95 research outputs found
Contact Ion Engine System for ATS Satellites D and E Annual Progress Report
Performance testing of ion microthruster systems for Applications Technology Satellite
Program to develop and demonstrate method to deflect beam for ion thrustor Final progress report, 6 Dec. 1965 - 6 Jun. 1966
Electrostatic electrodes used for deflecting ion beam from ion thrusto
Study and Design of a Cesium Bombardment Ion Engine System
Cesium bombardment ion engine system design, modification, and testin
Contact ion engine system for ATS satellites D and E Annual progress report, 22 Mar. 1967 - 22 Mar. 1968
Ion microthrustor systems and ground support equipment for Applications Technology Satellites D and
Tunability of the dielectric response of epitaxially strained SrTiO3 from first principles
The effect of in-plane strain on the nonlinear dielectric properties of
SrTiO3 epitaxial thin films is calculated using density-functional theory
within the local-density approximation. Motivated by recent experiments, the
structure, zone-center phonons, and dielectric properties with and without an
external electric field are evaluated for several misfit strains within +-3% of
the calculated cubic lattice parameter. In these calculations, the in-plane
lattice parameters are fixed, and all remaining structural parameters are
permitted to relax. The presence of an external bias is treated approximately
by applying a force to each ion proportional to the electric field. After
obtaining zero-field ground state structures for various strains, the
zone-center phonon frequencies and Born effective charges are computed,
yielding the zero-field dielectric response. The dielectric response at finite
electric field bias is obtained by computing the field dependence of the
structure and polarization using an approximate technique. The results are
compared with recent experiments and a previous phenomenological theory. The
tunability is found to be strongly dependent on the in-plane lattice parameter,
showing markedly different behavior for tensile and compressive strains. Our
results are expected to be of use for isolating the role of strain in the
tunability of real ultrathin epitaxial films.Comment: 11 pages, with postscript figures embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/ant_srti/index.htm
Photoproduction of Positive Mesons from Hydrogen: Results
The center-of-mass differential cross section for photoproduction of positive pions from hydrogen has been measured by the methods described in the two previous abstracts, in the angular range 40° to 150°, for photons from 220 to 475 Mev. (Photon energies refer to the Laboratory System.) Results obtained by the two methods are in essential agreement. At 90°, dσ/dω has a maximum of 2.7 X 10^(-29) cm^2/sterad near 280 Mev and falls by a factor 5 at 450 Mev. The maximum in the excitation curve is even more pronounced at larger angles, but less pronounced at smaller ones. At 40° (c.m.) the peak occurs near 350 Mev and at 450 Mev the cross section has decreased only to 0.7 the, peak value. Angular distributions in the center-of-mass system show a marked assymetry about 90°, which changes character from low energy to high. Below 325 Mev, there ii a backward maximum, whereas above 375 Mev, there is a forward maximum. The total cross section reaches a maximum near 290 Mev and decreases by about a factor 3 at 450 Mev. The results below 300 Mev agree with the data already reported from Berkeley and Cornell
Analogies of structural instabilities in EuTiO3 and SrTiO3
Specific heat measurements and theoretical calculations reveal an intimate
analogy between EuTiO3 and SrTiO3. For EuTiO3 a hitherto unknown specific heat
anomaly is discovered at TA=282(1)K which is analogous to the well known
specific heat anomaly of SrTiO3 at TA=105K caused by an antiferrodistortive
transition. Since the zone center soft phonon mode observed in both systems can
be modeled with the same parameters we ascribe the new 282(1)K instability of
EuTiO3 to an antiferrodistortive phase transition. The higher transition
temperature of EuTiO3 as compared to SrTiO3 results from spin phonon coupling.Comment: PRB to be published, 12 pages, 3 Figure
Lattice dynamical analogies and differences between SrTiO3 and EuTiO3 revealed by phonon-dispersion relations and double-well potentials
A comparative analysis of the structural phase transitions of EuTiO3 and
SrTiO3 (at TS = 282 and 105 K, respectively) is made on the basis of
phonon-dispersion and density functional calculations. The phase transition of
EuTiO3 is predicted to arise from the softening of a transverse acoustic
zone-boundary mode caused by the rotations of the TiO6 octahedra, as also found
for the phase transition of SrTiO3. While the temperature dependence of the
soft mode is similar in both compounds, their elastic properties differ
drastically due to a large difference in the double-well potentials associated
with the soft zone boundary-acoustic mode.Comment: 16 pages, 6 figure
Magnetic field dependence of the exciton energy in a quantum disk
The groundstate energy and binding energy of an exciton, confined in a^M
quantum disk, are calculated as a function of an external magnetic field. The
confinement potential is a hard wall of finite height. The diamagnetic shift is
investigated for magnetic fields up to 40. Our results are applied to
self-assembled quantum dots and very good
agreement with experiments is obtained. Furthermore, we investigated the
influence of the dot size on the diamagnetic shift by changing the disk radius.
The exciton excited states are found as a function of the magnetic field. The
relative angular momentum is not a quantum number and changes with the magnetic
field strength.Comment: 10 pages, 17 figure
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