6,774 research outputs found
Preliminary experimental results of gas recycling subsystems except carbon dioxide concentration
Oxygen concentration and separation is an essential factor for air recycling in a controlled ecological life support system (CELSS). Furthermore, if the value of the plant assimilatory quotient is not coincident with that of the animal respiratory quotient, the recovery of oxygen from the concentrated CO2 through chemical methods will become necessary to balance the gas contents in a CELSS. Therefore, oxygen concentration and separation equipment using Salcomine and O2 recovery equipment, such as Sabatier and Bosch reactors, were experimentally developed and tested
Magnetic ground state of pyrochlore oxides close to metal-insulator boundary probed by muon spin rotation
Magnetism of ruthernium pyrochlore oxides A2Ru2O7 (A = Hg, Cd, Ca), whose
electronic properties within a localized ion picture are characterized by
non-degenerate t2g orbitals (Ru5+, 4d3) and thereby subject to geometrical
frustration, has been investigated by muon spin rotation/relaxation (muSR)
technique. The A cation (mostly divalent) was varied to examine the effect of
covalency (Hg > Cd > Ca) on their electronic property. In a sample with A = Hg
that exhibits a clear metal-insulator (MI) transition below >> 100 K (which is
associated with a weak structural transition), a nearly commensurate magnetic
order is observed to develop in accordance with the MI transition. Meanwhile,
in the case of A = Cd where the MI transition is suppressed to the level of
small anomaly in the resistivity, the local field distribution probed by muon
indicates emergence of a certain magnetic inhomogeneity below {\guillemotright}
30 K. Moreover, in Ca2Ru2O7 that remains metallic, we find a highly
inhomogeneous local magnetism below >>25 K that comes from randomly oriented Ru
moments and thus described as a "frozen spin liquid" state. The systematic
trend of increasing randomness and itinerant character with decreasing
covalency suggests close relationship between these two characters. As a
reference for the effect of orbital degeneracy and associated Jahn-Teller
instability, we examine a tetravalent ruthernium pyrochlore, Tl2Ru2O7 (Ru4+,
4d4), where the result of muSR indicates a non-magnetic ground state that is
consistent with the formation of the Haldane chains suggested by neutron
diffraction experiment.Comment: 12 pages, 13 figure
Rotating and infalling motion around the high-mass young stellar object Cepheus A-HW2 observed with the methanol maser at 6.7 GHz
We have measured the internal proper motions of the 6.7 GHz methanol masers
associated with Cepheus A (Cep A) HW2 using Very Long Baseline Interferometery
(VLBI) observations. We conducted three epochs of VLBI monitoring observations
of the 6.7 GHz methanol masers in Cep A-HW2 with the Japanese VLBI Network
(JVN) over the period between 2006-2008. In 2006, we were able to use
phase-referencing to measure the absolute coordinates of the maser emission
with an accuracy of a few milliarcseconds. We compared the maser distribution
with other molecular line observations that trace the rotating disk. We
measured the internal proper motions for 29 methanol maser spots, of which 19
were identified at all three epochs and the remaining ten at only two epochs.
The magnitude of proper motions ranged from 0.2 to 7.4 km/s, with an average of
3.1 km/s. Although there are large uncertainties in the observed internal
proper motions of the methanol maser spots in Cep A, they are well fitted by a
disk that includes both rotation and infall velocity components. The derived
rotation and infall velocities at the disk radius of 680 au are 0.5 +- 0.7 and
1.8 +- 0.7 km/s, respectively. Assuming that the modeled disk motion accurately
represents the accretion disk around the Cep A-HW2 high-mass YSO, we estimated
the mass infall rate to be 3 x 10^{-4} n_8 Msun/yr (n_8 is the gas volume
density in units of 10^{8} cm^{-3}). The combination of the estimated mass
infall rate and the magnitude of the fitted infall velocity suggests that Cep
A-HW2 is at an evolutionary phase of active gas accretion from the disk onto
the central high-mass YSO. The infall momentum rate is estimated to be 5 x
10^{-4} n_8 Msun/yr km/s, which is larger than the estimated stellar radiation
pressure of the HW2 object, supporting the hypothesis that this object is in an
active gas accretion phase.Comment: 16 pages, 6 figures, 5 tables, accepted for publication in Astronomy
& Astrophysic
An Efficient Algorithm for Enumerating Chordless Cycles and Chordless Paths
A chordless cycle (induced cycle) of a graph is a cycle without any
chord, meaning that there is no edge outside the cycle connecting two vertices
of the cycle. A chordless path is defined similarly. In this paper, we consider
the problems of enumerating chordless cycles/paths of a given graph
and propose algorithms taking time for each chordless cycle/path. In
the existing studies, the problems had not been deeply studied in the
theoretical computer science area, and no output polynomial time algorithm has
been proposed. Our experiments showed that the computation time of our
algorithms is constant per chordless cycle/path for non-dense random graphs and
real-world graphs. They also show that the number of chordless cycles is much
smaller than the number of cycles. We applied the algorithm to prediction of
NMR (Nuclear Magnetic Resonance) spectra, and increased the accuracy of the
prediction
Effects of Surface Soil Removal on Dynamics of Dissolved Inorganic Nitrogen in a Snow-Dominated Forest
To clarify the effect of vegetation and surface soil removal on dissolved inorganic nitrogen (N) dynamics in a snow-dominated forest soil in northern Japan, the seasonal fluctuation of N concentrations in soil solution and the annual flux of N in soil were investigated at a treated site (in which surface soil, including understory vegetation and organic and A horizons, was removed) and control sites from July 1998 to June 2000. Nitrate (NO3–) concentration in soil solution at the treated site was significantly higher than that of the control in the no-snow period, and it was decreased by dilution from melting snow. The annual net outputs of NO3– from soil at the treated site and control sites were 257 and –12 mmol m–2 year–1, and about 57% of the net output at the treated site occurred during the snowmelt period. NO3– was transported from the upper level to the lower level of soil via water movement during late autumn and winter, and it was retained in soil and leached by melt water in early spring. Removing vegetation and surface soil resulted in an increase in NO3– concentration of soil solution, and snowmelt strongly affected the NO3– leaching from treated soil and the NO3– restoration process in a snow-dominated region
Electronic and magnetic properties of substitutional Mn clusters in (Ga,Mn)As
The magnetization and hole distribution of Mn clusters in (Ga,Mn)As are
investigated by all-electron total energy calculations using the projector
augmented wave method within the density-functional formalism. It is found that
the energetically most favorable clusters consist of Mn atoms surrounding one
center As atom. As the Mn cluster grows the hole band at the Fermi level splits
increasingly and the hole distribution gets increasingly localized at the
center As atom. The hole distribution at large distances from the cluster does
not depend significantly on the cluster size. As a consequence, the spin-flip
energy differences of distant clusters are essentially independent of the
cluster size. The Curie temperature is estimated directly from these
spin-flip energies in the mean field approximation. When clusters are present
estimated values are around 250 K independent of Mn concentration whereas
for a uniform Mn distribution we estimate a of about 600 K.Comment: 7 pages, 5 figures, 2 tables; Revised manuscript 26. May 200
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