1,567 research outputs found
Characterization of the 4-canonical birationality of algebraic threefolds
In this article we present a 3-dimensional analogue of a well-known theorem
of E. Bombieri (in 1973) which characterizes the bi-canonical birationality of
surfaces of general type. Let be a projective minimal 3-fold of general
type with -factorial terminal singularities and the geometric genus
. We show that the 4-canonical map is {\it not}
birational onto its image if and only if is birationally fibred by a family
of irreducible curves of geometric genus 2 with
where is a general irreducible member in .Comment: 25 pages, to appear in Mathematische Zeitschrif
State-Space Formulation of Frequency Transformation for 2-D Digital Filters
科研費報告書収録論文(課題番号:15560314/研究代表者:川又政征/多次元ディジタルフィルタの最適設計とその画像・映像処理への応用
On use of averaging in FxLMS algorithm for single-channel feedforward ANC systems
科研費報告書収録論文(課題番号:15560314/研究代表者:川又政征/多次元ディジタルフィルタの最適設計とその画像・映像処理への応用
Thermal Conductivity of the Quasi One-Dimensional Spin System Sr_2_V_3_O_9_
We have measured the thermal conductivity along the [101] direction,
kappa_[101]_, along the [10-1] direction, kappa_[10-1]_, and along the b-axis,
kappa_b_, of the quasi one-dimensional S=1/2 spin system Sr_2_V_3_O_9_ in
magnetic fields up to 14 T, in order to find the thermal conductivity due to
spinons and to clarify whether the spin-chains run along the [101] or [10-1]
direction. It has been found that both kappa_[101]_, kappa_[10-1]_ and kappa_b_
show one peak around 10 K in zero field and that the magnitude of kappa_[10-1]_
is larger than those of kappa_[101]_ and kappa_b_. By the application of
magnetic field along the heat current, the peak of kappa_[10-1]_ is markedly
suppressed, while the peaks of kappa_[101]_ and kappa_b_ little change. These
results indicate that there is a large contribution of spinons to kappa_[10-1]_
and suggest that the spin-chains run along the [10-1] direction.Comment: 3 pages, 4 figure
Hole-trapping by Ni, Kondo effect and electronic phase diagram in non-superconducting Ni-substituted La2-xSrxCu1-yNiyO4
In order to investigate the electronic state in the normal state of high-Tc
cuprates in a wide range of temperature and hole-concentration, specific-heat,
electrical-resistivity, magnetization and muon-spin-relaxation (muSR)
measurements have been performed in non-superconducting Ni-substituted
La2-xSrxCu1-yNiyO4 where the superconductivity is suppressed through the
partial substitution of Ni for Cu without disturbing the Cu-spin correlation in
the CuO2 plane so much. In the underdoped regime, it has been found that there
exist both weakly localized holes around Ni and itinerant holes at high
temperatures. With decreasing temperature, all holes tend to be localized,
followed by the occurrence of variable-range hopping conduction at low
temperatures. Finally, in the ground state, it has been found that each Ni2+
ion traps a hole strongly and that a magnetically ordered state appears. In the
overdoped regime, on the other hand, it has been found that a Kondo-like state
is formed around each Ni2+ spin at low temperatures. In conclusion, the ground
state of non-superconducting La2-xSrxCu1-yNiyO4 changes upon hole doping from a
magnetically ordered state with the strong hole-trapping by Ni2+ to a metallic
state with Kondo-like behavior due to Ni2+ spins, and the quantum phase
transition is crossover-like due to the phase separation into short-range
magnetically ordered and metallic regions.Comment: 9 pages, 8 figures, accepted for publication in Phys. Rev.
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