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  • 1
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 127, No. 5 ( 2007-08-07)
    Abstract: The complexes of the fluorescence probe coumarin 153 with apomyoglobin and apoleghemoglobin are used as model systems to study solvation dynamics in proteins. Time-resolved Stokes shift experiments are compared with molecular dynamics simulations, and very good agreement is obtained. The solvation of the coumarin probe is very rapid with approximately 60% occurring within 300fs and is attributed to interactions with water (or possibly to the protein itself). Differences in the solvation relaxation (or correlation) function C(t) for the two proteins are attributed to differences in their hemepockets.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2007
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 2
    Online Resource
    Online Resource
    AIP Publishing ; 1971
    In:  Journal of Applied Physics Vol. 42, No. 4 ( 1971-03-15), p. 1775-1777
    In: Journal of Applied Physics, AIP Publishing, Vol. 42, No. 4 ( 1971-03-15), p. 1775-1777
    Abstract: EuO films with ∼8-wt% Fe have saturation magnetic moments of about 180 emu/g at 4.2°K and Curie temperatures (Tc) as high as 200°K (for pure EuO, σ=232 emu/g, Tc=69.5°K). The temperature dependence of the magnetization does not scale relative to pure EuO but deviates from the normal magnetization curve in that it exhibits a long tail extending from about 100°K up to Tc. Optical absorption data at 6°K in the range 0.3–2.5 μ indicate a characteristic peak at λ=0.6 μ (due to the 4f-5d transition) with α=2.2×105/cm, about 50% higher than pure EuO. The wavelength dependence of the normal Faraday rotation at 4.2°K is similar in shape to pure EuO; both peak at 0.7 μ but the peak rotation of the Fe-doped film (6×105 deg/cm) is about 30% lower than pure EuO. Mössbauer measurements of 151Eu show mainly Eu+ + with an isomer shift of −12.25 mm/s as in bulk EuO. At 4.2°K the 151Eu hyperfine field is 280.8±5.6 kOe (pure EuO≈300 kOe). The isomer shift of the doublet observed on the 57Fe resonance at 300°K is characteristic for metallic iron. We conclude that only a small fraction of the Fe is effectively doping the EuO films.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1971
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 3
    In: Applied Physics Letters, AIP Publishing, Vol. 93, No. 13 ( 2008-09-29)
    Abstract: Supercollimation is the propagation of light without diffraction using the properties of photonic crystals. We present the first experimental demonstration of supercollimation in a planar photonic crystal composed of nanoscale rods. Supercollimation was observed over distances of up to 1000 lattice periods.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    RVK:
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2008
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 4
    In: APL Photonics, AIP Publishing, Vol. 5, No. 10 ( 2020-10-01)
    Abstract: Photon-counting detectors provide several potential advantages in biomedical x-ray imaging including fast and readout noise free data acquisition, sharp pixel response, and high dynamic range. Grating-based phase-contrast imaging is a biomedical imaging method, which delivers high soft-tissue contrast and strongly benefits from photon-counting properties. However, silicon sensors commonly used in photon-counting detectors have low quantum efficiency for mid- to high-energies, which limits high throughput capabilities when combined with grating-based phase contrast imaging. In this work, we characterize a newly developed photon-counting prototype detector with a gallium arsenide sensor, which enables imaging with higher quantum efficiency, and compare it with a silicon-based photon-counting and a scintillation-based charge integrating detector. In detail, we calculated the detective quantum efficiency (DQE) of all three detectors based on the experimentally measured modulation transfer function, noise power spectrum, and photon fluence. In addition, the DQEs were determined for two different spectra, namely, for a 28 kVp and a 50 kVp molybdenum spectrum. Among all tested detectors, the gallium arsenide prototype showed the highest DQE values for both x-ray spectra. Moreover, other than the comparison based on the DQE, we measured an ex vivo murine sample to assess the benefit using this detector for grating-based phase contrast computed tomography. Compared to the scintillation-based detector, the prototype revealed higher resolving power with an equal signal-to-noise ratio in the grating-based phase contrast computed tomography experiment.
    Type of Medium: Online Resource
    ISSN: 2378-0967
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2020
    detail.hit.zdb_id: 2857268-3
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  • 5
    Online Resource
    Online Resource
    AIP Publishing ; 1992
    In:  Journal of Applied Physics Vol. 71, No. 4 ( 1992-02-15), p. 1693-1698
    In: Journal of Applied Physics, AIP Publishing, Vol. 71, No. 4 ( 1992-02-15), p. 1693-1698
    Abstract: We demonstrate a means of controlling the microstructure and carbon content in amorphous hydrogenated silicon carbide (a-SiC:H) thin films prepared in a plasma-enhanced chemical vapor deposition system. The capacitively coupled, parallel-plate deposition apparatus includes provision for adjusting the potential of the powered electrode by application of an additional, independent dc voltage. This voltage affects the deposition chemistry. Films prepared when various positive and negative dc voltages are applied are studied with infrared absorption, nuclear magnetic resonance, and electron spin resonance. Their optical band gaps, electrical conductivities, and dark conductivity activation energies are also measured. The films have carbon contents ranging from 1 to 4 at. %. We find that we can alter the microstructure of a-SiC:H by adjusting the powered-electrode potential during deposition, and that these microstructural changes are reflected in the film properties. A small increase in the self-biased voltage of the powered electrode leads to a film with the least amount of infrared-observable microstructure and the highest photoconductivity. Applying an external dc voltage leads to an increase in deposition rate regardless of voltage polarity. The films prepared with externally applied voltage all have lower hydrogen contents than the film prepared with self-biased voltage, which may explain the observed property changes. The addition of an external dc voltage can have beneficial effects on the deposition rate, structure, and properties of a-SiC:H films.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1992
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 6
    Online Resource
    Online Resource
    AIP Publishing ; 2016
    In:  Review of Scientific Instruments Vol. 87, No. 1 ( 2016-01-01)
    In: Review of Scientific Instruments, AIP Publishing, Vol. 87, No. 1 ( 2016-01-01)
    Abstract: High magnetic fields ( & gt;1 T) are measured by NMR magnetometers with unrivaled precision if the precessing spin sample provides long coherence times. The longest coherence times are found in diluted 3He samples, which can be hyperpolarized for sufficient signal strength. In order to have minimal influence on the homogeneity and value of the measured magnetic field, the optimal container for the 3He should be a perfect sphere. A fused silica sphere with an inner diameter of 8 mm and an outer diameter of 12 mm was made from two hemispheres by diffusion bonding leaving only a small hole for cleaning and evacuation. This hole was closed in vacuum by a CO2 laser and the inner volume was filled with a few mbars of 3He via wall permeation. NMR-measurements on such a sample had coherence times of 5 min. While the hemispheres were produced with & lt;1 μm deviation from sphericity, the bonding left a step of ca. 50 μm at maximum. The influence of such a mismatch, its orientation, and the immediate environment of the sample is analyzed by FEM-simulations and discussed in view of coherence times and absolute field measurements.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2016
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 7
    Online Resource
    Online Resource
    AIP Publishing ; 1998
    In:  Physics of Fluids Vol. 10, No. 8 ( 1998-08-01), p. 2111-2113
    In: Physics of Fluids, AIP Publishing, Vol. 10, No. 8 ( 1998-08-01), p. 2111-2113
    Abstract: To investigate the nature of the forces involved in mechanical contact between fibers in a fluid, the interaction between a polymeric fiber settling under the influence of gravity and a fixed strand of the same material was observed. Initially after impact, the sedimenting fiber rotated about a fixed point. When the fiber came sufficiently close to vertical alignment so that the tangential component of gravity overcame the static friction, it slid along the surface of the fixed strand. The orientation of the fiber and its velocity were measured as a function of time, and compared to a simple model. The static coefficient of friction was found to be 0.38±0.06, in good agreement with published values. However, the velocity of the fiber after the onset of sliding was slower than that predicted by a theory incorporating friction and smooth cylinder lubrication, and an additional velocity-dependent resistance was required to model the fiber’s sliding motion. A possible source of this resistance is the coupling of normal and tangential lubrication forces as roughness elements are forced to lift past each other.
    Type of Medium: Online Resource
    ISSN: 1070-6631 , 1089-7666
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1998
    detail.hit.zdb_id: 1472743-2
    detail.hit.zdb_id: 241528-8
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  • 8
    Online Resource
    Online Resource
    AIP Publishing ; 1993
    In:  Journal of Applied Physics Vol. 73, No. 7 ( 1993-04-01), p. 3237-3241
    In: Journal of Applied Physics, AIP Publishing, Vol. 73, No. 7 ( 1993-04-01), p. 3237-3241
    Abstract: We deposit compact amorphous hydrogenated silicon (a-Si:H) films at 50 °C, using low silane partial pressures in silane/hydrogen reaction mixtures. The 29Si chemical shift and infrared signature of our films are strongly affected by the silane feed partial pressure, but are insensi- tive to the hydrogen feed partial pressure, indicating that hydrogen ‘‘etching’’ does not play a significant role in the film growth process. Interestingly, the 29Si chemical shift and infrared signature of our compact 50 °C films are similar to those of a-Si:H films deposited at standard ‘‘optimum’’ conditions, but the electronic properties are very different. Upon thermal annealing at 150 °C for 3 h, the spin defect density may be reduced by as much as 2 orders of magnitude, while the hydrogen content, 29Si chemical shift and infrared signature remain unchanged. Therefore, it seems possible to first grow a compact silicon network structure in a-Si:H at 50 °C, and then equilibrate the electronic structure at 150 °C, without significantly altering the silicon network.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1993
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 9
    Online Resource
    Online Resource
    AIP Publishing ; 1995
    In:  Applied Physics Letters Vol. 66, No. 9 ( 1995-02-27), p. 1062-1064
    In: Applied Physics Letters, AIP Publishing, Vol. 66, No. 9 ( 1995-02-27), p. 1062-1064
    Abstract: The incorporation of hydrogen in ZnSe:N and ZnSe:Cl films grown by gas source molecular beam epitaxy (GSMBE) using elemental Zn and H2Se as source material has been investigated. The hydrogenation behavior was found to be significantly enhanced when nitrogen was used as a dopant, and typically resulted in highly resistive films. On the other hand, Cl-doped ZnSe films showed a hydrogen concentration at or near the background levels independent of the Cl concentration. ZnSe was also grown by conventional molecular beam epitaxy with intentionally introduced H2 in order to clarify the source of the hydrogen. Significant hydrogen incorporation was observed in the MBE-grown ZnSe:N layers only when hydrogen gas was introduced. Injection of hydrogen in excess of the amount generated during typical GSMBE experiments was found to give rise to an unambiguous increase in the hydrogen concentration, but with a hydrogen:nitrogen ratio less than that measured in GSMBE films.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    RVK:
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1995
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 10
    Online Resource
    Online Resource
    AIP Publishing ; 1995
    In:  Applied Physics Letters Vol. 67, No. 2 ( 1995-07-10), p. 167-169
    In: Applied Physics Letters, AIP Publishing, Vol. 67, No. 2 ( 1995-07-10), p. 167-169
    Abstract: We introduce and analyze a new type of high-Q microcavity consisting of a channel waveguide and a one-dimensional photonic crystal. A band gap for the guided modes is opened and a sharp resonant state is created by adding a single defect in the periodic system. An analysis of the eigenstates shows that strong field confinement of the defect state can be achieved with a modal volume less than half of a cubic half-wavelength. We also present a feasibility study for the fabrication of suspended structures with micron-sized features using semiconductor materials.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    RVK:
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1995
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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