Sample records for l-band superconducting traveling

  1. Progress towards 3-cell superconducting traveling wave cavity cryogenic test

    NASA Astrophysics Data System (ADS)

    Kostin, R.; Avrakhov, P.; Kanareykin, A.; Yakovlev, V.; Solyak, N.

    2017-12-01

    This paper describes a superconducting L-band travelling wave cavity for electron linacs as an alternative to the 9-cell superconducting standing wave Tesla type cavity. A superconducting travelling wave cavity may provide 20-40% higher accelerating gradient by comparison with conventional cavities. This feature arises from an opportunity to use a smaller phase advance per cell which increases the transit time factor and affords the opportunity to use longer cavities because of its significantly smaller sensitivity to manufacturing errors. Two prototype superconducting travelling wave cavities were designed and manufactured for a high gradient travelling wave demonstration at cryogenic temperature. This paper presents the main milestones achieved towards this test.

  2. Superconducting magnet for a Ku-band maser.

    NASA Technical Reports Server (NTRS)

    Berwin, R.; Wiebe, E.; Dachel, P.

    1972-01-01

    A superconducting magnet to provide a uniform magnetic field of up to 8000 G in a 1.14-cm gap for the 15.3-GHz (Ku-band) traveling wave maser is described. The magnet operates in a persistent mode in the vacuum environment of a closed-cycle helium refrigerator (4.5 K). The features of a superconducting switch, which has both leads connected to 4.5 K heat stations and thereby does not receive heat generated by the magnet charging leads, are described.

  3. Superconducting traveling wave accelerators

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Farkas, Z.D.

    1984-11-01

    This note considers the applicability of superconductivity to traveling wave accelerators. Unlike CW operation of a superconducting standing wave or circulating wave accelerator section, which requires improvement factors (superconductor conductivity divided by copper conductivity) of about 10/sup 6/ in order to be of practical use, a SUperconducting TRaveling wave Accelerator, SUTRA, operating in the pulsed mode requires improvement factors as low as about 10/sup 3/, which are attainable with niobium or lead at 4.2K, the temperature of liquid helium at atmospheric pressure. Changing from a copper traveling wave accelerator to SUTRA achieves the following. (1) For a given gradient SUTRAmore » reduces the peak and average power requirements typically by a factor of 2. (2) SUTRA reduces the peak power still further because it enables us to increase the filling time and thus trade pulse width for gradient. (3) SUTRA makes possible a reasonably long section at higher frequencies. (4) SUTRA makes possible recirculation without additional rf average power. 8 references, 6 figures, 1 table.« less

  4. High Power RF Testing of A 3-Cell Superconducting Traveling Wave Accelerating Structure

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kanareykin, Alex; Kostin, Romna; Avrakhov, Pavel

    Euclid Techlabs has completed the Phase II SBIR project, entitled “High Power RF Testing of a 3-Cell Superconducting Traveling Wave Accelerating Structure” under Grant #DE-SC0006300. In this final technical report, we summarize the major achievements of Phase I of the project and review the details of Phase II of the project. The accelerating gradient in a superconducting structure is limited mainly by quenching, i.e., by the maximum surface RF magnetic field. Various techniques have been developed to increase the gradient. A traveling wave accelerating SC structure with a feedback waveguide was suggested to allow an increased transit time factor andmore » ultimately, a maximum gradient that is 22%-24% higher than in the best of the time standing wave SRF cavity solution. The proposed structure has an additional benefit in that it can be fabricated much longer than the standing wave ones that are limited by the field flatness factor. Taken together, all of these factors will result in a significant overall length and, correspondingly cost reduction of the SRF based linear collider ILC or SRF technology based FELs. In Phase I of this project, a 3-cell L-band SC traveling wave cavity was designed. Cavity shape, surface field ratios, inter-cell coupling coefficients, accelerating field flatness have been reviewed with the analysis of tuning issues. Moreover, the technological aspects of SC traveling wave accelerating structure fabrication have been studied. As the next step in the project, the Phase II experimental program included engineering design, manufacturing, surface processing and high gradient testing. Euclid Techlabs, LLC contracted AES, Inc. to manufacture two niobium cavities. Euclid Techlabs cold tested traveling wave regime in the cavity, and the results showed very good agreement with mathematical model specially developed for superconducting traveling wave cavity performance analysis. Traveling wave regime was adjusted by amplitude and phase

  5. Superconducting magnets for traveling-wave maser application. Technical documentary report, Oct 1960--Mar 1962

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Okwit, S.; Siegel, K.; Smith, J.G.

    1962-09-01

    Results of an investigation to determine the feasibility of incorporating superconducting magnet techniques in the design of traveling-wave maser systems are reported. Several different types of magnet configurations were investigated: isomagnets, Helmholtz coils, modified Helmholtz coils, air-core solenoids, and magnetic end-loaded air-core solenoids. The magnetic end-loaded air-core solenoid was found to be the best configuration for the S-band maser under consideration. This technique yielded relatively large regions of field homogeneity with relatively small aspect ratios (length of solenoid/diameter of solenoid). Several small-scale models of full-length superconducting magnets and foreshortened end-loaded superconducting magnets were constructed using un-annealed niobium wire. Measurements havemore » shown that these magnets were adequate for traveling-wave maser applications that require magnetic fields up to 2,200 G and marginal for magnetic fields up to 2,500 G.« less

  6. Graphite, graphene and the flat band superconductivity

    NASA Astrophysics Data System (ADS)

    Volovik, G. E.

    2018-04-01

    Superconductivity has been observed in bilayer graphene [1,2]. The main factor, which determines the mechanism of the formation of this superconductivity is the "magic angle" of twist of two graphene layers, at which the electronic band structure becomes nearly flat. The specific role played by twist and by the band flattening, has been earlier suggested for explanations of the signatures of room-temperature superconductivity observed in the highly oriented pyrolytic graphite (HOPG), when the quasi two-dimensional interfaces between the twisted domains are present. The interface contains the periodic array of misfit dislocations (analogs of the boundaries of the unit cell of the Moire superlattice in bilayer graphene), which provide the possible source of the flat band. This demonstrates that it is high time for combination of the theoretical and experimental efforts in order to reach the reproducible room-temperature superconductivity in graphite or in similar real or artificial materials.

  7. Superconductivity in an electron band just above the Fermi level: possible route to BCS-BEC superconductivity.

    PubMed

    Okazaki, K; Ito, Y; Ota, Y; Kotani, Y; Shimojima, T; Kiss, T; Watanabe, S; Chen, C-T; Niitaka, S; Hanaguri, T; Takagi, H; Chainani, A; Shin, S

    2014-02-28

    Conventional superconductivity follows Bardeen-Cooper-Schrieffer(BCS) theory of electrons-pairing in momentum-space, while superfluidity is the Bose-Einstein condensation(BEC) of atoms paired in real-space. These properties of solid metals and ultra-cold gases, respectively, are connected by the BCS-BEC crossover. Here we investigate the band dispersions in FeTe(0.6)Se(0.4)(Tc = 14.5 K ~ 1.2 meV) in an accessible range below and above the Fermi level(EF) using ultra-high resolution laser angle-resolved photoemission spectroscopy. We uncover an electron band lying just 0.7 meV (~8 K) above EF at the Γ-point, which shows a sharp superconducting coherence peak with gap formation below Tc. The estimated superconducting gap Δ and Fermi energy [Symbol: see text]F indicate composite superconductivity in an iron-based superconductor, consisting of strong-coupling BEC in the electron band and weak-coupling BCS-like superconductivity in the hole band. The study identifies the possible route to BCS-BEC superconductivity.

  8. Hole superconductivity in a generalized two-band model

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hong, X.Q.; Hirsch, J.E.

    1992-06-01

    We study superconductivity in a two-band model that generalizes the model introduced by Suhl, Matthias, and Walker: All possible interaction terms coupling both bands are included. The pairing interaction is assumed to originate in the momentum dependence of the intraband interactions that arises in the model of hole superconductivity. The model generically displays a single critical temperature and two gaps, with the larger gap associated with the band with strongest holelike character to the carriers. The dependence of the critical temperature and of the magnitudes of the gaps on the various parameters in the Hamiltonian is studied.

  9. Theory of multiwave mixing within the superconducting kinetic-inductance traveling-wave amplifier

    NASA Astrophysics Data System (ADS)

    Erickson, R. P.; Pappas, D. P.

    2017-03-01

    We present a theory of parametric mixing within the coplanar waveguide (CPW) of a superconducting nonlinear kinetic-inductance traveling-wave (KIT) amplifier engineered with periodic dispersion loadings. This is done by first developing a metamaterial band theory of the dispersion-engineered KIT using a Floquet-Bloch construction and then applying it to the description of mixing of the nonlinear RF traveling waves. Our theory allows us to calculate signal gain versus signal frequency in the presence of a frequency stop gap, based solely on loading design. We present results for both three-wave mixing (3WM), with applied dc bias, and four-wave mixing (4WM), without dc. Our theory predicts an intrinsic and deterministic origin to undulations of 4WM signal gain with signal frequency, apart from extrinsic sources, such as impedance mismatch, and shows that such undulations are absent from 3WM signal gain achievable with dc. Our theory is extensible to amplifiers based on Josephson junctions in a lumped LC-ladder transmission line (TWPA).

  10. Flat-band superconductivity in strained Dirac materials

    NASA Astrophysics Data System (ADS)

    Kauppila, V. J.; Aikebaier, F.; Heikkilä, T. T.

    2016-06-01

    We consider superconducting properties of a two-dimensional Dirac material such as graphene under strain that produces a flat-band spectrum in the normal state. We show that in the superconducting state, such a model results in a highly increased critical temperature compared to the case without the strain, inhomogeneous order parameter with two-peak shaped local density of states and yet a large and almost uniform and isotropic supercurrent. This model could be realized in strained graphene or ultracold atom systems and could be responsible for unusually strong superconductivity observed in some graphite interfaces and certain IV-VI semiconductor heterostructures.

  11. Universal phase diagrams with superconducting domes for electronic flat bands

    NASA Astrophysics Data System (ADS)

    Löthman, Tomas; Black-Schaffer, Annica M.

    2017-08-01

    Condensed matter systems with flat bands close to the Fermi level generally exhibit, due to their very large density of states, extraordinarily high critical ordering temperatures of symmetry-breaking orders, such as superconductivity and magnetism. Here we show that the critical temperatures follow one of two universal curves with doping away from a flat band depending on the ordering channel, which completely dictates both the general order competition and the phase diagram. Notably, we find that orders in the particle-particle channel (superconducting orders) survive decisively farther than orders in the particle-hole channel (magnetic or charge orders) because the channels have fundamentally different polarizabilities. Thus, even if a magnetic or charge order initially dominates, superconducting domes are still likely to exist on the flanks of flat bands. We apply these general results to both the topological surface flat bands of rhombohedral ABC-stacked graphite and to the Van Hove singularity of graphene.

  12. K-Band Traveling-Wave Tube Amplifier

    NASA Technical Reports Server (NTRS)

    Force, Dale A.; Simons, Rainee N.; Peterson, Todd T.; Spitsen, Paul C.

    2010-01-01

    A new space-qualified, high-power, high-efficiency, K-band traveling-wave tube amplifier (TWTA) will provide high-rate, high-capacity, direct-to-Earth communications for science data and video gathered by the Lunar Reconnaissance Orbiter (LRO) during its mission. Several technological advances were responsible for the successful demonstration of the K-band TWTA.

  13. Two-band induced superconductivity in single-layer graphene and topological insulator bismuth selenide

    NASA Astrophysics Data System (ADS)

    Talantsev, E. F.; Crump, W. P.; Tallon, J. L.

    2018-01-01

    Proximity-induced superconductivity in single-layer graphene (SLG) and in topological insulators represent almost ideal examples of superconductivity in two dimensions. Fundamental mechanisms governing superconductivity in the 2D limit are of central interest for modern condensed-matter physics. To deduce fundamental parameters of superconductor/graphene/superconductor and superconductor/bismuth selenide/superconductor junctions we investigate the self-field critical currents in these devices using the formalism of the Ambegaokar-Baratoff model. Our central finding is that the induced superconducting state in SLG and bismuth selenide each exhibits gapping on two superconducting bands. Based on recent results obtained on ultra-thin films of natural superconductors, including single-atomic layer of iron selenide, double and triple atomic layers of gallium, and several atomic layer tantalum disulphide, we conclude that a two-band induced superconducting state in SLG and bismuth selenide is part of a wider, more general multiple-band phenomenology of currently unknown origin.

  14. Exotic superconductivity with enhanced energy scales in materials with three band crossings

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Ping; Nandkishore, Rahul M.

    2018-04-01

    Three band crossings can arise in three-dimensional quantum materials with certain space group symmetries. The low energy Hamiltonian supports spin one fermions and a flat band. We study the pairing problem in this setting. We write down a minimal BCS Hamiltonian and decompose it into spin-orbit coupled irreducible pairing channels. We then solve the resulting gap equations in channels with zero total angular momentum. We find that in the s-wave spin singlet channel (and also in an unusual d-wave `spin quintet' channel), superconductivity is enormously enhanced, with a possibility for the critical temperature to be linear in interaction strength. Meanwhile, in the p-wave spin triplet channel, the superconductivity exhibits features of conventional BCS theory due to the absence of flat band pairing. Three band crossings thus represent an exciting new platform for realizing exotic superconducting states with enhanced energy scales. We also discuss the effects of doping, nonzero temperature, and of retaining additional terms in the k .p expansion of the Hamiltonian.

  15. Topological Maxwell Metal Bands in a Superconducting Qutrit

    NASA Astrophysics Data System (ADS)

    Tan, Xinsheng; Zhang, Dan-Wei; Liu, Qiang; Xue, Guangming; Yu, Hai-Feng; Zhu, Yan-Qing; Yan, Hui; Zhu, Shi-Liang; Yu, Yang

    2018-03-01

    We experimentally explore the topological Maxwell metal bands by mapping the momentum space of condensed-matter models to the tunable parameter space of superconducting quantum circuits. An exotic band structure that is effectively described by the spin-1 Maxwell equations is imaged. Threefold degenerate points dubbed Maxwell points are observed in the Maxwell metal bands. Moreover, we engineer and observe the topological phase transition from the topological Maxwell metal to a trivial insulator, and report the first experiment to measure the Chern numbers that are higher than one.

  16. Green's-function theory of dirty two-band superconductivity

    NASA Astrophysics Data System (ADS)

    Asano, Yasuhiro; Golubov, Alexander A.

    2018-06-01

    We study the effects of random nonmagnetic impurities on the superconducting transition temperature Tc in a two-band superconductor, where we assume an equal-time spin-singlet s -wave pair potential in each conduction band and the hybridization between the two bands as well as the band asymmetry. In the clean limit, the phase of hybridization determines the stability of two states, called s++ and s+-. The interband impurity scatterings decrease Tc of the two states exactly in the same manner when time-reversal symmetry is preserved in the Hamiltonian. We find that a superconductor with larger hybridization shows more moderate suppression of Tc. This effect can be explained by the presence of odd-frequency Cooper pairs, which are generated by the band hybridization in the clean limit and are broken by impurities.

  17. The modification of X and L band radar signals by monomolecular sea slicks

    NASA Technical Reports Server (NTRS)

    Huehnerfuss, H.; Alpers, W.; Cross, A.; Garrett, W. D.; Keller, W. C.; Plant, W. J.; Schuler, D. L.; Lange, P. A.; Schlude, F.

    1983-01-01

    One methyl oleate and two oleyl alcohol surface films were produced on the surface of the North Sea under comparable oceanographic and meteorological conditions in order to investigate their influence on X and L band radar backscatter. Signals are backscattered in these bands primarily by surface waves with lengths of about 2 and 12 cm, respectively, and backscattered power levels in both bands were reduced by the slicks. The reduction was larger at X band than at L band, however, indicating that shorter waves are more intensely damped by the surface films. The oleyl alcohol film caused greater attenuation of short gravity waves than the film of methyl oleate, thus demonstrating the importance of the physicochemical properties of films on the damping of wind-generated gravity capillary waves. Finally, these experiments indicate a distinct dependence of the degree of damping on the angle between wind and waves. Wind-generated waves traveling in the wind direction are more intensely damped by surface films than are waves traveling at large angles to the wind.

  18. Suppression of Gain Ripples in Superconducting Traveling-Wave Kinetic Inductance Amplifiers

    NASA Astrophysics Data System (ADS)

    Bal, Mustafa; Erickson, Robert P.; Ku, Hsiang Sheng; Wu, Xian; Pappas, David P.

    Superconducting traveling-wave kinetic inductance (KIT) amplifiers demonstrated gain over a wide bandwidth with high dynamic range and low noise. However, the gain curve exhibits ripples. Impedance mismatch at the input and output ports of the KIT amplifier as wells as split ground planes of the coplanar waveguide (CPW) geometry are potential contributors to the ripple in the gain curve. Here we study the origin of these ripples in KIT amplifiers configured in CPW geometry using approximately 20 nm thick NbTiN films grown by reactive co-sputtering of NbN and TiN. Our NbTiN films have non-linear kinetic inductance as a function of current, described by L =L0 (1 +(I /I*) 2) , where I* = 15 . 96 +/- 0 . 11 mA measured by time domain reflectometry. We report the results of implementing an impedance taper that takes into account a significantly reduced phase velocity as it narrows, adding Au onto the CPW split grounds, as well as employing different designs of dispersion engineering. Qubit Measurements using KIT amplifiers will also be reported.

  19. Dirty two-band superconductivity with interband pairing order

    NASA Astrophysics Data System (ADS)

    Asano, Yasuhiro; Sasaki, Akihiro; Golubov, Alexander A.

    2018-04-01

    We study theoretically the effects of random nonmagnetic impurities on the superconducting transition temperature T c in a two-band superconductor characterized by an equal-time s-wave interband pairing order parameter. Because of the two-band degree of freedom, it is possible to define a spin-triplet s-wave pairing order parameter as well as a spin-singlet s-wave order parameter. The former belongs to odd-band-parity symmetry class, whereas the latter belongs to even-band-parity symmetry class. In a spin-singlet superconductor, T c is insensitive to the impurity concentration when we estimate the self-energy due to the random impurity potential within the Born approximation. On the other hand in a spin-triplet superconductor, T c decreases with the increase of the impurity concentration. We conclude that Cooper pairs belonging to odd-band-parity symmetry class are fragile under the random impurity potential even though they have s-wave pairing symmetry.

  20. STS studies of the pi-band superconductivity in MgB2 in a transverse field

    NASA Astrophysics Data System (ADS)

    Griggs, C.; Eskildsen, M. R.; Zhigadlo, N. D.; Karpinski, J.

    2012-02-01

    Since being discovered MgB2 has become the paradigm for two-band/two-gap superconductivity. Early scanning tunneling spectroscopy (STS) measurements, showed a rapid suppression of the superconductivty in the isotropic π-band for modest applied fields H c. These measurements were performed with the tunnel current (It) parallel to the crystalline c-axis which couple, almost exclusively, to the π-band, and with the suppression attributed to vortex core overlap. Here we report STS measurements performed in a transverse field, such that Itc H. In this configuration no vortices are cutting through the image plane, and instead the superconducting phase is affected by the Meissner currents running within one penetration depth of the sample surface. Within this field orientation we observe far less suppression of the superconducting state in the π-band compared to the earlier measurements with H c. A clear gap is seen up to H= 0.9 T.

  1. Reentrant high-magnetic field superconductivity in a clean two-dimensional superconductor with shallow band

    NASA Astrophysics Data System (ADS)

    Koshelev, Alexei E.; Song, Kok Wee

    We investigate the superconducting instability in the magnetic field for a clean two-dimensional multiple-band superconductor in the vicinity of the Lifshitz transition when one of the bands is very shallow. Due to a small number of carriers in this band, the quasiclassical Werthamer-Helfand approximation breaks down and Landau quantization has to be taken into account. We found that the transition temperature Tc 2 (H) has giant oscillations and is resonantly enhanced at the magnetic fields corresponding to full occupancy of the Landau levels in the shallow band. This enhancement is especially pronounced for the lowest Landau level. As a consequence, the reentrant superconducting regions in the temperature-field phase diagram emerge at low temperatures near the magnetic fields at which the chemical potential matches the Landau levels. These regions may be disconnected from the main low-field superconducting region. The specific behavior depends on the relative strength of the intraband and interband coupling constants and the effect is most pronounced when the interband coupling dominates. The Zeeman spin splitting reduces sizes of the reentrant regions and changes their location in the parameter space. The predicted behavior may realize in the gate-tuned FeSe monolayer. This work was supported by the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the US DOE, Office of Science, under Award No. DEAC0298CH1088.

  2. Performance of horn-coupled transition edge sensors for L- and S-band optical detection on the SAFARI instrument

    NASA Astrophysics Data System (ADS)

    Goldie, D. J.; Glowacka, D. M.; Withington, S.; Chen, Jiajun; Ade, P. A. R.; Morozov, D.; Sudiwala, R.; Trappe, N. A.; Quaranta, O.

    2016-07-01

    We describe the geometry, architecture, dark- and optical performance of ultra-low-noise transition edge sensors as THz detectors for the SAFARI instrument. The TESs are fabricated from superconducting Mo/Au bilayers coupled to impedance-matched superconducting β-phase Ta thin-film absorbers. The detectors have phonon-limited dark noise equivalent powers of order 0.5 - 1.0 aW/ √ Hz and saturation powers of order 20 - 40 fW. The low temperature test configuration incorporating micro-machined backshorts is also described, and construction and typical performance characteristics for the optical load are shown. We report preliminary measurements of the optical performance of these TESs for two SAFARI bands; L-band at 110 - 210 μm and S-band 34 - 60 μm .

  3. A Novel Ku-Band/Ka-Band and Ka-Band/E-Band Multimode Waveguide Couplers for Power Measurement of Traveling-Wave Tube Amplifier Harmonic Frequencies

    NASA Technical Reports Server (NTRS)

    Wintucky, Edwin G.; Simons, Rainee N.

    2015-01-01

    This paper presents the design, fabrication and test results for a novel waveguide multimode directional coupler (MDC). The coupler, fabricated from two dissimilar frequency band waveguides, is capable of isolating power at the second harmonic frequency from the fundamental power at the output port of a traveling-wave tube (TWT) amplifier. Test results from proof-of-concept demonstrations are presented for a Ku-band/Ka-band MDC and a Ka-band/E-band MDC. In addition to power measurements at harmonic frequencies, a potential application of the MDC is in the design of a satellite borne beacon source for atmospheric propagation studies at millimeter-wave (mm-wave) frequencies (Ka-band and E-band).

  4. High-Power, High-Efficiency Ka-Band Space Traveling-Wave Tube

    NASA Technical Reports Server (NTRS)

    Krawczyk, Richard; Wilson, Jeffrey; Simons, Rainee; Williams, Wallace; Bhasin, Kul; Robbins, Neal; Dibb, Daniel; Menninger, William; Zhai, Xiaoling; Benton, Robert; hide

    2007-01-01

    The L-3 Communications Model 999H traveling-wave tube (TWT) has been demonstrated to generate an output power of 144 W at 60-percent overall efficiency in continuous-wave operation over the frequency band from 31.8 to 32.3 GHz. The best TWT heretofore commercially available for operation in the affected frequency band is characterized by an output power of only 35 W and an efficiency of 50 percent. Moreover, whereas prior TWTs are limited to single output power levels, it has been shown that the output power of the Model 999H can be varied from 54 to 144 W. A TWT is a vacuum electronic device used to amplify microwave signals. TWTs are typically used in free-space communication systems because they are capable of operating at power and efficiency levels significantly higher than those of solid-state devices. In a TWT, an electron beam is generated by an electron gun consisting of a cathode, focusing electrodes, and an anode. The electrons pass through a hole in the anode and are focused into a cylindrical beam by a stack of periodic permanent magnets and travel along the axis of an electrically conductive helix, along which propagates an electromagnetic wave that has been launched by an input signal that is to be amplified. The beam travels within the helix at a velocity close to the phase velocity of the electromagnetic wave. The electromagnetic field decelerates some of the electrons and accelerates others, causing the beam to become formed into electron bunches, which further interact with the electromagnetic wave in such a manner as to surrender kinetic energy to the wave, thereby amplifying the wave. The net result is to amplify the input signal by a factor of about 100,000. After the electrons have passed along the helix, they impinge on electrodes in a collector. The collector decelerates the electrons in such a manner as to recover most of the remaining kinetic energy and thereby significantly increase the power efficiency of the TWT.

  5. Realization of space-time inversion-invariant topological semimetal-bands in superconducting quantum circuits.

    NASA Astrophysics Data System (ADS)

    Yu, Y.; Tan, X.; Liu, Q.; Xue, G.; Yu, H.; Zhao, Y.; Wang, Z.

    Topological band theory has attracted much attention since several types of topological metals and semimetals have been explored. These robustness of nodal band structures are symmetry-protected, whose topological features have deepened and widened the understandings of condensed matter physics. Meanwhile, as artificial quantum systems superconducting circuits possess high controllability, supplying a powerful approach to investigate topological properties of condensed matter systems. We realize a Hamiltonian with space-time (PT) symmetry by mapping momentum space of nodal band structure to parameter space in a superconducting quantum circuit. By measuring energy spectrum of the system, we observe the gapless band structure of topological semimetals, shown as Dirac points in momentum space. The phase transition from topological semimetal to topological insulator can be realized by continuously tuning the parameter in Hamiltonian. We add perturbation to broken time reversal symmetry. As long as the combined PT symmetry is preserved, the Dirac points of the topological semimetal are still observable, suggesting the robustness of the topological protection of the gapless energy band. Our work open a platform to simulate the relation between the symmetry and topological stability in condensed matter systems. Supported by the NKRDP of China (2016YFA0301802) and the GRF of Hong Kong (HKU173051/14P&HKU173055/15P).

  6. Study of the model of hole superconductivity in multiple band cases and its application to transition metals

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hong, X.Q.

    1992-01-01

    The authors have studied a simple model consisting of a chain of atoms with two atoms per unit cell. This model develops two bands when the inter-cell and intra-cell hopping amplitudes are different. They have found that superconductivity predominantly occurs when the Fermi level is close to the top of the upper band where the wavefunction has antibonding feature both inside the unit cell and between unit cells. Superconductivity occurs only in a restricted parameter range when the Fermi level is close to the top of the lower band because of the repulsive interaction within the unit cell. They findmore » that pair expectation values that 'mix' carriers of both bands can exist when interband interactions other than V12 of Suhl et al are present. But the magnitude of the 'mixed pairs' order parameters is much smaller than that of the intra-band pairs. The V12 of Suhl et al is the most important interband interaction that gives rise to the main features of a two-band model: a single transition temperature and two different gaps. They have used the model of hole superconductivity to study the variation of T(sub c) among transition metal series--the Matthias rules. They have found that the observed T(sub c)'s are consistent with superconductivity of a metal with multiple bands at the Fermi level being caused by the single band with strongest antibonding character at the Fermi level. When the Fermi level is the lower part of a band, there is no T(sub c). As the band is gradually filled, T(sub c) rises, passes through a maximum, then drops to zero when the band is full. This characteristic feature is independent of any fine structure of the band. The position of the peak and the width of the peak are correlated. Quantitative agreement with the experimental results is obtained by choosing parameters of onsite Coulomb interaction U, modulated hopping term Delta-t, and nearest neighbor repulsion V to fit the magnitude of T(sub c) and the positions of experimental peaks.« less

  7. Elaboration of the α-model derived from the BCS theory of superconductivity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Johnston, David C.

    2013-10-14

    The single-band α-model of superconductivity (Padamsee et al 1973 J. Low Temp. Phys. 12 387) is a popular model that was adapted from the single-band Bardeen–Cooper–Schrieffer (BCS) theory of superconductivity mainly to allow fits to electronic heat capacity versus temperature T data that deviate from the BCS prediction. The model assumes that the normalized superconducting order parameter Δ(T)/Δ(0) and therefore the normalized London penetration depth λL(T)/λL(0) are the same as in BCS theory, calculated using the BCS value αBCS ≈ 1.764 of α ≡ Δ(0)/kBTc, where kB is The single-band α-model of superconductivity (Padamsee et al 1973 J. Low Temp.more » Phys. 12 387) is a popular model that was adapted from the single-band Bardeen–Cooper–Schrieffer (BCS) theory of superconductivity mainly to allow fits to electronic heat capacity versus temperature T data that deviate from the BCS prediction. The model assumes that the normalized superconducting order parameter Δ(T)/Δ(0) and therefore the normalized London penetration depth λL(T)/λL(0) are the same as in BCS theory, calculated using the BCS value αBCS ≈ 1.764 of α ≡ Δ(0)/kBTc, where kB is Boltzmann's constant and Tc is the superconducting transition temperature. On the other hand, to calculate the electronic free energy, entropy, heat capacity and thermodynamic critical field versus T, the α-model takes α to be an adjustable parameter. Here we write the BCS equations and limiting behaviors for the superconducting state thermodynamic properties explicitly in terms of α, as needed for calculations within the α-model, and present plots of the results versus T and α that are compared with the respective BCS predictions. Mechanisms such as gap anisotropy and strong coupling that can cause deviations of the thermodynamics from the BCS predictions, especially the heat capacity jump at Tc, are considered. Extensions of the α-model that have appeared in the literature, such as the two-band

  8. Magnetic, superconducting and electron-boson properties of GdO(F)FeAs oxypnictides

    NASA Astrophysics Data System (ADS)

    Kuzmicheva, Tatiana; Sadakov, Andrey; Muratov, Andrei; Kuzmichev, Svetoslav; Khlybov, Yevgeny; Kulikova, Lyudmila; Eltsev, Yuri

    2018-05-01

    We performed comprehensive studies of nearly optimal fluorine-substituted GdO1-xFx FeAs oxypnictide superconductors with TC = 48 - 53 K . Specific heat measurements revealed a sharp peak at T = 3.5 K that shifts to lower temperatures with magnetic field increase. This peak corresponds to an antiferromagnetic ordering in Gd3+ ion sublattice and may indicate coexistence between superconducting and magnetic orderings. Andreev transport through artificially made constriction demonstrated two channels for the carriers from the band(s) with the large superconducting gap as well as from those with the small gap. As expected, the presence of a transport channel with the bands mixing (ΔL +ΔS) was not detected. Using intrinsic multiple Andreev reflections effect (IMARE) spectroscopy, we determined two superconducting gaps, ΔS ≈ 2.7 meV , and ΔL ≈ 11.6 meV . The reproducible fine structure in the dI(V)/dV spectra of the Andreev contacts (satellites of the main subharmonic gap structure for ΔL) was interpreted as caused by a resonant emission of bosons with the energy ε0 = 12 - 15 meV ≈ΔL +ΔS during the process of multiple Andreev reflections (MAR) for normal carriers in ΔL-band(s) transport channel.

  9. Correlation between superconductivity, band filling, and electron confinement at the LaAlO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Smink, A. E. M.; Stehno, M. P.; de Boer, J. C.; Brinkman, A.; van der Wiel, W. G.; Hilgenkamp, H.

    2018-06-01

    By combined top- and backgating, we explore the correlation of superconductivity with band filling and electron confinement at the LaAlO3/SrTiO3 interface. We find that the top- and backgate voltages have distinctly different effects on the superconducting critical temperature, implying that the confining potential well has a profound effect on superconductivity. We investigate the origin of this behavior by comparing the gate dependence of Tc to the corresponding evolution of the band filling with gate voltage. For several backgate voltages, we observe maximum Tc to consistently coincide with a kink in tuning the band filling for high topgate voltage. Self-consistent Schrödinger-Poisson calculations relate this kink to a Lifshitz transition of the second dx y subband. These results establish a major role for confinement-induced subbands in the phase diagram of SrTiO3 surface states, and establish gating as a means to control the relative energy of these states.

  10. Precipitation Estimation Using L-Band and C-Band Soil Moisture Retrievals

    NASA Technical Reports Server (NTRS)

    Koster, Randal D.; Brocca, Luca; Crow, Wade T.; Burgin, Mariko S.; De Lannoy, Gabrielle J. M.

    2016-01-01

    An established methodology for estimating precipitation amounts from satellite-based soil moisture retrievals is applied to L-band products from the Soil Moisture Active Passive (SMAP) and Soil Moisture and Ocean Salinity (SMOS) satellite missions and to a C-band product from the Advanced Scatterometer (ASCAT) mission. The precipitation estimates so obtained are evaluated against in situ (gauge-based) precipitation observations from across the globe. The precipitation estimation skill achieved using the L-band SMAP and SMOS data sets is higher than that obtained with the C-band product, as might be expected given that L-band is sensitive to a thicker layer of soil and thereby provides more information on the response of soil moisture to precipitation. The square of the correlation coefficient between the SMAP-based precipitation estimates and the observations (for aggregations to approximately100 km and 5 days) is on average about 0.6 in areas of high rain gauge density. Satellite missions specifically designed to monitor soil moisture thus do provide significant information on precipitation variability, information that could contribute to efforts in global precipitation estimation.

  11. Superconductivity in compensated and uncompensated semiconductors.

    PubMed

    Yanase, Youichi; Yorozu, Naoyuki

    2008-12-01

    We investigate the localization and superconductivity in heavily doped semiconductors. The crossover from the superconductivity in the host band to that in the impurity band is described on the basis of the disordered three-dimensional attractive Hubbard model for binary alloys. The microscopic inhomogeneity and the thermal superconducting fluctuation are taken into account using the self-consistent 1-loop order theory. The superconductor-insulator transition accompanies the crossover from the host band to the impurity band. We point out an enhancement of the critical temperature T c around the crossover. Further localization of electron wave functions leads to the localization of Cooper pairs and induces the pseudogap. We find that both the doping compensation by additional donors and the carrier increase by additional acceptors suppress the superconductivity. A theoretical interpretation is proposed for the superconductivity in the boron-doped diamond, SiC, and Si.

  12. Superconductivity in compensated and uncompensated semiconductors

    PubMed Central

    Yanase, Youichi; Yorozu, Naoyuki

    2008-01-01

    We investigate the localization and superconductivity in heavily doped semiconductors. The crossover from the superconductivity in the host band to that in the impurity band is described on the basis of the disordered three-dimensional attractive Hubbard model for binary alloys. The microscopic inhomogeneity and the thermal superconducting fluctuation are taken into account using the self-consistent 1-loop order theory. The superconductor-insulator transition accompanies the crossover from the host band to the impurity band. We point out an enhancement of the critical temperature Tc around the crossover. Further localization of electron wave functions leads to the localization of Cooper pairs and induces the pseudogap. We find that both the doping compensation by additional donors and the carrier increase by additional acceptors suppress the superconductivity. A theoretical interpretation is proposed for the superconductivity in the boron-doped diamond, SiC, and Si. PMID:27878018

  13. Properties of the superconducting state in a two-band model

    NASA Astrophysics Data System (ADS)

    Nicol, E. J.; Carbotte, J. P.

    2005-02-01

    Eliashberg theory is used to investigate the range of thermodynamic properties possible within a two-band model for s -wave superconductivity and to identify signatures of its two-band nature. We emphasize dimensionless BCS ratios [those for the energy gaps, the specific heat jump, and the negative of its slope near Tc , the thermodynamic critical field Hc(0) , and the normalized slopes of the critical field and the penetration depth near Tc ], which are no longer universal even in weak coupling. We also give results for temperature-dependent quantities, such as the penetration depth and the energy gap. Results are presented both for microscopic parameters appropriate to MgB2 and for variations away from these. Strong coupling corrections are identified and found to be significant. Analytic formulas are provided that show the role played by the anisotropy in coupling in some special limits. Particular emphasis is placed on small interband coupling and on the opposite limit of no diagonal coupling. The effect of impurity scattering is considered, particularly for the interband case.

  14. A wideband superconducting filter at Ku-band based on interdigital coupling

    NASA Astrophysics Data System (ADS)

    Jiang, Ying; Wei, Bin; Cao, Bisong; Li, Qirong; Guo, Xubo; Jiang, Linan; Song, Xiaoke; Wang, Xiang

    2018-04-01

    In this paper, an interdigital-type resonator with strong electric coupling is proposed for the wideband high-frequency (>10 GHz) filter design. The proposed microstrip resonator consists of an H-shaped main line part with its both ends installed with interdigital finger parts. Strong electric coupling is achieved between adjacent resonators. A six-pole high-temperature superconducting filter at Ku-band using this resonator is designed and fabricated. The filter has a center frequency of 15.11 GHz with a fractional bandwidth of 30%. The insertion loss of the passband is less than 0.3 dB, and the return loss is greater than 14 dB without any tuning.

  15. Decorrelation of L-band and C-band interferometry to volcanic risk prevention

    NASA Astrophysics Data System (ADS)

    Malinverni, E. S.; Sandwell, D.; Tassetti, A. N.; Cappelletti, L.

    2013-10-01

    SAR has several strong key features: fine spatial resolution/precision and high temporal pass frequency. Moreover, the InSAR technique allows the accurate detection of ground deformations. This high potential technology can be invaluable to study volcanoes: it provides important information on pre-eruption surface deformation, improving the understanding of volcanic processes and the ability to predict eruptions. As a downside, SAR measurements are influenced by artifacts such as atmospheric effects or bad topographic data. Correlation gives a measure of these interferences, quantifying the similarity of the phase of two SAR images. Different approaches exists to reduce these errors but the main concern remain the possibility to correlate images with different acquisition times: snow-covered or heavily-vegetated areas produce seasonal changes on the surface. Minimizing the time between passes partly limits decorrelation. Though, images with a short temporal baseline aren't always available and some artifacts affecting correlation are timeindependent. This work studies correlation of pairs of SAR images focusing on the influence of surface and climate conditions, especially snow coverage and temperature. Furthermore, the effects of the acquisition band on correlation are taken into account, comparing L-band and C-band images. All the chosen images cover most of the Yellowstone caldera (USA) over a span of 4 years, sampling all the seasons. Interferograms and correlation maps are generated. To isolate temporal decorrelation, pairs of images with the shortest baseline are chosen. Correlation maps are analyzed in relation to snow depth and temperature. Results obtained with ENVISAT and ERS satellites (C-band) are compared with the ones from ALOS (L-band). Results show a good performance during winter and a bad attitude towards wet snow (spring and fall). During summer both L-band and C-band maintain a good coherence with L-band performing better over vegetation.

  16. Fidelity study of the superconducting phase diagram in the two-dimensional single-band Hubbard model

    NASA Astrophysics Data System (ADS)

    Jia, C. J.; Moritz, B.; Chen, C.-C.; Shastry, B. Sriram; Devereaux, T. P.

    2011-09-01

    Extensive numerical studies have demonstrated that the two-dimensional single-band Hubbard model contains much of the key physics in cuprate high-temperature superconductors. However, there is no definitive proof that the Hubbard model truly possesses a superconducting ground state or, if it does, of how it depends on model parameters. To answer these longstanding questions, we study an extension of the Hubbard model including an infinite-range d-wave pair field term, which precipitates a superconducting state in the d-wave channel. Using exact diagonalization on 16-site square clusters, we study the evolution of the ground state as a function of the strength of the pairing term. This is achieved by monitoring the fidelity metric of the ground state, as well as determining the ratio between the two largest eigenvalues of the d-wave pair/spin/charge-density matrices. The calculations show a d-wave superconducting ground state in doped clusters bracketed by a strong antiferromagnetic state at half filling controlled by the Coulomb repulsion U and a weak short-range checkerboard charge ordered state at larger hole doping controlled by the next-nearest-neighbor hopping t'. We also demonstrate that negative t' plays an important role in facilitating d-wave superconductivity.

  17. Precipitation estimation using L-Band and C-Band soil moisture retrievals

    USDA-ARS?s Scientific Manuscript database

    An established methodology for estimating precipitation amounts from satellite-based soil moisture retrievals is applied to L-band products from the Soil Moisture Active Passive (SMAP) and Soil Moisture and Ocean Salinity (SMOS) satellite missions and to a C-band product from the Advanced Scatterome...

  18. L Band Service Compatibility Part I: Optimum OOBE Compatibility

    DOT National Transportation Integrated Search

    2014-12-04

    Discussion: -- Two Parts - Today we focus on optimum L Band ABC Out of Band Emission into GPS L1, OOBE. - Next ABC meeting will examine GPS-side mitigation of Adjacent Band Interference, ABI. -- Greater Compatibility: OOBE and ABI are distinct but pa...

  19. Fabrication of Silicon Backshorts with Improved Out-of-Band Rejection for Waveguide-Coupled Superconducting Detectors

    NASA Technical Reports Server (NTRS)

    Crowe, Erik J.; Bennett, Charles L.; Chuss, David T.; Denis, Kevin L.; Eimer, Joseph; Lourie, Nathan; Marriage, Tobias; Moseley, Samuel H.; Rostem, Karwan; Stevenson, Thomas R.; hide

    2012-01-01

    The Cosmology Large Angular Scale Surveyor (CLASS) is a ground-based instrument that will measure the polarization of the cosmic microqave background to search for gravitational waves form a posited epoch of inflation early in the universe's history. This measurement will require integration of superconducting transition-edge sensors with microwave waveguide inputs with good conrol of systematic errors, such as unwanted coupling to stray signals at frequencies outside of a precisely defined microwave band. To address these needs we will present work on the fabrication of silicon quarter-wave backshorts for the CLASS 40GHz focal plane. The 40GHz backshort consists of three degeneratively doped silicon wafers. Two spacer wafers are micromachined with through wafer vins to provide a 2.0mm long square waveguide. The third wafer acts as the backshort cap. The three wafers are bonded at the wafer level by Au-Au thermal compression bonding then aligned and flip chip bonded to the CLASS detector at the chip level. The micromachining techniques used have been optimized to create high aspect ratio waveguides, silicon pillars, and relief trenches with the goal of providing improved out of band signal rejection. We will discuss the fabrication of integrated CLASS superconducting detectors with silicon quarter wave backshorts and present current measurement results.

  20. Reconfigurable L-Band Radar

    NASA Technical Reports Server (NTRS)

    Rincon, Rafael F.

    2008-01-01

    The reconfigurable L-Band radar is an ongoing development at NASA/GSFC that exploits the capability inherently in phased array radar systems with a state-of-the-art data acquisition and real-time processor in order to enable multi-mode measurement techniques in a single radar architecture. The development leverages on the L-Band Imaging Scatterometer, a radar system designed for the development and testing of new radar techniques; and the custom-built DBSAR processor, a highly reconfigurable, high speed data acquisition and processing system. The radar modes currently implemented include scatterometer, synthetic aperture radar, and altimetry; and plans to add new modes such as radiometry and bi-static GNSS signals are being formulated. This development is aimed at enhancing the radar remote sensing capabilities for airborne and spaceborne applications in support of Earth Science and planetary exploration This paper describes the design of the radar and processor systems, explains the operational modes, and discusses preliminary measurements and future plans.

  1. Earth Studies Using L-band Synthetic Aperture Radar

    NASA Technical Reports Server (NTRS)

    Rosen, Paul A.

    1999-01-01

    L-band SAR has played an important role in studies of the Earth by revealing the nature of the larger-scale (decimeter) surface features. JERS-1, by supplying multi-seasonal coverage of the much of the earth, has demonstrated the importance of L-band SARs. Future L-band SARs such as ALOS and LightSAR will pave the way for science missions that use SAR instruments. As technology develops to enable lower cost SAR instruments, missions will evolve to each have a unique science focus. International coordination of multi-parameter constellations and campaigns will maximize science return.

  2. Strong Landau-quantization effects in high-magnetic-field superconductivity of a two-dimensional multiple-band metal near the Lifshitz transition

    DOE PAGES

    Song, Kok Wee; Koshelev, Alexei E.

    2017-05-04

    We investigate the onset of superconductivity in a magnetic field for a clean two-dimensional multiple-band superconductor in the vicinity of the Lifshitz transition when one of the bands is very shallow. Due to the small number of carriers in this band, the quasiclassical Werthamer-Helfand approximation breaks down and Landau quantization has to be taken into account. We found that the transition temperature T C2( H) has giant oscillations and is resonantly enhanced at the magnetic fields corresponding to the matching of the chemical potential with the Landau levels in the shallow band. This enhancement is especially pronounced for the lowestmore » Landau level. As a consequence, the reentrant superconducting regions in the temperature-field phase diagram emerge at low temperatures near the magnetic fields at which the shallow-band Landau levels cross the chemical potential. The specific behavior depends on the relative strength of the intraband and interband pairing interactions and the reentrance is most pronounced in the purely interband coupling scenario. The reentrant behavior is suppressed by the Zeeman spin splitting in the shallow band; the separated regions disappear already for very small spin-splitting factors. On the other hand, the reentrance is restored in the resonance cases when the spin-splitting energy exactly matches the separation between the Landau levels. As a result, the predicted behavior may be realized in the gate-tuned FeSe monolayer.« less

  3. Strong Landau-quantization effects in high-magnetic-field superconductivity of a two-dimensional multiple-band metal near the Lifshitz transition

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Song, Kok Wee; Koshelev, Alexei E.

    We investigate the onset of superconductivity in a magnetic field for a clean two-dimensional multiple-band superconductor in the vicinity of the Lifshitz transition when one of the bands is very shallow. Due to the small number of carriers in this band, the quasiclassical Werthamer-Helfand approximation breaks down and Landau quantization has to be taken into account. We found that the transition temperature T C2( H) has giant oscillations and is resonantly enhanced at the magnetic fields corresponding to the matching of the chemical potential with the Landau levels in the shallow band. This enhancement is especially pronounced for the lowestmore » Landau level. As a consequence, the reentrant superconducting regions in the temperature-field phase diagram emerge at low temperatures near the magnetic fields at which the shallow-band Landau levels cross the chemical potential. The specific behavior depends on the relative strength of the intraband and interband pairing interactions and the reentrance is most pronounced in the purely interband coupling scenario. The reentrant behavior is suppressed by the Zeeman spin splitting in the shallow band; the separated regions disappear already for very small spin-splitting factors. On the other hand, the reentrance is restored in the resonance cases when the spin-splitting energy exactly matches the separation between the Landau levels. As a result, the predicted behavior may be realized in the gate-tuned FeSe monolayer.« less

  4. Superconductivity in engineered two-dimensional electron gases

    NASA Astrophysics Data System (ADS)

    Chubukov, Andrey V.; Kivelson, Steven A.

    2017-11-01

    We consider Kohn-Luttinger mechanism for superconductivity in a two-dimensional electron gas confined to a narrow well between two grounded metallic planes with two occupied subbands with Fermi momenta kF L>kF S . On the basis of a perturbative analysis, we conclude that non-s -wave superconductivity emerges even when the bands are parabolic. We analyze the conditions that maximize Tc as a function of the distance to the metallic planes, the ratio kF L/kF S , and rs, which measures the strength of Coulomb correlations. The largest attraction is in p -wave and d -wave channels, of which p wave is typically the strongest. For rs=O (1 ) we estimate that the dimensionless coupling λ ≈10-1 , but it likely continues increasing for larger rs (where we lose theoretical control).

  5. Anomalous resistivity and superconductivity in the two-band Hubbard model with one narrow band (Review)

    NASA Astrophysics Data System (ADS)

    Kagan, M. Yu.; Valkov, V. V.

    2011-01-01

    We search for marginal Fermi-liquid behavior in the two-band Hubbard model with one narrow band. We consider the limit of low electron densities in the bands and strong intraband and interband Hubbard interactions. We analyze the influence of electron-polaron effects and other mechanisms for mass-enhancement (related to the momentum dependence of the self-energies) on the effective mass and scattering times of light and heavy components in the clean case (electron-electron scattering and no impurities). We find a tendency towards phase separation (towards negative partial compressibility of heavy particles) in the 3D case with a large mismatch between the densities of heavy and light bands in the strong coupling limit. We also find that for low temperatures and equal densities, the resistivity in a homogeneous state R(T )∝T2 behaves as a Fermi-liquid in both 3D and 2D. For temperatures greater than the effective bandwidth for heavy electrons T >Wh*, the coherence of the heavy component breaks down completely. The heavy particles move diffusively in the surrounding light particles. At the same time, light particles scatter on heavy particles as if on immobile (static) impurities. Under these conditions, the heavy component is marginal, while the light component is not. The resistivity approaches saturation for T >Wh* in the 3D case. In 2D the resistivity has a maximum and a localization tail owing to weak-localization corrections of the Altshuler-Aronov type. This behavior of resistivity in 3D could be relevant for some uranium-based heavy-fermion compounds such as UNi2Al3 and in 2D, for some other mixed-valence compounds, possibly including layered manganites. We also consider briefly the superconductive (SC) instability in this model. The leading instability tends to p-wave pairing and is governed by an enhanced Kohn-Luttinger mechanism for SC at low electron densities. The critical temperature corresponds to the pairing of heavy electrons via polarization of

  6. The Pseudogap in Multiband Superconductivity

    NASA Astrophysics Data System (ADS)

    Kristoffel, N.; Rubin, P.

    2012-11-01

    The pseudogap (PG) excitation is analyzed as a natural event in multiband superconductivity. It corresponds to minimal quasiparticle excitation energy of an electron band not touched by the chemical potential. The critical points of the phase diagram are determined by vanishing conditions for normal state pseudogaps (NPG). For two bands (gapped or overlapping) these are positioned on edges of the superconducting dome. Theoretical background for a three-band system with two interband pairing channels is developed. There are three independent superconducting gaps (SCG). The PG is associated with the band component possessing a bare gap which can be quenched by doping. At low doping the PG and the SCG of another band component coexist. The critical point is not fixed in respect of the transition temperature (Tc) dome background. The depletion of the PG associated states is restored here. This effect can also be indirect by the participation of these states in determining the chemical potential position. At the critical point the PG looses its normal state contribution and continues as the SCG of the same band. Illustrative examples on the doping scale have been calculated.

  7. Superconductivity versus bound-state formation in a two-band superconductor with small Fermi energy: Applications to Fe pnictides/chalcogenides and doped SrTiO3

    NASA Astrophysics Data System (ADS)

    Chubukov, Andrey V.; Eremin, Ilya; Efremov, Dmitri V.

    2016-05-01

    We analyze the interplay between superconductivity and the formation of bound pairs of fermions (BCS-BEC crossover) in a 2D model of interacting fermions with small Fermi energy EF and weak attractive interaction, which extends to energies well above EF. The 2D case is special because a two-particle bound state forms at arbitrary weak interaction, and already at weak coupling, one has to distinguish between the bound-state formation and superconductivity. We briefly review the situation in the one-band model and then consider two different two-band models: one with one hole band and one electron band and another with two hole or two electron bands. In each case, we obtain the bound-state energy 2 E0 for two fermions in a vacuum and solve the set of coupled equations for the pairing gaps and the chemical potentials to obtain the onset temperature of the pairing Tins and the quasiparticle dispersion at T =0 . We then compute the superfluid stiffness ρs(T =0 ) and obtain the actual Tc. For definiteness, we set EF in one band to be near zero and consider different ratios of E0 and EF in the other band. We show that at EF≫E0 , the behavior of both two-band models is BCS-like in the sense that Tc≈Tins≪EF and Δ ˜Tc . At EF≪E0 , the two models behave differently: in the model with two hole/two electron bands, Tins˜E0/lnE/0EF , Δ ˜(E0EF) 1 /2 , and Tc˜EF , like in the one-band model. In between Tins and Tc, the system displays a preformed pair behavior. In the model with one hole and one electron bands, Tc remains of order Tins, and both remain finite at EF=0 and of the order of E0. The preformed pair behavior still does exist in this model because Tc is numerically smaller than Tins. For both models, we reexpress Tins in terms of the fully renormalized two-particle scattering amplitude by extending to the two-band case (the method pioneered by Gorkov and Melik-Barkhudarov back in 1961). We apply our results for the model with a hole and an electron band to

  8. An effective 2-band eg model of sulfur hydride H3S for high-Tc superconductivity

    NASA Astrophysics Data System (ADS)

    Nishiguchi, Kazutaka; Teranishi, Shingo; Miyao, Satoaki; Matsushita, Goh; Kusakabe, Koichi

    To understand high transition temperature (Tc) superconductivity in sulfur hydride H3S, we propose an effective 2-band model having the eg symmetry as the minimal model for H3S. Two eg orbitals centered on a sulfur S atom are chosen for the smallest representation of relevant bands with the van-Hove singularity around the Fermi levels except for the Γ-centered small hole pockets by the sulfur 3 p orbitals. By using the maximally localized Wannier functions, we derive the minimal effective model preserving the body-centered cubic (bcc) crystal symmetry of the H3S phase having the highest Tc ( 203 K under pressures) among the other polymorphs of H3S.

  9. Enhanced superconductivity of fullerenes

    DOEpatents

    Washington, II, Aaron L.; Teprovich, Joseph A.; Zidan, Ragaiy

    2017-06-20

    Methods for enhancing characteristics of superconductive fullerenes and devices incorporating the fullerenes are disclosed. Enhancements can include increase in the critical transition temperature at a constant magnetic field; the existence of a superconducting hysteresis over a changing magnetic field; a decrease in the stabilizing magnetic field required for the onset of superconductivity; and/or an increase in the stability of superconductivity over a large magnetic field. The enhancements can be brought about by transmitting electromagnetic radiation to the superconductive fullerene such that the electromagnetic radiation impinges on the fullerene with an energy that is greater than the band gap of the fullerene.

  10. Dispersion-Engineered Traveling Wave Kinetic Inductance Parametric Amplifier

    NASA Technical Reports Server (NTRS)

    Zmuidzinas, Jonas (Inventor); Day, Peter K. (Inventor)

    2014-01-01

    A traveling wave kinetic inductance parametric amplifier comprises a superconducting transmission line and a dispersion control element. The transmission line can include periodic variations of its dimension along its length. The superconducting material can include a high normal state resistivity material. In some instances the high normal state resistivity material includes nitrogen and a metal selected from the group consisting of titanium, niobium and vanadium. The traveling wave kinetic inductance parametric amplifier is expected to exhibit a noise temperature below 100 mK/GHz.

  11. Total Electron Content Retrieved From L-Band Radiometers and Potential Improvements to the IGS Model

    NASA Astrophysics Data System (ADS)

    Soldo, Yan; Hong, Liang; El-Nimri, Salem; Le Vine, David M.

    2018-04-01

    In recent years, several L-band microwave instruments have been launched into Earth's orbit to measure soil moisture and ocean salinity (e.g., Soil Moisture and Ocean Salinity [SMOS], Aquarius, and Soil Moisture Active/Passive [SMAP]). As the microwave signal travels through the ionosphere, the polarization vector rotates (Faraday rotation) and it is possible to estimate the total electron content (TEC) along the path by measuring this change. A comparison is presented of the TEC retrieved from Aquarius and SMAP over the ocean with the values provided by the IGS (International Global Navigation Satellite System Service (GNSS)). The TEC retrieved from Aquarius and SMAP measurements show good agreement with each other and, on a global scale, are in agreement with the TEC provided by the IGS. However, there are cases in which the TEC from the two satellite sensors are in good agreement with each other but differ significantly from the IGS TEC. The comparison suggests that the L-band instruments are a reliable source of TEC over the ocean and could be a valuable supplementary source of TEC values that could be assimilated in the IGS models, especially over the ocean, where GNSS ground stations are sparse.

  12. Realizing a Circuit Analog of an Optomechanical System with Longitudinally Coupled Superconducting Resonators

    NASA Astrophysics Data System (ADS)

    Eichler, C.; Petta, J. R.

    2018-06-01

    We realize a superconducting circuit analog of the generic cavity-optomechanical Hamiltonian by longitudinally coupling two superconducting resonators, which are an order of magnitude different in frequency. We achieve longitudinal coupling by embedding a superconducting quantum interference device into a high frequency resonator, making its resonance frequency depend on the zero point current fluctuations of a nearby low frequency L C resonator. By applying sideband drive fields we enhance the intrinsic coupling strength of about 15 kHz up to 280 kHz by controlling the amplitude of the drive field. Our results pave the way towards the exploration of optomechanical effects in a fully superconducting platform and could enable quantum optics experiments with photons in the yet unexplored radio frequency band.

  13. EMI survey for maritime satellite, L-band, shipboard terminal

    NASA Technical Reports Server (NTRS)

    Taylor, R. E.; Brandel, D. L.; Hill, J. S.

    1975-01-01

    The paper presents results of an onboard EMI survey of an L-band shipboard terminal for operation with two geostationary maritime satellites. Significant EMC results include: (1) antenna noise temperature measurements indicate a maximum of 70 K steady background component at 1.6 GHz at sea for elevation angles of 5 degrees and higher; (2) field intensity measurements from 1-10 GHz show that a L-band terminal can operate simultaneously with onboard S-band and X-band navigation radar; (3) radar transmitter case emissions, below deck, in-band from 1535-1660 MHz, at 1 m distance from the cabinet, are equivalent, or greater than above-deck emissions in the same frequency range; and (4) conducted-emission tests of a ship's power lines to both radars show both narrow band and broad band emissions are 15 dB to 50 dB higher than equivalent U.S. commercial power lines from 150 kHz to 32 MHz.

  14. Travel distance as factor in follow-up visit compliance in postlaparoscopic adjustable gastric banding population.

    PubMed

    DeNino, Walter F; Osler, Turner; Evans, Ellen G; Forgione, Patrick M

    2010-01-01

    Despite the 2008 "American Association of Clinical Endocrinologists, The Obesity Society, and American Society for Metabolic and Bariatric Surgery Medical Guidelines for Clinical Practice for the Perioperative Nutritional, Metabolic, and Nonsurgical Support of the Bariatric Surgery Patient," consensus does not exist for postoperative care in laparoscopic adjustable gastric banding (LAGB) patients (grade D evidence). It has been suggested that regular follow-up is related to better outcomes, specifically greater weight loss. The aim of the present study was to investigate the effects of travel distance to the clinic on the adherence to follow-up visits and weight loss in a cohort of LAGB patients in the setting of a rural, university-affiliated teaching hospital in the United States. A retrospective chart review was performed of all consecutive LAGB patients for a 1-year period. Linear regression analysis was used to identify the relationships between appointment compliance and the distance traveled and between the amount of weight loss and the distance traveled. Linear regression analysis was performed to investigate the effect of the travel distance to the clinic on the percentage of follow-up visits postoperatively. This effect was not significant (P = .4). Linear regression analysis was also performed to elucidate the effect of the travel distance to the clinic on the amount of weight loss. This effect was significant (P = .04). The travel distance to the clinic did not seem to be a significant predictor of compliance in a cohort of LAGB patients with ≤ 1 year of follow-up in a rural setting. However, a weak relationship was found between the travel distance to the clinic and weight loss, with patients who traveled further seeming to lose slightly more weight. Copyright © 2010 American Society for Metabolic and Bariatric Surgery. Published by Elsevier Inc. All rights reserved.

  15. Electronic Power Conditioner for Ku-band Travelling Wave Tube

    NASA Astrophysics Data System (ADS)

    Kowstubha, Palle; Krishnaveni, K.; Ramesh Reddy, K.

    2017-04-01

    A highly sophisticated regulated power supply is known as electronic power conditioner (EPC) is required to energise travelling wave tubes (TWTs), which are used as RF signal amplifiers in satellite payloads. The assembly consisting of TWT and EPC together is known as travelling wave tube amplifier (TWTA). EPC is used to provide isolated and conditioned voltage rails with tight regulation to various electrodes of TWT and makes its RF performance independent of solar bus variations which are caused due to varying conditions of eclipse and sunlit. The payload mass and their power consumption is mainly due to the existence of TWTAs that represent about 35 % of total mass and about 70-90 % (based on the type of satellite application) of overall dc power consumption. This situation ensures a continuous improvement in the design of TWTAs and their associated EPCs to realize more efficient and light products. Critical technologies involved in EPCs are design and configuration, closed loop regulation, component and material selection, energy limiting of high voltage (HV) outputs and potting of HV card etc. This work addresses some of these critical technologies evolved in realizing and testing the state of art of EPC and it focuses on the design of HV supply with a HV and high power capability, up to 6 kV and 170 WRF, respectively required for a space TWTA. Finally, an experimental prototype of EPC with a dc power of 320 W provides different voltages required by Ku-band TWT in open loop configuration.

  16. Method for making mirrored surfaces comprising superconducting material

    DOEpatents

    Early, J.T.; Hargrove, R.S.

    1989-12-12

    Superconducting mirror surfaces are provided by forming a mirror surface from a material which is superconductive at a temperature above about 40 K and adjusting the temperature of the surface to that temperature at which the material is superconducting. The mirror surfaces are essentially perfect reflectors for electromagnetic radiation with photon energy less than the superconducting band gap.

  17. Microwave time delays for the dual L-C-band feed system

    NASA Technical Reports Server (NTRS)

    Chen, J.

    1989-01-01

    A new dual-frequency feed system at Goldstone is designed to receive the Phobos spacecraft signal at L-band (1668 + or - 40 MHz) and transmit to the spacecraft at C-band (5008.75 + or - 5.00 MHz) simultaneously. Hence, calculations of the time delay from the C-band range calibration coupler to the phase center of the L-C dual feed and back to the L-band range calibration coupler are required to correct the range measurements. Time delays of the elements in the dual-frequency feed system are obtained mostly from computer calculations and partly from experimental measurements. The method used and results obtained are described.

  18. Performance of high-temperature superconducting band-pass filters with high selectivity for base transceiver applications of digital cellular communication systems

    NASA Astrophysics Data System (ADS)

    Kwak, J. S.; Lee, J. H.; Kim, C. O.; Hong, J. P.; Han, S. K.; Char, K.

    2002-07-01

    Highly selective high-temperature superconducting band-pass filters based on spiral meander line structures have been developed for base transceiver station applications of digital cellular communication systems. The filter comprised 12-pole microstrip line resonators with a circuit size of 0.5 × 17 × 41 mm3. The filter was designed to have a bandwidth of 25 MHz at a centre frequency of 834 MHz. Particularly, the physical size of each resonator was chosen not only to reduce far-field radiation, but also to have reasonable tunability in the filter. Device characteristics exhibited a low insertion loss of 0.4 dB with a 0.2 dB ripple and a return loss better than 10 dB in the pass-band at 65 K. The out-of-band signals were attenuated better than 60 dB at about 3.5 MHz from the lower band edge, and 3.8 MHz from the higher band edge.

  19. Superconductivity at 33-37 K in A L n2Fe4As4O2 (A =Kand Cs;L n =lanthanides)

    NASA Astrophysics Data System (ADS)

    Wu, Si-Qi; Wang, Zhi-Cheng; He, Chao-Yang; Tang, Zhang-Tu; Liu, Yi; Cao, Guang-Han

    2017-09-01

    We have synthesized ten iron oxyarsenides, K L n2Fe4As4O2 (L n =Gd,Tb,Dy, and Ho) and Cs L n2Fe4As4O2 (L n =Nd,Sm,Gd,Tb,Dy, and Ho) , with the aid of the lattice-match approach. The resultant compounds possess hole-doped conducting double FeAs layers [AFe4As4] 2 - that are separated by the insulating [Ln2O2] 2 + slabs. Measurements of electrical resistivity and dc magnetic susceptibility demonstrate bulk superconductivity at Tc=33 -37 K. We find that Tc correlates with the axial ratio c /a for all 12442-type superconductors discovered. Also, Tc tends to increase with the lattice mismatch, implying that lattice instability plays a role in the enhancement of superconductivity.

  20. Superconductivity in few-layer stanene

    NASA Astrophysics Data System (ADS)

    Liao, Menghan; Zang, Yunyi; Guan, Zhaoyong; Li, Haiwei; Gong, Yan; Zhu, Kejing; Hu, Xiao-Peng; Zhang, Ding; Xu, Yong; Wang, Ya-Yu; He, Ke; Ma, Xu-Cun; Zhang, Shou-Cheng; Xue, Qi-Kun

    2018-04-01

    A single atomic slice of α-tin—stanene—has been predicted to host the quantum spin Hall effect at room temperature, offering an ideal platform to study low-dimensional and topological physics. Although recent research has focused on monolayer stanene, the quantum size effect in few-layer stanene could profoundly change material properties, but remains unexplored. By exploring the layer degree of freedom, we discover superconductivity in few-layer stanene down to a bilayer grown on PbTe, while bulk α-tin is not superconductive. Through substrate engineering, we further realize a transition from a single-band to a two-band superconductor with a doubling of the transition temperature. In situ angle-resolved photoemission spectroscopy (ARPES) together with first-principles calculations elucidate the corresponding band structure. The theory also indicates the existence of a topologically non-trivial band. Our experimental findings open up novel strategies for constructing two-dimensional topological superconductors.

  1. Fluctuation diamagnetism in two-band superconductors

    NASA Astrophysics Data System (ADS)

    Adachi, Kyosuke; Ikeda, Ryusuke

    2016-04-01

    Anomalously large fluctuation diamagnetism around the superconducting critical temperature has been recently observed in iron selenide (FeSe) [Kasahara et al. (unpublished)]. This indicates that superconducting fluctuations (SCFs) play a more significant role in FeSe, which supposedly has a two-band structure, than in the familiar single-band superconductors. Motivated by the data on FeSe, SCF-induced diamagnetism is examined in a two-band system, on the basis of a phenomenological approach with a Ginzburg-Landau functional. The obtained results indicate that the SCF-induced diamagnetism may be more enhanced than that in a single-band system due to the existence of two distinct fluctuation modes. Such enhancement of diamagnetism unique to a two-band system seems consistent with the large diamagnetism observed in FeSe, though still far from a quantitative agreement.

  2. Fermiology of the strongly spin-orbit coupled superconductor Sn(1-x)In(x)Te: implications for topological superconductivity.

    PubMed

    Sato, T; Tanaka, Y; Nakayama, K; Souma, S; Takahashi, T; Sasaki, S; Ren, Z; Taskin, A A; Segawa, Kouji; Ando, Yoichi

    2013-05-17

    We have performed angle-resolved photoemission spectroscopy on the strongly spin-orbit coupled low-carrier density superconductor Sn(1-x)In(x)Te (x = 0.045) to elucidate the electronic states relevant to the possible occurrence of topological superconductivity, as recently reported for this compound based on point-contact spectroscopy. The obtained energy-band structure reveals a small holelike Fermi surface centered at the L point of the bulk Brillouin zone, together with a signature of a topological surface state, indicating that this material is a doped topological crystalline insulator characterized by band inversion and mirror symmetry. A comparison of the electronic states with a band-noninverted superconductor possessing a similar Fermi surface structure, Pb(1-x)Tl(x)Te, suggests that the anomalous behavior in the superconducting state of Sn(1-x)In(x)Te is related to the peculiar orbital characteristics of the bulk valence band and/or the presence of a topological surface state.

  3. Superconductivity in few-layer stanene

    DOE PAGES

    Liao, Menghan; Zang, Yunyi; Guan, Zhaoyong; ...

    2018-01-15

    A single atomic slice of α-tin—stanene—has been predicted to host the quantum spin Hall effect at room temperature, offering an ideal platform to study low-dimensional and topological physics. Although recent research has focused on monolayer stanene, the quantum size effect in few-layer stanene could profoundly change material properties, but remains unexplored. By exploring the layer degree of freedom, we discover superconductivity in few-layer stanene down to a bilayer grown on PbTe, while bulk α-tin is not superconductive. Through substrate engineering, we further realize a transition from a single-band to a two-band superconductor with a doubling of the transition temperature. Inmore » situ angle-resolved photoemission spectroscopy (ARPES) together with first-principles calculations elucidate the corresponding band structure. The theory also indicates the existence of a topologically non-trivial band. Thus, our experimental findings open up novel strategies for constructing two-dimensional topological superconductors.« less

  4. Superconductivity in few-layer stanene

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Liao, Menghan; Zang, Yunyi; Guan, Zhaoyong

    A single atomic slice of α-tin—stanene—has been predicted to host the quantum spin Hall effect at room temperature, offering an ideal platform to study low-dimensional and topological physics. Although recent research has focused on monolayer stanene, the quantum size effect in few-layer stanene could profoundly change material properties, but remains unexplored. By exploring the layer degree of freedom, we discover superconductivity in few-layer stanene down to a bilayer grown on PbTe, while bulk α-tin is not superconductive. Through substrate engineering, we further realize a transition from a single-band to a two-band superconductor with a doubling of the transition temperature. Inmore » situ angle-resolved photoemission spectroscopy (ARPES) together with first-principles calculations elucidate the corresponding band structure. The theory also indicates the existence of a topologically non-trivial band. Thus, our experimental findings open up novel strategies for constructing two-dimensional topological superconductors.« less

  5. Slant path L- and S-Band tree shadowing measurements

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.

    1994-01-01

    This contribution presents selected results from simultaneous L- and S-Band slant-path fade measurements through a pecan, a cottonwood, and a pine tree employing a tower-mounted transmitter and dual-frequency receiver. A single, circularly-polarized antenna was used at each end of the link. The objective was to provide information for personal communications satellite design on the correlation of tree shadowing between frequencies near 1620 and 2500 MHz. Fades were measured along 10 m lateral distance with 5 cm spacing. Instantaneous fade differences between L- and S-Band exhibited normal distribution with means usually near 0 dB and standard deviations from 5.2 to 7.5 dB. The cottonwood tree was an exception, with 5.4 dB higher average fading at S- than at L-Band. The spatial autocorrelation reduced to near zero with lags of about 10 lambda. The fade slope in dB/MHz is normally distributed with zero mean and standard deviation increasing with fade level.

  6. Slant path L- and S-Band tree shadowing measurements

    NASA Astrophysics Data System (ADS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.

    1994-08-01

    This contribution presents selected results from simultaneous L- and S-Band slant-path fade measurements through a pecan, a cottonwood, and a pine tree employing a tower-mounted transmitter and dual-frequency receiver. A single, circularly-polarized antenna was used at each end of the link. The objective was to provide information for personal communications satellite design on the correlation of tree shadowing between frequencies near 1620 and 2500 MHz. Fades were measured along 10 m lateral distance with 5 cm spacing. Instantaneous fade differences between L- and S-Band exhibited normal distribution with means usually near 0 dB and standard deviations from 5.2 to 7.5 dB. The cottonwood tree was an exception, with 5.4 dB higher average fading at S- than at L-Band. The spatial autocorrelation reduced to near zero with lags of about 10 lambda. The fade slope in dB/MHz is normally distributed with zero mean and standard deviation increasing with fade level.

  7. Passive Microwave Measurements Over Conifer Forests at L-Band and C-Band

    NASA Technical Reports Server (NTRS)

    LeVine, D. M.; Lang, R.; Chauhan, N.; Kim, E.; Bidwell, S.; Goodberlet, M.; Haken, M.; deMatthaeis, P.

    2000-01-01

    Measurements have been made at L-band and C-band over conifer forests in Virginia to study the response of passive microwave instruments to biomass and soil moisture. A series of aircraft measurements were made in July, August and November, 1999 over relatively homogenous conifer forests of varying biomass. Three radiometers participated in these measurements. These were: 1) the L-band radiometer ESTAR, a horizontally polarized synthetic aperture radiometer which has been used extensively in past measurements of soil moisture; 2) the L-band radiometer SLFMR, a vertically polarized cross-track scanner which has been used successfully in the past for mapping sea surface salinity; and 3) The ACMR, a new C-band radiometer which operates at V- and H-polarization and in the configuration for these experiments did not scan. All three radiometers were flown on the NASA P-3 aircraft based at the Goddard Space Flight Center's Wallops Flight Facility. The ESTAR and SLFMR were mounted in the bomb bay of the P-3 and imaged across track whereas the ACMR was mounted to look aft at 54 degrees up from nadir. Data was collected at altitudes of 915 meters and 457 meters. The forests consisted of relatively homogeneous "managed" stands of conifer located near Waverly, Virginia. This is a relatively flat area about 30 miles southeast of Richmond, VA with numerous stands of trees being grown for the forestry industry. The stands selected for study consisted of areas of regrowth and mature stands of pine. In addition, a small stand of very large trees was observed. Soil moisture sampling was done in each stand during the aircraft over flights. Data was collected on July 7, August 27, November 15 and November 30, 1999. Measurements were made with ESTAR on all days. The ACMR flew on the summer missions and the SLFMR was present only on the August 27 flight. Soil moisture varied from quite dry on July 7 to quite moist on November 30 (which was shortly after a period of rain). The microwave

  8. Temperature Evolution of Energy Gap and Band Structure in the Superconducting and Pseudogap States of Bi 2Sr 2CaCu 2O 8+δ Superconductor Revealed by Laser-Based Angle-Resolved Photoemission Spectroscopy

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sun, Xuan; Zhang, Wen-Tao; Zhao, Lin

    For this study, we carry out detailed momentum-dependent and temperature-dependent measurements on Bi 2Sr 2CaCu 2O 8+δ (Bi2212) superconductor in the superconducting and pseudogap states by super-high resolution laser-based angle-resolved photoemission spectroscopy. The precise determination of the superconducting gap for the nearly optimally doped Bi2212 (T c=91 K) at low temperature indicates that the momentum-dependence of the superconducting gap deviates from the standard d-wave form (cos(2Φ)). It can be alternatively fitted by including a high-order term (cos(6Φ)) in which the next nearest-neighbor interaction is considered. We find that the band structure near the antinodal region smoothly evolves across the pseudogapmore » temperature without a signature of band reorganization which is distinct from that found in Bi 2Sr 2CuO 6+δ superconductors. This indicates that the band reorganization across the pseudogap temperature is not a universal behavior in cuprate superconductors. These results provide new insights in understanding the nature of the superconducting gap and pseudogap in high-temperature cuprate superconductors.« less

  9. Temperature Evolution of Energy Gap and Band Structure in the Superconducting and Pseudogap States of Bi 2Sr 2CaCu 2O 8+δ Superconductor Revealed by Laser-Based Angle-Resolved Photoemission Spectroscopy

    DOE PAGES

    Sun, Xuan; Zhang, Wen-Tao; Zhao, Lin; ...

    2017-12-17

    For this study, we carry out detailed momentum-dependent and temperature-dependent measurements on Bi 2Sr 2CaCu 2O 8+δ (Bi2212) superconductor in the superconducting and pseudogap states by super-high resolution laser-based angle-resolved photoemission spectroscopy. The precise determination of the superconducting gap for the nearly optimally doped Bi2212 (T c=91 K) at low temperature indicates that the momentum-dependence of the superconducting gap deviates from the standard d-wave form (cos(2Φ)). It can be alternatively fitted by including a high-order term (cos(6Φ)) in which the next nearest-neighbor interaction is considered. We find that the band structure near the antinodal region smoothly evolves across the pseudogapmore » temperature without a signature of band reorganization which is distinct from that found in Bi 2Sr 2CuO 6+δ superconductors. This indicates that the band reorganization across the pseudogap temperature is not a universal behavior in cuprate superconductors. These results provide new insights in understanding the nature of the superconducting gap and pseudogap in high-temperature cuprate superconductors.« less

  10. Fate of superconductivity in three-dimensional disordered Luttinger semimetals

    NASA Astrophysics Data System (ADS)

    Mandal, Ipsita

    2018-05-01

    Superconducting instability can occur in three-dimensional quadratic band crossing semimetals only at a finite coupling strength due to the vanishing of density of states at the quadratic band touching point. Since realistic materials are always disordered to some extent, we study the effect of short-ranged-correlated disorder on this superconducting quantum critical point using a controlled loop-expansion applying dimensional regularization. The renormalization group (RG) scheme allows us to determine the RG flows of the various interaction strengths and shows that disorder destroys the superconducting quantum critical point. In fact, the system exhibits a runaway flow to strong disorder.

  11. Model construction and superconductivity analysis of organic conductors β-(BDA-TTP)2MF6 (M = P, As, Sb and Ta) based on first-principles band calculation

    NASA Astrophysics Data System (ADS)

    Aizawa, H.; Kuroki, K.; Yasuzuka, S.; Yamada, J.

    2012-11-01

    We perform a first-principles band calculation for a group of quasi-two-dimensional organic conductors β-(BDA-TTP)2MF6 (M = P, As, Sb and Ta). The ab-initio calculation shows that the density of states is correlated with the bandwidth of the singly occupied (highest) molecular orbital, while it is not necessarily correlated with the unit-cell volume. The direction of the major axis of the cross section of the Fermi surface lies in the Γ-B-direction, which differs from that obtained by the extended Hückel calculation. Then, we construct a tight-binding model which accurately reproduces the ab-initio band structure. The obtained transfer energies give a smaller dimerization than in the extended Hückel band. As to the difference in the anisotropy of the Fermi surface, the transfer energies along the inter-stacking direction are smaller than those obtained in the extended Hückel calculation. Assuming spin-fluctuation-mediated superconductivity, we apply random phase approximation to a two-band Hubbard model. This two-band Hubbard model is composed of the tight-binding model derived from the first-principles band structure and an on-site (intra-molecule) repulsive interaction taken as a variable parameter. The obtained superconducting gap changes sign four times along the Fermi surface like in a d-wave gap, and the nodal direction is different from that obtained in the extended Hückel model. Anion dependence of Tc is qualitatively consistent with the experimental observation.

  12. Mapping Greenland's Firn Aquifer using L-band Microwave Radiometry

    NASA Astrophysics Data System (ADS)

    Miller, J.; Bringer, A.; Jezek, K. C.; Johnson, J. T.; Scambos, T. A.; Long, D. G.

    2016-12-01

    Greenland's recently discovered firn aquifer is one of the most interesting, yet still mysterious, components of the ice sheet system. Many open questions remain regarding timescales of refreezing and/or englacial drainage of liquid meltwater, and the connections of firn aquifers to the subglacial hydrological system. If liquid meltwater production at the surface of the Greenland ice sheet continues to increase, subsequent increases in the volume of mobile liquid meltwater retained within Greenland's firn aquifer may increase the possibility of crevasse-deepening via hydrofracture. Hydrofracture is an important component of supraglacial lake drainage leading to at least temporary accelerated flow velocities and ice sheet mass balance changes. Firn aquifers may also support hydrofracture-induced drainage and thus are potentially capable of significantly influencing ice sheet mass balance and sea level rise. Spaceborne L-band microwave radiometers provide an innovative tool for ice-sheet wide mapping of the spatiotemporal variability of Greenland's firn aquifer. Both refreezing and englacial drainage may be observable given the sensitivity of the microwave response to the upper surface of liquid meltwater retained within snow and firn pore space as well as the ability of L band instruments to probe the ice sheet from the surface to the firn-ice transition at pore close-off depth. Here we combine L-band (1.4 GHz) brightness temperature observations from multiple sources to demonstrate the potential of mapping firn aquifers on ice sheets using L-band microwave radiometry. Data sources include the interferometric MIRAS instrument aboard ESA's Soil Moisture and Ocean Salinity (SMOS) satellite mission and the radiometer aboard NASA's Soil Moisture Active Passive (SMAP) satellite mission. We will also present mulit-frequency L-band brightness temperature data (0.5-2 GHz) that will be collected over several firn aquifer areas on the Greenland ice sheet by the Ohio State

  13. U.S. Aeronautical L-Band Satellite Technology Test Program : Interim Tests Results

    DOT National Transportation Integrated Search

    1975-06-01

    The U.S. Aeronautical L-Band satellite test program was performed between September 1974 and April 1975 as part of an international ATS-6 L-Band satellite test program. The U.S. program consisted of both technology and ATC communications demonstratio...

  14. Superconductivity in the two-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Beenen, J.; Edwards, D. M.

    1995-11-01

    Quasiparticle bands of the two-dimensional Hubbard model are calculated using the Roth two-pole approximation to the one-particle Green's function. Excellent agreement is obtained with recent Monte Carlo calculations, including an anomalous volume of the Fermi surface near half-filling, which can possibly be explained in terms of a breakdown of Fermi liquid theory. The calculated bands are very flat around the (π,0) points of the Brillouin zone in agreement with photoemission measurements of cuprate superconductors. With doping there is a shift in spectral weight from the upper band to the lower band. The Roth method is extended to deal with superconductivity within a four-pole approximation allowing electron-hole mixing. It is shown that triplet p-wave pairing never occurs. A self-consistent solution with singlet dx2-y2-wave pairing is found and optimal doping occurs when the van Hove singularity, corresponding to the flat band part, lies at the Fermi level. Nearest-neighbor antiferromagnetic correlations play an important role in flattening the bands near the Fermi level and in favoring superconductivity. However, the mechanism for superconductivity is a local one, in contrast to spin-fluctuation exchange models. For reasonable values of the hopping parameter the transition temperature Tc is in the range 10-100 K. The optimum doping δc lies between 0.14 and 0.25, depending on the ratio U/t. The gap equation has a BCS-like form and 2Δmax/kTc~=4.

  15. Theoretical band structure of the superconducting antiperovskite oxide Sr3-xSnO

    NASA Astrophysics Data System (ADS)

    Ikeda, Atsutoshi; Fukumoto, Toshiyuki; Oudah, Mohamed; Hausmann, Jan Niklas; Yonezawa, Shingo; Kobayashi, Shingo; Sato, Masatoshi; Tassel, Cédric; Takeiri, Fumitaka; Takatsu, Hiroshi; Kageyama, Hiroshi; Maeno, Yoshiteru

    2018-05-01

    In order to investigate the position of the strontium deficiency in superconductive Sr3-xSnO, we synthesized and measured X-ray-diffraction patterns of Sr3-xSnO (x ∼ 0.5). Because no clear peaks originating from superstructures were observed, strontium deficiency is most likely to be randomly distributed. We also performed first-principles band-structure calculations on Sr3-xSnO (x = 0, 0.5) using two methods: full-potential linearized-augmented plane-wave plus local orbitals method and the Korringa-Kohn-Rostoker Green function method combined with the coherent potential approximation. We revealed that the Fermi energy of Sr3-xSnO in case of x ∼ 0.5 is about 0.8 eV below the original Fermi energy of the stoichiometric Sr3SnO, where the mixing of the valence p and conduction d orbitals are considered to be small.

  16. Large Scale Assessment of Radio Frequency Interference Signatures in L-band SAR Data

    NASA Astrophysics Data System (ADS)

    Meyer, F. J.; Nicoll, J.

    2011-12-01

    Imagery of L-band Synthetic Aperture Radar (SAR) systems such as the PALSAR sensor on board the Advanced Land Observing Satellite (ALOS) has proven to be a valuable tool for observing environmental changes around the globe. Besides offering 24/7 operability, the L-band frequency provides improved interferometric coherence, and L-band polarimetric data has shown great potential for vegetation monitoring, sea ice classification, and the observation of glaciers and ice sheets. To maximize the benefit of missions such as ALOS PALSAR for environmental monitoring, data consistency and calibration are vital. Unfortunately, radio frequency interference (RFI) signatures from ground-based radar systems regularly impair L-band SAR data quality and consistency. With this study we present a large-scale analysis of typical RFI signatures that are regularly observed in L-band SAR data over the Americas. Through a study of the vast archive of L-band SAR data in the US Government Research Consortium (USGRC) data pool at the Alaska Satellite Facility (ASF) we were able to address the following research goals: 1. Assessment of RFI Signatures in L-band SAR data and their Effects on SAR Data Quality: An analysis of time-frequency properties of RFI signatures in L-band SAR data of the USGRC data pool is presented. It is shown that RFI-filtering algorithms implemented in the operational ALOS PALSAR processor are not sufficient to remove all RFI-related artifacts. In examples, the deleterious effects of RFI on SAR image quality, polarimetric signature, SAR phase, and interferometric coherence are presented. 2. Large-Scale Assessment of Severity, Spatial Distribution, and Temporal Variation of RFI Signatures in L-band SAR data: L-band SAR data in the USGRC data pool were screened for RFI using a custom algorithm. Per SAR frame, the algorithm creates geocoded frame bounding boxes that are color-coded according to RFI intensity and converted to KML files for analysis in Google Earth. From

  17. Superconductivity in doped Dirac semimetals

    NASA Astrophysics Data System (ADS)

    Hashimoto, Tatsuki; Kobayashi, Shingo; Tanaka, Yukio; Sato, Masatoshi

    2016-07-01

    We theoretically study intrinsic superconductivity in doped Dirac semimetals. Dirac semimetals host bulk Dirac points, which are formed by doubly degenerate bands, so the Hamiltonian is described by a 4 ×4 matrix and six types of k -independent pair potentials are allowed by the Fermi-Dirac statistics. We show that the unique spin-orbit coupling leads to characteristic superconducting gap structures and d vectors on the Fermi surface and the electron-electron interaction between intra and interorbitals gives a novel phase diagram of superconductivity. It is found that when the interorbital attraction is dominant, an unconventional superconducting state with point nodes appears. To verify the experimental signature of possible superconducting states, we calculate the temperature dependence of bulk physical properties such as electronic specific heat and spin susceptibility and surface state. In the unconventional superconducting phase, either dispersive or flat Andreev bound states appear between point nodes, which leads to double peaks or a single peak in the surface density of states, respectively. As a result, possible superconducting states can be distinguished by combining bulk and surface measurements.

  18. Design of dual band FSS by using quadruple L-slot technique

    NASA Astrophysics Data System (ADS)

    Fauzi, Noor Azamiah Md; Aziz, Mohamad Zoinol Abidin Abd.; Said, Maizatul Alice Meor; Othman, Mohd Azlishah; Ahmad, Badrul Hisham; Malek, Mohd Fareq Abd

    2015-05-01

    This paper presents a new design of dual band frequency selective surface (FSS) for band pass microwave transmission application. FSS can be used on energy saving glass to improve the transmission of wireless communication signals through the glass. The microwave signal will be attenuate when propagate throughout the different structure such as building. Therefore, some of the wireless communication system cannot be used in the optimum performance. The aim of this paper is designed, simulated and analyzed the new dual band FSS structure for microwave transmission. This design is based on a quadruple L slot combined with cross slot to produce pass band at 900 MHz and 2.4 GHz. The vertical of pair inverse L slot is used as the band pass for the frequency of 2.4GHz. While, the horizontal of pair inverse L slot is used as the band pass at frequency 900MHz. This design is simulated and analyzed by using Computer Simulation Technology (CST) Microwave Studio (MWS) software. The characteristics of the transmission (S21) and reflection (S11) of the dual band FSS were simulater and analyzed. The bandwidth of the first band is 118.91MHz which covered the frequency range from 833.4MHz until 952.31MHz. Meanwhile, the bandwidth for the second band is 358.84MHz which covered the frequency range from 2.1475GHz until 2.5063GHz. The resonance/center frequency of this design is obtained at 900MHz with a 26.902dB return loss and 2.37GHz with 28.506dB a return loss. This FSS is suitable as microwave filter for GSM900 and WLAN 2.4GHz application.

  19. L-Band System Engineering - Concepts of Use, Systems Performance Requirements, and Architecture

    NASA Technical Reports Server (NTRS)

    Henriksen, Stephen; Zelkin, Natalie

    2011-01-01

    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. Task 7 was motivated by the five year technology assessment performed for the Federal Aviation Administration (FAA) under the joint FAA-EUROCONTROL cooperative research Action Plan (AP-17), also known as the Future Communications Study (FCS). It was based on direction provided by the FAA project-level agreement (PLA FY09_G1M.02-02v1) for "New ATM Requirements-Future Communications." Task 7 was separated into two distinct subtasks, each aligned with specific work elements and deliverable items. Subtask 7-1 addressed C-band airport surface data communications standards development, systems engineering, test bed development, and tests/demonstrations to establish operational capability for what is now referred to as the Aeronautical Mobile Airport Communications System (AeroMACS). Subtask 7-2, which is the subject of this report, focused on preliminary systems engineering and support of joint FAA/EUROCONTROL development and evaluation of a future L-band (960 to 1164 MHz) air/ground (A/G) communication system known as the L-band digital aeronautical communications system (L-DACS), which was defined during the FCS. The proposed L-DACS will be capable of providing ATM services in continental airspace in the 2020+ timeframe. Subtask 7-2 was performed in two phases. Phase I featured development of Concepts of Use, high level functional analyses, performance of initial L-band system safety and security risk assessments, and development of high level requirements and architectures. It also included the aforementioned support of joint L-DACS development and evaluation, including inputs to L-DACS design specifications. Phase II provided a refinement of the systems engineering activities performed during Phase I, along

  20. Superconductivity, phase separation, and charge-transfer instability in the U = infinity limit of the three-band model of the CuO sub 2 planes

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Grilli, M.; Raimondi, R.; Castellani, C.

    1991-07-08

    The {ital U}={infinity} limit of the three-band Hubbard model with nearest-neighbor repulsion {ital V} is studied using the slave-boson approach and the large-{ital N} expansion technique to order 1/{ital N}. A charge-transfer instability is found as in weak-coupling theory. The charge-transfer instability is always associated with a diverging compressibility leading to a phase separation. Near the phase-separation, charge-transfer-instability region we find superconducting instabilities in the {ital s}- and {ital d}-wave channel. The requirement for superconductivity is that {ital V} be on the scale of the Cu-O hopping as suggested by Varma, Schmitt-Rink, and Abrahams.

  1. Thermal expansion of coexistence of ferromagnetism and superconductivity

    NASA Astrophysics Data System (ADS)

    Hatayama, Nobukuni; Konno, Rikio

    2010-01-01

    The temperature dependence of thermal expansion of coexistence of ferromag-netism and superconductivity below the superconducting transition temperature Tc↑ of a majority spin conduction band is investigated. Majority spin and minority spin superconducting gaps exist in the coexistent state. We assume that the Curie temperature is much larger than the superconducting transition temperatures. The free energy that Linder et al. [Phys. Rev. B76, 054511 (2007)] derived is used. The thermal expansion of coexistence of ferromagnetism and superconductivity is derived by the application of the method of Takahashi and Nakano [J. Phys.: Condens. Matter 18, 521 (2006)]. We find that we have the anomalies of the thermal expansion in the vicinity of the superconducting transition temperatures.

  2. Topological Magnon Bands and Unconventional Superconductivity in Pyrochlore Iridate Thin Films.

    PubMed

    Laurell, Pontus; Fiete, Gregory A

    2017-04-28

    We theoretically study the magnetic properties of pyrochlore iridate bilayer and trilayer thin films grown along the [111] direction using a strong coupling approach. We find the ground state magnetic configurations on a mean field level and carry out a spin-wave analysis about them. In the trilayer case the ground state is found to be the all-in-all-out (AIAO) state, whereas the bilayer has a deformed AIAO state. For all parameters of the spin-orbit coupled Hamiltonian we study, the lowest magnon band in the trilayer case has a nonzero Chern number. In the bilayer case we also find a parameter range with nonzero Chern numbers. We calculate the magnon Hall response for both geometries, finding a striking sign change as a function of temperature. Using a slave-boson mean-field theory we study the doping of the trilayer system and discover an unconventional time-reversal symmetry broken d+id superconducting state. Our study complements prior work in the weak coupling limit and suggests that the [111] grown thin film pyrochlore iridates are a promising candidate for topological properties and unconventional orders.

  3. Performance of a four-element Ka-band high-temperature superconducting microstrip antenna

    NASA Technical Reports Server (NTRS)

    Richard, M. A.; Bhasin, K. B.; Gilbert, C.; Metzler, S.; Koepf, G.; Claspy, P. C.

    1992-01-01

    Superconducting four-element microstrip array antennas operating at 30 GHz have been designed and fabricated on a lanthanum aluminate (LaAlO3) substrates. The experimental performance of these thin film Y-Ba-Cu-O superconducting antennas is compared with that of identical antenna patterned with evaporated gold. Efficiency measurements of these antennas show an improvement of 2 dB at 70 K and as much as 3.5 dB at 40 K in the superconducting antenna over the gold antenna.

  4. Superconducting transitions in flat-band systems

    DOE PAGES

    Iglovikov, V. I.; Hébert, F.; Grémaud, B.; ...

    2014-09-11

    The physics of strongly correlated quantum particles within a flat band was originally explored as a route to itinerant ferromagnetism and, indeed, a celebrated theorem by Lieb rigorously establishes that the ground state of the repulsive Hubbard model on a bipartite lattice with unequal number of sites in each sublattice must have nonzero spin S at half-filling. Recently, there has been interest in Lieb geometries due to the possibility of novel topological insulator, nematic, and Bose-Einstein condensed (BEC) phases. In this paper, we extend the understanding of the attractive Hubbard model on the Lieb lattice by using Determinant Quantum Montemore » Carlo to study real space charge and pair correlation functions not addressed by the Lieb theorems. Specifically, our results show unusual charge and charge transfer signatures within the flat band, and a reduction in pairing order at ρ = 2/3 and ρ = 4/3, the points at which the flat band is first occupied and then completely filled. Lastly, we compare our results to the case of flat bands in the Kagome lattice and demonstrate that the behavior observed in the two cases is rather different.« less

  5. Two-dimensional superconductivity at a Mott insulator/band insulator interface LaTiO3/SrTiO3.

    PubMed

    Biscaras, J; Bergeal, N; Kushwaha, A; Wolf, T; Rastogi, A; Budhani, R C; Lesueur, J

    2010-10-05

    Transition metal oxides show a great variety of quantum electronic behaviours where correlations often have an important role. The achievement of high-quality epitaxial interfaces involving such materials gives a unique opportunity to engineer artificial structures where new electronic orders take place. One of the most striking result in this area is the recent observation of a two-dimensional electron gas at the interface between a strongly correlated Mott insulator LaTiO(3) and a band insulator SrTiO(3). The mechanism responsible for such a behaviour is still under debate. In particular, the influence of the nature of the insulator has to be clarified. In this article, we show that despite the expected electronic correlations, LaTiO(3)/SrTiO(3) heterostructures undergo a superconducting transition at a critical temperature T(c)(onset)~300 mK. We have found that the superconducting electron gas is confined over a typical thickness of 12 nm and is located mostly on the SrTiO(3) substrate.

  6. FOREWORD: Focus on Superconductivity in Semiconductors Focus on Superconductivity in Semiconductors

    NASA Astrophysics Data System (ADS)

    Takano, Yoshihiko

    2008-12-01

    Since the discovery of superconductivity in diamond, much attention has been given to the issue of superconductivity in semiconductors. Because diamond has a large band gap of 5.5 eV, it is called a wide-gap semiconductor. Upon heavy boron doping over 3×1020 cm-3, diamond becomes metallic and demonstrates superconductivity at temperatures below 11.4 K. This discovery implies that a semiconductor can become a superconductor upon carrier doping. Recently, superconductivity was also discovered in boron-doped silicon and SiC semiconductors. The number of superconducting semiconductors has increased. In 2008 an Fe-based superconductor was discovered in a research project on carrier doping in a LaCuSeO wide-gap semiconductor. This discovery enhanced research activities in the field of superconductivity, where many scientists place particular importance on superconductivity in semiconductors. This focus issue features a variety of topics on superconductivity in semiconductors selected from the 2nd International Workshop on Superconductivity in Diamond and Related Materials (IWSDRM2008), which was held at the National Institute for Materials Science (NIMS), Tsukuba, Japan in July 2008. The 1st workshop was held in 2005 and was published as a special issue in Science and Technology of Advanced Materials (STAM) in 2006 (Takano 2006 Sci. Technol. Adv. Mater. 7 S1). The selection of papers describe many important experimental and theoretical studies on superconductivity in semiconductors. Topics on boron-doped diamond include isotope effects (Ekimov et al) and the detailed structure of boron sites, and the relation between superconductivity and disorder induced by boron doping. Regarding other semiconductors, the superconducting properties of silicon and SiC (Kriener et al, Muranaka et al and Yanase et al) are discussed, and In2O3 (Makise et al) is presented as a new superconducting semiconductor. Iron-based superconductors are presented as a new series of high

  7. A Passive Microwave L-Band Boreal Forest Freeze/Thaw and Vegetation Phenology Study

    NASA Astrophysics Data System (ADS)

    Roy, A.; Sonnentag, O.; Pappas, C.; Mavrovic, A.; Royer, A.; Berg, A. A.; Rowlandson, T. L.; Lemay, J.; Helgason, W.; Barr, A.; Black, T. A.; Derksen, C.; Toose, P.

    2016-12-01

    The boreal forest is the second largest land biome in the world and thus plays a major role in the global and regional climate systems. The extent, timing and duration of seasonal freeze/thaw (F/T) state influences vegetation developmental stages (phenology) and, consequently, constitute an important control on how boreal forest ecosystems exchange carbon, water and energy with the atmosphere. The effective retrieval of seasonal F/T state from L-Band radiometry was demonstrated using satellite mission. However, disentangling the seasonally differing contributions from forest overstory and understory vegetation, and the soil surface to the satellite signal remains challenging. Here we present initial results from a radiometer field campaign to improve our understanding of the L-Band derived boreal forest F/T signal and vegetation phenology. Two L-Band surface-based radiometers (SBR) are installed on a micrometeorological tower at the Southern Old Black Spruce site in central Saskatchewan over the 2016-2017 F/T season. One radiometer unit is installed on the flux tower so it views forest including all overstory and understory vegetation and the moss-covered ground surface. A second radiometer unit is installed within the boreal forest overstory, viewing the understory and the ground surface. The objectives of our study are (i) to disentangle the L-Band F/T signal contribution of boreal forest overstory from the understory and ground surface, (ii) to link the L-Band F/T signal to related boreal forest structural and functional characteristics, and (iii) to investigate the use of the L-Band signal to characterize boreal forest carbon, water and energy fluxes. The SBR observations above and within the forest canopy are used to retrieve the transmissivity (γ) and the scattering albedo (ω), two parameters that describe the emission of the forest canopy though the F/T season. These two forest parameters are compared with boreal forest structural and functional

  8. C- and L-band space-borne SAR incidence angle normalization for efficient Arctic sea ice monitoring

    NASA Astrophysics Data System (ADS)

    Mahmud, M. S.; Geldsetzer, T.; Howell, S.; Yackel, J.; Nandan, V.

    2017-12-01

    C-band Synthetic Aperture Radar (SAR) has been widely used effectively for operational sea ice monitoring, owing to its greater seperability between snow-covered first-year (FYI) and multi-year (MYI) ice types, during winter. However, during the melt season, C-band SAR backscatter contrast reduces between FYI and MYI. To overcome the limitations of C-band, several studies have recommended utlizing L-band SAR, as it has the potential to significantly improve sea ice classification. Given its longer wavelength, L-band can efficiently separate FYI and MYI types, especially during melt season. Therefore, the combination of C- and L-band SAR is an optimal solution for efficient seasonal sea ice monitoring. As SAR acquires images over a range of incidence angles from near-range to far-range, SAR backscatter varies substantially. To compensate this variation in SAR backscatter, incidence angle dependency of C- and L-band SAR backscatter for different FYI and MYI types is crucial to quantify, which is the objective of this study. Time-series SAR imagery from C-band RADARSAT-2 and L-band ALOS PALSAR during winter months of 2010 across 60 sites over the Canadian Arctic was acquired. Utilizing 15 images for each sites during February-March for both C- and L-band SAR, incidence angle dependency was calculated. Our study reveals that L- and C-band backscatter from FYI and MYI decreases with increasing incidence angle. The mean incidence angle dependency for FYI and MYI were estimated to be -0.21 dB/1° and -0.30 dB/1° respectively from L-band SAR, and -0.22 dB/1° and -0.16 dB/1° from C-band SAR, respectively. While the incidence angle dependency for FYI was found to be similar in both frequencies, it doubled in case of MYI from L-band, compared to C-band. After applying the incidence angle normalization method to both C- and L-band SAR images, preliminary results indicate improved sea ice type seperability between FYI and MYI types, with substantially lower number of mixed

  9. Color composite C-band and L-band image of Kilauea volcanoe on Hawaii

    NASA Technical Reports Server (NTRS)

    1994-01-01

    This color composite C-band and L-band image of the Kilauea volcano on the Big Island of Hawaii was acuired by the Spaceborne Imaging Radar-C/X-band Synthetic Aperature Radar (SIR-C/X-SAR) flying on the Space Shuttle Endeavour. The city of Hilo can be seen at the top. The image shows the different types of lava flows around the crater Pu'u O'o. Ash deposits which erupted in 1790 from the summit of Kilauea volcano show up as dark in this image, and fine details associated with lava flows which erupted in 1919 and 1974 can be seen to the south of the summit in an area called the Ka'u Desert. Other historic lava flows can also be seen. Highway 11 is the linear feature running from Hilo to the Kilauea volcano. The Jet Propulsion Laboratory alternative photo number is P-43918.

  10. Examples L-Band Interference will be Presented and Discussed, as well as the Importance of L-Band Soil Moisture Observations

    NASA Technical Reports Server (NTRS)

    Kim, Edward

    2010-01-01

    Examples of L-band interference will be presented and discussed, as well as the importance of L-band soil moisture observations, as part of this one-day GEOSS workshop XXXVII on "Data Quality and Radio Spectrum Allocation Impact on Earth Observations" will address the broad challenges of data quality and the impact of generating reliable information for decision makers who are Earth data users but not necessarily experts in the Earth observation field. GEO has initiated a data quality assessment task (DA-09-01a) and workshop users will review and debate the directions and challenges of this effort. Radio spectrum allocation is an element of data availability and data quality, and is also associated with a GEO task (AR-06-11). A recent U.S. National Research Council report on spectrum management will be addressed as part of the workshop. Key representatives from industry, academia, and government will provide invited talks on these and related issues that impact GEOSS implementation.

  11. Soil Moisture Limitations on Monitoring Boreal Forest Regrowth Using Spaceborne L-Band SAR Data

    NASA Technical Reports Server (NTRS)

    Kasischke, Eric S.; Tanase, Mihai A.; Bourgeau-Chavez, Laura L.; Borr, Matthew

    2011-01-01

    A study was carried out to investigate the utility of L-band SAR data for estimating aboveground biomass in sites with low levels of vegetation regrowth. Data to estimate biomass were collected from 59 sites located in fire-disturbed black spruce forests in interior Alaska. PALSAR L-band data (HH and HV polarizations) collected on two dates in the summer/fall of 2007 and one date in the summer of 2009 were used. Significant linear correlations were found between the log of aboveground biomass (range of 0.02 to 22.2 t ha-1) and (L-HH) and (L-HV) for the data collected on each of the three dates, with the highest correlation found using the LHV data collected when soil moisture was highest. Soil moisture, however, did change the correlations between L-band and aboveground biomass, and the analyses suggest that the influence of soil moisture is biomass dependent. The results indicate that to use L-band SAR data for mapping aboveground biomass and monitoring forest regrowth will require development of approaches to account for the influence that variations in soil moisture have on L-band microwave backscatter, which can be particularly strong when low levels of aboveground biomass occur

  12. Studying Notable Debris Disks In L-band with the Vortex Coronagraph

    NASA Astrophysics Data System (ADS)

    Patel, Rahul; Beichman, Charles; Choquet, Elodie; Mawet, Dimitri; Meshkat, Tiffany; ygouf, marie

    2018-01-01

    Resolved images of circumstellar disks are integral to our understanding of planetary systems, as the micron sized dust grains that comprise the disk are born from the collisional grinding of planetesimals by larger planets in the system. Resolved images are essential to determining grain properties that might otherwise be degenerate from analyzing the star’s spectral energy distribution. Though the majority of scattered light images of disks are obtained at optical and near-IR wavelengths, only a few have been imaged in the thermal IR at L-band. Probing the spatial features of disks at L-band opens up the possibility of constraining additional grain properties, such as water/ice features.Here, we present the results of our effort to image the disks of a few notable systems at L-band using the NIRC2 imager at Keck, in conjunction with the newly commissioned vector vortex coronagraph. The vortex, along with the QACITS fine guiding program installed at Keck, enables us to probe the small ~lambda/D angular separations of these systems, and reach contrasts of 1/100,000. We will discuss the systems that have been imaged, and lessons learned while imaging in L-band. Our analysis of these disks reveal features previously unseen, and will lay the foundation for followup studies by missions such as JWST at similar wavelengths from space.

  13. Hypervelocity impact testing of L-band truss cable meteoroid shielding on Skylab

    NASA Technical Reports Server (NTRS)

    Jex, D. W.

    1973-01-01

    A series of tests was performed to determine the protection provided by the L-band truss cable meteoroid shielding installed on Skylab space station at space environment temperatures of minus 180 F. The damage sustained when three test specimens were impacted by spherical projectiles at hypersonic speed was investigated. It is concluded that the L-band truss cable meteoroid shielding provides adequate protection at the indicated temperature.

  14. ELBARA II, an L-band radiometer system for soil moisture research.

    PubMed

    Schwank, Mike; Wiesmann, Andreas; Werner, Charles; Mätzler, Christian; Weber, Daniel; Murk, Axel; Völksch, Ingo; Wegmüller, Urs

    2010-01-01

    L-band (1-2 GHz) microwave radiometry is a remote sensing technique that can be used to monitor soil moisture, and is deployed in the Soil Moisture and Ocean Salinity (SMOS) Mission of the European Space Agency (ESA). Performing ground-based radiometer campaigns before launch, during the commissioning phase and during the operative SMOS mission is important for validating the satellite data and for the further improvement of the radiative transfer models used in the soil-moisture retrieval algorithms. To address these needs, three identical L-band radiometer systems were ordered by ESA. They rely on the proven architecture of the ETH L-Band radiometer for soil moisture research (ELBARA) with major improvements in the microwave electronics, the internal calibration sources, the data acquisition, the user interface, and the mechanics. The purpose of this paper is to describe the design of the instruments and the main characteristics that are relevant for the user.

  15. ELBARA II, an L-Band Radiometer System for Soil Moisture Research

    PubMed Central

    Schwank, Mike; Wiesmann, Andreas; Werner, Charles; Mätzler, Christian; Weber, Daniel; Murk, Axel; Völksch, Ingo; Wegmüller, Urs

    2010-01-01

    L-band (1–2 GHz) microwave radiometry is a remote sensing technique that can be used to monitor soil moisture, and is deployed in the Soil Moisture and Ocean Salinity (SMOS) Mission of the European Space Agency (ESA). Performing ground-based radiometer campaigns before launch, during the commissioning phase and during the operative SMOS mission is important for validating the satellite data and for the further improvement of the radiative transfer models used in the soil-moisture retrieval algorithms. To address these needs, three identical L-band radiometer systems were ordered by ESA. They rely on the proven architecture of the ETH L-Band radiometer for soil moisture research (ELBARA) with major improvements in the microwave electronics, the internal calibration sources, the data acquisition, the user interface, and the mechanics. The purpose of this paper is to describe the design of the instruments and the main characteristics that are relevant for the user. PMID:22315556

  16. Comparison of Measured Galactic Background Radiation at L-Band with Model

    NASA Technical Reports Server (NTRS)

    LeVine, David M.; Abraham, Saji; Kerr, Yann H.; Wilson, William J.; Skou, Niels; Sobjaerg, Sten

    2004-01-01

    Radiation from the celestial sky in the spectral window at 1.413 GHz is strong and an accurate accounting of this background radiation is needed for calibration and retrieval algorithms. Modern radio astronomy measurements in this window have been converted into a brightness temperature map of the celestial sky at L-band suitable for such applications. This paper presents a comparison of the background predicted by this map with the measurements of several modern L-band remote sensing radiometer Keywords-Galactic background, microwave radiometry; remote sensing;

  17. Theory of superconductivity in a three-orbital model of Sr2RuO4

    NASA Astrophysics Data System (ADS)

    Wang, Q. H.; Platt, C.; Yang, Y.; Honerkamp, C.; Zhang, F. C.; Hanke, W.; Rice, T. M.; Thomale, R.

    2013-10-01

    In conventional and high transition temperature copper oxide and iron pnictide superconductors, the Cooper pairs all have even parity. As a rare exception, Sr2RuO4 is the first prime candidate for topological chiral p-wave superconductivity, which has time-reversal breaking odd-parity Cooper pairs known to exist before only in the neutral superfluid 3He. However, there are several key unresolved issues hampering the microscopic description of the unconventional superconductivity. Spin fluctuations at both large and small wave vectors are present in experiments, but how they arise and drive superconductivity is not yet clear. Spontaneous edge current is expected but not observed conclusively. Specific experiments point to highly band- and/or momentum-dependent energy gaps for quasiparticle excitations in the superconducting state. Here, by comprehensive functional renormalization group calculations with all relevant bands, we disentangle the various competing possibilities. In particular, we show the small wave vector spin fluctuations, driven by a single two-dimensional band, trigger p-wave superconductivity with quasi-nodal energy gaps.

  18. Weak-coupling superconductivity in a strongly correlated iron pnictide

    PubMed Central

    Charnukha, A.; Post, K. W.; Thirupathaiah, S.; Pröpper, D.; Wurmehl, S.; Roslova, M.; Morozov, I.; Büchner, B.; Yaresko, A. N.; Boris, A. V.; Borisenko, S. V.; Basov, D. N.

    2016-01-01

    Iron-based superconductors have been found to exhibit an intimate interplay of orbital, spin, and lattice degrees of freedom, dramatically affecting their low-energy electronic properties, including superconductivity. Albeit the precise pairing mechanism remains unidentified, several candidate interactions have been suggested to mediate the superconducting pairing, both in the orbital and in the spin channel. Here, we employ optical spectroscopy (OS), angle-resolved photoemission spectroscopy (ARPES), ab initio band-structure, and Eliashberg calculations to show that nearly optimally doped NaFe0.978Co0.022As exhibits some of the strongest orbitally selective electronic correlations in the family of iron pnictides. Unexpectedly, we find that the mass enhancement of itinerant charge carriers in the strongly correlated band is dramatically reduced near the Γ point and attribute this effect to orbital mixing induced by pronounced spin-orbit coupling. Embracing the true band structure allows us to describe all low-energy electronic properties obtained in our experiments with remarkable consistency and demonstrate that superconductivity in this material is rather weak and mediated by spin fluctuations. PMID:26729630

  19. Aquarius Active-Passive RFI Environment at L-Band

    NASA Technical Reports Server (NTRS)

    Le Vine, David M.; De Matthaeis, Paolo

    2014-01-01

    Active/Passive instrument combinations (i.e., radiometer and radar) are being developed at L-band for remote sensing of sea surface salinity and soil moisture. Aquarius is already in orbit and SMAP is planned for launch in the Fall of 2014. Aquarius has provided for the first time a simultaneous look at the Radio Frequency Interference (RFI) environment from space for both active and passive instruments. The RFI environment for the radiometer observations is now reasonably well known and examples from Aquarius are presented in this manuscript that show that RFI is an important consideration for the scatterometer as well. In particular, extensive areas of the USA, Europe and Asia exhibit strong RFI in both the radiometer band at 1.41 GHz and in the band at 1.26 GHz employed by the Aquarius scatterometer. Furthermore, in areas such as the USA, where RFI at 1.4 GHz is relatively well controlled, RFI in the scatterometer band maybe the limiting consideration for the operation of combination active/passive instruments.

  20. Space-Qualified Traveling-Wave Tube

    NASA Technical Reports Server (NTRS)

    Wilson, Jeffrey D.; Krawczyk, Richard; Simons, Rainee N.; Williams, Wallace D.; Robbins, Neal R.; Dibb, Daniel R.; Menninger, William L.; Zhai, Xiaoling; Benton, Robert T.

    2010-01-01

    The L-3 Communications Electron Technologies, Inc. Model 999HA traveling-wave tube (TWT), was developed for use as a high-power microwave amplifier for high-rate transmission of data and video signals from deep space to Earth (see figure). The 999HA is a successor to the 999H a non-space qualified TWT described in High-Power, High-Efficiency Ka-Band Traveling-Wave Tube (LEW-17900-1), NASA Tech Briefs, Vol. 31, No. 2 (February 2007), page 32. Operating in the 31.8-to-32.3 GHz frequency band, the 999HA has been shown to generate 252 W of continuous- wave output power at 62 percent overall power efficiency a 75-percent increase in output power over the 999H. The mass of the 999HA is 35 percent less than that of the 999H. Moreover, taking account of the elimination of a Faraday cage that is necessary for operation of the 999H but is obviated by a redesign of high-voltage feed-throughs for the 999HA, the overall reduction in mass becomes 57 percent with an 82 percent reduction in volume. Through a series of rigorous tests, the 999HA has been qualified for operation aboard spacecraft with a lifetime exceeding seven years. Offspring of the 999HA will fly on the Kepler and Lunar Reconnaissance Orbiter missions.

  1. An experimental investigation of high temperature superconducting microstrip antennas at K- and Ka-band frequencies. Ph.D. Thesis Final Report

    NASA Technical Reports Server (NTRS)

    Richard, Mark A.

    1993-01-01

    The recent discovery of high temperature superconductors (HTS) has generated a substantial amount of interest in microstrip antenna applications. However, the high permittivity of substrates compatible with HTS results in narrow bandwidths and high patch edge impedances of such antennas. To investigate the performance of superconducting microstrip antennas, three antenna architectures at K and Ka-band frequencies are examined. Superconducting microstrip antennas that are directly coupled, gap coupled, and electromagnetically coupled to a microstrip transmission line were designed and fabricated on lanthanum aluminate substrates using YBa2Cu3O7 superconducting thin films. For each architecture, a single patch antenna and a four element array were fabricated. Measurements from these antennas, including input impedance, bandwidth, patterns, efficiency, and gain are presented. The measured results show usable antennas can be constructed using any of the architectures. All architectures show excellent gain characteristics, with less than 2 dB of total loss in the four element arrays. Although the direct and gap coupled antennas are the simplest antennas to design and fabricate, they suffer from narrow bandwidths. The electromagnetically coupled antenna, on the other hand, allows the flexibility of using a low permittivity substrate for the patch radiator, while using HTS for the feed network, thus increasing the bandwidth while effectively utilizing the low loss properties of HTS. Each antenna investigated in this research is the first of its kind reported.

  2. Journal of Superconductivity. Volume 8, Number 4. Special Issue: Miami University Workshop on High-Temperature Superconductivity. Part 1,

    DTIC Science & Technology

    1995-08-01

    Onellion Shadow Bands in Models of Correlated Electrons 475 Adriana Moreo, Stephan Haas, and Elbio Dagotto Electronic Properties of CuO 2 Planes 479...witlh each band, in agreement with experiments. lattice constant a, c(k) = -2t [cos(k/a) + cos(kya)] 3. CALCULATIONS +4t’ cos( ka ) cos(kya). (4) Using...C 170, 291 (1990). Journal of Superconductivity, Vol. 8, No. 4, 1995 Shadow Bands in Models of Correlated Electrons Adriana Moreo’, Stephan Haas

  3. Two regimes in the magnetic field response of superconducting MgB2

    NASA Astrophysics Data System (ADS)

    Kohen, A.; Giubileo, F.; Proslier, Th.; Bobba, F.; Cucolo, A. M.; Sacks, W.; Noat, Y.; Troianovski, A.; Roditchev, D.

    2007-05-01

    Using Scanning Tunneling Microscope at low temperature we explore the superconducting phase diagram in the π-band of the two-band superconductor MgB2. In this band the peculiar shape of the local tunneling spectra and their dynamics in the magnetic field reveal the complex character of the quasiparticle density of states (DOS). The gap in the DOS is first rapidly filled with states in raising the magnetic field up to 0.5 T and then slowly approaches the normal state value: the gap is observed up to 2 T. Such a change in the DOS dynamics suggests the existence of two terms in the DOS of the π-band: a first one, reflecting an intrinsic superconductivity in the band and a second one, originating from an inter-band coupling to the σ-band. Our findings allow a deeper understanding of the unique phase diagram of MgB2.

  4. Obituary: David L. Band (1957-2009)

    NASA Astrophysics Data System (ADS)

    Cominsky, Lynn

    2011-12-01

    David L. Band, of Potomac Maryland, died on March 16, 2009 succumbing to a long battle with spinal cord cancer. His death at the age of 52 came as a shock to his many friends and colleagues in the physics and astronomy community. Band showed an early interest and exceptional aptitude for physics, leading to his acceptance at the Massachusetts Institute of Technology as an undergraduate student in 1975. After graduating from MIT with an undergraduate degree in Physics, Band continued as a graduate student in Physics at Harvard University. His emerging interest in Astrophysics led him to the Astronomy Department at the Harvard Smithsonian Center for Astrophysics (CfA), where he did his dissertation work with Jonathan Grindlay. His dissertation (1985) entitled "Non-thermal Radiation Mechanisms and Processes in SS433 and Active Galactic Nuclei" was "pioneering work on the physics of jets arising from black holes and models for their emission, including self-absorption, which previewed much to come, and even David's own later work on Gamma-ray Bursts," according to Grindlay who remained a personal friend and colleague of Band's. Following graduate school, Band held postdoctoral positions at the Lawrence Livermore Laboratory, the University of California at Berkeley and the Center for Astronomy and Space Sciences at the University of California San Diego where he worked on the BATSE experiment that was part of the Compton Gamma Ray Observatory (CGRO), launched in 1991. BATSE had as its main objective the study of cosmic gamma-ray bursts (GRBs) and made significant advances in this area of research. Band became a world-renowned figure in the emerging field of GRB studies. He is best known for his widely-used analytic form of gamma-ray burst spectra known as the "Band Function." After the CGRO mission ended, Band moved to the Los Alamos National Laboratory where he worked mainly on classified research but continued to work on GRB energetics and spectra. When NASA planned

  5. L-Band Orthogonal-Mode Crossed-Slot Antenna and VHF Crossed-Loop Antenna

    DOT National Transportation Integrated Search

    1972-01-01

    A low-gain, circularly polarized, L-ban antenna; a low-gain, lineraly polarized, L-band antenna; and a low-gain, lineraly polarized, L-ban antenna; and a low-gain, circularly polarized, upper hemisphere, VHF satellite communications antenna intended ...

  6. Midlatitude Measurements of L-Band Ionospheric Scintillation with the ATS-5 Spacecraft

    DOT National Transportation Integrated Search

    1975-09-01

    The report presents some results of L-band signal level measurements taken from the ATS-5 spacecraft operating in the narrow-band frequency translation mode. The uplink signal was sent from the DOT/TSC/Westford Propagation Facility in Westford, Massa...

  7. Large enhancement of superconductivity in Zr point contacts.

    PubMed

    Aslam, Mohammad; Singh, Chandan; Das, Shekhar; Kumar, Ritesh; Datta, Soumya; Halder, Soumyadip; Gayen, Sirshendu; Kabir, Mukul; Sheet, Goutam

    2018-04-30

    For certain complex superconducting systems, the superconducting properties get enhanced under mesoscopic point contacts made of elemental non-superconducting metals. However, understanding of the mechanism through which such contact induced local enhancement of superconductivity happens has been limited due to the complex nature of such compounds. In this paper we present a large enhancement of superconducting transition temperature (T<sub>c</sub>) and superconducting energy gap (Δ) in a simple elemental superconductor Zr. While bulk Zr shows a critical temperature around 0.6K, superconductivity survives at Ag/Zr and Pt/Zr point contacts up to 3K with a corresponding five-fold enhancement of Δ. Further, the first-principles calculations on a model system provide useful insights. We show that the enhancement in superconducting properties can be attributed to a modification in the electron-phonon coupling accompanied by an enhancement of the density of states which involves the appearance of a new electron band at the Ag/Zr interfaces. © 2018 IOP Publishing Ltd.

  8. Coexistence of multiphase superconductivity and ferromagnetism in lithiated iron selenide hydroxide [(L i1 -xF ex) OH ]FeSe

    NASA Astrophysics Data System (ADS)

    Urban, Christian; Valmianski, Ilya; Pachmayr, Ursula; Basaran, Ali C.; Johrendt, Dirk; Schuller, Ivan K.

    2018-01-01

    We present experimental evidence for (a) multiphase superconductivity and (b) coexistence of magnetism and superconductivity in a single structural phase of lithiated iron selenide hydroxide [(L i1 -xF ex )OH]FeSe. Magnetic field modulated microwave spectroscopy data confirms superconductivity with at least two distinct transition temperatures attributed to well-defined superconducting phases at TSC 1=40 ±2 K and TSC 2=35 ±2 K. Magnetometry data for the upper critical fields reveal a change in the magnetic order (TM=12 K) below TSC 1 and TSC 2 that is consistent with ferromagnetism. This occurs because the superconducting coherence length is much smaller than the structural coherence length, allowing for several different electronic and magnetic states on a single crystallite. The results give insight into the physics of complex multinary materials, where several phenomena governed by different characteristic length scales coexist.

  9. RVB states in doped band insulators from Coulomb forces: theory and a case study of superconductivity in BiS2 layers

    NASA Astrophysics Data System (ADS)

    Baskaran, G.

    2016-12-01

    Doped band insulators, HfNCl, WO3, diamond, Bi2Se3, BiS2 families, STO/LAO interface, gate doped SrTiO3, MoS2 and so on are unusual superconductors. With an aim to build a general theory for superconductivity in doped band insulators, we focus on the BiS2 family which was discovered by Mizuguchi et al in 2012. While maximum Tc is only ˜11 K in {{LaO}}1-{{x}}{{{F}}}{{x}}{{BiS}}2, a number of experimental results are puzzling and anomalous in the sense that they resemble high T c and unconventional superconductors. Using a two orbital model of Usui, Suzuki and Kuroki, we show that the uniform low density free Fermi sea in {{LaO}}{0,5}{{{F}}}0.5{{BiS}}2 is unstable towards formation of the next nearest neighbor Bi-S-Bi diagonal valence bond (charged -2e Cooper pair) and their Wigner crystallization. Instability to this novel state of matter is caused by unscreened nearest neighbor coulomb repulsions (V ˜ 1 eV) and a hopping pattern with sulfur mediated diagonal next nearest neighbor Bi-S-Bi hopping t’ ˜ 0.88 eV, as well as larger than nearest neighbor Bi-Bi hopping, t ˜ 0.16 eV. Wigner crystals of Cooper pairs quantum melt for doping around x = 0.5 and stabilize certain resonating valence bond states and superconductivity. We study a few variational RVB states and suggest that BiS2 family members are latent high Tc superconductors, but challenged by competing orders and the fragile nature of many body states sustained by unscreened Coulomb forces. One of our superconducting states has d XY symmetry and a gap. We also predict a 2d Bose metal or vortex liquid normal state, as charged -2e valence bonds survive in the normal state.

  10. Combined observations of Arctic sea ice with near-coincident colocated X-band, C-band, and L-band SAR satellite remote sensing and helicopter-borne measurements

    NASA Astrophysics Data System (ADS)

    Johansson, A. M.; King, J. A.; Doulgeris, A. P.; Gerland, S.; Singha, S.; Spreen, G.; Busche, T.

    2017-01-01

    In this study, we compare colocated near-coincident X-, C-, and L-band fully polarimetry SAR satellite images with helicopter-borne ice thickness measurements acquired during the Norwegian Young sea ICE 2015 (N-ICE2015) expedition in the region of the Arctic Ocean north of Svalbard in April 2015. The air-borne surveys provide near-coincident snow plus ice thickness, surface roughness data, and photographs. This unique data set allows us to investigate how the different frequencies can complement one another for sea ice studies, but also to raise awareness of limitations. X-band and L-band satellite scenes were shown to be a useful complement to the standard SAR frequency for sea ice monitoring (C-band) for lead ice and newly formed sea ice identification. This may be in part be due to the frequency but also the high spatial resolution of these sensors. We found a relatively low correlation between snow plus ice thickness and surface roughness. Therefore, in our dataset ice thickness cannot directly be observed by SAR which has important implications for operational ice charting based on automatic segmentation.

  11. First principles Study on Transparent High-Tc Superconductivity in hole-doped Delafossite CuAlO2

    NASA Astrophysics Data System (ADS)

    Nakanishi, Akitaka; Katayama-Yoshida, Hiroshi

    2012-02-01

    The CuAlO2 is the transparent p-type conductor without any intentional doping. Transparent superdoncutivity and high thermoelectric power are suggested in p-type CuAlO2 [1]. Katayama-Yoshida et al. proposed that it may cause a strong electron-phonon interaction and a superconductivity. But, the calculation of superconducting critical temperature Tc is not performed. We performed the first principles calculation about the Tc of hole-doped CuAlO2 by shifting the Fermi level rigidly. In lightly hole-doped CuAlO2, the Fermi level is located at Cu and O anti-bonding band. The electrons of this band strongly interact with the A1L1 phonon mode because the direction of O-Cu-O dumbbell is parallel to the oscillation direction of the A1L1 phonon mode. As a result, Tc of lightly hole-doped CuAlO2 is about 50 K. We also discuss the materials design to enhance the Tc based on the charge-excitation-induced negative effective U system.[4pt] [1] H. Katayama-Yoshida, T. Koyanagi, H. Funashima, H. Harima, A. Yanase: Solid State Communication 126 (2003) 135. [0pt] [2] A. Nakanishi and H. Katayama-Yoshida: Solid State Communication, in printing. (arXiv:1107.2477v3

  12. Effective theory of exotic superconductivity in LaAlO3/SrTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Esmailzadeh, Haniyeh; Moghaddam, Ali G.

    2018-05-01

    Motivated by experimental and theoretical works about superconductivity at the oxide interfaces, we provide a simple model for possible unconventional pairings inside the exotic two-dimensional electron gas formed in heterostructures of SrTiO3 and LaAlO3. At the low energy limit, the electron gas at the interfaces is usually modeled with an effective three band model considering of 3d t2g orbitals which are slightly coupled by atomic spin-orbit couplings (SOC). Considering direct superconducting pairing in two higher delocalized bands and by exploiting a perturbative scheme based on canonical transformation, we derive the effective pairing amplitudes with possibly exotic nature inside the localized dxy band as well as various inter-band pairing components. In particular we show that equal-spin triplet pairings are possible between the band dxy and any of other dxz and dyz bands. In addition weaker effective pairings take place inside the localized band itself and between delocalized dxz and dyz bands with singlet and opposite-spin triplet characters. These unconventional effective pairings are indeed mediated by SOC-induced higher order virtual transitions between the bands and particularly into the localized band. Our model suggest that unconventional effective superconductivity is possible at oxide interfaces, simply, due to the special band structure and important role of atomic SOC and perhaps other magnetic effects present at these heterostructures.

  13. Comparison of Model Prediction with Measurements of Galactic Background Noise at L-Band

    NASA Technical Reports Server (NTRS)

    LeVine, David M.; Abraham, Saji; Kerr, Yann H.; Wilson, Willam J.; Skou, Niels; Sobjaerg, S.

    2004-01-01

    The spectral window at L-band (1.413 GHz) is important for passive remote sensing of surface parameters such as soil moisture and sea surface salinity that are needed to understand the hydrological cycle and ocean circulation. Radiation from celestial (mostly galactic) sources is strong in this window and an accurate accounting for this background radiation is often needed for calibration. Modem radio astronomy measurements in this spectral window have been converted into a brightness temperature map of the celestial sky at L-band suitable for use in correcting passive measurements. This paper presents a comparison of the background radiation predicted by this map with measurements made with several modem L-band remote sensing radiometers. The agreement validates the map and the procedure for locating the source of down-welling radiation.

  14. Tuning the band structure and superconductivity in single-layer FeSe by interface engineering.

    PubMed

    Peng, R; Xu, H C; Tan, S Y; Cao, H Y; Xia, M; Shen, X P; Huang, Z C; Wen, C H P; Song, Q; Zhang, T; Xie, B P; Gong, X G; Feng, D L

    2014-09-26

    The interface between transition metal compounds provides a rich playground for emergent phenomena. Recently, significantly enhanced superconductivity has been reported for single-layer FeSe on Nb-doped SrTiO3 substrate. Yet it remains mysterious how the interface affects the superconductivity. Here we use in situ angle-resolved photoemission spectroscopy to investigate various FeSe-based heterostructures grown by molecular beam epitaxy, and uncover that electronic correlations and superconducting gap-closing temperature (Tg) are tuned by interfacial effects. Tg up to 75 K is observed in extremely tensile-strained single-layer FeSe on Nb-doped BaTiO3, which sets a record high pairing temperature for both Fe-based superconductor and monolayer-thick films, providing a promising prospect on realizing more cost-effective superconducting device. Moreover, our results exclude the direct correlation between superconductivity and tensile strain or the energy of an interfacial phonon mode, and highlight the critical and non-trivial role of FeSe/oxide interface on the high Tg, which provides new clues for understanding its origin.

  15. Miniature L-Band Radar Transceiver

    NASA Technical Reports Server (NTRS)

    McWatters, Dalia; Price, Douglas; Edelstein, Wendy

    2007-01-01

    A miniature L-band transceiver that operates at a carrier frequency of 1.25 GHz has been developed as part of a generic radar electronics module (REM) that would constitute one unit in an array of many identical units in a very-large-aperture phased-array antenna. NASA and the Department of Defense are considering the deployment of such antennas in outer space; the underlying principles of operation, and some of those of design, also are applicable on Earth. The large dimensions of the antennas make it advantageous to distribute radio-frequency electronic circuitry into elements of the arrays. The design of the REM is intended to implement the distribution. The design also reflects a requirement to minimize the size and weight of the circuitry in order to minimize the weight of any such antenna. Other requirements include making the transceiver robust and radiation-hard and minimizing power demand. Figure 1 depicts the functional blocks of the REM, including the L-band transceiver. The key functions of the REM include signal generation, frequency translation, amplification, detection, handling of data, and radar control and timing. An arbitrary-waveform generator that includes logic circuitry and a digital-to-analog converter (DAC) generates a linear-frequency-modulation chirp waveform. A frequency synthesizer produces local-oscillator signals used for frequency conversion and clock signals for the arbitrary-waveform generator, for a digitizer [that is, an analog-to-digital converter (ADC)], and for a control and timing unit. Digital functions include command, timing, telemetry, filtering, and high-rate framing and serialization of data for a high-speed scientific-data interface. The aforementioned digital implementation of filtering is a key feature of the REM architecture. Digital filters, in contradistinction to analog ones, provide consistent and temperature-independent performance, which is particularly important when REMs are distributed throughout a large

  16. False-color L-band image of Manaus region of Brazil

    NASA Image and Video Library

    1994-04-13

    STS059-S-068 (13 April 1994) --- This false-color L-Band image of the Manaus region of Brazil was acquired by the Spaceborne Imaging Radar-C and X-Band Synthetic Aperture Radar (SIR-C/X-SAR) aboard the Space Shuttle Endeavour on orbit 46 of the mission. The area shown is approximately 8 kilometers by 40 kilometers (5 by 25 miles). At the top of the image are the Solimoes and Rio Negro Rivers just before they combine at Manaus to form the Amazon River. The image is centered at about 3 degrees south latitude, and 61 degrees west longitude. The false colors are created by displaying three L-Band polarization channels; red areas correspond to high backscatter at HH polarization, while green areas exhibit high backscatter at HV polarization. Blue areas show low returns at VV polarization; hence the bright blue colors of the smooth river surfaces. Using this color scheme, green areas in the image are heavily forested, while blue areas are either cleared forest or open water. The yellow and red areas are flooded forest. Between Rio Solimoes and Rio Negro a road can be seen running from some cleared areas (visible as blue rectangles north of Rio Solimoes) north towards a tributary of Rio Negro. SIR-C/X-SAR is part of NASA's Mission to Planet Earth (MTPE). SIR-C/X-SAR radars illuminate Earth with microwaves allowing detailed observations at any time, regardless of weather or sunlight conditions. SIR-C/X-SAR uses three microwave wavelengths: L-Band (24 cm), C-Band (6 cm), and X-Band (3 cm). The multi-frequency data will be used by the international scientific community to better understand the global environment and how it is changing. The SIR-C/X-SAR data, complemented by aircraft and ground studies, will give scientists clearer insights into those environmental changes which are caused by nature and those changes which are induced by human activity. SIR-C was developed by NASA's Jet Propulsion Laboratory (JPL). X-SAR was developed by the Dornire and Alenia Spazio Companies

  17. Superconductivity bordering Rashba type topological transition

    DOE PAGES

    Jin, M. L.; Sun, F.; Xing, L. Y.; ...

    2017-01-04

    Strong spin orbital interaction (SOI) can induce unique quantum phenomena such as topological insulators, the Rashba effect, or p-wave superconductivity. Combining these three quantum phenomena into a single compound has important scientific implications. Here we report experimental observations of consecutive quantum phase transitions from a Rashba type topological trivial phase to topological insulator state then further proceeding to superconductivity in a SOI compound BiTeI tuned via pressures. The electrical resistivity measurement with V shape change signals the transition from a Rashba type topological trivial to a topological insulator phase at 2 GPa, which is caused by an energy gap closemore » then reopen with band inverse. Superconducting transition appears at 8 GPa with a critical temperature T C of 5.3 K. Structure refinements indicate that the consecutive phase transitions are correlated to the changes in the Bi–Te bond and bond angle as function of pressures. As a result, the Hall Effect measurements reveal an intimate relationship between superconductivity and the unusual change in carrier density that points to possible unconventional superconductivity.« less

  18. Challenges for continuity of L-Band observations over land

    USDA-ARS?s Scientific Manuscript database

    Over land, L-band observations are primarily used for the detection of soil freeze/thaw events and the quantification of surface soil moisture content. Both products have important science, climate and decision support applications and would benefit from longer historical data records derived from s...

  19. Role of hybridization in the superconducting properties of an extended d p Hubbard model: a detailed numerical study

    NASA Astrophysics Data System (ADS)

    Calegari, E. J.; Magalhães, S. G.; Gomes, A. A.

    2005-04-01

    The Roth's two-pole approximation has been used by the present authors to study the effects of the hybridization in the superconducting properties of a strongly correlated electron system. The model used is the extended Hubbard model which includes the d-p hybridization, the p-band and a narrow d-band. The present work is an extension of our previous work (J. Mod. Phys. B 18(2) (2004) 241). Nevertheless, some important correlation functions necessary to estimate the Roth's band shift, are included together with the temperature T and the Coulomb interaction U to describe the superconductivity. The superconducting order parameter of a cuprate system, is obtained following Beenen and Edwards formalism. Here, we investigate in detail the change of the order parameter associated to temperature, Coulomb interaction and Roth's band shift effects on superconductivity. The phase diagram with Tc versus the total occupation number nT, shows the difference respect to the previous work.

  20. Phonons and superconductivity in fcc and dhcp lanthanum

    NASA Astrophysics Data System (ADS)

    Baǧcı, S.; Tütüncü, H. M.; Duman, S.; Srivastava, G. P.

    2010-04-01

    We have investigated the structural and electronic properties of lanthanum in the face-centered-cubic (fcc) and double hexagonal-close-packed (dhcp) phases using a generalized gradient approximation of the density functional theory and the ab initio pseudopotential method. It is found that double hexagonal-close-packed is the more stable phase for lanthanum. Differences in the density of states at the Fermi level between these two phases are pointed out and discussed in detail. Using the calculated lattice constant and electronic band structure for both phases, a linear response approach based on the density functional theory has been applied to study phonon modes, polarization characteristics of phonon modes, and electron-phonon interaction. Our phonon results show a softening behavior of the transverse acoustic branch along the Γ-L direction and the Γ-M direction for face-centered-cubic and double hexagonal-close-packed phases, respectively. Thus, the transverse-phonon linewidth shows a maximum at the zone boundary M(L) for the double hexagonal-close-packed phase (face-centered-cubic phase), where the transverse-phonon branch exhibits a dip. The electron-phonon coupling parameter λ is found to be 0.97 (1.06) for the double hexagonal-close-packed phase (face-centered-cubic phase), and the superconducting critical temperature is estimated to be 4.87 (dhcp) and 5.88 K (fcc), in good agreement with experimental values of around 5.0 (dhcp) and 6.0 K (fcc). A few superconducting parameters for the double hexagonal-close-packed phase have been calculated and compared with available theoretical and experimental results. Furthermore, the calculated superconducting parameters for both phases are compared between each other in detail.

  1. Design and Performance of a Miniature Radar L-Band Transceiver

    NASA Technical Reports Server (NTRS)

    McWatters, D.; Price, D.; Edelstein, W.

    2004-01-01

    Radar electronics developed for past JPL space missions historically had been custom designed and as such, given budgetary, time, and risk constraints, had not been optimized for maximum flexibility or miniaturization. To help reduce cost and risk of future radar missions, a generic radar module was conceived. The module includes a 1.25-GHz (L-band) transceiver and incorporates miniature high-density packaging of integrated circuits in die/chip form. The technology challenges include overcoming the effect of miniaturization and high packaging density to achieve the performance, reliability, and environmental ruggedness required for space missions. The module was chosen to have representative (generic) functionality most likely required from an L-band radar. For very large aperture phased-array spaceborne radar missions, the large dimensions of the array suggest the benefit of distributing the radar electronics into the antenna array. For such applications, this technology is essential in order to bring down the cost, mass, and power of the radar electronics module replicated in each panel of the array. For smaller sized arrays, a single module can be combined with the central radar controller and still provide the bene.ts of configuration .exibility, low power, and low mass. We present the design approach for the radar electronics module and the test results for its radio frequency (RF) portion: a miniature, low-power, radiation-hard L-band transceiver.

  2. Conduction-band valley spin splitting in single-layer H-T l2O

    NASA Astrophysics Data System (ADS)

    Ma, Yandong; Kou, Liangzhi; Du, Aijun; Huang, Baibiao; Dai, Ying; Heine, Thomas

    2018-02-01

    Despite numerous studies, coupled spin and valley physics is currently limited to two-dimensional (2D) transition-metal dichalcogenides (TMDCs). Here, we predict an exceptional 2D valleytronic material associated with the spin-valley coupling phenomena beyond 2D TMDCs—single-layer (SL) H-T l2O . It displays large valley spin splitting (VSS), significantly larger than that of 2D TMDCs, and a finite band gap, which are both critically attractive for the integration of valleytronics and spintronics. More importantly, in sharp contrast to all the experimentally confirmed 2D valleytronic materials, where the strong valence-band VSS (0.15-0.46 eV) supports the spin-valley coupling, the VSS in SL H-T l2O is pronounced in its conduction band (0.61 eV), but negligibly small in its valence band (21 meV), thus opening a way for manipulating the coupled spin and valley physics. Moreover, SL H-T l2O possesses extremely high carrier mobility, as large as 9.8 ×103c m2V-1s-1 .

  3. The application of airborne imaging radars (L and X-band) to earth resources problems

    NASA Technical Reports Server (NTRS)

    Drake, B.; Shuchman, R. A.; Bryan, M. L.; Larson, R. W.; Liskow, C. L.; Rendleman, R. A.

    1974-01-01

    A multiplexed synthetic aperture Side-Looking Airborne Radar (SLAR) that simultaneously images the terrain with X-band (3.2 cm) and L-band (23.0 cm) radar wavelengths was developed. The Feasibility of using multiplexed SLAR to obtain useful information for earth resources purposes. The SLAR imagery, aerial photographs, and infrared imagery are examined to determine the qualitative tone and texture of many rural land-use features imaged. The results show that: (1) Neither X- nor L-band SLAR at moderate and low depression angles can directly or indirectly detect pools of water under standing vegetation. (2) Many of the urban and rural land-use categories present in the test areas can be identified and mapped on the multiplexed SLAR imagery. (3) Water resources management can be done using multiplexed SLAR. (4) Drainage patterns can be determined on both the X- and L-band imagery.

  4. Excitonic Order and Superconductivity in the Two-Orbital Hubbard Model: Variational Cluster Approach

    NASA Astrophysics Data System (ADS)

    Fujiuchi, Ryo; Sugimoto, Koudai; Ohta, Yukinori

    2018-06-01

    Using the variational cluster approach based on the self-energy functional theory, we study the possible occurrence of excitonic order and superconductivity in the two-orbital Hubbard model with intra- and inter-orbital Coulomb interactions. It is known that an antiferromagnetic Mott insulator state appears in the regime of strong intra-orbital interaction, a band insulator state appears in the regime of strong inter-orbital interaction, and an excitonic insulator state appears between them. In addition to these states, we find that the s±-wave superconducting state appears in the small-correlation regime, and the dx2 - y2-wave superconducting state appears on the boundary of the antiferromagnetic Mott insulator state. We calculate the single-particle spectral function of the model and compare the band gap formation due to the superconducting and excitonic orders.

  5. Observation of direct evolution from antiferromagnetism to superconductivity in C u1 -xL ixFeAs (0 ≤x ≤1.0 )

    NASA Astrophysics Data System (ADS)

    Li, Kunkun; Yuan, Duanduan; Guo, Jiangang; Chen, Xiaolong

    2018-04-01

    We report the structure, antiferromagnetism, and superconductivity in C u1 -xL ixFeAs (0 ≤x ≤1.0 ) samples. A direct evolution from antiferromagnetism to superconductivity is observed as increasing doping level of Li. A phase diagram is constructed to show this evolution, which features no coexistence region between superconductivity and antiferromagnetism. This behavior shows that antiferromagnetic CuFeAs can be regarded as a parent compound to the observed superconductivity by equivalent doping, which is different from the cases with other FeAs-based superconductors. Structural analyses and first-principles calculations indicate that the anion height of F e2A s2 tetrahedral layer plays a crucial role on the physical properties. Moreover, the simple Fermi surface nesting picture adopted to explain the evolution from spin-density wave to superconductor in other FeAs-based superconductors might be not applicable to C u1 -xL ixFeAs .

  6. Stable L-band multi-wavelength SOA fiber laser based on polarization rotation.

    PubMed

    Liu, Tonghui; Jia, Dongfang; Yang, Tianxin; Wang, Zhaoying; Liu, Ying

    2017-04-01

    We propose and experimentally demonstrate a stable multi-wavelength fiber ring laser operating in the L-band with wavelength spacing of 25 GHz. The mechanism is induced by a polarization rotation intensity equalizer consisting of a semiconductor optical amplifier and polarization devices. A Fabry-Perot filter is inserted into the cavity to serve as a multi-wavelength selection device. Stable L-band multi-wavelength lasing with 3 dB uniformity of 21.2 nm, and simultaneous oscillation of 101 lines with wavelength spacing of 25 GHz, is obtained.

  7. Tropical forest tree stands characterization with L-band polarimetric radar

    NASA Technical Reports Server (NTRS)

    Wu, Shih-Tseng

    1990-01-01

    The effectiveness of using L-band polarimetric data to determine tropical tree-stand parameters is discussed with specific attention given to the correction of the radar data. Tree-parameter data from ground studies is compared to L-band polarimetric data (in both uncorrected and topographically corrected forms) for two test areas. The test sites are at two different elevations but both include 81 test plots with topographic data and tree-characteristic data given. Synthetic-aperture radar (SAR) data are found to be related to bole volume and tree volume, and the topographically corrected data show results similar to the uncorrected data. Similar r-values are given for both data sets because the data with incidence-angle values below 35 and above 55 are removed. Topographical correction is important when local incidence angles exceed the limits.

  8. Topological Superconductivity on the Surface of Fe-Based Superconductors.

    PubMed

    Xu, Gang; Lian, Biao; Tang, Peizhe; Qi, Xiao-Liang; Zhang, Shou-Cheng

    2016-07-22

    As one of the simplest systems for realizing Majorana fermions, the topological superconductor plays an important role in both condensed matter physics and quantum computations. Based on ab initio calculations and the analysis of an effective 8-band model with superconducting pairing, we demonstrate that the three-dimensional extended s-wave Fe-based superconductors such as Fe_{1+y}Se_{0.5}Te_{0.5} have a metallic topologically nontrivial band structure, and exhibit a normal-topological-normal superconductivity phase transition on the (001) surface by tuning the bulk carrier doping level. In the topological superconductivity (TSC) phase, a Majorana zero mode is trapped at the end of a magnetic vortex line. We further show that the surface TSC phase only exists up to a certain bulk pairing gap, and there is a normal-topological phase transition driven by the temperature, which has not been discussed before. These results pave an effective way to realize the TSC and Majorana fermions in a large class of superconductors.

  9. Color composite C-band and L-band image of Kilauea volcanoe on Hawaii

    NASA Image and Video Library

    1994-04-15

    STS059-S-074 (15 April 1994) --- This color composite C-Band and L-Band image of the Kilauea volcano on the big island of Hawaii was acquired by the Spaceborne Imaging Radar-C and X-Band Synthetic Aperture Radar (SIR-C/X-SAR) flying on the Space Shuttle Endeavour. The city of Hilo can be seen at the top. The image shows the different types of lava flows around the crater Pu'u O'o. Ash deposits which erupted in 1790 from the summit of Kilauea volcano show up as dark in this image, and fine details associated with lava flows which erupted in 1919 and 1974 can be seen to the south of the summit in an area called the Ka'u Desert. In addition, the other historic lava flows created in 1881 and 1984 from Mauna Loa volcano (out of view to the left of this image) can easily be seen despite the fact that the surrounding area is covered by forest. Such information will be used to map the extent of such flows, which can pose a hazard to the subdivisions of Hilo. Highway 11 is the linear feature running from Hilo to the Kilauea volcano. The Kilauea volcano has been almost continuously active for more than the last 11 years. Field teams that were on the ground specifically to support these radar observations report that there was vigorous surface activity about 400 meters (one-quarter mile) inland from the coast. A moving lava flow about 200 meters (660 feet) in length was observed at the time of the Shuttle over flight, raising the possibility that subsequent images taken during this mission will show changes in the landscape. SIR-C/X-SAR is part of NASA's Mission to Planet Earth (MTPE). SIR-C/X-SAR radars illuminate Earth with microwaves allowing detailed observations at any time, regardless of weather or sunlight conditions. SIR-C/X-SAR uses three microwave wavelengths: L-Band (24 cm), C-Band (6 cm), and X-Band (3 cm). The multi-frequency data will be used by the international scientific community to better understand the global environment and how it is changing. The SIR

  10. The role of engineered materials in superconducting tunnel junction X-ray detectors - Suppression of quasiparticle recombination losses via a phononic band gap

    NASA Technical Reports Server (NTRS)

    Rippert, Edward D.; Ketterson, John B.; Chen, Jun; Song, Shenian; Lomatch, Susanne; Maglic, Stevan R.; Thomas, Christopher; Cheida, M. A.; Ulmer, Melville P.

    1992-01-01

    An engineered structure is proposed that can alleviate quasi-particle recombination losses via the existence of a phononic band gap that overlaps the 2-Delta energy of phonons produced during recombination of quasi-particles. Attention is given to a 1D Kronig-Penny model for phonons normally incident to the layers of a multilayered superconducting tunnel junction as an idealized example. A device with a high density of Bragg resonances is identified as desirable; both Nb/Si and NbN/SiN superlattices have been produced, with the latter having generally superior performance.

  11. Soil moisture limitations on monitoring boreal forest regrowth using spaceborne L-band SAR data

    Treesearch

    Eric S. Kasischke; Mihai A. Tanase; Laura L. Bourgeau-Chavez; Matthew Borr

    2011-01-01

    A study was carried out to investigate the utility of L-band SAR data for estimating aboveground biomass in sites with low levels of vegetation regrowth. Data to estimate biomass were collected from 59 sites located in fire-disturbed black spruce forests in interior Alaska. PALSAR L-band data (HH and HV polarizations) collected on two dates in the summer/fall of 2007...

  12. Effect of Forest Canopy on Remote Sensing Soil Moisture at L-band

    NASA Technical Reports Server (NTRS)

    LeVine, D. M.; Lang, R. H.; Jackson, T. J.; Haken, M.

    2005-01-01

    Global maps of soil moisture are needed to improve understanding and prediction of the global water and energy cycles. Accuracy requirements imply the use of lower frequencies (L-band) to achieve adequate penetration into the soil and to minimize attenuation by the vegetation canopy and effects of surface roughness. Success has been demonstrated over agricultural areas, but canopies with high biomass (e.g. forests) still present a challenge. Examples from recent measurements over forests with the L-band radiometer, 2D-STAR, and its predecessor, ESTAR, will be presented to illustrate the problem. ESTAR and 2D-STAR are aircraft-based synthetic aperture radiometers developed to help resolve both the engineering and algorithm issues associated with future remote sensing of soil moisture. ESTAR, which does imaging across track, was developed to demonstrate the viability of aperture synthesis for remote sensing. The instrument has participated several soil moisture experiments (e.g. at the Little Washita Watershed in 1992 and the Southern Great Plains experiments in 1997 and 1999). In addition, measurements have been made at a forest site near Waverly, VA which contains conifer forests with a variety of biomass. These data have demonstrated the success of retrieving soil moisture at L-band over agricultural areas and the response of passive observations at L-band to biomass over forests. 2D-STAR is a second generation instrument that does aperture synthesis in two dimensions (along track and cross track) and is dual polarized. This instrument has the potential to provide measurements at L-band that simulate the measurements that will be made by the two L-band sensors currently being developed for future remote sensing of soil moisture from space: Hydros (conical scan and real aperture) and SMOS (multiple incidence angle and synthetic aperture). 2D-STAR participated in the SMEX-03 soil moisture experiment, providing images from the NASA P-3 aircraft. Preliminary results

  13. An L Band Spectrum of the Coldest Brown Dwarf

    NASA Astrophysics Data System (ADS)

    Morley, Caroline V.; Skemer, Andrew J.; Allers, Katelyn N.; Marley, Mark. S.; Faherty, Jacqueline K.; Visscher, Channon; Beiler, Samuel A.; Miles, Brittany E.; Lupu, Roxana; Freedman, Richard S.; Fortney, Jonathan J.; Geballe, Thomas R.; Bjoraker, Gordon L.

    2018-05-01

    The coldest brown dwarf, WISE 0855, is the closest known planetary-mass, free-floating object and has a temperature nearly as cold as the solar system gas giants. Like Jupiter, it is predicted to have an atmosphere rich in methane, water, and ammonia, with clouds of volatile ices. WISE 0855 is faint at near-infrared wavelengths and emits almost all its energy in the mid-infrared. Skemer et al. presented a spectrum of WISE 0855 from 4.5–5.1 μm (M band), revealing water vapor features. Here, we present a spectrum of WISE 0855 in the L band, from 3.4–4.14 μm. We present a set of atmosphere models that include a range of compositions (metallicities and C/O ratios) and water ice clouds. Methane absorption is clearly present in the spectrum. The mid-infrared color can be better matched with a methane abundance that is depleted relative to solar abundance. We find that there is evidence for water ice clouds in the M band spectrum, and we find a lack of phosphine spectral features in both the L and M band spectra. We suggest that a deep continuum opacity source may be obscuring the near-infrared flux, possibly a deep phosphorous-bearing cloud, ammonium dihyrogen phosphate. Observations of WISE 0855 provide critical constraints for cold planetary atmospheres, bridging the temperature range between the long-studied solar system planets and accessible exoplanets. The James Webb Space Telescope will soon revolutionize our understanding of cold brown dwarfs with high-precision spectroscopy across the infrared, allowing us to study their compositions and cloud properties, and to infer their atmospheric dynamics and formation processes.

  14. RF Control and Measurement of Superconducting Qubits

    DTIC Science & Technology

    2015-02-14

    Schoelkopf, Leonid I. Glazman, Michel H. Devoret. Coherent suppression of electromagnetic dissipation due to superconducting quasiparticles ...Frunzio, L.?I. Glazman, M.?H. Devoret. Non-Poissonian Quantum Jumps of a Fluxonium Qubit due to Quasiparticle Excitations, Physical Review Letters...Devoret, G. Catelani, L. I. Glazman, R. J. Schoelkopf. Measurement and control of quasiparticle dynamics in a superconducting qubit, Nature

  15. Coastal flood inundation monitoring with Satellite C-band and L-band Synthetic Aperture Radar data

    USGS Publications Warehouse

    Ramsey, Elijah W.; Rangoonwala, Amina; Bannister, Terri

    2013-01-01

    Satellite Synthetic Aperture Radar (SAR) was evaluated as a method to operationally monitor the occurrence and distribution of storm- and tidal-related flooding of spatially extensive coastal marshes within the north-central Gulf of Mexico. Maps representing the occurrence of marsh surface inundation were created from available Advanced Land Observation Satellite (ALOS) Phased Array type L-Band SAR (PALSAR) (L-band) (21 scenes with HH polarizations in Wide Beam [100 m]) data and Environmental Satellite (ENVISAT) Advanced SAR (ASAR) (C-band) data (24 scenes with VV and HH polarizations in Wide Swath [150 m]) during 2006-2009 covering 500 km of the Louisiana coastal zone. Mapping was primarily based on a decrease in backscatter between reference and target scenes, and as an extension of previous studies, the flood inundation mapping performance was assessed by the degree of correspondence between inundation mapping and inland water levels. Both PALSAR- and ASAR-based mapping at times were based on suboptimal reference scenes; however, ASAR performance seemed more sensitive to reference-scene quality and other types of scene variability. Related to water depth, PALSAR and ASAR mapping accuracies tended to be lower when water depths were shallow and increased as water levels decreased below or increased above the ground surface, but this pattern was more pronounced with ASAR. Overall, PALSAR-based inundation accuracies averaged 84% (n = 160), while ASAR-based mapping accuracies averaged 62% (n = 245).

  16. Prediction of phonon-mediated superconductivity in hole-doped black phosphorus.

    PubMed

    Feng, Yanqing; Sun, Hongyi; Sun, Junhui; Lu, Zhibin; You, Yong

    2018-01-10

    We study the conventional electron-phonon mediated superconducting properties of hole-doped black phosphorus by density functional calculations and get quite a large electron-phonon coupling (EPC) constant λ ~ 1.0 with transition temperature T C ~ 10 K, which is comparable to MgB 2 when holes are doped into the degenerate and nearly flat energy bands around the Fermi level. We predict that the softening of low-frequency [Formula: see text] optical mode and its phonon displacement, which breaks the lattice nonsymmorphic symmetry of gliding plane and lifts the band double degeneracy, lead to a large EPC. These factors are favorable for BCS superconductivity.

  17. Prediction of phonon-mediated superconductivity in hole-doped black phosphorus

    NASA Astrophysics Data System (ADS)

    Feng, Yanqing; Sun, Hongyi; Sun, Junhui; Lu, Zhibin; You, Yong

    2018-01-01

    We study the conventional electron-phonon mediated superconducting properties of hole-doped black phosphorus by density functional calculations and get quite a large electron-phonon coupling (EPC) constant λ ~ 1.0 with transition temperature T C ~ 10 K, which is comparable to MgB2 when holes are doped into the degenerate and nearly flat energy bands around the Fermi level. We predict that the softening of low-frequency B3g1 optical mode and its phonon displacement, which breaks the lattice nonsymmorphic symmetry of gliding plane and lifts the band double degeneracy, lead to a large EPC. These factors are favorable for BCS superconductivity.

  18. Anomalous electron doping independent two-dimensional superconductivity

    NASA Astrophysics Data System (ADS)

    Zhou, Wei; Xing, Xiangzhuo; Zhao, Haijun; Feng, Jiajia; Pan, Yongqiang; Zhou, Nan; Zhang, Yufeng; Qian, Bin; Shi, Zhixiang

    2017-07-01

    Transition metal (Co and Ni) co-doping effects are investigated on an underdoped Ca0.94La0.06Fe2As2 compound. It is discovered that electron doping from substituting Fe with transition metal (TM = Co, Ni) can trigger high-{T}{{c}} superconductivity around 35 K, which emerges abruptly before the total suppression of the innate spin-density-wave/anti-ferromagnetism (SDW/AFM) state. Remarkably, the critical temperature for the high-{T}{{c}} superconductivity remains constant against a wide range of TM doping levels. And the net electron doping density dependence of the superconducting {T}{{c}} based on the rigid band model can be nicely scaled into a single curve for Co and Ni substitutions, in stark contrast to the case of Ba(Fe1-x TM x )2As2. This carrier density independent superconductivity and the unusual scaling behavior are presumably resulted from the interface superconductivity based on the similarity with the interface superconductivity in a La2-x Sr x CuO4-La2CuO4 bilayer. Evidence of the two-dimensional character of the superfluid by angle-resolved magneto-resistance measurements can further strengthen the interface nature of the high-{T}{{c}} superconductivity.

  19. μ SR Investigation of Superconducting PbTaSe2

    NASA Astrophysics Data System (ADS)

    Wilson, Murray; Hallas, Alannah; Cai, Yipeng; Guo, Shengli; Gong, Zizhou; Ali, Mazhar; Cava, Robert; Uemura, Yasutomo; Luke, Graeme

    Noncentrosymmetric superconductors are a topic of considerable interest in the condensed matter physics community. These materials have the potential to exhibit exotic superconducting states, particularly in the presence of strong spin orbit coupling. PbTaSe2 is a noncentrosymmetric material which has very strong spin orbit coupling, and is superconducting with a TC of 3.6 K. Previous studies of this material have identified exotic properties such as Dirac cones gapped by spin-orbit coupling, a topological semi-metal state, and possible multi-band superconductivity. To further explore this material, it is of considerable interest to investigate the pairing symmetry of the superconducting state, and determine whether odd-parity superconductivity may exist. In this talk we will present a μSR investigation of the penetration depth temperature dependece to infer the pairing symmetry. We will also present zero field μSR measurements which suggest that this material has an even-parity superconducting state.

  20. Importance of the van Hove singularity in superconducting PdTe2

    NASA Astrophysics Data System (ADS)

    Kim, Kyoo; Kim, Sooran; Kim, J. S.; Kim, Heejung; Park, J.-H.; Min, B. I.

    2018-04-01

    We have investigated the electronic, phononic, and superconducting properties of the transition-metal dichalcogenide superconductor PdTe2, and explored the origin of different superconducting behaviors between PdTe2 and its isostructural PtTe2 that is nonsuperconducting. We have found that the saddle-point van Hove singularity (vHs) near the Fermi level, which interacts strongly with Te phonon modes, plays an important role in the BCS-type superconductivity of PdTe2. We show that, with electron doping, the vHs in PdTe2 shifts down toward the Fermi level to enhance Tc, as is consistent with the observed enhancement of Tc in Cu-doped PdTe2. We ascribe the absence of superconductivity in PtTe2 to the different dispersion behavior of the saddle-point vHs band from that of PdTe2. We also suggest that this difference in the vHs band behaviors is responsible for the different structural responses of PdTe2 and PtTe2 to external pressure.

  1. Strong temperature effect on the sizes of the Cooper pairs in a two-band superconductor

    NASA Astrophysics Data System (ADS)

    Örd, Teet; Rägo, Küllike; Vargunin, Artjom; Litak, Grzegorz

    2018-01-01

    We study the temperature dependencies of the mean sizes of the Cooper pairs in a two-band BCS-type s-wave superconductivity model with coupling cut-off in the momentum space. It is found that, in contrast to single-band systems, the size of Cooper pairs in the weaker superconductivity band can significantly decrease with a temperature increase due to an interband proximity effect. The relevant spatial behaviour of the wave functions of the Cooper pairs is analyzed. The results also indicate a possibility that the size of Cooper pairs in two-band systems may increase with an increase in temperature.

  2. Simultaneous measurements of L- and S-band tree shadowing for space-Earth communications

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.; Lin, Hsin P.

    1995-01-01

    We present results from simultaneous L- and S-Band slant-path fade measurements through trees. One circularly-polarized antenna was used at each end of the dual-frequency link to provide information on the correlation of tree shadowing at 1620 and 2500 MHz. Fades were measured laterally in the shadow region with 5 cm spacing. Fade differences between L- and S-Band had a normal distribution with low means and standard deviations from 5.2 to 7.5 dB. Spatial variations occurred with periods larger than 1-2 wavelengths. Swept measurements over 160 MHz spans showed that the stdv. of power as function of frequency increased from approximately 1-6 dB at locations with mean fades of 4 and 20 dB, respectively. At a 5 dB fade, the central 90% of fade slopes were within a range of 0.7 (1.9) dB/MHz at L-(S-) Band.

  3. Mitigating reentry radio blackout by using a traveling magnetic field

    NASA Astrophysics Data System (ADS)

    Zhou, Hui; Li, Xiaoping; Xie, Kai; Liu, Yanming; Yu, Yuanyuan

    2017-10-01

    A hypersonic flight or a reentry vehicle is surrounded by a plasma layer that prevents electromagnetic wave transmission, which results in radio blackout. The magnetic-window method is considered a promising means to mitigate reentry communication blackout. However, the real application of this method is limited because of the need for strong magnetic fields. To reduce the required magnetic field strength, a novel method that applies a traveling magnetic field (TMF) is proposed in this study. A mathematical model based on magneto-hydrodynamic theory is adopted to analyze the effect of TMF on plasma. The mitigating effects of the TMF on the blackout of typical frequency bands, including L-, S-, and C-bands, are demonstrated. Results indicate that a significant reduction of plasma density occurs in the magnetic-window region by applying a TMF, and the reduction ratio is positively correlated with the velocity of the TMF. The required traveling velocities for eliminating the blackout of the Global Positioning System (GPS) and the typical telemetry system are also discussed. Compared with the constant magnetic-window method, the TMF method needs lower magnetic field strength and is easier to realize in the engineering field.

  4. Uniaxial strain orientation dependence of superconducting transition temperature (Tc) and critical superconducting pressure (Pc) in β-(BDA-TTP)2I3.

    PubMed

    Kikuchi, Koichi; Isono, Takayuki; Kojima, Masayuki; Yoshimoto, Haruo; Kodama, Takeshi; Fujita, Wataru; Yokogawa, Keiichi; Yoshino, Harukazu; Murata, Keizo; Kaihatsu, Takayuki; Akutsu, Hiroki; Yamada, Jun-ichi

    2011-12-14

    Dependence of the superconducting transition temperature (T(c)) and critial superconducting pressure (P(c)) of the pressure-induced superconductor β-(BDA-TTP)(2)I(3) [BDA-TTP = 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene] on the orientation of uniaxial strain has been investigated. On the basis of the overlap between the upper and lower bands in the energy dispersion curve, the pressure orientation is thought to change the half-filled band to the quarter-filled one. The observed variations in T(c) and P(c) are explained by considering the degree of application of the pressure and the degree of contribution of the effective electronic correlation at uniaxial strains with different orientations parallel to the conducting donor layer. © 2011 American Chemical Society

  5. Unconventional superconductivity and surface pairing symmetry in half-Heusler compounds

    NASA Astrophysics Data System (ADS)

    Wang, Qing-Ze; Yu, Jiabin; Liu, Chao-Xing

    2018-06-01

    Signatures of nodal line/point superconductivity [Kim et al., Sci. Adv. 4, eaao4513 (2018), 10.1126/sciadv.aao4513; Brydon et al., Phys. Rev. Lett. 116, 177001 (2016), 10.1103/PhysRevLett.116.177001] have been observed in half-Heusler compounds, such as LnPtBi (Ln = Y, Lu). Topologically nontrivial band structures, as well as topological surface states, have also been confirmed by angular-resolved photoemission spectroscopy in these compounds [Liu et al., Nat. Commun. 7, 12924 (2016), 10.1038/ncomms12924]. In this paper, we present a systematical classification of possible gap functions of bulk states and surface states in half-Heusler compounds and the corresponding topological properties based on the representations of crystalline symmetry group. Different from all the previous studies based on the four band Luttinger model, our study starts with the six-band Kane model, which involves both four p-orbital type of Γ8 bands and two s-orbital type of Γ6 bands. Although the Γ6 bands are away from the Fermi energy, our results reveal the importance of topological surface states, which originate from the band inversion between Γ6 and Γ8 bands, in determining surface properties of these compounds in the superconducting regime by combining topological bulk state picture and nontrivial surface state picture.

  6. Multipole Superconductivity in Nonsymmorphic Sr2IrO4

    NASA Astrophysics Data System (ADS)

    Sumita, Shuntaro; Nomoto, Takuya; Yanase, Youichi

    2017-07-01

    Discoveries of marked similarities to high-Tc cuprate superconductors point to the realization of superconductivity in the doped Jeff=1 /2 Mott insulator Sr2IrO4. Contrary to the mother compound of cuprate superconductors, several stacking patterns of in-plane canted antiferromagnetic moments have been reported, which are distinguished by the ferromagnetic components as -++-, ++++, and -+-+ . In this paper, we clarify unconventional features of the superconductivity coexisting with -++- and -+-+ structures. Combining the group theoretical analysis and numerical calculations for an effective Jeff=1 /2 model, we show unusual superconducting gap structures in the -++- state protected by nonsymmorphic magnetic space group symmetry. Furthermore, our calculation shows that the Fulde-Ferrell-Larkin-Ovchinnikov superconductivity is inevitably stabilized in the -+-+ state since the odd-parity magnetic -+-+ order makes the band structure asymmetric by cooperating with spin-orbit coupling. These unusual superconducting properties are signatures of magnetic multipole order in nonsymmorphic crystal.

  7. Effective Tree Scattering and Opacity at L-Band

    NASA Technical Reports Server (NTRS)

    Kurum, Mehmet; O'Neill, Peggy E.; Lang, Roger H.; Joseph, Alicia T.; Cosh, Michael H.; Jackson, Thomas J.

    2011-01-01

    This paper investigates vegetation effects at L-band by using a first-order radiative transfer (RT) model and truck-based microwave measurements over natural conifer stands to assess the applicability of the tau-omega) model over trees. The tau-omega model is a zero-order RT solution that accounts for vegetation effects with effective vegetation parameters (vegetation opacity and single-scattering albedo), which represent the canopy as a whole. This approach inherently ignores multiple-scattering effects and, therefore, has a limited validity depending on the level of scattering within the canopy. The fact that the scattering from large forest components such as branches and trunks is significant at L-band requires that zero-order vegetation parameters be evaluated (compared) along with their theoretical definitions to provide a better understanding of these parameters in the retrieval algorithms as applied to trees. This paper compares the effective vegetation opacities, computed from multi-angular pine tree brightness temperature data, against the results of two independent approaches that provide theoretical and measured optical depths. These two techniques are based on forward scattering theory and radar corner reflector measurements, respectively. The results indicate that the effective vegetation opacity values are smaller than but of similar magnitude to both radar and theoretical estimates. The effective opacity of the zero-order model is thus set equal to the theoretical opacity and an explicit expression for the effective albedo is then obtained from the zero- and first- order RT model comparison. The resultant albedo is found to have a similar magnitude as the effective albedo value obtained from brightness temperature measurements. However, it is less than half of that estimated using the theoretical calculations (0.5 - 0.6 for tree canopies at L-band). This lower observed albedo balances the scattering darkening effect of the large theoretical albedo

  8. In-harbor and at-sea electromagnetic compatibility survey for maritime satellite L-band shipboard terminal

    NASA Technical Reports Server (NTRS)

    1974-01-01

    Geostationary maritime satellites, one over the Pacific and one over the Atlantic Ocean, are planned to make available high-speed communications and navigation (position determination) services to ships at sea. A shipboard satellite terminal, operating within the authorized maritime L-band, 1636.5 to 1645.0 MHz, will allow ships to pass voice, teletype, facsimile, and data messages to shore communication facilities with a high degree of reliability. The shore-to-ship link will also operate in the maritime L-band from 1535.0 to 1543.5 MHz. A significant number or maritime/commercial ships are expected to be equipped with an L-band satellite terminal by the year 1980, and so consequently, there is an interest in determining electromagnetic compatibility between the proposed L-band shipboard terminal and existing, on-board, shipboard communications/electronics and electrical systems, as well as determining the influence of shore-based interference sources. The shipboard electromagnetic interference survey described was conducted on-board the United States Line's American Leader class (15,690 tons) commercial container ship, the "American Alliance" from June 16 to 20, 1974. Details of the test plan and measurements are given.

  9. ATS-5 ranging receiver and L-band experiment. Volume 2: Data reduction and analysis

    NASA Technical Reports Server (NTRS)

    1971-01-01

    The results of ranging and position location experiments performed at the NASA Application Technology Satellite ground station at Mojave California are presented. The experiments are simultaneous C-band and L-band ranging to ATS-5, simultaneous C-band and VHF ranging, simultaneous 24-hour ranging and position location using ATS-1, ATS-3, and ATS-5. The data handling and processing technique is also described.

  10. Superconductivity Series in Transition Metal Dichalcogenides by Ionic Gating

    PubMed Central

    Shi, Wu; Ye, Jianting; Zhang, Yijin; Suzuki, Ryuji; Yoshida, Masaro; Miyazaki, Jun; Inoue, Naoko; Saito, Yu; Iwasa, Yoshihiro

    2015-01-01

    Functionalities of two-dimensional (2D) crystals based on semiconducting transition metal dichalcogenides (TMDs) have now stemmed from simple field effect transistors (FETs) to a variety of electronic and opto-valleytronic devices, and even to superconductivity. Among them, superconductivity is the least studied property in TMDs due to methodological difficulty accessing it in different TMD species. Here, we report the systematic study of superconductivity in MoSe2, MoTe2 and WS2 by ionic gating in different regimes. Electrostatic gating using ionic liquid was able to induce superconductivity in MoSe2 but not in MoTe2 because of inefficient electron accumulation limited by electronic band alignment. Alternative gating using KClO4/polyethylene glycol enabled a crossover from surface doping to bulk doping, which induced superconductivities in MoTe2 and WS2 electrochemically. These new varieties greatly enriched the TMD superconductor families and unveiled critical methodology to expand the capability of ionic gating to other materials. PMID:26235962

  11. Superconductivity Series in Transition Metal Dichalcogenides by Ionic Gating.

    PubMed

    Shi, Wu; Ye, Jianting; Zhang, Yijin; Suzuki, Ryuji; Yoshida, Masaro; Miyazaki, Jun; Inoue, Naoko; Saito, Yu; Iwasa, Yoshihiro

    2015-08-03

    Functionalities of two-dimensional (2D) crystals based on semiconducting transition metal dichalcogenides (TMDs) have now stemmed from simple field effect transistors (FETs) to a variety of electronic and opto-valleytronic devices, and even to superconductivity. Among them, superconductivity is the least studied property in TMDs due to methodological difficulty accessing it in different TMD species. Here, we report the systematic study of superconductivity in MoSe2, MoTe2 and WS2 by ionic gating in different regimes. Electrostatic gating using ionic liquid was able to induce superconductivity in MoSe2 but not in MoTe2 because of inefficient electron accumulation limited by electronic band alignment. Alternative gating using KClO4/polyethylene glycol enabled a crossover from surface doping to bulk doping, which induced superconductivities in MoTe2 and WS2 electrochemically. These new varieties greatly enriched the TMD superconductor families and unveiled critical methodology to expand the capability of ionic gating to other materials.

  12. Multipole Superconductivity in Nonsymmorphic Sr_{2}IrO_{4}.

    PubMed

    Sumita, Shuntaro; Nomoto, Takuya; Yanase, Youichi

    2017-07-14

    Discoveries of marked similarities to high-T_{c} cuprate superconductors point to the realization of superconductivity in the doped J_{eff}=1/2 Mott insulator Sr_{2}IrO_{4}. Contrary to the mother compound of cuprate superconductors, several stacking patterns of in-plane canted antiferromagnetic moments have been reported, which are distinguished by the ferromagnetic components as -++-, ++++, and -+-+. In this paper, we clarify unconventional features of the superconductivity coexisting with -++- and -+-+ structures. Combining the group theoretical analysis and numerical calculations for an effective J_{eff}=1/2 model, we show unusual superconducting gap structures in the -++- state protected by nonsymmorphic magnetic space group symmetry. Furthermore, our calculation shows that the Fulde-Ferrell-Larkin-Ovchinnikov superconductivity is inevitably stabilized in the -+-+ state since the odd-parity magnetic -+-+ order makes the band structure asymmetric by cooperating with spin-orbit coupling. These unusual superconducting properties are signatures of magnetic multipole order in nonsymmorphic crystal.

  13. Soil Moisture Active/Passive (SMAP) L-band microwave radiometer post-launch calibration

    USDA-ARS?s Scientific Manuscript database

    The SMAP microwave radiometer is a fully-polarimetric L-band radiometer flown on the SMAP satellite in a 6 AM / 6 PM sun-synchronous orbit at 685-km altitude. Since April 2015, the radiometer has been under calibration and validation to assess the quality of the radiometer L1B data product. Calibrat...

  14. Hybrid quantum systems: Outsourcing superconducting qubits

    NASA Astrophysics Data System (ADS)

    Cleland, Andrew

    Superconducting qubits offer excellent prospects for manipulating quantum information, with good qubit lifetimes, high fidelity single- and two-qubit gates, and straightforward scalability (admittedly with multi-dimensional interconnect challenges). One interesting route for experimental development is the exploration of hybrid systems, i.e. coupling superconducting qubits to other systems. I will report on our group's efforts to develop approaches that will allow interfacing superconducting qubits in a quantum-coherent fashion to spin defects in solids, to optomechanical devices, and to resonant nanomechanical structures. The longer term goals of these efforts include transferring quantum states between different qubit systems; generating and receiving ``flying'' acoustic phonon-based as well as optical photon-based qubits; and ultimately developing systems that can be used for quantum memory, quantum computation and quantum communication, the last in both the microwave and fiber telecommunications bands. Work is supported by Grants from AFOSR, ARO, DOE and NSF.

  15. Conventional superconductivity in the type-II Dirac semimetal PdTe2

    NASA Astrophysics Data System (ADS)

    Das, Shekhar; Amit, Sirohi, Anshu; Yadav, Lalit; Gayen, Sirshendu; Singh, Yogesh; Sheet, Goutam

    2018-01-01

    The transition metal dichalcogenide PdTe2 was recently shown to be a unique system where a type-II Dirac semimetallic phase and a superconducting phase coexist. This observation has led to wide speculation on the possibility of the emergence of an unconventional topological superconducting phase in PdTe2. Here, through direct measurement of the superconducting energy gap by scanning tunneling spectroscopy, and temperature and magnetic-field evolution of same, we show that the superconducting phase in PdTe2 is conventional in nature. The superconducting energy gap is measured to be 326 μ eV at 0.38 K, and it follows a temperature dependence that is well described within the framework of Bardeen-Cooper-Schrieffer's theory of conventional superconductivity. This is surprising because our quantum oscillation measurements confirm that at least one of the bands participating in transport has topologically nontrivial character.

  16. Imprinting superconducting vortex footsteps in a magnetic layer

    PubMed Central

    Brisbois, Jérémy; Motta, Maycon; Avila, Jonathan I.; Shaw, Gorky; Devillers, Thibaut; Dempsey, Nora M.; Veerapandian, Savita K. P.; Colson, Pierre; Vanderheyden, Benoît; Vanderbemden, Philippe; Ortiz, Wilson A.; Nguyen, Ngoc Duy; Kramer, Roman B. G.; Silhanek, Alejandro V.

    2016-01-01

    Local polarization of a magnetic layer, a well-known method for storing information, has found its place in numerous applications such as the popular magnetic drawing board toy or the widespread credit cards and computer hard drives. Here we experimentally show that a similar principle can be applied for imprinting the trajectory of quantum units of flux (vortices), travelling in a superconducting film (Nb), into a soft magnetic layer of permalloy (Py). In full analogy with the magnetic drawing board, vortices act as tiny magnetic scribers leaving a wake of polarized magnetic media in the Py board. The mutual interaction between superconducting vortices and ferromagnetic domains has been investigated by the magneto-optical imaging technique. For thick Py layers, the stripe magnetic domain pattern guides both the smooth magnetic flux penetration as well as the abrupt vortex avalanches in the Nb film. It is however in thin Py layers without stripe domains where superconducting vortices leave the clearest imprints of locally polarized magnetic moment along their paths. In all cases, we observe that the flux is delayed at the border of the magnetic layer. Our findings open the quest for optimizing magnetic recording of superconducting vortex trajectories. PMID:27263660

  17. Imprinting superconducting vortex footsteps in a magnetic layer

    NASA Astrophysics Data System (ADS)

    Brisbois, Jérémy; Motta, Maycon; Avila, Jonathan I.; Shaw, Gorky; Devillers, Thibaut; Dempsey, Nora M.; Veerapandian, Savita K. P.; Colson, Pierre; Vanderheyden, Benoît; Vanderbemden, Philippe; Ortiz, Wilson A.; Nguyen, Ngoc Duy; Kramer, Roman B. G.; Silhanek, Alejandro V.

    2016-06-01

    Local polarization of a magnetic layer, a well-known method for storing information, has found its place in numerous applications such as the popular magnetic drawing board toy or the widespread credit cards and computer hard drives. Here we experimentally show that a similar principle can be applied for imprinting the trajectory of quantum units of flux (vortices), travelling in a superconducting film (Nb), into a soft magnetic layer of permalloy (Py). In full analogy with the magnetic drawing board, vortices act as tiny magnetic scribers leaving a wake of polarized magnetic media in the Py board. The mutual interaction between superconducting vortices and ferromagnetic domains has been investigated by the magneto-optical imaging technique. For thick Py layers, the stripe magnetic domain pattern guides both the smooth magnetic flux penetration as well as the abrupt vortex avalanches in the Nb film. It is however in thin Py layers without stripe domains where superconducting vortices leave the clearest imprints of locally polarized magnetic moment along their paths. In all cases, we observe that the flux is delayed at the border of the magnetic layer. Our findings open the quest for optimizing magnetic recording of superconducting vortex trajectories.

  18. Superconductivity in Potassium-Doped Metallic Polymorphs of MoS2.

    PubMed

    Zhang, Renyan; Tsai, I-Ling; Chapman, James; Khestanova, Ekaterina; Waters, John; Grigorieva, Irina V

    2016-01-13

    Superconducting layered transition metal dichalcogenides (TMDs) stand out among other superconductors due to the tunable nature of the superconducting transition, coexistence with other collective electronic excitations (charge density waves), and strong intrinsic spin-orbit coupling. Molybdenum disulfide (MoS2) is the most studied representative of this family of materials, especially since the recent demonstration of the possibility to tune its critical temperature, Tc, by electric-field doping. However, just one of its polymorphs, band-insulator 2H-MoS2, has so far been explored for its potential to host superconductivity. We have investigated the possibility to induce superconductivity in metallic polytypes, 1T- and 1T'-MoS2, by potassium (K) intercalation. We demonstrate that at doping levels significantly higher than that required to induce superconductivity in 2H-MoS2, both 1T and 1T' phases become superconducting with Tc = 2.8 and 4.6 K, respectively. Unusually, K intercalation in this case is responsible both for the structural and superconducting phase transitions. By adding new members to the family of superconducting TMDs, our findings open the way to further manipulate and enhance the electronic properties of these technologically important materials.

  19. Study on W-band sheet-beam traveling-wave tube based on flat-roofed sine waveguide

    NASA Astrophysics Data System (ADS)

    Fang, Shuanzhu; Xu, Jin; Jiang, Xuebing; Lei, Xia; Wu, Gangxiong; Li, Qian; Ding, Chong; Yu, Xiang; Wang, Wenxiang; Gong, Yubin; Wei, Yanyu

    2018-05-01

    A W-band sheet electron beam (SEB) traveling-wave tube (TWT) based on flat-roofed sine waveguide slow-wave structure (FRSWG-SWS) is proposed. The sine wave of the metal grating is replaced by a flat-roofed sine wave around the electron beam tunnel. The slow-wave characteristics including the dispersion properties and interaction impedance have been investigated by using the eigenmode solver in the 3-D electromagnetic simulation software Ansoft HFSS. Through calculations, the FRSWG SWS possesses the larger average interaction impedance than the conventional sine waveguide (SWG) SWS in the frequency range of 86-110 GHz. The beam-wave interaction was studied and particle-in-cell simulation results show that the SEB TWT can produce output power over 120 W within the bandwidth ranging from 90 to 100 GHz, and the maximum output power is 226 W at typical frequency 94 GHz, corresponding electron efficiency of 5.89%.

  20. Coexistence of superconductivity and ferromagnetism in two dimensions.

    PubMed

    Dikin, D A; Mehta, M; Bark, C W; Folkman, C M; Eom, C B; Chandrasekhar, V

    2011-07-29

    Ferromagnetism is usually considered to be incompatible with conventional superconductivity, as it destroys the singlet correlations responsible for the pairing interaction. Superconductivity and ferromagnetism are known to coexist in only a few bulk rare-earth materials. Here we report evidence for their coexistence in a two-dimensional system: the interface between two bulk insulators, LaAlO(3) (LAO) and SrTiO(3) (STO), a system that has been studied intensively recently. Magnetoresistance, Hall, and electric-field dependence measurements suggest that there are two distinct bands of charge carriers that contribute to the interface conductivity. The sensitivity of properties of the interface to an electric field makes this a fascinating system for the study of the interplay between superconductivity and magnetism. © 2011 American Physical Society

  1. Quantum Device Applications of Mesoscopic Superconductivity

    NASA Astrophysics Data System (ADS)

    Hakonen, P. J.

    2006-08-01

    A brief account is given on the possibilities of mesoscopic superconductivity in low-noise amplifier and detector applications. In particular, three devices will be described: 1) Bloch oscillating transistor (BOT), 2) Inductively-read superconducting Cooper pair transistor (L-SET), and 3) Quantum capacitive phase detector (C-SET). The BOT is a low-noise current amplifier while the L-SET and C-SET act as ultra-sensitive charge and phase detectors, respectively. The basic operating principles and the main characteristics of these devices will be reviewed and discussed.

  2. Use of ground-based radiometers for L-Band Freeze/Thaw retrieval in a boreal forest site

    NASA Astrophysics Data System (ADS)

    Roy, A.; Sonnentag, O.; Derksen, C.; Toose, P.; Pappas, C.; Mavrovic, A.; El Amine, M.; Royer, A.; Berg, A. A.; Rowlandson, T. L.; Barr, A.; Black, T. A.

    2017-12-01

    The boreal forest is the second largest land biome in the world and thus plays a major role in the global and regional climate systems. The extent, timing and duration of the seasonal freeze/thaw (F/T) state influences vegetation developmental stages (phenology) and, consequently, constitutes an important control on how boreal forest ecosystems exchange carbon, water and energy with the atmosphere. Recently, new L-Band satellite-derived F/T information has become available. However, disentangling the seasonally differing contributions from forest overstory and understory vegetation, and the ground surface to the satellite signal remains challenging. Here we present results from an ongoing campaign with two L-Band surface-based radiometers (SBR) installed on a micrometeorological tower at the Southern Old Black Spruce site (53.99°N / 105.12°W) in central Saskatchewan. One radiometer unit is installed on top of the tower viewing the multi-layer vegetation canopy from above. A second radiometer unit is installed within the multi-layer canopy, viewing the understory and the ground surface only. The objectives of our study are to (i) disentangle the L-Band F/T signal contribution of boreal forest overstory from the combined understory and ground surface contribution, and (ii) link the L-Band F/T signal to related boreal forest structural and functional characteristics. Analysis of these radiometer measurements made from September to November 2016 shows that when the ground surface is thawed, the main contributor to both radiometer signals is soil moisture. The Pearson correlation coefficient between brightness temperature (TB) at vertical polarization (V-pol) and soil permittivity is 0.79 for the radiometer above the canopy and 0.74 for the radiometer below the canopy. Under cold conditions when the soil was thawed (snow insulation) and the trees were frozen (below 0°C), TB at V-pol is negatively correlated with tree permittivity. The freezing tree contribution to

  3. Phonon-mediated high-T c superconductivity in hole-doped diamond-like crystalline hydrocarbon

    DOE PAGES

    Lian, Chao-Sheng; Wang, Jian-Tao; Duan, Wenhui; ...

    2017-05-03

    We here predict by ab initio calculations phonon-mediated high-T c superconductivity in hole-doped diamond-like cubic crystalline hydrocarbon K 4-CH (space group I2 1/3). This material possesses three key properties: (i) an all-sp 3 covalent carbon framework that produces high-frequency phonon modes, (ii) a steep-rising electronic density of states near the top of the valence band, and (iii) a Fermi level that lies in the σ-band, allowing for a strong coupling with the C-C bond-stretching modes. The simultaneous presence of these properties generates remarkably high superconducting transition temperatures above 80 K at an experimentally accessible hole doping level of only amore » few percent. These results identify a new extraordinary electron-phonon superconductor and pave the way for further exploration of this novel superconducting covalent metal.« less

  4. Omni-directional L-band antenna for mobile communications

    NASA Technical Reports Server (NTRS)

    Kim, C. S.; Moldovan, N.; Kijesky, J.

    1988-01-01

    The principle and design of an L-band omni-directional mobile communication antenna are discussed. The antenna is a circular wave guide aperture with hybrid circuits attached to higher order mode excitation. It produces polarized and symmetric two split beams in elevation. The circular waveguide is fed by eight probes with a 90 degree phase shift between their inputs. Radiation pattern characteristics are controlled by adjusting the aperture diameter and mode excitation. This antenna satisfies gain requirements as well as withstanding the harsh environment.

  5. L-band ultrafast fiber laser mode locked by carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Sun, Z.; Rozhin, A. G.; Wang, F.; Scardaci, V.; Milne, W. I.; White, I. H.; Hennrich, F.; Ferrari, A. C.

    2008-08-01

    We fabricate a nanotube-polyvinyl alcohol saturable absorber with a broad absorption at 1.6 μm. We demonstrate a pulsed fiber laser working in the telecommunication L band by using this composite as a mode locker. This gives ˜498±16 fs pulses at 1601 nm with a 26.7 MHz repetition rate.

  6. Wide applicability of high-Tc pairing originating from coexisting wide and incipient narrow bands in quasi-one-dimensional systems

    NASA Astrophysics Data System (ADS)

    Matsumoto, Karin; Ogura, Daisuke; Kuroki, Kazuhiko

    2018-01-01

    We study superconductivity in the Hubbard model on various quasi-one-dimensional lattices with coexisting wide and narrow bands originating from multiple sites within a unit cell, where each site corresponds to a single orbital. The systems studied are the two-leg and three-leg ladders, the diamond chain, and the crisscross ladder. These one-dimensional lattices are weakly coupled to form two-dimensional (quasi-one-dimensional) ones, and the fluctuation exchange approximation is adopted to study spin-fluctuation-mediated superconductivity. When one of the bands is perfectly flat and the Fermi level intersecting the wide band is placed in the vicinity of, but not within, the flat band, superconductivity arising from the interband scattering processes is found to be strongly enhanced owing to the combination of the light electron mass of the wide band and the strong pairing interaction due to the large density of states of the flat band. Even when the narrow band has finite bandwidth, the pairing mechanism still works since the edge of the narrow band, due to its large density of states, plays the role of the flat band. The results indicate the wide applicability of the high-Tc pairing mechanism due to coexisting wide and "incipient" narrow bands in quasi-one-dimensional systems.

  7. Impact of the ionosphere on an L-band space based radar

    NASA Technical Reports Server (NTRS)

    Chapin, Elaine; Chan, Samuel F.; Chapman, Bruce D.; Chen, Curtis W.; Martin, Jan M.; Michel, Thierry R.; Muellerschoen, Ronald J.; Pi, Xiaoqing; Rosen, Paul A.

    2006-01-01

    We have quantified the impact that the ionosphere would have on a L-band interferometric Synthetic Aperture Radar (SAR) mission using a combination of simulation, modeling, Global Positioning System (GPS) data collected during the last solar maximum, and existing spaceborne SAR data.

  8. Superconductivity in epitaxially grown self-assembled indium islands: progress towards hybrid superconductor/semiconductor optical sources

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gehl, Michael; Gibson, Ricky; Zandbergen, Sander

    Currently, superconducting qubits lead the way in potential candidates for quantum computing. This is a result of the robust nature of superconductivity and the non-linear Josephson effect which make possible many types of qubits. At the same time, transferring quantum information over long distances typically relies on the use of photons as the elementary qubit. Converting between stationary electronic qubits in superconducting systems and traveling photonic qubits is a challenging yet necessary goal for the interface of quantum computing and communication. The most promising path to achieving this goal appears to be the integration of superconductivity with optically active semiconductors,more » with quantum information being transferred between the two by means of the superconducting proximity effect. Obtaining good interfaces between superconductor and semiconductor is the next obvious step for improving these hybrid systems. As a result, we report on our observation of superconductivity in self-assembled indium structures grown epitaxially on the surface of semiconductor material.« less

  9. Superconductivity in epitaxially grown self-assembled indium islands: progress towards hybrid superconductor/semiconductor optical sources

    DOE PAGES

    Gehl, Michael; Gibson, Ricky; Zandbergen, Sander; ...

    2016-02-01

    Currently, superconducting qubits lead the way in potential candidates for quantum computing. This is a result of the robust nature of superconductivity and the non-linear Josephson effect which make possible many types of qubits. At the same time, transferring quantum information over long distances typically relies on the use of photons as the elementary qubit. Converting between stationary electronic qubits in superconducting systems and traveling photonic qubits is a challenging yet necessary goal for the interface of quantum computing and communication. The most promising path to achieving this goal appears to be the integration of superconductivity with optically active semiconductors,more » with quantum information being transferred between the two by means of the superconducting proximity effect. Obtaining good interfaces between superconductor and semiconductor is the next obvious step for improving these hybrid systems. As a result, we report on our observation of superconductivity in self-assembled indium structures grown epitaxially on the surface of semiconductor material.« less

  10. PREFACE: Superconductivity in ultrathin films and nanoscale systems Superconductivity in ultrathin films and nanoscale systems

    NASA Astrophysics Data System (ADS)

    Bianconi, Antonio; Bose, Sangita; Garcia-Garcia, Antonio Miguel

    2012-12-01

    The recent technological developments in the synthesis and characterization of high-quality nanostructures and developments in the theoretical techniques needed to model these materials, have motivated this focus section of Superconductor Science and Technology. Another motivation is the compelling evidence that all new superconducting materials, such as iron pnictides and chalcogenides, diborides (doped MgB2) and fullerides (alkali-doped C60 compounds), are heterostrucures at the atomic limit, such as the cuprates made of stacks of nanoscale superconducting layers intercalated by different atomic layers with nanoscale periodicity. Recently a great amount of interest has been shown in the role of lattice nano-architecture in controlling the fine details of Fermi surface topology. The experimental and theoretical study of superconductivity in the nanoscale started in the early 1960s, shortly after the discovery of the BCS theory. Thereafter there has been rapid progress both in experiments and the theoretical understanding of nanoscale superconductors. Experimentally, thin films, granular films, nanowires, nanotubes and single nanoparticles have all been explored. New quantum effects appear in the nanoscale related to multi-component condensates. Advances in the understanding of shape resonances or Fano resonances close to 2.5 Lifshitz transitions near a band edge in nanowires, 2D films and superlattices [1, 2] of these nanosized modules, provide the possibility of manipulating new quantum electronic states. Parity effects and shell effects in single, isolated nanoparticles have been reported by several groups. Theoretically, newer techniques based on solving Richardson's equation (an exact theory incorporating finite size effects to the BCS theory) numerically by path integral methods or solving the entire Bogoliubov-de Gennes equation in these limits have been attempted, which has improved our understanding of the mechanism of superconductivity in these confined

  11. Ka-band to L-band frequency down-conversion based on III-V-on-silicon photonic integrated circuits

    NASA Astrophysics Data System (ADS)

    Van Gasse, K.; Wang, Z.; Uvin, S.; De Deckere, B.; Mariën, J.; Thomassen, L.; Roelkens, G.

    2017-12-01

    In this work, we present the design, simulation and characterization of a frequency down-converter based on III-V-on-silicon photonic integrated circuit technology. We first demonstrate the concept using commercial discrete components, after which we demonstrate frequency conversion using an integrated mode-locked laser and integrated modulator. In our experiments, five channels in the Ka-band (27.5-30 GHz) with 500 MHz bandwidth are down-converted to the L-band (1.5 GHz). The breadboard demonstration shows a conversion efficiency of - 20 dB and a flat response over the 500 MHz bandwidth. The simulation of a fully integrated circuit indicates that a positive conversion gain can be obtained on a millimeter-sized photonic integrated circuit.

  12. Novel high-gain, improved-bandwidth, finned-ladder V-band Traveling-Wave Tube slow-wave circuit design

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.; Wilson, Jeffrey D.

    1994-01-01

    The V-band frequency range of 59-64 GHz is a region of the millimeter-wave spectrum that has been designated for inter-satellite communications. As a first effort to develop a high-efficiency V-band Traveling-Wave Tube (TWT), variations on a ring-plane slow-wave circuit were computationally investigated to develop an alternative to the more conventional ferruled coupled-cavity circuit. The ring-plane circuit was chosen because of its high interaction impedance, large beam aperture, and excellent thermal dissipation properties. Despite these advantages, however, low bandwidth and high voltage requirements have, until now, prevented its acceptance outside the laboratory. In this paper, the three-dimensional electrodynamic simulation code MAFIA (solution of MAxwell's Equation by the Finite-Integration-Algorithm) is used to investigate methods of increasing the bandwidth and lowering the operating voltage of the ring-plane circuit. Calculations of frequency-phase dispersion, beam on-axis interaction impedance, attenuation and small-signal gain per wavelength were performed for various geometric variations and loading distributions of the ring-plane TWT slow-wave circuit. Based on the results of the variations, a circuit termed the finned-ladder TWT slow-wave circuit was designed and is compared here to the scaled prototype ring-plane and a conventional ferruled coupled-cavity TWT circuit over the V-band frequency range. The simulation results indicate that this circuit has a much higher gain, significantly wider bandwidth, and a much lower voltage requirement than the scaled ring-plane prototype circuit, while retaining its excellent thermal dissipation properties. The finned-ladder circuit has a much larger small-signal gain per wavelength than the ferruled coupled-cavity circuit, but with a moderate sacrifice in bandwidth.

  13. High Efficiency Traveling-Wave Tube Power Amplifier for Ka-Band Software Defined Radio on International Space Station-A Platform for Communications Technology Development

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Force, Dale A.; Kacpura, Thomas J.

    2013-01-01

    The design, fabrication and RF performance of the output traveling-wave tube amplifier (TWTA) for a space based Ka-band software defined radio (SDR) is presented. The TWTA, the SDR and the supporting avionics are integrated to forms a testbed, which is currently located on an exterior truss of the International Space Station (ISS). The SDR in the testbed communicates at Ka-band frequencies through a high-gain antenna directed to NASA s Tracking and Data Relay Satellite System (TDRSS), which communicates to the ground station located at White Sands Complex. The application of the testbed is for demonstrating new waveforms and software designed to enhance data delivery from scientific spacecraft and, the waveforms and software can be upgraded and reconfigured from the ground. The construction and the salient features of the Ka-band SDR are discussed. The testbed is currently undergoing on-orbit checkout and commissioning and is expected to operate for 3 to 5 years in space.

  14. Method for obtaining large levitation pressure in superconducting magnetic bearings

    DOEpatents

    Hull, John R.

    1997-01-01

    A method and apparatus for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap.

  15. Method for obtaining large levitation pressure in superconducting magnetic bearings

    DOEpatents

    Hull, John R.

    1996-01-01

    A method and apparatus for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap.

  16. Electride and superconductivity behaviors in Mn5Si3-type intermetallics

    NASA Astrophysics Data System (ADS)

    Zhang, Yaoqing; Wang, Bosen; Xiao, Zewen; Lu, Yangfan; Kamiya, Toshio; Uwatoko, Yoshiya; Kageyama, Hiroshi; Hosono, Hideo

    2017-08-01

    Electrides are unique in the sense that they contain localized anionic electrons in the interstitial regions. Yet they exist with a diversity of chemical compositions, especially under extreme conditions, implying generalized underlying principles for their existence. What is rarely observed is the combination of electride state and superconductivity within the same material, but such behavior would open up a new category of superconductors. Here, we report a hexagonal Nb5Ir3 phase of Mn5Si3-type structure that falls into this category and extends the electride concept into intermetallics. The confined electrons in the one-dimensional cavities are reflected by the characteristic channel bands in the electronic structure. Filling these free spaces with foreign oxygen atoms serves to engineer the band topology and increase the superconducting transition temperature to 10.5 K in Nb5Ir3O. Specific heat analysis indicates the appearance of low-lying phonons and two-gap s-wave superconductivity. Strong electron-phonon coupling is revealed to be the pairing glue with an anomalously large ratio between the superconducting gap Δ0 and Tc, 2Δ0/kBTc = 6.12. The general rule governing the formation of electrides concerns the structural stability against the cation filling/extraction in the channel site.

  17. Light-Induced Type-II Band Inversion and Quantum Anomalous Hall State in Monolayer FeSe

    NASA Astrophysics Data System (ADS)

    Wang, Z. F.; Liu, Zhao; Yang, Jinlong; Liu, Feng

    2018-04-01

    Coupling a quantum anomalous Hall (QAH) state with a superconducting state offers an attractive approach to detect the signature alluding to a topological superconducting state [Q. L. He et al., Science 357, 294 (2017), 10.1126/science.aag2792], but its explanation could be clouded by disorder effects in magnetic doped QAH materials. On the other hand, an antiferromagnetic (AFM) quantum spin Hall (QSH) state is identified in the well-known high-temperature 2D superconductor of monolayer FeSe [Z. F. Wang et al., Nat. Mater. 15, 968 (2016), 10.1038/nmat4686]. Here, we report a light-induced type-II band inversion (BI) and a QSH-to-QAH phase transition in the monolayer FeSe. Depending on the handedness of light, a spin-tunable QAH state with a high Chern number of ±2 is realized. In contrast to the conventional type-I BI resulting from intrinsic spin-orbital coupling (SOC), which inverts the band an odd number of times and respects time reversal symmetry, the type-II BI results from a light-induced handedness-dependent effective SOC, which inverts the band an even number of times and does not respect time reversal symmetry. The interplay between these two SOC terms makes the spin-up and -down bands of an AFM QSH state respond oppositely to a circularly polarized light, leading to the type-II BI and an exotic topological phase transition. Our finding affords an exciting opportunity to detect Majorana fermions in one single material without magnetic doping.

  18. Polarimetric and Structural Properties of a Boreal Forest at P-Band and L-Band

    NASA Astrophysics Data System (ADS)

    Tebaldini, S.; Rocca, F.

    2010-12-01

    With this paper we investigate the structural and polarimetric of the boreal forest within the Krycklan river catchment, Northern Sweden, basing on multi-polarimetric and multi-baseline SAR surveys at P-Band and L-Band collected in the framework of the ESA campaign BioSAR 2008. The analysis has been carried out by applying the Algebraic Synthesis (AS) technique, recently introduced in literature, which provides a theoretical framework for the decomposition of the backscattered signal into ground-only and volume-only contributions, basing on both baseline and polarization diversity. The availability of multiple baselines allows the formation of a synthetic aperture not only along the azimuth direction but also in elevation. Accordingly, the backscattered echoes can be focused not only in the slant range, azimuth plane, but in the whole 3D space. This is the rationale of the SAR Tomography (T-SAR) concept, which has been widely considered in the literature of the last years. It follows that, as long as the penetration in the scattering volume is guaranteed, the vertical profile of the vegetation layer is retrieved by separating backscatter contributions along the vertical direction, which is the main reason for the exploitation of Tomographic techniques at longer wavelengths. Still, the capabilities of T-SAR are limited to imaging the global vertical structure of the electromagnetic scattering in a certain polarization. It then becomes important to develop methodologies for the investigation of the vertical structure of different Scattering Mechanisms (SMs), such as ground and volume scattering, in such a way as to derive information that can be delivered also outside the field of Radar processing. This is an issue that may become relevant at longer wavelengths, such as P-Band, where the presence of multiple scattering arising from the interaction with terrain could hinder the correct reconstruction of the forest structure. The availability of multiple polarizations

  19. Broadening of effective photonic band gaps in biological chiral structures: From intrinsic narrow band gaps to broad band reflection spectra

    NASA Astrophysics Data System (ADS)

    Vargas, W. E.; Hernández-Jiménez, M.; Libby, E.; Azofeifa, D. E.; Solis, Á.; Barboza-Aguilar, C.

    2015-09-01

    Under normal illumination with non-polarized light, reflection spectra of the cuticle of golden-like and red Chrysina aurigans scarabs show a structured broad band of left-handed circularly polarized light. The polarization of the reflected light is attributed to a Bouligand-type left-handed chiral structure found through the scarab's cuticle. By considering these twisted structures as one-dimensional photonic crystals, a novel approach is developed from the dispersion relation of circularly polarized electromagnetic waves traveling through chiral media, to show how the broad band characterizing these spectra arises from an intrinsic narrow photonic band gap whose spectral position moves through visible and near-infrared wavelengths.

  20. On-chip integration of a superconducting microwave circulator and a Josephson parametric amplifier

    NASA Astrophysics Data System (ADS)

    Rosenthal, Eric I.; Chapman, Benjamin J.; Moores, Bradley A.; Kerckhoff, Joseph; Malnou, Maxime; Palken, D. A.; Mates, J. A. B.; Hilton, G. C.; Vale, L. R.; Ullom, J. N.; Lehnert, K. W.

    Recent progress in microwave amplification based on parametric processes in superconducting circuits has revolutionized the measurement of feeble microwave signals. These devices, which operate near the quantum limit, are routinely used in ultralow temperature cryostats to: readout superconducting qubits, search for axionic dark matter, and characterize astrophysical sensors. However, these amplifiers often require ferrite circulators to separate incoming and outgoing traveling waves. For this reason, measurement efficiency and scalability are limited. In order to facilitate the routing of quantum signals we have created a superconducting, on-chip microwave circulator without permanent magnets. We integrate our circulator on-chip with a Josephson parametric amplifier for the purpose of near quantum-limited directional amplification. In this talk I will present a design overview and preliminary measurements.

  1. High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides.

    PubMed

    Charnukha, A; Evtushinsky, D V; Matt, C E; Xu, N; Shi, M; Büchner, B; Zhigadlo, N D; Batlogg, B; Borisenko, S V

    2015-12-18

    In the family of the iron-based superconductors, the REFeAsO-type compounds (with RE being a rare-earth metal) exhibit the highest bulk superconducting transition temperatures (Tc) up to 55 K and thus hold the key to the elusive pairing mechanism. Recently, it has been demonstrated that the intrinsic electronic structure of SmFe0.92Co0.08AsO (Tc = 18 K) is highly nontrivial and consists of multiple band-edge singularities in close proximity to the Fermi level. However, it remains unclear whether these singularities are generic to the REFeAsO-type materials and if so, whether their exact topology is responsible for the aforementioned record Tc. In this work, we use angle-resolved photoemission spectroscopy (ARPES) to investigate the inherent electronic structure of the NdFeAsO0.6F0.4 compound with a twice higher Tc = 38 K. We find a similarly singular Fermi surface and further demonstrate that the dramatic enhancement of superconductivity in this compound correlates closely with the fine-tuning of one of the band-edge singularities to within a fraction of the superconducting energy gap Δ below the Fermi level. Our results provide compelling evidence that the band-structure singularities near the Fermi level in the iron-based superconductors must be explicitly accounted for in any attempt to understand the mechanism of superconducting pairing in these materials.

  2. High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides

    NASA Astrophysics Data System (ADS)

    Charnukha, A.; Evtushinsky, D. V.; Matt, C. E.; Xu, N.; Shi, M.; Büchner, B.; Zhigadlo, N. D.; Batlogg, B.; Borisenko, S. V.

    2015-12-01

    In the family of the iron-based superconductors, the REFeAsO-type compounds (with RE being a rare-earth metal) exhibit the highest bulk superconducting transition temperatures (Tc) up to 55 K and thus hold the key to the elusive pairing mechanism. Recently, it has been demonstrated that the intrinsic electronic structure of SmFe0.92Co0.08AsO (Tc = 18 K) is highly nontrivial and consists of multiple band-edge singularities in close proximity to the Fermi level. However, it remains unclear whether these singularities are generic to the REFeAsO-type materials and if so, whether their exact topology is responsible for the aforementioned record Tc. In this work, we use angle-resolved photoemission spectroscopy (ARPES) to investigate the inherent electronic structure of the NdFeAsO0.6F0.4 compound with a twice higher Tc = 38 K. We find a similarly singular Fermi surface and further demonstrate that the dramatic enhancement of superconductivity in this compound correlates closely with the fine-tuning of one of the band-edge singularities to within a fraction of the superconducting energy gap Δ below the Fermi level. Our results provide compelling evidence that the band-structure singularities near the Fermi level in the iron-based superconductors must be explicitly accounted for in any attempt to understand the mechanism of superconducting pairing in these materials.

  3. Status of maglev: Opportunities in cryogenics and superconductivity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Coffey, H.T.

    1994-12-31

    A program to develop a prototype of a magnetically levitated (maglev) high-speed-ground-transportation system has been announced by the U.S. administration. This paper reviews the development of maglev and steel-wheel-on-steel-rail trains and examines the unique right-of-way requirements for these systems. The basic principles of maglev are discussed, highlighting U.S. efforts in this field. Japanese and German maglev systems and four recently designed U.S. systems are discussed. Five of these systems use superconducting magnets. The trend in the demand for intercity transportation capacity is reviewed, and the need for maglev to supplement or replace short-haul aircraft is discussed in terms of itsmore » competitiveness in travel time, capacity to transport large numbers of passengers, and environmental considerations, including energy, emissions, land use, and noise. The unusual consideration that the superconducting magnets should be sacrificed, if necessary, to permit the vehicle to stop safely is discussed, and various design and development issues related to the cryogenics and superconductivity in the system are listed.« less

  4. Metallization of a Rashba wire by a superconducting layer in the strong-proximity regime

    NASA Astrophysics Data System (ADS)

    Reeg, Christopher; Loss, Daniel; Klinovaja, Jelena

    2018-04-01

    Semiconducting quantum wires defined within two-dimensional electron gases and strongly coupled to thin superconducting layers have been extensively explored in recent experiments as promising platforms to host Majorana bound states. We study numerically such a geometry, consisting of a quasi-one-dimensional wire coupled to a disordered three-dimensional superconducting layer. We find that, in the strong-coupling limit of a sizable proximity-induced superconducting gap, all transverse subbands of the wire are significantly shifted in energy relative to the chemical potential of the wire. For the lowest subband, this band shift is comparable in magnitude to the spacing between quantized levels that arises due to the finite thickness of the superconductor (which typically is ˜500 meV for a 10-nm-thick layer of aluminum); in higher subbands, the band shift is much larger. Additionally, we show that the width of the system, which is usually much larger than the thickness, and moderate disorder within the superconductor have almost no impact on the induced gap or band shift. We provide a detailed discussion of the ramifications of our results, arguing that a huge band shift and significant renormalization of semiconducting material parameters in the strong-coupling limit make it challenging to realize a topological phase in such a setup, as the strong coupling to the superconductor essentially metallizes the semiconductor. This metallization of the semiconductor can be tested experimentally through the measurement of the band shift.

  5. A Dual Polarization, Active, Microstrip Antenna for an Orbital Imaging Radar System Operating at L-Band

    NASA Technical Reports Server (NTRS)

    Kelly, Kenneth C.; Huang, John

    1999-01-01

    A highly successful Earth orbiting synthetic antenna aperture radar (SAR) system, known as the SIR-C mission, was carried into orbit in 1994 on a U.S. Shuttle (Space Transportation System) mission. The radar system was mounted in the cargo bay with no need to fold, or in any other way reduce the size of the antennas for launch. Weight and size were not limited for the L-Band, C-Band, and X-Band radar systems of the SIR-C radar imaging mission; the set of antennas weighed 10,500 kg, the L-Band antenna having the major share of the weight. This paper treats designing an L-Band antenna functionally similar to that used for SIR-C, but at a fraction of the cost and at a weight in the order of 250 kg. Further, the antenna must be folded to fit into the small payload shroud of low cost booster rocket systems. Over 31 square meters of antenna area is required. This low weight, foldable, electronic scanning antenna is for the proposed LightSAR radar system which is to be placed in Earth orbit on a small, dedicated space craft at the lowest possible cost for an efficient L-Band radar imaging system. This LightSAR spacecraft radar is to be continuously available for at least five operational years, and have the ability to map or repeat-map any area on earth within a few days of any request. A microstrip patch array, with microstrip transmission lines heavily employed in the aperture and in the corporate feed network, was chosen as the low cost approach for this active dual-polarization, 80 MHz (6.4%) bandwidth antenna design.

  6. A Dual Polarization, Active, Microstrip Antenna for an Orbital Imaging Radar System Operating at L-Band

    NASA Technical Reports Server (NTRS)

    Kelly, Kenneth C.; Huang, John

    2000-01-01

    A highly successful Earth orbiting synthetic antenna aperture radar (SAR) system, known as the SIR-C mission, was carried into orbit in 1994 on a U.S. Shuttle (Space Transportation System) mission. The radar system was mounted in the cargo bay with no need to fold, or in any other way reduce the size of the antennas for launch. Weight and size were not limited for the L-Band, C-Band, and X-Band radar systems of the SIR-C radar imaging mission; the set of antennas weighed 10,500 kg, the L-Band antenna having the major share of the weight. This paper treats designing an L-Band antenna functionally similar to that used for SIR-C, but at a fraction of the cost and at a weight in the order of 250 kg. Further, the antenna must be folded to fit into the small payload shroud of low cost booster rocket systems. Over 31 square meters of antenna area is required. This low weight, foldable, electronic scanning antenna is for the proposed LightSAR radar system which is to be placed in Earth orbit on a small, dedicated space craft at the lowest possible cost for an efficient L- Band radar imaging system. This LightSAR spacecraft radar is to be continuously available for at least five operational years, and have the ability to map or repeat-map any area on earth within a few days of any request. A microstrip patch array, with microstrip transmission lines heavily employed in the aperture and in the corporate feed network, was chosen as the low cost approach for this active dual-polarization, 80 MHz (6.4%) bandwidth antenna design.

  7. Theory of the β-Type Organic Superconductivity under Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Suzuki, Takeo; Onari, Seiichiro; Ito, Hiroshi; Tanaka, Yukio

    2011-09-01

    We study theoretically the shift of the superconducting transition temperature (Tc) under uniaxial compression in β-type organic superconductors, β-(BEDT-TTF)2I3 and β-(BDA-TTP)2X (X=SbF6, AsF6), in order to clarify the electron correlation, the spin frustration, and the effect of dimerization. The transfer integrals are calculated by the extended Hückel method assuming the uniaxial strain, and the superconducting state mediated by the spin fluctuation is solved using Eliashberg's equation with the fluctuation--exchange approximation. The calculation is carried out on both the dimerized (one-band) and nondimerized (two-band) Hubbard models. We have found that (i) the behavior of Tc in β-(BEDT-TTF)2I3 with a stronger dimerization is well reproduced by the dimer model, while that in weakly dimerized β-BDA-TTP salts is rather well reproduced by the two-band model, and (ii) the competition between the spin frustration and the effect induced by the fluctuation is important in these materials, which causes the nonmonotonic shift of Tc against uniaxial compression.

  8. Method for obtaining large levitation pressure in superconducting magnetic bearings

    DOEpatents

    Hull, J.R.

    1997-08-05

    A method and apparatus are disclosed for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap. 4 figs.

  9. Method for obtaining large levitation pressure in superconducting magnetic bearings

    DOEpatents

    Hull, J.R.

    1996-10-08

    A method and apparatus are disclosed for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap. 4 figs.

  10. L-band InSAR Penetration Depth Experiment, North Slope Alaska

    NASA Astrophysics Data System (ADS)

    Muskett, Reginald

    2017-04-01

    Since the first spacecraft-based synthetic aperture radar (SAR) mission NASA's SEASAT in 1978 radars have been flown in Low Earth Orbit (LEO) by other national space agencies including the Canadian Space Agency, European Space Agency, India Space Research Organization and the Japanese Aerospace Exploration Agency. Improvements in electronics, miniaturization and production have allowed for the deployment of SAR systems on aircraft for usage in agriculture, hazards assessment, land-use management and planning, meteorology, oceanography and surveillance. LEO SAR systems still provide a range of needful and timely information on large and small-scale weather conditions like those found across the Arctic where ground-base weather radars currently provide limited coverage. For investigators of solid-earth deformation attention must be given to the atmosphere on Interferometric SAR (InSAR) by aircraft and spacecraft multi-pass operations. Because radar has the capability to penetrate earth materials at frequencies from the P- to X-band attention must be given to the frequency dependent penetration depth and volume scattering. This is the focus of our new research project: to test the penetration depth of L-band SAR/InSAR by aircraft and spacecraft systems at a test site in Arctic Alaska using multi-frequency analysis and progressive burial of radar mesh-reflectors at measured depths below tundra while monitoring environmental conditions. Knowledge of the L-band penetration depth on lowland Arctic tundra is necessary to constrain analysis of carbon mass balance and hazardous conditions arising form permafrost degradation and thaw, surface heave and subsidence and thermokarst formation at local and regional scales.

  11. Metastable Superconductivity in Two-Dimensional IrTe2 Crystals.

    PubMed

    Yoshida, Masaro; Kudo, Kazutaka; Nohara, Minoru; Iwasa, Yoshihiro

    2018-05-09

    Two-dimensional (2D) materials exhibit unusual physical and chemical properties that are attributed to the thinning-induced modification of their electronic band structure. Recently, reduced thickness was found to dramatically impact not only the static electronic structure, but also the dynamic ordering kinetics. The ordering kinetics of first-order phase transitions becomes significantly slowed with decreasing thickness, and metastable supercooled states can be realized by thinning alone. We therefore focus on layered iridium ditelluride (IrTe 2 ), a charge-ordering system that is transformed into a superconductor by suppressing its first-order transition. Here, we discovered a persistent superconducting zero-resistance state in mechanically exfoliated IrTe 2 thin flakes. The maximum superconducting critical temperature ( T c ) was identical to that which is chemically optimized, and the emergent superconductivity was revealed to have a metastable nature. The discovered robust metastable superconductivity suggests that 2D material is a new platform to induce, control, and functionalize metastable electronic states that are inaccessible in bulk crystals.

  12. Investigation of L-band shipboard antennas for maritime satellite applications

    NASA Technical Reports Server (NTRS)

    Heckert, G. P.

    1972-01-01

    A basic conceptual investigation of low cost L-band antenna subsystems for shipboard use was conducted by identifying the various pertinent design trade-offs and related performance characteristics peculiar to the civilian maritime application, and by comparing alternate approaches for their simplicity and general suitability. The study was not directed at a single specific proposal, but was intended to be parametric in nature. Antenna system concepts were to be investigated for a range of gain of 3 to 18 dB, with a value of about 10 dB considered as a baseline reference. As the primary source of potential complexity in shipboard antennas, which have beamwidths less than hemispherical as the beam pointing or selecting mechanism, major emphasis was directed at this aspect. Three categories of antenna system concepts were identified: (1) mechanically pointed, single-beam antennas; (2) fixed antennas with switched-beams; and (3) electronically-steered phased arrays. It is recommended that an L-band short backfire antenna subsystem, including a two-axis motor driven gimbal mount, and necessary single channel monopulse tracking receiver portions be developed for demonstration of performance and subsystem simplicity.

  13. Superconductivity, pseudo-gap, and stripe correlations in high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Zhang, Zailan; Denis, Sylvain; Lebert, Blair W.; Bertran, Francois; Le Fèvre, Patrick; Taleb-Ibrahimi, Amina; Castellan, John-Paul; Bolloc'h, David Le; Jacques, Vincent L. R.; Sidis, Yvan; Baptiste, Benoît; Decorse, Claudia; Berthet, Patrick; Perfetti, Luca; d'Astuto, Matteo

    2018-05-01

    Under-doped La-214 cuprates show a charge- and spin-modulation known as "stripes" [1]. These stripe modulations are (quasi)-static close to 1/8 hole doping where superconductivity is suppressed. The pseudo-gap phase of other cuprate compounds recently also revealed charge modulation, but interpreted rather as a charge density wave (CDW) [2-4], that possibly competes with superconductivity. In this context, to better understand the interplay between the stripe phase and the superconductivity, we use angle-resolved photoemission spectroscopy to study the electronic band structure and gap in La-214 cuprates near 1/8 doping (La2-x-yNdySrxCuO4 (x = 0.12; y = 0.0 & 0.4)) and compare with the previous results in the same system [5] and La1.86Ba0.14CuO4 [6]. Our data shows a loss of spectral intensity towards the end of the Fermi arcs, that is possibly due to a strong renormalisation, as already pointed out elsewhere [6], with a noisy but still measurable gap. On the nodal direction no gap is observed within our statistics, but a sizeable decrease in intensity with temperature. Moreover, we do not see any shadow band, but our Fermi surface can be well modelled with a single electron band calculation in the tight binding approximation, even very close to the 1/8 doping La2-x-yNdySrxCuO4 with and without Nd substitution.

  14. Giant phonon anomaly associated with superconducting fluctuations in the pseudogap phase of cuprates

    DOE PAGES

    Liu, Ye-Hua; Konik, Robert M.; Rice, T. M.; ...

    2016-01-20

    The pseudogap in underdoped cuprates leads to significant changes in the electronic structure, and was later found to be accompanied by anomalous fluctuations of superconductivity and certain lattice phonons. Here we propose that the Fermi surface breakup due to the pseudogap, leads to a breakup of the pairing order into two weakly coupled sub-band amplitudes, and a concomitant low energy Leggett mode due to phase fluctuations between them. This increases the temperature range of superconducting fluctuations containing an overdamped Leggett mode. In this range inter-sub-band phonons show strong damping due to resonant scattering into an intermediate state with a pairmore » of overdamped Leggett modes. In the ordered state, the Leggett mode develops a finite energy, changing the anomalous phonon damping into an anomaly in the dispersion. Finally, this proposal explains the intrinsic connection between the anomalous pseudogap phase, enhanced superconducting fluctuations and giant anomalies in the phonon spectra.« less

  15. Superconductivity between standard types: Multiband versus single-band materials

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Vagov, A.; Shanenko, A. A.; Milošević, M. V.

    In the nearest vicinity of the critical temperature, types I and II of conventional single-band superconductors interchange at the Ginzburg-Landau parameter κ = 1/√2. At lower temperatures this point unfolds into a narrow but finite interval of κ’s, shaping an intertype (transitional) domain in the (κ,T ) plane. In the present work, based on the extended Ginzburg-Landau formalism, we show that the same picture of the two standard types with the transitional domain in between applies also to multiband superconductors. However, the intertype domain notably widens in the presence of multiple bands and can become extremely large when the systemmore » has a significant disparity between the band parameters. It is concluded that many multiband superconductors, such as recently discovered borides and iron-based materials, can belong to the intertype regime.« less

  16. Active-passive synergy for interpreting ocean L-band emissivity: Results from the CAROLS airborne campaigns

    NASA Astrophysics Data System (ADS)

    Martin, A. C. H.; Boutin, J.; Hauser, D.; Dinnat, E. P.

    2014-08-01

    The impact of the ocean surface roughness on the ocean L-band emissivity is investigated using simultaneous airborne measurements from an L-band radiometer (CAROLS) and from a C-band scatterometer (STORM) acquired in the Gulf of Biscay (off-the French Atlantic coasts) in November 2010. Two synergetic approaches are used to investigate the impact of surface roughness on the L-band brightness temperature (Tb). First, wind derived from the scatterometer measurements is used to analyze the roughness contribution to Tb as a function of wind and compare it with the one simulated by SMOS and Aquarius roughness models. Then residuals from this mean relationship are analyzed in terms of mean square slope derived from the STORM instrument. We show improvement of new radiometric roughness models derived from SMOS and Aquarius satellite measurements in comparison with prelaunch models. Influence of wind azimuth on Tb could not be evidenced from our data set. However, we point out the importance of taking into account large roughness scales (>20 cm) in addition to small roughness scale (5 cm) rapidly affected by wind to interpret radiometric measurements far from nadir. This was made possible thanks to simultaneous estimates of large and small roughness scales using STORM at small (7-16°) and large (30°) incidence angles.

  17. L-Band Digital Aeronautical Communications System Engineering - Initial Safety and Security Risk Assessment and Mitigation

    NASA Technical Reports Server (NTRS)

    Zelkin, Natalie; Henriksen, Stephen

    2011-01-01

    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." ITT has completed a safety hazard analysis providing a preliminary safety assessment for the proposed L-band (960 to 1164 MHz) terrestrial en route communications system. The assessment was performed following the guidelines outlined in the Federal Aviation Administration Safety Risk Management Guidance for System Acquisitions document. The safety analysis did not identify any hazards with an unacceptable risk, though a number of hazards with a medium risk were documented. This effort represents a preliminary safety hazard analysis and notes the triggers for risk reassessment. A detailed safety hazards analysis is recommended as a follow-on activity to assess particular components of the L-band communication system after the technology is chosen and system rollout timing is determined. The security risk analysis resulted in identifying main security threats to the proposed system as well as noting additional threats recommended for a future security analysis conducted at a later stage in the system development process. The document discusses various security controls, including those suggested in the COCR Version 2.0.

  18. Simulated Biomass Retrieval from the Spaceborne Tomographic SAOCOM-CS Mission at L-Band

    NASA Astrophysics Data System (ADS)

    Blomberg, Erik; Soja, Maciej J.; Ferro-Famil, Laurent; Ulander, Lars M. H.; Tebaldini, Stefano

    2016-08-01

    This paper presents an evaluation of above-ground biomass (ABG) retrieval in boreal forests using simulated tomographic synthetic-aperture radar (SAR) data corresponding to the future SAOCOM-CS (L-band 1.275 GHz) mission. Using forest and radar data from the BioSAR 2008 campaign at the Krycklan test site in northern Sweden the expected performance of SAOCOM-CS is evaluated and compared with the E-SAR airborne L- band SAR (1.300 GHz). It is found that SAOCOM-CS data produce retrievals on par with those obtained with E-SAR, with retrievals having a relative RMSE of 30% or less. This holds true even if the acquisitions are limited to a single polarization, with HH results shown as an example.

  19. Preliminary study of superconducting bulk magnets for Maglev

    NASA Astrophysics Data System (ADS)

    Fujimoto, Hiroyuki; Kamijo, Hiroki

    Recent development shows that melt-processed YBaCuO (Y123) or Rare Earth (RE)123 superconductors have a high Jc at 77 K and high magnetic field, leading to high field application as a superconducting quasi-permanent bulk magnet with the liquid nitrogen refrigeration. One of the promising applications is a superconducting magnet for the magnetically levitated (Maglev) train. We discuss a superconducting bulk magnet for the Maglev train in the aspect of a preliminary design of the bulk magnet and also processing for (L)REBaCuO bulk superconductors and their characteristic superconducting properties.

  20. p -wave superconductivity in weakly repulsive 2D Hubbard model with Zeeman splitting and weak Rashba spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Hugdal, Henning G.; Sudbø, Asle

    2018-01-01

    We study the superconducting order in a two-dimensional square lattice Hubbard model with weak repulsive interactions, subject to a Zeeman field and weak Rashba spin-orbit interactions. Diagonalizing the noninteracting Hamiltonian leads to two separate bands, and by deriving an effective low-energy interaction we find the mean field gap equations for the superconducting order parameter on the bands. Solving the gap equations just below the critical temperature, we find that superconductivity is caused by Kohn-Luttinger-type interaction, while the pairing symmetry of the bands is indirectly affected by the spin-orbit coupling. The dominating attractive momentum channel of the Kohn-Luttinger term depends on the filling fraction n of the system, and it is therefore possible to change the momentum dependence of the order parameter by tuning n . Moreover, n also determines which band has the highest critical temperature. Rotating the magnetic field changes the momentum dependence from states that for small momenta reduce to a chiral px±i py type state for out-of-plane fields, to a nodal p -wave-type state for purely in-plane fields.

  1. Superconductivity switch from spin-singlet to -triplet pairing in a topological superconducting junction.

    PubMed

    Tao, Ze; Chen, F J; Zhou, L Y; Li, Bin; Tao, Y C; Wang, J

    2018-06-06

    The interedge coupling is the cardinal characteristic of the narrow quantum spin Hall (QSH) insulator, and thus could bring about exotic transport phenomena. Herein, we present a theoretical investigation of the spin-resolved Andreev reflection (AR) in a QSH insulator strip touching on two neighbouring ferromagnetic insulators and one s-wave superconductor. It is demonstrated that, due to the interplay of the interedge coupling and ferromagnetic configuration, there could be not only usual local ARs leading to the spin-singlet pairing with the incident electron and Andreev-reflected hole from different spin subbands, but also novel local ARs giving rise to the spin-triplet pairing from the same spin subband. However, only the latter exists in the absence of the interedge coupling, and therefore the two pairings in turn testify the helical spin texture of the edge states. By proper tuning of the band structures of the ferromagnetic layers, under the resonance bias voltage, the usual and novel local ARs of [Formula: see text] can be all exhibited, resulting in fully spin-polarized pure spin-singlet superconductivity and pure spin-triplet superconductivity, respectively, which suggests a superconductivity switch from spin-singlet to -triplet pairing by electrical control. The results can be experimentally confirmed by the tunneling conductance and the noise power.

  2. Superconductivity switch from spin-singlet to -triplet pairing in a topological superconducting junction

    NASA Astrophysics Data System (ADS)

    Tao, Ze; Chen, F. J.; Zhou, L. Y.; Li, Bin; Tao, Y. C.; Wang, J.

    2018-06-01

    The interedge coupling is the cardinal characteristic of the narrow quantum spin Hall (QSH) insulator, and thus could bring about exotic transport phenomena. Herein, we present a theoretical investigation of the spin-resolved Andreev reflection (AR) in a QSH insulator strip touching on two neighbouring ferromagnetic insulators and one s-wave superconductor. It is demonstrated that, due to the interplay of the interedge coupling and ferromagnetic configuration, there could be not only usual local ARs leading to the spin-singlet pairing with the incident electron and Andreev-reflected hole from different spin subbands, but also novel local ARs giving rise to the spin-triplet pairing from the same spin subband. However, only the latter exists in the absence of the interedge coupling, and therefore the two pairings in turn testify the helical spin texture of the edge states. By proper tuning of the band structures of the ferromagnetic layers, under the resonance bias voltage, the usual and novel local ARs of can be all exhibited, resulting in fully spin-polarized pure spin-singlet superconductivity and pure spin-triplet superconductivity, respectively, which suggests a superconductivity switch from spin-singlet to -triplet pairing by electrical control. The results can be experimentally confirmed by the tunneling conductance and the noise power.

  3. Soil Moisture Active Passive (SMAP) L-Band Microwave Radiometer Post-Launch Calibration

    NASA Technical Reports Server (NTRS)

    Peng, Jinzheng; Piepmeier, Jeffrey R.; Misra, Sidharth; Dinnat, Emmanuel P.; Hudson, Derek; Le Vine, David M.; De Amici, Giovanni; Mohammed, Priscilla N.; Yueh, Simon H.; Meissner, Thomas

    2016-01-01

    The SMAP microwave radiometer is a fully-polarimetric L-band radiometer flown on the SMAP satellite in a 6 AM/ 6 PM sun-synchronous orbit at 685 km altitude. Since April, 2015, the radiometer is under calibration and validation to assess the quality of the radiometer L1B data product. Calibration methods including the SMAP L1B TA2TB (from Antenna Temperature (TA) to the Earth's surface Brightness Temperature (TB)) algorithm and TA forward models are outlined, and validation approaches to calibration stability/quality are described in this paper including future work. Results show that the current radiometer L1B data satisfies its requirements.

  4. Soil Moisture ActivePassive (SMAP) L-Band Microwave Radiometer Post-Launch Calibration

    NASA Technical Reports Server (NTRS)

    Peng, Jinzheng; Piepmeier, Jeffrey R.; Misra, Sidharth; Dinnat, Emmanuel P.; Hudson, Derek; Le Vine, David M.; De Amici, Giovanni; Mohammed, Priscilla N.; Yueh, Simon H.; Meissner, Thomas

    2016-01-01

    The SMAP microwave radiometer is a fully-polarimetric L-band radiometer flown on the SMAP satellite in a 6 AM/ 6 PM sun-synchronous orbit at 685 km altitude. Since April, 2015, the radiometer is under calibration and validation to assess the quality of the radiometer L1B data product. Calibration methods including the SMAP L1B TA2TB (from Antenna Temperature (TA) to the Earth’s surface Brightness Temperature (TB)) algorithm and TA forward models are outlined, and validation approaches to calibration stability/quality are described in this paper including future work. Results show that the current radiometer L1B data satisfies its requirements.

  5. Designing heterostructures with higher-temperature superconductivity

    NASA Astrophysics Data System (ADS)

    Le Hur, Karyn; Chung, Chung-Hou; Paul, I.

    2011-07-01

    We propose to increase the superconducting transition temperature Tc of strongly correlated materials by designing heterostructures which exhibit a high pairing energy as a result of magnetic fluctuations. More precisely, applying an effective theory of the doped Mott insulator, we envisage a bilayer Hubbard system where both layers exhibit intrinsic intralayer (intraband) d-wave superconducting correlations. Introducing a finite asymmetry between the hole densities of the two layers such that one layer becomes slightly more underdoped and the other more overdoped, we show a visible enhancement of Tc compared to the optimally doped isolated layer. Using the bonding and antibonding band basis, we show that the mechanism behind this enhancement of Tc is the interband pairing correlation mediated by the hole asymmetry which strives to decrease the paramagnetic nodal contribution to the superfluid stiffness. For two identical layers, Tc remains comparable to that of the isolated layer until moderate values of the interlayer single-particle tunneling term. These heterostructures shed new light on fundamental questions related to superconductivity.

  6. Fermi-surface-free superconductivity in underdoped (Bi,Pb)(Sr,La) 2CuO 6+δ (Bi2201)

    DOE PAGES

    Mistark, Peter; Hafiz, Hasnain; Markiewicz, Robert S.; ...

    2015-06-18

    Fermi-surface-free superconductivity arises when the superconducting order pulls down spectral weight from a band that is completely above the Fermi energy in the normal state. Here, we show that this can arise in hole-doped cuprates when a competing order causes a reconstruction of the Fermi surface. The change in Fermi surface topology is accompanied by a characteristic rise in the spectral weight. Finally, our results support the presence of a trisected superconducting dome, and suggest that superconductivity is responsible for stabilizing the (π,π) magnetic order at higher doping.

  7. Precisely determined the surface displacement by the ionospheric mitigation using the L-band SAR Interferometry over Mt.Baekdu

    NASA Astrophysics Data System (ADS)

    Lee, Won-Jin; Jung, Hyung-Sup; Park, Sun-Cheon; Lee, Duk Kee

    2016-04-01

    Mt. Baekdu (Changbaishan in Chinese) is located on the border between China and North Korea. It has recently attracted the attention of volcanic unrest during 2002-2005. Many researchers have applied geophysical approaches to detect magma system of beneath Mt.Baekdu such as leveling, Global Positioning System (GPS), gases analysis, seismic analysis, etc. Among them, deformation measuring instruments are important tool to evaluate for volcanism. In contrast to GPS or other deformation measuring instruments, Synthetic Aperture Radar Interferometry (InSAR) has provided high resolution of 2-D surface displacement from remote sensed data. However, Mt. Baekdu area has disturbed by decorrelation on interferogram because of wide vegetation coverage. To overcome this limitation, L-band system of long wavelength is more effective to detect surface deformation. In spite of this advantage, L-band can surfer from more severe ionospheric phase distortions than X- or C- band system because ionospheric phase distortions are inverse proportion to the radar frequency. Recently, Multiple Aperture Interferometry (MAI) based ionospheric phase distortions mitigation method have proposed and investigated. We have applied this technique to the Mt.Baekdu area to measure surface deformation precisely using L-band Advanced Land Observing Satellite-1(ALOS-1) Phased Array type L-band Synthetic Aperture Radar(PALSAR) data acquiring from 2006 to 2011.

  8. L-band InSAR Penetration Depth Experiment, North Slope Alaska

    NASA Astrophysics Data System (ADS)

    Muskett, R. R.

    2017-12-01

    Since the first spacecraft-based synthetic aperture radar (SAR) mission NASA's SEASAT in 1978 radars have been flown in Low Earth Orbit (LEO) by other national space agencies including the Canadian Space Agency, European Space Agency, India Space Research Organization and the Japanese Aerospace Exploration Agency. Improvements in electronics, miniaturization and production have allowed for the deployment of SAR systems on aircraft for usage in agriculture, hazards assessment, land-use management and planning, meteorology, oceanography and surveillance. LEO SAR systems still provide a range of needful and timely information on large and small-scale weather conditions like those found across the Arctic where ground-base weather radars currently provide limited coverage. For investigators of solid-earth deformation attention must be given to the atmosphere on Interferometric SAR (InSAR) by aircraft and spacecraft multi-pass operations. Because radar has the capability to penetrate earth materials at frequencies from the P- to X-band attention must be given to the frequency dependent penetration depth and volume scattering. This is the focus of our new research project: to test the penetration depth of L-band SAR/InSAR by aircraft and spacecraft systems at a test site in Arctic Alaska using multi-frequency analysis and progressive burial of radar mesh-reflectors at measured depths below tundra while monitoring environmental conditions. Knowledge of the L-band penetration depth on lowland Arctic tundra is necessary to constrain analysis of carbon mass balance and hazardous conditions arising form permafrost degradation and thaw, surface heave and subsidence and thermokarst formation at local and regional scales. Ref.: Geoscience and Environment Protection, vol. 5, no. 3, p. 14-30, 2017. DOI: 10.4236/gep.2017.53002.

  9. L-band radiometry for sea ice applications

    NASA Astrophysics Data System (ADS)

    Heygster, G.; Hedricks, S.; Mills, P.; Kaleschke, L.; Stammer, D.; Tonboe, R.

    2009-04-01

    Although sea ice remote sensing has reached the level of operational exploitation with well established retrieval methods, several important tasks are still unsolved. In particular during freezing and melting periods with mixed ice and water surfaces, estimates of ice concentration with passive and active microwave sensors remain challenging. Newly formed thin ice is also hard to distinguish from open water with radiometers for frequencies above 8 GHz. The SMOS configuration (planned launch 2009) with a radiometer at 1.4 GHz is a promising technique to complement observations at higher microwave frequencies. ESA has initiated a project to investigate the possibilities for an additional Level-2 sea ice data product based on SMOS. In detail, the project objectives are (1) to model the L band emission of sea ice, and to assess the potential (2) to retrieve sea ice parameters, especially concentration and thickness, and (3) to use cold water regions for an external calibration of SMOS. Modelling of L band emission: Several models have are investigated. All of them work on the same basic principles and have a vertically-layered, plane-parallel geometry. They are comprised of three basic components: (1) effective permittivities are calculated for each layer based on ice bulk and micro-structural properties; (2) these are integrated across the total depth to derive emitted brightness temperature; (3) scattering terms can also be added because of the granular structure of ice and snow. MEMLS (Microwave Emission Model of Layered Snowpacks (Wiesmann and Matzler 1999)) is one such model that contains all three elements in a single Matlab program. In the absence of knowledge about the internal structure of the sea ice, three-layer (air, ice and water) dielectric slab models which take as input a single effective permittivity for the ice layer are appropriate. By ignoring scattering effects one can derive a simple analytic expression for a dielectric slab as shown by Apinis and

  10. UAVSAR: Airborne L-band Radar for Repeat Pass Interferometry

    NASA Technical Reports Server (NTRS)

    Moes, Timothy R.

    2009-01-01

    The primary objectives of the UAVSAR Project were to: a) develop a miniaturized polarimetric L-band synthetic aperture radar (SAR) for use on an unmanned aerial vehicle (UAV) or piloted vehicle. b) develop the associated processing algorithms for repeat-pass differential interferometric measurements using a single antenna. c) conduct measurements of geophysical interest, particularly changes of rapidly deforming surfaces such as volcanoes or earthquakes. Two complete systems were developed. Operational Science Missions began on February 18, 2009 ... concurrent development and testing of the radar system continues.

  11. Modeling Periodic Adiabatic Shear Bands Evolution in a 304L Stainless Steel Thick-Walled Cylinder

    NASA Astrophysics Data System (ADS)

    Liu, Mingtao; Hu, Haibo; Fan, Cheng; Tang, Tiegang

    2015-06-01

    The self-organization of multiple shear bands in a 304L stainless steel thick-walled cylinder (TWC) was numerically studied. The microstructures of material lead to the non-uniform distribution of local yield stress, which plays a key role in the formation of spontaneous shear localization. We introduced a probability factor satisfied Gauss distribution into the macroscopic constitutive relationship to describe the non-uniformity of local yield stress. Using the probability factor, the initiation and propagation of multiple shear bands in TWC were numerically replicated in our 2D FEM simulation. Experimental results in the literature indicate that the machined surface at the internal boundary of a 304L stainless steel cylinder provides a work-hardened layer (about 20 μm) which has significantly different microstructures from base material. The work-hardened layer leads to the phenomenon that most shear bands are in clockwise or counterclockwise direction. In our simulation, periodic oriented perturbations were applied to describe the grain orientation in the work-hardened layer, and the spiral pattern of shear bands was successfully replicated.

  12. The Pressure Coefficients of the Superconducting Order Parameters at the Ground State of Ferromagnetic Superconductors

    NASA Astrophysics Data System (ADS)

    Konno, R.; Hatayama, N.; Chaudhury, R.

    2014-04-01

    We investigated the pressure coefficients of the superconducting order parameters at the ground state of ferromagnetic superconductors based on the microscopic single band model by Linder et al. The superconducting gaps (i) similar to the ones seen in the thin film of A2 phase in liquid 3He and (ii) with the line node were used. This study shows that we would be able to estimate the pressure coefficients of the superconducting and magnetic order parameters at the ground state of ferromagnetic superconductors.

  13. Realizing a Circuit Analog of an Optomechanical System with Longitudinally Coupled Superconducting Resonators.

    PubMed

    Eichler, C; Petta, J R

    2018-06-01

    We realize a superconducting circuit analog of the generic cavity-optomechanical Hamiltonian by longitudinally coupling two superconducting resonators, which are an order of magnitude different in frequency. We achieve longitudinal coupling by embedding a superconducting quantum interference device into a high frequency resonator, making its resonance frequency depend on the zero point current fluctuations of a nearby low frequency LC resonator. By applying sideband drive fields we enhance the intrinsic coupling strength of about 15 kHz up to 280 kHz by controlling the amplitude of the drive field. Our results pave the way towards the exploration of optomechanical effects in a fully superconducting platform and could enable quantum optics experiments with photons in the yet unexplored radio frequency band.

  14. Spectroscopic signatures of different symmetries of the superconducting order parameter in metal-decorated graphene

    NASA Astrophysics Data System (ADS)

    Saari, Timo; Nieminen, Jouko; Bansil, Arun

    2017-06-01

    Motivated by the recent experiments indicating superconductivity in metal-decorated graphene sheets, we investigate their quasi-particle structure within the framework of an effective tight-binding Hamiltonian augmented by appropriate BCS-like pairing terms for p-type order parameter. The normal state band structure of graphene is modified not only through interaction with adsorbed metal atoms, but also due to the folding of bands at Brillouin zone boundaries resulting from a \\sqrt{3}× \\sqrt{3}R{{30}\\circ} reconstruction. Several different types of pairing symmetries are analyzed utilizing Nambu-Gorkov Green’s function techniques to show that p+\\text{i}p -symmetric nearest-neighbor pairing yields the most enhanced superconducting gap. The character of the order parameter depends on the nature of the atomic orbitals involved in the pairing process and exhibits interesting angular and radial asymmetries. Finally, we suggest a method to distinguish between singlet and triplet type superconductivity in the presence of magnetic substitutional impurities using scanning tunneling spectroscopy.

  15. Wide Band Gyrotron Traveling Wave Amplifier Analysis.

    DTIC Science & Technology

    1987-12-01

    phase versus frequency characteristics. It is in these aspects that the gyrotron amplifier effort has been less than successful. A C-band gyro- TWT ...proposals were made several years ago, no experimental results have yet been reported. Another concept for increasing the bandwidth of the gyro- TWT is to...including dielectric loading of the waveguide [24], helix loaded waveguide (25]-[26], and disc-loaded waveguide [26]-(27). No experimental results on

  16. Broad-band beam buncher

    DOEpatents

    Goldberg, David A.; Flood, William S.; Arthur, Allan A.; Voelker, Ferdinand

    1986-01-01

    A broad-band beam buncher is disclosed, comprising an evacuated housing, an electron gun therein for producing an electron beam, a buncher cavity having entrance and exit openings through which the beam is directed, grids across such openings, a source providing a positive DC voltage between the cavity and the electron gun, a drift tube through which the electron beam travels in passing through such cavity, grids across the ends of such drift tube, gaps being provided between the drift tube grids and the entrance and exit grids, a modulator for supplying an ultrahigh frequency modulating signal to the drift tube for producing velocity modulation of the electrons in the beam, a drift space in the housing through which the velocity modulated electron beam travels and in which the beam is bunched, and a discharge opening from such drift tube and having a grid across such opening through which the bunched electron beam is discharged into an accelerator or the like. The buncher cavity and the drift tube may be arranged to constitute an extension of a coaxial transmission line which is employed to deliver the modulating signal from a signal source. The extended transmission line may be terminated in its characteristic impedance to afford a broad-band response and the device as a whole designed to effect broad-band beam coupling, so as to minimize variations of the output across the response band.

  17. Direct evidence for a magnetic f-electron–mediated pairing mechanism of heavy-fermion superconductivity in CeCoIn5

    PubMed Central

    Van Dyke, John S.; Massee, Freek; Allan, Milan P.; Davis, J. C. Séamus; Petrovic, Cedomir; Morr, Dirk K.

    2014-01-01

    To identify the microscopic mechanism of heavy-fermion Cooper pairing is an unresolved challenge in quantum matter studies; it may also relate closely to finding the pairing mechanism of high-temperature superconductivity. Magnetically mediated Cooper pairing has long been the conjectured basis of heavy-fermion superconductivity but no direct verification of this hypothesis was achievable. Here, we use a novel approach based on precision measurements of the heavy-fermion band structure using quasiparticle interference imaging to reveal quantitatively the momentum space (k-space) structure of the f-electron magnetic interactions of CeCoIn5. Then, by solving the superconducting gap equations on the two heavy-fermion bands Ekα,β with these magnetic interactions as mediators of the Cooper pairing, we derive a series of quantitative predictions about the superconductive state. The agreement found between these diverse predictions and the measured characteristics of superconducting CeCoIn5 then provides direct evidence that the heavy-fermion Cooper pairing is indeed mediated by f-electron magnetism. PMID:25062692

  18. Spectroscopic evidence of a new energy scale for superconductivity in H3S.

    PubMed

    Capitani, F; Langerome, B; Brubach, J-B; Roy, P; Drozdov, A; Eremets, M I; Nicol, E J; Carbotte, J P; Timusk, T

    2017-09-01

    The discovery of a superconducting phase in sulfur hydride under high pressure with a critical temperature above 200 K has provided fresh impetus to the search for superconductors at ever higher temperatures. Although this systems displays all the hallmarks of superconductivity, the mechanism through which it arises remains to be determined. Here we provide a first optical spectroscopy study of this superconductor. Experimental results for the optical reflectivity of H 3 S, under hydrostatic pressure of 150 GPa, for several temperatures and over the range 60 to 600 meV of photon energies, are compared with theoretical calculations based on Eliashberg theory. Two significant features stand out: some remarkably strong infrared active phonons at around 160 meV, and a band with a depressed reflectance in the superconducting state in the region from 450 meV to 600 meV. In this energy range H3S becomes more reflecting with increasing temperature, a change that is traced to superconductivity originating from the electron-phonon interaction. The shape, magnitude, and energy dependence of this band at 150 K agrees with our calculations. This provides strong evidence of a conventional mechanism. However, the unusually strong optical phonon suggests a contribution of electronic degrees of freedom.

  19. Superconductivity in the Narrow Gap Semiconductor RbBi 11/3Te 6

    DOE PAGES

    Malliakas, Christos D.; Chung, Duck Young; Claus, Helmut; ...

    2016-10-16

    Superconductivity was discovered in the layered compound RbBi 11/3Te 6, featuring Bi vacancies and a narrow band gap of 0.25(2) eV at room temperature. In addition, a sharp superconducting transition at similar to 3.2 K was observed in polycrystalline ingots. The superconducting volume fraction of oriented single crystals is almost 100%, confirming bulk superconductivity. Systematic Se and Sb substitutions in RbBi 11/3-ySb ySe xTe 6-x, revealed a dependence of the superconducting transition on composition that can increase the T c up to similar to 10%. The RbBi 11/3Te 6 system is the first member of the new homologous series Rb[Bimore » 2n+11/3Te 3n+6] with infinite Bi 2Te 3-like layers. Lastly, the large degree of chemical tunability of the electronic structure of the homology via doping and/or substitution gives rise to a new family of superconductors.« less

  20. Generation of microwave oscillations in a superconducting tunnel mesa-structure with a ferromagnetic insulator interlayer

    NASA Astrophysics Data System (ADS)

    Constantinian, K. Y.; Ovsyannikov, G. A.; Kislinskii, Yu. V.; Petrzhik, A. M.; Shadrin, A. V.

    2017-10-01

    Spin-polarized current in thin-film tunnel mesa-structures formed by epitaxial cuprate superconducting (YBa2Cu3O7-δ) and manganite (LaMnO3) films and an upper superconducting Au-Nb bilayer is studied experimentally. Intrinsic narrow-band generation in the microwave range is reported. Its frequency is tuned by the bias voltage and an external magnetic field.

  1. Multi-band description of the specific heat and thermodynamic critical field in MgB2 superconductor

    NASA Astrophysics Data System (ADS)

    Szcześniak, R.; Jarosik, M. W.; Tarasewicz, P.; Durajski, A. P.

    2018-05-01

    The thermodynamic properties of MgB2 superconductor can be explained using the multi-band models. In the present paper we have examined the experimental data available in literature and we have found out that it is possible to reproduce the measured values of the superconducting energy gaps, the thermodynamic critical magnetic field and specific heat jump within the framework of two-band Eliashberg formalism and appropriate defined free energy difference between superconducting and normal state. Moreover, we found that the obtained results differ significantly from the predictions of the conventional Bardeen-Cooper-Schrieffer theory.

  2. Superconducting pipes and levitating magnets.

    PubMed

    Levin, Yan; Rizzato, Felipe B

    2006-12-01

    Motivated by a beautiful demonstration of the Faraday and the Lenz laws in which a small neodymium magnet falls slowly through a conducting nonferromagnetic tube, we consider the dynamics of a magnet falling coaxially through a superconducting pipe. Unlike the case of normal conducting pipes, in which the magnet quickly reaches the terminal velocity, inside a superconducting tube the magnet falls freely. On the other hand, to enter the pipe the magnet must overcome a large electromagnetic energy barrier. For sufficiently strong magnets, the barrier is so large that the magnet will not be able to penetrate it and will be levitated over the mouth of the pipe. We calculate the work that must done to force the magnet to enter a superconducting tube. The calculations show that superconducting pipes are very efficient at screening magnetic fields. For example, the magnetic field of a dipole at the center of a short pipe of radius a and length L approximately > a decays, in the axial direction, with a characteristic length xi approximately 0.26a. The efficient screening of the magnetic field might be useful for shielding highly sensitive superconducting quantum interference devices. Finally, the motion of the magnet through a superconducting pipe is compared and contrasted to the flow of ions through a trans-membrane channel.

  3. Deep L'- and M-band Imaging for Planets around Vega and epsilon Eridani

    NASA Astrophysics Data System (ADS)

    Heinze, A. N.; Hinz, Philip M.; Kenworthy, Matthew; Miller, Douglas; Sivanandam, Suresh

    2008-11-01

    We have obtained deep adaptive optics (AO) images of Vega and epsilon Eri to search for planetary mass companions. We observed at the MMT in the L' (3.8 μm) and M (4.8 μm) bands using Clio, a recently commissioned imager optimized for these wavelengths. Observing at these long wavelengths represents a departure from the H band (1.65 μm) more commonly used for AO imaging searches for extrasolar planets. The long wavelengths offer better predicted planet/star flux ratios and cleaner (higher Strehl) AO images at the cost of lower diffraction-limited resolution and higher sky background. We have not detected any planets or planet candidates around Vega or epsilon Eri. We report the sensitivities obtained around both stars, which correspond to upper limits on any planetary companions which may exist. The sensitivities of our L'- and M-band observations are comparable to those of the best H-regime observations of these stars. For epsilon Eri, our M-band observations deliver considerably better sensitivity to close-in planets than any previously published results, and we show that the M band is by far the best wavelength choice for attempts at ground-based AO imaging of the known planet epsilon Eri b. The Clio camera itself, with MMTAO, may be capable of detecting epsilon Eri b at its 2010 apastron, given a multinight observing campaign. Clio appears to be the only currently existing AO imager that has a realistic possibility of detecting epsilon Eri b. Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution.

  4. Superconductivity of Ba8Si46-xGax clathrates

    NASA Astrophysics Data System (ADS)

    Li, Yang; Zhang, Ruihong; Chen, Ning; Ma, Xingqiao; Cao, Guohui; Luo, Z. P.; Hu, C. R.; Ross, Joseph H., Jr.

    2007-03-01

    We have presented a combined experimental and theoretical study of the effect of Gallium substitution on the superconductivity of the type I clathrate Ba8Si46-xGax. In Ga-doped clathrates, the Ga state is found to be strongly hybridized with the cage conduction-band state. Ga substitution results in a shift toward to a lower energy, a decrease of density of states at Fermi level, a lowering of the carrier concentration and a breakage of integrity of the sp3 hybridized networks. These play key roles in the suppression of superconductivity. For Ba8Si40Ga6, the onset of the superconducting transition occurs at Tc=3.3 K. The investigation of the magnetic superconducting state shows that Ba8Si40Ga6 is a type II superconductor. The critical magnetic fields were measured to be Hc1=35 Oe and Hc2=8.5 kOe. Our estimate of the lectron-phonon coupling reveals that Ba8Si40Ga6 is a moderate phonon-mediated BCS superconductor.

  5. Ultrasonic investigation of the superconducting properties of the Nb-Mo system

    NASA Technical Reports Server (NTRS)

    Lacy, L. L.

    1972-01-01

    The superconducting properties of single crystals of Nb and two alloys of Nb with Mo were investigated by ultrasonic techniques. The results of measurements of the ultrasonic attenuation and velocities as a function of temperature, Mo composition, crystallographic direction, and ultrasonic frequency are reported. The attenuation and small velocity changes associated with the superconductivity of the samples are shown to be dependent on the sample resistivity ratio which varied from 4.3 for Nb-9% Mo to 6500 for pure Nb. The ultrasonic attenuation data are analyzed in terms of the superconducting energy gap term of the BCS theory. A new model is proposed for the analysis of ultrasonic attenuation in pure superconductors with two partially decoupled energy bands. To analyze the attenuation in pure superconducting Nb, the existence of two energy gaps was assumed to be associated with the two partially decoupled energy bands. One of the gaps was found to have the normal BCS value of 3.4 and the other gap was found to have the anomalously large value of 10. No experimental evidence was found to suggest that the second energy gap had a different transition temperature. The interpretation of the results for the Nb-Mo alloys is shown to be complicated by the possible existence of a second superconducting phase in Nb-Mo alloys with a transition temperature of 0.35 of the transition temperature of the first phase. The elastic constants of Nb and Nb-Mo alloys are shown to be approximately independent of Mo composition to nine atomic percent Mo. These results do not agree with the current microscopic theory of transition temperature for the transition elements.

  6. Music Travel: Avoiding the Potholes

    ERIC Educational Resources Information Center

    Olson, Cathy Applefeld

    2010-01-01

    Even given the countless hours clocked in class and rehearsal time, there's nothing that compares to a road trip to seal the bond among band, orchestra, and vocal music students. "Nothing can replace travel," says Peter Markes, orchestra director at Edmond North High School in Oklahoma. "It's safe, well-structured and, for many of…

  7. Inter-comparison of SMAP, Aquarius and SMOS L-band brightness temperature observations

    USDA-ARS?s Scientific Manuscript database

    Soil Moisture Active Passive (SMAP) mission is scheduled for launch on January 29, 2015. SMAP will make observations with an L-band radar and radiometer using a shared 6 m rotating reflector antenna. SMAP is a fully polarimetric radiometer with the center frequency of 1.41 GHz. The target accuracy o...

  8. Inter-spin distance determination using L-band (1-2 GHz) non-adiabatic rapid sweep electron paramagnetic resonance (NARS EPR)

    PubMed Central

    Kittell, Aaron W.; Hustedt, Eric J.; Hyde, James S.

    2014-01-01

    Site-directed spin-labeling electron paramagnetic resonance (SDSL EPR) provides insight into the local structure and motion of a spin probe strategically attached to a molecule. When a second spin is introduced to the system, macromolecular information can be obtained through measurement of inter-spin distances either by continuous wave (CW) or pulsed electron double resonance (ELDOR) techniques. If both methodologies are considered, inter-spin distances of 8 to 80 Å can be experimentally determined. However, there exists a region at the upper limit of the conventional X-band (9.5 GHz) CW technique and the lower limit of the four-pulse double electron-electron resonance (DEER) experiment where neither method is particularly reliable. The work presented here utilizes L-band (1.9 GHz) in combination with non-adiabatic rapid sweep (NARS) EPR to address this opportunity by increasing the upper limit of the CW technique. Because L-band linewidths are three to seven times narrower than those at X-band, dipolar broadenings that are small relative to the X-band inhomogeneous linewidth become observable, but the signal loss due to the frequency dependence of the Boltzmann factor, has made L-band especially challenging. NARS has been shown to increase sensitivity by a factor of five, and overcomes much of this loss, making L-band distance determination more feasible [1]. Two different systems are presented and distances of 18–30 Å have been experimentally determined at physiologically relevant temperatures. Measurements are in excellent agreement with a helical model and values determined by DEER. PMID:22750251

  9. The effect of ASE reinjection configuration through FBGs on the gain and noise figure performance of L-Band EDFA

    NASA Astrophysics Data System (ADS)

    Durak, Fırat Ertaç; Altuncu, Ahmet

    2017-03-01

    In this study, we present the gain and noise figure performance improvement in L-band erbium-doped fiber amplifier (L-EDFA) provided by amplified spontaneous emission (ASE) reinjection through different configurations of 1533 nm band FBGs. The experimental results are compared with a single-stage bidirectionally pumped conventional L-EDFA design. It is shown that when the forward and/or the backward ASE noise is partly reinjected to L-EDFA using a double/single 1533 nm fiber Bragg gratings (FBG), the gain and noise figure performance of L-EDFA increases depending on the FBG configuration. The best gain and NF performance in our L-EDFA was achieved by reinjection of forward and backward ASE through FBG1 and FBG2 leading to an 4.5 dB increase in gain and 1 dB decrease in NF at 1585 nm and -30 dBm input signal power. The results show that both FBGs must be used at the same time to improve gain and NF performance in L-band EDFAs.

  10. Unconventional Superconductivity in the BiS_{2}-Based Layered Superconductor NdO_{0.71}F_{0.29}BiS_{2}.

    PubMed

    Ota, Yuichi; Okazaki, Kozo; Yamamoto, Haruyoshi Q; Yamamoto, Takashi; Watanabe, Shuntaro; Chen, Chuangtian; Nagao, Masanori; Watauchi, Satoshi; Tanaka, Isao; Takano, Yoshihiko; Shin, Shik

    2017-04-21

    We investigate the superconducting-gap anisotropy in one of the recently discovered BiS_{2}-based superconductors, NdO_{0.71}F_{0.29}BiS_{2} (T_{c}∼5  K), using laser-based angle-resolved photoemission spectroscopy. Whereas the previously discovered high-T_{c} superconductors such as copper oxides and iron-based superconductors, which are believed to have unconventional superconducting mechanisms, have 3d electrons in their conduction bands, the conduction band of BiS_{2}-based superconductors mainly consists of Bi 6p electrons, and, hence, the conventional superconducting mechanism might be expected. Contrary to this expectation, we observe a strongly anisotropic superconducting gap. This result strongly suggests that the pairing mechanism for NdO_{0.71}F_{0.29}BiS_{2} is an unconventional one and we attribute the observed anisotropy to competitive or cooperative multiple paring interactions.

  11. Impact of the Ionosphere on an L-band Space Based Radar

    NASA Technical Reports Server (NTRS)

    Chapin, Elaine; Chan, Samuel F.; Chapman, Bruce D.; Chen, Curtis W.; Martin, Jan M.; Michel, Thierry R.; Muellerschoen, Ronald J.; Pi, Xiaoqing; Rosen, Paul A.

    2006-01-01

    We have quantified the impact that the ionosphere would have on a L-band interferometric Synthetic Aperture Radar (SAR) mission using a combination of simulation, modeling, Global Positioning System (GPS) data collected during the last solar maximum, and existing spaceborne SAR data. We conclude that, except for high latitude scintillation related effects, the ionosphere will not significantly impact the performance of an L-band InSAR mission in an appropriate orbit. We evaluated the strength of the ionospheric irregularities using GPS scintillation data collected at Fairbanks, Alaska and modeled the impact of these irregularities on azimuth resolution, azimuth displacement, peak sidelobe ratio (PSLR), and integrated sidelobe ratio (ISLR). Although we predict that less than 5% of auroral zone data would show scintillation related artifacts, certain sites imaged near the equinoxes could be effected up to 25% of the time because the frequency of occurrence of scintillation is a strong function of season and local time of day. Our examination of ionospheric artifacts observed in InSAR data has revealed that the artifacts occur primarily in the polar cap data, not auroral zone data as was previously thought.

  12. Impact of Co-Site Interference on L/C-Band Spectrum for UAS Control and Non-Payload Communications

    NASA Technical Reports Server (NTRS)

    Kerczewski, Robert J.; Bishop, William D.; Hoder, Douglas J.; Shalkhauser, Kurt A.; Wilson, Jeffrey D.

    2015-01-01

    In order to provide for the safe integration of unmanned aircraft systems into the National Airspace System, the control and non-payload communications (CNPC) link connecting the ground-based pilot with the unmanned aircraft must be highly reliable. A specific requirement is that it must operate using aviation safety radiofrequency spectrum. The 2012 World Radiocommunication Conference (WRC-12) provided a potentially suitable allocation for LOS CNPC spectrum in C-Band at 5030-5091 MHz band which, when combined with a previous allocation in L-Band (960-1164 MHz) may satisfy the LOS spectrum requirement and provide for high reliability through dual-band redundancy. However, the LBand spectrum hosts a number of aeronautical navigation systems which require high-power transmitters on-board the aircraft. These high-power transmitters co-located with sensitive CNPC receivers operating in the same frequency band have the potential to create co-site interference, reducing the performance of the CNPC receivers and ultimately reducing the usability of the L-Band for CNPC. This paper examines the potential for co-site interference, as highlighted in recent flight tests, and discusses the impact on the UAS CNPC spectrum availability and requirements for further testing and analysis.

  13. Electron—phonon Coupling and the Superconducting Phase Diagram of the LaAlO3—SrTiO3 Interface

    PubMed Central

    Boschker, Hans; Richter, Christoph; Fillis-Tsirakis, Evangelos; Schneider, Christof W.; Mannhart, Jochen

    2015-01-01

    The superconductor at the LaAlO3—SrTiO3 interface provides a model system for the study of two-dimensional superconductivity in the dilute carrier density limit. Here we experimentally address the pairing mechanism in this superconductor. We extract the electron—phonon spectral function from tunneling spectra and conclude, without ruling out contributions of further pairing channels, that electron—phonon mediated pairing is strong enough to account for the superconducting critical temperatures. Furthermore, we discuss the electron—phonon coupling in relation to the superconducting phase diagram. The electron—phonon spectral function is independent of the carrier density, except for a small part of the phase diagram in the underdoped region. The tunneling measurements reveal that the increase of the chemical potential with increasing carrier density levels off and is zero in the overdoped region of the phase diagram. This indicates that the additionally induced carriers do not populate the band that hosts the superconducting state and that the superconducting order parameter therefore is weakened by the presence of charge carriers in another band. PMID:26169351

  14. Cryogenic filters for RFI protection

    NASA Technical Reports Server (NTRS)

    Bautista, J. J.; Petty, S. M.

    1981-01-01

    The increased bandwidth and sensitivity of the DSN maser-based receiver systems along with the increase in worldwide microwave spectrum usage dictated the need for employing additional measures to protect these systems from RFI (radio frequency inerference). Both in-band and out-of-band microwave signals at the input of the Deep Space Network (DSN) traveling wave masers (TWM) can adversely affect the maser performance in a variety of ways. Filters fabricated from superconducting materials operating below their superconducting transition temperature (Tc) possess the most potential for providing the necessary RFI protection without degrading the system performance.

  15. Superconductivity in Li-intercalated bilayer arsenene and hole-doped monolayer arsenene: a first-principles prediction

    NASA Astrophysics Data System (ADS)

    Chen, Jianyong; Ge, Yanfeng; Zhou, Wenzhe; Peng, Mengqi; Pan, Jiangling; Ouyang, Fangping

    2018-06-01

    Using first-principles calculations, we find Li-intercalated bilayer arsenene with AB stacking is dynamically stable, which is different from pristine bilayer with AA stacking. Electron–phonon coupling of the stable Li-intercalated bilayer arsenene are dominated by the low frequency vibrational modes (E″(1), (1), E‧(1) and acoustic modes) and lead to an superconductivity with T c  =  8.68 K with isotropical Eliashberg function. Small biaxial tensile strain (2%) can improve T c to 11.22 K due to the increase of DOS and phonon softening. By considering the fully anisotropic Migdal–Eliashberg theory, T c are found to be enhanced by 50% and exhibits a single anisotropic gap nature. In addition, considering its nearly flat top valence band which is favorable for high temperature superconductivity, we also explore the superconducting properties of hole-doped monolayer arsenene under different strains. the unstrained monolayer arsenene superconducts at T c  =  0.22 K with 0.1 hole/cell doping. By applying 3% biaxial strain, T c can be lifted up strikingly to 6.69 K due to a strong Fermi nesting of the nearly flat band. Then T c decreases slowly with strain. Our findings provide another insight to realize 2D superconductivity and suggest that the strain is crucial to further enhance the transition temperature.

  16. Superconducting quantum circuits theory and application

    NASA Astrophysics Data System (ADS)

    Deng, Xiuhao

    states. The model and toolbox are engineered with a superconducting quantum circuit where two superconducting resonators are coupled via the UQDP circuit. Using fourth order perturbation theory one can realize a complete set of quantum operations between these two photon modes. This helps open a new field to treat photon modes as qubits. Additional, a three-wave mixing scheme using phase qubits permits one to engineer the coupling Hamiltonian using a phase qubit as a tunable coupler. Along with Feynman's idea using quantum to simulate quantum, superconducting quantum simulators have been studied intensively recently. Taking the advantage of mesoscopic size of superconducting circuit and local tunability, we came out the idea to simulate quantum phase transition due to disorder. Our first paper was to propose a superconducting quantum simulator of Bose-Hubbard model to do site-wise manipulation and observe Mott-insulator to superfluid phase transition. The side-band cooling of an array of superconducting resonators is solved after the paper was published. In light of the developed technology in manipulating quantum information with superconducting circuit, one can couple other quantum oscillator system to superconducting resonators in order manipulation of its quantum states or parametric amplification of weak quantum signal. A theory that works for different coupling schemes has been studied in chapter 5. This will be a platform for further research.

  17. Oil spill analysis by means of full polarimetric UAVSAR (L-band) and Radarsat-2 (C-band) products acquired during Deepwater Horizon Disaster

    NASA Astrophysics Data System (ADS)

    Latini, Daniele; Del Frate, Fabio; Jones, Cathleen E.

    2014-10-01

    SAR instruments with polarimetric capabilities, high resolution and short revisit time can provide powerful support in oil spill monitoring and different techniques of analysis have been developed for this purpose [1][2]. An oil film on the sea surface results in darker areas in SAR images, but careful interpretation is required because dark spots can also be caused by natural phenomena. In view of the very low backscatter from slicks, the Noise Equivalent Sigma Zero (NESZ) is a primary sensor parameter to be considered when using a sensor for slick analysis. Among the existing full polarimetric sensors, the high resolution and very low NESZ values of UAVSAR (L-band) and RADARSAT-2 (C-band) make them preferable for oil spill analysis compared to the last generation SAR instruments. The Deepwater Horizon disaster that occurred in the Gulf of Mexico in 2010 represents a unique and extensive test site where large amounts of SAR imagery and ground validation data are available. By applying the Cloude-Pottier decomposition method to full polarimetric UAVSAR (L-band) and RADARSAT-2 (C-band), it is possible to extract parameters that describe the scattering mechanism of the target. By comparing quasi-simultaneous acquisitions and exploiting the different penetration capabilities of the sensors, we investigate the potential of full polarimetric SAR to discriminate oil on the sea surface from look-alike phenomena covering the full range of backscattering values down to those at the instrument noise floor.

  18. A ground based L-band radiometer for the monitoring of soil moisture in the region of Millbrook, New York, USA

    USDA-ARS?s Scientific Manuscript database

    A field experiment was performed in grassland near Millbrook, New York, using a NOAA Microwave Observation Facility, which comprises a network for in situ observation of soil moisture and a mobile dual polarized L band radiometer. During the field campaign, intensive measurements of L band brightnes...

  19. Design of an Airborne L-Band Cross-Track Scanning Scatterometer

    NASA Technical Reports Server (NTRS)

    Hilliard, Lawrence M. (Technical Monitor)

    2002-01-01

    In this report, we describe the design of an airborne L-band cross-track scanning scatterometer suitable for airborne operation aboard the NASA P-3 aircraft. The scatterometer is being designed for joint operation with existing L-band radiometers developed by NASA for soil moisture and ocean salinity remote sensing. In addition, design tradeoffs for a space-based radar system have been considered, with particular attention given to antenna architectures suitable for sharing the antenna between the radar and radiometer. During this study, we investigated a number of imaging techniques, including the use of real and synthetic aperture processing in both the along track and cross-track dimensions. The architecture selected will permit a variety of beamforming algorithms to be implemented, although real aperture processing, with hardware beamforming, provides better sidelobe suppression than synthetic array processing and superior signal-to-noise performance. In our discussions with the staff of NASA GSFC, we arrived at an architecture that employs complete transmit/receive modules for each subarray. Amplitude and phase control at each of the transmit modules will allow a low-sidelobe transmit pattern to be generated over scan angles of +/- 50 degrees. Each receiver module will include all electronics necessary to downconvert the received signal to an IF offset of 30 MHz where it will be digitized for further processing.

  20. Oversized 250 GHz Traveling Wave Tube with a Photonic Band-Gap Structure

    NASA Astrophysics Data System (ADS)

    Rosenzweig, Guy; Shapiro, Michael A.; Temkin, Richard J.

    2017-10-01

    The challenge in manufacturing traveling wave tubes (TWTs) at high frequencies is that the sizes of the structures scale with, and are much smaller than, the wavelength. We have designed and are building a 250 GHz TWT that uses an oversized structure to overcome fabrication and power handling issues that result from the small dimensions. Using a photonic band-gap (PBG) structure, we succeeded to design the TWT with a beam tunnel diameter of 0.72 mm. The circuit consists of metal plates with the beam tunnel drilled down their center. Twelve posts are protruding on one side of each plate in a triangular array and corresponding sockets are drilled on the other side. The posts of each plate are inserted into the sockets of an adjacent plate, forming a PBG lattice. The vacuum spacing between adjacent plates forms the `PBG cavity''. The full structure is a series of PBG coupled cavities, with microwave power coupling through the beam tunnel. The PBG lattice provides confinement of microwave power in each of the cavities and can be tuned to give the right amount of diffraction per cavity so that no sever is needed to suppress oscillations in the operating mode. CST PIC simulations predict over 38 dB gain with 67 W peak power, using a 30 kV, 310 mA electron beam, 0.6 mm in diameter. Research supported by the AFOSR Program on Plasma and Electro-Energetic Physics and by the NIH National Institute of Biomedical Imaging and Bioengineering.

  1. Use of C-band Sentinel-1 and L-band UAVSAR data for flood extent mapping during Hurricane Harvey

    NASA Astrophysics Data System (ADS)

    Lakshmi, V.; Kundu, S.; Torres, R.

    2017-12-01

    Hurricane Harvey was one of the most destructive storms that struck the Houston area in August 2017 causing loss of life and property. In this study, an estimation of flooding extent is done using two sets of microwave remote sensing data, Unmanned Aerial Vehicle Synthetic Aperture Radar (UAVSAR) and Sentinel-1. UAVSAR is an L-band SAR (Synthetic Aperture Radar) data which is an airborne repeat-pass interferometric observation system and has 16 km swath. Sentinel-1 is the C band microwave data developed by European Space Agency covering a large area (250 km). Data are analyzed to examine the flood extent over Houston during Harvey. Flood extent mapping is carried out using the Sentinel-1 data and UAVSAR using backscatter signatures which displays the extent of changes and destruction during the flood. Keywords: Harvey, UAVSAR, Sentinel-1, flood extent

  2. Empirical Soil Moisture Estimation with Spaceborne L-band Polarimetric Radars: Aquarius, SMAP, and PALSAR-2

    NASA Astrophysics Data System (ADS)

    Burgin, M. S.; van Zyl, J. J.

    2017-12-01

    Traditionally, substantial ancillary data is needed to parametrize complex electromagnetic models to estimate soil moisture from polarimetric radar data. The Soil Moisture Active Passive (SMAP) baseline radar soil moisture retrieval algorithm uses a data cube approach, where a cube of radar backscatter values is calculated using sophisticated models. In this work, we utilize the empirical approach by Kim and van Zyl (2009) which is an optional SMAP radar soil moisture retrieval algorithm; it expresses radar backscatter of a vegetated scene as a linear function of soil moisture, hence eliminating the need for ancillary data. We use 2.5 years of L-band Aquarius radar and radiometer derived soil moisture data to determine two coefficients of a linear model function on a global scale. These coefficients are used to estimate soil moisture with 2.5 months of L-band SMAP and L-band PALSAR-2 data. The estimated soil moisture is compared with the SMAP Level 2 radiometer-only soil moisture product; the global unbiased RMSE of the SMAP derived soil moisture corresponds to 0.06-0.07 cm3/cm3. In this study, we leverage the three diverse L-band radar data sets to investigate the impact of pixel size and pixel heterogeneity on soil moisture estimation performance. Pixel sizes range from 100 km for Aquarius, over 3, 9, 36 km for SMAP, to 10m for PALSAR-2. Furthermore, we observe seasonal variation in the radar sensitivity to soil moisture which allows the identification and quantification of seasonally changing vegetation. Utilizing this information, we further improve the estimation performance. The research described in this paper is supported by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Copyright 2017. All rights reserved.

  3. High-Efficiency K-Band Space Traveling-Wave Tube Amplifier for Near-Earth High Data Rate Communications

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Force, Dale A.; Spitsen, Paul C.; Menninger, William L.; Robbins, Neal R.; Dibb, Daniel R.; Todd, Phillip

    2010-01-01

    The RF performance of a new K-Band helix conduction cooled traveling-wave tube amplifier (TWTA) is presented in this paper. A total of three such units were manufactured, tested and delivered. The first unit is currently flying onboard NASA s Lunar Reconnaissance Orbiter (LRO) spacecraft and has flawlessly completed over 2000 orbits around the Moon. The second unit is a proto-flight model. The third unit will fly onboard NASA s International Space Station (ISS) as a very compact and lightweight transmitter package for the Communications, Navigation and Networking Reconfigurable Testbed (CoNNeCT), which is scheduled for launch in 2011. These TWTAs were characterized over the frequencies 25.5 to 25.8 GHz. The saturated RF output power is >40 W and the saturated RF gain is >46 dB. The saturated AM-to- PM conversion is 3.5 /dB and the small signal gain ripple is 0.46 dB peak-to-peak. The overall efficiency of the TWTA, including that of the electronic power conditioner (EPC) is as high as 45 percent.

  4. High-Efficiency K-Band Space Traveling-Wave Tube Amplifier for Near-Earth High Data Rate Communications

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Force, Dale A.; Spitsen, Paul C.; Menninger, William L.; Robbins, Neal R.; Dibb, Daniel R.; Todd, Phillip C.

    2010-01-01

    The RF performance of a new K-Band helix conduction cooled traveling-wave tube amplifier (TWTA), is presented in this paper. A total of three such units were manufactured, tested and delivered. The first unit is currently flying onboard NASA's Lunar Reconnaissance Orbiter (LRO) spacecraft and has flawlessly completed over 2000 orbits around the Moon. The second unit is a proto-flight model. The third unit will fly onboard NASA's International Space Station (ISS) as a very compact and lightweight transmitter package for the Communications, Navigation and Networking Reconfigurable Testbed (CoNNeCT), which is scheduled for launch in 2011. These TWTAs were characterized over the frequencies 25.5 to 25.8 GHz. The saturated RF output power is greater than 40 W and the saturated RF gain is greater than 46 dB. The saturated AM-to-PM conversion is 3.5 /dB and the small signal gain ripple is 0.46 dB peak-to-peak. The overall efficiency of the TWTA, including that of the electronic power conditioner (EPC) is as high as 45%.

  5. The elderly traveller.

    PubMed

    Ramos-Sesma, V; Górgolas-Hernández Mora, M; Ramos-Rincón, J M

    2018-04-20

    Improved living conditions and advances in medicine have extended life expectancy and quality of life, resulting in an increasing number of elderly travellers. Pathophysiological changes and treatments can reduce the efficacy of vaccines and facilitate drug interactions. Elderly travellers have various characteristics that should be considered when offering pre-trip counselling, which should include proper management of chronic diseases that are susceptible to worsening during the trip, as well as an appropriate study and follow-up after the trip. We performed a narrative review of the main problems of elderly travellers. Copyright © 2018 Elsevier España, S.L.U. and Sociedad Española de Medicina Interna (SEMI). All rights reserved.

  6. Inducing Strong Superconductivity in WTe2 by a Proximity Effect.

    PubMed

    Huang, Ce; Narayan, Awadhesh; Zhang, Enze; Liu, Yanwen; Yan, Xiao; Wang, Jiaxiang; Zhang, Cheng; Wang, Weiyi; Zhou, Tong; Yi, Changjiang; Liu, Shanshan; Ling, Jiwei; Zhang, Huiqin; Liu, Ran; Sankar, Raman; Chou, Fangcheng; Wang, Yihua; Shi, Youguo; Law, Kam Tuen; Sanvito, Stefano; Zhou, Peng; Han, Zheng; Xiu, Faxian

    2018-06-21

    The search for proximity-induced superconductivity in topological materials has generated widespread interest in the condensed matter physics community. The superconducting states inheriting nontrivial topology at interfaces are expected to exhibit exotic phenomena such as topological superconductivity and Majorana zero modes, which hold promise for applications in quantum computation. However, a practical realization of such hybrid structures based on topological semimetals and superconductors has hitherto been limited. Here, we report the strong proximity-induced superconductivity in type-II Weyl semimetal WTe 2 , in a van der Waals hybrid structure obtained by mechanically transferring NbSe 2 onto various thicknesses of WTe 2 . When the WTe 2 thickness ( t WTe 2 ) reaches 21 nm, the superconducting transition occurs around the critical temperature ( T c ) of NbSe 2 with a gap amplitude (Δ p ) of 0.38 meV and an unexpected ultralong proximity length ( l p ) up to 7 μm. With the thicker 42 nm WTe 2 layer, however, the proximity effect yields T c ≈ 1.2 K, Δ p = 0.07 meV, and a short l p of less than 1 μm. Our theoretical calculations, based on the Bogoliubov-de Gennes equations in the clean limit, predict that the induced superconducting gap is a sizable fraction of the NbSe 2 superconducting one when t WTe 2 is less than 30 nm and then decreases quickly as t WTe 2 increases. This agrees qualitatively well with the experiments. Such observations form a basis in the search for superconducting phases in topological semimetals.

  7. False-color L-band image of Manaus region of Brazil

    NASA Technical Reports Server (NTRS)

    1994-01-01

    This false-color L-band image of the Manaus region of Brazil was acquired by the Spaceborne Imaging Radar-C/X-band Synthetic Aperature Radar (SIR-C/X-SAR) flying on the Space Shuttle Endeavour on its 46th orbit. The area shown is approximately 8 kilometers by 40 kilometers (5 by 25 miles). At the top of the image are the Solimoes and Rio Negro River. The image is centered at about 3 degrees south latitude, and 61 degrees west longitude. Blue areas show low returns at VV poloarization; hence the bright blue colors of the smooth river surfaces. Green areas in the image are heavily forested, while blue areas are either cleared forest or open water. The yellow and red areas are flooded forest. Between Rio Solimoes and Rio Negro, a road can be seen running from some cleared areas (visible as blue rectangles north of Rio Solimoes) north toward a tributary or Rio Negro. The Jet Propulsion Laboratory alternative photo number is P-43895.

  8. Topological aspect and transport property in multi-band spin-triplet chiral p-wave superconductor Sr2RuO4

    NASA Astrophysics Data System (ADS)

    Imai, Yoshiki; Wakabayashi, Katsunori; Sigrist, Manfred

    2015-03-01

    Considering the superconductor Sr2RuO4, we analyze a three-band tight-binding model with one hole-like and two electron-like Fermi surfaces corresponding to the α, β and γ bands of Sr2RuO4 by means of a self-consistent Bogoliubov-de Gennes approach for ribbonshaped system to investigate topological properties and edge states. In the superconducting phase two types of gapless edge states can be identified, one of which displays an almost flat dispersion at zero energy, while the other, originating from the γ band, has a linear dispersion and constitutes a genuine chiral edge states. Not only a charge current appears at the edges but also a spin current due to the multi-band effect in the superconducting phase. In particular, the chiral edge state from the γ band is closely tied to topological properties, and the chiral p-wave superconducting states are characterized by an integer topological number, the so-called Chern number. We show that the γ band is close to a Lifshitz transition. Since the sign of the Chern number may be very sensitive to the surface condition, we consider the effect of the surface reconstruction observed in Sr2RuO4 on the topological property and show the possibility of the hole-like Fermi surface at the surface.

  9. Simple and efficient L-band erbium-doped fiber amplifiers for WDM networks

    NASA Astrophysics Data System (ADS)

    Choi, H. B.; Oh, J. M.; Lee, D.; Ahn, S. J.; Park, B. S.; Lee, S. B.

    2002-11-01

    The performance of L-band erbium-doped fiber amplifier (EDFA) of a simple structure with a fiber Bragg grating (FBG) was investigated. The injected C-band ASE by the FBG offers low-cost amplification and greatly improves the efficiency of the EDFA. There are 9 and 4 dB improvements with the FBG at 1587 nm, at low and high input, respectively. The flat gain of 18 dB, up to a total input of -5 dBm at 150 mW of 980 nm pump, is obtained over 30 nm with less than ±0.5 dB gain variations without any gain equalizer. The proposed EDFA provides a cost-effective solution for wavelength division multiplexing systems.

  10. Electronic, phonon and superconducting properties of LaPtBi half-Heusler compound

    NASA Astrophysics Data System (ADS)

    Shrivastava, Deepika; Sanyal, Sankar P.

    2018-05-01

    In the framework of density functional theory based on plane wave pseudopotential method and linear response technique, we have studied the electronic, phonon and superconducting properties of LaPtBi half-Heusler compound. The electronic band structure and density of states show that it is gapless semiconductor which is consistent with previous results. The positive phonon frequencies confirm the stability of this compound in cubic MgAgAs phase. Superconductivity is studied in terms of Eliashberg spectral function (α2F(ω)), electron-phonon coupling constants (λ). The value of electron-phonon coupling parameter is found to be 0.41 and the superconducting transition temperature is calculated to be 0.76 K, in excellent agreement with the experimentally reported values.

  11. An increase in Tc under hydrostatic pressure in the superconducting doped topological insulator Nb0.25Bi2Se3

    NASA Astrophysics Data System (ADS)

    Smylie, M. P.; Willa, K.; Ryan, K.; Claus, H.; Kwok, W.-K.; Qiu, Y.; Hor, Y. S.; Welp, U.

    2017-12-01

    We report a positive hydrostatic pressure derivative of the superconducting transition temperature in the doped topological insulator Nb0.25Bi2Se3 via dc SQUID magnetometry in pressures up to 0.6 GPa. This result is contrary to reports on the homologues CuxBi2Se3 and SrxBi2Se3 where smooth suppression of Tc is observed. This difference may be attributable to an electronic structure composed of multiple bands whereas the other materials in the superconducting doped Bi2Se3 family are believed to be single-band.

  12. Electronic network for monitoring travellers' diarrhoea and detection of an outbreak caused by Salmonella enteritidis among overseas travellers.

    PubMed

    Osaka, K; Inouye, S; Okabe, N; Taniguchi, K; Izumiya, H; Watanabe, H; Matsumoto, Y; Yokota, T; Hashimoto, S; Sagara, H

    1999-12-01

    The Traveller's Diarrhoea Network, by which the Infectious Disease Surveillance Center is electronically connected with two major airport quarantine stations and three infectious disease hospitals, was launched in February 1988 in Japan. The data on travellers' diarrhoea detected is reported weekly by e-mail. Two clusters of infection among travellers returning from Italy were reported by two airport quarantine stations at the end of September 1998. A total of 12 salmonella isolates from 2 clusters were examined. All were identified as Salmonella enteritidis, phage type 4 and showed identical banding patterns on pulsed-field gel electrophoresis. A case-control study showed that the scrambled eggs served at the hotel restaurant in Rome were the likely source of this outbreak. This outbreak could not have been detected promptly and investigated easily without the e-mail network. International exchange of data on travellers' diarrhoea is important for preventing and controlling food-borne illnesses infected abroad.

  13. Subgap transport in silicene-based superconducting hybrid structures

    NASA Astrophysics Data System (ADS)

    Li, Hai

    2016-08-01

    We investigate the influences of exchange field and perpendicular electric field on the subgap transport in silicene-based ferromagnetic/superconducting (FS) and ferromagnetic/superconducting/ferromagnetic (FSF) junctions. Owing to the unique buckling structure of silicene, the Andreev reflection and subgap conductance can be effectively modulated by a perpendicular electric field. It is revealed that the subgap conductance in the FS junction can be distinctly enhanced by an exchange field. Remarkably, resorting to the tunable band gap of silicene, an exclusive crossed Andreev reflection (CAR) process in the FSF junction can be realized within a wide range of related parameters. Moreover, in the FSF junction the exclusive CAR and exclusive elastic cotunneling processes can be switched by reversing the magnetization direction in one of the ferromagnetic regions.

  14. Superconducting Magnet Shielding of Astronauts from Cosmic Rays

    NASA Astrophysics Data System (ADS)

    Fisher, Peter; Hoffman, Jeffrey; Zhou, Feng; Batishchev, Oleg

    2004-11-01

    Protecting astronauts traveling outside the Earth's protective magnetic field from cosmic and solar radiation [1] is one of the critical problems that must be solved in order to realize the nation's new human space exploration vision. Superconducting magnets, such as those under construction for the ATLAS experiment [2] at CERN, have achieved sufficient size to be able to surround a reasonable habitable volume, and their field strength is high enough to deflect a significant portion of the incoming radiation. We have undertaken a research effort aimed at developing an accurate numerical model of a crew compartment surrounded by a large magnetic field, with which we can calculate the effect on incoming charged particles. We will use this model to optimize the magnetic configuration to produce the maximum shielding effect while minimizing the mass of the superconducting magnet system. We are also investigating some of the practical problems that must be solved if large, superconducting magnet systems are to be incorporated into human space systems. We will present preliminary results of our modeling, showing the reduction of radiation exposure as a function of energy and atomic species. [1] Review of Particle Physics, Ed. Particle Data Group, Phys. Lett. B, 1-4 (592) 1-1109, 2004 [2] http://atlasexperiment.org/

  15. G-band harmonic multiplying gyrotron traveling-wave amplifier with a mode-selective circuit

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Yeh, Y. S.; Chen, Chang-Hong; Wang, Z. W.

    Harmonic multiplying gyrotron traveling-wave amplifiers (gyro-TWAs) permit for magnetic field reduction and frequency multiplication. A high-order-mode harmonic multiplying gyro-TWA with large circuit dimensions and low ohmic loss can achieve a high average power. By amplifying a fundamental harmonic TE{sub 01} drive wave, the second harmonic component of the beam current initiates a TE{sub 02} wave to be amplified. Wall losses can suppress some competing modes because they act as an effective sink of the energy of the modes. However, such wall losses do not suppress all competing modes as the fields are contracted in the copper section in the gyro-TWA.more » An improved mode-selective circuit, using circular waveguides with the specified radii, can provide the rejection points within the frequency range to suppress the competing modes. The simulated results reveal that the mode-selective circuit can provide an attenuation of more than 10 dB to suppress the competing modes (TE{sub 21}, TE{sub 51}, TE{sub 22}, and TE{sub 03}). A G-band second harmonic multiplying gyro-TWA with the mode-selective circuit is predicted to yield a peak output power of 50 kW at 198.8 GHz, corresponding to a saturated gain of 55 dB at an interaction efficiency of 10%. The full width at half maximum bandwidth is 5 GHz.« less

  16. Effects of the equatorial ionosphere on L-band Earth-space transmissions

    NASA Technical Reports Server (NTRS)

    Smith, Ernest K.; Flock, Warren L.

    1993-01-01

    Ionosphere scintillation can effect satellite telecommunication up to Ku-band. Nighttime scintillation can be attributed to large-scale inhomogeneity in the F-region of the ionosphere predominantly between heights of 200 and 600 km. Daytime scintillation has been attributed to sporadic E. It can be thought of as occurring in three belts: equatorial, high-latitude, and mid-latitude, in order of severity. Equatorial scintillation occurs between magnetic latitudes +/- 25 degrees, peaking near +/- 10 degrees. It commonly starts abruptly near 2000 local time and dies out shortly after midnight. There is a strong solar cycle dependence and a seasonal preference for the equinoxes, particularly the vernal one. Equatorial scintillation occurs more frequently on magnetically quiet than on magnetically disturbed days in most longitudes. At the peak of the sunspot cycle scintillation depths as great as 20 dB were observed at L-band.

  17. Superconductivity Induced by Oxygen Doping in Y2 O2 Bi.

    PubMed

    Cheng, Xiyue; Gordon, Elijah E; Whangbo, Myung-Hwan; Deng, Shuiquan

    2017-08-14

    When doped with oxygen, the layered Y 2 O 2 Bi phase becomes a superconductor. This finding raises questions about the sites for doped oxygen, the mechanism of superconductivity, and practical guidelines for discovering new superconductors. We probed these questions in terms of first-principles calculations for undoped and O-doped Y 2 O 2 Bi. The preferred sites for doped O atoms are the centers of Bi 4 squares in the Bi square net. Several Bi 6p x/y bands of Y 2 O 2 Bi are raised in energy by oxygen doping because the 2p x/y orbitals of the doped oxygen make antibonding possible with the 6p x/y orbitals of surrounding Bi atoms. Consequently, the condition necessary for the "flat/steep" band model for superconductivity is satisfied in O-doped Y 2 O 2 Bi. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. An L-band SAR for repeat pass deformation measurements on a UAV platform

    NASA Technical Reports Server (NTRS)

    Wheeler, Kevin; Hensley, Scott; Lou, Yunling

    2004-01-01

    We are proposing to develop a miniaturized polarimetric L-band synthetic aperture radar (SAR) for repeatpass differential interferometric measurements of deformation for rapidly deforming surfaces of geophysical interest such as volcanoes or earthquakes that is to be flown on a unmanned aerial vehicle (UAV or minimally piloted vehicle (MPV).

  19. An L-band transit-time oscillator with mechanical frequency tunability

    NASA Astrophysics Data System (ADS)

    Song, Lili; He, Juntao; Ling, Junpu; Cao, Yibing

    2017-02-01

    An L-band coaxial Transit-time Oscillator (TTO) with mechanical frequency tunability is introduced in this paper. Particle-in-cell simulations have been done. The output power efficiency has been improved at least 20% under a 10.2 GW input power and with a tunable range from 1.57 GHz to 1.90 GHz by modulating the outer conductor. It is worth to note that the efficiency can reach as high as 41% at 1.75 GHz. The mechanical engineering method is also detailed in this work. The frequency tuning range of the coaxial TTO is 22.6% of the central frequency. On the other hand, the frequency can be tuned from 1.6 GHz to 1.85 GHz by modulating the inner conductor. The author highlights a hollow structure of the L-band coaxial TTO which can work from 1.03 GHz to 1.31 GHz via modulating the outer conductor in the rest of the article. The frequency tuning range of the hollow TTO is 21.4% of the central frequency. More importantly, the hollow TTO can be easily achieved after the inner conductor is removed from the coaxial TTO. The electric field distributions of the coaxial and hollow TTOs are analyzed, resulting in that the longitudinal and transverse working modes are TM01 and π mode, respectively. The same working mode from these two structures implies the stability of the TTOs mentioned above.

  20. Single-sideband modulator for frequency domain multiplexing of superconducting qubit readout

    NASA Astrophysics Data System (ADS)

    Chapman, Benjamin J.; Rosenthal, Eric I.; Kerckhoff, Joseph; Vale, Leila R.; Hilton, Gene C.; Lehnert, K. W.

    2017-04-01

    We introduce and experimentally characterize a superconducting single-sideband modulator compatible with cryogenic microwave circuits and propose its use for frequency domain multiplexing of superconducting qubit readout. The monolithic double-balanced modulators that comprise the device are formed with purely reactive elements (capacitors and Josephson junction inductors) and require no microwave-frequency control tones. Microwave signals in the 4 to 8 GHz band, with power up to -85 dBm, are converted up or down in frequency by as much as 120 MHz. Spurious harmonics in the device can be suppressed by up to 25 dB for select probe and modulation frequencies.

  1. [Vaccination for international travelers].

    PubMed

    Arrazola, M Pilar; Serrano, Almudena; López-Vélez, Rogelio

    2016-05-01

    Traveler's vaccination is one of the key strategies for the prevention of infectious diseases during international travel. The risk of acquiring an infectious disease is determined in each case by the characteristics of the traveler and the travel, so the pre-departure medical advice of the traveler must be individualized. The World Health Organization classifies travelerś vaccines into three groups. - Vaccines for routine use in national immunization programs: Haemophilus influenzae type b, hepatitis B, polio, measles-mumps-rubella, tetanus-diphtheria-whooping a cough, and chickenpox. - Vaccinations required by law in certain countries before to enter them: yellow fever, meningococcal disease and poliomyelitis. - Vaccines recommended depending on the circumstances: cholera, japanese encephalitis, tick-borne encephalitis, meningococcal disease, typhoid fever, influenza, hepatitis A, hepatitis B, rabies and BCG. This review is intended to introduce the reader to the field of international vaccination. Copyright © 2016 Elsevier España, S.L.U. y Sociedad Española de Enfermedades Infecciosas y Microbiología Clínica. All rights reserved.

  2. Aquarius L-Band Radiometers Calibration Using Cold Sky Observations

    NASA Technical Reports Server (NTRS)

    Dinnat, Emmanuel P.; Le Vine, David M.; Piepmeier, Jeffrey R.; Brown, Shannon T.; Hong, Liang

    2015-01-01

    An important element in the calibration plan for the Aquarius radiometers is to look at the cold sky. This involves rotating the satellite 180 degrees from its nominal Earth viewing configuration to point the main beams at the celestial sky. At L-band, the cold sky provides a stable, well-characterized scene to be used as a calibration reference. This paper describes the cold sky calibration for Aquarius and how it is used as part of the absolute calibration. Cold sky observations helped establish the radiometer bias, by correcting for an error in the spillover lobe of the antenna pattern, and monitor the long-term radiometer drift.

  3. Radar measurement of L-band signal fluctuations caused by propagation through trees

    NASA Technical Reports Server (NTRS)

    Durden, Stephen L.; Klein, Jeffrey D.; Zebker, Howard A.

    1991-01-01

    Fluctuations of an L-band, horizontally polarized signal that was transmitted from the ground through a coniferous forest canopy to an airborne radar are examined. The azimuth synthetic aperture radar (SAR) impulse response in the presence of the measured magnitude fluctuations shows increased sidelobes over the case with no trees. Statistics of the observed fluctuations are similar to other observations.

  4. In-plane magnetic penetration depth of superconducting CaKFe4As4

    NASA Astrophysics Data System (ADS)

    Khasanov, Rustem; Meier, William R.; Wu, Yun; Mou, Daixiang; Bud'ko, Sergey L.; Eremin, Ilya; Luetkens, Hubertus; Kaminski, Adam; Canfield, Paul C.; Amato, Alex

    2018-04-01

    The temperature dependence of the in-plane magnetic penetration depth (λa b) in an extensively characterized sample of superconducting CaKFe4As4(Tc≃35 K ) was investigated using muon-spin rotation (μ SR ). A comparison of λab -2(T ) measured by μ SR with the one inferred from angle-resolved photoemission spectroscopy (ARPES) data confirms the presence of multiple gaps at the Fermi level. An agreement between μ SR and ARPES requires the presence of additional bands, which are not resolved by ARPES experiments. These bands are characterized by small superconducting gaps with an average zero-temperature value of Δ0=2.4 (2 ) meV . Our data suggest that in CaKFe4As4 the s± order parameter symmetry acquires a more sophisticated form by allowing a sign change not only between electron and hole pockets, but also within pockets of similar type.

  5. Magnetic scattering effects in two-band superconductor: the ferromagnetic dopants in MgB₂.

    PubMed

    Li, W X; Zeng, R; Poh, C K; Li, Y; Dou, S X

    2010-04-07

    This paper demonstrates the magnetic scattering effects on the electron-phonon interaction in two-band superconductors based on the transition-metal-doped MgB₂ to clarify the effects of magnetic dopants on multi-band superconductivity. The phonon properties of polycrystalline Mg(1-x)M(x)B₂ (M = Fe, Ni and Co), with x up to 0.05, were studied, with the investigation based on the normal state Raman spectra, especially the variation of the E(2g) mode. The magnetic scattering effect of Fe is much weaker than that of Mn in MgB₂, while it is stronger than that of Ni. The weak magnetic scattering effects are responsible for the superconducting behaviors of Mg(1 - x)Fe(x)B₂ and Mg(1 - x)Ni(x)B₂. Co shows almost no magnetic scattering effects on the superconductivity, while the depression of the critical temperature, T(c), in Mg(1 - x)Co(x)B₂ is attributed to the phonon behavior and is independent of the ferromagnetic nature of cobalt.

  6. Spectroscopic evidence for two-gap superconductivity in the quasi-1D chalcogenide Nb2Pd0.81S5

    NASA Astrophysics Data System (ADS)

    Park, Eunsung; Lee, Sangyun; Ronning, Filip; Thompson, Joe D.; Zhang, Qiu; Balicas, Luis; Lu, Xin; Park, Tuson

    2018-04-01

    Low-dimensional electronic systems with confined electronic wave functions have attracted interest due to their propensity toward novel quantum phases and their use in wide range of nanotechnologies. The newly discovered chalcogenide Nb2PdS5 possesses a quasi-one-dimensional electronic structure and becomes superconducting. Here, we report spectroscopic evidence for two-band superconductivity, where soft point-contact spectroscopic measurements in the superconducting (SC) state reveal Andreev reflection in the differential conductance G. Multiple peaks in G are observed at 1.8 K and explained by the two-band Blonder–Tinkham–Klapwijk model with two gaps Δ1  =  0.61 meV and Δ2  =  1.20 meV. The progressive evolution of G with temperature and magnetic field corroborates the multiple nature of the SC gaps.

  7. X-band preamplifier filter

    NASA Technical Reports Server (NTRS)

    Manshadi, F.

    1986-01-01

    A low-loss bandstop filter designed and developed for the Deep Space Network's 34-meter high-efficiency antennas is described. The filter is used for protection of the X-band traveling wave masers from the 20-kW transmitter signal. A combination of empirical and theoretical techniques was employed as well as computer simulation to verify the design before fabrication.

  8. Wide-band fanned-out supercontinuum source covering O-, E-, S-, C-, L- and U-bands

    NASA Astrophysics Data System (ADS)

    Ahmad, H.; Latif, A. A.; Awang, N. A.; Zulkifli, M. Z.; Thambiratnam, K.; Ghani, Z. A.; Harun, S. W.

    2012-10-01

    A wide-band supercontinuum source generated by mode-locked pulses injected into a Highly Non-Linear Fiber (HNLF) is proposed and demonstrated. A 49 cm long Bismuth-Erbium Doped Fiber (Bi-EDF) pumped by two 1480 nm laser diodes acts as the active gain medium for a ring fiber laser, from which mode-locked pulses are obtained using the Non-Polarization Rotation (NPR) technique. The mode-locked pulses are then injected into a 100 m long HLNF with a dispersion of 0.15 ps/nm km at 1550 nm to generate a supercontinuum spectrum spanning from 1340 nm to more than 1680 nm with a pulse width of 0.08 ps and an average power of -17 dBm. The supercontinuum spectrum is sliced using a 24 channel Arrayed Waveguide Grating (AWG) with a channel spacing of 100 GHz to obtain a fanned-out laser output covering the O-, E-, S-, C-, L- and U-bands. The lasing wavelengths obtained have an average pulse width of 9 ps with only minor fluctuations and a mode-locked repetition rate of 40 MHz, and is sufficiently stable to be used in a variety of sensing and communication applications, most notably as cost-effective sources for Fiber-to-the-Home (FTTH) networks.

  9. 200 MW S-band traveling wave resonant ring development at IHEP

    NASA Astrophysics Data System (ADS)

    Zhou, Zu-Sheng; Chi, Yun-Long; Git, Meng-Ping; Pei, Guo-Xi

    2010-03-01

    The resonant-ring is a traveling wave circuit, which is used to produce high peak power with comparatively smaller stored energy. The application to be considered is its use as a high power simulator mainly for testing the klystron ceramic output window, as well as for high power microwave transmission devices. This paper describes the principle of a resonant ring and introduces the structure and property of the newly constructed traveling wave resonant ring at IHEP. Our goal is to produce a 200 MW class resonant ring at 2.856 GHz with a pulse length of 2 μs and repetition rate of 25 Hz. The installation, commissioning and testing of the ring have been completed and a peak power of 200 MW at 3 μs has been achieved. The conditioning results show that all the parameters of the resonant ring reach the design goals.

  10. Use of IRI to Model the Effect of Ionosphere Emission on Earth Remote Sensing at L-Band

    NASA Technical Reports Server (NTRS)

    Abraham, Saji; LeVine, David M.

    2004-01-01

    Microwave remote sensing in the window at 1.413 GHz (L-band) set aside for passive use only is important for monitoring sea surface salinity and soil moisture. These parameters are important for understanding ocean dynamics and energy exchange between the surface and atmosphere, and both NASA and ESA plan to launch satellite sensors to monitor these parameters at L-band (Aquarius, Hydros and SMOS). The ionosphere is an important source of error for passive remote sensing at this frequency. In addition to Faraday rotation, emission from the ionosphere is also a potential source of error at L-band. As an aid for correcting for emission, a regression model is presented that relates ionosphere emission to the integrated electron density (TEC). The goal is to use TEC from sources such as TOPEX, JASON or GPS to obtain estimates of emission over the oceans where the electron density profiles needed to compute emission are not available. In addition, data will also be presented to evaluate the use of the IRI for computing emission over the ocean.

  11. Measurement and Analysis of L-Band (1535-1660 MHz) Electromagnetic (EM) Noise on Ships

    DOT National Transportation Integrated Search

    1974-12-01

    A program of L-band (1535-1660 MHz) electromagnetic (EM) noise measurements conducted on ships is described. The magnitude and duration of EM noise on ships is of particular significance in terms of potential radio frequency interference (RFI) to fut...

  12. Systems implications of L-band fade data statistics for LEO mobile systems

    NASA Astrophysics Data System (ADS)

    Devieux, Carrie L.

    This paper examines and analyzes research data on the role of foliage attenuation in signal fading between a satellite transmitter and a terrestrial vehicle-mounted receiver. The frequency band of measurement, called L-Band, includes the region 1610.0 to 1626.5 MHz. Data from tests involving various combinations of foliage and vehicle movement conditions clearly show evidence of fast fading (in excess of 0.5 dB per millisecond) and fade depths as great or greater than 16 dB. As a result, the design of a communications link power control that provides the level of accuracy necessary for power sensitive systems could be significantly impacted. Specific examples of this include the communications links that employ Code Division Multiple Access (CDMA) as a modulation technique.

  13. Systems implications of L-band fade data statistics for LEO mobile systems

    NASA Technical Reports Server (NTRS)

    Devieux, Carrie L.

    1993-01-01

    This paper examines and analyzes research data on the role of foliage attenuation in signal fading between a satellite transmitter and a terrestrial vehicle-mounted receiver. The frequency band of measurement, called L-Band, includes the region 1610.0 to 1626.5 MHz. Data from tests involving various combinations of foliage and vehicle movement conditions clearly show evidence of fast fading (in excess of 0.5 dB per millisecond) and fade depths as great or greater than 16 dB. As a result, the design of a communications link power control that provides the level of accuracy necessary for power sensitive systems could be significantly impacted. Specific examples of this include the communications links that employ Code Division Multiple Access (CDMA) as a modulation technique.

  14. Superconductivity with extremely large upper critical fields in Nb2Pd0.81S5

    PubMed Central

    Zhang, Q.; Li, G.; Rhodes, D.; Kiswandhi, A.; Besara, T.; Zeng, B.; Sun, J.; Siegrist, T.; Johannes, M. D.; Balicas, L.

    2013-01-01

    Here, we report the discovery of superconductivity in a new transition metal-chalcogenide compound, i.e. Nb2Pd0.81S5, with a transition temperature Tc ≅ 6.6 K. Despite its relatively low Tc, it displays remarkably high and anisotropic superconducting upper critical fields, e.g. μ0Hc2 (T → 0 K) > 37 T for fields applied along the crystallographic b-axis. For a field applied perpendicularly to the b-axis, μ0Hc2 shows a linear dependence in temperature which coupled to a temperature-dependent anisotropy of the upper critical fields, suggests that Nb2Pd0.81S5 is a multi-band superconductor. This is consistent with band structure calculations which reveal nearly cylindrical and quasi-one-dimensional Fermi surface sheets having hole and electron character, respectively. The static spin susceptibility as calculated through the random phase approximation, reveals strong peaks suggesting proximity to a magnetic state and therefore the possibility of unconventional superconductivity. PMID:23486091

  15. Theory of parametrically amplified electron-phonon superconductivity

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Babadi, Mehrtash; Knap, Michael; Martin, Ivar

    2017-07-01

    Ultrafast optical manipulation of ordered phases in strongly correlated materials is a topic of significant theoretical, experimental, and technological interest. Inspired by a recent experiment on light-induced superconductivity in fullerenes [M. Mitrano et al., Nature (London) 530, 461 (2016)], we develop a comprehensive theory of light-induced superconductivity in driven electron-phonon systemswith lattice nonlinearities. In analogy with the operation of parametric amplifiers, we show how the interplay between the external drive and lattice nonlinearities lead to significantly enhanced effective electron-phonon couplings. We provide a detailed and unbiased study of the nonequilibrium dynamics of the driven system using the real-time Green's functionmore » technique. To this end, we develop a Floquet generalization of the Migdal-Eliashberg theory and derive a numerically tractable set of quantum Floquet-Boltzmann kinetic equations for the coupled electron-phonon system. We study the role of parametric phonon generation and electronic heating in destroying the transient superconducting state. Finally, we predict the transient formation of electronic Floquet bands in time-and angle-resolved photoemission spectroscopy experiments as a consequence of the proposed mechanism.« less

  16. Superconducting properties of under- and over-doped BaxK1‑xBiO3 perovskite oxide

    NASA Astrophysics Data System (ADS)

    Szczȩśniak, D.; Kaczmarek, A. Z.; Szczȩśniak, R.; Turchuk, S. V.; Zhao, H.; Drzazga, E. A.

    2018-06-01

    In this study, we investigate the thermodynamic properties of the BaxK1‑xBiO3 (BKBO) superconductor in the under- (x = 0.5) and over-doped (x = 0.7) regime, within the framework of the Migdal-Eliashberg formalism. The analysis is conducted to verify that the electron-phonon pairing mechanism is responsible for the induction of the superconducting phase in the mentioned compound. In particular, we show that BKBO is characterized by the relatively high critical value of the Coulomb pseudopotential, which changes with doping level and does not follow the Morel-Anderson model. In what follows, the corresponding superconducting band gap size and related dimensionless ratio are estimated to increase with the doping, in agreement with the experimental predictions. Moreover, the effective mass of electrons is found to take on high values in the entire doping and temperature region. Finally, the characteristic dimensionless ratios for the superconducting band gap, the critical magnetic field and the specific heat for the superconducting state are predicted to exceed the limits set within the Bardeen-Cooper-Schrieffer theory, suggesting pivotal role of the strong-coupling and retardation effects in the analyzed compound. Presented results supplement our previous investigations and account for the strong-coupling phonon-mediated character of the superconducting phase in BKBO at any doping level.

  17. Chiral plaquette polaron theory of cuprate superconductivity

    NASA Astrophysics Data System (ADS)

    Tahir-Kheli, Jamil; Goddard, William A., III

    2007-07-01

    Ab initio density functional calculations on explicitly doped La2-xSrxCuO4 find that doping creates localized holes in out-of-plane orbitals. A model for cuprate superconductivity is developed based on the assumption that doping leads to the formation of holes on a four-site Cu plaquette composed of the out-of-plane A1 orbitals apical Opz , planar Cud3z2-r2 , and planar Opσ . This is in contrast to the assumption of hole doping into planar Cudx2-y2 and Opσ orbitals as in the t-J model. Allowing these holes to interact with the d9 spin background leads to chiral polarons with either a clockwise or anticlockwise charge current. When the polaron plaquettes percolate through the crystal at x≈0.05 for La2-xSrxCuO4 , a Cudx2-y2 and planar Opσ band is formed. The computed percolation doping of x≈0.05 equals the observed transition to the “metallic” and superconducting phase for La2-xSrxCuO4 . Spin exchange Coulomb repulsion with chiral polarons leads to d -wave superconducting pairing. The equivalent of the Debye energy in phonon superconductivity is the maximum energy separation between a chiral polaron and its time-reversed partner. This energy separation is on the order of the antiferromagnetic spin coupling energy, Jdd˜0.1eV , suggesting a higher critical temperature. An additive skew-scattering contribution to the Hall effect is induced by chiral polarons and leads to a temperature dependent Hall effect that fits the measured values for La2-xSrxCuO4 . The integrated imaginary susceptibility, observed by neutron spin scattering, satisfies ω/T scaling due to chirality and spin-flip scattering of polarons along with a uniform distribution of polaron energy splittings. The derived functional form is compatible with experiments. The static spin structure factor for chiral spin coupling of the polarons to the undoped antiferromagnetic Cud9 spins is computed for classical spins on large two-dimensional lattices and is found to be incommensurate with a

  18. Evaluation of Spaceborne L-band Radiometer Measurements for Terrestrial Freeze/Thaw Retrievals in Canada

    NASA Technical Reports Server (NTRS)

    Roy, A.; Royer, A.; Derksen, C.; Brucker, L.; Langlois, A.; Mailon, A.; Kerr, Y.

    2015-01-01

    The landscape freeze/thaw (FT) state has an important impact on the surface energy balance, carbon fluxes, and hydrologic processes; the timing of spring melt is linked to active layer dynamics in permafrost areas. L-band (1.4 GHz) microwave emission could allow the monitoring of surface state dynamics due to its sensitivity to the pronounced permittivity difference between frozen and thawed soil. The aim of this paper is to evaluate the performance of both Aquarius and Soil Moisture and Ocean Salinity (SMOS) L-band passive microwave measurements using a polarization ratio-based algorithm for landscape FT monitoring. Weekly L-band satellite observations are compared with a large set of reference data at 48 sites across Canada spanning three environments: tundra, boreal forest, and prairies. The reference data include in situ measurements of soil temperature (Tsoil) and air temperature (Tair), and Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) and snow cover area (SCA) products. Results show generally good agreement between Lband FT detection and the surface state estimated from four reference datasets. The best apparent accuracies for all seasons are obtained using Tair as the reference. Aquarius radiometer 2 (incidence angle of 39.6) data gives the best accuracies (90.8), while for SMOS the best results (87.8 of accuracy) are obtained at higher incidence angles (55- 60). The FT algorithm identifies both freeze onset and end with a delay of about one week in tundra and two weeks in forest and prairies, when compared to Tair. The analysis shows a stronger FT signal at tundra sites due to the typically clean transitions between consistently frozen and thawed conditions (and vice versa) and the absence of surface vegetation. Results in the prairies were poorer because of the influence of vegetation growth in summer (which decreases the polarization ratio) and the high frequency of ephemeral thaw events during winter. Freeze onset

  19. Traveling-Wave Maser for 32 GHz

    NASA Technical Reports Server (NTRS)

    Shell, James; Clauss, Robert

    2009-01-01

    The figure depicts a traveling-wave ruby maser that has been designed (though not yet implemented in hardware) to serve as a low-noise amplifier for reception of weak radio signals in the frequency band of 31.8 to 32.3 GHz. The design offers significant improvements over previous designs of 32-GHz traveling-wave masers. In addition, relative to prior designs of 32-GHz amplifiers based on high-electron-mobility transistors, this design affords higher immunity to radio-frequency interference and lower equivalent input noise temperature. In addition to the basic frequency-band and low-noise requirements, the initial design problem included a requirement for capability of operation in a closed-cycle helium refrigerator at a temperature .4 K and a requirement that the design be mechanically simplified, relative to prior designs, in order to minimize the cost of fabrication and assembly. Previous attempts to build 32- GHz traveling-wave masers involved the use of metallic slow-wave structures comprising coupled transverse electromagnetic (TEM)-mode resonators that were subject to very tight tolerances and, hence, were expensive to fabricate and assemble. Impedance matching for coupling signals into and out of these earlier masers was very difficult. A key feature of the design is a slow-wave structure, the metallic portions of which would be mechanically relatively simple in that, unlike in prior slow-wave structures, there would be no internal metal steps, irises, or posts. The metallic portions of the slow-wave structure would consist only of two rectangular metal waveguide arms. The arms would contain sections filled with the active material (ruby) alternating with evanescent-wave sections. This structure would be transparent in both the signal-frequency band (the aforementioned range of 31.8 to 32.3 GHz) and the pump-frequency band (65.75 to 66.75 GHz), and would impose large slowing factors in both frequency bands. Resonant ferrite isolators would be placed in the

  20. Anomalous anisotropic compression behavior of superconducting CrAs under high pressure

    PubMed Central

    Yu, Zhenhai; Wu, Wei; Hu, Qingyang; Zhao, Jinggeng; Li, Chunyu; Yang, Ke; Cheng, Jinguang; Luo, Jianlin; Wang, Lin; Mao, Ho-kwang

    2015-01-01

    CrAs was observed to possess the bulk superconductivity under high-pressure conditions. To understand the superconducting mechanism and explore the correlation between the structure and superconductivity, the high-pressure structural evolution of CrAs was investigated using the angle-dispersive X-ray diffraction (XRD) method. The structure of CrAs remains stable up to 1.8 GPa, whereas the lattice parameters exhibit anomalous compression behaviors. With increasing pressure, the lattice parameters a and c both demonstrate a nonmonotonic change, and the lattice parameter b undergoes a rapid contraction at ∼0.18−0.35 GPa, which suggests that a pressure-induced isostructural phase transition occurs in CrAs. Above the phase transition pressure, the axial compressibilities of CrAs present remarkable anisotropy. A schematic band model was used to address the anomalous compression behavior of CrAs. The present results shed light on the structural and related electronic responses to high pressure, which play a key role toward understanding the superconductivity of CrAs. PMID:26627230

  1. An increase in Tc under hydrostatic pressure in the superconducting doped topological insulator Nb 0.25Bi 2Se 3

    DOE PAGES

    Smylie, M. P.; Willa, K.; Ryan, K.; ...

    2017-10-26

    Here, we report a positive hydrostatic pressure derivative of the superconducting transition temperature in the doped topological insulator Nb 0.25Bi 2Se 3 via dc SQUID magnetometry in pressures up to 0.6 GPa. This result is contrary to reports on the homologues Cu xBi 2Se 3 and Sr xBi 2Se 3 where smooth suppression of T c is observed. This difference may be attributable to an electronic structure composed of multiple bands whereas the other materials in the superconducting doped Bi 2Se 3 family are believed to be single-band.

  2. Unconventional superconductivity in magic-angle graphene superlattices.

    PubMed

    Cao, Yuan; Fatemi, Valla; Fang, Shiang; Watanabe, Kenji; Taniguchi, Takashi; Kaxiras, Efthimios; Jarillo-Herrero, Pablo

    2018-04-05

    The behaviour of strongly correlated materials, and in particular unconventional superconductors, has been studied extensively for decades, but is still not well understood. This lack of theoretical understanding has motivated the development of experimental techniques for studying such behaviour, such as using ultracold atom lattices to simulate quantum materials. Here we report the realization of intrinsic unconventional superconductivity-which cannot be explained by weak electron-phonon interactions-in a two-dimensional superlattice created by stacking two sheets of graphene that are twisted relative to each other by a small angle. For twist angles of about 1.1°-the first 'magic' angle-the electronic band structure of this 'twisted bilayer graphene' exhibits flat bands near zero Fermi energy, resulting in correlated insulating states at half-filling. Upon electrostatic doping of the material away from these correlated insulating states, we observe tunable zero-resistance states with a critical temperature of up to 1.7 kelvin. The temperature-carrier-density phase diagram of twisted bilayer graphene is similar to that of copper oxides (or cuprates), and includes dome-shaped regions that correspond to superconductivity. Moreover, quantum oscillations in the longitudinal resistance of the material indicate the presence of small Fermi surfaces near the correlated insulating states, in analogy with underdoped cuprates. The relatively high superconducting critical temperature of twisted bilayer graphene, given such a small Fermi surface (which corresponds to a carrier density of about 10 11 per square centimetre), puts it among the superconductors with the strongest pairing strength between electrons. Twisted bilayer graphene is a precisely tunable, purely carbon-based, two-dimensional superconductor. It is therefore an ideal material for investigations of strongly correlated phenomena, which could lead to insights into the physics of high

  3. Superconductive wire

    DOEpatents

    Korzekwa, David A.; Bingert, John F.; Peterson, Dean E.; Sheinberg, Haskell

    1995-01-01

    A superconductive article is made by inserting a rigid mandrel into an internal cavity of a first metallic tube, said tube having an interior surface and an exterior surface, said interior surface defining the interior cavity, forming a layer of a superconductive material or superconductive precursor upon the exterior surface of said first metallic tube, machining the layer of superconductive material or superconductive precursor to a predetermined diameter to form an intermediate article configured for insertion into a second metallic tube having an interior diameter corresponding to the predetermined diameter, inserting the machined intermediate article into a second metallic tube having an internal diameter corresponding to the predetermined diameter of the intermediate article to form a composite intermediate article, reducing or ironing the composite intermediate article to a predetermined cross-sectional diameter, and sintering the reduced or ironed composite intermediate article at temperatures and for time sufficient for the superconductive material or superconductive precursor to exhibit superconductivity.

  4. Superconductive wire

    DOEpatents

    Korzekwa, D.A.; Bingert, J.F.; Peterson, D.E.; Sheinberg, H.

    1995-07-18

    A superconductive article is made by inserting a rigid mandrel into an internal cavity of a first metallic tube, said tube having an interior surface and an exterior surface, said interior surface defining the interior cavity, forming a layer of a superconductive material or superconductive precursor upon the exterior surface of said first metallic tube, machining the layer of superconductive material or superconductive precursor to a predetermined diameter to form an intermediate article configured for insertion into a second metallic tube having an interior diameter corresponding to the predetermined diameter, inserting the machined intermediate article into a second metallic tube having an internal diameter corresponding to the predetermined diameter of the intermediate article to form a composite intermediate article, reducing or ironing the composite intermediate article to a predetermined cross-sectional diameter, and sintering the reduced or ironed composite intermediate article at temperatures and for time sufficient for the superconductive material or superconductive precursor to exhibit superconductivity. 2 figs.

  5. L band brightness temperature observations over a corn canopy during the entire growth cycle

    USDA-ARS?s Scientific Manuscript database

    During a field campaign covering the 2002 corn growing season, a dual polarized tower mounted L-band (1.4 GHz) radiometer (LRAD) provided brightness temperature (T¬B) measurements at preset intervals, incidence and azimuth angles. These radiometer measurements were supported by an extensive characte...

  6. Full superconducting dome of strong Ising protection in gated monolayer WS2.

    PubMed

    Lu, Jianming; Zheliuk, Oleksandr; Chen, Qihong; Leermakers, Inge; Hussey, Nigel E; Zeitler, Uli; Ye, Jianting

    2018-04-03

    Many recent studies show that superconductivity not only exists in atomically thin monolayers but can exhibit enhanced properties such as a higher transition temperature and a stronger critical field. Nevertheless, besides being unstable in air, the weak tunability in these intrinsically metallic monolayers has limited the exploration of monolayer superconductivity, hindering their potential in electronic applications (e.g., superconductor-semiconductor hybrid devices). Here we show that using field effect gating, we can induce superconductivity in monolayer WS 2 grown by chemical vapor deposition, a typical ambient-stable semiconducting transition metal dichalcogenide (TMD), and we are able to access a complete set of competing electronic phases over an unprecedented doping range from band insulator, superconductor, to a reentrant insulator at high doping. Throughout the superconducting dome, the Cooper pair spin is pinned by a strong internal spin-orbit interaction, making this material arguably the most resilient superconductor in the external magnetic field. The reentrant insulating state at positive high gating voltages is attributed to localization induced by the characteristically weak screening of the monolayer, providing insight into many dome-like superconducting phases observed in field-induced quasi-2D superconductors.

  7. William Band at Yenching University

    NASA Astrophysics Data System (ADS)

    Hu, Danian

    2008-04-01

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

  8. Tail-like regime and BCS-BEC crossover due to hybridization in a two-band superconductor.

    PubMed

    Reyes, D; Continentino, M A; Deus, F; Thomas, C

    2018-05-02

    Superconductivity in strongly correlated systems is a remarkable phenomenon that attracts huge interest. The study of this problem is relevant for materials such as the high T c oxides, pnictides and heavy fermions. These systems also have in common the existence of electrons of several orbitals that coexist at a common Fermi surface. In this paper we study the effect of pressure, chemical or applied on multi-band superconductivity. Pressure varies the atomic distances and consequently the overlap of the wave-functions in the crystal. This rearranges the electronic structure that we model including a pressure dependent hybridization between the bands. We consider the case of two-dimensional systems in a square lattice with inverted bands. We study the conditions for obtaining a pressure induced superconductor quantum critical point and show that hybridization, i.e. pressure can induce a Bardeen-Cooper-Schrieffer-Bose-Einstein condensation crossover in multi-band systems even for moderate interactions. We found a tail-like superconductor regime and briefly discuss the influence of the symmetry of the order parameter in the results.

  9. Tail-like regime and BCS-BEC crossover due to hybridization in a two-band superconductor

    NASA Astrophysics Data System (ADS)

    Reyes, D.; Continentino, M. A.; Deus, F.; Thomas, C.

    2018-05-01

    Superconductivity in strongly correlated systems is a remarkable phenomenon that attracts huge interest. The study of this problem is relevant for materials such as the high T c oxides, pnictides and heavy fermions. These systems also have in common the existence of electrons of several orbitals that coexist at a common Fermi surface. In this paper we study the effect of pressure, chemical or applied on multi-band superconductivity. Pressure varies the atomic distances and consequently the overlap of the wave-functions in the crystal. This rearranges the electronic structure that we model including a pressure dependent hybridization between the bands. We consider the case of two-dimensional systems in a square lattice with inverted bands. We study the conditions for obtaining a pressure induced superconductor quantum critical point and show that hybridization, i.e. pressure can induce a Bardeen–Cooper–Schrieffer-Bose–Einstein condensation crossover in multi-band systems even for moderate interactions. We found a tail-like superconductor regime and briefly discuss the influence of the symmetry of the order parameter in the results.

  10. Band-edges and band-gap in few-layered transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Bhunia, Hrishikesh; Pal, Amlan J.

    2018-05-01

    We have considered liquid-exfoliated transition metal dichalcogenides (WS2, WSe2, MoS2, and MoSe2) and studied their band-edges and band-gap through scanning tunneling spectroscopy (STS) and density of states. A monolayer, bilayer (2L), and trilayer (3L) of each of the layered materials were characterized to derive the energies. Upon an increase in the number of layers, both the band-edges were found to shift towards the Fermi energy. The results from the exfoliated nanosheets have been compared with reported STS studies of MoS2 and WSe2 formed through chemical vapor deposition or molecular beam epitaxy methods; an uncontrolled lattice strain existed in such 2L and 3L nanoflakes due to mismatch in stacking-patterns between the monolayers affecting their energies. In the present work, the layers formed through the liquid-exfoliation process retained their interlayer coupling or stacking-sequence prevalent to the bulk and hence allowed determination of band-energies in these strain-free two-dimensional materials.

  11. Pass-Band Characteristics of an L-Shaped Waveguide in a Diamond Structure Photonic Crystal

    NASA Astrophysics Data System (ADS)

    Chen, Shibin; Ma, Jingcun; Yao, Yunshi; Liu, Xin; Lin, Ping

    2018-06-01

    The conduction characteristics of a L-shaped waveguide in a diamond structure photonic crystal is investigated in this paper. The waveguides were fabricated with titanium dioxide ceramic via 3-D printing and sintering. The effects of the position and size of line defects on the transmission characteristics are first simulated using a finite-difference time-domain method. The simulated results show that, when the length of the rectangular defect equals the lattice constant, multiple extended modes are generated. When the centers of the single unit cell of the diamond structure and the line defect waveguide coincide, higher transmission efficiency in the line defect can be achieved. In addition, the corner of the L-shaped waveguide was optimized to reduce reflection loss at the turning point using the arc transition of the large diameter. Our experimental results indicate that L-shaped waveguides with an optimized photonic band gap structure and high-K materials can produce a pass-band between 13.8 GHz and 14.4 GHz and increase transmission efficiency. The computed results agree with the experimental results. Our results may help the integration of microwave devices in the future and possibly enable new applications of photonic crystals.

  12. Recalibration and Validation of the SMAP L-Band Radiometer

    NASA Technical Reports Server (NTRS)

    Peng, Jinzheng; Piepmeier, Jeffrey; Le Vine, David M.; Dinnat, Emmanuel; Bindlish, Rajat; De amici, Giovanni; Mohammed, Priscilla; Misra, Sidharth; Yueh, Simon; Meissner, Thomas

    2017-01-01

    SMAP mission was launched on 31st January 2015 in a 6 AM 6 PM sun-synchronous orbit at 685 km altitude to measure soil moisture and freethaw globally. The passive instrument of SMAP is a fully polarimetric L-band radiometer (1.4GHz) operating with a bandwidth of 24MHz. The radiometer L1B data product version 3 has been released for public science activities. Post-launch calibration and validation activities are described in [4,5]. Validation results show that SMAP antenna temperature (TA) is 2.6 K warmer over galactic Cold Sky (CS), and land TB is 2.6 K colder comparing to SMOS land TB (compared at the top of the atmosphere) after the update of the reflectors thermal model. Due to the biases, the SMAP radiometer is under re-calibration for next data release in 2018.We present the updated calibration approaches for the SMAP radiometer product. We will discuss the various radiometer calibration parameters and part of the validation process and result.

  13. In-plane magnetic penetration depth of superconducting CaKFe 4 As 4

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Khasanov, Rustem; Meier, William R.; Wu, Yun

    Here, the temperature dependence of the in-plane magnetic penetration depth (λ ab) in an extensively characterized sample of superconducting CaKFe 4As 4(T c≃35K) was investigated using muon-spin rotation (μSR). A comparison of λ –2 ab(T) measured by μSR with the one inferred from angle-resolved photoemission spectroscopy (ARPES) data confirms the presence of multiple gaps at the Fermi level. An agreement between μSR and ARPES requires the presence of additional bands, which are not resolved by ARPES experiments. These bands are characterized by small superconducting gaps with an average zero-temperature value of Δ 0=2.4(2)meV. Our data suggest that in CaKFe 4Asmore » 4 the s ± order parameter symmetry acquires a more sophisticated form by allowing a sign change not only between electron and hole pockets, but also within pockets of similar type.« less

  14. In-plane magnetic penetration depth of superconducting CaKFe 4 As 4

    DOE PAGES

    Khasanov, Rustem; Meier, William R.; Wu, Yun; ...

    2018-04-09

    Here, the temperature dependence of the in-plane magnetic penetration depth (λ ab) in an extensively characterized sample of superconducting CaKFe 4As 4(T c≃35K) was investigated using muon-spin rotation (μSR). A comparison of λ –2 ab(T) measured by μSR with the one inferred from angle-resolved photoemission spectroscopy (ARPES) data confirms the presence of multiple gaps at the Fermi level. An agreement between μSR and ARPES requires the presence of additional bands, which are not resolved by ARPES experiments. These bands are characterized by small superconducting gaps with an average zero-temperature value of Δ 0=2.4(2)meV. Our data suggest that in CaKFe 4Asmore » 4 the s ± order parameter symmetry acquires a more sophisticated form by allowing a sign change not only between electron and hole pockets, but also within pockets of similar type.« less

  15. L band InSAR sudy on the Ganos section of the North Anatolian Fault Zone (NAFZ)

    NASA Astrophysics Data System (ADS)

    de Michele, Marcello

    2016-04-01

    The North Anatolian Fault (NAF), with a total length of about 1500 km, is one of the most active right-lateral strike-slip faults in the world. It defines the tectonic boundary between the Anatolian Plate and the Eurasian Plate in northern Turkey, accommodating ~14-30 mm/yr of relative plate motion between the two plates (fig. 1). The Gazikoy-Saros segment (the Ganos fault, GF) is the onshore segment of the northern strand of the NAF between the Marmara Sea and the Gulf of Saros. It was last ruptured in 1912 with a Ms=7.4 earthquake that broke the entire inland segment of the fault, a length of about 50 km, and produced a right-lateral strike-slip component of at least 3 m. Other large historical earthquakes that have been attributed to the Ganos fault occurred in A.D. 824, 1343, 1509 and 1766 (e. g. Reilinger et al., 2000; Meade et al., 2002; Motagh et al., 2007; Janssen et al., 2009; Megraoui et al., 2012 ; Ersen Aksoy et al., 2010). The GF forms a 45 km long linear fault system and represents the link between the northern strand of the NAFZ in the Sea of Marmara and the North Aegean Trough where slip partitioning results in branching of the fault zone. The present study aims at showing the results retrieved from L band Interferometric Syntethic Aperture Radar (InSAR) measurements for the monitoring of Crustal Deformation in the Anatolian Fault Zone in the frame of the MARMARA SUPERSITE PROJECT "MARSITE" on the Ganos section of the North Anatolian fault zone. We processed SAR data made available through the CAT-1 ESA (European Space Agency) archives, acquired by the L-band radar sensor ALOS PALSAR between 2007 and 2011. The aim of this exercise is to test L-band capabilities to map the spatial and temporal evolution of the present-day crustal deformation phenomena affecting the Ganos section of the NAFZ with high level of spatial details. The goal of this task is to assess whether InSAR L-Band data can be useful to evaluate the long-term behavior of active faults

  16. Influence of calcium on transport properties, band spectrum and superconductivity of YBa2Cu3O(y) and YBa(1.5)La(0.5)Cu3O(y)

    NASA Technical Reports Server (NTRS)

    Gasumyants, V. E.; Vladimirskaya, E. V.; Patrina, I. B.

    1995-01-01

    The comparative investigation of transport phenomena in Y(1-x)Ca(x)Ba2Cu3O(y) (0 is less than x is less than 0.25; 6.96 is greater than y is greater than 6.87 and 6.73 is less than x is less than 6.53); Y(1-x)Ca(x)Ba(1.5)La(0.5)Cu3O(y) (0 is less than x is less than 0.5; 7.12 is greater than y is greater than 6.96) and YBa(2-x)La(x)Cu3O(y) (0 is less than x is less than 0.5; 6.95 is less than y is less than 7.21) systems have been carried out. The temperature dependencies of resistivity and thermopower have been measured. It was found that the S(T) dependencies take some additional features with Ca content increase. The results obtained have been analyzed on the basis of the phenomenological theory of electron transport in the case of the narrow conductive band. The main parameters of the band spectrum (the band filling with electrons degree and the total effective band width) have been determined. The dependencies of these from contents of substituting elements are discussed. Analyzing the results obtained simultaneously with the tendencies in oxygen content and critical temperature change we have confirmed the conclusion that the oxygen sublattice disordering has a determinant effect on band structure parameters and superconductive properties of YBa2Cu3O(y). The results obtained suggest that Ca gives rise to some peculiarities in band spectrum of this compound.

  17. 21-nm-range wavelength-tunable L-band Er-doped fiber linear-cavity laser

    NASA Astrophysics Data System (ADS)

    Yang, Shiquan; Zhao, Chunliu; Li, Zhaohui; Ding, Lei; Yuan, Shuzhong; Dong, Xiaoyi

    2001-10-01

    A novel method, which utilizes amplified spontaneous emission (ASE) as a secondary pump source, is presented for implanting a linear cavity erbium-doped fiber laser operating in L-Band. The output wavelength tuned from 1566 nm to 1587 nm, about 21 nm tuning range, was obtained in the experiment and the stability of the laser is very good.

  18. Magnetoresistance in the superconducting state at the (111) LaAlO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Davis, S.; Huang, Z.; Han, K.; Ariando, Venkatesan, T.; Chandrasekhar, V.

    2017-10-01

    Condensed-matter systems that simultaneously exhibit superconductivity and ferromagnetism are rare due the antagonistic relationship between conventional spin-singlet superconductivity and ferromagnetic order. In materials in which superconductivity and magnetic order are known to coexist (such as some heavy-fermion materials), the superconductivity is thought to be of an unconventional nature. Recently, the conducting gas that lives at the interface between the perovskite band insulators LaAlO3 (LAO) and SrTiO3 (STO) has also been shown to host both superconductivity and magnetism. Most previous research has focused on LAO/STO samples in which the interface is on the (001) crystal plane. Relatively little work has focused on the (111) crystal orientation, which has hexagonal symmetry at the interface, and has been predicted to have potentially interesting topological properties, including unconventional superconducting pairing states. Here we report measurements of the magnetoresistance of (111) LAO/STO heterostructures at temperatures at which they are also superconducting. As with the (001) structures, the magnetoresistance is hysteretic, indicating the coexistence of magnetism and superconductivity, but in addition, we find that this magnetoresistance is anisotropic. Such an anisotropic response is completely unexpected in the superconducting state and suggests that (111) LAO/STO heterostructures may support unconventional superconductivity.

  19. Development of a High-Stability Microstrip-based L-band Radiometer for Ocean Salinity Measurements

    NASA Technical Reports Server (NTRS)

    Pellerano, Fernando A.; Horgan, Kevin A.; Wilson, William J.; Tanner, Alan B.

    2004-01-01

    The development of a microstrip-based L-band Dicke radiometer with the long-term stability required for future ocean salinity measurements to an accuracy of 0.1 psu is presented. This measurement requires the L-band radiometers to have calibration stabilities of less than or equal to 0.05 K over 2 days. This research has focused on determining the optimum radiometer requirements and configuration to achieve this objective. System configuration and component performance have been evaluated with radiometer test beds at both JPL and GSFC. The GSFC testbed uses a cryogenic chamber that allows long-term characterization at radiometric temperatures in the range of 70 - 120 K. The research has addressed several areas including component characterization as a function of temperature and DC bias, system linearity, optimum noise diode injection calibration, and precision temperature control of components. A breadboard radiometer, utilizing microstrip-based technologies, has been built to demonstrate this long-term stability.

  20. Positron Annihilation in Superconducting 123 Compounds

    NASA Astrophysics Data System (ADS)

    Peter, M.; Manuel, A. A.; Erb, A.

    After a brief review of the theory of angular correlation of positron annihilation radiation (ACAR), we illustrate experimental principles and give examples of successful determination of electron momentum density (EMD) and of positron lifetime in solids. The central question which we try to answer concerns the contribution of positron spectroscopy to the knowledge and understanding of the new high temperature superconducting oxides. We find that in these oxides also, partially filled bands exist and we can observe parts of their Fermi surface and measure lifetimes in accordance with band theoretical calculations. There are characteristic differences, however. The intensity of the anisotropy of the ACAR signal is below theoretical expectation and signals depend on sample preparation. Recent studies by the Geneva group have concerned dependence of the signals on impurities, on oxygen content and on the thermal history of preparation. Of particular interest are correlations between the variations of these signals and between the variations of structural and transport properties in these substances. Besides deliberate additions of impurities, the Geneva group also reports progress in the preparations of samples of highest purity (barium zirconate crucibles). The alloy series PrxY1-xBa2Cu3O7-δ is of special interest because of exceptional transport properties. The recent positron results on these materials will be presented and commented in the light of theoretical models and in the light of the reported superconductivity of the Pr-compound.

  1. Analysis of transmittance properties in 1D hybrid dielectric photonic crystal containing superconducting thin films

    NASA Astrophysics Data System (ADS)

    Soltani, Osswa; Zaghdoudi, Jihene; Kanzari, Mounir

    2018-06-01

    By means of two fluid model and transfer matrix method (TMM), we investigate theoretically the transmittance properties of a defective hybrid dielectric-dielectric photonic crystal that contains a superconducting material as a defect layer. The considered hybrid photonic structure is: H(LH) 7(HLSLH) P H(LH) 7 , where H is the high refractive index dielectric, L is the low refractive index dielectric, S is the superconducting material and P is the repetitive number. The results show that the variation of the number and the positions of the transmissions modes depend strongly on the repetitive number P, the temperature T and the thickness of the layer S. An improvement of the spectral response is obtained with the exponential gradation of layer thicknesses dj =d0 + βejα , where d0 is the initial thickness of the layer j, α and β are two particular constants for each material. In addition, the effect of the incident angle for both transverse electric (TE) and transverse magnetic (TM) polarizations on the transmittance spectrum is discussed. As a result, we propose a tunable narrow stop-band polychromatic filter that covers the visible wavelength.

  2. Proposal of a gigawatt-class L/Ku dual-band magnetically insulated transmission line oscillator

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ju, J.-C., E-mail: jujinchuan@126.com; Fan, Y.-W.; Shu, T.

    2014-10-15

    We present a gigawatt (GW)-class magnetically insulated transmission line oscillator (MILO) which is capable of generating dual-band high power microwaves (HPMs). The proposed device, deriving from previously studied complex MILO and dual-frequency MILO, is designed to produce two HPMs in L-band and Ku-band, respectively. It is found in particle-in-cell (PIC) simulation that when the diode voltage is 610 kV, HPMs with frequencies of 1.72 GHz and 14.6 GHz can be achieved with powers of 3.3 GW and 2.4 GW, respectively. The corresponding total power conversion efficiency is approximately 12.8%. Power difference of the two generated HPMs is approximately 1.4 dB, and frequency difference of themmore » reaches a level as high as ∼10 dB.« less

  3. Coexistence of Topological Edge State and Superconductivity in Bismuth Ultrathin Film.

    PubMed

    Sun, Hao-Hua; Wang, Mei-Xiao; Zhu, Fengfeng; Wang, Guan-Yong; Ma, Hai-Yang; Xu, Zhu-An; Liao, Qing; Lu, Yunhao; Gao, Chun-Lei; Li, Yao-Yi; Liu, Canhua; Qian, Dong; Guan, Dandan; Jia, Jin-Feng

    2017-05-10

    Ultrathin freestanding bismuth film is theoretically predicted to be one kind of two-dimensional topological insulators. Experimentally, the topological nature of bismuth strongly depends on the situations of the Bi films. Film thickness and interaction with the substrate often change the topological properties of Bi films. Using angle-resolved photoemission spectroscopy, scanning tunneling microscopy or spectroscopy and first-principle calculation, the properties of Bi(111) ultrathin film grown on the NbSe 2 superconducting substrate have been studied. We find the band structures of the ultrathin film is quasi-freestanding, and one-dimensional edge state exists on Bi(111) film as thin as three bilayers. Superconductivity is also detected on different layers of the film and the pairing potential exhibits an exponential decay with the layer thicknesses. Thus, the topological edge state can coexist with superconductivity, which makes the system a promising platform for exploring Majorana Fermions.

  4. Pressure-induced superconductivity in the giant Rashba system BiTeI.

    PubMed

    VanGennep, D; Linscheid, A; Jackson, D E; Weir, S T; Vohra, Y K; Berger, H; Stewart, G R; Hennig, R G; Hirschfeld, P J; Hamlin, J J

    2017-03-08

    At ambient pressure, BiTeI exhibits a giant Rashba splitting of the bulk electronic bands. At low pressures, BiTeI undergoes a transition from trivial insulator to topological insulator. At still higher pressures, two structural transitions are known to occur. We have carried out a series of electrical resistivity and AC magnetic susceptibility measurements on BiTeI at pressure up to  ∼40 GPa in an effort to characterize the properties of the high-pressure phases. A previous calculation found that the high-pressure orthorhombic P4/nmm structure BiTeI is a metal. We find that this structure is superconducting with T c values as high as 6 K. AC magnetic susceptibility measurements support the bulk nature of the superconductivity. Using electronic structure and phonon calculations, we compute T c and find that our data is consistent with phonon-mediated superconductivity.

  5. Development of a W-band Serpentine Waveguide Amplifier based on a UV-LIGA Microfabricated Copper Circuit

    DTIC Science & Technology

    2013-03-01

    beam tunnel [5,6] for a high - power , wideband W- band traveling-wave tube (TWT) amplifier. UV-LIGA is also a promising technique at higher...wide- band , high - power operation of the amplifier [7, 8]. The interaction circuit consists of two traveling-wave stages separated by a power ...technique produces monolithic all-copper circuits, integrated with electron beam tunnel, suitable for high - power continuous-wave operation [1]. We

  6. Progress on applications of high temperature superconducting microwave filters

    NASA Astrophysics Data System (ADS)

    Chunguang, Li; Xu, Wang; Jia, Wang; Liang, Sun; Yusheng, He

    2017-07-01

    In the past two decades, various kinds of high performance high temperature superconducting (HTS) filters have been constructed and the HTS filters and their front-end subsystems have been successfully applied in many fields. The HTS filters with small insertion loss, narrow bandwidth, flat in-band group delay, deep out-of-band rejection, and steep skirt slope are reviewed. Novel HTS filter design technologies, including those in high power handling filters, multiband filters and frequency tunable filters, are reviewed, as well as the all-HTS integrated front-end receivers. The successful applications to various civilian fields, such as mobile communication, radar, deep space detection, and satellite technology, are also reviewed.

  7. L-Band RFI in Japan

    NASA Technical Reports Server (NTRS)

    Soldo, Yan; de Matthaeis, Paolo; Le Vine, David M.

    2016-01-01

    In recent years, three instruments have been launched into orbit with the aim of producing global maps of sea surface salinity and soil moisture using the 1400-1427 MHz band: SMOS, Aquarius and SMAP. Although this frequency band is allocated to passive measurements only, RFI (Radio-Frequency Interference) is present in the data of all three missions. On a global scale, the three sensors have observed approximately the same distribution of RFI. Japan is an important exception that has implications for the design of RFI detection algorithms. RFI in Japan is caused by a large number of emitters belonging to the same system (TV receivers) and for this reason some traditional RFI detection strategies detect little to no RFI over Japan. The study of this case has led to an improvement of the approach to detect RFI in Aquarius data.

  8. 41 CFR 301-71.105 - Must we issue a written or electronic travel authorization in advance of travel?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...; (c) Use of reduced fares for group or charter arrangements; (d) Use of cash to pay for common carrier... Government aircraft; (i) Payment of a reduced rate per diem; (j) Payment of actual expenses; (k) Travel expenses related to emergency travel; (l) Transportation expenses related to threatened law enforcement...

  9. Superconducting coil and method of stress management in a superconducting coil

    DOEpatents

    McIntyre, Peter M.; Shen, Weijun; Diaczenko, Nick; Gross, Dan A.

    1999-01-01

    A superconducting coil (12) having a plurality of superconducting layers (18) is provided. Each superconducting layer (18) may have at least one superconducting element (20) which produces an operational load. An outer support structure (24) may be disposed outwardly from the plurality of layers (18). A load transfer system (22) may be coupled between at least one of the superconducting elements (20) and the outer support structure (24). The load transfer system (22) may include a support matrix structure (30) operable to transfer the operational load from the superconducting element (20) directly to the outer support structure (24). A shear release layer (40) may be disposed, in part, between the superconducting element (20) and the support matrix structure (30) for relieving a shear stress between the superconducting element (20) and the support matrix structure (30). A compliant layer (42) may also be disposed, in part, between the superconducting element (20) and the support matrix structure (30) for relieving a compressive stress on the superconducting element (20).

  10. Superconducting Cable

    DOEpatents

    Hughey, Raburn L.; Sinha, Uday K.; Reece, David S.; Muller, Albert C.

    2005-03-08

    In order to provide a flexible oxide superconducting cable which is reduced in AC loss, tape-shaped superconducting wires covered with a stabilizing metal are wound on a flexible former. The superconducting wires are preferably laid on the former at a bending strain of not more than 0.2%. In laying on the former, a number of tape-shaped superconducting wires are laid on a core member in a side-by-side manner, to form a first layer. A prescribed number of tape-shaped superconducting wires are laid on top of the first layer in a side-by-side manner, to form a second layer. The former may be made of a metal, plastic, reinforced plastic, polymer, or a composite and provides flexibility to the superconducting wires and the cable formed therewith.

  11. Superconducting Cable

    DOEpatents

    Hughey, Raburn L.; Sinha, Uday K.; Reece, David S.; Muller, Albert C.

    2005-07-22

    In order to provide a flexible oxide superconducting cable which is reduced in AC loss, tape-shaped superconducting wires covered with a stabilizing metal are wound on a flexible former. The superconducting wires are preferably laid on the former at a bending strain of not more than 0.2%. In laying on the former, a number of tape-shaped superconducting wires are laid on a core member in a side-by-side manner, to form a first layer. A prescribed number of tape-shaped superconducting wires are laid on top of the first layer in a side-by-side manner, to form a second layer. The former may be made of a metal, plastic, reinforced plastic, polymer, or a composite and provides flexibility to the superconducting wires and the cable formed therewith.

  12. Multipolarization P-, L-, and C-band radar for coastal zone mapping - The Louisiana example

    NASA Technical Reports Server (NTRS)

    Wu, Shih-Tseng

    1989-01-01

    Multipolarization P-, L-, and C-band airborne SAR data sets were acquired over a coastal zone and a forested wetland of southern Louisiana. The data sets were used with field-collected surface-parameter data in order to determine the value of SAR systems in assessing and mapping coastal-zone surface features. The coastal-zone surface features in this study are sediments, sediment distribution, and the formation of new isles and banks. Results of the data analysis indicate that the P-band radar with 68-cm wavelength is capable of detecting the submerged sediment if the area is very shallow (i.e., a water depth of less than one meter). The penetration capability of P-band radar is also demonstrated in the forested wetland area. The composition and condition of the ground surface can be detected, as well as the standing water beneath dense tree leaves.

  13. Longitudinal Proximity Effects in Superconducting Transition-Edge Sensors

    NASA Technical Reports Server (NTRS)

    Sadleir, John E.; Smith, Stephen J.; Bandler, SImon R.; Chervenak, James A.; Clem, John R.

    2009-01-01

    We have found experimentally that the critical current of a square superconducting transition-edge sensor (TES) depends exponentially upon the side length L and the square root of the temperature T. As a consequence, the effective transition temperature T(sub c) of the TES is current-dependent and at fixed current scales as 1/L(sup 2). We also have found that the critical current can show clear Fraunhofer-like oscillations in an applied magnetic field, similar to those found in Josephson junctions. The observed behavior has a natural theoretical explanation in terms of longitudinal proximity effects if the TES is regarded as a weak link between superconducting leads. We have observed the proximity effect in these devices over extraordinarily long lengths exceeding 100 microns.

  14. The DSS-14 C-band exciter

    NASA Technical Reports Server (NTRS)

    Rowan, D. R.

    1989-01-01

    The development and implementation of a C-band exciter for use with the Block IV Receiver-Exciter Subsystem at Deep Space Station 14 (DSS-14) has been completed. The exciter supplements the standard capabilities of the Block IV system by providing a drive signal for the C-band transmitter while generating coherent translation frequencies for C-band (5-GHz) to S-band (2.2- to 2.3-GHz) Doppler extraction, C-band to L-band (1.6-GHz) zero delay measurements, and a level calibrated L-band test signal. Exciter functions are described, and a general explanation and description of the C-band uplink controller is presented.

  15. Unusual large-pitch banding in poly(L-lactic acid): Effects of composition and geometry confinement

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Woo, Eamor M.; Lugito, Graecia; Hsieh, Ya-Ting

    2014-02-24

    Lamellar patterns and orientations in blends of two crystalline polymers: poly(ethylene oxide) (PEO) and low-molecular-weight poly(L-lactic acid) (PLLA) were investigated using polarizing light optical microscopy (POM), and atomic and scanning electron microscopy (AFM, SEM). Specific etching off of PEO was used to reveal the complex earlier-grown PLLA lamellae patterns with various PEO content in blends. Banding of extremely long pitch (50 μm) in crystallized PLLA spherulites was induced by two kinetic factors: geometry confinement by top cover and introduction of diluent such as PEO. The mechanisms and correlation among the lamellar assembly, ring bands, and cracks are exemplified. Lamellar patternsmore » and ring-band types in blends were found to vary with respect to not only blend compositions, but also confinement of top-cover.« less

  16. Quantum Criticality and Superconductivity in β-YbAlB4

    NASA Astrophysics Data System (ADS)

    Nakatsuji, Satoru

    2009-03-01

    Heavy fermion systems have provided a number of prototypical compounds to study unconventional superconductivity and non-Fermi-liquid (NFL) states. A long standing issue in the research of heavy fermion superconductivity in 4f intermetallics is the dramatically different behavior between the electron like Ce (4f^1) and hole like Yb (4f^13) compounds. While superconductivity has been found in a number of Ce based heavy fermion compounds, no superconductivity has been reported for the corresponding Yb systems. In this talk, I present our recent finding of the superconductivity in the new heavy fermion system β-YbAlB4 [1-3]. The superconducting transition temperature is 80 mK, and above it, the system exhibits pronounced NFL behavior in the transport and thermodynamic properties [2,3]. Furthermore, the magnetic field dependence of the NFL behavior indicates that the system is a rare example of a pure metal that displays quantum criticality at ambient pressure and under zero magnetic field. Using our latest results, we discuss the detailed properties of superconductivity and quantum criticality. This is the work performed in collaboration with K. Kuga, Y. Matsumoto, T. Tomita, Y. Machida, T. Tayama, T. Sakakibara, Y. Karaki, H. Ishimoto, S. Yonezawa, Y. Maeno, E. Pearson, G. G. Lonzarich, L.Balicas, H. Lee, and Z. Fisk. [4pt] [1] Robin T. Macaluso, Satoru Nakatsuji, Kentaro Kuga, Evan Lyle Thomas, Yo Machida, Yoshiteru Maeno, Zachary Fisk, and Julia Y. Chan, Chem. Mater. 19 1918 (2007). [0pt] [2] S. Nakatsuji, K.Kuga, Y. Machida, T. Tayama, T. Sakakibara, Y. Karaki, H. Ishimoto, S. Yonezawa, Y. Maeno, E. Pearson, G. G. Lonzarich, L.Balicas, H. Lee, and Z. Fisk, Nature Phys 4, 603-607 (2008). [0pt] [3] K. Kuga, Y. Karaki, Y. Matsumoto, Y. Machida, and S. Nakatsuji, Phys. Rev. Lett. 101, 137004 (2008).

  17. Single-Gap Superconductivity and Dome of Superfluid Density in Nb-Doped SrTiO 3

    NASA Astrophysics Data System (ADS)

    Thiemann, Markus; Beutel, Manfred H.; Dressel, Martin; Lee-Hone, Nicholas R.; Broun, David M.; Fillis-Tsirakis, Evangelos; Boschker, Hans; Mannhart, Jochen; Scheffler, Marc

    2018-06-01

    SrTiO3 exhibits a superconducting dome upon doping with Nb, with a maximum critical temperature Tc≈0.4 K . Using microwave stripline resonators at frequencies from 2 to 23 GHz and temperatures down to 0.02 K, we probe the low-energy optical response of superconducting SrTiO3 with a charge carrier concentration from 0.3 to 2.2 ×1020 cm-3 , covering the majority of the superconducting dome. We find single-gap electrodynamics even though several electronic bands are superconducting. This is explained by a single energy gap 2 Δ due to gap homogenization over the Fermi surface consistent with the low level of defect scattering in Nb-doped SrTiO3 . Furthermore, we determine Tc, 2 Δ , and the superfluid density as a function of charge carrier concentration, and all three quantities exhibit the characteristic dome shape.

  18. Pressure-induced superconductivity in the giant Rashba system BiTeI

    DOE PAGES

    VanGennep, D.; Linscheid, A.; Jackson, D. E.; ...

    2017-01-27

    We present that at ambient pressure, BiTeI exhibits a giant Rashba splitting of the bulk electronic bands. At low pressures, BiTeI undergoes a transition from trivial insulator to topological insulator. At still higher pressures, two structural transitions are known to occur. We have carried out a series of electrical resistivity and AC magnetic susceptibility measurements on BiTeI at pressure up to ~40 GPa in an effort to characterize the properties of the high-pressure phases. A previous calculation found that the high-pressure orthorhombic P4/nmm structure BiTeI is a metal. We find that this structure is superconducting with T c values asmore » high as 6 K. AC magnetic susceptibility measurements support the bulk nature of the superconductivity. Using electronic structure and phonon calculations, we compute T c and find that our data is consistent with phonon-mediated superconductivity.« less

  19. Superconductivity in SnO: a nonmagnetic analog to Fe-based superconductors?

    PubMed

    Forthaus, M K; Sengupta, K; Heyer, O; Christensen, N E; Svane, A; Syassen, K; Khomskii, D I; Lorenz, T; Abd-Elmeguid, M M

    2010-10-08

    We discovered that under pressure SnO with α-PbO structure, the same structure as in many Fe-based superconductors, e.g., β-FeSe, undergoes a transition to a superconducting state for p≳6 GPa with a maximum Tc of 1.4 K at p=9.3 GPa. The pressure dependence of Tc reveals a domelike shape and superconductivity disappears for p≳16 GPa. It is further shown from band structure calculations that SnO under pressure exhibits a Fermi surface topology similar to that reported for some Fe-based superconductors and that the nesting between the hole and electron pockets correlates with the change of Tc as a function of pressure.

  20. Superconducting structure

    DOEpatents

    Kwon, Chuhee; Jia, Quanxi; Foltyn, Stephen R.

    2003-04-01

    A superconductive structure including a dielectric oxide substrate, a thin buffer layer of a superconducting material thereon; and, a layer of a rare earth-barium-copper oxide superconducting film thereon the thin layer of yttrium-barium-copper oxide, the rare earth selected from the group consisting of samarium, gadolinium, ytterbium, erbium, neodymium, dysprosium, holmium, lutetium, a combination of more than one element from the rare earth group and a combination of one or more elements from the rare earth group with yttrium, the buffer layer of superconducting material characterized as having chemical and structural compatibility with the dielectric oxide substrate and the rare earth-barium-copper oxide superconducting film is provided.

  1. Superconducting Structure

    DOEpatents

    Kwon, Chuhee; Jia, Quanxi; Foltyn, Stephen R.

    2005-09-13

    A superconductive structure including a dielectric oxide substrate, a thin buffer layer of a superconducting material thereon; and, a layer of a rare earth-barium-copper oxide superconducting film thereon the thin layer of yttrium-barium-copper oxide, the rare earth selected from the group consisting of samarium, gadolinium, ytterbium, erbium, neodymium, dysprosium, holmium, lutetium, a combination of more than one element from the rare earth group and a combination of one or more elements from the rare earth group with yttrium, the buffer layer of superconducting material characterized as having chemical and structural compatibility with the dielectric oxide substrate and the rare earth-barium-copper oxide superconducting film is provided.

  2. Suppressing multiples using an adaptive multichannel filter based on L1-norm

    NASA Astrophysics Data System (ADS)

    Shi, Ying; Jing, Hongliang; Zhang, Wenwu; Ning, Dezhi

    2017-08-01

    Adaptive subtraction is an important link for removing surface-related multiples in the wave equation-based method. In this paper, we propose an adaptive multichannel subtraction method based on the L1-norm. We achieve enhanced compensation for the mismatch between the input seismogram and the predicted multiples in terms of the amplitude, phase, frequency band, and travel time. Unlike the conventional L2-norm, the proposed method does not rely on the assumption that the primary and the multiples are orthogonal, and also takes advantage of the fact that the L1-norm is more robust when dealing with outliers. In addition, we propose a frequency band extension via modulation to reconstruct the high frequencies to compensate for the frequency misalignment. We present a parallel computing scheme to accelerate the subtraction algorithm on graphic processing units (GPUs), which significantly reduces the computational cost. The synthetic and field seismic data tests show that the proposed method effectively suppresses the multiples.

  3. Coherent model of L-band radar scattering by soybean plants: model development, validation and retrieval

    USDA-ARS?s Scientific Manuscript database

    An improved coherent branching model for L-band radar remote sensing of soybean is proposed by taking into account the correlated scattering among scatterers. The novel feature of the analytic coherent model consists of conditional probability functions to eliminate the overlapping effects of branc...

  4. The Breakthrough Listen Search for Intelligent Life: L-Band Data Recovery and Analysis

    NASA Astrophysics Data System (ADS)

    Lifset, Noah

    2018-01-01

    Breakthrough Listen is a next generation SETI project conducted under the leadership of UC Berkeley. In January 2016, it began collecting data with the Green Bank Telescope in West Virginia. It started a targeted campaign of stars within 50 pc with the L-band receiver (1.1-1.9 GHz). Enriquez et al. (2017) analyzed two thirds of this data comprising an homogeneous sample. The remaining one third of the L-band data taken since then is incomplete in some way, and thus required a different analysis. This project identified all possible issues with this data, and classified it based on its ability to be analyzed. Seven issues were found, and six are able to be accounted for with adapted analysis techniques. The data set consisted of observations of 366 stars within 50 pc, with 297 able to be analyzed and 69 needing to be re-observed. The Breakthrough Listen observation strategy uses 6 five minute observations per target star alternating between ON-target and OFF-target in the form ABACAD, which allows for easier radio-frequency interference identification. The analysis techniques, called turboSETI, search for a narrowband signal with a drifting doppler shift. For this data, a maximum drift rate of 4 Hz/s was chosen, which corresponds to an ET emitter on a planet three times the size of earth rotating three times as fast. An SNR threshold for signal detection of 15 was chosen, which allows for detection of signals with an EIRP (Equivalent Isotropic Radiated Power) of 9.72 x109 W for an emitter at a distance of 10 Ly. A total of 10 candidates signals were found, which were all determined to be either a satellite or another type of RFI. We can infer an upper limit of ~ 5 x108 stars in the milky way transmitting continuously towards earth in the L-band with a EIRP of 1012 W or greater.

  5. Satellite Based Soil Moisture Product Validation Using NOAA-CREST Ground and L-Band Observations

    NASA Astrophysics Data System (ADS)

    Norouzi, H.; Campo, C.; Temimi, M.; Lakhankar, T.; Khanbilvardi, R.

    2015-12-01

    Soil moisture content is among most important physical parameters in hydrology, climate, and environmental studies. Many microwave-based satellite observations have been utilized to estimate this parameter. The Advanced Microwave Scanning Radiometer 2 (AMSR2) is one of many remotely sensors that collects daily information of land surface soil moisture. However, many factors such as ancillary data and vegetation scattering can affect the signal and the estimation. Therefore, this information needs to be validated against some "ground-truth" observations. NOAA - Cooperative Remote Sensing and Technology (CREST) center at the City University of New York has a site located at Millbrook, NY with several insitu soil moisture probes and an L-Band radiometer similar to Soil Moisture Passive and Active (SMAP) one. This site is among SMAP Cal/Val sites. Soil moisture information was measured at seven different locations from 2012 to 2015. Hydra probes are used to measure six of these locations. This study utilizes the observations from insitu data and the L-Band radiometer close to ground (at 3 meters height) to validate and to compare soil moisture estimates from AMSR2. Analysis of the measurements and AMSR2 indicated a weak correlation with the hydra probes and a moderate correlation with Cosmic-ray Soil Moisture Observing System (COSMOS probes). Several differences including the differences between pixel size and point measurements can cause these discrepancies. Some interpolation techniques are used to expand point measurements from 6 locations to AMSR2 footprint. Finally, the effect of penetration depth in microwave signal and inconsistencies with other ancillary data such as skin temperature is investigated to provide a better understanding in the analysis. The results show that the retrieval algorithm of AMSR2 is appropriate under certain circumstances. This validation algorithm and similar study will be conducted for SMAP mission. Keywords: Remote Sensing, Soil

  6. Weekly Gridded Aquarius L-band Radiometer-Scatterometer Observations and Salinity Retrievals over the Polar Regions - Part 2: Initial Product Analysis

    NASA Technical Reports Server (NTRS)

    Brucker, L.; Dinnat, E. P.; Koenig, L. S.

    2014-01-01

    Following the development and availability of Aquarius weekly polar-gridded products, this study presents the spatial and temporal radiometer and scatterometer observations at L band (frequency1.4 GHz) over the cryosphere including the Greenland and Antarctic ice sheets, sea ice in both hemispheres, and over sub-Arctic land for monitoring the soil freeze-thaw state. We provide multiple examples of scientific applications for the L-band data over the cryosphere. For example, we show that over the Greenland Ice Sheet, the unusual 2012 melt event lead to an L-band brightness temperature (TB) sustained decrease of 5 K at horizontal polarization. Over the Antarctic ice sheet, normalized radar cross section (NRCS) observations recorded during ascending and descending orbits are significantly different, highlighting the anisotropy of the ice cover. Over sub-Arctic land, both passive and active observations show distinct values depending on the soil physical state (freeze-thaw). Aquarius sea surface salinity (SSS) retrievals in the polar waters are also presented. SSS variations could serve as an indicator of fresh water input to the ocean from the cryosphere, however the presence of sea ice often contaminates the SSS retrievals, hindering the analysis. The weekly grided Aquarius L-band products used a redistributed by the US Snow and Ice Data Center at http:nsidc.orgdataaquariusindex.html, and show potential for cryospheric studies.

  7. Towards an improved soil moisture retrieval for organic-rich soils from SMOS passive microwave L-band observations

    NASA Astrophysics Data System (ADS)

    Bircher, Simone; Richaume, Philippe; Mahmoodi, Ali; Mialon, Arnaud; Fernandez-Moran, Roberto; Wigneron, Jean-Pierre; Demontoux, François; Jonard, François; Weihermüller, Lutz; Andreasen, Mie; Rautiainen, Kimmo; Ikonen, Jaakko; Schwank, Mike; Drusch, Mattias; Kerr, Yann H.

    2017-04-01

    From the passive L-band microwave radiometer onboard the Soil Moisture and Ocean Salinity (SMOS) space mission global surface soil moisture data is retrieved every 2 - 3 days. Thus far, the empirical L-band Microwave Emission of the Biosphere (L-MEB) radiative transfer model applied in the SMOS soil moisture retrieval algorithm is exclusively calibrated over test sites in dry and temperate climate zones. Furthermore, the included dielectric mixing model relating soil moisture to relative permittivity accounts only for mineral soils. However, soil moisture monitoring over the higher Northern latitudes is crucial since these regions are especially sensitive to climate change. A considerable positive feedback is expected if thawing of these extremely organic soils supports carbon decomposition and release to the atmosphere. Due to differing structural characteristics and thus varying bound water fractions, the relative permittivity of organic material is lower than that of the most mineral soils at a given water content. This assumption was verified by means of L-band relative permittivity laboratory measurements of organic and mineral substrates from various sites in Denmark, Finland, Scotland and Siberia using a resonant cavity. Based on these data, a simple empirical dielectric model for organic soils was derived and implemented in the SMOS Soil Moisture Level 2 Prototype Processor (SML2PP). Unfortunately, the current SMOS retrieved soil moisture product seems to show unrealistically low values compared to in situ soil moisture data collected from organic surface layers in North America, Europe and the Tibetan Plateau so that the impact of the dielectric model for organic soils cannot really be tested. A simplified SMOS processing scheme yielding higher soil moisture levels has recently been proposed and is presently under investigation. Furthermore, recalibration of the model parameters accounting for vegetation and roughness effects that were thus far only

  8. The design of a linear L-band high power amplifier for mobile communication satellites

    NASA Technical Reports Server (NTRS)

    Whittaker, N.; Brassard, G.; Li, E.; Goux, P.

    1990-01-01

    A linear L-band solid state high power amplifier designed for the space segment of the Mobile Satellite (MSAT) mobile communication system is described. The amplifier is capable of producing 35 watts of RF power with multitone signal at an efficiency of 25 percent and with intermodulation products better than 16 dB below carrier.

  9. Chiral d -wave superconductivity in a triangular surface lattice mediated by long-range interaction

    NASA Astrophysics Data System (ADS)

    Cao, Xiaodong; Ayral, Thomas; Zhong, Zhicheng; Parcollet, Olivier; Manske, Dirk; Hansmann, Philipp

    2018-04-01

    Adatom systems on the Si(111) surface have recently attracted an increasing attention as strongly correlated systems with a rich phase diagram. We study these materials by a single band model on the triangular lattice, including 1 /r long-range interaction. Employing the recently proposed TRILEX method, we find an unconventional superconducting phase of chiral d -wave symmetry in hole-doped systems. Contrary to usual scenarios where charge and spin fluctuations are seen to compete, here the superconductivity is driven simultaneously by both charge and spin fluctuations and crucially relies on the presence of the long-range tail of the interaction. We provide an analysis of the relevant collective bosonic modes and predict how a cumulative charge and spin paring mechanism leads to superconductivity in doped silicon adatom materials.

  10. Transition-edge superconducting antenna-coupled bolometer

    NASA Astrophysics Data System (ADS)

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

    2003-02-01

    We report test results for a single pixel antenna-coupled bolometric detector. Our device consists of a dual slot microstrip antenna coupled to an Al/Ti/Au voltage-biased transition edge superconducting bolometer (TES). The coupling architecture involves propagating the signal along superconducting microstrip lines and terminating the lines at a normal metal resistor colocated with a TES on a thermally isolated island. The device, which is inherently polarization sensitive, is optimized for 140 GHz band measurements. In the thermal bandwidth of the TES, we measure a noise equivalent power of 2.0 × 10-17 W/√Hz in dark tests that agrees with calculated NEP including only contributions from thermal, Johnson and amplifier noise. We do not measure any excess noise at frequencies between 1 and 200 Hz. We measure a thermal conductance G ~5.5 × 10-11 W/K. We measure a thermal time constant as low as 437μs at 3μV bias when stimulating the TES directly using an LED.

  11. Station to instrumented aircraft L-band telemetry system and RF signal controller for spacecraft simulations and station calibration

    NASA Technical Reports Server (NTRS)

    Scaffidi, C. A.; Stocklin, F. J.; Feldman, M. B.

    1971-01-01

    An L-band telemetry system designed to provide the capability of near-real-time processing of calibration data is described. The system also provides the capability of performing computerized spacecraft simulations, with the aircraft as a data source, and evaluating the network response. The salient characteristics of a telemetry analysis and simulation program (TASP) are discussed, together with the results of TASP testing. The results of the L-band system testing have successfully demonstrated the capability of near-real-time processing of telemetry test data, the control of the ground-received signal to within + or - 0.5 db, and the computer generation of test signals.

  12. High Resolution UAV-based Passive Microwave L-band Imaging of Soil Moisture

    NASA Astrophysics Data System (ADS)

    Gasiewski, A. J.; Stachura, M.; Elston, J.; McIntyre, E. M.

    2013-12-01

    Due to long electrical wavelengths and aperture size limitations the scaling of passive microwave remote sensing of soil moisture from spaceborne low-resolution applications to high resolution applications suitable for precision agriculture requires use of low flying aerial vehicles. This presentation summarizes a project to develop a commercial Unmanned Aerial Vehicle (UAV) hosting a precision microwave radiometer for mapping of soil moisture in high-value shallow root-zone crops. The project is based on the use of the Tempest electric-powered UAV and a compact digital L-band (1400-1427 MHz) passive microwave radiometer developed specifically for extremely small and lightweight aerial platforms or man-portable, tractor, or tower-based applications. Notable in this combination are a highly integrated UAV/radiometer antenna design and use of both the upwelling emitted signal from the surface and downwelling cold space signal for precise calibration using a lobe-correlating radiometer architecture. The system achieves a spatial resolution comparable to the altitude of the UAV above the ground while referencing upwelling measurements to the constant and well-known background temperature of cold space. The radiometer incorporates digital sampling and radio frequency interference mitigation along with infrared, near-infrared, and visible (red) sensors for surface temperature and vegetation biomass correction. This NASA-sponsored project is being developed both for commercial application in cropland water management, L-band satellite validation, and estuarian plume studies.

  13. Excitation of acoustic oscillations in superconducting films

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Golub, A.A.

    1973-11-01

    A study is made of the excitation of sound in a superconducting film by electromagnetic waves incident on the surface of the film. It is assumed that the thickness of the film d is much greater than the penetration depth of the field. If the acoustic wave is damped over a distance of the order of d, traveling acoustic waves can be excited in the superconductor; otherwise, standing waves are excited. The low-temperature contribution of acoustic oseillations to the surface resistence of pure superconductors ia calculated. At very low temperatures, the absorption of electromagnetic waves is mainly governed by themore » loss due to acoustic oscillations. (auth)« less

  14. Doping influence on Sm1 - x Th x OFeAs superconducting properties: Observation of the effect of intrinsic multiple Andreev reflections and determination of the superconducting parameters

    NASA Astrophysics Data System (ADS)

    Kuzmicheva, T. E.; Kuzmichev, S. A.; Zhigadlo, N. D.

    2014-04-01

    We studied SNS and S-N-S-N-...-S contacts (where S is a superconductor and N is a normal metal) formed by "break-junction" technique in polycrystalline Sm1 - x Th x OFeAs superconductor samples with critical temperatures T C = 34-45 K. In such contacts (intrinsic) multiple Andreev reflections effects were observed. Using spectroscopies based on these effects, we detected two independent bulk order parameters and determined their magnitudes. Theoretical analysis of the large and the small gap temperature dependences revealed superconducting properties of Sm1 - x Th x OFeAs to be driven by intraband coupling, and (where V ij are the electron-boson interaction matrix elements), whereas the ratio between density of states for the bands with the small and the large gap, N 2/ N 1, correspondingly, was roughly of an order. We estimated "solo" BCS-ratio values in a hypothetic case of zero interband coupling ( V i ≠ j = 0) for each condensate as 2ΔL, S/ k B T {C/L,S} ≤ 4.5. The values are constant within the range of critical temperatures studied, and correspond to a case of strong intraband electron-phonon coupling.

  15. Excitation spectrum for an inhomogeneously dipole-field-coupled superconducting qubit chain

    NASA Astrophysics Data System (ADS)

    Ian, Hou; Liu, Yu-xi; Nori, Franco

    2012-05-01

    When a chain of N superconducting qubits couples to a coplanar resonator, each of the qubits experiences a different dipole-field coupling strength due to the wave form of the cavity field. We find that this inhomogeneous coupling leads to a dependence of the collective ladder operators of the qubit chain on the qubit-interspacing l. Varying the spacing l changes the transition amplitudes between the angular momentum levels. We derive an exact diagonalization of the general N-qubit Hamiltonian and, through the N=4 case, demonstrate how the l-dependent operators lead to a denser one-excitation spectrum and a probability redistribution of the eigenstates. Moreover, we show that the variation of l between its two limiting values coincides with the crossover between Frenkel- and Wannier-type excitons in the superconducting qubit chain.

  16. Survey of L Band Tower and Airborne Sensor Systems Relevant to Upcoming Soil Moisture Missions

    USDA-ARS?s Scientific Manuscript database

    Basic research on the physics of microwave remote sensing of soil moisture has been conducted for almost thirty years using ground-based (tower- or truck-mounted) microwave instruments at L band frequencies. Early small point-scale studies were aimed at improved understanding and verification of mi...

  17. The p-wave superconductivity in the presence of Rashba interaction in 2DEG

    PubMed Central

    Weng, Ke-Chuan; Hu, C. D.

    2016-01-01

    We investigate the effect of the Rashba interaction on two dimensional superconductivity. The presence of the Rashba interaction lifts the spin degeneracy and gives rise to the spectrum of two bands. There are intraband and interband pairs scattering which result in the coupled gap equations. We find that there are isotropic and anisotropic components in the gap function. The latter has the form of cos φk where . The former is suppressed because the intraband and the interband scatterings nearly cancel each other. Hence, −the system should exhibit the p-wave superconductivity. We perform a detailed study of electron-phonon interaction for 2DEG and find that, if only normal processes are considered, the effective coupling strength constant of this new superconductivity is about one-half of the s-wave case in the ordinary 2DEG because of the angular average of the additional in the anisotropic gap function. By taking into account of Umklapp processes, we find they are the major contribution in the electron-phonon coupling in superconductivity and enhance the transition temperature Tc. PMID:27459677

  18. Broadband Direct Detection Submillimeter Spectrometer with Multiplexed Superconducting Transition Edge Thermometer Bolometers

    NASA Technical Reports Server (NTRS)

    Benford, D. J.; Ames, T. A.; Chervenak, J. A.; Moseley, S. H.; Shafer, R. A.; Staguhn, J. G.; Voellmer, G. M.; Pajot, F.; Rioux, C.; Phillips, T. G.; hide

    2002-01-01

    We present performance results based on the first astronomical use of multiplexed superconducting bolometers as direct detectors (i.e., with cold electrons) for spectroscopy. The Fabry-Perot Interferometer Bolometer Research Experiment (FIBRE) is a broadband submillimeter spectrometer for the Caltech Submillimeter Observatory (CSO). FIBRE's detectors are superconducting transition edge sensor (TES) bolometers read out by a SQUID multiplexer. The Fabry-Perot uses a low resolution grating to order sort the incoming light. A linear bolometer array consisting of 16 elements detects this dispersed light, capturing 5 orders simultaneously from one position on the sky. With tuning of the Fabry-Perot over one free spectral range, a spectrum covering Delta lambda/lambda = 1/7 at a resolution of delta lambda/lambda = 1/1200 can be acquired. This spectral resolution is sufficient to resolve Doppler-broadened line emission from external galaxies. FIBRE has been operated in the 350 Am (850 GHz) band. These bands cover line emission from the important star formation tracers neutral carbon [CI] and carbon monoxide (CO).

  19. Superconducting antennas for telecommunication applications based on dual mode cross slotted patches

    NASA Astrophysics Data System (ADS)

    Cassinese, A.; Barra, M.; Fragalà, I.; Kusunoki, M.; Malandrino, G.; Nakagawa, T.; Perdicaro, L. M. S.; Sato, K.; Ohshima, S.; Vaglio, R.

    2002-08-01

    Dual mode devices based on high temperature superconducting films represent an interesting class for telecommunication applications since they combine a miniaturized size with a good power handling. Here we report on a novel compact antenna obtained by crossing a square patch with two or more slots. The proposed design has an antenna size reduction of about 40% as compared to the conventional square patch microstrip antennas. Single patch antenna both with linear (LP) and circular (CP) polarization operating in the X-band have been designed and tested at prototype level. They are realized by using double sided (YBa 2Cu 3O 7- x) YBCO and Tl 2Ba 2Ca 1Cu 2O 8 (Tl-2212) superconducting films grown on MgO substrates and tested with a portable cryocooler. They showed at T=77 K a return loss <25 dB and a power handling of 23 dBm. Exemplary 16 elements arrays LP antennas operating in the X band have been also realized by using YBCO film grown on 2 ″ diameter MgO substrate.

  20. Evaluation of Airborne l- Band Multi-Baseline Pol-Insar for dem Extraction Beneath Forest Canopy

    NASA Astrophysics Data System (ADS)

    Li, W. M.; Chen, E. X.; Li, Z. Y.; Jiang, C.; Jia, Y.

    2018-04-01

    DEM beneath forest canopy is difficult to extract with optical stereo pairs, InSAR and Pol-InSAR techniques. Tomographic SAR (TomoSAR) based on different penetration and view angles could reflect vertical structure and ground structure. This paper aims at evaluating the possibility of TomoSAR for underlying DEM extraction. Airborne L-band repeat-pass Pol-InSAR collected in BioSAR 2008 campaign was applied to reconstruct the 3D structure of forest. And sum of kronecker product and algebraic synthesis algorithm were used to extract ground structure, and phase linking algorithm was applied to estimate ground phase. Then Goldstein cut-branch approach was used to unwrap the phases and then estimated underlying DEM. The average difference between the extracted underlying DEM and Lidar DEM is about 3.39 m in our test site. And the result indicates that it is possible for underlying DEM estimation with airborne L-band repeat-pass TomoSAR technique.

  1. Accurate Measurements of the Dielectric Constant of Seawater at L Band

    NASA Technical Reports Server (NTRS)

    Lang, Roger H.; Utku, Cuneyt; Tarkocin, Yalcin; LeVine, David M.

    2010-01-01

    This report describes measurements of the dielectric constant of seawater at a frequency of 1.413 GHz that is at the center of the L-Sand radiometric protected frequency spectrum. Aquarius will be sensing the sea surface salinity from space in this band. The objective of the project is to refine the model function for the dielectric constant as a function of salinity and temperature so that remote sensing measurements can be made with the accuracy needed to meet the measurement goals (0.2 psu) of the Aquarius mission. The measurements were made, using a microwave cavity operated in the transmission configuration. The cavity's temperature was accurately regulated to 0.02 C by immersing it in a temperature controlled bath of distilled water and ethanol glycol. Seawater had been purchased from Ocean Scientific International Limited (OS1L) at salinities of 30, 35 and 38 psu. Measurements of these seawater samples were then made over a range of temperatures, from l0 C to 35 C in 5 C intervals. Repeated measurements were made at each temperature and salinity, Mean values and standard deviations were then computed. Total error budgets indicated that the real and imaginary parts of the dielectric constant had a relative accuracy of about l%.

  2. Longitudinal Proximity Effects in Superconducting Transition-Edge Sensors

    NASA Technical Reports Server (NTRS)

    Sadlier, John E.; Smith, Stephen J.; Bandler, Simon R.; Chervenak, James A.; Clem, John R.

    2009-01-01

    We have found experimentally that the critical current of a square thin-film superconducting transition-edge sensor (TES) depends exponentially upon the side length L and the square root of the temperature T, a behavior that has a natural theoretical explanation in terms of longitudinal proximity effects if the TES is regarded as a weak link between superconducting leads. As a consequence, the effective transition temperature T(sub c) of the TES is current-dependent and at fixed current scales as 1/L(sup 2). We also have found that the critical current can show clear Fraunhofer-like oscillations in an applied magnetic field, similar to those found in Josephson junctions. We have observed the longitudinal proximity effect in these devices over extraordinarily long lengths up to 290 micrometers, 1450 times the mean-free path.

  3. Longitudinal Proximity Effects in Superconducting Transition-Edge Sensors

    NASA Technical Reports Server (NTRS)

    Sadleir, John E.; Smith, Stephen J.; Bandler, Simon R.; Chervenak, James A.; Clem, John R.

    2010-01-01

    We have found experimentally that the critical current of a square thin-film superconducting transition-edge sensor (TES) depends exponentially upon the side length L and the square root of the temperature T, a behavior that has a natural theoretical explanation in terms of longitudinal proximity effects if the TES is regarded as a weak link between superconducting leads. As a consequence, the effective transition temperature T(sub c) of the TES is current-dependent and at fixed current scales as 1/L(sup 2). We also have found that the critical current can show clear Fraunhofer-like oscillations in an applied magnetic field, similar to those found in Josephson junctions. We have observed the longitudinal proximity effect in these devices over extraordinarily long lengths up to 290 micrometers, 1450 times the mean-free path.

  4. Mixed-pairing superconductivity in 5 d Mott insulators with antisymmetric exchange: Application to Sr2IrO4

    NASA Astrophysics Data System (ADS)

    Zare, Mohammad-Hossein; Biderang, Mehdi; Akbari, Alireza

    2017-11-01

    We study the symmetry of the potential superconducting order parameter in 5 d Mott insulators with an eye toward hole-doped Sr2IrO4 . Using a mean-field method, a mixed singlet-triplet superconductivity, d +p , is observed due to the antisymmetric exchange originating from a quasi-spin-orbit coupling. Our calculation on ribbon geometry shows the possible existence of the topologically protected edge states, because of the nodal structure of the superconducting gap. These edge modes are spin polarized and emerge as zero-energy flat bands, supporting a symmetry-protected Majorana state, verified by evaluation of the winding number and Z2 topological invariant. At the end, a possible experimental approach for observation of these edge states and determination of the superconducting gap symmetry is discussed based on the quasiparticle interference technique.

  5. The impact of travel distance, travel time and waiting time on health-related quality of life of diabetes patients: An investigation in six European countries.

    PubMed

    Konerding, Uwe; Bowen, Tom; Elkhuizen, Sylvia G; Faubel, Raquel; Forte, Paul; Karampli, Eleftheria; Mahdavi, Mahdi; Malmström, Tomi; Pavi, Elpida; Torkki, Paulus

    2017-04-01

    The effects of travel distance and travel time to the primary diabetes care provider and waiting time in the practice on health-related quality of life (HRQoL) of patients with type 2 diabetes are investigated. Survey data of 1313 persons with type 2 diabetes from six regions in England (274), Finland (163), Germany (254), Greece (165), the Netherlands (354), and Spain (103) were analyzed. Various multiple linear regression analyses with four different EQ-5D-3L indices (English, German, Dutch and Spanish index) as target variables, with travel distance, travel time, and waiting time in the practice as focal predictors and with control for study region, patient's gender, patient's age, patient's education, time since diagnosis, thoroughness of provider-patient communication were computed. Interactions of regions with the remaining five control variables and the three focal predictors were also tested. There are no interactions of regions with control variables or focal predictors. The indices decrease with increasing travel time to the provider and increasing waiting time in the provider's practice. HRQoL of patients with type 2 diabetes might be improved by decreasing travel time to the provider and waiting time in the provider's practice. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. Pressure-induced multiband superconductivity in pyrite PtB i2 with perfect electron-hole compensation

    NASA Astrophysics Data System (ADS)

    Chen, Xuliang; Shao, Dexi; Gu, Chuanchuan; Zhou, Yonghui; An, Chao; Zhou, Ying; Zhu, Xiangde; Chen, Tong; Tian, Mingliang; Sun, Jian; Yang, Zhaorong

    2018-05-01

    We report on the discovery of pressure-induced superconductivity in the compensated semimetal pyrite PtB i2 , which exhibits extreme magnetoresistance (XMR) and nontrivial band structure at ambient pressure. The appearance of superconductivity, first observed at PC˜13 GPa with an onset critical temperature TC of ˜2.2 K , is accompanied by a pronounced enhancement of the density of electrons and holes based on Hall-effect measurements. Upon further compression, TC remains almost unchanged up to 50.0 GPa; remarkably, the perfect electron-hole compensation still holds, while the carrier mobility greatly reduces. No evident trace of structural phase transitions is detected through synchrotron x-ray diffraction over the measured pressure range of 1.5-51.2 GPa. These results highlight a multiband characteristic of the observed superconductivity, making pyrite PtB i2 unique among the compensated XMR materials where the pressure-induced superconductivity usually links to structural transitions and carrier imbalance.

  7. Project #8 (95-08), Traveler Information Services (TIS), Appendices

    DOT National Transportation Integrated Search

    1995-12-15

    THE L-95 CORRIDOR COALITION'S TRAVELER INFORMATION SERVICES (TIS) PROJECT IS INTENDED TO IMPLEMENT AN ADVANCED TRAVELER INFORMATION SYSTEM TAILORED TO THE UNIQUE NEEDS OF THE NORTHEAST CORRIDOR. THE SYSTEM WILL ACQUIRE AND DISSEMINATE INFORMATION ON ...

  8. Sensitive Superconducting Gravity Gradiometer Constructed with Levitated Test Masses

    NASA Astrophysics Data System (ADS)

    Griggs, C. E.; Moody, M. V.; Norton, R. S.; Paik, H. J.; Venkateswara, K.

    2017-12-01

    We demonstrate basic operations of a two-component superconducting gravity gradiometer (SGG) that is constructed with a pair of magnetically levitated test masses coupled to superconducting quantum-interference devices. A design that gives a potential sensitivity of 1.4 ×10-4 E Hz-1 /2 (1 E ≡10-9 s-2 ) in the frequency band of 1 to 50 mHz and better than 2 ×10-5 E Hz-1 /2 between 0.1 and 1 mHz for a compact tensor SGG that fits within a 22-cm-diameter sphere. The SGG has the capability of rejecting the platform acceleration and jitter in all 6 degrees of freedom to one part in 109 . Such an instrument has applications in precision tests of fundamental laws of physics, earthquake early warning, and gravity mapping of Earth and the planets.

  9. 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)

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

    2012-01-01

    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

  10. Incorporating travel time reliability into the Highway Capacity Manual.

    DOT National Transportation Integrated Search

    2014-01-01

    This final report documents the activities performed during SHRP 2 Reliability Project L08: Incorporating Travel Time Reliability into the Highway Capacity Manual. It serves as a supplement to the proposed chapters for incorporating travel time relia...

  11. Enhancement of pairing interaction and magnetic fluctuations toward a band insulator in an electron-doped Li(x)ZrNCl Superconductor.

    PubMed

    Kasahara, Yuichi; Kishiume, Tsukasa; Takano, Takumi; Kobayashi, Katsuki; Matsuoka, Eiichi; Onodera, Hideya; Kuroki, Kazuhiko; Taguchi, Yasujiro; Iwasa, Yoshihiro

    2009-08-14

    The doping dependence of specific heat and magnetic susceptibility has been investigated for Li(x)ZrNCl superconductors derived from a band insulator. As the carrier concentration is decreased, the anisotropy of superconducting gap changes from highly anisotropic to almost isotropic. It was also found that, upon reducing carrier density, the superconducting coupling strength and the magnetic susceptibility are concomitantly enhanced in parallel with T(c), while the density of states at the Fermi level is kept almost constant. Theoretical calculations taking into account the on-site Coulomb interaction reproduced the experimental results, suggesting a possible pairing mediated by magnetic fluctuations, even in the doped band insulators.

  12. Intermediate coupled superconductivity in yttrium intermetallics

    NASA Astrophysics Data System (ADS)

    Sharma, Ramesh; Ahmed, Gulzar; Sharma, Yamini

    2017-09-01

    Non-magnetic YIn3, LaIn3 and LuIn3 with a superconducting transition temperature Tc of 0.78, 0.71 and 0.24 K were investigated for superconductivity. Similarly, rare-earth compound LaSn3 has been reported to exhibit superconductivity around 6.25 K, whereas the non-magnetic YSn3 is a superconductor with Tc of 7 K. The substitution of 13th group In-atoms by 14th group Sn-atoms is seen to enhance Tc by nearly one order, although the lattice parameters increase by ∼1.0% in YSn3 compared to YIn3 compound. It is observed from the ground state properties that the slight difference in the energy band structures of YIn3, YIn2Sn and YSn3 gives rise to various complex Fermi surfaces which are multiply connected and exhibit vast differences. The Fermi level lies on a sharp peak in YSn3 which has a higher density of states N(EF), whereas Fermi level lies on the shoulder of a sharp peak in YIn3. The electron localization function (ELF) and difference charge density maps clearly illustrate the difference in the nature of bonding; the Ysbnd Sn bonds are clearly more ionic (due to larger bond length) than Ysbnd In bonds. These results are consistent with the Bader charges which show loss of charges from Y-atoms and a gain of charges by In/Sn atoms. The dynamical properties also clearly illustrate the difference in the nature of bonds in YX3 intermetallics. A softening of the lowermost acoustic modes is observed in YIn3, whereas all the modes in YSn3 are observed to have positive frequencies which imply its greater stability. Since λel-ph < 1, both YIn3 and YSn3 compounds exhibit type I superconductivity according to BCS theory. However, the smaller N(EF) obtained from the density of states (DOS); the electron-phonon coupling constant λel-ph obtained from the temperature dependent specific heat as well as the instability in phonon modes due to stronger Ysbnd In and Insbnd In bonds in YIn3 may be the cause of lower Tc and filamentary nature of superconductivity. Insertion of Sn

  13. High field superconducting magnets

    NASA Technical Reports Server (NTRS)

    Hait, Thomas P. (Inventor); Shirron, Peter J. (Inventor)

    2011-01-01

    A superconducting magnet includes an insulating layer disposed about the surface of a mandrel; a superconducting wire wound in adjacent turns about the mandrel to form the superconducting magnet, wherein the superconducting wire is in thermal communication with the mandrel, and the superconducting magnet has a field-to-current ratio equal to or greater than 1.1 Tesla per Ampere; a thermally conductive potting material configured to fill interstices between the adjacent turns, wherein the thermally conductive potting material and the superconducting wire provide a path for dissipation of heat; and a voltage limiting device disposed across each end of the superconducting wire, wherein the voltage limiting device is configured to prevent a voltage excursion across the superconducting wire during quench of the superconducting magnet.

  14. An L-band SAR for repeat pass deformation measurements on a UAV platform

    NASA Technical Reports Server (NTRS)

    Hensley, Scott; Lou, Yunling; Rosen, Paul; Wheeler, Kevin; Zebker, Howard; Madsen, Soren; Miller, Tim; Hoffman, Jim; Farra, Don

    2003-01-01

    We are proposing to develop a miniaturized polarimetric L-band synthetic aperture radar (SAR) for repeat-pass differential interferometric measurements of deformation for rapidly deforming surfaces of geophysical interest such as volcanoes or earthquakes that is to be flown on a unmanned aerial vehicle (UAV) or minimally piloted vehicle (MPV). Upon surveying the capabilities and availabilities of such aircraft, the Proteus aircraft and the ALTAIR UAV appear to meet our criteria in terms of payload capabilities, flying altitude, and endurance. To support the repeat pass deformation capability it is necessary to control flight track capability of the aircraft to be within a specified 10 m tube with a goal of 1 m. This requires real-time GPS control of the autopilot to achieve these objectives that has not been demonstrated on these aircraft. Based on the Proteus and ALTAIR's altitude of 13.7 km (45,000 ft), we are designing a fully polarimetric L-band radar with 80 MHz bandwidth and a 16 km range swath. The radar will have an active electronic beam steering antenna to achieve a Doppler centroid stability that is necessary for repeat-pass interferometry. This paper presents some of the trade studies for the platform, instrument and the expected science.

  15. Weekly gridded Aquarius L-band radiometer/scatterometer observations and salinity retrievals over the polar regions - Part 2: Initial product analysis

    NASA Astrophysics Data System (ADS)

    Brucker, L.; Dinnat, E. P.; Koenig, L. S.

    2014-05-01

    Following the development and availability of Aquarius weekly polar-gridded products, this study presents the spatial and temporal radiometer and scatterometer observations at L band (frequency ~1.4 GHz) over the cryosphere including the Greenland and Antarctic ice sheets, sea ice in both hemispheres, and over sub-Arctic land for monitoring the soil freeze/thaw state. We provide multiple examples of scientific applications for the L-band data over the cryosphere. For example, we show that over the Greenland Ice Sheet, the unusual 2012 melt event lead to an L-band brightness temperature (TB) sustained decrease of ~5 K at horizontal polarization. Over the Antarctic ice sheet, normalized radar cross section (NRCS) observations recorded during ascending and descending orbits are significantly different, highlighting the anisotropy of the ice cover. Over sub-Arctic land, both passive and active observations show distinct values depending on the soil physical state (freeze/thaw). Aquarius sea surface salinity (SSS) retrievals in the polar waters are also presented. SSS variations could serve as an indicator of fresh water input to the ocean from the cryosphere, however the presence of sea ice often contaminates the SSS retrievals, hindering the analysis. The weekly grided Aquarius L-band products used are distributed by the US Snow and Ice Data Center at http://nsidc.org/data/aquarius/index.html , and show potential for cryospheric studies.

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

    NASA Technical Reports Server (NTRS)

    Yueh, Simon H.; Chaubell, Mario J.

    2012-01-01

    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

  17. Detecting sign-changing superconducting gap in LiFeAs using quasiparticle interference

    NASA Astrophysics Data System (ADS)

    Altenfeld, D.; Hirschfeld, P. J.; Mazin, I. I.; Eremin, I.

    2018-02-01

    Using a realistic ten-orbital tight-binding model Hamiltonian fitted to the angle-resolved photoemission spectroscopy data on LiFeAs, we analyze the temperature, frequency, and momentum dependencies of quasiparticle interference to identify gap sign changes in a qualitative way, following our original proposal [Phys. Rev. B 92, 184513 (2015), 10.1103/PhysRevB.92.184513]. We show that all features present for the simple two-band model for the sign-changing s+--wave superconducting gap employed previously are still present in the realistic tight-binding approximation and gap values observed experimentally. We discuss various superconducting gap structures proposed for LiFeAs and identify various features of these superconducting gap functions in the quasiparticle interference patterns. On the other hand, we show that it will be difficult to identify the more complicated possible sign structures of the hole pocket gaps in LiFeAs due to the smallness of the pockets and the near proximity of two of the gap energies.

  18. Experimental observation of incoherent-coherent crossover and orbital-dependent band renormalization in iron chalcogenide superconductors

    DOE PAGES

    Liu, Z. K.; Yi, M.; Zhang, Y.; ...

    2015-12-22

    The level of electronic correlation has been one of the key questions in understanding the nature of superconductivity. Among the iron-based superconductors, the iron chalcogenide family exhibits the strongest electron correlations. To gauge the correlation strength, we performed a systematic angle-resolved photoemission spectroscopy study on the iron chalcogenide series Fe 1+ySe xTe 1-x (0 < x < 0.59), a model system with the simplest structure. Our measurement reveals an incoherent-to-coherent crossover in the electronic structure as the selenium ratio increases and the system evolves from a weakly localized to a more itinerant state. Furthermore, we found that the effective massmore » of bands dominated by the d xy orbital character significantly decreases with increasing selenium ratio, as compared to the d xz/d yz orbital-dominated bands. The orbital-dependent change in the correlation level agrees with theoretical calculations on the band structure renormalization, and may help to understand the onset of superconductivity in Fe 1+ySe xTe 1-x.« less

  19. Alcohol sensing over O+E+S+C+L+U transmission band based on porous cored octagonal photonic crystal fiber

    NASA Astrophysics Data System (ADS)

    Paul, Bikash Kumar; Islam, Md. Shadidul; Ahmed, Kawsar; Asaduzzaman, Sayed

    2017-06-01

    A micro structure porous cored octagonal photonic crystal fiber (P-OPCF) has been proposed to sense aqueous analysts (alcohol series) over a wavelength range of 0.80 μm to 2.0 μm. By implementing a full vectorial finite element method (FEM), the numerical simulation on the proposed O-PCF has been analyzed. Numerical investigation shows that high sensitivity can be gained by changing the structural parameters. The obtained result shows the sensitivities of 66.78%, 67.66%, 68.34%, 68.72%, and 69.09%, and the confinement losses of 2.42×10-10 dB/m, 3.28×10-11 dB/m, 1.21×10-6 dB/m, 4.79×10-10 dB/m, and 4.99×10-9 dB/m at the 1.33 μm wavelength for methanol, ethanol, propanol, butanol, and pentanol, respectively can satisfy the condition of much legibility to install an optical system. The effects of the varying core and cladding diameters, pitch distance, operating wavelength, and effective refractive index are also reported here. It reflects that a significant sensitivity and low confinement loss can be achieved by the proposed P-OPCF. The proposed P-OPCF also covers the wavelength band (O+E+S+C+L+U). The investigation also exhibits that the sensitivity increases when the wavelength increases like S O-band< S E-band < S S-band < S C-band < S L-band < S U-band. This research observation has much pellucidity which has remarkable impact on the field of optical fiber sensor.

  20. Full-gap superconductivity in spin-polarised surface states of topological semimetal β-PdBi2.

    PubMed

    Iwaya, K; Kohsaka, Y; Okawa, K; Machida, T; Bahramy, M S; Hanaguri, T; Sasagawa, T

    2017-10-17

    A bulk superconductor possessing a topological surface state at the Fermi level is a promising system to realise long-sought topological superconductivity. Although several candidate materials have been proposed, experimental demonstrations concurrently exploring spin textures and superconductivity at the surface have remained elusive. Here we perform spectroscopic-imaging scanning tunnelling microscopy on the centrosymmetric superconductor β-PdBi 2 that hosts a topological surface state. By combining first-principles electronic-structure calculations and quasiparticle interference experiments, we determine the spin textures at the surface, and show not only the topological surface state but also all other surface bands exhibit spin polarisations parallel to the surface. We find that the superconducting gap fully opens in all the spin-polarised surface states. This behaviour is consistent with a possible spin-triplet order parameter expected for such in-plane spin textures, but the observed superconducting gap amplitude is comparable to that of the bulk, suggesting that the spin-singlet component is predominant in β-PdBi 2 .Although several materials have been proposed as topological superconductors, spin textures and superconductivity at the surface remain elusive. Here, Iwaya et al. determine the spin textures at the surface of a superconductor β-PdBi 2 and find the superconducting gap opening in all spin-polarised surface states.

  1. Superconductivity in Doped sp3 Semiconductors: The Case of the Clathrates

    NASA Astrophysics Data System (ADS)

    Connétable, D.; Timoshevskii, V.; Masenelli, B.; Beille, J.; Marcus, J.; Barbara, B.; Saitta, A. M.; Rignanese, G.-M.; Mélinon, P.; Yamanaka, S.; Blase, X.

    2003-12-01

    We present a joint experimental and theoretical study of the superconductivity in doped silicon clathrates. The critical temperature in Ba8@Si-46 is shown to strongly decrease with applied pressure. These results are corroborated by ab initio calculations using MacMillan's formulation of the BCS theory with the electron-phonon coupling constant λ calculated from perturbative density functional theory. Further, the study of I8@Si-46 and of gedanken pure silicon diamond and clathrate phases doped within a rigid-band approach show that the superconductivity is an intrinsic property of the sp3 silicon network. As a consequence, carbon clathrates are predicted to yield large critical temperatures with an effective electron-phonon interaction much larger than in C60.

  2. Fermiology and Superconductivity of Topological Surface States in PdTe2

    NASA Astrophysics Data System (ADS)

    Clark, O. J.; Neat, M. J.; Okawa, K.; Bawden, L.; Marković, I.; Mazzola, F.; Feng, J.; Sunko, V.; Riley, J. M.; Meevasana, W.; Fujii, J.; Vobornik, I.; Kim, T. K.; Hoesch, M.; Sasagawa, T.; Wahl, P.; Bahramy, M. S.; King, P. D. C.

    2018-04-01

    We study the low-energy surface electronic structure of the transition-metal dichalcogenide superconductor PdTe2 by spin- and angle-resolved photoemission, scanning tunneling microscopy, and density-functional theory-based supercell calculations. Comparing PdTe2 with its sister compound PtSe2 , we demonstrate how enhanced interlayer hopping in the Te-based material drives a band inversion within the antibonding p -orbital manifold well above the Fermi level. We show how this mediates spin-polarized topological surface states which form rich multivalley Fermi surfaces with complex spin textures. Scanning tunneling spectroscopy reveals type-II superconductivity at the surface, and moreover shows no evidence for an unconventional component of its superconducting order parameter, despite the presence of topological surface states.

  3. Simulation of L-band and HH microwave backscattering from coniferous forest stands - A comparison with SIR-B data

    NASA Technical Reports Server (NTRS)

    Sun, Guo-Qing; Simonett, David S.

    1988-01-01

    SIR-B images of the Mt. Shasta region of northern California are used to evaluate a composite L-band HH backscattering model of coniferous forest stands. It is found that both SIR-B and simulated backscattering coefficients for eight stands studied have similar trends and relations to average tree height and average number of trees per pixel. Also, the dispersion and distribution of simulated backscattering coefficients from each stand broadly match SIR-B data from the same stand. Although the limited quality and quantity of experimental data makes it difficult to draw any strong conclusions, the comparisons indicate that a stand-based L-band HH composite model seems promising for explaining backscattering features.

  4. Wide-Band, High-Quantum-Efficiency Photodetector

    NASA Technical Reports Server (NTRS)

    Jackson, Deborah; Wilson, Daniel; Stern, Jeffrey

    2007-01-01

    A design has been proposed for a photodetector that would exhibit a high quantum efficiency (as much as 90 percent) over a wide wavelength band, which would typically be centered at a wavelength of 1.55 m. This and similar photodetectors would afford a capability for detecting single photons - a capability that is needed for research in quantum optics as well as for the practical development of secure optical communication systems for distribution of quantum cryptographic keys. The proposed photodetector would be of the hot-electron, phonon-cooled, thin-film superconductor type. The superconducting film in this device would be a meandering strip of niobium nitride. In the proposed photodetector, the quantum efficiency would be increased through incorporation of optiA design has been proposed for a photodetector that would exhibit a high quantum efficiency (as much as 90 percent) over a wide wavelength band, which would typically be centered at a wavelength of 1.55 m. This and similar photodetectors would afford a capability for detecting single photons - a capability that is needed for research in quantum optics as well as for the practical development of secure optical communication systems for distribution of quantum cryptographic keys. The proposed photodetector would be of the hot-electron, phonon-cooled, thin-film superconductor type. The superconducting film in this device would be a meandering strip of niobium nitride. In the proposed photodetector, the quantum efficiency would be increased through incorporation of opti-

  5. Banded whistlers observed on OGO-4

    NASA Technical Reports Server (NTRS)

    Paymar, E. M.

    1972-01-01

    Inspection of broadband VLF records from OGO-4 shows that some whistlers exhibit a banded structure in which one or more bands of frequencies are missing from the whistler's spectrum. The phenomenon is commonly observed by satellites on midlatitude field lines at all local times and at various longitudes around the world. The dispersion of banded whistlers (BW) is of several tens of sec to the 1/2 power, indicating that they originated in the opposite hemisphere and are propagating downward at the satellite. BW are generally spread in time (tenths of seconds) rather than sharply defined and tend to occur at random. The frequency spacing of the bands may be either uniform or irregular, and may vary radically between successive events. Several possible explanations for BW are considered. In particular, an analysis of the interaction of plane electromagnetic waves traveling in an anisotropic plasma with a field aligned slab of enhanced ionization is presented with promising results.

  6. Optimization of radial-type superconducting magnetic bearing using the Taguchi method

    NASA Astrophysics Data System (ADS)

    Ai, Liwang; Zhang, Guomin; Li, Wanjie; Liu, Guole; Liu, Qi

    2018-07-01

    It is important and complicated to model and optimize the levitation behavior of superconducting magnetic bearing (SMB). That is due to the nonlinear constitutive relationships of superconductor and ferromagnetic materials, the relative movement between the superconducting stator and PM rotor, and the multi-parameter (e.g., air-gap, critical current density, and remanent flux density, etc.) affecting the levitation behavior. In this paper, we present a theoretical calculation and optimization method of the levitation behavior for radial-type SMB. A simplified model of levitation force calculation is established using 2D finite element method with H-formulation. In the model, the boundary condition of superconducting stator is imposed by harmonic series expressions to describe the traveling magnetic field generated by the moving PM rotor. Also, experimental measurements of the levitation force are performed and validate the model method. A statistical method called Taguchi method is adopted to carry out an optimization of load capacity for SMB. Then the factor effects of six optimization parameters on the target characteristics are discussed and the optimum parameters combination is determined finally. The results show that the levitation behavior of SMB is greatly improved and the Taguchi method is suitable for optimizing the SMB.

  7. Probing the unconventional superconducting state of LiFeAs by quasiparticle interference.

    PubMed

    Hänke, Torben; Sykora, Steffen; Schlegel, Ronny; Baumann, Danny; Harnagea, Luminita; Wurmehl, Sabine; Daghofer, Maria; Büchner, Bernd; van den Brink, Jeroen; Hess, Christian

    2012-03-23

    A crucial step in revealing the nature of unconventional superconductivity is to investigate the symmetry of the superconducting order parameter. Scanning tunneling spectroscopy has proven a powerful technique to probe this symmetry by measuring the quasiparticle interference (QPI) which sensitively depends on the superconducting pairing mechanism. A particularly well-suited material to apply this technique is the stoichiometric superconductor LiFeAs as it features clean, charge neutral cleaved surfaces without surface states and a relatively high T(c)∼18  K. Our data reveal that in LiFeAs the quasiparticle scattering is governed by a van Hove singularity at the center of the Brillouin zone which is in stark contrast to other pnictide superconductors where nesting is crucial for both scattering and s(±) superconductivity. Indeed, within a minimal model and using the most elementary order parameters, calculations of the QPI suggest a dominating role of the holelike bands for the quasiparticle scattering. Our theoretical findings do not support the elementary singlet pairing symmetries s(++), s(±), and d wave. This brings to mind that the superconducting pairing mechanism in LiFeAs is based on an unusual pairing symmetry such as an elementary p wave (which provides optimal agreement between the experimental data and QPI simulations) or a more complex order parameter (e.g., s+id wave symmetry).

  8. Interband quasiparticle scattering in superconducting LiFeAs reconciles photoemission and tunneling measurements.

    PubMed

    Hess, Christian; Sykora, Steffen; Hänke, Torben; Schlegel, Ronny; Baumann, Danny; Zabolotnyy, Volodymyr B; Harnagea, Luminita; Wurmehl, Sabine; van den Brink, Jeroen; Büchner, Bernd

    2013-01-04

    Several angle-resolved photoemission spectroscopy (ARPES) studies reveal a poorly nested Fermi surface of LiFeAs, far away from a spin density wave instability, and clear-cut superconducting gap anisotropies. On the other hand a very different, more nested Fermi surface and dissimilar gap anisotropies have been obtained from quasiparticle interference (QPI) data, which were interpreted as arising from intraband scattering within holelike bands. Here we show that this ARPES-QPI paradox is completely resolved by interband scattering between the holelike bands. The resolution follows from an excellent agreement between experimental quasiparticle scattering data and T-matrix QPI calculations (based on experimental band structure data), which allows disentangling interband and intraband scattering processes.

  9. Dual-band frequency selective surface with large band separation and stable performance

    NASA Astrophysics Data System (ADS)

    Zhou, Hang; Qu, Shao-Bo; Peng, Wei-Dong; Lin, Bao-Qin; Wang, Jia-Fu; Ma, Hua; Zhang, Jie-Qiu; Bai, Peng; Wang, Xu-Hua; Xu, Zhuo

    2012-05-01

    A new technique of designing a dual-band frequency selective surface with large band separation is presented. This technique is based on a delicately designed topology of L- and Ku-band microwave filters. The two band-pass responses are generated by a capacitively-loaded square-loop frequency selective surface and an aperture-coupled frequency selective surface, respectively. A Faraday cage is located between the two frequency selective surface structures to eliminate undesired couplings. Based on this technique, a dual-band frequency selective surface with large band separation is designed, which possesses large band separation, high selectivity, and stable performance under various incident angles and different polarizations.

  10. Design analysis and simulation study of an efficiency enhanced L-band MILO

    NASA Astrophysics Data System (ADS)

    Dixit, Gargi; Kumar, Arjun; Jain, P. K.

    2017-01-01

    In this article, an experimental L-band compact magnetically insulated transmission line oscillator (MILO) has been simulated using the 3D PIC simulation code "Particle Studio," and an improvement in the device efficiency has been obtained. The detailed interaction and operating mechanism describing the role of sub-assemblies have been explained. The performance of the device was found to be the function of the distance between the end-surface of the cathode and the beam-dump disk. During simulation, a high power microwave of the TM01 mode is generated with the peak RF-power of 6 GW and the power conversion efficiency of 19.2%, at the operating voltage of ˜600 kV and at the current of 52 kA. For better impedance matching or maximum power transfer, four stubs have been placed at the λg/4 distance from the extractor cavity, which results in the stable RF power output. In this work, an improved L-band MILO along with a new type beam-dump disk is selected for performance improvement with typical design parameters and beam parameters. The total peak power of improved MILO is 7 GW, and the maximum power conversion efficiency is 22.4%. This improvement is achieved due to the formation of the virtual cathode at the load side, which helps in modulating the energy of electrons owing to maximum reflection of electrons from the mesh or foil.

  11. Modelling of the L-band brightness temperatures measured with ELBARA III radiometer on Bubnow wetland

    NASA Astrophysics Data System (ADS)

    Gluba, Lukasz; Sagan, Joanna; Lukowski, Mateusz; Szlazak, Radoslaw; Usowicz, Boguslaw

    2017-04-01

    Microwave radiometry has become the main tool for investigating soil moisture (SM) with remote sensing methods. ESA - SMOS (Soil Moisture and Ocean Salinity) satellite operating at L-band provides global distribution of soil moisture. An integral part of SMOS mission are calibration and validation activities involving measurements with ELBARA III which is an L-band microwave passive radiometer. It is done in order to improve soil moisture retrievals - make them more time-effective and accurate. The instrument is located at Bubnow test-site, on the border of cultivated field, fallow, meadow and natural wetland being a part of Polesie National Park (Poland). We obtain both temporal and spatial dependences of brightness temperatures for varied types of land covers with the ELBARA III directed at different azimuths. Soil moisture is retrieved from brightness temperature using L-band Microwave Emission of the Biosphere (L-MEB) model, the same as currently used radiative transfer model for SMOS. Parametrization of L-MEB, as well as input values are still under debate. We discuss the results of SM retrievals basing on data obtained during first year of the radiometer's operation. We analyze temporal dependences of retrieved SM for one-parameter (SM), two-parameter (SM, τ - optical depth) and three-parameter (SM, τ, Hr - roughness parameter) retrievals, as well as spatial dependences for specific dates. Special case of Simplified Roughness Parametrization, combining the roughness parameter and optical depth, is considered. L-MEB processing is supported by the continuous measurements of soil moisture and temperature obtained from nearby agrometeorological station, as well as studies on the soil granulometric composition of the Bubnow test-site area. Furthermore, for better estimation of optical depth, the satellite-derived Normalized Difference Vegetation Index (NDVI) was employed, supported by measured in situ vegetation parameters (such as Leaf Area Index and Vegetation

  12. Superconducting levitating bearing

    NASA Technical Reports Server (NTRS)

    Moon, Francis C. (Inventor)

    1996-01-01

    A superconducting bearing assembly includes a coil field source that may be superconducting and a superconducting structure. The coil field source assembly and superconducting structure are positioned so as to enable relative rotary movement therebetween. The structure and coil field source are brought to a supercooled temperature before a power supply induces a current in the coil field source. A Meissner-like effect is thereby obtained and little or no penetration of the field lines is seen in the superconducting structure. Also, the field that can be obtained from the superconducting coil is 2-8 times higher than that of permanent magnets. Since the magnetic pressure is proportioned to the square of the field, magnetic pressures from 4 to 64 times higher are achieved.

  13. Vaccinations for international travellers travelling from Greece.

    PubMed

    Pavli, Androula; Spilioti, Athina; Lymperi, Ioanna; Katerelos, Panagiotis; Maltezou, Helena C

    2013-01-01

    The aim of this prospective, questionnaire-based study is to assess pre-travel vaccinations for international travellers who receive pre-travel advice in Greece. A total of 2494 travellers were studied from January 1, 2009 through December 31, 2010. Travellers sought pre-travel advice at a median of 16 days (range: 0-349 days) before departure. Sub-Saharan Africa was the most common destination (34.7%). Most travellers (60.8%) travelled for <1 month, for recreation purposes (58.9%), stayed in hotels (65.3%), and in urban areas (53.6%). Yellow fever, tetravalent meningococcal, typhoid fever, cholera, and rabies vaccines were administered to 1629 (65.3%), 666 (26.7%), 615 (24.7%), 28 (1.1%), and/or 12 (0.5%) travellers, respectively. Of those who received Yellow fever vaccine, 737 (45.2%) travelled to sub-Saharan Africa, 332 (20.4%) travelled to South America, 949 (58.3%) stayed for short term, and 762 (46.8%) stayed in urban areas. Of the 1629 travellers vaccinated against Yellow fever, 150 (9.2%) and 226 (13.8%) travelled to areas of sub-Saharan Africa and South America respectively, where the vaccine is not or generally not recommended. Of those travellers who received meningococcal vaccine, 327 (49.1%) travelled to the Middle East for the Hajj, 251 (29%) travelled to sub-Saharan Africa, 410 (61.6%) for short term, and 540 (64.4%) stayed in urban areas. Of those travellers who received typhoid vaccine, 241 (39.2%) travelled to sub-Saharan Africa, 78 (12.7%) to the Indian subcontinent, 234 (38%) for short term, and 419 (68.1%) stayed in urban areas. Regarding routine vaccines, tetanus-diphtheria, poliomyelitis, and measles-mumps-rubella vaccines were administered to 707 (28.3%), 639 (25.6%) and/or 149 (6%) travellers, respectively. Of those to whom poliomyelitis vaccine was recommended, 295 (46.2%) and 137 (21.4%) travelled to sub-Saharan Africa and the Middle East, respectively, and 362 (56.7%) travelled for short term. In conclusion, this study revealed that

  14. Interplay between superconductivity and magnetism in iron-based superconductors

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chubukov, Andrey V

    2015-06-10

    This proposal is for theoretical work on strongly correlated electron systems, which are at the center of experimental and theoretical activities in condensed-matter physics. The interest to this field is driven fascinating variety of observed effects, universality of underlying theoretical ideas, and practical applications. I propose to do research on Iron-based superconductors (FeSCs), which currently attract high attention in the physics community. My goal is to understand superconductivity and magnetism in these materials at various dopings, the interplay between the two, and the physics in the phase in which magnetism and superconductivity co-exist. A related goal is to understand themore » origin of the observed pseudogap-like behavior in the normal state. My research explores the idea that superconductivity is of electronic origin and is caused by the exchange of spin-fluctuations, enhanced due to close proximity to antiferromagnetism. The multi-orbital/multi-band nature of FeSCs opens routes for qualitatively new superconducting states, particularly the ones which break time-reversal symmetry. By all accounts, the coupling in pnictdes is below the threshold for Mott physics and I intend to analyze these systems within the itinerant approach. My plan is to do research in two stages. I first plan to address several problems within weak-coupling approach. Among them: (i) what sets stripe magnetic order at small doping, (ii) is there a preemptive instability into a spin-nematic state, and how stripe order affects fermions; (iii) is there a co-existence between magnetism and superconductivity and what are the system properties in the co-existence state; (iv) how superconductivity emerges despite strong Coulomb repulsion and can the gap be s-wave but with nodes along electron FSs, (v) are there complex superconducting states, like s+id, which break time reversal symmetry. My second goal is to go beyond weak coupling and derive spin-mediated, dynamic interaction

  15. Common electronic origin of superconductivity in (Li,Fe)OHFeSe bulk superconductor and single-layer FeSe/SrTiO3 films.

    PubMed

    Zhao, Lin; Liang, Aiji; Yuan, Dongna; Hu, Yong; Liu, Defa; Huang, Jianwei; He, Shaolong; Shen, Bing; Xu, Yu; Liu, Xu; Yu, Li; Liu, Guodong; Zhou, Huaxue; Huang, Yulong; Dong, Xiaoli; Zhou, Fang; Liu, Kai; Lu, Zhongyi; Zhao, Zhongxian; Chen, Chuangtian; Xu, Zuyan; Zhou, X J

    2016-02-08

    The mechanism of high-temperature superconductivity in the iron-based superconductors remains an outstanding issue in condensed matter physics. The electronic structure plays an essential role in dictating superconductivity. Recent revelation of distinct electronic structure and high-temperature superconductivity in the single-layer FeSe/SrTiO3 films provides key information on the role of Fermi surface topology and interface in inducing or enhancing superconductivity. Here we report high-resolution angle-resolved photoemission measurements on the electronic structure and superconducting gap of an FeSe-based superconductor, (Li0.84Fe0.16)OHFe0.98Se, with a Tc at 41 K. We find that this single-phase bulk superconductor shows remarkably similar electronic behaviours to that of the superconducting single-layer FeSe/SrTiO3 films in terms of Fermi surface topology, band structure and the gap symmetry. These observations provide new insights in understanding high-temperature superconductivity in the single-layer FeSe/SrTiO3 films and the mechanism of superconductivity in the bulk iron-based superconductors.

  16. Common electronic origin of superconductivity in (Li,Fe)OHFeSe bulk superconductor and single-layer FeSe/SrTiO3 films

    PubMed Central

    Zhao, Lin; Liang, Aiji; Yuan, Dongna; Hu, Yong; Liu, Defa; Huang, Jianwei; He, Shaolong; Shen, Bing; Xu, Yu; Liu, Xu; Yu, Li; Liu, Guodong; Zhou, Huaxue; Huang, Yulong; Dong, Xiaoli; Zhou, Fang; Liu, Kai; Lu, Zhongyi; Zhao, Zhongxian; Chen, Chuangtian; Xu, Zuyan; Zhou, X. J.

    2016-01-01

    The mechanism of high-temperature superconductivity in the iron-based superconductors remains an outstanding issue in condensed matter physics. The electronic structure plays an essential role in dictating superconductivity. Recent revelation of distinct electronic structure and high-temperature superconductivity in the single-layer FeSe/SrTiO3 films provides key information on the role of Fermi surface topology and interface in inducing or enhancing superconductivity. Here we report high-resolution angle-resolved photoemission measurements on the electronic structure and superconducting gap of an FeSe-based superconductor, (Li0.84Fe0.16)OHFe0.98Se, with a Tc at 41 K. We find that this single-phase bulk superconductor shows remarkably similar electronic behaviours to that of the superconducting single-layer FeSe/SrTiO3 films in terms of Fermi surface topology, band structure and the gap symmetry. These observations provide new insights in understanding high-temperature superconductivity in the single-layer FeSe/SrTiO3 films and the mechanism of superconductivity in the bulk iron-based superconductors. PMID:26853801

  17. A time-series approach to estimating soil moisture from vegetated surfaces using L-band radar backscatter

    USDA-ARS?s Scientific Manuscript database

    Many previous studies have shown the sensitivity of radar backscatter to surface soil moisture content, particularly at L-band. Moreover, the estimation of soil moisture from radar for bare soil surfaces is well-documented, but estimation underneath a vegetation canopy remains unsolved. Vegetation s...

  18. Momentum dependence of the superconducting gap and in-gap states in MgB 2 multiband superconductor

    DOE PAGES

    Mou, Daixiang; Jiang, Rui; Taufour, Valentin; ...

    2015-06-29

    We use tunable laser-based angle-resolved photoemission spectroscopy to study the electronic structure of the multiband superconductor MgB 2. These results form the baseline for detailed studies of superconductivity in multiband systems. We find that the magnitude of the superconducting gap on both σ bands follows a BCS-like variation with temperature with Δ 0 ~ 7meV. Furthermore, the value of the gap is isotropic within experimental uncertainty and in agreement with a pure s-wave pairing symmetry. We observe in-gap states confined to k F of the σ band that occur at some locations of the sample surface. As a result, themore » energy of this excitation, ~ 3 meV, was found to be somewhat larger than the previously reported gap on π Fermi sheet and therefore we cannot exclude the possibility of interband scattering as its origin.« less

  19. CHARACTERIZATION OF THE INNER DISK AROUND HD 141569 A FROM KECK/NIRC2 L-BAND VORTEX CORONAGRAPHY

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Mawet, Dimitri; Bottom, Michael; Matthews, Keith

    HD 141569 A is a pre-main sequence B9.5 Ve star surrounded by a prominent and complex circumstellar disk, likely still in a transition stage from protoplanetary to debris disk phase. Here, we present a new image of the third inner disk component of HD 141569 A made in the Lband (3.8 μ m) during the commissioning of the vector vortex coronagraph that has recently been installed in the near-infrared imager and spectrograph NIRC2 behind the W.M. Keck Observatory Keck II adaptive optics system. We used reference point-spread function subtraction, which reveals the innermost disk component from the innermore » working distance of ≃23 au and up to ≃70 au. The spatial scale of our detection roughly corresponds to the optical and near-infrared scattered light, thermal Q , N , and 8.6 μ m PAH emission reported earlier. We also see an outward progression in dust location from the Lband to the H band (Very Large Telescope/SPHERE image) to the visible ( Hubble Space Telescope ( HST )/STIS image), which is likely indicative of dust blowout. The warm disk component is nested deep inside the two outer belts imaged by HST-NICMOS in 1999 (at 406 and 245 au, respectively). We fit our new L ′-band image and spectral energy distribution of HD 141569 A with the radiative transfer code MCFOST. Our best-fit models favor pure olivine grains and are consistent with the composition of the outer belts. While our image shows a putative very faint point-like clump or source embedded in the inner disk, we did not detect any true companion within the gap between the inner disk and the first outer ring, at a sensitivity of a few Jupiter masses.« less

  20. Radiotelemetric analysis of the effects of prevailing wind direction on Mormon cricket migratory band movement.

    PubMed

    Sword, G A; Lorch, P D; Gwynne, D T

    2008-08-01

    During outbreaks, flightless Mormon crickets [Anabrus simplex Haldeman (Orthoptera: Tettigoniidae)] form large mobile groups known as migratory bands. These bands can contain millions of individuals that march en masse across the landscape. The role of environmental cues in influencing the movement direction of migratory bands is poorly understood and has been the subject of little empirical study. We examined the effect of wind direction on Mormon cricket migratory band movement direction by monitoring the local weather conditions and daily movement patterns of individual insects traveling in bands over the same time course at three close, but spatially distinct sites. Although weather conditions were relatively homogeneous across sites, wind directions tended to be more variable across sites during the morning hours, the period during which directional movement begins. Migratory bands at different sites traveled in distinctly different directions. However, we failed to find any evidence to suggest that the observed variation in migratory band movement direction was correlated with local wind direction at any time during the day. These results support the notion that the cues mediating migratory band directionality are likely to be group specific and that a role for landscape-scale environmental cues such as wind direction is unlikely.

  1. Sea Surface Salinity and Wind Retrieval Algorithm Using Combined Passive-Active L-Band Microwave Data

    NASA Technical Reports Server (NTRS)

    Yueh, Simon H.; Chaubell, Mario J.

    2011-01-01

    Aquarius is a combined passive/active L-band microwave instrument developed to map the salinity field at the surface of the ocean from space. The data will support studies of the coupling between ocean circulation, the global water cycle, and climate. The primary science objective of this mission is to monitor the seasonal and interannual variation of the large scale features of the surface salinity field in the open ocean with a spatial resolution of 150 kilometers and a retrieval accuracy of 0.2 practical salinity units globally on a monthly basis. The measurement principle is based on the response of the L-band (1.413 gigahertz) sea surface brightness temperatures (T (sub B)) to sea surface salinity. To achieve the required 0.2 practical salinity units accuracy, the impact of sea surface roughness (e.g. wind-generated ripples and waves) along with several factors on the observed brightness temperature has to be corrected to better than a few tenths of a degree Kelvin. To the end, Aquarius includes a scatterometer to help correct for this surface roughness effect.

  2. When travel is a challenge: Travel medicine and the 'dis-abled' traveller.

    PubMed

    Bauer, Irmgard

    Travellers with recognised disabilities or the dis-ability to function as required during a trip have been overlooked in the travel medicine literature. This paper provides a starting point for further discussion and research into this neglected traveller population. In contrast, tourism research has explored travel with a disability for some time in order to understand the travellers' needs and to improve services accordingly. The contemporary bio-psycho-social understanding of disability serves as the framework for exploring motivations to travel as well as barriers, such as inter and intrapersonal, economic, structural and attitudinal obstacles. The demands of complex travel planning are acknowledged. Attention is also drawn to the particular issue of acquired disability. The theoretical discussion is complemented by travellers' own accounts using as examples mobility impairment on aeroplanes, sensory impairments, and obesity. These insights should inform high quality travel health care starting with an exploration of the health professionals' own views on such endeavours. Important are appropriate communication skills, an understanding of the travellers'/carers' views, wishes and judgment of abilities, as well as the appreciation of the reason for the trip, destination and planned activities. Challenging may be the need to accept that the traveller/carer will be more knowledgeable about the disability, needs, potential problems and solutions than the health professional. Finally, medical requirements for destination and activity need to be combined with the medical requirements for the dis-abling condition. Scarce literature and increasing numbers of travellers with disabilities should make this field a research priority in travel medicine. Unless there is an absolute medical contraindication, travel health professionals should encourage and support travellers for whom travel is a challenge. Copyright © 2018 Elsevier Ltd. All rights reserved.

  3. Simultaneous retrieval of sea ice thickness and snow depth using concurrent active altimetry and passive L-band remote sensing data

    NASA Astrophysics Data System (ADS)

    Zhou, L.; Xu, S.; Liu, J.

    2017-12-01

    The retrieval of sea ice thickness mainly relies on satellite altimetry, and the freeboard measurements are converted to sea ice thickness (hi) under certain assumptions over snow loading. The uncertain in snow depth (hs) is a major source of uncertainty in the retrieved sea ice thickness and total volume for both radar and laser altimetry. In this study, novel algorithms for the simultaneous retrieval of hi and hs are proposed for the data synergy of L-band (1.4 GHz) passive remote sensing and both types of active altimetry: (1) L-band (1.4GHz) brightness temperature (TB) from Soil Moisture Ocean Salinity (SMOS) satellite and sea ice freeboard (FBice) from radar altimetry, (2) L-band TB data and snow freeboard (FBsnow) from laser altimetry. Two physical models serve as the forward models for the retrieval: L-band radiation model, and the hydrostatic equilibrium model. Verification with SMOS and Operational IceBridge (OIB) data is carried out, showing overall good retrieval accuracy for both sea ice parameters. Specifically, we show that the covariability between hs and FBsnow is crucial for the synergy between TB and FBsnow. Comparison with existing algorithms shows lower uncertainty in both sea ice parameters, and that the uncertainty in the retrieved sea ice thickness as caused by that of snow depth is spatially uncorrelated, with the potential reduction of the volume uncertainty through spatial sampling. The proposed algorithms can be applied to the retrieval of sea ice parameters at basin-scale, using concurrent active and passive remote sensing data based on satellites.

  4. Monitoring Everglades freshwater marsh water level using L-band synthetic aperture radar backscatter

    USGS Publications Warehouse

    Kim, Jin-Woo; Lu, Zhong; Jones, John W.; Shum, C.K.; Lee, Hyongki; Jia, Yuanyuan

    2014-01-01

    The Florida Everglades plays a significant role in controlling floods, improving water quality, supporting ecosystems, and maintaining biodiversity in south Florida. Adaptive restoration and management of the Everglades requires the best information possible regarding wetland hydrology. We developed a new and innovative approach to quantify spatial and temporal variations in wetland water levels within the Everglades, Florida. We observed high correlations between water level measured at in situ gages and L-band SAR backscatter coefficients in the freshwater marsh, though C-band SAR backscatter has no close relationship with water level. Here we illustrate the complementarity of SAR backscatter coefficient differencing and interferometry (InSAR) for improved estimation of high spatial resolution water level variations in the Everglades. This technique has a certain limitation in applying to swamp forests with dense vegetation cover, but we conclude that this new method is promising in future applications to wetland hydrology research.

  5. Travel Health Advisory Group: a joint travel industry and travel health Special Interest Group promoting healthy travel in Australia.

    PubMed

    Leggat, Peter A; Zwar, Nicholas; Hudson, Bernie

    2012-09-01

    The Travel Health Advisory Group (THAG), established in 1997, is a joint initiative between the travel industry and travel health professionals in Australia that aims to promote healthy travel. THAG seeks to promote cooperation in improving the health of travellers between the travel industry and travel medicine professionals and to raise public awareness of the importance of travel health. From 2011, THAG has been a Special Interest Group of The Australasian College of Tropical Medicine and its membership has been active in several areas, including web-based travel health information, travel health promotion, media releases, research and education in Australia. Information is given on the objectives, membership and an overview of the various activities of the group. Copyright © 2012 Elsevier Ltd. All rights reserved.

  6. Project #8 (95-008), Traveler Information Services (TIS), Final Report

    DOT National Transportation Integrated Search

    1995-12-15

    THE L-95 CORRIDOR COALITION'S TRAVELER INFORMATION SERVICES (TIS) PROJECT IS INTENDED TO IMPLEMENT AN ADVANCED TRAVELER INFORMATION SYSTEM TAILORED TO THE UNIQUE NEEDS OF THE NORTHEAST CORRIDOR. THE SYSTEM WILL ACQUIRE AND DISSEMINATE INFORMATION ON ...

  7. Superconductivity in CaBi 2

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Winiarski, M. J.; Wiendlocha, B.; Golba, S.

    We observed superconductivity with critical temperature T c = 2.0 K in self-flux-grown single crystals of CaBi 2. This material adopts the ZrSi 2 structure type with lattice parameters a = 4.696(1) Å, b = 17.081(2) Å and c = 4.611(1) Å. The crystals of CaBi 2 were studied by means of magnetic susceptibility, specific heat and electrical resistivity measurements. The heat capacity jump at T c is ΔC/γT c = 1.41, confirming bulk superconductivity; the Sommerfeld coefficient γ = 4.1 mJ mol -1 K -2 and the Debye temperature Θ D = 157 K. The electron–phonon coupling strength ismore » λ el–ph = 0.59, and the thermodynamic critical field H c is low, between 111 and 124 Oe CaBi 2 is a moderate coupling type-I superconductor. Our results of electronic structure calculations are reported and charge densities, electronic bands, densities of states and Fermi surfaces are discussed, focusing on the effects of spin–orbit coupling and electronic property anisotropy. Furthermore, we find a mixed quasi-2D + 3D character in the electronic structure, which reflects the layered crystal structure of the material.« less

  8. Superconductivity in CaBi 2

    DOE PAGES

    Winiarski, M. J.; Wiendlocha, B.; Golba, S.; ...

    2016-07-12

    We observed superconductivity with critical temperature T c = 2.0 K in self-flux-grown single crystals of CaBi 2. This material adopts the ZrSi 2 structure type with lattice parameters a = 4.696(1) Å, b = 17.081(2) Å and c = 4.611(1) Å. The crystals of CaBi 2 were studied by means of magnetic susceptibility, specific heat and electrical resistivity measurements. The heat capacity jump at T c is ΔC/γT c = 1.41, confirming bulk superconductivity; the Sommerfeld coefficient γ = 4.1 mJ mol -1 K -2 and the Debye temperature Θ D = 157 K. The electron–phonon coupling strength ismore » λ el–ph = 0.59, and the thermodynamic critical field H c is low, between 111 and 124 Oe CaBi 2 is a moderate coupling type-I superconductor. Our results of electronic structure calculations are reported and charge densities, electronic bands, densities of states and Fermi surfaces are discussed, focusing on the effects of spin–orbit coupling and electronic property anisotropy. Furthermore, we find a mixed quasi-2D + 3D character in the electronic structure, which reflects the layered crystal structure of the material.« less

  9. Designing broad phononic band gaps for in-plane modes

    NASA Astrophysics Data System (ADS)

    Li, Yang Fan; Meng, Fei; Li, Shuo; Jia, Baohua; Zhou, Shiwei; Huang, Xiaodong

    2018-03-01

    Phononic crystals are known as artificial materials that can manipulate the propagation of elastic waves, and one essential feature of phononic crystals is the existence of forbidden frequency range of traveling waves called band gaps. In this paper, we have proposed an easy way to design phononic crystals with large in-plane band gaps. We demonstrated that the gap between two arbitrarily appointed bands of in-plane mode can be formed by employing a certain number of solid or hollow circular rods embedded in a matrix material. Topology optimization has been applied to find the best material distributions within the primitive unit cell with maximal band gap width. Our results reveal that the centroids of optimized rods coincide with the point positions generated by Lloyd's algorithm, which deepens our understandings on the formation mechanism of phononic in-plane band gaps.

  10. Spin-orbit coupling enhanced superconductivity in Bi-rich compounds ABi₃ (A = Sr and Ba).

    PubMed

    Shao, D F; Luo, X; Lu, W J; Hu, L; Zhu, X D; Song, W H; Zhu, X B; Sun, Y P

    2016-02-19

    Recently, Bi-based compounds have attracted attentions because of the strong spin-orbit coupling (SOC). In this work, we figured out the role of SOC in ABi3 (A = Sr and Ba) by theoretical investigation of the band structures, phonon properties, and electron-phonon coupling. Without SOC, strong Fermi surface nesting leads to phonon instabilities in ABi3. SOC suppresses the nesting and stabilizes the structure. Moreover, without SOC the calculation largely underestimates the superconducting transition temperatures (Tc), while with SOC the calculated Tc are very close to those determined by measurements on single crystal samples. The SOC enhanced superconductivity in ABi3 is due to not only the SOC induced phonon softening, but also the SOC related increase of electron-phonon coupling matrix elements. ABi3 can be potential platforms to construct heterostructure of superconductor/topological insulator to realize topological superconductivity.

  11. Travel-related health problems in Japanese travelers.

    PubMed

    Mizuno, Yasutaka; Kudo, Koichiro

    2009-09-01

    Although the number of Japanese individuals traveling abroad has increased steadily, reaching approximately 17.3 million in 2007, the incidence of various travel-related health problems in Japan remains unknown. The travel-related health problems of Japanese travelers returning to Japan from abroad are analyzed by assessing the records. Data were collected retrospectively on returning travelers who visited the authors' travel clinic during the period from January 2005 through to December 2006 with any health problem acquired overseas. A total of 345 patients were included in this study (200 male, 145 female; average age, 34+/-12.3 years). Reasons for travel included leisure (45.8%); business (39.1%); visiting friends and relatives or accompanying other travelers (8.7%); volunteering (3.8%); and long stays in order to study or live (2.6%). The most visited destination was Asia (n=260), followed by Africa (n=105). The most commonly reported health problems were gastro-intestinal infections (39.1%), followed by respiratory tract infections (16.2%), animal bites (8.1%), and skin problems (5.8%). Together, malaria and dengue accounted for 10% of diagnoses in 125 febrile patients (36.2%). Although the profile of travel-related health problems in Japanese travelers is similar to that of Western travelers, the characteristics of travel were quite different. Therefore Japanese travel advice should be tailored to suit the Japanese traveler.

  12. Design of a high speed, high resolution thermometry system for 1.5 GHz superconducting radio frequency cavities

    NASA Astrophysics Data System (ADS)

    Knobloch, Jens; Muller, Henry; Padamsee, Hasan

    1994-11-01

    Presented in this paper are the description and the test results of a new stationary thermometry system used to map the temperature of the outer surface of 1.5 GHz superconducting single-cell cavities during operation at 1.6 K. The system comprises 764 removable carbon thermometers whose signals are multiplexed and scanned by a Macintosh computer. A complete temperature map can be obtained in as little as 0.1 s at a temperature resolution of about 0.2 mK. Alternatively, it has been demonstrated that if the acquisition time is increased to several seconds, then a temperature resolution on the order of 30 μK is possible. To our knowledge, these are the fastest acquisition times so far achieved with L-band cavities at these resolutions.

  13. Ethnicity predicts viral rebound after travel to the tropics in HIV-infected travelers to the tropics in the Swiss HIV Cohort Study.

    PubMed

    Gebreselassie, H M; Kraus, D; Fux, C A; Haubitz, S; Scherrer, A; Hatz, C; Veit, O; Stoeckle, M; Fehr, J; de Lucia, S; Cavassini, M; Bernasconi, E; Schmid, P; Furrer, H; Staehelin, C

    2017-09-01

    The number of HIV-infected individuals from developed countries travelling to tropical and subtropical areas has increased as a result of the clinical and survival benefits of combination antiretroviral therapy. The aim of our study was to describe the traveler population in the SHCS and to determine the frequency of viral rebound in virologically suppressed individuals after a travel episode to the tropics compared to non-travelers. Swiss HIV Cohort Study participants with at least one follow-up visit between 1 January 1989 and 28 February 2015 were eligible for inclusion in the study. The primary outcome was the occurrence of viral rebound (viral load > 200 HIV-1 RNA copies/mL) after a travel episode compared with a nontravel episode in previously suppressed individuals (≤ 200 copies/mL). All virologically suppressed patients contributed multiple travel or nontravel episodes to the analysis. Logistic regression was performed including factors associated with viral rebound. We included 16 635 patients in the study, of whom 6084 (36.5%) had ever travelled to the tropics. Travel frequency increased over time, with travellers showing better HIV parameters than nontravellers [less advanced Centers for Disease Control and Prevention (CDC) stage and higher CD4 count nadir]. Viral rebound was seen in 477 (3.9%) of 12 265 travel episodes and in 5121 (4.5%) of 114 884 nontravel episodes [unadjusted odds ratio (OR) 0.87; 95% confidence interval (CI) 0.78-0.97]. Among these 477 post-travel viral rebounds, 115 had a resistance test performed and 51 (44%) of these showed new resistance mutations. Compared with European and North American patients, the odds for viral rebound were significantly lower in Southeast Asian (OR 0.67; 95% CI 0.51-0.88) and higher in sub-Saharan African (SSA) patients (OR 1.41; 95% CI 1.22-1.62). Travel further increased the odds of viral rebound in SSA patients (OR 2.00; 95% CI 1.53-2.61). Region of origin is the main risk factor for viral rebound

  14. Protective link for superconducting coil

    DOEpatents

    Umans, Stephen D [Belmont, MA

    2009-12-08

    A superconducting coil system includes a superconducting coil and a protective link of superconducting material coupled to the superconducting coil. A rotating machine includes first and second coils and a protective link of superconducting material. The second coil is operable to rotate with respect to the first coil. One of the first and second coils is a superconducting coil. The protective link is coupled to the superconducting coil.

  15. Foliar spray banding characteristics

    Treesearch

    A.R. Womac; C.W. Smith; Joseph E. Mulrooney

    2004-01-01

    Foliar spray banding was explored as a means of reducing peticide use compared to broadcast applications. Barious geometric spray patterns and delivery angles of foliar spray bands were investigated to increase spray deposits in a crop row at a constant spray rate of 94 L/ha. Wind-free laboratory results indicated that a banded application using three 65° hollow-cone...

  16. Design studies of the Ku-band, wide-band Gyro-TWT amplifier

    NASA Astrophysics Data System (ADS)

    Jung, Sang Wook; Lee, Han Seul; Jang, Kwong Ho; Choi, Jin Joo; Hong, Yong Jun; Shin, Jin Woo; So, Jun Ho; Won, Jong Hyo

    2014-02-01

    This paper reports a Ku-band, wide band Gyrotron-Traveling-wave-tube(Gyro-TWT) that is currently being developed at Kwangwoon University. The Gyro-TWT has a two stage linear tapered interaction circuit to obtain a wide operating bandwidth. The linearly-tapered interaction circuit and nonlinearly-tapered magnetic field gives the Gyro-TWT a wide operating bandwidth. The Gyro-TWT bandwidth is 23%. The 2d-Particle-in-cell(PIC) and MAGIC2d code simulation results are 17.3 dB and 24.34 kW, respectively for the maximum saturated output power. A double anode MIG was simulated with E-Gun code. The results were 0.7 for the transvers to the axial beam velocity ratio (=alpha) and a 2.3% axial velocity spread at 50 kV and 4 A. A magnetic field profile simulation was performed by using the Poisson code to obtain the grazing magnetic field of the entire interaction circuit with Poisson code.

  17. Beyond triplet: Unconventional superconductivity in a spin-3/2 topological semimetal

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Kim, Hyunsoo; Wang, Kefeng; Nakajima, Yasuyuki

    In all known fermionic super fluids, Cooper pairs are composed of spin-1/2 quasi-particles that pair to form either spin-singlet or spin-triplet bound states. The "spin" of a Bloch electron, however, is xed by the symmetries of the crystal and the atomic orbitals from which it is derived, and in some cases can behave as if it were a spin-3/2 particle. The superconducting state of such a system allows pairing beyond spin-triplet, with higher spin quasi-particles combining to form quintet or even septet pairs. Here, we report evidence of unconventional superconductivity emerging from a spin-3/2 quasiparticle electronic structure in the half-Heuslermore » semimetal YPtBi, a low-carrier density noncentrosymmetric cubic material with a high symmetry that preserves the p-like j = 3/2 manifold in the Bi-based Γ 8 band in the presence of strong spin-orbit coupling. With a striking linear temperature dependence of the London penetration depth, the existence of line nodes in the superconducting order parameter Δ is directly explained by a mixed-parity Cooper pairing model with high total angular momentum, consistent with a high-spin fermionic super fluid state. We propose a k ∙ p model of the j = 3/2 fermions to explain how a dominant J=3 septet pairing state is the simplest solution that naturally produces nodes in the mixed even-odd parity gap. Together with the underlying topologically non-trivial band structure, the unconventional pairing in this system represents a truly novel form of super fluidity that has strong potential for leading the development of a new generation of topological superconductors.« less

  18. Beyond triplet: Unconventional superconductivity in a spin-3/2 topological semimetal

    DOE PAGES

    Kim, Hyunsoo; Wang, Kefeng; Nakajima, Yasuyuki; ...

    2018-04-06

    In all known fermionic super fluids, Cooper pairs are composed of spin-1/2 quasi-particles that pair to form either spin-singlet or spin-triplet bound states. The "spin" of a Bloch electron, however, is xed by the symmetries of the crystal and the atomic orbitals from which it is derived, and in some cases can behave as if it were a spin-3/2 particle. The superconducting state of such a system allows pairing beyond spin-triplet, with higher spin quasi-particles combining to form quintet or even septet pairs. Here, we report evidence of unconventional superconductivity emerging from a spin-3/2 quasiparticle electronic structure in the half-Heuslermore » semimetal YPtBi, a low-carrier density noncentrosymmetric cubic material with a high symmetry that preserves the p-like j = 3/2 manifold in the Bi-based Γ 8 band in the presence of strong spin-orbit coupling. With a striking linear temperature dependence of the London penetration depth, the existence of line nodes in the superconducting order parameter Δ is directly explained by a mixed-parity Cooper pairing model with high total angular momentum, consistent with a high-spin fermionic super fluid state. We propose a k ∙ p model of the j = 3/2 fermions to explain how a dominant J=3 septet pairing state is the simplest solution that naturally produces nodes in the mixed even-odd parity gap. Together with the underlying topologically non-trivial band structure, the unconventional pairing in this system represents a truly novel form of super fluidity that has strong potential for leading the development of a new generation of topological superconductors.« less

  19. L Band EPR Tooth Dosimetry for Heavy Ion Irradiation

    PubMed Central

    Yamaguchi, Ichiro; Sato, Hitoshi; Kawamura, Hiraku; Hamano, Tsuyoshi; Yoshii, Hiroshi; Suda, Mitsuru; Miyake, Minoru; Kunugita, Naoki

    2016-01-01

    Electron Paramagnetic Resonance (EPR) tooth dosimetry is being developed as a device to rapidly assess large populations that were potentially exposed to radiation during a major radiation accident or terrorist event. While most exposures are likely to be due to fallout and therefore involve low linear energy transfer (LET) radiation, there is also a potential for exposures to high LET radiation, for which the effect on teeth has been less well characterized by EPR. Therefore, the aim of this paper is to acquire fundamental response curves for high LET radiation in tooth dosimetry using L band EPR. For this purpose, we exposed human teeth to high energy carbon ions using the heavy ion medical accelerator in Chiba at the National Institute of Radiological Sciences. The primary findings were that EPR signals for carbon ion irradiation were about one-tenth the amplitude of the response to the same dose of 150 kVp X-rays. PMID:27542817

  20. High-efficiency L-band T/R Module: Development Results

    NASA Technical Reports Server (NTRS)

    Edelstein, Wendy N.; Andricos, Constantine; Wang, Feiyu; Rutled, David B.

    2005-01-01

    Future interferometric synthetic aperture radar (InSAR) systems require electronically scanned phased-array antennas, where the transmit/receive (T/R) module is a key component. The T/R module efficiency is a critical figure of merit and has direct implications on the power dissipation and power generation requirements of the system. Significant improvements in the efficiency of the T/R module will make SAR missions more feasible and affordable. The results of two high-efficiency T/R modules are presented, each based on different power amplifier technologies. One module uses a 30W GaAs Class-AlB power amplifier and the second module uses a 70W LD-MOS Class-ElF power amplifier, where both modules use a common low power section. Each module operates over an 80MHz bandwidth at L-band (1.2GHz) with an overall module efficiency greater than 58%. We will present the results of these two T/R modules that have been designed, built and tested.

  1. Validation of Forested Inundation Extent Revealed by L-Band Polarimetric and Interferometric SAR Data

    NASA Technical Reports Server (NTRS)

    Chapman, Bruce; Celi, Jorge; Hamilton, Steve; McDonald, Kyle

    2013-01-01

    UAVSAR, NASA's airborne Synthetic Aperture Radar (SAR), conducted an extended observational campaign in Central and South America in March 2013, primarily related to volcanic deformations along the Andean Mountain Range but also including a large number of flights studying other scientific phenomena. During this campaign, the L-Band SAR collected data over the Napo River in Ecuador. The objectives of this experiment were to acquire polarimetric and interferometric L-Band SAR data over an inundated tropical forest in Ecuador simultaneously with on-the-ground field work ascertaining the extent of inundation, and to then derive from this data a quantitative estimate for the error in the SAR-derived inundation extent. In this paper, we will first describe the processing and preliminary analysis of the SAR data. The polarimetric SAR data will be classified by land cover and inundation state. The interferometric SAR data will be used to identify those areas where change in inundation extent occurred, and to measure the change in water level between two observations separated by a week. Second, we will describe the collection of the field estimates of inundation, and have preliminary comparisons of inundation extent measured in the field field versus that estimated from the SAR data.

  2. L-Band Brightness Temperature Variations at Dome C and Snow Metamorphism at the Surface

    NASA Technical Reports Server (NTRS)

    Brucker, Ludovic; Dinnat, Emmanuel; Picard, Ghislain; Champollion, Nicolas

    2014-01-01

    The Antarctic Plateau is a promising site to monitor microwave radiometers' drift, and to inter-calibrate microwave radiometers, especially 1.4 GigaHertz (L-band) radiometers on board the Soil Moisture and Ocean Salinity (SMOS), and AquariusSAC-D missions. The Plateau is a thick ice cover, thermally stable in depth, with large dimensions, and relatively low heterogeneities. In addition, its high latitude location in the Southern Hemisphere enables frequent observations by polar-orbiting satellites, and no contaminations by radio frequency interference. At Dome C (75S, 123E), on the Antarctic Plateau, the substantial amount of in-situ snow measurements available allows us to interpret variations in space-borne microwave brightness temperature (TB) (e.g. Macelloni et al., 2007, 2013, Brucker et al., 2011, Champollion et al., 2013). However, to analyze the observations from the Aquarius radiometers, whose sensitivity is 0.15 K, the stability of the snow layers near the surface that are most susceptible to rapidly change needs to be precisely assessed. This study focuses on the spatial and temporal variations of the Aquarius TB over the Antarctic Plateau, and at Dome C in particular, to highlight the impact of snow surface metamorphism on the TB observations at L-band.

  3. Specific heat, Electrical resistivity and Electronic band structure properties of noncentrosymmetric Th7Fe3 superconductor.

    PubMed

    Tran, V H; Sahakyan, M

    2017-11-17

    Noncentrosymmetric superconductor Th 7 Fe 3 has been investigated by means of specific heat, electrical resisitivity measurements and electronic properties calculations. Sudden drop in the resistivity at 2.05 ± 0.15 K and specific heat jump at 1.98 ± 0.02 K are observed, rendering the superconducting transition. A model of two BCS-type gaps appears to describe the zero-magnetic-field specific heat better than those based on the isotropic BCS theory or anisotropic functions. A positive curvature of the upper critical field H c2 (T c ) and nonlinear field dependence of the Sommerfeld coefficient at 0.4 K qualitatively support the two-gap scenario, which predicts H c2 (0) = 13 kOe. The theoretical densities of states and electronic band structures (EBS) around the Fermi energy show a mixture of Th 6d- and Fe 3d-electrons bands, being responsible for the superconductivity. Furthermore, the EBS and Fermi surfaces disclose significantly anisotropic splitting associated with asymmetric spin-orbit coupling (ASOC). The ASOC sets up also multiband structure, which presumably favours a multigap superconductivity. Electron Localization Function reveals the existence of both metallic and covalent bonds, the latter may have different strengths depending on the regions close to the Fe or Th atoms. The superconducting, electronic properties and implications of asymmetric spin-orbit coupling associated with noncentrosymmetric structure are discussed.

  4. Transfer-matrices for series-type microwave antenna circuits. [L-band radiometer

    NASA Technical Reports Server (NTRS)

    Schmidt, R. F.

    1981-01-01

    Transfer matrices are developed which permit analysis and computer evaluation of certain series type microwave antenna circuits associated with an L-Band microwave radiometer (LBMR) under investigation at Goddard Space Flight Center. This radiometer is one of several diverse instrument designs to be used for the determination of soil moisture, sea state, salinity, and temperature data. Four port matrix notation is used throughout for the evaluation of LBMR circuits with mismatched couplers and lossy transmission lines. Matrix parameters in examples are predicted on an impedance analysis and an assumption of an array aperture distribution. The notation presented is easily adapted to longer and more varied chains of matrices, and to matrices of larger dimension.

  5. Analysis of light propagation in quasiregular and hybrid Rudin-Shapiro one-dimensional photonic crystals with superconducting layers

    NASA Astrophysics Data System (ADS)

    Gómez-Urrea, H. A.; Escorcia-García, J.; Duque, C. A.; Mora-Ramos, M. E.

    2017-11-01

    The transmittance spectrum of a one-dimensional hybrid photonic crystal built from the suitable arrangement of periodic and quasiregular Rudin-Shapiro heterolayers that include superconducting slabs is investigated. The four-layer Rudin-Shapiro structure is designed with three lossless dielectric layers and a low-temperature superconductor one. The dielectric function of the superconducting layer is modeled by the two-fluid Gorter-Casimir theory, and the transmittance is calculated with the use of the transfer matrix method. The obtained results reveal the presence of a cut-off frequency fc - a forbidden frequency band for propagation - that can be manipulated by changing the width of the superconducting layer, the temperature and the order of the Rudin-Shapiro sequence. In addition, the spatial distribution of the electric field amplitude for the propagating TM modes is also discussed. It is found that the maximum of localized electric field relative intensity - which reaches a value of several tens - corresponds to the frequency values above to the cut-off frequency, at which, the effective dielectric function of the hybrid unit cell becomes zero. The proposed structure could be another possible system for optical device design for temperature-dependent optical devices such as stop-band filters, or as bolometers.

  6. Superconducting transmission line particle detector

    DOEpatents

    Gray, K.E.

    1988-07-28

    A microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non- superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plus the slow electromagnetic wave propagating in a superconducting transmission line are used to resolve N/sup 2/ ambiguity of charged particle events. 6 figs.

  7. Superconducting transmission line particle detector

    DOEpatents

    Gray, Kenneth E.

    1989-01-01

    A microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non-superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plus the slow electromagnetic wave propogating in a superconducting transmission line are used to resolve N.sup.2 ambiguity of charged particle events.

  8. Superconducting transmission line particle detector

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gray, K.E.

    A microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non- superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plus the slowmore » electromagnetic wave propagating in a superconducting transmission line are used to resolve N/sup 2/ ambiguity of charged particle events. 6 figs.« less

  9. Studies on two-gap superconductivity in 2H-NbS2

    NASA Astrophysics Data System (ADS)

    Kačmarčík, J.; Pribulová, Z.; Marcenat, C.; Klein, T.; Rodière, P.; Cario, L.; Samuely, P.

    2010-12-01

    We present the ac-calorimetry measurements of superconducting 2H-NbS2 in the temperature range down to 0.6 K and magnetic fields up to 8 T. The temperature and magnetic field dependence of the electronic specific heat consistently indicate existence of two superconducting energy gaps in the system - one of them with the coupling ratio below the BCS weak-coupling limit and the other above that value. These results support previous findings by scanning tunneling microscopy and spectroscopy measurements [I. Guillamón, H. Suderow, S. Vieira, L. Cario, et al., Phys. Rev. Lett. 101 (2008) 166407] of two pronounced features in density of states related to a two-gap superconductivity in this system.

  10. Travel characteristics and health practices among travellers at the travellers' health and vaccination clinic in Singapore.

    PubMed

    Lee, Vernon J; Wilder-Smith, Annelies

    2006-10-01

    Singapore has a fast-growing travel industry, but few studies have been done on travel characteristics and travel health practices. This study describes the profile and healthseeking behaviour of travellers attending a travel health clinic in Singapore. A cross-sectional survey was conducted on travellers attending the Traveller's Health and Vaccination Centre (THVC) between September and November 2002 using a standardised questionnaire. Information obtained included individual demographic and medical information, travel patterns, vaccination status and travel health practices. Four hundred and ninetyfive (74%) eligible travellers seen at THVC responded to the questionnaire. Their mean age was 36 years; 77% were professionals, managers, executives, and businessmen, students, and white collar workers. Asia was the main travel destination, and most travelled for leisure and resided in hotels or hostels. The median duration of travel was 16 days. Although >90% had previously travelled overseas, only 20% had previously sought pre-travel advice. Malays were significantly underrepresented (P < 0.01); and Caucasians and Eurasians were significantly more likely (P < 0.01) to have previously sought pre-travel advice compared with Chinese, Indians and Malays. Factors associated with seeking pre-travel advice included travel outside of Asia, especially Africa and South America. Singaporean travellers travel more often to cities rather than rural areas, compared with non-Asian travellers. Asia is the preferred destination, and travel outside of Asia is perceived as more risky and is associated with seeking pre-travel advice and vaccinations. Travel patterns and behaviours need to be taken into account when developing evidence-based travel medicine in Asia.

  11. Sensitivity of gap symmetry to an incipient band: Application to iron based superconductors

    NASA Astrophysics Data System (ADS)

    Mishra, Vivek; Scalapino, Douglas; Maier, Thomas

    Observation of high temperature superconductivity in iron-based superconductors with a submerged hole band has attracted wide interest. A spin fluctuation mediated pairing mechanism has been proposed as a possible explanation for the high transition temperatures observed in these systems. Here we discuss the importance of the submerged band in the context of the gap symmetry. We show that the incipient band can lead to an attractive pairing interaction and thus have significant effects on the pairing symmetry. We propose a framework to include the effect of the incipient band in the standard multi-orbital spin-fluctuation theories which are widely used for studying various iron-based superconductors. Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy.

  12. Effect of current and travel speed variation of TIG welding on microstructure and hardness of stainless steel SS 316L

    NASA Astrophysics Data System (ADS)

    Jatimurti, Wikan; Abdillah, Fakhri Aulia; Kurniawan, Budi Agung; Rochiem, Rochman

    2018-04-01

    One of the stainless steel types that widely used in industry is SS 316L, which is austenitic stainless steel. One of the welding methods to join stainless steel is Tungsten Inert Gas (TIG), which can affect its morphology, microstructure, strength, hardness, and even lead to cracks in the weld area due to the given heat input. This research has a purpose of analyzing the relationship between microstructure and hardness value of SS 316L stainless steel after TIG welding with the variation of current and travel speed. The macro observation shows a distinct difference in the weld metal and base metal area, and the weld form is not symmetrical. The metallographic test shows the phases that formed in the specimen are austenite and ferrite, which scattered in three welding areas. The hardness test showed that the highest hardness value found in the variation of travel speed 12 cm/min with current 100 A. Welding process and variation were given do not cause any defects in the microstructure, such as carbide precipitation and sigma phase, means that it does not affect the hardness and corrosion resistance of all welded specimen.

  13. Characterizing the temporal variability of L-band backscatter using dense UAVSAR time-series in preparation for the NISAR mission

    NASA Astrophysics Data System (ADS)

    Lavalle, M.; Lee, A.; Shiroma, G. X. H.; Rosen, P. A.

    2017-12-01

    The NASA-ISRO SAR (NISAR) mission will deliver unprecedented global maps of L-band HH/HV backscatter every 12 days with resolution ranging from a few to tens of meters in support of ecosystem, solid Earth and cryosphere science and applications. Understanding and modeling the temporal variability of L-band backscatter over temporal scales of years, months and days is critical for developing retrieval algorithms that can robustly extract the biophysical variables of interest (e.g., forest biomass, soil moisture, etc.) from NISAR time series. In this talk, we will focus on the 5-year time series of 60 JPL/UAVSAR polarimetric images collected near the Sacramento Delta to characterize the inter-annual, seasonal and short-scale variability of the L-band polarimetric backscatter for a broad range of land cover types. Our preliminary analysis reveals that backscatter from man-made structures is very stable over time, whereas backscatter from bare soil and herbaceous vegetation fluctuates over time with standard deviation of 2.3 dB. Land-cover classes with larger biomass such as trees and tall vegetation show about 1.5 dB standard deviation in temporal backscatter variability. Closer examination of high-spatial resolution UAVSAR imagery reveal also that vegetation structure, speckle noise and horizontal forest heterogeneity in the Sacramento Delta area can significantly affect the point-wise backscatter value. In our talk, we will illustrate the long UAVSAR time series, describe our data analysis strategy, show the results of polarimetric variability for different land cover classes and number of looks, and discuss the implications for the development of NISAR L2/L3 retrieval algorithms of ecosystem science.

  14. Mangrove vegetation structure in Southeast Brazil from phased array L-band synthetic aperture radar data

    NASA Astrophysics Data System (ADS)

    de Souza Pereira, Francisca Rocha; Kampel, Milton; Cunha-Lignon, Marilia

    2016-07-01

    The potential use of phased array type L-band synthetic aperture radar (PALSAR) data for discriminating distinct physiographic mangrove types with different forest structure developments in a subtropical mangrove forest located in Cananéia on the Southern coast of São Paulo, Brazil, is investigated. The basin and fringe physiographic types and the structural development of mangrove vegetation were identified with the application of the Kruskal-Wallis statistical test to the SAR backscatter values of 10 incoherent attributes. The best results to separate basin to fringe types were obtained using copolarized HH, cross-polarized HV, and the biomass index (BMI). Mangrove structural parameters were also estimated using multiple linear regressions. BMI and canopy structure index were used as explanatory variables for canopy height, mean height, and mean diameter at breast height regression models, with significant R2=0.69, 0.73, and 0.67, respectively. The current study indicates that SAR L-band images can be used as a tool to discriminate physiographic types and to characterize mangrove forests. The results are relevant considering the crescent availability of freely distributed SAR images that can be more utilized for analysis, monitoring, and conservation of the mangrove ecosystem.

  15. Superconducting transmission line particle detector

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gray, K.E.

    This paper describes a microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non-superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plusmore » the slow electromagnetic wave propogating in a superconducting transmission line are used to resolve N{sup 2} ambiguity of charged particle events.« less

  16. Simulation and development of novel slow-wave structures for miniaturized THz-band vacuum-tube devices

    NASA Astrophysics Data System (ADS)

    Benedik, Andrey I.; Karetnikova, Tatiana A.; Torgashov, Roman A.; Terentyuk, Artem G.; Rozhnev, Andrey G.; Torgashov, Gennadiy V.; Ryskin, Nikita M.

    2018-04-01

    Microfabricated vacuum-tube millimeter- and THz-band sources are of great interest for numerous applications such as communications, radar, sensors, imaging, etc. Recently, miniaturized sheet-beam traveling-wave tubes for sub-THz and THz operation have attracted a considerable interest. In this paper, we present the results of modeling and development of slow-wave structures (SWS) for medium power (10-100 W) traveling-wave tube (TWT) amplifiers and backwardwave oscillators (BWO) in near-THz frequency band. Different types of SWSs are considered, such as double-vane SWS for TWT with a sheet electron beam, a folded-waveguide SWS, and novel planar SWSs on dielectric substrates.

  17. Anticorrelation between polar lattice instability and superconductivity in the Weyl semimetal candidate MoTe2

    NASA Astrophysics Data System (ADS)

    Takahashi, H.; Akiba, T.; Imura, K.; Shiino, T.; Deguchi, K.; Sato, N. K.; Sakai, H.; Bahramy, M. S.; Ishiwata, S.

    2017-03-01

    The relation between the polar structural instability and superconductivity in a Weyl semimetal candidate MoTe2 has been clarified by finely controlled physical and chemical pressure. The physical pressure as well as the chemical pressure, i.e., the Se substitution for Te, enhances the superconducting transition temperature Tc at around the critical pressure where the polar structure transition disappears. From the heat capacity and thermopower measurements, we ascribe the significant enhancement of Tc at the critical pressure to a subtle modification of the phonon dispersion or the semimetallic band structure upon the polar-to-nonpolar transition. On the other hand, the physical pressure, which strongly reduces the interlayer distance, is more effective on the suppression of the polar structural transition and the enhancement of Tc as compared with the chemical pressure, which emphasizes the importance of the interlayer coupling on the structural and superconducting instability in MoTe2.

  18. Pre-travel advice seeking from GPs by travellers with chronic illness seen at a travel clinic.

    PubMed

    Gagneux-Brunon, Amandine; Andrillat, Carole; Fouilloux, Pascale; Daoud, Fatiha; Defontaine, Christiane; Charles, Rodolphe; Lucht, Frédéric; Botelho-Nevers, Elisabeth

    2016-03-01

    Travellers are ageing and frequently report chronic illness. Pre-travel health advice is crucial, particularly in this subgroup, and general practitioners (GPs) are first in line for treatment adjustment before departure. Our aim is to evaluate pre-travel health advice seeking from GPs by travellers with chronic illness seen at a travel clinic. A cross-sectional observational survey using a questionnaire was conducted between August 2013 and July 2014 in travellers attending the travel medicine clinic of a tertiary university hospital in France. During the study, 2019 travellers were included. Mean age was 39.4 years (±18.8). Three hundred and ninety-one (19.4%) travellers reported a history of a chronic illness. Arterial hypertension and diabetes mellitus were the most frequently reported illnesses, affecting, respectively, 168 (8.3%) travellers and 102 (5.1%). Hajj pilgrims were more likely to report a history of chronic illness than other travellers. Only 810 (40.1%) travellers sought pre-travel advice from their GP. Six hundred and fifty-two (40.1%) healthy travellers and 158 (40.5%) travellers reporting chronic illness sought pre-travel advice from their GP (P = 0.96). Travellers with a history of chronic illness do not seek pre-travel health advice from their GP more frequently than healthy travellers. Travel health specialists are generally not the best practitioners to manage the care of underlying medical conditions presenting risks during travel. However, GPs offer continuity and disease management expertise to improve the specificity of pre-travel planning. Thus, ongoing collaboration between the traveller, GP and travel health specialist is likely to yield the best outcomes. © International Society of Travel Medicine, 2016. All rights reserved. Published by Oxford University Press. For permissions, please e-mail: journals.permissions@oup.com.

  19. Estimation of Soil Moisture with L-band Multi-polarization Radar

    NASA Technical Reports Server (NTRS)

    Shi, J.; Chen, K. S.; Kim, Chung-Li Y.; Van Zyl, J. J.; Njoku, E.; Sun, G.; O'Neill, P.; Jackson, T.; Entekhabi, D.

    2004-01-01

    Through analyses of the model simulated data-base, we developed a technique to estimate surface soil moisture under HYDROS radar sensor (L-band multi-polarizations and 40deg incidence) configuration. This technique includes two steps. First, it decomposes the total backscattering signals into two components - the surface scattering components (the bare surface backscattering signals attenuated by the overlaying vegetation layer) and the sum of the direct volume scattering components and surface-volume interaction components at different polarizations. From the model simulated data-base, our decomposition technique works quit well in estimation of the surface scattering components with RMSEs of 0.12,0.25, and 0.55 dB for VV, HH, and VH polarizations, respectively. Then, we use the decomposed surface backscattering signals to estimate the soil moisture and the combined surface roughness and vegetation attenuation correction factors with all three polarizations.

  20. A user's manual for the NASA/JPL synthetic aperture radar and the NASA/JPL L and C band scatterometers

    NASA Technical Reports Server (NTRS)

    Thompson, T. W.

    1983-01-01

    Airborne synthetic aperture radars and scatterometers are operated with the goals of acquiring data to support shuttle imaging radars and support ongoing basic active microwave remote sensing research. The aircraft synthetic aperture radar is an L-band system at the 25-cm wavelength and normally operates on the CV-990 research aircraft. This radar system will be upgraded to operate at both the L-band and C-band. The aircraft scatterometers are two independent radar systems that operate at 6.3-cm and 18.8-cm wavelengths. They are normally flown on the C-130 research aircraft. These radars will be operated on 10 data flights each year to provide data to NASA-approved users. Data flights will be devoted to Shuttle Imaging Radar-B (SIR-B) underflights. Standard data products for the synthetic aperture radars include both optical and digital images. Standard data products for the scatterometers include computer compatible tapes with listings of radar cross sections (sigma-nought) versus angle of incidence. An overview of these radars and their operational procedures is provided by this user's manual.

  1. Project #8, Task 3 - Travel Information Services (TIS), Requirements Analysis Report

    DOT National Transportation Integrated Search

    1995-03-24

    THE L-95 CORRIDOR COALITION'S TRAVELER INFORMATION SERVICES (TIS) PROJECT IS INTENDED TO IMPLEMENT AN ADVANCED TRAVELER INFORMATION SYSTEM TAILORED TO THE UNIQUE NEEDS OF THE NORTHEAST CORRIDOR. THE SYSTEM WILL ACQUIRE AND DISSEMINATE INFORMATION ON ...

  2. Project #8, Task 5 - Traveler Information Services (TIS), TIS Conceptual Design

    DOT National Transportation Integrated Search

    1995-09-15

    THE L-95 CORRIDOR COALITION'S TRAVELER INFORMATION SERVICES (TIS) PROJECT IS INTENDED TO IMPLEMENT AN ADVANCED TRAVELER INFORMATION SYSTEM TAILORED TO THE UNIQUE NEEDS OF THE NORTHEAST CORRIDOR. THE SYSTEM WILL ACQUIRE AND DISSEMINATE INFORMATION ON ...

  3. Travelling-wave resonant four-wave mixing breaks the limits of cavity-enhanced all-optical wavelength conversion.

    PubMed

    Morichetti, Francesco; Canciamilla, Antonio; Ferrari, Carlo; Samarelli, Antonio; Sorel, Marc; Melloni, Andrea

    2011-01-01

    Wave mixing inside optical resonators, while experiencing a large enhancement of the nonlinear interaction efficiency, suffers from strong bandwidth constraints, preventing its practical exploitation for processing broad-band signals. Here we show that such limits are overcome by the new concept of travelling-wave resonant four-wave mixing (FWM). This approach combines the efficiency enhancement provided by resonant propagation with a wide-band conversion process. Compared with conventional FWM in bare waveguides, it exhibits higher robustness against chromatic dispersion and propagation loss, while preserving transparency to modulation formats. Travelling-wave resonant FWM has been demonstrated in silicon-coupled ring resonators and was exploited to realize a 630-μm-long wavelength converter operating over a wavelength range wider than 60 nm and with 28-dB gain with respect to a bare waveguide of the same physical length. Full compatibility of the travelling-wave resonant FWM with optical signal processing applications has been demonstrated through signal retiming and reshaping at 10 Gb s(-1).

  4. Travelling-wave resonant four-wave mixing breaks the limits of cavity-enhanced all-optical wavelength conversion

    PubMed Central

    Morichetti, Francesco; Canciamilla, Antonio; Ferrari, Carlo; Samarelli, Antonio; Sorel, Marc; Melloni, Andrea

    2011-01-01

    Wave mixing inside optical resonators, while experiencing a large enhancement of the nonlinear interaction efficiency, suffers from strong bandwidth constraints, preventing its practical exploitation for processing broad-band signals. Here we show that such limits are overcome by the new concept of travelling-wave resonant four-wave mixing (FWM). This approach combines the efficiency enhancement provided by resonant propagation with a wide-band conversion process. Compared with conventional FWM in bare waveguides, it exhibits higher robustness against chromatic dispersion and propagation loss, while preserving transparency to modulation formats. Travelling-wave resonant FWM has been demonstrated in silicon-coupled ring resonators and was exploited to realize a 630-μm-long wavelength converter operating over a wavelength range wider than 60 nm and with 28-dB gain with respect to a bare waveguide of the same physical length. Full compatibility of the travelling-wave resonant FWM with optical signal processing applications has been demonstrated through signal retiming and reshaping at 10 Gb s−1 PMID:21540838

  5. Free surfaces recast superconductivity in few-monolayer MgB2: Combined first-principles and ARPES demonstration.

    PubMed

    Bekaert, J; Bignardi, L; Aperis, A; van Abswoude, P; Mattevi, C; Gorovikov, S; Petaccia, L; Goldoni, A; Partoens, B; Oppeneer, P M; Peeters, F M; Milošević, M V; Rudolf, P; Cepek, C

    2017-10-31

    Two-dimensional materials are known to harbour properties very different from those of their bulk counterparts. Recent years have seen the rise of atomically thin superconductors, with a caveat that superconductivity is strongly depleted unless enhanced by specific substrates, intercalants or adatoms. Surprisingly, the role in superconductivity of electronic states originating from simple free surfaces of two-dimensional materials has remained elusive to date. Here, based on first-principles calculations, anisotropic Eliashberg theory, and angle-resolved photoemission spectroscopy (ARPES), we show that surface states in few-monolayer MgB 2 make a major contribution to the superconducting gap spectrum and density of states, clearly distinct from the widely known, bulk-like σ- and π-gaps. As a proof of principle, we predict and measure the gap opening on the magnesium-based surface band up to a critical temperature as high as ~30 K for merely six monolayers thick MgB 2 . These findings establish free surfaces as an unavoidable ingredient in understanding and further tailoring of superconductivity in atomically thin materials.

  6. Modeling L-band synthetic aperture radar observations through dielectric changes in soil moisture and vegetation over shrublands

    USDA-ARS?s Scientific Manuscript database

    L-band airborne synthetic aperture radar observations were made over California shrublands to better understand the effects by soil and vegetation parameters on backscatter. Temporal changes in radar backscattering coefficient (s0) of up to 3 dB were highly correlated to surface soil moisture but no...

  7. Superconductivity-insensitive order at q~1/4 in electron doped cuprates

    DOE PAGES

    Lee, Jun -Sik; Jang, H.; Asano, S.; ...

    2017-12-15

    One of the central questions in the cuprate research is the nature of the ‘normal state’ which develops into high temperature superconductivity (HTSC). In the normal state of hole-doped cuprates, the existence of charge density wave (CDW) is expected to shed light on the mechanism of HTSC. With evidence emerging for CDW order in the electron-doped cuprates, the CDW would be thought to be a universal phenomenon in high-T c cuprates. However, the CDW phenomena in electron-doped cuprate are quite different than those in hole-doped cuprates. Here we study the nature of the putative CDW in an electron-doped cuprate throughmore » direct comparisons between as-grown and post-annealed Nd 1.86Ce 0.14CuO 4 (NCCO) single crystals using Cu L 3-edge resonant soft x-ray scattering (RSXS) and angleresolved photoemission spectroscopy (ARPES). The RSXS result reveals that the non-superconducting NCCO shows the same reflections at the wavevector (~1/4, 0, l) as like the reported superconducting NCCO. This superconductivity-insensitivesignal is quite different with the characteristics of the CDW reflection in hole-doped cuprates. Moreover, the ARPES result suggests that the fermiology cannot account for such wavevector. Furthermore, these results call into question the universality of CDW phenomenon in the cuprates.« less

  8. Terahertz Mixing Characteristics of NbN Superconducting Tunnel Junctions and Related Astronomical Observations

    NASA Astrophysics Data System (ADS)

    Li, J.

    2010-01-01

    (5hω/kB), which is the best among NbN superconducting SIS mixers developed in this frequency band; (4) demonstration of high sensitivity for NbN superconducting SIS mixers operated at temperatures as high as 10 K, and demonstration of much less interference resulting from the Josephson effect; (5) demonstration of the first astronomical observation ever done with an NbN superconducting SIS mixer. This study has provided further understanding of the quantum mixing behaviors of NbN superconducting SIS mixers. It has been demonstrated that NbN superconducting SIS mixers can reach nearly quantum-limited sensitivity and have good stability. Furthermore, NbN superconducting SIS mixers have less stringent requirement for cooling and magnetic field compared with Nb ones. Hence they can be used in astronomical applications, especially for space-borne projects and complex systems such as multi-beam receivers.

  9. Fully gapped spin-singlet superconductivity in noncentrosymmetric PbTaSe2: 207Pb nuclear magnetic resonance study

    NASA Astrophysics Data System (ADS)

    Maeda, S.; Matano, K.; Zheng, Guo-qing

    2018-05-01

    We report the 207Pb nuclear magnetic resonance (NMR) measurements on polycrystalline sample of PbTaSe2 with noncentrosymmetric crystal structure and topological electronic band. The nuclear spin-lattice relaxation rate 1 /T1 shows a suppressed coherence peak below the superconducting transition temperature Tc=4.05 K and decreases as an exponential function of temperature. The penetration depth derived from the NMR spectrum is almost temperature independent below T =0.7 Tc. The Knight shift K decreases below Tc. These results suggest spin-singlet superconductivity with a fully opened gap 2 Δ =3.5 kBTc in PbTaSe2.

  10. Aircraft L-Band Balloon - Simulated Satellite Experiments Volume I: Experiment Description and Voice and Data Modem Test Results

    DOT National Transportation Integrated Search

    1975-10-01

    This report details the result of an experiment performed by the Transportation Systems Center of the Department of Transportation to evaluate candidate voice and data modulation systems for use in an L-Band Air Traffic Control System. The experiment...

  11. Travel Schooling: Helping Children Learn through Travel.

    ERIC Educational Resources Information Center

    Byrnes, Deborah A.

    2001-01-01

    Provides information for teachers to help parents create rewarding and educational travel experiences for children. Examines the benefits of travel schooling, fundamental elements of a meaningful travel schooling experience, fostering cross cultural sensitivity through travel, and returning to the traditional classroom. (SD)

  12. Airborne Active and Passive L-Band Observations in Soil Moisture Active Passive Validation Experiment 2012 (SMAPVEX12)

    NASA Astrophysics Data System (ADS)

    Colliander, A.; Yueh, S. H.; Chazanoff, S.; Jackson, T. J.; McNairn, H.; Bullock, P.; Wiseman, G.; Berg, A. A.; Magagi, R.; Njoku, E. G.

    2012-12-01

    NASA's (National Aeronautics and Space Administration) Soil Moisture Active Passive (SMAP) Mission is scheduled for launch in October 2014. The objective of the mission is global mapping of soil moisture and freeze/thaw state. Merging of active and passive L-band observations of the mission will enable unprecedented combination of accuracy, resolution, coverage and revisit-time for soil moisture and freeze/thaw state retrieval. For pre-launch algorithm development and validation the SMAP project and NASA coordinated a field campaign named as SMAPVEX12 (Soil Moisture Active Passive Validation Experiment 2012) together with Agriculture and Agri-Food Canada in the vicinity of Winnipeg, Canada in June-July, 2012. The main objective of SMAPVEX12 was acquisition of data record that features long-time series with varying soil moisture and vegetation conditions (for testing the application of time-series approach) over aerial domain of multiple parallel lines (for spatial disaggregation studies). The coincident active and passive L-band data were acquired using the Passive Active L-band System (PALS), which is an airborne radiometer and radar developed for testing L-band retrieval algorithms. For SMAPVEX12 PALS was installed on a Twin Otter aircraft. The flight plan included flights at two altitudes. The higher altitude was used to map the whole experiment domain and the lower altitude was used to obtain measurements over a specific set of field sites. The spatial resolution (and swath) of the radar and radiometer from low altitude was about 600 m and from high altitude about 1500 m. The PALS acquisitions were complemented with high resolution (~10 m) L-band SAR measurements carried out by UAVSAR instrument on-board G-III aircraft. The campaign ran from June 7 until July 19. The PALS instrument conducted 17 brightness temperature and backscatter measurement flights and the UAVSAR conducted 14 backscatter measurement flights. The airborne data acquisition was supported by

  13. The Tor Vergata Scattering Model Applied to L Band Backscatter During the Corn Growth Cycle

    NASA Astrophysics Data System (ADS)

    Joseph, A. T.; van der Velde, R.; Ferrazzoli, P.; Lang, R. H.; Gish, T.

    2013-12-01

    At the USDA's Optimizing Production Inputs for Economic and Environmental Enhancement (OPE3) experimental site in Beltsville (Maryland, USA) a field campaign took place throughout the 2002 corn growth cycle from May 10th (emergence of corn crops) to October 2nd (harvest). One of the microwave instruments deployed was the multi-frequency (X-, C- and L-band) quad-polarized (HH, HV, VV, VH) NASA GSFC / George Washington University (GWU) truck mounted radar. During the field campaign, this radar system provided once a week fully polarized C- and L-band (4.75 and 1.6 GHz) backscatter measurements from incidence angle of 15, 35, and 55 degrees. In support of these microwave observations, an extensive ground characterization took place, which included measurements of surface roughness, soil moisture, vegetation biomass and morphology. The field conditions during the campaign are characterized by several dry downs with a period of drought in the month of August. Peak biomass of the corn canopies was reached at July 24, 2002 with a total biomass of approximately 6.5 kg m-2. This dynamic range in both soil moisture and vegetation conditions within the data set is ideal for the validation of discrete medium vegetation scattering models. In this study, we compare the L band backscatter measurements with simulations by the Tor Vergata model (Bracaglia et al., 1995). The measured soil moisture, vegetation biomass and most reliably measured vegetation morphological parameters (e.g. number of leaves, number of stems and stem height) were used as input for the Tor Vergata model. The more uncertain model parameters (e.g. surface roughness, leaf thickness) and the stem diameter were optimized using a parameter estimation routine based on the Levenberg-Marquardt algorithm. As cost function for this optimization, the HH and VV polarized backscatter measured and simulated by the Tor Vergata model for incidence angle of 15, 35 and 55 degrees were used (6 measurements in total). The

  14. Fluxoids configurations in finite superconducting networks

    NASA Astrophysics Data System (ADS)

    Sharon, Omri J.; Haham, Noam; Shaulov, Avner A.; Yeshurun, Yosef

    2017-12-01

    Analysis of superconducting ladders consisting of rectangular loops, yields an Ising like expression for the total energy of the ladders as a function of the loops vorticities and the applied magnetic field. This expression shows that fluxoids can be treated as repulsively interacting objects driven towards the ladder center by the applied field. Distinctive repulsive interactions between fluxoids are obtained depending on the ratio l between the loops length and the common width of adjacent loops. A 'short range' and a 'long range' interactions obtained for l ≳ 1 and l ≪ 1, respectively, give rise to remarkably different fluxoid configurations. The different configurations of fluxoids in different types of ladders are illustrated by simulations.

  15. Superconductivity in transition metals.

    PubMed

    Slocombe, Daniel R; Kuznetsov, Vladimir L; Grochala, Wojciech; Williams, Robert J P; Edwards, Peter P

    2015-03-13

    A qualitative account of the occurrence and magnitude of superconductivity in the transition metals is presented, with a primary emphasis on elements of the first row. Correlations of the important parameters of the Bardeen-Cooper-Schrieffer theory of superconductivity are highlighted with respect to the number of d-shell electrons per atom of the transition elements. The relation between the systematics of superconductivity in the transition metals and the periodic table high-lights the importance of short-range or chemical bonding on the remarkable natural phenomenon of superconductivity in the chemical elements. A relationship between superconductivity and lattice instability appears naturally as a balance and competition between localized covalent bonding and so-called broken covalency, which favours d-electron delocalization and superconductivity. In this manner, the systematics of superconductivity and various other physical properties of the transition elements are related and unified. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  16. Spin-orbit-coupled superconductivity

    PubMed Central

    Lo, Shun-Tsung; Lin, Shih-Wei; Wang, Yi-Ting; Lin, Sheng-Di; Liang, C.-T.

    2014-01-01

    Superconductivity and spin-orbit (SO) interaction have been two separate emerging fields until very recently that the correlation between them seemed to be observed. However, previous experiments concerning SO coupling are performed far beyond the superconducting state and thus a direct demonstration of how SO coupling affects superconductivity remains elusive. Here we investigate the SO coupling in the critical region of superconducting transition on Al nanofilms, in which the strength of disorder and spin relaxation by SO coupling are changed by varying the film thickness. At temperatures T sufficiently above the superconducting critical temperature Tc, clear signature of SO coupling reveals itself in showing a magneto-resistivity peak. When T < Tc, the resistivity peak can still be observed; however, its line-shape is now affected by the onset of the quasi two-dimensional superconductivity. By studying such magneto-resistivity peaks under different strength of spin relaxation, we highlight the important effects of SO interaction on superconductivity. PMID:24961726

  17. Unconventional Superconductivity in Luttinger Semimetals: Theory of Complex Tensor Order and the Emergence of the Uniaxial Nematic State

    NASA Astrophysics Data System (ADS)

    Boettcher, Igor; Herbut, Igor F.

    2018-02-01

    We investigate unconventional superconductivity in three-dimensional electronic systems with the chemical potential close to a quadratic band touching point in the band dispersion. Short-range interactions can lead to d -wave superconductivity, described by a complex tensor order parameter. We elucidate the general structure of the corresponding Ginzburg-Landau free energy and apply these concepts to the case of an isotropic band touching point. For a vanishing chemical potential, the ground state of the system is given by the superconductor analogue of the uniaxial nematic state, which features line nodes in the excitation spectrum of quasiparticles. In contrast to the theory of real tensor order in liquid crystals, however, the ground state is selected here by the sextic terms in the free energy. At a finite chemical potential, the nematic state has an additional instability at weak coupling and low temperatures. In particular, the one-loop coefficients in the free energy indicate that at weak coupling genuinely complex orders, which break time-reversal symmetry, are energetically favored. We relate our analysis to recent measurements in the half-Heusler compound YPtBi and discuss the role of cubic crystal symmetry.

  18. Pre-Travel Medical Preparation of Business and Occupational Travelers

    PubMed Central

    Khan, Nomana M.; Jentes, Emily S.; Brown, Clive; Han, Pauline; Rao, Sowmya R.; Kozarsky, Phyllis; Hagmann, Stefan H.F.; LaRocque, Regina C.; Ryan, Edward T.

    2016-01-01

    Objectives: The aim of the study was to understand more about pre-travel preparations and itineraries of business and occupational travelers. Methods: De-identified data from 18 Global TravEpiNet clinics from January 2009 to December 2012 were analyzed. Results: Of 23,534 travelers, 61% were non-occupational and 39% occupational. Business travelers were more likely to be men, had short times to departure and shorter trip durations, and commonly refused influenza, meningococcal, and hepatitis B vaccines. Most business travelers indicated that employers suggested the pre-travel health consultation, whereas non-occupational travelers sought consultations because of travel health concerns. Conclusions: Sub-groups of occupational travelers have characteristic profiles, with business travelers being particularly distinct. Employers play a role in encouraging business travelers to seek pre-travel consultations. Such consultations, even if scheduled immediately before travel, can identify vaccination gaps and increase coverage. PMID:26479857

  19. Transportation Systems Center/U.S. Coast Guard L-Band Maritime Satellite Test Program : Test Summary: September - November 1974

    DOT National Transportation Integrated Search

    1975-06-01

    Several L-band satellite communications tests with the NASA ATS-6 spacecraft and the U.S. Coast Guard Cutter SHERMAN are described. The tests included 1200 bit per second digital data, voice, simultaneous data and voice, ranging, multipath and antenn...

  20. Evidence of s-wave superconductivity in the noncentrosymmetric La7Ir3.

    PubMed

    Li, B; Xu, C Q; Zhou, W; Jiao, W H; Sankar, R; Zhang, F M; Hou, H H; Jiang, X F; Qian, B; Chen, B; Bangura, A F; Xu, Xiaofeng

    2018-01-12

    Superconductivity in noncentrosymmetric compounds has attracted sustained interest in the last decades. Here we present a detailed study on the transport, thermodynamic properties and the band structure of the noncentrosymmetric superconductor La 7 Ir 3 (T c  ~ 2.3 K) that was recently proposed to break the time-reversal symmetry. It is found that La 7 Ir 3 displays a moderately large electronic heat capacity (Sommerfeld coefficient γ n  ~ 53.1 mJ/mol K 2 ) and a significantly enhanced Kadowaki-Woods ratio (KWR ~32 μΩ cm mol 2 K 2 J -2 ) that is greater than the typical value (~10 μΩ cm mol 2 K 2 J -2 ) for strongly correlated electron systems. The upper critical field H c2 was seen to be nicely described by the single-band Werthamer-Helfand-Hohenberg model down to very low temperatures. The hydrostatic pressure effects on the superconductivity were also investigated. The heat capacity below T c reveals a dominant s-wave gap with the magnitude close to the BCS value. The first-principles calculations yield the electron-phonon coupling constant λ = 0.81 and the logarithmically averaged frequency ω ln  = 78.5 K, resulting in a theoretical T c  = 2.5 K, close to the experimental value. Our calculations suggest that the enhanced electronic heat capacity is more likely due to electron-phonon coupling, rather than the electron-electron correlation effects. Collectively, these results place severe constraints on any theory of exotic superconductivity in this system.

  1. Superconductivity under uniaxial compression in β-(BDA-TTP) salts

    NASA Astrophysics Data System (ADS)

    Suzuki, T.; Onari, S.; Ito, H.; Tanaka, Y.

    2009-10-01

    In order to clarify the mechanism of organic superconductor β-(BDA-TTP) salts. We study the superconductivity under uniaxial compression with non-dimerized two-band Hubbard model. We have calculated the uniaxial compression dependence of T c by solving the Eliashberg’s equation using the fluctuation exchange (FLEX) approximation. The transfer integral under the uniaxial compression was estimated by the extended Huckel method. We have found that non-monotonic behaviors of T c in experimental results under uniaxial compression are understood taking the spin frustration and spin fluctuation into account.

  2. Structure and superconductivity in the ternary silicide CaAlSi

    NASA Astrophysics Data System (ADS)

    Ma, Rong; Huang, Gui-Qin; Liu, Mei

    2007-06-01

    Using the linear response-linearized Muffin-tin orbital (LR-LMTO) method, we study the electronic band structure, phonon spectra, electron-phonon coupling and superconductivity for c-axis ferromagnetic-like (F-like) and antiferromagnetic-like (AF-like) structures in ternary silicide CaAlSi. The following conclusions are drawn from our calculations. If Al and Si atoms are assumed to arrange along the c axis in an F-like long-range ordering (-Al-Al-Al-and-Si-Si-Si-), one could obtain the ultrasoft B1g phonon mode and thus very strong electron-phonon coupling in CaAlSi. However, the appearance of imaginary frequency phonon modes indicates the instability of such a structure. For Al and Si atoms arranging along the c axis in an AF-like long-range ordering (-Al-Si-Al-), the calculated electron-phonon coupling constant is equal to 0.8 and the logarithmically averaged frequency is 146.8 K. This calculated result can correctly yield the superconducting transition temperature of CaAlSi by the standard BCS theory in the moderate electron-phonon coupling strength. We propose that an AF-like superlattice model for Al (or Si) atoms along the c direction may mediate the inconsistency estimated from theory and experiment, and explain the anomalous superconductivity in CaAlSi.

  3. Electronic structure and relaxation dynamics in a superconducting topological material

    DOE PAGES

    Neupane, Madhab; Ishida, Yukiaki; Sankar, Raman; ...

    2016-03-03

    Topological superconductors host new states of quantum matter which show a pairing gap in the bulk and gapless surface states providing a platform to realize Majorana fermions. Recently, alkaline-earth metal Sr intercalated Bi2Se3 has been reported to show superconductivity with a Tc~3K and a large shielding fraction. Here we report systematic normal state electronic structure studies of Sr0.06Bi2Se3 (Tc~2.5K) by performing photoemission spectroscopy. Using angle-resolved photoemission spectroscopy (ARPES), we observe a quantum well confined two-dimensional (2D) state coexisting with a topological surface state in Sr0.06Bi2Se3. Furthermore, our time-resolved ARPES reveals the relaxation dynamics showing different decay mechanism between the excitedmore » topological surface states and the two-dimensional states. Our experimental observation is understood by considering the intra-band scattering for topological surface states and an additional electron phonon scattering for the 2D states, which is responsible for the superconductivity. Our first-principles calculations agree with the more effective scattering and a shorter lifetime of the 2D states. In conclusion, our results will be helpful in understanding low temperature superconducting states of these topological materials.« less

  4. Superconductivity in epitaxial InN thin films with large critical fields

    NASA Astrophysics Data System (ADS)

    Pal, Buddhadeb; Joshi, Bhanu P.; Chakraborti, Himadri; Jain, Aditya K.; Barick, Barun K.; Ghosh, Kankat; Laha, Apurba; Dhar, Subhabrata; Gupta, Kantimay Das

    2018-04-01

    We report superconductivity in Chemical Vapor Deposition (CVD) and Plasma-Assisted Molecular Beam Epitaxy (PA-MBE) grown epitaxial InN films having carrier density ˜ 1019 - 1020cm-3. The superconducting phase transition starts at temperatures around Tc,onset˜3 K and the resistance goes to zero completely at Tc0 ˜ 1.6 K. The temperature dependence of the critical field HC2(T) does not obey a two fluid Casimir-Gorter (C-G) model rather it is well explained by the 2-D Tinkham model. The extrapolated value of the zero-temperature perpendicular critical field HC2(0) is found to be between 0.25 - 0.9 T, which is ten times greater than that of Indium metal. It may indicate the intrinsic nature of superconductivity in InN films. The angle dependence of critical field is well described by Lawrence-Doniach (L-D) model, which suggest the existence of quasi-2D superconducting layers.

  5. Airborne active and passive L-band measurements using PALS instrument in SMAPVEX12 soil moisture field campaign

    NASA Astrophysics Data System (ADS)

    Colliander, Andreas; Yueh, Simon; Chazanoff, Seth; Dinardo, Steven; O'Dwyer, Ian; Jackson, Thomas; McNairn, Heather; Bullock, Paul; Wiseman, Grant; Berg, Aaron; Magagi, Ramata; Njoku, Eni

    2012-10-01

    NASA's (National Aeronautics and Space Administration) Soil Moisture Active Passive (SMAP) Mission is scheduled for launch in late 2014. The objective of the mission is global mapping of soil moisture and freeze/thaw state. Merging of active and passive L-band observations of the mission will enable unprecedented combination of accuracy, resolution, coverage and revisit-time for soil moisture and freeze/thaw state retrieval. For pre-launch algorithm development and validation the SMAP project and NASA coordinated a field campaign named as SMAPVEX12 (Soil Moisture Active Passive Validation Experiment 2012) together with Agriculture and Agri-Food Canada, and other Canadian and US institutions in the vicinity of Winnipeg, Canada in June-July, 2012. The main objective of SMAPVEX12 was acquisition of a data record that features long time-series with varying soil moisture and vegetation conditions over an aerial domain of multiple parallel flight lines. The coincident active and passive L-band data was acquired with the PALS (Passive Active L-band System) instrument. The measurements were conducted over the experiment domain every 2-3 days on average, over a period of 43 days. The preliminary calibration of the brightness temperatures obtained in the campaign has been performed. Daily lake calibrations were used to adjust the radiometer calibration parameters, and the obtained measurements were compared against the raw in situ soil moisture measurements. The evaluation shows that this preliminary calibration of the data produces already a consistent brightness temperature record over the campaign duration, and only secondary adjustments and cleaning of the data is need before the data can be applied to the development and validation of SMAP algorithms.

  6. Investigating the Materials Limits on Coherence in Superconducting Charge Qubits

    DTIC Science & Technology

    2014-12-04

    Brecht, R. W. Heeres, L. Frunzio, M. H. Devoret, G. Catelani, L. I. Glazman, R. J. Schoelkopf. Measurement and control of quasiparticle dynamics in a... quasiparticles injection on the ac response of a superconductor, Physical Review B, (10 2010): 0. doi: 10.1103/PhysRevB.82.134502 M H Devoret, R J Schoelkopf...Frunzio, R. J. Schoelkopf, M. H. Devoret, L. I. Glazman. Quasiparticle Relaxation of Superconducting Qubits in the Presence of Flux, Physical

  7. Superconductivity of lanthanum revisited

    NASA Astrophysics Data System (ADS)

    Loeptien, Peter; Zhou, Lihui; Wiebe, Jens; Khajetoorians, Alexander Ako; Wiesendanger, Roland

    2014-03-01

    The thickness dependence of the superconductivity in clean hexagonal lanthanum films grown on tungsten (110) is studied by means of scanning tunneling microscopy (STM) and spectroscopy (STS). Fitting of the measured spectra to BCS theory yields the superconducting energy gaps from which the critical temperatures are determined. For the case of thick, bulk-like films, the bulk energy gap and critical temperature of dhcp lanthanum turn out to be considerably higher as compared to values from the literature measured by other techniques. In thin films the superconductivity is quenched by the boundary condition for the superconducting wavefunction imposed by the substrate and surface, leading to a linear decrease of the superconducting transition temperature as a function of the inverse film thickness. This opens up the possibility to grow lanthanum films with defined superconducting properties.

  8. L-Band Transmit/Receive Module for Phase-Stable Array Antennas

    NASA Technical Reports Server (NTRS)

    Andricos, Constantine; Edelstein, Wendy; Krimskiy, Vladimir

    2008-01-01

    Interferometric synthetic aperture radar (InSAR) has been shown to provide very sensitive measurements of surface deformation and displacement on the order of 1 cm. Future systematic measurements of surface deformation will require this capability over very large areas (300 km) from space. To achieve these required accuracies, these spaceborne sensors must exhibit low temporal decorrelation and be temporally stable systems. An L-band (24-cmwavelength) InSAR instrument using an electronically steerable radar antenna is suited to meet these needs. In order to achieve the 1-cm displacement accuracy, the phased array antenna requires phase-stable transmit/receive (T/R) modules. The T/R module operates at L-band (1.24 GHz) and has less than 1- deg absolute phase stability and less than 0.1-dB absolute amplitude stability over temperature. The T/R module is also high power (30 W) and power efficient (60-percent overall efficiency). The design is currently implemented using discrete components and surface mount technology. The basic T/R module architecture is augmented with a calibration loop to compensate for temperature variations, component variations, and path loss variations as a function of beam settings. The calibration circuit consists of an amplitude and phase detector, and other control circuitry, to compare the measured gain and phase to a reference signal and uses this signal to control a precision analog phase shifter and analog attenuator. An architecture was developed to allow for the module to be bidirectional, to operate in both transmit and receive mode. The architecture also includes a power detector used to maintain a transmitter power output constant within 0.1 dB. The use of a simple, stable, low-cost, and high-accuracy gain and phase detector made by Analog Devices (AD8302), combined with a very-high efficiency T/R module, is novel. While a self-calibrating T/R module capability has been sought for years, a practical and cost-effective solution has

  9. On the retrieval of sea ice thickness and snow depth using concurrent laser altimetry and L-band remote sensing data

    NASA Astrophysics Data System (ADS)

    Zhou, Lu; Xu, Shiming; Liu, Jiping; Wang, Bin

    2018-03-01

    The accurate knowledge of sea ice parameters, including sea ice thickness and snow depth over the sea ice cover, is key to both climate studies and data assimilation in operational forecasts. Large-scale active and passive remote sensing is the basis for the estimation of these parameters. In traditional altimetry or the retrieval of snow depth with passive microwave remote sensing, although the sea ice thickness and the snow depth are closely related, the retrieval of one parameter is usually carried out under assumptions over the other. For example, climatological snow depth data or as derived from reanalyses contain large or unconstrained uncertainty, which result in large uncertainty in the derived sea ice thickness and volume. In this study, we explore the potential of combined retrieval of both sea ice thickness and snow depth using the concurrent active altimetry and passive microwave remote sensing of the sea ice cover. Specifically, laser altimetry and L-band passive remote sensing data are combined using two forward models: the L-band radiation model and the isostatic relationship based on buoyancy model. Since the laser altimetry usually features much higher spatial resolution than L-band data from the Soil Moisture Ocean Salinity (SMOS) satellite, there is potentially covariability between the observed snow freeboard by altimetry and the retrieval target of snow depth on the spatial scale of altimetry samples. Statistically significant correlation is discovered based on high-resolution observations from Operation IceBridge (OIB), and with a nonlinear fitting the covariability is incorporated in the retrieval algorithm. By using fitting parameters derived from large-scale surveys, the retrievability is greatly improved compared with the retrieval that assumes flat snow cover (i.e., no covariability). Verifications with OIB data show good match between the observed and the retrieved parameters, including both sea ice thickness and snow depth. With

  10. Traveling-Wave Tube Amplifier Second Harmonic as Millimeter-Wave Beacon Source for Atmospheric Propagation Studies

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.

    2014-01-01

    This paper presents the design and test results of a CW millimeter-wave satellite beacon source, based on the second harmonic from a traveling-wave tube amplifier and utilizes a novel waveguide multimode directional coupler. A potential application of the beacon source is for investigating the atmospheric effects on Q-band (37 to 42 GHz) and V/W-band (71 to 76 GHz) satellite-to-ground signals.

  11. Traveling-Wave Tube Amplifier Second Harmonic as Millimeter-Wave Beacon Source for Atmospheric Propagation Studies

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.

    2014-01-01

    This paper presents the design and test results of a CW millimeter-wave satellite beacon source, based on the second harmonic from a traveling-wave tube amplifier and utilizes a novel waveguide multimode directional coupler. A potential application of the beacon source is for investigating the atmospheric effects on Q-band (37-42 GHz) and V/W-band (71- 76 GHz) satellite-to-ground signals.

  12. Travel health knowledge, attitudes and practices among Australasian travelers.

    PubMed

    Wilder-Smith, Annelies; Khairullah, Nor S; Song, Jae-Hoon; Chen, Ching-Yu; Torresi, Joseph

    2004-01-01

    Although the Asia Pacific region is the focus of the fastest-growing tourist and travel industry, few data are available on the knowledge, attitudes and practices (KAP) of travelers from this region with regard to travel-related infectious diseases. We conducted a cross-sectional survey among travelers at the departure lounges of five airports in Australasia (Singapore, Kuala Lumpur, Taipeh, Melbourne, Seoul) whose travel destinations were Asia, Africa or South America. Two standardized questionnaires directed towards KAP in travel health, travel immunizations and malaria were administered. Of 2,101 respondents (82% Asian, 17% Western), 31% had sought pretravel health advice and only 4% sought travel health advice from the travel medicine specialist. The risk of vaccine-preventable infectious diseases and malaria at the destination country was perceived to be low. Overall, fewer than 5% of travelers had been vaccinated in preparation for their trip. The most frequent travel vaccinations were for hepatitis A and B. Only 40% of travelers to malaria-endemic areas carried malaria prophylaxis. Compared to Western travelers, those of Asian nationality were significantly less likely to obtain pretravel advice and malaria prophylaxis and to receive travel vaccinations. There is an urgent need for increased awareness about travel-related infectious diseases among Asian travelers, and greater uptake of pretravel health advice, vaccinations and malaria prophylactic measures.

  13. Travel medicine

    PubMed Central

    Aw, Brian; Boraston, Suni; Botten, David; Cherniwchan, Darin; Fazal, Hyder; Kelton, Timothy; Libman, Michael; Saldanha, Colin; Scappatura, Philip; Stowe, Brian

    2014-01-01

    Abstract Objective To define the practice of travel medicine, provide the basics of a comprehensive pretravel consultation for international travelers, and assist in identifying patients who might require referral to travel medicine professionals. Sources of information Guidelines and recommendations on travel medicine and travel-related illnesses by national and international travel health authorities were reviewed. MEDLINE and EMBASE searches for related literature were also performed. Main message Travel medicine is a highly dynamic specialty that focuses on pretravel preventive care. A comprehensive risk assessment for each individual traveler is essential in order to accurately evaluate traveler-, itinerary-, and destination-specific risks, and to advise on the most appropriate risk management interventions to promote health and prevent adverse health outcomes during travel. Vaccinations might also be required and should be personalized according to the individual traveler’s immunization history, travel itinerary, and the amount of time available before departure. Conclusion A traveler’s health and safety depends on a practitioner’s level of expertise in providing pretravel counseling and vaccinations, if required. Those who advise travelers are encouraged to be aware of the extent of this responsibility and to refer all high-risk travelers to travel medicine professionals whenever possible. PMID:25500599

  14. Cryogenic Design of a Large Superconducting Magnet for Astro-particle Shielding on Deep Space Travel Missions

    NASA Astrophysics Data System (ADS)

    Bruce, Romain; Baudouy, Bertrand

    The Space Radiation Superconducting Shield (SR2S) European project aims at studying a large superconducting toroid magnet to protect the human habitat from the ionizing radiations coming from Galactic Cosmic Ray during long term missions in deep space. Titanium clad MgB2 conductor is used to afford a bending power greater than 5 T.m at 10 K. A specific cryogenic design is needed to cool down this 10 m long and 12.8 m in diameter magnet. A passive cooling system, using a V-groove sunshield, is considered to reduce the heat flux coming from the Sun or Mars. An active configuration, using pulse tube cryocoolers, will be linked to the 80 K thermal screen intercepting most of the heat fluxes coming from the human habitat. The toroid magnet will be connected also to cryocoolers to absorb the few watts reaching its surface. Two kinds of thermal link are being considered to absorb the heat on the 80 K thermal screen. The first one is active, with a pump circulating helium gas in a network of exchange tubes. The second one is passive using long cryogenic pulse heat pipe (PHP) with the evaporator on the surface of the thermal screen and the condenser attached to the pulse tube.

  15. Relation between L-band soil emittance and soil water content

    NASA Technical Reports Server (NTRS)

    Stroosnijder, L.; Lascano, R. J.; Van Bavel, C. H. M.; Newton, R. W.

    1986-01-01

    An experimental relation between soil emittance (E) at L-band and soil surface moisture content (M) is compared with a theoretical one. The latter depends on the soil dielectric constant, which is a function of both soil moisture content and of soil texture. It appears that a difference of 10 percent in the surface clay content causes a change in the estimate of M on the order of 0.02 cu m/cu m. This is based on calculations with a model that simulates the flow of water and energy, in combination with a radiative transfer model. It is concluded that an experimental determination of the E-M relation for each soil type is not required, and that a rough estimate of the soil texture will lead to a sufficiently accurate estimate of soil moisture from a general, theoretical relationship obtained by numerical simulation.

  16. Spin-orbit coupling enhanced superconductivity in Bi-rich compounds ABi3 (A = Sr and Ba)

    PubMed Central

    Shao, D. F.; Luo, X.; Lu, W. J.; Hu, L.; Zhu, X. D.; Song, W. H.; Zhu, X. B.; Sun, Y. P.

    2016-01-01

    Recently, Bi-based compounds have attracted attentions because of the strong spin-orbit coupling (SOC). In this work, we figured out the role of SOC in ABi3 (A = Sr and Ba) by theoretical investigation of the band structures, phonon properties, and electron-phonon coupling. Without SOC, strong Fermi surface nesting leads to phonon instabilities in ABi3. SOC suppresses the nesting and stabilizes the structure. Moreover, without SOC the calculation largely underestimates the superconducting transition temperatures (Tc), while with SOC the calculated Tc are very close to those determined by measurements on single crystal samples. The SOC enhanced superconductivity in ABi3 is due to not only the SOC induced phonon softening, but also the SOC related increase of electron-phonon coupling matrix elements. ABi3 can be potential platforms to construct heterostructure of superconductor/topological insulator to realize topological superconductivity. PMID:26892681

  17. Enhancement of superconductivity under pressure and the magnetic phase diagram of tantalum disulfide single crystals

    PubMed Central

    Abdel-Hafiez, M.; Zhao, X.-M.; Kordyuk, A. A.; Fang, Y.-W.; Pan, B.; He, Z.; Duan, C.-G.; Zhao, J.; Chen, X.-J.

    2016-01-01

    In low-dimensional electron systems, charge density waves (CDW) and superconductivity are two of the most fundamental collective quantum phenomena. For all known quasi-two-dimensional superconductors, the origin and exact boundary of the electronic orderings and superconductivity are still attractive problems. Through transport and thermodynamic measurements, we report on the field-temperature phase diagram in 2H-TaS2 single crystals. We show that the superconducting transition temperature (Tc) increases by one order of magnitude from temperatures at 0.98 K up to 9.15 K at 8.7 GPa when the Tc becomes very sharp. Additionally, the effects of 8.7 GPa illustrate a suppression of the CDW ground state, with critically small Fermi surfaces. Below the Tc the lattice of magnetic flux lines melts from a solid-like state to a broad vortex liquid phase region. Our measurements indicate an unconventional s-wave-like picture with two energy gaps evidencing its multi-band nature. PMID:27534898

  18. Optimization of superconducting tiling pattern for superconducting bearings

    DOEpatents

    Hull, John R.

    1996-01-01

    An apparatus and method for reducing magnetic field inhomogeneities which produce rotational loss mechanisms in high temperature superconducting magnetic bearings. Magnetic field inhomogeneities are reduced by dividing high temperature superconducting structures into smaller structures, and arranging the smaller structures into tiers which stagger the magnetic field maximum locations of the smaller structures.

  19. Ku-Band Traveling Wave Slot Array Using Simple Scanning Control

    NASA Technical Reports Server (NTRS)

    Host, Nicholas K.; Chen, Chi-Chih; Volakis, John L.; Miranda, Felix A.

    2015-01-01

    This paper introduces a feeding concept aimed at simplifying the backend (phase shifters) of traditional phased arrays. As an alternative to traditional phased arrays, we employ a traveling wave array (TWA) using a single feedline whose propagation constant is controlled via a single, small mechanical movement without a need for phase shifters to enable scanning. Specifically, a dielectric plunger is positioned within a parallel plate waveguide (PPW) transmission line (TL) that feeds the TWA. By adjusting the position of the dielectric plunger within the PPW feeding the TWA, beam steering is achieved. A 20 element array is designed at 13GHz shown to give stable realized gain across the angular range of -25 deg. less than or equal to theta less than or equal to 25 deg. A proof of concept array is fabricated and measured to demonstrate and validate the concept's operation.

  20. Palm-size miniature superconducting bulk magnet

    NASA Astrophysics Data System (ADS)

    Saho, Norihide; Matsuda, Kazuya; Nishijima, Noriyo

    The development of a small, light, powerful and energy-efficient superconducting magnet has been desired in order to realize better efficiency and manipulability in guiding magnetic nano-particles, magnetic organic cells and other items to the right place. This study focuses on the development of a high-temperature superconducting (HTS) bulk magnet characterized by comparatively low leak magnetism despite a relatively high magnetic field. On this basis, the authors developed a palm-sized superconducting bulk magnet, which is the world's smallest, lightest, and lowest power consuming, as well as a new technology to effectively magnetize such a bulk magnet in a compact Stirling-cycle cryocooler (magnet C) with a pre-magnetized HTS bulk magnet (magnet B) in a compact cryocooler. This technology is demonstrated in two steps. In the first step, magnet B is magnetized using a superconducting solenoid magnet with a high magnetic field (magnet A) via the field cooling method. In the second step, magnet C is magnetized in the high magnetic field of magnet B. The prototype magnet C weighs 1.8 kg, and measures 235 × 65 × 115 mm (L × W × H). Magnet B was magnetized to 4.9 T using a 5 T magnet, and the target, magnet C, was magnetized using magnet B so that its maximum trapped magnetic flux density reached the value of 3.15 T. The net power consumption in a steady cooling state was 23 W, which is very low and comparable to that of a laptop computer.

  1. International business travel: impact on families and travellers

    PubMed Central

    Espino, C; Sundstrom, S; Frick, H; Jacobs, M; Peters, M

    2002-01-01

    Objectives: Spouses and staff of the World Bank Group (WBG) were questioned about the impact of international business travel on families and travellers. Dependent variables were self reported stress, concern about the health of the traveller, and negative impact on the family. We hypothesised that several travel factors (independent variables) would be associated with these impacts. These travel factors had to do with the frequency, duration, and predictability of travel and its interference with family activities. Methods: Survey forms were developed and distributed to all spouses of travelling staff as well as a small sample of operational staff. Kendall's tau b correlation coefficients of response frequencies were computed with the data from scaled items. Written responses to open ended questions were categorised. Results: Response rates for spouses and staff were 24% and 36%, respectively. Half the spouse sample (n=533) and almost 75% of the staff sample (n=102) reported high or very high stress due to business travel. Self reported spouse stress was associated with six out of eight travel factors. Female spouses, those with children, and younger spouses reported greater stress. Self reported staff stress was significantly associated with four out of nine travel factors. Further insight into how business travel affects families and staff (including children's behavioural changes) and how families cope was gained through responses to written questions. Conclusions: The findings support the notion that lengthy and frequent travel and frequent changes in travel dates which affect family plans, all characteristic of WBG missions, negatively affects many spouses and children (particularly young children) and that the strain on families contributes significantly to the stress staff feel about their travel. Policies or management practices that take into consideration family activities and give staff greater leeway in controlling and refusing travel may help relieve

  2. International business travel: impact on families and travellers.

    PubMed

    Espino, C M; Sundstrom, S M; Frick, H L; Jacobs, M; Peters, M

    2002-05-01

    Spouses and staff of the World Bank Group (WBG) were questioned about the impact of international business travel on families and travellers. Dependent variables were self reported stress, concern about the health of the traveller, and negative impact on the family. We hypothesised that several travel factors (independent variables) would be associated with these impacts. These travel factors had to do with the frequency, duration, and predictability of travel and its interference with family activities. Survey forms were developed and distributed to all spouses of travelling staff as well as a small sample of operational staff. Kendall's tau b correlation coefficients of response frequencies were computed with the data from scaled items. Written responses to open ended questions were categorised. Response rates for spouses and staff were 24% and 36%, respectively. Half the spouse sample (n=533) and almost 75% of the staff sample (n=102) reported high or very high stress due to business travel. Self reported spouse stress was associated with six out of eight travel factors. Female spouses, those with children, and younger spouses reported greater stress. Self reported staff stress was significantly associated with four out of nine travel factors. Further insight into how business travel affects families and staff (including children's behavioural changes) and how families cope was gained through responses to written questions. The findings support the notion that lengthy and frequent travel and frequent changes in travel dates which affect family plans, all characteristic of WBG missions, negatively affects many spouses and children (particularly young children) and that the strain on families contributes significantly to the stress staff feel about their travel. Policies or management practices that take into consideration family activities and give staff greater leeway in controlling and refusing travel may help relieve stress.

  3. Random forest wetland classification using ALOS-2 L-band, RADARSAT-2 C-band, and TerraSAR-X imagery

    NASA Astrophysics Data System (ADS)

    Mahdianpari, Masoud; Salehi, Bahram; Mohammadimanesh, Fariba; Motagh, Mahdi

    2017-08-01

    Wetlands are important ecosystems around the world, although they are degraded due both to anthropogenic and natural process. Newfoundland is among the richest Canadian province in terms of different wetland classes. Herbaceous wetlands cover extensive areas of the Avalon Peninsula, which are the habitat of a number of animal and plant species. In this study, a novel hierarchical object-based Random Forest (RF) classification approach is proposed for discriminating between different wetland classes in a sub-region located in the north eastern portion of the Avalon Peninsula. Particularly, multi-polarization and multi-frequency SAR data, including X-band TerraSAR-X single polarized (HH), L-band ALOS-2 dual polarized (HH/HV), and C-band RADARSAT-2 fully polarized images, were applied in different classification levels. First, a SAR backscatter analysis of different land cover types was performed by training data and used in Level-I classification to separate water from non-water classes. This was followed by Level-II classification, wherein the water class was further divided into shallow- and deep-water classes, and the non-water class was partitioned into herbaceous and non-herbaceous classes. In Level-III classification, the herbaceous class was further divided into bog, fen, and marsh classes, while the non-herbaceous class was subsequently partitioned into urban, upland, and swamp classes. In Level-II and -III classifications, different polarimetric decomposition approaches, including Cloude-Pottier, Freeman-Durden, Yamaguchi decompositions, and Kennaugh matrix elements were extracted to aid the RF classifier. The overall accuracy and kappa coefficient were determined in each classification level for evaluating the classification results. The importance of input features was also determined using the variable importance obtained by RF. It was found that the Kennaugh matrix elements, Yamaguchi, and Freeman-Durden decompositions were the most important parameters

  4. WISEP J061135.13-041024.0 AB: A J-band Flux Reversal Binary at the L/T Transition

    NASA Astrophysics Data System (ADS)

    Gelino, Christopher R.; Smart, R. L.; Marocco, Federico; Kirkpatrick, J. Davy; Cushing, Michael C.; Mace, Gregory; Mendez, Rene A.; Tinney, C. G.; Jones, Hugh R. A.

    2014-07-01

    We present Keck II laser guide star adaptive optics observations of the brown dwarf WISEP J061135.13-041024.0 showing it is a binary with a component separation of 0.''4. This system is one of the six known resolved binaries in which the magnitude differences between the components show a reversal in sign between the Y/J band and the H/K bands. Deconvolution of the composite spectrum results in a best-fit binary solution with L9 and T1.5 components. We also present a preliminary parallax placing the system at a distance of 21.2 ± 1.3 pc. Using the distance and resolved magnitudes we are able to place WISEP J061135.13-041024.0 AB on a color-absolute magnitude diagram, showing that this system contributes to the well-known "J-band bump" and the components' properties appear similar to other late-type L and early-type T dwarfs. Fitting our data to a set of cloudy atmosphere models suggests the system has an age >1 Gyr with WISE 0611-0410 A having an effective temperature (T eff) of 1275-1325 K and mass of 64-65 M Jup, and WISE 0611-0410 B having T eff = 1075-1115 K and mass 40-65 M Jup.

  5. Spin-imbalanced pairing and Fermi surface deformation in flat bands

    NASA Astrophysics Data System (ADS)

    Huhtinen, Kukka-Emilia; Tylutki, Marek; Kumar, Pramod; Vanhala, Tuomas I.; Peotta, Sebastiano; Törmä, Päivi

    2018-06-01

    We study the attractive Hubbard model with spin imbalance on two lattices featuring a flat band: the Lieb and kagome lattices. We present mean-field phase diagrams featuring exotic superfluid phases, similar to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, whose stability is confirmed by dynamical mean-field theory. The nature of the pairing is found to be richer than just the Fermi surface shift responsible for the usual FFLO state. The presence of a flat band allows for changes in the particle momentum distributions at null energy cost. This facilitates formation of nontrivial superfluid phases via multiband Cooper pair formation: the momentum distribution of the spin component in the flat band deforms to mimic the Fermi surface of the other spin component residing in a dispersive band. The Fermi surface of the unpaired particles that are typical for gapless superfluids becomes deformed as well. The results highlight the profound effect of flat dispersions on Fermi surface instabilities, and provide a potential route for observing spin-imbalanced superfluidity and superconductivity.

  6. [Pre-travel advice and patient education of Hungarian travellers].

    PubMed

    Lengyel, Ingrid; Felkai, Péter

    2018-03-01

    According to international surveys, over half of the travellers face some kind of health issue when travelling. The overwhelming majority of travel-related illnesses can be prevented with pre-travel medical consultations, but the syllabus and content of the consultation have to match the travel habits and culture of the given society. This publication explores the specificities and travel habits of Hungarian travellers. One hundred participants of a travel exhibition completed a survey about their international travel. As the survey was not representative, the data could only be processed through simple statistical methods. However, since the exhibition was presumably attended by those wishing to travel, the conclusions drawn from the results are worth publishing, since no similar survey in Hungary has been published before. Based on the suitable classification of age groups in travel medicine, 11% of the participants were adolescents / young adults (aged 15-24), 81% adults (25-59) and 8% elderly (60-74). Twenty-eight percent of the participants travel multiple times a year, 40% yearly and 32% of them less frequently; 16% of the adults, 8% of the adolescents and 4% of the elderly age group travel multiple times a year. The travel destinations of Hungarian travellers have remained practically unchanged since a study was conducted 13 years ago: the vast majority (95%) travelled within Europe, 2% to the United States, and 11% of them elsewhere. Since Hungarians do not travel to endemic areas, only 5% consulted their general practitioners (GPs) prior to travelling, and 29% did when they had to be vaccinated. Forty-two percent of those wishing to travel never consult their GPs, even though 29% of them are aware of some chronic illness. Instead, 51% gather their health information from the internet and only 6% from their doctors. By the contradiction between the poor health status of the majority of Hungarian travellers and the negligence of seeking pre-travel advice

  7. Quasiparticle self-consistent GW study of cuprates: electronic structure, model parameters, and the two-band theory for Tc

    PubMed Central

    Jang, Seung Woo; Kotani, Takao; Kino, Hiori; Kuroki, Kazuhiko; Han, Myung Joon

    2015-01-01

    Despite decades of progress, an understanding of unconventional superconductivity still remains elusive. An important open question is about the material dependence of the superconducting properties. Using the quasiparticle self-consistent GW method, we re-examine the electronic structure of copper oxide high-Tc materials. We show that QSGW captures several important features, distinctive from the conventional LDA results. The energy level splitting between and is significantly enlarged and the van Hove singularity point is lowered. The calculated results compare better than LDA with recent experimental results from resonant inelastic xray scattering and angle resolved photoemission experiments. This agreement with the experiments supports the previously suggested two-band theory for the material dependence of the superconducting transition temperature, Tc. PMID:26206417

  8. Process for producing clad superconductive materials

    DOEpatents

    Cass, Richard B.; Ott, Kevin C.; Peterson, Dean E.

    1992-01-01

    A process for fabricating superconducting composite wire by the steps of placing a superconductive precursor admixture capable of undergoing a self propagating combustion in stoichiometric amounts sufficient to form a superconductive product within a metal tube, sealing one end of said tube, igniting said superconductive precursor admixture whereby said superconductive precursor admixture endburns along the length of the admixture, and cross-section reducing said tube at a rate substantially equal to the rate of burning of said superconductive precursor admixture and at a point substantially planar with the burnfront of the superconductive precursor mixture, whereby a clad superconductive product is formed in situ, the product characterized as superconductive without a subsequent sintering stage, is disclosed.

  9. Fabrication of a Silicon Backshort Assembly for Waveguide-Coupled Superconducting Detectors

    NASA Technical Reports Server (NTRS)

    Crowe, Erik J.; Bennett, Charles L.; Chuss, David T.; Denis, Kevin L.; Eimer, Joseph; Lourie, Nathan; Marriage, Tobias; Moseley, Samuel H.; Rostem, Karwan; Stevenson, Thomas R.; hide

    2012-01-01

    The Cosmology Large Angular Scale Surveyor (CLASS) is a ground-based instrument that will measure the polarization of the cosmic microwave background to search for evidence for gravitational waves from a posited epoch of inflation early in the Universe s history. This measurement will require integration of superconducting transition-edge sensors with microwave waveguide inputs with excellent control of systematic errors, such as unwanted coupling to stray signals at frequencies outside of a precisely defined microwave band. To address these needs we present work on the fabrication of micromachined silicon, producing conductive quarter-wave backshort assemblies for the CLASS 40 GHz focal plane. Each 40 GHz backshort assembly consists of three degeneratively doped silicon wafers. Two spacer wafers are micromachined with through-wafer vias to provide a 2.04 mm long square waveguide delay section. The third wafer terminates the waveguide delay in a short. The three wafers are bonded at the wafer level by Au-Au thermal compression bonding then aligned and flip chip bonded to the CLASS detector at the chip level. The micromachining techniques used have been optimized to create high aspect ratio waveguides, silicon pillars, and relief trenches with the goal of providing improved out of band signal rejection. We will discuss the fabrication of integrated CLASS superconducting detector chips with the quarter-wave backshort assemblies.

  10. Travel: a long-range goal of retired women.

    PubMed

    Staats, Sara; Pierfelice, Loretta

    2003-09-01

    The authors surveyed retired persons (predominately women) with regard to their immediate, intermediate, and long-range activities following retirement. As predicted, leisure travel emerged as a frequent long-range goal for persons retired more than 5 years. The travel activity preferences of long-retired older women present challenges and opportunities to both researchers and marketers. Length of trips and frequency of trips have been predicted from regression models, with trip length in particular being well predicted by the problem of daily life hassles. A theoretical model of continued post-retirement travel is presented as a variant of Solomon's opponent process theory of affect (R. L. Solomon, 1980). The authors suggest that to the degree that places traveled to are varied and different, older people may remain stimulated and continue to enjoy retirement.

  11. Investigation on the Frequency Allocation for Radio Astronomy at the L Band

    NASA Astrophysics Data System (ADS)

    Abidin, Z. Z.; Umar, R.; Ibrahim, Z. A.; Rosli, Z.; Asanok, K.; Gasiprong, N.

    2013-09-01

    In this paper, the frequency allocation reserved for radio astronomy in the L band set by the International Telecommunication Union (ITU), which is between 1400 and 1427 MHz, is reviewed. We argue that the nearby frequencies are still very important for radio astronomers on the ground by investigating radio objects (H i sources) around 1300-1500 MHz. The L-band window is separated into a group of four windows, namely 1400-1427 MHz (window A), 1380-1400 MHz (window B), 1350-1380 MHz (window C), and 1300-1350 MHz (window D). These windows are selected according to their redshifts from a rest frequency for hydrogen spectral line at 1420.4057 MHz. Radio objects up to z ≈ 0.1 or frequency down to 1300 MHz are examined. We argue that since window B has important radio objects within the four windows, this window should also be given to radio astronomy. They are galaxies, spiral galaxies, and galaxy clusters. This underlines the significance of window B for radio astronomers on the ground. By investigating the severeness of radio frequency interference (RFI) within these windows, we have determined that window B still has significant, consistent RFI. The main RFI sources in the four windows have also been identified. We also found that the Department of Civil Aviation of Malaysia is assigned a frequency range of 1215-1427 MHz, which is transmitted within the four windows and inside the protected frequency for radio astronomy. We also investigated the RFI in the four windows on proposed sites of future radio astronomy observatories in Malaysia and Thailand and found the two best sites as Universiti Pendidikan Sultan Idris (UPSI) and Ubon Ratchathani, respectively. It has also been determined that RFI in window B increases with population density.

  12. From Livingstone to ecotourism. What's new in travel medicine?

    PubMed

    Houston, S

    2000-01-01

    To review recent developments in the field of travel medicine and to outline the knowledge and resources family physicians need for providing health advice to travelers headed for tropical or developing countries. Personal files; references from review articles and from a recent textbook of travel medicine; current guidelines on pretravel advice; and a review of the 1996 to 1999 MEDLINE database using "travel medicine" as a term and subject heading, "trave(l)lers' diarrhea" as a text word and subject heading, "immunization + travel," and "malaria + chemo prevention" were used as information sources. Priority was given to randomized controlled trials and recommendations of expert or national bodies. Some elements of travel medicine, such as malaria chemoprophylaxis, have become more complex. Some valuable new preventive measures, such as hepatitis A vaccine, treated bed nets, and antimalarial drugs, have become available. Some health risks, such as cholera, have been overemphasized in the past, whereas others, such as tuberculosis and sexually transmitted diseases, have been underemphasized. Information sources relevant for providing travel health advice have improved and expanded. Canadian evidence-based guidelines addressing most important travel health issues are now available. Travel medicine is a rapidly evolving field. Physicians intending to provide health advice to travelers to high-risk parts of the world should be well prepared and have access to good, up-to-date information.

  13. Optimization of superconducting tiling pattern for superconducting bearings

    DOEpatents

    Hull, J.R.

    1996-09-17

    An apparatus and method for reducing magnetic field inhomogeneities which produce rotational loss mechanisms in high temperature superconducting magnetic bearings are disclosed. Magnetic field inhomogeneities are reduced by dividing high temperature superconducting structures into smaller structures, and arranging the smaller structures into tiers which stagger the magnetic field maximum locations of the smaller structures. 20 figs.

  14. Distributed Ferrite Isolation in Traveling-Wave Tubes.

    DTIC Science & Technology

    coupling to broadband edge modes of ferrite slabs. Evidence of coupling to the lower branch of edge mode, i.e., magnetostatic, has been obtained with L...band helix . Cold tests and analysis suggest coupling to ferrite edge modes from helix is easier at higher microwave frequencies. Plans for a hot...test at the 1-2 kW power level is an L-band TWT incorporating such distributed ferrites are described.

  15. Parameterization of L-, C- and X-band Radiometer-based Soil Moisture Retrieval Algorithm Using In-situ Validation Sites

    NASA Astrophysics Data System (ADS)

    Gao, Y.; Colliander, A.; Burgin, M. S.; Walker, J. P.; Chae, C. S.; Dinnat, E.; Cosh, M. H.; Caldwell, T. G.

    2017-12-01

    Passive microwave remote sensing has become an important technique for global soil moisture estimation over the past three decades. A number of missions carrying sensors at different frequencies that are capable for soil moisture retrieval have been launched. Among them, there are Japan Aerospace Exploration Agency's (JAXA's) Advanced Microwave Scanning Radiometer-EOS (AMSR-E) launched in May 2002 on the National Aeronautics and Space Administration (NASA) Aqua satellite (ceased operation in October 2011), European Space Agency's (ESA's) Soil Moisture and Ocean Salinity (SMOS) mission launched in November 2009, JAXA's Advanced Microwave Scanning Radiometer 2 (AMSR2) onboard the GCOM-W satellite launched in May 2012, and NASA's Soil Moisture Active Passive (SMAP) mission launched in January 2015. Therefore, there is an opportunity to develop a consistent inter-calibrated long-term soil moisture data record based on the availability of these four missions. This study focuses on the parametrization of the tau-omega model at L-, C- and X-band using the brightness temperature (TB) observations from the four missions and the in-situ soil moisture and soil temperature data from core validation sites across various landcover types. The same ancillary data sets as the SMAP baseline algorithm are applied for retrieval at different frequencies. Preliminary comparison of SMAP and AMSR2 TB observations against forward-simulated TB at the Yanco site in Australia showed a generally good agreement with each other and higher correlation for the vertical polarization (R=0.96 for L-band and 0.93 for C- and X-band). Simultaneous calibrations of the vegetation parameter b and roughness parameter h at both horizontal and vertical polarizations are also performed. Finally, a set of model parameters for successfully retrieving soil moisture at different validation sites at L-, C- and X-band respectively are presented. The research described in this paper is supported by the Jet Propulsion

  16. Traveling-Wave Tube Amplifier Second Harmonic as Millimeter-Wave Beacon Source for Atmospheric Propagation Studies

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.

    2014-01-01

    The design and test results of a novel waveguide multimode directional coupler for a CW millimeter-wave satellite beacon source are presented. The coupler separates the second harmonic power from the fundamental output power of a traveling-wave tube amplifier. A potential application of the beacon source is for investigating the atmospheric effects on Q-band (37 to 42 GHz) and VW-band (71 to 76 GHz) satellite-to-ground signals.

  17. A New Vacuum Brazing Route for Niobium-316L Stainless Steel Transition Joints for Superconducting RF Cavities

    NASA Astrophysics Data System (ADS)

    Kumar, Abhay; Ganesh, P.; Kaul, R.; Bhatnagar, V. K.; Yedle, K.; Ram Sankar, P.; Sindal, B. K.; Kumar, K. V. A. N. P. S.; Singh, M. K.; Rai, S. K.; Bose, A.; Veerbhadraiah, T.; Ramteke, S.; Sridhar, R.; Mundra, G.; Joshi, S. C.; Kukreja, L. M.

    2015-02-01

    The paper describes a new approach for vacuum brazing of niobium-316L stainless steel transition joints for application in superconducting radiofrequency cavities. The study exploited good wettability of titanium-activated silver-base brazing alloy (CuSil-ABA®), along with nickel as a diffusion barrier, to suppress brittle Fe-Nb intermetallic formation, which is well reported during the established vacuum brazing practice using pure copper filler. The brazed specimens displayed no brittle intermetallic layers on any of its interfaces, but instead carried well-distributed intermetallic particles in the ductile matrix. The transition joints displayed room temperature tensile and shear strengths of 122-143 MPa and 80-113 MPa, respectively. The joints not only exhibited required hermeticity (helium leak rate <1.1 × 10-10 mbar l/s) for service in ultra-high vacuum but also withstood twelve hour degassing heat treatment at 873 K (suppresses Q-disease in niobium cavities), without any noticeable degradation in the microstructure and the hermeticity. The joints retained their leak tightness even after undergoing ten thermal cycles between the room temperature and the liquid nitrogen temperature, thereby establishing their ability to withstand service-induced low cycle fatigue conditions. The study proposes a new lower temperature brazing route to form niobium-316L stainless steel transition joints, with improved microstructural characteristics and acceptable hermeticity and mechanical properties.

  18. BorealScat: A Tower Experiment for Understanding Temporal Changes in P- and L-Band Backscattering from a Boreal Forest

    NASA Astrophysics Data System (ADS)

    Ulander, Lars M. H.; Soja, Maciej J.; Monteith, Albert R.; Eriksson, Leif E. B.; Fransson, Johan E. S.; Persson, Henrik, J.

    2016-08-01

    This paper describes the tower-based radar BorealScat, which is being developed for polarimetric, tomographic and Doppler measurements at the hemi-boreal forest test site in Remningstorp, Sweden. The facility consists of a 50-m high tower equipped with an antenna array at the top of the tower, a 20-port vector network analyser (VNA), 20 low-loss cables for interconnection, and a calibration loop with a switching network. The first version of BorealScat will perform the full set of measurements in the frequency range 0.4 - 1.4 GHz, i.e. P-band and L-band. The tower is currently under construction at a forest stand dominated by Norway spruce (Picea abies (L.) Karst.). The mature stand has an above-ground dry biomass of 300 tons/ha. Data collections are planned to commence in autumn 2016.

  19. Simultaneous dual-band radar development

    NASA Technical Reports Server (NTRS)

    Liskow, C. L.

    1974-01-01

    Efforts to design and construct an airborne imaging radar operating simultaneously at L band and X band with an all-inertial navigation system in order to form a dual-band radar system are described. The areas of development include duplex transmitters, receivers, and recorders, a control module, motion compensation for both bands, and adaptation of a commercial inertial navigation system. Installation of the system in the aircraft and flight tests are described. Circuit diagrams, performance figures, and some radar images are presented.

  20. Ku-Band Traveling Wave Slot Array Using Simple Scanning Control

    NASA Technical Reports Server (NTRS)

    Host, Nicholas K.; Chen, Chi-Chih; Volakis, John L.; Miranda, Felix A.

    2015-01-01

    This poster introduces a feeding concept aimed at simplifying the backend (phase shifters) of traditional phased arrays. As an alternative to traditional phased arrays, we employ a traveling wave array (TWA) using a single feedline whose propagation constant is controlled via a single, small mechanical movement without a need for phase shifters to enable scanning. Specifically, a dielectric plunger is positioned within a parallel plate waveguide (PPW) transmission line (TL) that feeds the TWA. By adjusting the position of the dielectric plunger within the PPW feeding the TWA, beam steering is achieved. A 20-element array is designed at 13 gigaherz shown to give stable realized gain across the angular range of minus 25 degrees less than or equal to theta and less than or equal to 25 degrees. A proof of concept array is fabricated and measured to demonstrate and validate the concept's operation.

  1. Unconventional superconductivity in magic-angle graphene superlattices

    NASA Astrophysics Data System (ADS)

    Cao, Yuan; Fatemi, Valla; Fang, Shiang; Watanabe, Kenji; Taniguchi, Takashi; Kaxiras, Efthimios; Jarillo-Herrero, Pablo

    2018-04-01

    The behaviour of strongly correlated materials, and in particular unconventional superconductors, has been studied extensively for decades, but is still not well understood. This lack of theoretical understanding has motivated the development of experimental techniques for studying such behaviour, such as using ultracold atom lattices to simulate quantum materials. Here we report the realization of intrinsic unconventional superconductivity—which cannot be explained by weak electron–phonon interactions—in a two-dimensional superlattice created by stacking two sheets of graphene that are twisted relative to each other by a small angle. For twist angles of about 1.1°—the first ‘magic’ angle—the electronic band structure of this ‘twisted bilayer graphene’ exhibits flat bands near zero Fermi energy, resulting in correlated insulating states at half-filling. Upon electrostatic doping of the material away from these correlated insulating states, we observe tunable zero-resistance states with a critical temperature of up to 1.7 kelvin. The temperature–carrier-density phase diagram of twisted bilayer graphene is similar to that of copper oxides (or cuprates), and includes dome-shaped regions that correspond to superconductivity. Moreover, quantum oscillations in the longitudinal resistance of the material indicate the presence of small Fermi surfaces near the correlated insulating states, in analogy with underdoped cuprates. The relatively high superconducting critical temperature of twisted bilayer graphene, given such a small Fermi surface (which corresponds to a carrier density of about 1011 per square centimetre), puts it among the superconductors with the strongest pairing strength between electrons. Twisted bilayer graphene is a precisely tunable, purely carbon-based, two-dimensional superconductor. It is therefore an ideal material for investigations of strongly correlated phenomena, which could lead to insights into the physics of high

  2. Making Superconducting Welds between Superconducting Wires

    NASA Technical Reports Server (NTRS)

    Penanen, Konstantin I.; Eom, Byeong Ho

    2008-01-01

    A technique for making superconducting joints between wires made of dissimilar superconducting metals has been devised. The technique is especially suitable for fabrication of superconducting circuits needed to support persistent electric currents in electromagnets in diverse cryogenic applications. Examples of such electromagnets include those in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) systems and in superconducting quantum interference devices (SQUIDs). Sometimes, it is desirable to fabricate different parts of a persistent-current-supporting superconducting loop from different metals. For example, a sensory coil in a SQUID might be made of Pb, a Pb/Sn alloy, or a Cu wire plated with Pb/Sn, while the connections to the sensory coil might be made via Nb or Nb/Ti wires. Conventional wire-bonding techniques, including resistance spot welding and pressed contact, are not workable because of large differences between the hardnesses and melting temperatures of the different metals. The present technique is not subject to this limitation. The present technique involves the use (1) of a cheap, miniature, easy-to-operate, capacitor-discharging welding apparatus that has an Nb or Nb/Ti tip and operates with a continuous local flow of gaseous helium and (2) preparation of a joint in a special spark-discharge welding geometry. In a typical application, a piece of Nb foil about 25 m thick is rolled to form a tube, into which is inserted a wire that one seeks to weld to the tube (see figure). The tube can be slightly crimped for mechanical stability. Then a spark weld is made by use of the aforementioned apparatus with energy and time settings chosen to melt a small section of the niobium foil. The energy setting corresponds to the setting of a voltage to which the capacitor is charged. In an experiment, the technique was used to weld an Nb foil to a copper wire coated with a Pb/Sn soft solder, which is superconducting. The joint was evaluated as

  3. Hybrid superconducting a.c. current limiter extrapolation 63 kV-1 250 A

    NASA Astrophysics Data System (ADS)

    Tixador, P.; Levêque, J.; Brunet, Y.; Pham, V. D.

    1994-04-01

    Following the developement of a.c. superconducting wires a.c. current superconducting limiters have emerged. These limiters limit the fault currents nearly instantaneously, without detection nor order giver and may be suitable for high voltages. They are based on the natural transition from the superconducting state to the normal resistive state by overstepping the critical current of a superconducting coil which limits or triggers the limitation. Our limiter device consists essentially of two copper windings coupled through a saturable magnetic circuit and of a non inductively wound superconducting coil with a reduced current compared to the line current. This design allows a simple superconducting cable and reduced cryogenic losses but the dielectric stresses are high during faults. A small model (150 V/50 A) has experimentally validated our design. An industrial scale current limiter is designed and the comparisons between this design and other superconducting current limiters are given. Les courants de court-circuit sur les grands réseaux électriques ne cessent d'augmenter. Dans ce contexte sont apparus les limiteurs supraconducteurs de courant suite au développement des brins supraconducteurs alternatifs. Ces limiteurs peuvent limiter les courants de défaut presque instantanément, sans détection de défaut ni donneur d'ordre et ils sont extrapolables aux hautes tensions. Ils sont fondés sur la transition naturelle de l'état supraconducteur à l'état normal très résistif par dépassement du courant critique d'un enroulement supraconducteur qui limite ou déclenche la limitation. Notre limiteur est composé de deux enroulements en cuivre couplés par un circuit magnétique saturable et d'une bobine supraconductrice à courant réduit par rapport au courant de la ligne. Cette conception permet un câble supraconducteur simple et des pertes cryogéniques réduites mais les contraintes diélectriques en régime de défaut sont importantes. Une maquette

  4. The Aquarius Ocean Salinity Mission High Stability L-band Radiometer

    NASA Technical Reports Server (NTRS)

    Pellerano, Fernando A.; Piepmeier, Jeffrey; Triesky, Michael; Horgan, Kevin; Forgione, Joshua; Caldwell, James; Wilson, William J.; Yueh, Simon; Spencer, Michael; McWatters, Dalia; hide

    2006-01-01

    The NASA Earth Science System Pathfinder (ESSP) mission Aquarius, will measure global ocean surface salinity with approx.120 km spatial resolution every 7-days with an average monthly salinity accuracy of 0.2 psu (parts per thousand). This requires an L-band low-noise radiometer with the long-term calibration stability of less than or equal to 0.15 K over 7 days. The instrument utilizes a push-broom configuration which makes it impractical to use a traditional warm load and cold plate in front of the feedhorns. Therefore, to achieve the necessary performance Aquarius utilizes a Dicke radiometer with noise injection to perform a warm - hot calibration. The radiometer sequence between antenna, Dicke load, and noise diode has been optimized to maximize antenna observations and therefore minimize NEDT. This is possible due the ability to thermally control the radiometer electronics and front-end components to 0.1 Crms over 7 days.

  5. Superconductive radiofrequency window assembly

    DOEpatents

    Phillips, Harry Lawrence; Elliott, Thomas S.

    1998-01-01

    The present invention is a superconducting radiofrequency window assembly for use in an electron beam accelerator. The srf window assembly (20) has a superconducting metal-ceramic design. The srf window assembly (20) comprises a superconducting frame (30), a ceramic plate (40) having a superconducting metallized area, and a superconducting eyelet (50) for sealing plate (40) into frame (30). The plate (40) is brazed to eyelet (50) which is then electron beam welded to frame (30). A method for providing a ceramic object mounted in a metal member to withstand cryogenic temperatures is also provided. The method involves a new metallization process for coating a selected area of a ceramic object with a thin film of a superconducting material. Finally, a method for assembling an electron beam accelerator cavity utilizing the srf window assembly is provided. The procedure is carried out within an ultra clean room to minimize exposure to particulates which adversely affect the performance of the cavity within the electron beam accelerator.

  6. Superconductive radiofrequency window assembly

    DOEpatents

    Phillips, H.L.; Elliott, T.S.

    1998-05-19

    The present invention is a superconducting radiofrequency window assembly for use in an electron beam accelerator. The SRF window assembly has a superconducting metal-ceramic design. The SRF window assembly comprises a superconducting frame, a ceramic plate having a superconducting metallized area, and a superconducting eyelet for sealing plate into frame. The plate is brazed to eyelet which is then electron beam welded to frame. A method for providing a ceramic object mounted in a metal member to withstand cryogenic temperatures is also provided. The method involves a new metallization process for coating a selected area of a ceramic object with a thin film of a superconducting material. Finally, a method for assembling an electron beam accelerator cavity utilizing the SRF window assembly is provided. The procedure is carried out within an ultra clean room to minimize exposure to particulates which adversely affect the performance of the cavity within the electron beam accelerator. 11 figs.

  7. Superconducting radiofrequency window assembly

    DOEpatents

    Phillips, Harry L.; Elliott, Thomas S.

    1997-01-01

    The present invention is a superconducting radiofrequency window assembly for use in an electron beam accelerator. The srf window assembly (20) has a superconducting metal-ceramic design. The srf window assembly (20) comprises a superconducting frame (30), a ceramic plate (40) having a superconducting metallized area, and a superconducting eyelet (50) for sealing plate (40) into frame (30). The plate (40) is brazed to eyelet (50) which is then electron beam welded to frame (30). A method for providing a ceramic object mounted in a metal member to withstand cryogenic temperatures is also provided. The method involves a new metallization process for coating a selected area of a ceramic object with a thin film of a superconducting material. Finally, a method for assembling an electron beam accelerator cavity utilizing the srf window assembly is provided. The procedure is carried out within an ultra clean room to minimize exposure to particulates which adversely affect the performance of the cavity within the electron beam accelerator.

  8. Superconducting radiofrequency window assembly

    DOEpatents

    Phillips, H.L.; Elliott, T.S.

    1997-03-11

    The present invention is a superconducting radiofrequency window assembly for use in an electron beam accelerator. The srf window assembly has a superconducting metal-ceramic design. The srf window assembly comprises a superconducting frame, a ceramic plate having a superconducting metallized area, and a superconducting eyelet for sealing plate into frame. The plate is brazed to eyelet which is then electron beam welded to frame. A method for providing a ceramic object mounted in a metal member to withstand cryogenic temperatures is also provided. The method involves a new metallization process for coating a selected area of a ceramic object with a thin film of a superconducting material. Finally, a method for assembling an electron beam accelerator cavity utilizing the srf window assembly is provided. The procedure is carried out within an ultra clean room to minimize exposure to particulates which adversely affect the performance of the cavity within the electron beam accelerator. 11 figs.

  9. Superfluid density and carrier concentration across a superconducting dome: The case of strontium titanate

    NASA Astrophysics Data System (ADS)

    Collignon, Clément; Fauqué, Benoît; Cavanna, Antonella; Gennser, Ulf; Mailly, Dominique; Behnia, Kamran

    2017-12-01

    We present a study of the lower critical field, Hc 1, of SrTi1 -xNbxO3 as a function of carrier concentration with the aim of quantifying the superfluid density. At low carrier concentration (i.e., the underdoped side), superfluid density and the carrier concentration in the normal state are equal within experimental margin. A significant deviation between the two numbers starts at optimal doping and gradually increases with doping. The inverse of the penetration depth and the critical temperature follow parallel evolutions as in the case of cuprate superconductors. In the overdoped regime, the zero-temperature superfluid density becomes much lower than the normal-state carrier density before vanishing all together. We show that the density mismatch and the clean-to-dirty crossover are concomitant. Our results imply that the discrepancy between normal and superconducting densities is expected whenever the superconducting gap becomes small enough to put the system in the dirty limit. A quantitative test of the dirty BCS theory is not straightforward, due to the multiplicity of the bands in superconducting strontium titanate.

  10. Electronic structures and superconductivity in LuTE2Si2 phases (TE = d-electron transition metal)

    NASA Astrophysics Data System (ADS)

    Samsel-Czekała, M.; Chajewski, G.; Wiśniewski, P.; Romanova, T.; Hackemer, A.; Gorzelniak, R.; Pikul, A. P.; Kaczorowski, D.

    2018-05-01

    In the course of our search for unconventional superconductors amidst the 1:2:2 phases, we have re-investigated the LuTE2Si2 compounds with TE = Fe, Co, Ni, Ru, Pd and Pt. In this paper, we present the results of our fully relativistic ab initio calculations of the band structures, performed using the full-potential local-orbital code. The theoretical data are supplemented by the results of low-temperature electrical transport and specific heat measurements performed down to 0.35 K. All the materials studied but LuPt2Si2 crystallize with the body-centered tetragonal ThCr2Si2-type structure (space group I4/mmm). Their Fermi surfaces exhibit a three-dimensional multi-band character. In turn, the Pt-bearing compound adopts the primitive tetragonal CaBe2Ge2-type structure (space group P4/nmm), and its Fermi surface consists of predominantly quasi-two-dimensional sheets. Bulk superconductivity was found only in LuPd2Si2 and LuPt2Si2 (independent of the structure type and dimensionality of the Fermi surface). The key superconducting characteristics indicate a fully-gapped BCS type character. Though the electronic structure of LuFe2Si2 closely resembles that of the unconventional superconductor YFe2Ge2, this Lu-based silicide exhibits neither superconductivity nor spin fluctuations at least down to 0.35 K.

  11. The c-axis charge traveling wave in a coupled system of Josephson junctions

    NASA Astrophysics Data System (ADS)

    Shukrinov, Yu. M.; Hamdipour, M.

    2012-05-01

    We demonstrate a manifestation of the charge traveling wave along the c axis (TW) in current voltage characteristics of coupled Josephson junctions in high- T c superconductors. The branches related to the TW with different wavelengths are found for the stacks with different number of Josephson junctions at different values of system's parameters. Transitions between the TW branches and the outermost branch are observed. The electric charge in the superconducting layers and charge-charge correlation functions for TW and outermost branches show different behavior with bias current. We propose an experimental testing of the TW branching by microwave irradiation.

  12. Superconducting Mixers for Far-Infrared Spectroscopy

    NASA Technical Reports Server (NTRS)

    Betz, A. L.; Boreiko, R. T.; Grossman, E. R.; Reintsema, C. D.; Ono, R. H.; Gerecht, E.

    2002-01-01

    The goal of this project was to fabricate and test planar arrays of superconducting mixers for the 2-6 THz band. The technology is intended for multi-beam receivers aboard Explorer-class missions and the SOFIA Airborne Observatory. The mixer technology is the superconducting transition-edge microbolometer, which is more commonly known as the Hot-Electron micro-Bolometer (HEB). As originally proposed, two superconducting technologies were to be developed: (1) low-Tc niobium HEBs which could approach quantum-noise-limited sensitivities but require cooling to 2- 4 K, and (2) high-Tc YBCO HEBs with sensitivities 10 times worse but with a relaxed cooling requirement of 30-60 K. The low-Tc devices would be best for astronomy applications on SOFIA, whereas the high-Tc devices would be more suitable for planetary missions using systems without stored cryogens. The work plan called for planar micro-fabrication and initial testing of HEB devices at the NIST Boulder clean-room facility. Subsequent assembly and RF testing of selected devices would be done at the CASA laboratory at U. Colorado. Approximately 1-year after work began on this project, Dr. Eyal Gerecht joined the NIST group, and assumed day-to-day responsibility for Nb-HEB development at NIST outside of micro-fabrication. The YBCO-HEB work was to be guided by Dr. Ron Ono, who was the NIST expert in YBCO technology. Unfortunately, recurrent health problems limited the time Ron could devote to the project in its first year. These problems became aggravated in early 2001, and sadly led to Ron's death in October, 2001. His loss was not only a blow to his friends and associates at NIST, but was mounted by the US superconductivity community at large. With his passing, work on high-Tc HEBs ceased at NIST. There was no one to replace him or his expertise. Our work subsequently shifted solely to Nb-HEB devices. In the sections which follow, our progress in the development of diffusion-cooled Nb-HEB mixers is detailed. To

  13. Coherence Effects in L-Band Active and Passive Remote Sensing of Quasi-Periodic Corn Canopies

    NASA Technical Reports Server (NTRS)

    Utku, Cuneyt; Lang, Roger H.

    2011-01-01

    Due to their highly random nature, vegetation canopies can be modeled using the incoherent transport theory for active and passive remote sensing applications. Agricultural vegetation canopies however are generally more structured than natural vegetation. The inherent row structure in agricultural canopies induces coherence effects disregarded by the transport theory. The objective of this study is to demonstrate, via Monte-Carlo simulations, these coherence effects on L-band scattering and thermal emission from corn canopies consisting of only stalks.

  14. Spin-resolved band structure of a densely packed Pb monolayer on Si(111)

    NASA Astrophysics Data System (ADS)

    Brand, C.; Muff, S.; Fanciulli, M.; Pfnür, H.; Tringides, M. C.; Dil, J. H.; Tegenkamp, C.

    2017-07-01

    Monolayer structures of Pb on Si(111) attracted recently considerable interest as superconductivity was found in these truly two-dimensional (2D) structures. In this study, we analyzed the electronic surface band structure of the so-called striped incommensurate Pb phase with 4/3 ML coverage by means of spin-resolved photoemission spectroscopy. Our results fully agree with density functional theory calculations done by Ren et al. [Phys. Rev. B 94, 075436 (2016), 10.1103/PhysRevB.94.075436]. We observe a local Zeeman-type splitting of a fully occupied and spin-polarized surface band at the K¯√{3} points. The growth of this densely packed Pb structure results in the formation of imbalanced rotational domains, which triggered the detection of C3 v symmetry forbidden spin components for surface states around the Fermi energy. Moreover, the Fermi surface of the metallic surface state of this phase is Rashba spin split and revealed a pronounced warping. However, the 2D nesting vectors are incommensurate with the atomic structure, thus keeping this system rather immune against charge density wave formation and possibly enabling a superconducting behavior.

  15. Newly Formed Sea Ice in Arctic Leads Monitored by C- and L-Band SAR

    NASA Astrophysics Data System (ADS)

    Johansson, A. Malin; Brekke, Camilla; Spreen, Gunnar; King, Jennifer A.; Gerland, Sebastian

    2016-08-01

    We investigate the scattering entropy and co-polarization ratio for Arctic lead ice using C- and L-band synthetic aperture radar (SAR) satellite scenes. During the Norwegian Young sea ICE (N-ICE2015) cruise campaign overlapping SAR scenes, helicopter borne sea ice thickness measurements and photographs were collected. We can therefore relate the SAR signal to sea ice thickness measurements as well as photographs taken of the sea ice. We show that a combination of scattering and co-polarization ratio values can be used to distinguish young ice from open water and surrounding sea ice.

  16. Development of NASA's Next Generation L-Band Digital Beamforming Synthetic Aperture Radar (DBSAR-2)

    NASA Technical Reports Server (NTRS)

    Rincon, Rafael; Fatoyinbo, Temilola; Osmanoglu, Batuhan; Lee, Seung-Kuk; Ranson, K. Jon; Marrero, Victor; Yeary, Mark

    2014-01-01

    NASA's Next generation Digital Beamforming SAR (DBSAR-2) is a state-of-the-art airborne L-band radar developed at the NASA Goddard Space Flight Center (GSFC). The instrument builds upon the advanced architectures in NASA's DBSAR-1 and EcoSAR instruments. The new instrument employs a 16-channel radar architecture characterized by multi-mode operation, software defined waveform generation, digital beamforming, and configurable radar parameters. The instrument has been design to support several disciplines in Earth and Planetary sciences. The instrument was recently completed, and tested and calibrated in a anechoic chamber.

  17. Travel health attitudes among Turkish business travellers to African countries.

    PubMed

    Selcuk, Engin Burak; Kayabas, Uner; Binbasioglu, Hulisi; Otlu, Baris; Bayindir, Yasar; Bozdogan, Bulent; Karatas, Mehmet

    The number of international travellers is increasing worldwide. Although health risks related to international travel are important and generally well-understood, the perception of these risks was unclear among Turkish travellers. We aimed to evaluate the attitudes and health risk awareness of Turkish travellers travelling to African countries. A survey was performed of Turkish travellers bound for Africa from Istanbul International Ataturk Airport in July 2013. A total of 124 travellers were enrolled in the study. Among them, 62.9% had information about their destination but only 11.3% had looked for information on health problems related to travel and their destination. Of all travellers, 53.2% had at least one vaccination before travelling. The most commonly administered vaccine was for typhoid. Among the travellers, 69.3% and 80.6% had "no idea" about yellow fever vaccination and malaria prophylaxis, respectively. A positive correlation was found between a higher level of travellers' education and receiving the recommended vaccination for the destination. Our study revealed significant gaps in the vaccination and chemoprophylaxis uptake of Turkish travellers departing to Africa. An awareness and training program should be developed for travellers, as well as public health workers, to address health risks related to travel. Copyright © 2016 Elsevier Ltd. All rights reserved.

  18. Dynamical generation of Floquet Majorana flat bands in s-wave superconductors

    NASA Astrophysics Data System (ADS)

    Poudel, A.; Ortiz, G.; Viola, L.

    2015-04-01

    We present quantum control techniques to engineer flat bands of symmetry-protected Majorana edge modes in s-wave superconductors. Specifically, we show how periodic control may be employed for designing time-independent effective Hamiltonians, which support Floquet Majorana flat bands, starting from equilibrium conditions that are either topologically trivial or only support a Majorana pair per edge. In the first approach, a suitable modulation of the chemical potential simultaneously induces Majorana flat bands and dynamically activates a pre-existing chiral symmetry which is responsible for their protection. In the second approach, the application of effective parity kicks dynamically generates a desired chiral symmetry by suppressing chirality-breaking terms in the static Hamiltonian. Our results demonstrate how the use of time-dependent control enlarges the range of possibilities for realizing gapless topological superconductivity, potentially enabling access to topological states of matter that have no known equilibrium counterpart.

  19. Lattice instability and enhancement of superconductivity in YB6

    NASA Astrophysics Data System (ADS)

    Sluchanko, N.; Glushkov, V.; Demishev, S.; Azarevich, A.; Anisimov, M.; Bogach, A.; Voronov, V.; Gavrilkin, S.; Mitsen, K.; Kuznetsov, A.; Sannikov, I.; Shitsevalova, N.; Filipov, V.; Kondrin, M.; Gabáni, S.; Flachbart, K.

    2017-10-01

    The superconducting and normal state characteristics of yttrium hexaboride (YB6) have been investigated for the single crystals with a transition temperatures Tc ranging between 4.2 K and 7.6 K. The extracted set of microscopic parameters [the coherence length ξ (0 )˜320 -340 Å , the penetration depth λ (0 )˜1100 -3250 Å and the mean free path of charge carriers l =11 -58 Å , the Ginzburg-Landau-Maki parameters κ1 ,2(0 ) ˜3.3 -9.5, and the superconducting gap Δ (0 )˜6.2 -14.8 K] confirms the type II superconductivity in "dirty limit" (ξ ≫l ) with a medium to strong electron-phonon interaction (the electron-phonon interaction constant λe -ph=0.32 -0.96 ) and s -type pairing of charge carriers in this compound [2 Δ (0 ) /kBTc≈3 -4]. The comparative analysis of charge transport (resistivity, Hall and Seebeck coefficients) and thermodynamic (heat capacity, magnetization) properties in the normal state in YB6 allowed to assume a transition into the cage-glass state at T*˜50 K with a static disorder in the arrangement of the Y3 + ions. We argue that the significant Tc variations in YB6 single crystals are determined by two main factors: (i) the superconductivity enhancement is related with the increase of the number of vacancies, both at yttrium and boron sites, leading to nonstoichiometric composition, which is accompanied by the enhancement of electron-phonon interaction in the hexaboride lattice; (ii) stronger Tc depression is observed in near stoichiometric and more dense crystals and it is induced by the development of bcc lattice instability producing strong distortion, disordering, and formation of defect complexes in the matrix of YB6.

  20. Discovery of superconductivity in quasicrystal.

    PubMed

    Kamiya, K; Takeuchi, T; Kabeya, N; Wada, N; Ishimasa, T; Ochiai, A; Deguchi, K; Imura, K; Sato, N K

    2018-01-11

    Superconductivity is ubiquitous as evidenced by the observation in many crystals including carrier-doped oxides and diamond. Amorphous solids are no exception. However, it remains to be discovered in quasicrystals, in which atoms are ordered over long distances but not in a periodically repeating arrangement. Here we report electrical resistivity, magnetization, and specific-heat measurements of Al-Zn-Mg quasicrystal, presenting convincing evidence for the emergence of bulk superconductivity at a very low transition temperature of [Formula: see text] K. We also find superconductivity in its approximant crystals, structures that are periodic, but that are very similar to quasicrystals. These observations demonstrate that the effective interaction between electrons remains attractive under variation of the atomic arrangement from periodic to quasiperiodic one. The discovery of the superconducting quasicrystal, in which the fractal geometry interplays with superconductivity, opens the door to a new type of superconductivity, fractal superconductivity.