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Phonon density of states in Fe/Cr (001) superlattices and Tb-Fe thin-film alloys.
Inelastic nuclear scattering of X-rays from the 14.413 keV nuclear resonance of {sup 57}Fe was employed to measure directly the Fe-projected phonon density of states (DOS) in MBE-grown Fe/Cr(00l) superlattices on MgO(001). The Moessbauer-inactive {sup 56}Fe isotope was used in the Fe layers. A 1{angstrom} thick Moessbauer-active {sup 57}Fe-probe layer (95% enriched) was placed at different locations within the Fe layers. This procedure permits one to distinguish phonon density of states at the Fe-Cr-interface from that at the center of the Fe-film. Distinct differences have been observed in the DOS of our samples. The phonon DOS of an amorphous Tb{sub 33}Fe{sub 67} alloy film was found to be a broad and structureless hump, contrary to that of an epitaxial TbFe{sub 2} film, which exhibits characteristic features.
Date:
February 15, 1999
Creator:
Alp, E. E.; Keune, W.; Roehlsberger, R.; Ruckert, T.; Schror, H. & Sturhahn, W.
Object Type:
Article
System:
The UNT Digital Library
Magnetic correlations in doped transition metal oxides
The authors review recent reactor- and spallation-source-based neutron scattering experiments on the magnetic fluctuations and order in a variety of doped transition metal oxides. In particular, data are shown for the NiO chain compound, Y{sub 2{minus}x}Ca{sub x}BaNiO{sub 5}, the two-dimensional cuprate superconductors La{sub 2{minus}x}Sr{sub x}CuO{sub 4} and YBa{sub 2}Cu{sub 3} O{sub 6+x}, and the classical three-dimensional ``Mott-Hubbard`` system V{sub 2{minus}y}O{sub 3}.
Date:
February 15, 1995
Creator:
Aeppli, G.; Bao, W. & Broholm, C.
Object Type:
Article
System:
The UNT Digital Library
Ball lens reflections by direct solution of Maxwell`s equations
Ball lenses are important for many applications. For example, ball lenses can be used to match the mode of a laser diode (LD) to a single mode fiber (SMF), essential for low-loss, high bit rate communication systems. Modeling the propagation of LD light through a ball lens presents a challenge due to the large angular divergence of the LD field (typically > 20{degrees} HWHM) and the subsequent significant effect of spherical aberration. Accurately calculating the reflected power is also difficult, but essential, since reflections as small as {minus}30 dB can destabilize the LID. A full-wave analysis of this system using, e.g., a finite-difference time-domain method is not practical because of the size of the ball lens, typically hundreds of wavelengths in diameter. Approximate scalar methods can give good results in some cases, but fail to calculate reflected power and miss polarization effects entirely. The authors` approach exploits the fact that the scattering of an arbitrary electromagnetic beam from a sphere is an exactly solvable problem. The scattering of a plane wave from a sphere is a classical problem which was solved by Mie in 1908. More recently, various workers have considered the scattering of a Gaussian beam from a sphere …
Date:
February 15, 1995
Creator:
Ratowsky, R. P.; Deri, R. J.; Kallman, J. S. & Trott, G.
Object Type:
Article
System:
The UNT Digital Library
Large eddy simulation and its implementation in the COMMIX code.
Large eddy simulation (LES) is a numerical simulation method for turbulent flows and is derived by spatial averaging of the Navier-Stokes equations. In contrast with the Reynolds-averaged Navier-Stokes equations (RANS) method, LES is capable of calculating transient turbulent flows with greater accuracy. Application of LES to differing flows has given very encouraging results, as reported in the literature. In recent years, a dynamic LES model that presented even better results was proposed and applied to several flows. This report reviews the LES method and its implementation in the COMMIX code, which was developed at Argonne National Laboratory. As an example of the application of LES, the flow around a square prism is simulated, and some numerical results are presented. These results include a three-dimensional simulation that uses a code developed by one of the authors at the University of Notre Dame, and a two-dimensional simulation that uses the COMMIX code. The numerical results are compared with experimental data from the literature and are found to be in very good agreement.
Date:
February 15, 1999
Creator:
Sun, J. & Yu, D.-H.
Object Type:
Report
System:
The UNT Digital Library
Preparation of bismuth powder
The Purpose of this manual is to describe preparation of bismuth powder for use in process operations. Bismuth powder is to be prepared in Room 232 of ``T`` Building where all necessary apparatus is installed.
Date:
February 15, 1949
Creator:
Cox, G.C.
Object Type:
Report
System:
The UNT Digital Library