14,281 research outputs found
DIRBE Minus 2MASS: Confirming the CIRB in 40 New Regions at 2.2 and 3.5 Microns
With the release of the 2MASS All-Sky Point Source Catalog, stellar fluxes
from 2MASS are used to remove the contribution due to Galactic stars from the
intensity measured by DIRBE in 40 new regions in the North and South Galactic
polar caps. After subtracting the interplanetary and Galactic foregrounds, a
consistent residual intensity of 14.69 +/- 4.49 kJy/sr at 2.2 microns is found.
Allowing for a constant calibration factor between the DIRBE 3.5 microns and
the 2MASS 2.2 microns fluxes, a similar analysis leaves a residual intensity of
15.62 +/- 3.34 kJy/sr at 3.5 microns. The intercepts of the DIRBE minus 2MASS
correlation at 1.25 microns show more scatter and are a smaller fraction of the
foreground, leading to a still weak limit on the CIRB of 8.88 +/- 6.26 kJy/sr
(1 sigma).Comment: 25 pages LaTeX, 10 figures, 5 tables; Version accepted by the ApJ.
Includes minor changes to the text including further discussion of zodiacal
light issues and the allowance for variable stars in computing uncertainties
in the stellar contribution to the DIRBE intensitie
Three-Dimensional Evolution of the Parker Instability under a Uniform Gravity
Using an isothermal MHD code, we have performed three-dimensional,
high-resolution simulations of the Parker instability. The initial equilibrium
system is composed of exponentially-decreasing isothermal gas and magnetic
field (along the azimuthal direction) under a uniform gravity. The evolution of
the instability can be divided into three phases: linear, nonlinear, and
relaxed. During the linear phase, the perturbations grow exponentially with a
preferred scale along the azimuthal direction but with smallest possible scale
along the radial direction, as predicted from linear analyses. During the
nonlinear phase, the growth of the instability is saturated and flow motion
becomes chaotic. Magnetic reconnection occurs, which allows gas to cross field
lines. This, in turn, results in the redistribution of gas and magnetic field.
The system approaches a new equilibrium in the relaxed phase, which is
different from the one seen in two-dimensional works. The structures formed
during the evolution are sheet-like or filamentary, whose shortest dimension is
radial. Their maximum density enhancement factor relative to the initial value
is less than 2. Since the radial dimension is too small and the density
enhancement is too low, it is difficult to regard the Parker instability alone
as a viable mechanism for the formation of giant molecular clouds.Comment: 8 pages of text, 4 figures (figure 2 in degraded gif format), to
appear in The Astrophysical Journal Letters, original quality figures
available via anonymous ftp at
ftp://ftp.msi.umn.edu/pub/users/twj/parker3d.uu or
ftp://canopus.chungnam.ac.kr/ryu/parker3d.u
Continuum-discretized coupled-channels method for four-body breakup reactions
Development of the method of CDCC (Continuum-Discretized Coupled-Channels)
from the level of three-body CDCC to that of four-body CDCC is reviewed.
Introduction of the pseudo-state method based on the Gaussian expansion method
for discretizing the continuum states of two-body and three-body projectiles
plays an essential role in the development. Furthermore, introduction of the
complex-range Gaussian basis functions is important to improve the CDCC for
nuclear breakup so as to accomplish that for Coulomb and nuclear breakup. A
successful application of the four-body CDCC to He+C scattering at
18 and 229.8 MeV is reported.Comment: Latex file of revtex4 class, 14 pages, 10 figures. A talk given at
the Workshop on Reaction Mechanisms for Rare Isotope Beams, Michigan State
University, March 9-12, 2005 (to appear in an AIP Conference Proceedings
Irradiation-energy Dependence on the Spectral Changes of Hydrous C-Type Asteroids Based on 4kev and 20kev He Exposure Experiments of Murchison Cm Chondrite
C-type asteroid 162173 Ryugu was observed by remote sensing apparatus onboard Hayabusa2 spacecraft and found to be very dark object whose reflectance is (1.60 0.15) % at 0.55m and showed a small 2.7m absorption band indicative of phyllosilicates. The optical navigation camera detected color variations of Ryugus surface in the wavelength range from 0.4 to 0.95m: Bluer spectra are ob-served at both poles and on the equatorial ridge, both of which are topographic highs and thus may be fresh material exposed by gradual erosion. On the other hand, many locations at middle-latitude areas exhibit redder and darker colors. Similar color variations are also detected in the near-infrared wavelength range. These observations suggest that a surface-correlated process is responsible for the color variation, most prob-ably from blue to red, but the mechanism for the change is not yet identified. Space weathering is one possible mechanism responsible for the color variation, but the spectral changes of C-type asteroids from space weathering are far from being fully understood. Past experimental studies using hydrous carbonaceous chondrites such as Murchison and Tagish Lake show that He exposure (simulating solar wind irradiation) changes spectra to bluer and brighter. Recently our He exposure experiments indicate that spectral changes depend on physical properties such as porosity of exposed material. In this study, we per-formed further He exposure experiments using Murchison CM chondrite in order to understand energy dependence on the spectral changes. We found that He energy is a critical parameter, as well as physical properties of the samples, that affects spectral changes of space weathering of hydrated C-type asteroids
Robustly Unstable Eigenmodes of the Magnetoshearing Instability in Accretion Disk
The stability of nonaxisymmetric perturbations in differentially rotating
astrophysical accretion disks is analyzed by fully incorporating the properties
of shear flows. We verify the presence of discrete unstable eigenmodes with
complex and pure imaginary eigenvalues, without any artificial disk edge
boundaries, unlike Ogilvie & Pringle(1996)'s claim. By developing the
mathematical theory of a non-self-adjoint system, we investigate the nonlocal
behavior of eigenmodes in the vicinity of Alfven singularities at
omega_D=omega_A, where omega_D is the Doppler-shifted wave frequency and
omega_A=k_// v_A is the Alfven frequency. The structure of the spectrum of
discrete eigenmodes is discussed and the magnetic field and wavenumber
dependence of the growth rate are obtained. Exponentially growing modes are
present even in a region where the local dispersion relation theory claims to
have stable eigenvalues. The velocity field created by an eigenmode is
obtained, which explains the anomalous angular momentum transport in the
nonlinear stage of this stability.Comment: 11pages, 11figures, to be published in ApJ. For associated eps files,
see http://dino.ph.utexas.edu/~knoguchi
On Witten multiple zeta-functions associated with semisimple Lie algebras IV
In our previous work, we established the theory of multi-variable Witten
zeta-functions, which are called the zeta-functions of root systems. We have
already considered the cases of types , , , and . In
this paper, we consider the case of -type. We define certain analogues of
Bernoulli polynomials of -type and study the generating functions of them
to determine the coefficients of Witten's volume formulas of -type. Next
we consider the meromorphic continuation of the zeta-function of -type and
determine its possible singularities. Finally, by using our previous method, we
give explicit functional relations for them which include Witten's volume
formulas.Comment: 22 pag
Single crystal growth and physical properties of a new uranium compound URhIn
We have grown the new uranium compound URhIn with the tetragonal
HoCoGa-type by the In self flux method. In contrast to the nonmagnetic
ground state of the isoelectronic analogue URhGa, URhIn is an
antiferromagnet with antiferromagnetic transition temperature = 98
K. The moderately large electronic specific heat coefficient = 50
mJ/Kmol demonstrates the contribution of 5 electrons to the conduction
band. On the other hand, magnetic susceptibility in the paramagnetic state
roughly follows a Curie-Weiss law with a paramagnetic effective moment
corresponding to a localized uranium ion. The crossover from localized to
itinerant character at low temperature may occur around the characteristic
temperature 150 K where the magnetic susceptibility and electrical resistivity
show a marked anomaly.Comment: 7 pages, 7 figure
Improvement of stabilizer based entanglement distillation protocols by encoding operators
This paper presents a method for enumerating all encoding operators in the
Clifford group for a given stabilizer. Furthermore, we classify encoding
operators into the equivalence classes such that EDPs (Entanglement
Distillation Protocol) constructed from encoding operators in the same
equivalence class have the same performance. By this classification, for a
given parameter, the number of candidates for good EDPs is significantly
reduced. As a result, we find the best EDP among EDPs constructed from [[4,2]]
stabilizer codes. This EDP has a better performance than previously known EDPs
over wide range of fidelity.Comment: 22 pages, 2 figures, In version 2, we enumerate all encoding
operators in the Clifford group, and fix the wrong classification of encoding
operators in version
Spontaneous Hall effect in chiral p-wave superconductor
In a chiral superconductor with broken time-reversal symmetry a ``spontaneous
Hall effect'' may be observed. We analyze this phenomenon by taking into
account the surface properties of a chiral superconductor. We identify two main
contributions to the spontaneous Hall effect. One contribution originates from
the Bernoulli (or Lorentz) force from spontaneous currents running along the
surfaces of the superconductor. The other contribution has a topological origin
and is related to the intrinsic angular momentum of Cooper pairs. The latter
can be described in terms of a Chern-Simons-like term in the low-energy field
theory of the superconductor and has some similarities with the quantum Hall
effect. The spontaneous Hall effect in a chiral superconductor is, however,
non-universal. Our analysis is based on three approaches to the problem: a
self-consistent solution of the Bogoliubov-de Gennes equation, a generalized
Ginzburg-Landau theory, and a hydrodynamic formulation. All three methods
consistently lead to the same conclusion that the spontaneous Hall resistance
of a two-dimensional superconducting Hall bar is of order h/(e k_F\lambda)^2,
where k_F is the Fermi wave vector and \lambda is the London penetration depth;
the Hall resistance is substantially suppressed from a quantum unit of
resistance. Experimental issues in measuring this effect are briefly discussed.Comment: 22 pages including 12 figure
Spectral properties of a spin-incoherent Luttinger Liquid
We present time-dependent density matrix renormalization group (DMRG) results
for strongly interacting one dimensional fermionic systems at finite
temperature. When interactions are strong the characteristic spin energy can be
greatly suppressed relative to the characteristic charge energy, allowing for
the possibility of spin-incoherent Luttinger liquid physics when the
temperature is high compared to the spin energy, but small compared to the
charge energy. Using DMRG we compute the spectral properties of the model
at arbitrary temperatures with respect to both spin and charge energies. We
study the full crossover from the Luttinger liquid regime to the
spin-incoherent regime,focusing on small , where the signatures of
spin-incoherent behavior are more manifest. Our method allows us to access the
analytically intractable regime where temperature is of the order of the spin
energy, . Our results should be helpful in the interpretation of
experiments that may be in the crossover regime, , and apply to
one-dimensional cold atomic gases where finite-temperature effects are
appreciable. The technique may also be used to guide the development of
analytical approximations for the crossover regime.Comment: 7 pages, 5 figure
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