8,965 research outputs found
A study of high-speed AD and DA converters using redundancy techniques Interim report, May 10, 1963 - May 9, 1964
High speed analog-to-digital converters compared using redundancy encoding technique
A nonlinear encoder Technical report no. 1, 9 May - 9 Sep. 1964
Nonlinear encoder - sinusoidal reference voltage, comparator, nonlinear counter, and clock inhibit circui
Theoretical investigation of the magnetic structure in YBa_2Cu_3O_6
As experimentally well established, YBa_2Cu_3O_6 is an antiferromagnet with
the magnetic moments lying on the Cu sites. Starting from this experimental
result and the assumption, that nearest-neighbor Cu atoms within a layer have
exactly antiparallel magnetic moments, the orientation of the magnetic moments
has been determined within a nonadiabatic extension of the Heisenberg model of
magnetism, called nonadiabatic Heisenberg model. Within this group-theoretical
model there exist four stable magnetic structures in YBa_2Cu_3O_6, two of them
are obviously identical with the high- and low-temperature structure
established experimentally. However, not all the magnetic moments which appear
to be antiparallel in neutron-scattering experiments are exactly antiparallel
within this group-theoretical model. Furthermore, within this model the
magnetic moments are not exactly perpendicular to the orthorhombic c axis
Continuous Transition between Antiferromagnetic Insulator and Paramagnetic Metal in the Pyrochlore Iridate Eu2Ir2O7
Our single crystal study of the magneto-thermal and transport properties of
the pyrochlore iridate Eu2Ir2O7 reveals a continuous phase transition from a
paramagnetic metal to an antiferromagnetic insulator for a sample with
stoichiometry within ~1% resolution. The insulating phase has strong proximity
to an antiferromagnetic semimetal, which is stabilized by several % level of
the off-stoichiometry. Our observations suggest that in addition to electronic
correlation and spin-orbit coupling the magnetic order is essential for opening
the charge gap.Comment: 6 pages, 6 figure
The Vector Analyzing Power in Elastic Electron-Nucleus Scattering
The vector analyzing power A_n is calculated for elastic electron scattering
from a variety of spin zero nuclei at energies from 14 MeV to 3 GeV. Time
reversal symmetry insures that A_n vanish in first Born approximation.
Therefore A_n depends on Coulomb distortions and can be large for scattering
from heavy nuclei. The vector analyzing power is a potential source of
systematic error for parity violation experiments. We find that A_n=-0.361 ppm
for the kinematics of the Parity Radius Experiment (PREX) involving 850 MeV
electrons scattering at six degrees from 208Pb. This is comparable to the
parity violating asymmetry. However for HAPPEX He involving 3 GeV electrons
scattering on 4He we find that A_n is very small.Comment: 6 pages, 6 figures, submitted to Phys. Rev.
Failure of classical elasticity in auxetic foams
A recent derivation [P.H. Mott and C.M. Roland, Phys. Rev. B 80, 132104
(2009).] of the bounds on Poisson's ratio, v, for linearly elastic materials
showed that the conventional lower limit, -1, is wrong, and that v cannot be
less than 0.2 for classical elasticity to be valid. This is a significant
result, since it is precisely for materials having small values of v that
direct measurements are not feasible, so that v must be calculated from other
elastic constants. Herein we measure directly Poisson's ratio for four
materials, two for which the more restrictive bounds on v apply, and two having
values below this limit of 0.2. We find that while the measured v for the
former are equivalent to values calculated from the shear and tensile moduli,
for two auxetic materials (v < 0), the equations of classical elasticity give
inaccurate values of v. This is experimental corroboration that the correct
lower limit on Poisson's ratio is 0.2 in order for classical elasticity to
apply.Comment: 9 pages, 2 figure
Location of pattern-disturbing structures in the vicinity of an antenna Final report, Jun. 5, 1963 - Sep. 15, 1966
Location of radiation pattern disturbing structures in vicinity of satellite antenn
Electronic Griffiths phase of the d=2 Mott transition
We investigate the effects of disorder within the T=0 Brinkman-Rice (BR)
scenario for the Mott metal-insulator transition (MIT) in two dimensions (2d).
For sufficiently weak disorder the transition retains the Mott character, as
signaled by the vanishing of the local quasiparticles (QP) weights Z_{i} and
strong disorder screening at criticality. In contrast to the behavior in high
dimensions, here the local spatial fluctuations of QP parameters are strongly
enhanced in the critical regime, with a distribution function P(Z) ~
Z^{\alpha-1} and \alpha tends to zero at the transition. This behavior
indicates a robust emergence of an electronic Griffiths phase preceding the
MIT, in a fashion surprisingly reminiscent of the "Infinite Randomness Fixed
Point" scenario for disordered quantum magnets.Comment: 4+ pages, 5 figures, final version to appear in Physical Review
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