988 research outputs found
A Scanning Electron Microscopic Study of Chromosomes and Nuclei
The fine structure of metaphase chromosomes and nuclei were studied by scanning electron microscopy. A coiled-coil structure of chromosomes was suggested by hypotonically unravelled chromosomes observed under light microscope. But chromosome preparations made for the light microscopic studies were not adequate for detailed examination with scanning electron microscope. Surface-spread chromosomes revealed that they were composed of nodular, twisted looping fibers of about 300 Ã… in diameter. Surface-spread nuclei were also composed of fibers identical to the chromosome fibers
Full counting statistics of information content
We review connections between the cumulant generating function of full
counting statistics of particle number and the R\'enyi entanglement entropy. We
calculate these quantities based on the fermionic and bosonic path-integral
defined on multiple Keldysh contours. We relate the R\'enyi entropy with the
information generating function, from which the probability distribution
function of self-information is obtained in the nonequilibrium steady state. By
exploiting the distribution, we analyze the information content carried by a
single bosonic particle through a narrow-band quantum communication channel.
The ratio of the self-information content to the number of bosons fluctuates.
For a small boson occupation number, the average and the fluctuation of the
ratio are enhanced.Comment: 16 pages, 5 figure
Ab initio study of the formation of transparent carbon under pressure
A body-centered tetragonal carbon (bct-Carbon) allotrope has been predicted
to be a transparent carbon polymorph obtained under pressure. The structural
transition pathways from graphite to diamond, M-Carbon, and bct-Carbon are
simulated and the lowest activation barrier is found for the graphite-bct
transition. Furthermore, bct-Carbon has higher shear strength than diamond due
to its perpendicular graphene-like structure. Our results provide a possible
explanation for the formation of a transparent carbon allotrope via the cold
compression of graphite. We also verify that this allotrope is hard enough to
crack diamond.Comment: [email protected] or [email protected]
On-line Learning of an Unlearnable True Teacher through Mobile Ensemble Teachers
On-line learning of a hierarchical learning model is studied by a method from
statistical mechanics. In our model a student of a simple perceptron learns
from not a true teacher directly, but ensemble teachers who learn from the true
teacher with a perceptron learning rule. Since the true teacher and the
ensemble teachers are expressed as non-monotonic perceptron and simple ones,
respectively, the ensemble teachers go around the unlearnable true teacher with
the distance between them fixed in an asymptotic steady state. The
generalization performance of the student is shown to exceed that of the
ensemble teachers in a transient state, as was shown in similar
ensemble-teachers models. Further, it is found that moving the ensemble
teachers even in the steady state, in contrast to the fixed ensemble teachers,
is efficient for the performance of the student.Comment: 18 pages, 8 figure
Energy Dissipation and Fluctuation-Response in Driven Quantum Langevin Dynamics
Energy dissipation in a nonequilibrium steady state is studied in driven
quantum Langevin systems. We study energy dissipation flow to thermal
environment, and obtain a general formula for the average rate of energy
dissipation using an autocorrelation function for the system variable. This
leads to a general expression of the equality that connects the violation of
the fluctuation-response relation to the rate of energy dissipation, the
classical version of which was first studied by Harada and Sasa. We also point
out that the expression depends on coupling form between system and reservoir.Comment: 4 pages, 1 figur
Systematic search for low-enthalpy sp3 carbon using evolutionary metadynamics
We present a systematic search for low-energy metastable superhard carbon
allotropes by using the recently developed evolutionary metadynamics technique.
It is known that cold compression of graphite produces an allotrope at 15-20
GPa. Here we look for all low-enthalpy structures accessible from graphite.
Starting from 2H- or 3R-graphite and applying the pressure of 20 GPa, a large
variety of intermediate carbon allotropes were observed in evolutionary
metadynamics simulation. Our calculation not only found all the previous
proposed candidates for `superhard graphite', but also predicted two allotropes
(\emph{X}-carbon and \emph{Y}-carbon) showing novel 5+7 and 4+8 topologies.
These superhard carbon allotropes can be classified into five families based on
6 (diamond/lonsdaleite), 5+7 (\emph{M/W}-carbon), 5+7 (\emph{X}-carbon), 4+8
(bct C), and 4+8 (\emph{Y}-carbon) topologies. This study shows
evolutionary metadynamics is a powerful approach both to find the global minima
and systematically search for low-energy metastable phases reachable from given
starting materials.Comment: 6 pages, 7 figure
Spectroscopy of the spatially-extended Lya emission around a QSO at z=6.4
We have taken a deep, moderate-resolution Keck/Deimos spectra of QSO,
CFHQS2329, at z=6.4. At the wavelength of Lya, the spectrum shows a
spatially-extended component, which is significantly more extended than a
stellar spectrum, and also a continuum part of the spectrum. The restframe line
width of the extended component is 21+-7 A, and thus smaller than that of QSO
(52+-4 A), where they should be identical if the light is incomplete
subtraction of the QSO component. Therefore, these comparisons argue for the
detection of a spatially extended Lya nebulae around this QSO. This is the
first z>6 QSO that an extended Lya halo has been observed around. Careful
subtraction of the central QSO spectrum reveals a lower limit to the Lya
luminosity of (1.7+-0.1)x 10^43 erg s^-1. This emission may be from the
theoretically predicted infalling gas in the process of forming a primordial
galaxy that is ionized by a central QSO. On the other hand, if it is
photoionized by the host galaxy, an estimated star-formation rate of >3.0 Msun
yr^-1 is required.
If we assume the gas is virialized, we obtain dynamical mass estimate of
Mdyn=1.2x10^12 Msun. The derived MBH/Mhost is 2.1x10^-4, which is two orders
smaller than those from more massive z~6 QSOs, and places this galaxy in
accordance with the local M-sigma relation, in contrast to a previous claim on
the evolution of M-sigma relation at z~6. We do not claim evolution or
non-evolution of the M-sigma relation based on a single object, but our result
highlights the importance of investigating fainter QSOs at z~6.Comment: 5 pages, 5 figures. Accepted for publication in MNRAS. A minor
computational error fixe
Non-equilibrium Fluctuation Relations in a Quantum Coherent Conductor
We experimentally demonstrate the validity of non-equilibrium fluctuation
relations by using a quantum coherent conductor. In equilibrium the
fluctuation-dissipation relation leads to the correlation between current and
current noise at the conductor, namely, Johnson-Nyqusit relation. When the
conductor is voltage-biased so that the non-linear regime is entered, the
fluctuation theorem has predicted similar non-equilibrium fluctuation
relations, which hold true even when the Onsager-Casmir relations are broken in
magnetic fields. Our experiments qualitatively validate the predictions as the
first evidence of this theorem in the non-equilibrium quantum regime.
In the appendix, we give simple deduction of the higher order correlations
between the current and the current noise based on the fluctuation theorem.Comment: 4 pages, 4 figures with 1-page appendix
Aharonov-Bohm Effect for Parallel and T-shaped Double Quantum Dots
We investigate the Aharonov-Bohm (AB) effect for the double quantum dots in
the Kondo regime using the slave-boson mean-field approximation. In contrast to
the non-interacting case, where the AB oscillation generally has the period of
4 when the two-subring structure is formed via the interdot tunneling
, we find that the AB oscillation has the period of 2 in the Kondo
regime. Such effects appear for the double quantum dots close to the T-shaped
geometry even in the charge-fluctuation regime. These results follow from the
fact that the Kondo resonance is always fixed to the Fermi level irrespective
of the detailed structure of the bare dot-levels.Comment: 3 pages, 4 figures; minor change
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