948 research outputs found
Lattice QCD calculation of scattering length
We study s-wave pion-pion () scattering length in lattice QCD for
pion masses ranging from 330 MeV to 466 MeV. In the "Asqtad" improved staggered
fermion formulation, we calculate the four-point functions for isospin
I=0 and 2 channels, and use chiral perturbation theory at next-to-leading order
to extrapolate our simulation results. Extrapolating to the physical pion mass
gives the scattering lengths as and for isospin I=2 and 0 channels, respectively. Our lattice
simulation for scattering length in the I=0 channel is an exploratory
study, where we include the disconnected contribution, and our preliminary
result is near to its experimental value. These simulations are performed with
MILC 2+1 flavor gauge configurations at lattice spacing fm.Comment: Remove some typo
2,2-Dimethyl-5-{[(4-nitrophenyl)amino]methylidene}-1,3-dioxane-4,6-dione
In the title compound, C13H12N2O6, the dihedral angle between the benzene ring and the aminomethylene unit is 5.42 (16)°, while the angle between the aminomethylene unit and the dioxane ring is 3.06 (43)°. The dioxane ring shows a half-boat conformation, in which the C atom between the dioxane ring O atoms is 0.464 (10) Å out of the plane. An intramolecular N—H⋯O hydrogen bond stabilizes the molecular conformation. In the crystal, a three-dimensional framework is built up via intermolecular N—H⋯O hydrogen bonds
The juxtamembrane and carboxy-terminal domains of Arabidopsis PRK2 are critical for ROP-induced growth in pollen tubes.
Polarized growth of pollen tubes is a critical step for successful reproduction in angiosperms and is controlled by ROP GTPases. Spatiotemporal activation of ROP (Rho GTPases of plants) necessitates a complex and sophisticated regulatory system, in which guanine nucleotide exchange factors (RopGEFs) are key components. It was previously shown that a leucine-rich repeat receptor-like kinase, Arabidopsis pollen receptor kinase 2 (AtPRK2), interacted with RopGEF12 for its membrane recruitment. However, the mechanisms underlying AtPRK2-mediated ROP activation in vivo are yet to be defined. It is reported here that over-expression of AtPRK2 induced tube bulging that was accompanied by the ectopic localization of ROP-GTP and the ectopic distribution of actin microfilaments. Tube depolarization was also induced by a potentially kinase-dead mutant, AtPRK2K366R, suggesting that the over-expression effect of AtPRK2 did not require its kinase activity. By contrast, deletions of non-catalytic domains in AtPRK2, i.e. the juxtamembrane (JM) and carboxy-terminal (CT) domains, abolished its ability to affect tube polarization. Notably, AtPRK2K366R retained the ability to interact with RopGEF12, whereas AtPRK2 truncations of these non-catalytic domains did not. Lastly, it has been shown that the JM and CT domains of AtPRK2 were not only critical for its interaction with RopGEF12 but also critical for its distribution at the plasma membrane. These results thus provide further insight into pollen receptor kinase-mediated ROP activation during pollen tube growth
A Solvable Model for Discrete Time Crystal Enforced by Nonsymmorphic Dynamical Symmetry
Discrete time crystal is a class of nonequilibrium quantum systems exhibiting
subharmonic responses to external periodic driving. Here we propose a class of
discrete time crystals enforced by nonsymmorphic dynamical symmetry. We start
with a system with nonsymmorphic dynamical symmetry, in which the instantaneous
eigenstates become M\"obius twisted, hence doubling the period of the
instantaneous state. The exact solution of the time-dependent Schr\"odinger
equation shows that the system spontaneously exhibits a period extension
without undergoing quantum superposition states for a series of specifc
evolution frequencies or in the limit of long evolution period. Moreover, in
such case the system gains a {\pi} Berry phase after two periods' evolution.
Finally, we show that the subharmonic response is stable even when many-body
interactions are introduced, indicating a DTC phase in the thermodynamic limit.Comment: 5 pages, 4 figure
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