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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1265-1276 
    ISSN: 0392-6737
    Keywords: Polaritons (including photon-phonon and photon-magnon interactions) ; Optical properties of thin films, surfaces, and layer structures (superlattices, heterojunctions, and multilayers) ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The transport of radiative and electronic excitations in coherently driven semiconductor quantum wells is analysed. On ultrashort time scales the spatial dynamics is determined by light propagation only, whereas for longer times the propagation of light and electronic excitations may be coupled. The theory is applied to the propagation of electronic excitations in the plane of a single quantum well and to polariton propagation in quantum well wave guides.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Il nuovo cimento della Società Italiana di Fisica 17 (1995), S. 1735-1741 
    ISSN: 0392-6737
    Keywords: Wave propagation, transmission and absorption ; Optical properties of thin films, surfaces and layer structures (superlattices, heterojunctions, and multilayers) ; Excitons and related phenomena (including electron-hole drops) ; Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary It is shown that collective effects determine the optical response of radiatively coupled multiple-quantum-well structures. Stimulated decay of the coherent electronic excitations is predicted for systems where the periodicity unit is an integer multiple of half the optical wavelength. For quarter wavelength structures it is shown that the induced optical coupling causes an interwell energy transport and a splitting of the excitonic resonances leading to quantum beats in the time-resolved transmitted and reflected signal.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0009-3084
    Keywords: branched chain fatty acids ; differential scanning calorimetry phase transitions ; molar heat capacities ; phosphatidylcholines
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6748-6750 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic properties of an isolated ferromagnetic bond of coupling constant K embedded in a layered spin-1/2 Heisenberg antiferromagnet with interplane coupling strength J⊥=αJ(parallel) (0≤α≤1.0) have been studied using linear-spin-wave (LSW) theory. In the pure lattice, the sublattice magnetization 〈Szi〉 is 0.304 at α=0 and saturates to 0.422 at α=1.0. The spin correlations 〈SxiSxj〉 decrease with increasing α within the plane and increase along the interplane direction. The introduction of an isolated ferromagnetic bond into the host lattice tends to enhance 〈Szi〉 at lattice sites joining the bond as K approaches zero. Increasing K will drastically suppress 〈SxiSxj〉 across the bond. Whereas, 〈SxiSxj〉 is enhanced between the neighboring sites close to the impurity link resulting in the suppression of 〈Szi〉. This behavior persists for all α values. The LSW theory breaks down at a certain K value. Increasing α, the critical value of K extends to a larger number.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Molecular Spectroscopy 167 (1994), S. 176-190 
    ISSN: 0022-2852
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Molecular Spectroscopy 164 (1994), S. 445-455 
    ISSN: 0022-2852
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 16 (2000), S. 393-396 
    ISSN: 1434-6036
    Keywords: PACS. 75.10.Jm Quantized spin models - 75.30.-m Intrinsic properties of magnetically ordered materials - 75.50.Ee Antiferromagnetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Three-dimensional magnetic ordering transitions are studied theoretically in strongly anisotropic quantum magnets. An external magnetic field can drive quasi-one-dimensional subsystems with a spin gap into a gapless regime, thus inducing long-range three-dimensional magnetic ordering due to weak residual magnetic coupling between the subsystems. Compounds with higher spin degrees of freedom, such as N-leg spin-1/2 ladders, are shown to have cascades of ordering transitions. At high magnetic fields, zero-point fluctuations within the quasi-1D subsystems are suppressed, causing quantum corrections to the ordering temperature to be reduced.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 70 (2000), S. 17-29 
    ISSN: 1432-0681
    Keywords: Key words free-surface flow ; solidification ; strip casting ; steady state ; nonuniqueness ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary The paper is concerned with a one-dimensional analysis of plane open-channel flow with continuous solidification. The process is of relevance for recent developments in the casting of steel and other metals. The bottom of the channel consists of a rotating casting roll and a horizontal cooling table, where the solidified material is withdrawn with given velocity. The study is restricted to the region downstream of the top of the casting roll. Surface tension is neglected. In the main part of the analysis inviscid fluid flow is considered since the Reynolds number is very large in the applications. It is found that the steady-state solutions are nonunique in a certain parameter range. In addition to a continuous solution, there are two solutions including hydraulic jumps, with one hydraulic jump being located on the casting roll, the other one on the cooling table. Regarding the stability of the non unique solutions, the evolution of disturbances is investigated numerically as an initial-value problem. It is concluded that the hydraulic jump on the cooling table is unstable, while the other discontinuous solution as well as the continuous solution are stable for sufficiently small disturbances. Which stable solution is attained in the steady state, depends on the history of the process. Friction at the liquid/solid interface is taken into account in the last part of the analysis. A constant friction coefficient is assumed. It is found that the history of the process determines the steady-state solution if, and only if, the friction coefficient is sufficiently small. For larger values of the friction coefficient, the steady-state solution is unique and independent of the history of the transient process. Furthermore, for sufficiently large friction coefficients, stable hydraulic jumps are found, in contrast to the inviscid case, also on the cooling table.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    International journal of infrared and millimeter waves 17 (1996), S. 493-506 
    ISSN: 1572-9559
    Keywords: SIS-mixer ; SIS-receiver ; tunerless mixer ; submillimeter wavelength
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have developed broadband SIS heterodyne receivers for the frequency ranges from 440 to 500 GHz and 630 to 690 GHz. The mixerblocks contain a punched waveguide cavity which forms a fixed backshort. The substrate channel is sawed across the waveguide. The horn antenna is flanged to the mixerblock. The blocks are easy and quickly to manufacture even for the small dimensions needed in the submm wavelength range. We use Nb-Al2O3-Nb junctions with areas of 0.8 µm2 and integrated three step niobium tuning structures. With this design we achieve instantaneous double sideband receiver noise temperatures around 120 K over the frequency range from 660 to 690 GHz and around 80 K from 440 to 500 GHz. The mixer performance agrees well with the design calculations for the tuning structures.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1435-1536
    Keywords: Key words Double chain surfactants ; Aggregates ; Phase diagrams ; Lamellar phases ; Electron microscopy ; SANS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We present the phase diagrams and the properties of newly synthesised double-chain cationic N-alkyl-N-alkyl′-N,N-dimethylammonium bromide surfactants [C x C y DMABr (x = 12, 14 and 16; y = 10, 11, 12, 14 and 16)]. All the systems studied form liquid-crystalline lamellar phases but with different morphologies: unilamellar vesicles at low surfactant concentrations, multilamellar vesicles and tubular aggregates for surfactant concentrations between 2 and 10 wt% and at even higher concentrations planar bilayers of surfactant molecules in the classical Lα phase. The phase diagrams were determined with macroscopic and microscopic methods (polarisation microscopy, freeze-fracture transmission electron microscopy, scanning electron microscopy and differential interference contrast microscopy). The properties of the surfactant solutions were determined with differential scanning calorimetry measurements for Krafft point determination and small-angle neutron scattering measurements for interlamellar spacing and bilayer thickness. Finally, conductivity and viscosity measurements for phase characterisation were carried out.
    Type of Medium: Electronic Resource
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