39,327 research outputs found
Structure and kinematics of edge-on galaxy discs -- V. The dynamics of the stellar discs
In earlier papers in this series we determined the intrinsic stellar disc
kinematics of fifteen intermediate to late type edge-on spiral galaxies using a
dynamical modeling technique. From the photometry we find that intrinsically
more flattened discs tend to have a lower face-on central surface brightness
and a larger dynamica mass-to-light ratio. This observation suggests that at a
constant maximum rotational velocity lower surface brightness discs have
smaller vertical stellar velocity dispersions.Although the individual
uncertainties are large, we find from the dynamical modeling that at least
twelve discs are submaximal. The average disc contributes 534 percent to
the observed rotation at 2.2 disc scalelengths, with a 1 scatter of 15
percent. This percentage becomes somewhat lower when effects of finite disc
flattening and gravity by the dark halo and the gas are taken into account.
Since boxy and peanut-shaped bulges are probably associated with bars, the
result suggests that at 2.2 the submaximal nature of discs is
independent of barredness. The possibility remains that very high surface
brightness discs are maximal.We confirm that the radial stellar disc velocity
dispersion is related to the galaxy maximum rotational velocity. The scatter in
this relation appears to correlate with the disc
flattening, face-on central surface brightness and dynamical mass-to-light
ratio. Low surface brightness discs tend to be more flattened and have smaller
stellar velocity dispersions. The findings are consistent with the observed
correlation between disc flattening and dynamical mass-to-light ratio.Comment: Accepted for publication by Mon. Not. R.A.
Appearance of phloridzin-sensitive glucose transport is not controlled at mRNA level in rabbit jejunal enterocytes
Stable quantum memories with limited measurement
We demonstrate the existence of a finite temperature threshold for a 1D
stabilizer code under an error correcting protocol that requires only a
fraction of the syndrome measurements. Below the threshold temperature, encoded
states have exponentially long lifetimes, as demonstrated by numerical and
analytical arguments. We sketch how this algorithm generalizes to higher
dimensional stabilizer codes with string-like excitations, like the toric code.Comment: 11 Pages, 7 Figure
Relaxation dynamics of the toric code in contact with a thermal reservoir: Finite-size scaling in a low temperature regime
We present an analysis of the relaxation dynamics of finite-size topological
qubits in contact with a thermal bath. Using a continuous-time Monte Carlo
method, we explicitly compute the low-temperature nonequilibrium dynamics of
the toric code on finite lattices. In contrast to the size-independent bound
predicted for the toric code in the thermodynamic limit, we identify a
low-temperature regime on finite lattices below a size-dependent crossover
temperature with nontrivial finite-size and temperature scaling of the
relaxation time. We demonstrate how this nontrivial finite-size scaling is
governed by the scaling of topologically nontrivial two-dimensional classical
random walks. The transition out of this low-temperature regime defines a
dynamical finite-size crossover temperature that scales inversely with the log
of the system size, in agreement with a crossover temperature defined from
equilibrium properties. We find that both the finite-size and
finite-temperature scaling are stronger in the low-temperature regime than
above the crossover temperature. Since this finite-temperature scaling competes
with the scaling of the robustness to unitary perturbations, this analysis may
elucidate the scaling of memory lifetimes of possible physical realizations of
topological qubits.Comment: 14 Pages, 13 figure
What do gas-rich galaxies actually tell us about modified Newtonian dynamics?
It has recently been claimed that measurements of the baryonic Tully-Fisher
relation (BTFR), a power-law relationship between the observed baryonic masses
and outer rotation velocities of galaxies, support the predictions of modified
Newtonian dynamics for the slope and scatter in the relation, while challenging
the cold dark matter (CDM) paradigm. We investigate these claims, and find
that: 1) the scatter in the data used to determine the BTFR is in conflict with
observational uncertainties on the data; 2) these data do not make strong
distinctions regarding the best-fit BTFR parameters; 3) the literature contains
a wide variety of measurements of the BTFR, many of which are discrepant with
the recent results; and 4) the claimed CDM "prediction" for the BTFR is a gross
oversimplification of the complex galaxy-scale physics involved. We conclude
that the BTFR is currently untrustworthy as a test of CDM.Comment: 5 pages, 2 figures; minor revisions to match published versio
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