193 research outputs found
MacWilliams' Extension Theorem for Bi-Invariant Weights over Finite Principal Ideal Rings
A finite ring R and a weight w on R satisfy the Extension Property if every
R-linear w-isometry between two R-linear codes in R^n extends to a monomial
transformation of R^n that preserves w. MacWilliams proved that finite fields
with the Hamming weight satisfy the Extension Property. It is known that finite
Frobenius rings with either the Hamming weight or the homogeneous weight
satisfy the Extension Property. Conversely, if a finite ring with the Hamming
or homogeneous weight satisfies the Extension Property, then the ring is
Frobenius.
This paper addresses the question of a characterization of all bi-invariant
weights on a finite ring that satisfy the Extension Property. Having solved
this question in previous papers for all direct products of finite chain rings
and for matrix rings, we have now arrived at a characterization of these
weights for finite principal ideal rings, which form a large subclass of the
finite Frobenius rings. We do not assume commutativity of the rings in
question.Comment: 12 page
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Profoundly reduced neovascularization capacity of bone marrow mononuclear cells derived from patients with chronic ischemic heart disease
Background— Cell therapy with bone marrow–derived stem/progenitor cells is a novel option for improving neovascularization and cardiac function in ischemic heart disease. Circulating endothelial progenitor cells in patients with coronary heart disease are impaired with respect to number and functional activity. However, whether this impairment also extends to bone marrow–derived mononuclear cells (BM-MNCs) in patients with chronic ischemic cardiomyopathy (ICMP) is unclea
A new quantum fluid at high magnetic fields in the marginal charge-density-wave system -(BEDT-TTF)Hg(SCN) (where ~K and Rb)
Single crystals of the organic charge-transfer salts
-(BEDT-TTF)Hg(SCN) have been studied using Hall-potential
measurements (K) and magnetization experiments ( = K, Rb). The data show
that two types of screening currents occur within the high-field,
low-temperature CDW phases of these salts in response to time-dependent
magnetic fields. The first, which gives rise to the induced Hall potential, is
a free current (), present at the surface of the sample.
The time constant for the decay of these currents is much longer than that
expected from the sample resistivity. The second component of the current
appears to be magnetic (), in that it is a microscopic,
quasi-orbital effect; it is evenly distributed within the bulk of the sample
upon saturation. To explain these data, we propose a simple model invoking a
new type of quantum fluid comprising a CDW coexisting with a two-dimensional
Fermi-surface pocket which describes the two types of current. The model and
data are able to account for the body of previous experimental data which had
generated apparently contradictory interpretations in terms of the quantum Hall
effect or superconductivity.Comment: 13 pages, 11 figure
Quantization of the Hall conductivity well beyond the adiabatic limit in pulsed magnetic fields
We measure the Hall conductivity, , on a Corbino geometry sample
of a high-mobility AlGaAs/GaAs heterostructure in a pulsed magnetic field. At a
bath temperature about 80 mK, we observe well expressed plateaux in
at integer filling factors. In the pulsed magnetic field, the
Laughlin condition of the phase coherence of the electron wave functions is
strongly violated and, hence, is not crucial for quantization.Comment: 4 pages, 4 figures, submitted to PR
Enhancement of de Haas-van Alphen Oscillation due to Spin in the Magnetic Breakdown System
The effects of the Zeeman term on the de Haas-van Alphen oscillation is
studied in the magnetic breakdown system. We find that the amplitude of the
oscillation with the frequencies of and are enhanced by the Zeeman term, while they are expected to be
reduced in the semiclassical theory. A possible interpretation of the
experiments in organic conductors is discussed.Comment: 4 pages,4 figures. Submitted to Journal of Physical Society of Japa
Recent high-magnetic-field studies of unusual groundstates in quasi-two-dimensional crystalline organic metals and superconductors
After a brief introduction to crystalline organic superconductors and metals,
we shall describe two recently-observed exotic phases that occur only in high
magnetic fields. The first involves measurements of the non-linear electrical
resistance of single crystals of the charge-density-wave (CDW) system
(Per)Au(mnt) in static magnetic fields of up to 45 T and temperatures
as low as 25 mK. The presence of a fully gapped CDW state with typical CDW
electrodynamics at fields higher that the Pauli paramagnetic limit of 34 T
suggests the existence of a modulated CDW phase analogous to the
Fulde-Ferrell-Larkin-Ovchinnikov state. Secondly, measurements of the Hall
potential of single crystals of -(BEDT-TTF)KHg(SCN), made using
a variant of the Corbino geometry in quasistatic magnetic fields, show
persistent current effects that are similar to those observed in conventional
superconductors. The longevity of the currents, large Hall angle, flux
quantization and confinement of the reactive component of the Hall potential to
the edge of the sample are all consistent with the realization of a new state
of matter in CDW systems with significant orbital quantization effects in
strong magnetic fields.Comment: SNS 2004 Conference presentatio
The transverse magnetoresistance of the two-dimensional chiral metal
We consider the two-dimensional chiral metal, which exists at the surface of
a layered, three-dimensional sample exhibiting the integer quantum Hall effect.
We calculate its magnetoresistance in response to a component of magnetic field
perpendicular to the sample surface, in the low temperature, but macroscopic,
regime where inelastic scattering may be neglected. The magnetoresistance is
positive, following a Drude form with a field scale,
, given by the transverse field strength at which
one quantum of flux, , passes through a rectangle with sides set by the
layer-spacing, , and the elastic mean free path, .
Experimental measurement of this magnetoresistance may therefore provide a
direct determination of the elastic mean free path in the chiral metal.Comment: submitted to Phys Rev
de Haas-van Alphen Effect in the Two-Dimensional and the Quasi-Two-Dimensional Systems
We study the de Haas-van Alphen (dHvA) oscillation in two-dimensional and
quasi-two-dimensional systems. We give a general formula of the dHvA
oscillation in two-dimensional multi-band systems. By using this formula, the
dHvA oscillation and its temperature-dependence for the two-band system are
shown. By introducing the interlayer hopping , we examine the crossover
from the two-dimension, where the oscillation of the chemical potential plays
an important role in the magnetization oscillation, to the three-dimension,
where the oscillation of the chemical potential can be neglected as is well
know as the Lifshitz and Kosevich formula. The crossover is seen at , where a and b are lattice constants, is the flux
quantum and 8t is the width of the total energy band. We also study the dHvA
oscillation in quasi-two-dimensional magnetic breakdown systems. The quantum
interference oscillations such as oscillation as well as the
fundamental oscillations are suppressed by the interlayer hopping , while
the oscillation gradually increases as increases and it
has a maximum at . This interesting dependence on the
dimensionality can be observed in the quasi-two-dimensional organic conductors
with uniaxial pressure.Comment: 11 pages, 14 figure
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