392 research outputs found
Finite volume QCD at fixed topological charge
In finite volume the partition function of QCD with a given is a sum
of different topological sectors with a weight primarily determined by the
topological susceptibility. If a physical observable is evaluated only in a
fixed topological sector, the result deviates from the true expectation value
by an amount proportional to the inverse space-time volume 1/V. Using the
saddle point expansion, we derive formulas to express the correction due to the
fixed topological charge in terms of a 1/V expansion. Applying this formula, we
propose a class of methods to determine the topological susceptibility in QCD
from various correlation functions calculated in a fixed topological sector.Comment: 22pages, references adde
Effects of a Supermassive Black Hole Binary on a Nuclear Gas Disk
We study influence of a galactic central supermassive black hole (SMBH)
binary on gas dynamics and star formation activity in a nuclear gas disk by
making three-dimensional Tree+SPH simulations. Due to orbital motions of SMBHs,
there are various resonances between gas motion and the SMBH binary motion. We
have shown that these resonances create some characteristic structures of gas
in the nuclear gas disk, for examples, gas elongated or filament structures,
formation of gaseous spiral arms, and small gas disks around SMBHs. In these
gaseous dense regions, active star formations are induced. As the result, many
star burst regions are formed in the nuclear region.Comment: 19 pages, 11 figures, accepted for publication in Ap
Classical and quantum radiation from a moving charge in an expanding universe
We investigate photon emission from a moving particle in an expanding
universe. This process is analogous to the radiation from an accelerated charge
in the classical electromagnetic theory. Using the framework of quantum field
theory in curved spacetime, we demonstrate that the Wentzel-Kramers-Brillouin
(WKB) approximation leads to the Larmor formula for the rate of the radiation
energy from a moving charge in an expanding universe. Using exactly solvable
models in a radiation-dominated universe and in a Milne universe, we examine
the validity of the WKB formula. It is shown that the quantum effect suppresses
the radiation energy in comparison with the WKB formula.Comment: 16 pages, JCAP in pres
Quantum critical Bose gas in the two-dimensional limit in the honeycomb antiferromagnet YbCl under magnetic fields
BEC is a quantum phenomenon, where a macroscopic number of bosons occupy the
lowest energy state and acquire coherence at low temperatures. It is realized
not only in He and dilute atomic gases, but also in quantum magnets, where
hardcore bosons, introduced by the Matsubara-Matsuda transformation of spins,
condense. In 3D antiferromagnets, an XY-type long-range ordering (LRO) occurs
near a magnetic-field-induced transition to a fully polarized state (FP) and
has been successfully described as a BEC in the last few decades. An attractive
extension of the BEC in 3D magnets is to make their 2D analogue. For a strictly
2D system, BEC cannot take place due to the presence of a finite density of
states at zero energy, and a Berezinskii-Kosterlitz-Thouless (BKT) transition
may instead emerge. In a realistic quasi-2D magnet consisting of stacked 2D
magnets, a small but finite interlayer coupling stabilizes marginal LRO and
BEC, but such that 2D physics, including BKT fluctuations, is still expected to
dominate. A few systems were reported to show such 2D-limit BEC, but at very
high magnetic fields that are difficult to access. The honeycomb = 1/2
Heisenberg antiferromagnet YbCl with an intra-layer coupling 5 K
exhibits a transition to a FP state at a low in-plane magnetic field of = 5.93 T. Here, we demonstrate that the LRO right below is a
BEC in the 2D-limit stabilized by an extremely small interlayer coupling
of 10. At the quantum critical point Hs, we capture
2D-limit quantum fluctuations as the formation of a highly mobile, interacting
2D Bose gas in the dilute limit. A much-reduced effective boson-boson repulsion
Ueff as compared with that of a prototypical 3D system indicates the presence
of a logarithmic renormalization of interaction unique to 2D.Comment: 24 pages, 12 figure
Mixing model of Phobos' bulk elemental composition for the determination of its origin: Multivariate analysis of MMX/MEGANE data
The formation process of the two Martian moons, Phobos and Deimos, is still
debated with two main competing hypotheses: the capture of an asteroid or a
giant impact onto Mars. In order to reveal their origin, the Martian Moons
eXploration (MMX) mission by Japan Aerospace Exploration Agency (JAXA) plans to
measure Phobos' elemental composition by a gamma-ray and neutron spectrometer
called MEGANE. This study provides a model of Phobos' bulk elemental
composition, assuming the two formation hypotheses. Using the mixing model, we
established a MEGANE data analysis flow to discriminate between the formation
hypotheses by multivariate analysis. The mixing model expresses the composition
of Phobos in 6 key lithophile elements that will be measured by MEGANE (Fe, Si,
O, Ca, Mg, and Th) as a linear mixing of two mixing components: material from
Mars and material from an asteroid as represented by primitive meteorite
compositions. The inversion calculation includes consideration of MEGANE's
measurement errors () and derives the mixing ratio for a given Phobos
composition, based on which the formation hypotheses are judged. For at least
65\% of the modeled compositions, MEGANE measurements will determine the origin
uniquely ( = 30\%), and this increases from 74 to 87\% as decreases
from 20 to 10\%. Although the discrimination performance depends on , the
current operation plan for MEGANE predicts an instrument performance for
of 20--30\%, resulting in ~70\% discrimination between the original hypotheses.
MEGANE observations can also enable the determination of the asteroid type of
the captured body or the impactor. The addition of other measurements, such as
MEGANE's measurements of the volatile element K, as well as observations by
other MMX remote sensing instruments, will also contribute to the MMX mission's
goal to constrain the origin of Phobos.Comment: 34 pages, 7 figures, accepted for publication in Icaru
Two-Dimensional Dynamic Fusion for Continuous Authentication
Continuous authentication has been widely studied to provide high security
and usability for mobile devices by continuously monitoring and authenticating
users. Recent studies adopt multibiometric fusion for continuous authentication
to provide high accuracy even when some of captured biometric data are of a low
quality. However, existing continuous fusion approaches are resource-heavy as
they rely on all classifiers being activated all the time and may not be
suitable for mobile devices.
In this paper, we propose a new approach to multibiometric continuous
authentication: two-dimensional dynamic fusion. Our key insight is that
multibiometric continuous authentication calculates two-dimensional matching
scores over classifiers and over time. Based on this, we dynamically select a
set of classifiers based on the context in which authentication is taking
place, and fuse matching scores by multi-classifier fusion and multi-sample
fusion. Through experimental evaluation, we show that our approach provides a
better balance between resource usage and accuracy than the existing fusion
methods. In particular, we show that our approach provides higher accuracy than
the existing methods with the same number of score calculations by adopting
multi-sample fusion.Comment: Accepted to IJCB'2
Si and Fe depletion in Galactic star-forming regions observed by the Spitzer Space Telescope
We report the results of the mid-infrared spectroscopy of 14 Galactic
star-forming regions with the high-resolution modules of the Infrared
Spectrograph (IRS) on board the Spitzer Space Telescope. We detected [SiII]
35um, [FeII] 26um, and [FeIII] 23um as well as [SIII] 33um and H2 S(0) 28um
emission lines. Using the intensity of [NII] 122um or 205um and [OI] 146um or
63um reported by previous observations in four regions, we derived the ionic
abundance Si+/N+ and Fe+/N+ in the ionized gas and Si+/O0 and Fe+/O0 in the
photodissociation gas. For all the targets, we derived the ionic abundance of
Si+/S2+ and Fe2+/S2+ for the ionized gas. Based on photodissociation and HII
region models the gas-phase Si and Fe abundance are suggested to be 3-100% and
<8% of the solar abundance, respectively, for the ionized gas and 16-100% and
2-22% of the solar abundance, respectively, for the photodissociation region
gas. Since the [FeII] 26um and [FeIII] 23um emissions are weak, the high
sensitivity of the IRS enables to derive the gas-phase Fe abundance widely in
star-forming regions. The derived gas-phase Si abundance is much larger than
that in cool interstellar clouds and that of Fe. The present study indicates
that 3-100% of Si atoms and <22% of Fe atoms are included in dust grains which
are destroyed easily in HII regions, probably by the UV radiation. We discuss
possible mechanisms to account for the observed trend; mantles which are
photodesorbed by UV photons, organometallic complexes, or small grains.Comment: 43 pages with 7 figures, accepted in Astrophysical Journa
Simulation of propofol anaesthesia for intracranial decompression using brain hypothermia treatment
<p>Abstract</p> <p>Background</p> <p>Although propofol is commonly used for general anaesthesia of normothermic patients in clinical practice, little information is available in the literature regarding the use of propofol anaesthesia for intracranial decompression using brain hypothermia treatment. A novel propofol anaesthesia scheme is proposed that should promote such clinical application and improve understanding of the principles of using propofol anaesthesia for hypothermic intracranial decompression.</p> <p>Methods</p> <p>Theoretical analysis was carried out using a previously-developed integrative model of the thermoregulatory, hemodynamic and pharmacokinetic subsystems. Propofol kinetics is described using a framework similar to that of this model and combined with the thermoregulation subsystem through the pharmacodynamic relationship between the blood propofol concentration and the thermoregulatory threshold. A propofol anaesthesia scheme for hypothermic intracranial decompression was simulated using the integrative model.</p> <p>Results</p> <p>Compared to the empirical anaesthesia scheme, the proposed anaesthesia scheme can reduce the required propofol dosage by more than 18%.</p> <p>Conclusion</p> <p>The integrative model of the thermoregulatory, hemodynamic and pharmacokinetic subsystems is effective in analyzing the use of propofol anaesthesia for hypothermic intracranial decompression. This propofol infusion scheme appears to be more appropriate for clinical application than the empirical one.</p
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