysics Data System (ADS)

We present the theoretical analysis and computer simulation of the wakefields in a 17 GHz photonic band-gap (PBG) structure for accelerator applications. Using the commercial code CST Particle Studio, the fundamental accelerating mode and dipole modes are excited by passing an 18 MeV electron beam through a seven-cell traveling-wave PBG structure. The characteristics of the longitudinal and transverse wakefields, wake potential spectrum, dipole mode distribution, and their quality factors are calculated and analyzed theoretically. Unlike in conventional disk-loaded waveguide (DLW) structures, three dipole modes (TM11-like, TM12-like, and TM13-like) are excited in the PBG structure with comparable initial amplitudes. These modes are separated by less than 4 GHz in frequency and are damped quickly due to low radiative Q factors. Simulations verify that a PBG structure provides wakefield damping relative to a DLW structure. Simulations were done with both single-bunch excitation to determine the frequency spectrum of the wakefields and multibunch excitation to compare to wakefield measurements taken at MIT using a 17 GHz bunch train. These simulation results will guide the design of next-generation high-gradient accelerator PBG structures.

Hu, Min; Munroe, Brian J.; Shapiro, Michael A.; Temkin, Richard J.

2013-02-01

392

The full 3D electronic band structure of MgB2 determined by soft x-ray ARPES  

NASA Astrophysics Data System (ADS)

MgB2 is a prototypical multi-band multi-gap superconductor with electron-phonon coupling driving Tc up to 40 K. Surprisingly, the experimental knowledge of the electronic band structure is rather limited. Here, we present the first results of angle-resolved photoelectron spectroscopy (ARPES) studies on high quality MgB2 single crystals, employing photons in the soft x-ray range with variable energy. We have been able to measure the band dispersion not only in the kx-ky plane, but also probe in detail the kz dependence and thus, the 3D nature of the bands. Furthermore, we have found the ARPES intensities to be strongly polarization dependent and their analysis provides an excellent agreement with the orbital nature of the electronic states. The calculated electronic band structure captures very well all the features revealed in our experiment.

Sassa, Yasmine; Mansson, Martin; Wojek, Bastian M.; Kobayashi, Masaki; Gotberg, Olof; Strocov, Vladimir; Zhigadlo, Nikolai; Tjernberg, Oscar; Batlogg, Bertram

2013-03-01

393

Low Wind Speed Radar Backscatter Measurements at C- and Ku-Band Obtained During the Surface Wave Dynamics Experiment  

NASA Technical Reports Server (NTRS)

Radar backscatter measurements collected at both C- and Ku-Band during the recent SurfaceWaves Dynamics Experiment (SWADE) on 1 March 1991 show dramatic variabilities of thenormalized radar cross section (sigma degree) of the ocean surface at low wind speed. Additionally,measurements of the sigma degree in the cross wind direction fluctuated much more than the sigmadegree in the upwind direction. The C- and Ku-band data are quite similar, both exhibiting a morepronounced roll off of sigma degree with decreasing neutral stability wind than indicated bypreviously published empirical model functions. The data show extremely large azimuthalmodulations, in some cases greater than 20 dB, and show good qualitative agreement with theazimuthal modulation predicted.

Carson, S. C.; Carswell, J. C.; McIntosh, R. E.; Li, F. K.; Nghiem, S. V.; Lou, S. H.; Neumann, G.; McLaughlin, D. J.

1993-01-01

394

Kinetics of band bending and electron affinity at GaAs(001) surface with nonequilibrium cesium overlayers  

NASA Astrophysics Data System (ADS)

The dosage dependences of surface band bending and effective electron affinity under cesium deposition on the Ga-rich GaAs(001) surface, along with the relaxation of these electronic properties after switching off the Cs source are experimentally studied by means of modified photoreflectance spectroscopy and photoemission quantum yield spectroscopy. At small Cs coverages, below half of a monolayer, additional features in the dosage dependence and subsequent downward relaxation of the photoemission current are determined by the variations of band bending. At coverages above half of a monolayer the upward relaxation of the photocurrent is caused supposedly by the decrease of the electron affinity due to restructuring in the nonequilibrium cesium overlayer.

Zhuravlev, A. G.; Savchenko, M. L.; Paulish, A. G.; Scheibler, H. E.; Jaroshevich, A. S.; Alperovich, V. L.

2013-12-01

395

Kinetics of band bending and electron affinity at GaAs(001) surface with nonequilibrium cesium overlayers  

SciTech Connect

The dosage dependences of surface band bending and effective electron affinity under cesium deposition on the Ga-rich GaAs(001) surface, along with the relaxation of these electronic properties after switching off the Cs source are experimentally studied by means of modified photoreflectance spectroscopy and photoemission quantum yield spectroscopy. At small Cs coverages, below half of a monolayer, additional features in the dosage dependence and subsequent downward relaxation of the photoemission current are determined by the variations of band bending. At coverages above half of a monolayer the upward relaxation of the photocurrent is caused supposedly by the decrease of the electron affinity due to restructuring in the nonequilibrium cesium overlayer.

Zhuravlev, A. G.; Savchenko, M. L.; Paulish, A. G.; Alperovich, V. L. [Rzhanov Institute of Semiconductor Physics, Lavrentieva, 13, 630090 Novosibirsk, Russia and Novosibirsk State University, Pirogova, 2, 630090 Novosibirsk (Russian Federation); Scheibler, H. E.; Jaroshevich, A. S. [Rzhanov Institute of Semiconductor Physics, Lavrentieva, 13, 630090 Novosibirsk (Russian Federation)

2013-12-04

396

Stellar Surface Structure, IAU Colloquium No. 176  

NASA Astrophysics Data System (ADS)

The IAU Symposium No. 176 on the topic "Stellar Surface Structure" was held between October 9-13th 1995 in Vienna. Five scientific Sessions - Stellar Surface Mapping Techniques, Direct Mapping: The Last Frontier, Photospheric Phenomena: Results, Outer Atmosphere Structures, Next Generation Model Atmospheres with more than 200 participants presenting 55 talks and 105 poster papers cook place at the premises of the famous Vienna University. The Vienna symposium was carefully prepared and organized by the LOC (the head of the LOC Professor K. G. Strassmeier). The Abstracts of all the scientific contributions as well as the volume of Poster Proceedings have been published by the hosts and were distributed among the participants of the Symposium. The attendees and their accompanying guests could enjoy several sightseeing tours of the Austrian capital and a rich cultural program including a reception by the Mayor of Vienna Dr M. Haupl in the Rathaus. Symposium No. 176 was sponsored by several institutions and businesses including the Austrian Government Department of Science, Research and Culture, European Space Agency, Austrian Academy of Sciences, Austrian Space Agency and many others. A generous support from the IAU in form of travel grants gave the chance to attend IAU Symposium No. 176 to more than 20 astronomers from FSU and East European countries.

Pustylnik, I.

397

The role of beryllium in the band structure of MgZnO: Lifting the valence band maximum  

NASA Astrophysics Data System (ADS)

We investigate the effect of Be on the valence band maximum (VBM) of MgZnO by measuring the band offsets of MgxZn1-xO/BexMgyZn1-x-yO heterojunctions using X-ray photoelectron spectroscopy measurements. MgxZn1-xO and BexMgyZn1-x-yO films have been grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The valence band offset ( ? E V) of Mg0.15Zn0.85O ( E g = 3.62 eV)/Be0.005Mg0.19Zn0.805O ( E g = 3.73 eV) heterojunction is 0.01 eV and Be0.005Mg0.19Zn0.805O has a lower VBM. The increased Mg composition is the main factor for the reduction of VBM. The VBM of MgxZn1-xO is lower by 0.03 eV with the enlargement of E g from 3.62 eV to 3.73 eV by increasing Mg composition. Considering the effect of increased Mg composition, it is concluded that the little amount of Be makes the VBM go up by 0.02 eV when the E g of the alloy is 3.73 eV. The ? E V of Mg0.11Zn0.89O ( E g = 3.56 eV)/Be0.007Mg0.12Zn0.873O ( E g = 3.56 eV) heterojunction is calculated to be 0.03 eV and Be0.007Mg0.12Zn0.873O has a higher VBM than Mg0.11Zn0.89O, which means that a little amount Be lifts the VBM by 0.03 eV when the E g of the alloy is 3.56 eV. The experimental measurements have offered a strong support for the theoretical research that alloying Be in MgxZn1-xO alloys is hopeful to form a higher VBM and to enhance the p-type dopability of MgZnO.

Chen, S. S.; Pan, X. H.; Chen, W.; Zhang, H. H.; Dai, W.; Ding, P.; Huang, J. Y.; Lu, B.; Ye, Z. Z.

2014-09-01

398

Structural stability and electronic properties of low-index surfaces of SnS  

NASA Astrophysics Data System (ADS)

Thin film photovoltaic cells are increasingly important for cost-effective solar energy harvesting. Layered SnS is a promising absorber material due to its high optical absorption in the visible and good doping characteristics. We use first-principles calculations based on density functional theory to study structures of low-index surfaces of SnS using stoichiometric and oxygen-containing structural models, in order to elucidate their possible effect on the efficiency of the photovoltaic device. We find that the surface energy is minimized for the surface with orientation parallel to the layer stacking direction. Compared to stoichiometric surfaces, the oxygen-containing surfaces exhibit fewer electronic states near the band gap. This reduction of near-gap surface states by oxygen should reduce recombination losses at grain boundaries and interfaces of the SnS absorber, and should be beneficial to the efficiency of the solar cell.

Tritsaris, Georgios A.; Malone, Brad D.; Kaxiras, Efthimios

2014-05-01

399

30 CFR 75.1708 - Surface structures, fireproofing.  

Code of Federal Regulations, 2010 CFR

...2010-07-01 2010-07-01 false Surface structures, fireproofing. 75.1708 Section 75.1708 Mineral Resources ...MINES Miscellaneous § 75.1708 Surface structures, fireproofing. [Statutory Provisions] After March 30, 1970,...

2010-07-01

400

30 CFR 75.1708 - Surface structures, fireproofing.  

Code of Federal Regulations, 2012 CFR

...2012-07-01 2012-07-01 false Surface structures, fireproofing. 75.1708 Section 75.1708 Mineral Resources ...MINES Miscellaneous § 75.1708 Surface structures, fireproofing. [Statutory Provisions] After March 30, 1970,...

2012-07-01

401

30 CFR 75.1708 - Surface structures, fireproofing.  

Code of Federal Regulations, 2011 CFR

...2011-07-01 2011-07-01 false Surface structures, fireproofing. 75.1708 Section 75.1708 Mineral Resources ...MINES Miscellaneous § 75.1708 Surface structures, fireproofing. [Statutory Provisions] After March 30, 1970,...

2011-07-01

402

Femtosecond laser surface structuring technique for making human enamel and dentin surfaces superwetting  

NASA Astrophysics Data System (ADS)

It is known that good wettability of enamel and dentin surfaces is a key factor in enhancing adhesion of restorative materials in dentistry. Here, we report on a femtosecond laser surface texturing approach that makes both the enamel and dentine surfaces superwetting. In contrast to the traditional chemical etching that yields random surface structures, this new approach produces engineered surface structures. The surface structure engineered and tested here is an array of femtosecond laser-produced parallel microgrooves that generates a strong capillary force. Due to the powerful capillary action, water is rapidly sucked into this engineered surface structure and spreads even on a vertical surface.

Vorobyev, A. Y.; Guo, Chunlei

2013-12-01

403

Dissociable Processes for Learning the Surface Structure and Abstract Structure of  

E-print Network

Dissociable Processes for Learning the Surface Structure and Abstract Structure of Sensorimotor for the learning of surface structure and abstract structure, respec- tively, of sensorimotor sequences. Surface structure is the sim- ple serial order of the sequence elements, whereas abstract structure is de ned

Dominey, Peter F.

404

A study of the band structures of elastic wave propagating in piezoelectric/piezomagnetic layered periodic structures  

NASA Astrophysics Data System (ADS)

This paper is concerned with wave propagation and localization in piezoelectric (PE) and piezomagnetic (PM) layered periodic structures. Both normal and oblique propagation of waves are considered. The materials are assumed to be transversely isotropic. Wave behaviors are analyzed by calculating the dispersion curves, localization factors and response spectra using the transfer matrix and/or the stiffness matrix methods. The results show that all these quantities can be used to characterize the band structures. Frequency passbands and band gaps exist in PE/PM periodic layered structures. The width of the gaps is determined by the differences between material constants of each constituent in PE/PM composites. The bigger the difference is, the wider the gap is. Most energy is carried by the transmitted waves which are of the same mode as the incident wave. However, the transmission coefficients of the quasi-shear or quasi-pressure waves arising from wave mode conversion may be relatively large at some particular frequencies in some passbands. Compared to coupled transmitted magnetoacoustic and electroacoustic waves, the transmission coefficients of electric potential and magnetic potential waves are a little bigger. This study is useful for the possible applications of PE/PM materials in the fabrication of high frequency acoustic resonance devices.

Pang, Yu; Wang, Yue-Sheng; Liu, Jin-Xi; Fang, Dai-Ning

2010-05-01

405

Fratricide-preventing friend identification tag based on photonic band structure coding  

NASA Astrophysics Data System (ADS)

A new friend foe identification tag based on photonic band structure (PBS) is presented. The tag utilizes frequency-coded radar signal return. Targets that include the passive tag responds selectively to slightly different frequencies generated by interrogating MMW radar. It is possible to use in- and out-of-band gap frequencies or defect modes of the PBS in order to obtain frequency dependent radar waves reflections. This tag can be made in the form of patch attachable such as plate or corner reflectors, to be worn by an individual marine, or to be integrated into the platform camouflage. Ultimately, it can be incorporated as smart skin or a ground or airborne vehicle. The proposed tag takes full advantage of existing sensors for interrogation (minimal chances required), it is lightweight and small in dimensions, it operates in degraded environments, it has no impact on platform vulnerability, it has low susceptibility to spoofing and mimicking (code of the day) and it has low susceptibility to active jamming. We demonstrated the operation of the tag using multi-layer dielectric (Duroid) having periodic structure of metal on top of each of the layers (metal strips in this case). The experimental results are consistent with numerical simulation. The device can be combined with temporal coding to increase target detection and identification resolution.

Eliyahu, Danny; Sadovnik, Lev S.; Manasson, Vladimir A.

2000-07-01

406

Silicon carbide embedded in carbon nanofibres: structure and band gap determination.  

PubMed

Materials drastically alter their electronic properties when being reduced to the nanoscale due to quantum effects. Concerning semiconductors, the band gap is expected to broaden as a result of the quantum confinement. In this study we report on the successful synthesis of wide bandgap SiC nanowires (with great potential for applications) and the local determination of their band gap. Their value was found to be higher with respect to bulk SiC. The nanowires are grown as a heterostructure, i.e. encapsulated in carbon nanofibres via dc hot-filament Plasma-Enhanced Chemical Vapour Deposition on the Si/SiO2 substrate. The structure of the as-produced carbon nanofibres was characterized by means of aberration-corrected high-resolution transmission electron microscopy. Two different pure SiC polytypes, namely the 3C (cubic) and the 6H (hexagonal) as well as distorted structures are observed. The SiC nanowires have diameters in the range of 10-15 nm and lengths of several hundred nanometers. The formation of the SiC is a result of the substrate etching during the growth of the CNFs and a subsequent simultaneous diffusion of not only carbon, but also silicon through the catalyst particle. PMID:25307877

Minella, Anja Bonatto; Pohl, Darius; Täschner, Christine; Erni, Rolf; Ummethala, Raghu; Rümmeli, Mark H; Schultz, Ludwig; Rellinghaus, Bernd

2014-10-21

407

Y-Shaped Amphiphilic Brushes with Switchable Micellar Surface Structures  

E-print Network

Y-Shaped Amphiphilic Brushes with Switchable Micellar Surface Structures Duangrut Julthongpiput to a functionalized silicon surface. Postgrafting hydrolysis of poly(tert-butyl acrylate) arms imparts amphiphilicity adaptive macroscopic wetting surface properties of the amphiphilic Y-shaped brushes. This surface structure

Zubarev, Eugene

408

Conceptual design of an L-band recirculating superconducting traveling wave accelerating structure for ILC  

SciTech Connect

With this paper, we propose the conceptual design of a traveling wave accelerating structure for a superconducting accelerator. The overall goal is to study a traveling wave (TW) superconducting (SC) accelerating structure for ILC that allows an increased accelerating gradient and, therefore reduction of the length of the collider. The conceptual studies were performed in order to optimize the acceleration structure design by minimizing the surface fields inside the cavity of the structure, to make the design compatible with existing technology, and to determine the maximum achievable gain in the accelerating gradient. The proposed solution considers RF feedback system redirecting the accelerating wave that passed through the superconducting traveling wave acceleration (STWA) section back to the input of the accelerating structure. The STWA structure has more cells per unit length than a TESLA structure but provides an accelerating gradient higher than a TESLA structure, consequently reducing the cost. In this paper, the STWA cell shape optimization, coupler cell design and feedback waveguide solution are considered. We also discuss the field flatness in the superconducting TW structure, the HOM modes and multipactor performance have been studied as well. The proposed TW structure design gives an overall 46% gain over the SW ILC structure if the 10 m long TW structure is employed.

Avrakhov, P.; Kanareykin, A.; Liu, Z.; Kazakov, S.; /KEK, Tsukuba; Solyak, N.; /Fermilab; Yakovlev, V.; /Omega-P, New Haven /Yale U.; Gai, W.; /Argonne

2007-06-01

409

The valence band structure of AgxRh1-x alloy nanoparticles  

NASA Astrophysics Data System (ADS)

The valence band (VB) structures of face-centered-cubic Ag-Rh alloy nanoparticles (NPs), which are known to have excellent hydrogen-storage properties, were investigated using bulk-sensitive hard x-ray photoelectron spectroscopy. The observed VB spectra profiles of the Ag-Rh alloy NPs do not resemble simple linear combinations of the VB spectra of Ag and Rh NPs. The observed VB hybridization was qualitatively reproduced via a first-principles calculation. The electronic structure of the Ag0.5Rh0.5 alloy NPs near the Fermi edge was strikingly similar to that of Pd NPs, whose superior hydrogen-storage properties are well known.

Yang, Anli; Sakata, Osami; Kusada, Kohei; Yayama, Tomoe; Yoshikawa, Hideki; Ishimoto, Takayoshi; Koyama, Michihisa; Kobayashi, Hirokazu; Kitagawa, Hiroshi

2014-10-01

410

Properties of entangled photon pairs generated in one-dimensional nonlinear photonic-band-gap structures  

E-print Network

We have developed a rigorous quantum model of spontaneous parametric down-conversion in a nonlinear 1D photonic-band-gap structure based upon expansion of the field into monochromatic plane waves. The model provides a two-photon amplitude of a created photon pair. The spectra of the signal and idler fields, their intensity profiles in the time domain, as well as the coincidence-count interference pattern in a Hong-Ou-Mandel interferometer are determined both for cw and pulsed pumping regimes in terms of the two-photon amplitude. A broad range of parameters characterizing the emitted down-converted fields can be used. As an example, a structure composed of 49 layers of GaN/AlN is analyzed as a suitable source of photon pairs having high efficiency.

Perina, Jan; Sibilia, C; Bertolotti, M; Scalora, M; Jr., Jan Perina; Centini, Marco; Sibilia, Concita; Bertolotti, Mario; Scalora, Michael

2006-01-01

411

Properties of entangled photon pairs generated in one-dimensional nonlinear photonic-band-gap structures  

E-print Network

We have developed a rigorous quantum model of spontaneous parametric down-conversion in a nonlinear 1D photonic-band-gap structure based upon expansion of the field into monochromatic plane waves. The model provides a two-photon amplitude of a created photon pair. The spectra of the signal and idler fields, their intensity profiles in the time domain, as well as the coincidence-count interference pattern in a Hong-Ou-Mandel interferometer are determined both for cw and pulsed pumping regimes in terms of the two-photon amplitude. A broad range of parameters characterizing the emitted down-converted fields can be used. As an example, a structure composed of 49 layers of GaN/AlN is analyzed as a suitable source of photon pairs having high efficiency.

Jan Perina Jr.; Marco Centini; Concita Sibilia; Mario Bertolotti; Michael Scalora

2006-04-04

412

Properties of entangled photon pairs generated in one-dimensional nonlinear photonic-band-gap structures  

SciTech Connect

We have developed a rigorous quantum model of spontaneous parametric down-conversion in a nonlinear 1D photonic-band-gap structure based upon expansion of the field into monochromatic plane waves. The model provides a two-photon amplitude of a created photon pair. The spectra of the signal and idler fields, their intensity profiles in the time domain, as well as the coincidence-count interference pattern in a Hong-Ou-Mandel interferometer are determined both for cw and pulsed pumping regimes in terms of the two-photon amplitude. A broad range of parameters characterizing the emitted down-converted fields can be used. As an example, a structure composed of 49 layers of GaN/AlN is analyzed as a suitable source of photon pairs having high efficiency.

Perina, Jan Jr.; Centini, Marco; Sibilia, Concita; Bertolotti, Mario; Scalora, Michael [Joint Laboratory of Optics of Palacky University and Institute of Physics of Academy of Sciences of the Czech Republic, 17. listopadu 50A, 772 07 Olomouc (Czech Republic); Dipartimento di Energetica, Universita La Sapienza di Roma, Via A. Scarpa 16, 00161 Rome (Italy); Charles M. Bowden Research Center, RD and EC, Redstone Arsenal, Bldg. 7804, Alabama 35898-5000 (United States)

2006-03-15

413

High-spin structure in {sup 157}Er up to and above band termination  

SciTech Connect

The high-spin structure of {sup 157}Er has been greatly expanded using the Gammasphere spectrometer to investigate the {sup 114}Cd({sup 48}Ca,5n) reaction at 215 MeV. Many new transitions have been placed in a greatly augmented level scheme up to spin 40({Dirac_h}/2{pi}) with many collective rotational sequences established. With increasing angular momentum, this nucleus undergoes a Coriolis-induced shape transition from a deformed state of collective rotation to a noncollective configuration. This transition manifests itself as favored band termination near I=45({Dirac_h}/2{pi}) in three rotational structures. Many weakly populated states lying at high excitation energy that decay into the terminating states have been discovered. Cranked-Nilsson-Strutinsky calculations suggest that the levels that feed the terminating states arise from weakly collective configurations that break the Z=64 semimagic core.

Evans, A.O.; Paul, E.S.; Choy, P.T.W.; Nolan, P.J. [Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE (United Kingdom); Simpson, J.; Appelbe, D.E.; Joss, D.T. [CCLRC Daresbury Laboratory, Daresbury, Warrington WA4 4AD (United Kingdom); Riley, M.A.; Campbell, D.B.; Pipidis, A. [Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States); Clark, R.M.; Cromaz, M.; Fallon, P.; Goergen, A.; Lee, I.Y.; Macchiavelli, A.O.; Ward, D. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Ragnarsson, I. [Department of Mathematical Physics, Lund Institute of Technology, P.O. Box 118, S-22100 Lund (Sweden)

2006-06-15

414

A combined representation method for use in band structure calculations. 1: Method  

NASA Technical Reports Server (NTRS)

A representation was described whose basis levels combine the important physical aspects of a finite set of plane waves with those of a set of Bloch tight-binding levels. The chosen combination has a particularly simple dependence on the wave vector within the Brillouin Zone, and its use in reducing the standard one-electron band structure problem to the usual secular equation has the advantage that the lattice sums involved in the calculation of the matrix elements are actually independent of the wave vector. For systems with complicated crystal structures, for which the Korringa-Kohn-Rostoker (KKR), Augmented-Plane Wave (APW) and Orthogonalized-Plane Wave (OPW) methods are difficult to apply, the present method leads to results with satisfactory accuracy and convergence.

Friedli, C.; Ashcroft, N. W.

1975-01-01

415

Perfect dual-band circular polarizer based on twisted split-ring structure asymmetric chiral metamaterial.  

PubMed

A near-perfect dual-band circular polarizer based on bilayer twisted, single split-ring resonator structure asymmetric chiral metamaterial was proposed and investigated. The simple bilayer structure with a 90° twisted angle allows for equalizing the orthogonal components of the electric field at the output interface with a 90° phase difference for a y-polarized wave propagating along the backward (-z) direction. It is found that right- and left-hand circular polarization are realized in transmissions at 7.8 and 10.1 GHz, respectively. Experiments agree well with numerical simulations, which exhibit that the polarization extinction ratio is more than 30 dB at the resonant frequencies. Further, the simple design also can be operated at the terahertz range by scaling down the geometrical parameters of the unit cell. PMID:25321375

Cheng, Yongzhi; Gong, Rongzhou; Cheng, Zhengze; Nie, Yan

2014-09-01

416

Structure of the K{sup {pi}} = 4{sup +} bands in {sup 186,188}Os  

SciTech Connect

The structures of {sub 3}{sup +} states in Os have been debated over several decades. Based on measured B(E2) values they were interpreted in {sup 186-192}Os as K{sup {pi}} = 4{sup +} two-phonon vibrations, whereas inelastic scattering, and (t,{alpha}) work imply a hexadecapole phonon description. To clarify the nature of these K{sup {pi}} = 4{sup +} bands in {sup 186,188}Os, we performed a ({sup 3}He,d) reaction on {sup 185,187}Re targets using 30 MeV {sup 3}He beams and a Q3D spectrograph. Absolute cross sections were obtained for excited states up to 3 MeV at 9 angles from 5 deg. to 50 deg. Results indicate a significant (5/2){sup +}[402]{sub {pi}}+(3/2){sup +}[402]{sub {pi}} component in agreement with quasiparticle phonon model predictions for a single hexadecapole phonon structure.

Phillips, A. A.; Garrett, P. E.; Demand, G. A.; Finlay, P.; Green, K. L.; Leach, K. G.; Schumaker, M. A.; Svensson, C. E.; Wong, J. [Dept. of Physics, University of Guelph, Guelph, ON (Canada); Bettermann, L.; Braun, N. [Institut fuer Kernphysik, Universitaet zu Koeln (Germany); Burke, D. G. [Dept. of Physics and Astronomy, McMaster University, Hamilton, ON (Canada); Faestermann, T.; Kruecken, R.; Wirth, H.-F. [Physik Dept., Technische Universitaet Muenchen, Garching (Germany); Hertenberger, R. [Fakultaet fuer Physik, Ludwig-Maximillians-Universitaet Muenchen, Garching (Germany)

2009-01-28

417

AVHRR Surface Temperature and Narrow-Band Albedo Comparison with Ground Measurements for the Greenland Ice Sheet  

NASA Technical Reports Server (NTRS)

An ice-surface temperature retrieval algorithm for the Greenland ice sheet was developed using NOAA 11 thermal radiances from channels 4 and 5. Temperature, pressure and humidity profiles, cloud observations and skin temperatures from the Swiss Federal Institute of Technology (ETH) camp, located at the equilibrium line altitude at 49 deg17 min W, 69 deg 34 min N, were used in the LOWTRAN 7 model. Through a statistical analysis of daily clear sky profiles, the coefficients that correct for the atmospheric effects were determined for the ETH-Camp field season (May to August). Surface temperatures retrieved by this method were then compared against the in situ observations with a maximum difference of 0.6 K. The NOAA 11 narrow-band planetary albedo values for channels 1 and 2 were calculated using pre-launch calibration coefficients. Scattering and absorption by the atmosphere were modelled with LOWTRAN 7. Then, narrow-band albedo values for the AVHRR visible and near infrared channels were compared with in situ high resolution spectral reflectance measurements. In the visible band (580-680 nm), AVHRR-derived narrow-band albedo and the in situ measurements corrected with radiative transfer model LOWTRAN 7 showed a difference of less than 2%. For the near infrared channel (725-1100 nm) the difference between the measured and modelled narrow-band albedo was 14%. These discrepancies could be either the result of inaccurate aerosol scattering modelling (lack of the in situ observation), or the result of sensor drift due to degradation.

Haefliger, M.; Steffen, K.; Fowler, C.

1993-01-01

418

Electronic band structure of Cu3Au: An angle-resolved photoemission study along the [111]-direction  

NASA Astrophysics Data System (ADS)

High-resolution normal photoemission (ARPE) spectra have been recorded for Cu3Au(111) with the use of polarized synchrotron and rare-gas resonance radiation in the photon energy range from 9 to 27 eV. It is for the first time that dispersions of the gold-like bands have been found experimentally. Using a fully relativistic layer-KKR photoemission formalism, occupied and unoccupied bands as well as one-step-model photoemission spectra have been calculated. The comparison of calculated spectra with experimental ones and the observation of direct-transition resonances upon photon energy near the Brillouin zone-center reveal a shift of the unoccupied ground-state bands by about +2.5 eV (self-energy shift). The direct-transition structures in the experimental spectra have been exploited to determine the dispersions of the occupied bands along the [111] direction (A line in k space). In order to determine the wave vector of the experimental direct transitions we used as final state that calculated unoccupied band along [111], which also exists in pure copper and gold up to about 20 eV above the Fermi energy (unfolded band structure), shifted by + 2.5 eV. The experimental occupied bands with Cu character are in very good agreement with theory after shifting the latter by about 0.3 eV to lower energy, whereas somewhat bigger discrepancies exist for the gold-like bands.

Lau, Markus; Löbus, Stefan; Courths, Ralf; H