76 research outputs found
Magnetic order in the quasi-two-dimensional easy-plane XXZ model
A Green's-function theory of antiferromagnetic short-range and long-range
order (LRO) in the quasi-two-dimensional easy-plane XXZ model is
presented. As the main new result, {\it two} phase transitions due to the
combined influence of spatial and spin anisotropy are found, where below the
higher and lower N\'{e}el temperature there occurs LRO in the transverse and in
both the transverse and longitudinal spin correlators, respectively. Comparing
the theory with neutron-scattering data for the correlation length of , a very good agreement in the whole temperature dependence is
obtained. Moreover, for , , and the second phase with longitudinal LRO is predicted to
appear far below room temperature.Comment: 7 pages, 5 figure
Effective Field Theory for Layered Quantum Antiferromagnets with Non-Magnetic Impurities
We propose an effective two-dimensional quantum non-linear sigma model
combined with classical percolation theory to study the magnetic properties of
site diluted layered quantum antiferromagnets like
LaCuMO (MZn, Mg). We calculate the staggered
magnetization at zero temperature, , the magnetic correlation length,
, the NMR relaxation rate, , and the N\'eel temperature,
, in the renormalized classical regime. Due to quantum fluctuations we
find a quantum critical point (QCP) at at lower doping than
the two-dimensional percolation threshold . We compare our
results with the available experimental data.Comment: Final version accepted for publication as a Rapid Communication on
Physical Review B. A new discussion on the effect of disorder in layered
quantum antiferromagnets is include
Mass Spectra of Supersymmetric Yang-Mills Theories in 1+1 Dimensions
Physical mass spectra of supersymmetric Yang-Mills theories in 1+1 dimensions
are evaluated in the light-cone gauge with a compact spatial dimension. The
supercharges are constructed and the infrared regularization is unambiguously
prescribed for supercharges, instead of the light-cone Hamiltonian. This
provides a manifestly supersymmetric infrared regularization for the
discretized light-cone approach. By an exact diagonalization of the supercharge
matrix between up to several hundred color singlet bound states, we find a
rapidly increasing density of states as mass increases.Comment: LaTeX file, 32 page, 7 eps figure
Nuclear Alpha-Particle Condensates
The -particle condensate in nuclei is a novel state described by a
product state of 's, all with their c.o.m. in the lowest 0S orbit. We
demonstrate that a typical -particle condensate is the Hoyle state
( MeV, state in C), which plays a crucial role for
the synthesis of C in the universe. The influence of antisymmentrization
in the Hoyle state on the bosonic character of the particle is
discussed in detail. It is shown to be weak. The bosonic aspects in the Hoyle
state, therefore, are predominant. It is conjectured that -particle
condensate states also exist in heavier nuclei, like O,
Ne, etc. For instance the state of O at MeV
is identified from a theoretical analysis as being a strong candidate of a
condensate. The calculated small width (34 keV) of ,
consistent with data, lends credit to the existence of heavier Hoyle-analogue
states. In non-self-conjugated nuclei such as B and C, we discuss
candidates for the product states of clusters, composed of 's,
triton's, and neutrons etc. The relationship of -particle condensation
in finite nuclei to quartetting in symmetric nuclear matter is investigated
with the help of an in-medium modified four-nucleon equation. A nonlinear order
parameter equation for quartet condensation is derived and solved for
particle condensation in infinite nuclear matter. The strong qualitative
difference with the pairing case is pointed out.Comment: 71 pages, 41 figures, review article, to be published in "Cluster in
Nuclei (Lecture Notes in Physics) - Vol.2 -", ed. by C. Beck,
(Springer-Verlag, Berlin, 2011
Hydrodynamic Limit of the Boltzmann Equation with Contact Discontinuities
The hydrodynamic limit for the Boltzmann equation is studied in the case when
the limit system, that is, the system of Euler equations contains contact
discontinuities. When suitable initial data is chosen to avoid the initial
layer, we prove that there exists a unique solution to the Boltzmann equation
globally in time for any given Knudsen number. And this family of solutions
converge to the local Maxwellian defined by the contact discontinuity of the
Euler equations uniformly away from the discontinuity as the Knudsen number
tends to zero. The proof is obtained by an appropriately chosen
scaling and the energy method through the micro-macro decomposition.Comment: 34 pages. submitte
Evaluation of the mutagenic effects of SV40 in mouse, hamster, and mouse-human hybrid cells
We have examined the ability of SV40 to induce changes in drug or temperature resistance in mouse, hamster, and mouse-human hybrid cells. SV40 induced a substantial increase of cells resistant to 5-bromodeoxyuridine + trifluorothymidine in Balb/c 3T3 cells and induced an increase of hybrid cells resistant to 6-thioguanine. SV40 was found to be nonmutagenic or weakly mutagenic in other test systems. The 3T3 cells were T-antigen positive, exhibited a marked reduction in TK activity, were heterogeneous for [ 3 H]BrdU incorporation by autoradiography, and exhibited instability of the drug-resistance phenotype, suggesting that SV40 may be inducing resistance by an epigenetic process. SV40-induced 6-thioguanine resistance in the hybrids appears to occur predominantly by chromosome loss.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45539/1/11188_2005_Article_BF01233058.pd
Pro-active Meeting Assistants: Attention Please!
This paper gives an overview of pro-active meeting assistants, what they are and when they can be useful. We explain how to develop such assistants with respect to requirement definitions and elaborate on a set of Wizard of Oz experiments, aiming to find out in which form a meeting assistant should operate to be accepted by participants and whether the meeting effectiveness and efficiency can be improved by an assistant at all. This paper gives an overview of pro-active meeting assistants, what they are and when they can be useful. We explain how to develop such assistants with respect to requirement definitions and elaborate on a set of Wizard of Oz experiments, aiming to find out in which form a meeting assistant should operate to be accepted by participants and whether the meeting effectiveness and efficiency can be improved by an assistant at all
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