18,856 research outputs found
Theoretical studies of tone noise from a fan rotor
An analytical study was made of some possible rotor alone noise sources of dipole, quadrapole and monopole characters which generate discrete tone noise. Particular emphasis is given to the tone noise caused by fan inlet flow distortion and turbulence. Analytical models are developed to allow prediction of absolute levels. Experimental data measured on a small scale fan is presented which indicates inlet turbulence interaction with a fan rotor can be a source of tone noise. Predicted and measured tone noise for the small scale rotor are shown to be in reasonable agreement
High performance turboalternator and associated hardware. 3. Design of backup gas bearings
Turboalternator gas bearing system for spacecraft electric power productio
Theoretical studies on tone noise from a ducted fan rotor
The method of computing radiated noise from a ducted rotor due to inflow distortion and turbulence are examined. Analytical investigations include an appropriate description of sources, the cut-off conditions imposed on the modal propagation of the pressure waves in the annular duct, and reflections at the upstream end of the duct. Far field sound pressure levels at blade passing frequency due to acoustic radiation from a small scale low speed fan are computed. Theoretical predictions are in reasonable agreement with experimental measurements
Evidence for the Role of Instantons in Hadron Structure from Lattice QCD
Cooling is used as a filter on a set of gluon fields sampling the Wilson
action to selectively remove essentially all fluctuations of the gluon field
except for the instantons. The close agreement between quenched lattice QCD
results with cooled and uncooled configurations for vacuum correlation
functions of hadronic currents and for density-density correlation functions in
hadronic bound states provides strong evidence for the dominant role of
instantons in determining light hadron structure and quark propagation in the
QCD vacuum.Comment: 26 pages in REVTeX, plus 10 figures, uuencoded. Submitted to Physical
Review D. MIT-CTP-226
Magnetoelectricity and Magnetostriction due to the Rare Earth Moment in TmAl(BO)
The magnetic properties, the magnetostriction, and the magnetoelectric effect
in the d-electron free rare-earth aluminum borate TmAl(BO) are
investigated between room temperature and 2 K. The magnetic susceptibility
reveals a strong anisotropy with the hexagonal c-axis as the hard magnetic
axis. Magnetostriction measurements show a large effect of an in-plane field
reducing both, the a- and c-axis lattice parameters. The magnetoelectric
polarization change in a- and c-directions reaches up to 300 C/m at 70
kOe with the field applied along the a-axis. The magnetoelectric polarization
is proportional to the lattice contraction in magnetic field. The results of
this investigation prove the existence of a significant coupling between the
rare earth magnetic moment and the lattice in Al(BO) compounds
( = rare earth). They further show that the rare earth moment itself will
generate a large magnetoelectric effect which makes it easier to study and to
understand the origin of the magnetoelectric interaction in this class of
materials.Comment: 4 pages, 5 figure
Comparative Raman Studies of Sr2RuO4, Sr3Ru2O7 and Sr4Ru3O10
The polarized Raman spectra of layered ruthenates of the Srn+1RunO3n+1
(n=1,2,3) Ruddlesden-Popper series were measured between 10 and 300 K. The
phonon spectra of Sr3Ru2O7 and Sr4Ru3O10 confirmed earlier reports for
correlated rotations of neighboring RuO6 octahedra within double or triple
perovskite blocks. The observed Raman lines of Ag or B1g symmetry were assigned
to particular atomic vibrations by considering the Raman modes in simplified
structures with only one double or triple RuO6 layer per unit cell and by
comparison to the predictions of lattice dynamical calculations for the real
Pban and Pbam structures. Along with discrete phonon lines, a continuum
scattering, presumably of electronic origin, is present in the zz, xx and xy,
but not in the x'y' and zx spectra. Its interference with phonons results in
Fano shape for some of the lines in the xx and xy spectra. The temperature
dependencies of phonon parameters of Sr3Ru2O7 exhibit no anomaly between 10 and
300 K where no magnetic transition occurs. In contrast, two B1g lines in the
spectra of Sr4Ru3O10, corresponding to oxygen vibrations modulating the Ru-O-Ru
bond angle, show noticeable hardening with ferromagnetic ordering at 105 K,
thus indicating strong spin-phonon interaction.Comment: 9 pages, 12 figure
Raman scattering study of (KSr)FeAs ( = 0.0, 0.4)
Polarized Raman spectra of non-superconducting SrFeAs and
superconducting KSrFeAs ( K) are reported.
All four phonon modes (A + B + 2E) allowed by symmetry, are
found and identified. Shell model gives reasonable description of the spectra.
No detectable anomalies are observed near the tetragonal-to-orthorhombic
transition in SrFeAs or the superconducting transition in
KSrFeAs.Comment: 4 pages, 4 figures, 2 table
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