3,542 research outputs found
Optimizing Hartree-Fock orbitals by the density-matrix renormalization group
We have proposed a density-matrix renormalization group (DMRG) scheme to
optimize the one-electron basis states of molecules. It improves significantly
the accuracy and efficiency of the DMRG in the study of quantum chemistry or
other many-fermion system with nonlocal interactions. For a water molecule, we
find that the ground state energy obtained by the DMRG with only 61 optimized
orbitals already reaches the accuracy of best quantum Monte Carlo calculation
with 92 orbitals.Comment: published version, 4 pages, 4 figure
Plaquette order and deconfined quantum critical point in the spin-1 bilinear-biquadratic Heisenberg model on the honeycomb lattice
We have precisely determined the ground state phase diagram of the quantum
spin-1 bilinear-biquadratic Heisenberg model on the honeycomb lattice using the
tensor renormalization group method. We find that the ferromagnetic,
ferroquadrupolar, and a large part of the antiferromagnetic phases are stable
against quantum fluctuations. However, around the phase where the ground state
is antiferroquadrupolar ordered in the classical limit, quantum fluctuations
suppress completely all magnetic orders, leading to a plaquette order phase
which breaks the lattice symmetry but preserves the spin SU(2) symmetry. On the
evidence of our numerical results, the quantum phase transition between the
antiferromagnetic phase and the plaquette phase is found to be either a direct
second order or a very weak first order transition.Comment: 6 pages, 9 figures, published versio
Quantum transfer matrix method for one-dimensional disordered electronic systems
We develop a novel quantum transfer matrix method to study thermodynamic
properties of one-dimensional (1D) disordered electronic systems. It is shown
that the partition function can be expressed as a product of local
transfer matrices. We demonstrate this method by applying it to the 1D
disordered Anderson model. Thermodynamic quantities of this model are
calculated and discussed.Comment: 7 pages, 10 figure
A threshold dislocation dynamics method
The Merriman-Bence-Osher threshold dynamics method is an efficient algorithm
to simulate the motion by mean curvature. It has the advantages of being easy
to implement and with high efficiency. In this paper, we propose a threshold
dynamics method for dislocation dynamics in a slip plane, in which the spatial
operator is essentially an anisotropic fractional Laplacian. We show that this
threshold dislocation dynamics method is able to give { two correct leading
orders} in dislocation velocity, including both the local
curvature force and the nonlocal force due to the long-range stress
field generated by the dislocations as well as the force due to the applied
stress, where is the dislocation core size, { if the time step is
set to be . This generalizes the available result of
threshold dynamics with the corresponding fractional Laplacian, which is on the
leading order local curvature velocity under the isotropic
kernel.} We also propose a numerical method based on spatial variable
stretching to correct the mobility and to rescale the velocity for efficient
and accurate simulations, which can be applied generally to any threshold
dynamics method. We validate the proposed threshold dislocation dynamics method
by numerical simulations of various motions and interaction of dislocations.Comment: 35 pages, 13 figure
Practical decoy state method in quantum key distribution with heralded single photon source
We propose a practical decoy state method with heralded single photon source
for quantum key distribution (QKD). In the protocol, 3 intensities are used and
one can estimate the fraction of single-photon counts. The final key rate over
transmission distance is simulated under various parameter sets. Due to the
lower dark count than that of a coherent state, it is shown that a 3-intensity
decoy-state QKD with a heralded source can work for a longer distance than that
of a coherent state.Comment: 10 pages, 4 Postscript figure
Genetically Encoded Biosensors Reveal PKA Hyperphosphorylation on the Myofilaments in Rabbit Heart Failure
RATIONALE:
In heart failure, myofilament proteins display abnormal phosphorylation, which contributes to contractile dysfunction. The mechanisms underlying the dysregulation of protein phosphorylation on myofilaments is not clear.
OBJECTIVE:
This study aims to understand the mechanisms underlying altered phosphorylation of myofilament proteins in heart failure.
METHODS AND RESULTS:
We generate a novel genetically encoded protein kinase A (PKA) biosensor anchored onto the myofilaments in rabbit cardiac myocytes to examine PKA activity at the myofilaments in responses to adrenergic stimulation. We show that PKA activity is shifted from the sarcolemma to the myofilaments in hypertrophic failing rabbit myocytes. In particular, the increased PKA activity on the myofilaments is because of an enhanced β2 adrenergic receptor signal selectively directed to the myofilaments together with a reduced phosphodiesterase activity associated with the myofibrils. Mechanistically, the enhanced PKA activity on the myofilaments is associated with downregulation of caveolin-3 in the hypertrophic failing rabbit myocytes. Reintroduction of caveolin-3 in the failing myocytes is able to normalize the distribution of β2 adrenergic receptor signal by preventing PKA signal access to the myofilaments and to restore contractile response to adrenergic stimulation.
CONCLUSIONS:
In hypertrophic rabbit myocytes, selectively enhanced β2 adrenergic receptor signaling toward the myofilaments contributes to elevated PKA activity and PKA phosphorylation of myofilament proteins. Reintroduction of caveolin-3 is able to confine β2 adrenergic receptor signaling and restore myocyte contractility in response to β adrenergic stimulation
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