753 research outputs found
A New Approach to Stochastic State selections in Quantum Spin Systems
We propose a new type of Monte Carlo approach in numerical studies of quantum
systems. Introducing a probability function which determines whether a state in
the vector space survives or not, we can evaluate expectation values of powers
of the Hamiltonian from a small portion of the full vector space. This method
is free from the negative sign problem because it is not based on importance
sampling techniques. In this paper we describe our method and, in order to
examine how effective it is, present numerical results on the 4x4, 6x6 and 8x8
Heisenberg spin one-half model. The results indicate that we can perform useful
evaluations with limited computer resources. An attempt to estimate the lowest
energy eigenvalue is also stated.Comment: 10 pages, 2 figures, 8 table
Dynamic regulation of Ero1 and peroxiredoxin 4 localization in the secretory pathway
In the early secretory compartment (ESC), a network of chaper-
ones and enzymes assists oxidative folding of nascent proteins.
Ero1 flavoproteins oxidize protein disulfide isomerase (PDI), gen-
erating H2O2 as a byproduct. Peroxiredoxin 4 (Prx4) can utilize
luminal H2O2 to oxidize PDI, thus favoring oxidative folding while
limiting oxidative stress. Interestingly, neither ER oxidase contains
known ER retention signal(s), raising the question of how cells pre-
vent their secretion. Here we show that the two proteins share sim-
ilar intracellular localization mechanisms. Their secretion is pre-
vented by sequential interactions with PDI and ERp44, two
resident proteins of the ESC-bearing KDEL-like motifs. PDI binds
preferentially Ero1 , whereas ERp44 equally retains Ero1 and
Prx4. The different binding properties of Ero1 and Prx4 increase
the robustness of ER redox homeostasis
An Obstruction to Quantization of the Sphere
In the standard example of strict deformation quantization of the symplectic
sphere , the set of allowed values of the quantization parameter
is not connected; indeed, it is almost discrete. Li recently constructed a
class of examples (including ) in which can take any value in an
interval, but these examples are badly behaved. Here, I identify a natural
additional axiom for strict deformation quantization and prove that it implies
that the parameter set for quantizing is never connected.Comment: 23 page. v2: changed sign conventio
Frustrated quantum-spin system on a triangle coupled with lattice vibrations - Correspondence to Longuet-Higgins et al.'s Jahn-Teller model -
We investigate the quantum three spin model
of spin on a triangle, in which spins are coupled with
lattice-vibrational modes through the exchange interaction depending on
distances between spin sites. The present model corresponds to the dynamic
Jahn-Teller system proposed by Longuet-Higgins {\it et al.},
Proc.R.Soc.A.{\bf 244},1(1958). This correspondence is revealed by using the
transformation to Nakamura-Bishop's bases proposed in Phys.Rev.Lett.{\bf
54},861(1985). Furthermore, we elucidate the relationship between the behavior
of a chiral order parameter and
that of the electronic orbital angular momentum in vibronic model: The regular oscillatory behavior of the expectation value
. The increase of the additional
anharmonicity(chaoticity) is found to yield a rapidly decaying irregular
oscillation of
Electron Spin Resonance in S=1/2 antiferromagnetic chains
A systematic field-theory approach to Electron Spin Resonance (ESR) in the
quantum antiferromagnetic chain at low temperature (compared to the
exchange coupling ) is developed. In particular, effects of a transverse
staggered field and an exchange anisotropy (including a dipolar
interaction) on the ESR lineshape are discussed. In the lowest order
of perturbation theory, the linewidth is given as and
, respectively. In the case of a transverse staggered
field, the perturbative expansion diverges at lower temperature;
non-perturbative effects at very low temperature are discussed using exact
results on the sine-Gordon field theory. We also compare our field-theory
results with the predictions of Kubo-Tomita theory for the high-temperature
regime, and discuss the crossover between the two regimes. It is argued that a
naive application of the standard Kubo-Tomita theory to the
Dzyaloshinskii-Moriya interaction gives an incorrect result. A rigorous and
exact identity on the polarization dependence is derived for certain class of
anisotropy, and compared with the field-theory results.Comment: 53 pages in REVTEX, 7 figures in EPS included; revised version with
missing references and correction
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