4,932 research outputs found
Recommended from our members
Political Circumstances and Political Choices: A Reading of the Fluctuations of Japanese "Modernity" in North American History-Writing, 1940-2000
E. Herbert Norman's Japan's Emergence as a Modern State put into operation the category of "modernity" for North American history-writing about Japan. After 1940, uses of "modernity" existed in tension with relative disuses of the category, and the category itself changed definition. This paper tracks the variable of "modernity" in relation to variables of political circumstances and political choices made by historians starting with the publication of Norman's book and continuing through the publication of Harry Harootunian's Things Seen and Unseen in 1988. It concludes with a brief consideration of scholarship of the 1990s
Unknotting numbers and triple point cancelling numbers of torus-covering knots
It is known that any surface knot can be transformed to an unknotted surface
knot or a surface knot which has a diagram with no triple points by a finite
number of 1-handle additions. The minimum number of such 1-handles is called
the unknotting number or the triple point cancelling number, respectively. In
this paper, we give upper bounds and lower bounds of unknotting numbers and
triple point cancelling numbers of torus-covering knots, which are surface
knots in the form of coverings over the standard torus . Upper bounds are
given by using -charts on presenting torus-covering knots, and lower
bounds are given by using quandle colorings and quandle cocycle invariants.Comment: 26 pages, 14 figures, added Corollary 1.7, to appear in J. Knot
Theory Ramification
Microlensing of collimated Gamma-Ray Burst afterglows
We investigate stellar microlensing of the collimated gamma-ray burst
afterglows. A spherical afterglow appears on the sky as a superluminally
expanding thin ring (``ring-like'' image), which is maximally amplified as it
crosses the lens. We find that the image of the collimated afterglow becomes
quite uniform (``disk-like'' image) after the jet break time (after the Lorentz
factor of the jet drops below the inverse of the jet opening angle).
Consequently, the amplification peak in the light curve after the break time is
lower and broader. Therefore detailed monitoring of the amplification history
will be able to test whether the afterglows are jets or not, i.e.,
``disk-like'' or not, if the lensing occurs after the break time. We also show
that some proper motion and polarization is expected, peaking around the
maximum amplification. The simultaneous detection of the proper motion and the
polarization will strengthen that the brightening of the light curve is due to
microlensing.Comment: 16 pages, 6 figures, accepted for publication in Ap
High frequency dynamics in liquid nickel: an IXS study
Owing to their large relatively thermal conductivity, peculiar,
non-hydrodynamic features are expected to characterize the acoustic-like
excitations observed in liquid metals. We report here an experimental study of
collective modes in molten nickel, a case of exceptional geophysical interest
for its relevance in Earth interior science. Our result shed light on
previously reported contrasting evidences: in the explored energy-momentum
region no deviation from the generalized hydrodynamic picture describing non
conductive fluids are observed. Implications for high frequency transport
properties in metallic fluids are discussed.Comment: 6 pages, 4 figures, to appear in "Journal of Chemical Physics
Episodic excursions of low-mass protostars on the Hertzsprung-Russell diagram
Following our recent work devoted to the effect of accretion on the
pre-main-sequence evolution of low-mass stars, we perform a detailed analysis
of episodic excursions of low-mass protostars in the Hertzsprung-Russell (H-R)
diagram triggered by strong mass accretion bursts typical of FU Orionis-type
objects (FUors). These excursions reveal themselves as sharp increases in the
stellar total luminosity and/or effective temperature of the protostar and can
last from hundreds to a few thousands of years, depending on the burst strength
and characteristics of the protostar. During the excursions, low-mass
protostars occupy the same part of the H-R diagram as young intermediate-mass
protostars in the quiescent phase of accretion. Moreover, the time spent by
low-mass protostars in these regions is on average a factor of several longer
than that spent by the intermediate-mass stars in quiescence. During the
excursions, low-mass protostars pass close to the position of most known FUors
in the H-R diagram, but owing to intrinsic ambiguity the model stellar
evolutionary tracks are unreliable in determining the FUor properties. We find
that the photospheric luminosity in the outburst state may dominate the
accretion luminosity already after a few years after the onset of the outburst,
meaning that the mass accretion rates of known FUors inferred from the
bolometric luminosity may be systematically overestimated, especially in the
fading phase.Comment: 15 pages, 12 figure
Structural and dynamical properties of liquid Si. An orbital-free molecular dynamics study
Several static and dynamic properties of liquid silicon near melting have
been determined from an orbital free {\em ab-initio} molecular dynamics
simulation. The calculated static structure is in good agreement with the
available X-ray and neutron diffraction data. The dynamical structure shows
collective density excitations with an associated dispersion relation which
closely follows recent experimental data. It is found that liquid silicon can
not sustain the propagation of shear waves which can be related to the power
spectrum of the velocity autocorrelation function. Accurate estimates have also
been obtained for several transport coefficients. The overall picture is that
the dynamic properties have many characteristics of the simple liquid metals
although some conspicuous differences have been found.Comment: 12 pages, 11 figure
Cosmological Growth History of Supermassive Black Holes and Demographics in the High-z Universe : Do Lyman-Break Galaxies Have Supermassive Black Holes?
We study the demographics of supermassive black holes (SMBHs) in the local
and high-z universe with hard X-ray luminosity functions (HXLFs) of AGNs.
First, we compare the mass accretion history at z>0 with optical luminosity
functions (OLFs) and that with HXLFs. We consider the constraints on parameters
of mass accretion (energy conversion efficiency and Eddington ratio) and
conclude that the constraints based on HXLFs are more adequate rather than that
based on OLFs. The sub-Eddington case is allowed only when we use HXLFs. Next,
we estimate the upper limit of the cumulative mass density of SMBHs at any
redshifts. For an application, we examine if Lyman-Break galaxies (LBGs) at z=3
already have SMBHs in their centers which is suggested by recent observations.
If most of LBGs already has massive SMBHs at z=3, the resultant mass density of
SMBHs at z=0 should exceed the observational estimate because such SMBHs should
further grow by accretion. We show that the special conditions should be met in
order that a large part of LBGs have SMBHs (for example, large energy
conversion efficiency and frequent mergers and/or direct formations at z>3).
The possibility that nearly all LBGs have SMBHs with large mass ratio, such as
M_BH/M_stellar > 0.005, is reliably ruled out.(abridged)Comment: 30 pages including 5 figures, accepted for publication in Ap
- …