8,812 research outputs found
Super-Eddington accretion rates in Narrow Line Seyfert 1 galaxies
Using the BH masses deduced from the empirical relation of Kaspi et al.
(2000) and assuming that the optical luminosity is provided by the accretion
disc, we show that Narrow Line Seyfert Galaxies 1 (NLS1s) accrete at
super-Eddington rates, while their luminosity stays of the order of the
Eddington limit. We take into account the possibility of a non-viscous energy
release in the gravitationally unstable region of the disc. It leads to a
smaller accretion rate and to a redder continuum than a standard disc, which
agrees better with the observations. The observed bolometric luminosities
appear to saturate at a few times the Eddington luminosity for super-Eddington
accretion rates, as predicted by slim disc models. The accretion rate stays
always of the order of a few M/yr, indicating that the growing of the
BH is mass supply limited . Since the masses of the BH increases by one order
of magnitude in a few 10 years, it could explain why NLS1s appear to not
follow the same BH - bulge relation as other galaxies. NLS1s should thus play
an important role in shaping the mass function of local BHs. We discuss the
possibility that the masses could be systematically underestimated due to an
inclination effect, and we conclude that the accretion rates could thus be
strongly overestimated, but only in a small proportion of objects.Comment: 13 pages, 8 figures, accepted in A &
Experimental evidence of enhancement without the influence of spin fluctuations: NMR study on LaFeAsO_{1-x}H_x under a pressure of 3.0 GPa
The electron-doped high-transition-temperature (T_c) iron-based pnictide
superconductor LaFeAsO_{1-x}H_x has a unique phase diagram: superconducting
(SC) double domes are sandwiched by antiferromagnetic phases at ambient
pressure and they turn to a single dome with a maximum T_c that exceeds 45K at
a pressure of 3.0 GPa. We studied whether spin fluctuations are involved in
increasing T_c under a pressure of 3.0 GPa by using ^{75}As nuclear magnetic
resonance (NMR) technique. The ^{75}As-NMR results for the powder samples show
that T_c increases up to 48 K without the influence of spin fluctuations. The
fact indicates that spin fluctuations are not involved in raising T_c, which
implies that other factors, such as orbital degrees of freedom, may be
important for achieving a high T_c of almost 50 K.Comment: Correponding Author: Naoki Fujiwar
Aggregate Impacts of a Gift of Time
How would people spend additional time if confronted by permanent declines in market work? We examine the impacts of cuts in legislated standard hours that raised employers' overtime costs in Japan around 1990 and Korea in the early 2000s. Using time-diaries from before and after these shocks, we show that these shocks were effective – per-capita hours of market work declined discretely. The economy-wide drops in market work were reallocated solely to leisure and personal maintenance. In the absence of changing household technology a permanent time gift leads to no increase in time spent in household production by the average individual.time use, household production, demand shock, macroeconomic effects
Aggregate Impacts of a Gift of Time
How would people spend additional time if confronted by permanent declines in market work? We examine the impacts of cuts in legislated standard hours that raised employers’ overtime costs in Japan around 1990 and Korea in the early 2000s. Using time-diaries from before and after these shocks, we show that these shocks were effective—per-capita hours of market work declined discretely. The economy-wide drops in market work were reallocated solely to leisure and personal maintenance. In the absence of changing household technology a permanent time gift leads to no increase in time spent in household production by the average individual.
Temporal 1/f^\alpha Fluctuations from Fractal Magnetic Fields in Black Hole Accretion Flow
Rapid fluctuation with a frequency dependence of (with ) is characteristic of radiation from black-hole objects. Its
origin remains poorly understood. We examine the three-dimensional
magnetohydrodynamical (MHD) simulation data, finding that a magnetized
accretion disk exhibits both fluctuation (with )
and a fractal magnetic structure (with the fractal dimension of ).
The fractal field configuration leads reconnection events with a variety of
released energy and of duration, thereby producing fluctuations.Comment: 5 pages, 4 figures. Accepted for publication in PASJ Letters, vol. 52
No.1 (Feb 2000
Scalable Sparse Cox's Regression for Large-Scale Survival Data via Broken Adaptive Ridge
This paper develops a new scalable sparse Cox regression tool for sparse
high-dimensional massive sample size (sHDMSS) survival data. The method is a
local -penalized Cox regression via repeatedly performing reweighted
-penalized Cox regression. We show that the resulting estimator enjoys the
best of - and -penalized Cox regressions while overcoming their
limitations. Specifically, the estimator is selection consistent, oracle for
parameter estimation, and possesses a grouping property for highly correlated
covariates. Simulation results suggest that when the sample size is large, the
proposed method with pre-specified tuning parameters has a comparable or better
performance than some popular penalized regression methods. More importantly,
because the method naturally enables adaptation of efficient algorithms for
massive -penalized optimization and does not require costly data driven
tuning parameter selection, it has a significant computational advantage for
sHDMSS data, offering an average of 5-fold speedup over its closest competitor
in empirical studies
The classical origin of quantum affine algebra in squashed sigma models
We consider a quantum affine algebra realized in two-dimensional non-linear
sigma models with target space three-dimensional squashed sphere. Its affine
generators are explicitly constructed and the Poisson brackets are computed.
The defining relations of quantum affine algebra in the sense of the Drinfeld
first realization are satisfied at classical level. The relation to the
Drinfeld second realization is also discussed including higher conserved
charges. Finally we comment on a semiclassical limit of quantum affine algebra
at quantum level.Comment: 25 pages, 2 figure
Quantum critical behavior in heavily doped LaFeAsOH pnictide superconductors analyzed using nuclear magnetic resonance
We studied the quantum critical behavior of the second antiferromagnetic (AF)
phase in the heavily electron-doped high- pnictide, LaFeAsOH
by using As and H nuclear-magnetic-resonance (NMR) technique. In
the second AF phase, we observed a spatially modulated spin-density-wave-like
state up to =0.6 from the NMR spectral lineshape and detected a low-energy
excitation gap from the nuclear relaxation time of As. The
excitation gap closes at the AF quantum critical point (QCP) at . The superconducting (SC) phase in a lower-doping regime contacts the
second AF phase only at the AF QCP, and both phases are segregated from each
other. The absence of AF critical fluctuations and the enhancement of the
in-plane electric anisotropy are key factors for the development of
superconductivity.Comment: accepted in Phys. Rev.
- …