37 research outputs found
Optically Detected Structural Change in the N-Terminal Region of the Voltage-Sensor Domain
AbstractThe voltage-sensor domain (VSD) is a functional module that undergoes structural transitions in response to membrane potential changes and regulates its effectors, thereby playing a crucial role in amplifying and decoding membrane electrical signals. Ion-conductive pore and phosphoinositide phosphatase are the downstream effectors of voltage-gated channels and the voltage-sensing phosphatase, respectively. It is known that upon transition, the VSD generally acts on the region C-terminal to S4. However, whether the VSD also induces any structural changes in the N-terminal region of S1 has not been addressed directly. Here, we report the existence of such an N-terminal effect. We used two distinct optical reporters—one based on the Förster resonance energy transfer between a pair of fluorescent proteins, and the other based on fluorophore-labeled HaloTag—and studied the behavior of these reporters placed at the N-terminal end of the monomeric VSD derived from voltage-sensing phosphatase. We found that both of these reporters were affected by the VSD transition, generating voltage-dependent fluorescence readouts. We also observed that whereas the voltage dependencies of the N- and C-terminal effects appear to be tightly coupled, the local structural rearrangements reflect the way in which the VSD is loaded, demonstrating the flexible nature of the VSD
Repulsive potentials in dense neutron star matter and binding energy of in hypernuclei
The repulsive three-body force between the lambda () hyperon and
medium nucleons is a key element in solving the hyperon puzzle in neutron
stars. We investigate the binding energies of hyperon in hypernuclei
to verify the repulsive potentials from the chiral effective field
theory (EFT) employing the Skyrme Hartree-Fock method. We find that the
EFT potential with the three-body forces
reproduces the existing hypernuclear binding energy data, whereas the
binding energies are overestimated without the three-body force.
Additionally, we search for the parameter space of the potentials by
varying the Taylor coefficients of the potential and the effective
mass of at the saturation density. Our analysis demonstrates that the
parameter region consistent with the binding energy data spans a wide
range of the parameter space, including even more repulsive potentials than the
EFT prediction. We confirm that these strong repulsive
potentials suppress the presence of in the neutron star matter. We
found that the potentials repulsive at high densities are favored
when the depth of the potential at the saturation density,
, is , while
attractive ones are favored when . This
suggests that the future high-resolution data of hypernuclei could rule out the
scenario in which s appear through the precise determination of
within the accuracy of .Comment: 15 pages, 11 figures, 3 tables, figures updated and extended,
(Published in Physical Review C
Directed flow of in high-energy heavy-ion collisions and potential in dense nuclear matter
We investigate the sensitivity of the directed flow to the
potential in mid-central Au + Au collisions at
-- GeV. The potential obtained from the
chiral effective field theory (EFT) is used in a microscopic transport
model, a vector version of relativistic quantum molecular dynamics (RQMDv). We
find that the density-dependent potentials, obtained from the
EFT assuming weak momentum dependence of the potential, reproduce the
rapidity and the beam-energy dependence of the directed flow measured
by the STAR collaboration in the Beam Energy Scan program. Although the
directed flow is insensitive to the density dependence of the
potential, it is susceptible to the momentum dependence. We also show that a
hydrodynamics picture based on the blast-wave model predicts a similarity of
the proton, , and directed flows, but the directed flow of
baryons slightly deviates from other baryons. We also show that the
quark coalescence predicts different rapidity dependence of the directed flows
for hyperons. These investigations suggest that measurements of a wide range of
the rapidity dependence of the directed flow of hyperons may provide important
information about the properties of hot and dense matter created in high-energy
heavy-ion collisions.Comment: 11 pages, 9 figure
A Poincar\'e covariant cascade method for high-energy nuclear collisions
We present a Poincar\'e covariant cascade algorithm based on the constrained
Hamiltonian dynamics in an -dimensional phase space to simulate the
Boltzmann-type two-body collision term. We compare this covariant cascade
algorithm with traditional -dimensional phase-space cascade algorithms. To
validate the covariant cascade algorithm, we perform box calculations. We
examine the frame dependence of the algorithm in a one-dimensionally expanding
system as well as the compression stages of colliding two nuclei. We confirm
that our covariant cascade method is reliable to simulate high-energy nuclear
collisions. Furthermore, we present Lorentz-covariant equations of motion for
the -body system interacting via potentials, which can be efficiently solved
numerically.Comment: 13 pages, 10 figures, 1 table, typos fixe
Directed flow of Λ from heavy-ion collisions and hyperon puzzle of neutron stars
We examine the Λ potential from the chiral effective field theory (χEFT) via the Λ directed flow from heavy-ion collisions. We implement the Λ potential obtained from the χEFT in a vector potential version of relativistic quantum molecular dynamics. We find that the Λ potentials obtained from the χEFT assuming weak momentum dependence reproduce the Λ directed flow measured by the STAR collaboration in the Beam Energy Scan program. While the Λ directed flow is not very sensitive to the density dependence of the potential, the directed flow at large rapidities is susceptible to the momentum dependence. Thus understanding the directed flow of hyperons in a wide range of beam energy and rapidity is helpful in understanding hyperon potentials in dense matter