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  • 1
    Unknown
    Amsterdam [u.a.] : North Holland
    ISBN: 0444864253 (U.S.)
    Language: English
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  • 2
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report high resolution x-ray diffraction studies of the structures and phase transitions of monolayer krypton, adsorbed on both powder and single crystal graphite substrates. A comprehensive series of powder diffraction profiles is used to construct the two dimensional phase diagram. The melting of the $$\sqrt 3 x\sqrt 3$$ commensurate solid is shown to be strongly first order throughout the region where tricritical behavior was previously thought to occur; fluid solid coexistence extends up to the termination of the commensurate phase at 130 K. A disordered weakly incommensurate phase is shown to be a reentrant fluid, a system which may be described as a disordered network of domain walls and which evolves continuously into a more conventional 2D fluid. This evolution is marked by the disappearance of satellite peaks which are caused by the modulation of the overlayer by the substrate. The freezing of the reentrant fluid into the commensurate phase is shown to be consistent with a chiral Potts transition, its freezing into the incommensurate solid consistent with a dislocation binding transition. Single crystal experiments reveal the orientation of the weakly incommensurate phase. The reentrant fluid is found to have no visible orientational fluctuations, manifesting isotropic diffraction peaks. This is attributed to the strong epitaxy of domain walls. The incommensurate solid is shown to undergo an aligned-rotated transition which is well described by zerotemperature calculations.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Advanced Photon Source planned for construction at Argonne National Laboratory is based on a low-emittance storage-ring operated at 7 GeV and capable of providing tunable undulator radiation from 4 to 40 keV (using the first and the third harmonics). A technical description of the accelerator facility and the storage ring is presented in this overview, along with a brief summary of the characteristics of radiation that will be available from the insertion devices. Various plans for user access to this national user facility are also given.
    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 63 (1988), S. 4015-4018 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic susceptibility measurements on La2CuO4−y have revealed maxima in temperature indicative of antiferromagnetic ordering. Powder diffraction measurements have demonstrated the existence of superlattice peaks at temperatures below those corresponding to the susceptibility maxima, and polarized neutron measurements have confirmed that the peaks are indeed of magnetic origin. The deduced antiferromagnetic structure in the orthorhombic (Cmca) phase of La2CuO4−y consists of ferromagnetic sheets of Cu atoms in the b-c plane which are alternating in sign along the a axis [100]. The moment is parallel to the c axis. The Neel temperature is extremely sensitive to the oxygen deficiency y and decreases rapidly to zero as y goes from 0.03 to 0. The saturated moment is (approximately-equal-to)0.4 μB/Cu atom for samples with the highest TN (290 K). Antiferromagnetic spin fluctuations have also been observed by polarized neutron scattering in the paramagnetic phase above TN. Recent results obtained on magnetic ordering in the YBa2Cu3O6−y family of compounds are also discussed, together with the possible implications for novel superconductivity mechanisms.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 3619-3622 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present the results of recent magnetic x-ray scattering experiments on the rare-earth metal Ho performed using both a rotating anode source and synchrotron radiation. Specifically, we have measured the Ho(00l)+ magnetic satellites in the simple spiral antiferromagnetic phase between 132 and 20 K and in the conical phase below 20 K. Although the cross section for magnetic x-ray scattering is reduced from the usual Thomson cross section by a factor of ≈105, the incommensurate magnetic satellites are well separated from the main Bragg peaks. Thus, detection of the satellites is possible with a rotating anode source and extensive high-resolution studies of them are straightforward with synchrotron radiation. The assembled data are in good agreement with the results of magnetic neutron scattering published previously for different Ho samples.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Advanced Photon Source at Argonne National Laboratory is designed as a national synchrotron radiation user facility where extremely bright 1–100 keV x-ray beams will be used for multidisciplinary research. Construction of the facility has begun. Accelerator components, insertion devices, optical elements, and optical element cooling schemes have been and continue to be the subjects of intensive research and development. Proposals to conduct research at the Advanced Photon Source have been received from industrial, university, and national laboratory scientists representing a broad range of scientific disciplines.
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2019-07-13
    Description: Because of their wave nature, thermal and cold neutrons can be reflected from smooth surfaces at grazing incidence angles, be reflected by multilayer coatings or be refracted at boundaries of different materials. The optical properties of materials are characterized by their refractive indices which are slightly less than unity for most elements and their isotopes in the case of cold and thermal neutrons as well as for x-rays. The motivation for the optics use for neutrons as well as for x-rays is to increase the signal rate and, by virtue of the optic's angular resolution, to improve the signal-to-noise level by reducing the background so the efficiency of the existing neutron sources use can be significantly enhanced. Both refractive and reflective optical techniques developed for x-ray applications can be applied to focus neutron beams. Typically neutron sources have lower brilliance compared to conventional x-ray sources so in order to increase the beam throughput the neutron optics has to be capable of capturing large solid angles. Because of this, the replicated optics techniques developed for x-ray astronomy applications would be a perfect match for neutron applications, so the electroformed nickel optics under development at the Marshall Space Flight Center (MSFC) can be applied to focus neutron beams. In this technique, nickel mirror shells are electroformed onto a figured and superpolished nickel-plated aluminum cylindrical mandrel from which they are later released by differential thermal contraction. Cylindrical mirrors with different diameters, but the same focal length, can be nested together to increase the system throughput. The throughput can be increased further with the use of the multilayer coatings deposited on the reflectivr surface of the mirror shells. While the electroformed nickel replication technique needs to be adopted for neutron focusing, the technology to coat the inside of cylindrical mirrors with neutron multilayers has to be developed. The availability of these technologies would bring new capabilities to neutron instrumentation and, hence, lead to new scientific breakthroughs. We have established a program to adopt the electroformed nickel replication optics technique for neutron applications and to develop the neutron multilayer replication technology.
    Keywords: Optics
    Type: M12-1921 , M12-1981 , Neutron Scattering Principal Investigators'' Meeting; 22-25 Jul. 2012; Gaithersburg, MD; United States
    Format: application/pdf
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  • 8
    Publication Date: 2019-07-19
    Description: In the case of neutrons the refractive index is slightly less than unity for most elements and their isotopes. Consequently, thermal and cold neutrons can be reflected from smooth surfaces at grazing-incidence angles. Hence, the optical technologies developed for x-ray astronomy can be applied for neutron focusing. The focusing capabilities of grazing incidence neutron imaging optics have been successfully demonstrated using nickel mirrors. The mirrors were fabricated using an electroformed nickel replication process at Marshall Space Flight Center. Results of the neutron optics experiments will be presented. Challenges of the neutron imaging optics as well as possible applications of the optics will be discussed.
    Keywords: Optics
    Type: M11-0372 , SPIE Annual Meeting - Optics EUV, X-Ray, and Gamma-Ray Astronomy V (Conference OP403); 21-25 Aug. 2011; San Diego,CA; United States
    Format: application/pdf
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  • 9
    Publication Date: 1981-08-16
    Print ISSN: 0567-7394
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 10
    Publication Date: 1982-08-20
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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