667 research outputs found
Environmental mineralogical study of soils of the Csepel island (Hungary); Tracing the toxic heavy metals (V, Ni)
SzitakötĆk Ă©s tegzesek (Insecta: Odonata, Trichoptera) kutatĂĄsa Batanta szigeten (IndonĂ©zia, Nyugat-PĂĄpua) = Study of dragonflies and caddisflies (Insecta: Odonata, Trichoptera) on Batanta Island (Indonesia, West Papua)
Semigroups with operation-compatible Greenâs quasiorders
We call a semigroup on which the Greenâs quasiorder †J (†L, †R) is operation-compatible, a †J-compatible (†L-compatible, †R-compatible) semigroup. We study the classes of †J-compatible, †L-compatible and †R-compatible semigroups, using the smallest operation-compatible quasiorders containing Greenâs quasiorders as a tool. We prove a number of results, including the following. The class of †L-compatible (†R-compatible) semigroups is closed under taking homomorphic images. A regular periodic semigroup is †J-compatible if and only if it is a semilattice of simple semigroups. Every negatively orderable semigroup can be embedded into a negatively orderable †J-compatible semigroup
Environmental minerological study of soil of the Csepel Island (Hungary): tracing the toxic heavy metals (V, Ni)
Weakly coupled, antiparallel, totally asymmetric simple exclusion processes
We study a system composed of two parallel totally asymmetric simple
exclusion processes with open boundaries, where the particles move in the two
lanes in opposite directions and are allowed to jump to the other lane with
rates inversely proportional to the length of the system. Stationary density
profiles are determined and the phase diagram of the model is constructed in
the hydrodynamic limit, by solving the differential equations describing the
steady state of the system, analytically for vanishing total current and
numerically for nonzero total current. The system possesses phases with a
localized shock in the density profile in one of the lanes, similarly to
exclusion processes endowed with nonconserving kinetics in the bulk. Besides,
the system undergoes a discontinuous phase transition, where coherently moving
delocalized shocks emerge in both lanes and the fluctuation of the global
density is described by an unbiased random walk. This phenomenon is analogous
to the phase coexistence observed at the coexistence line of the totally
asymmetric simple exclusion process, however, as a consequence of the
interaction between lanes, the density profiles are deformed and in the case of
asymmetric lane change, the motion of the shocks is confined to a limited
domain.Comment: 14 pages, 15 figures, to appear in Phys. Rev.
The effect of detachment and attachment to a kink motion in the asymmetric simple exclusion process
We study the dynamics of a kink in a one-lane asymmetric simple exclusion
process with detachment and attachment of the particle at arbitrary sites. For
a system with one site of detachment and attachment we find that the kink is
trapped by the site, and the probability distribution of the kink position is
described by the overdumped Fokker-Planck equation with a V-shaped potential.
Our results can be applied to the motion of a kink in arbitrary number of sites
where detachment and attachment take place. When detachment and attachment take
place at every site, we confirm that the kink motion obeys the diffusion in a
harmonic potential. We compare our results with the Monte Carlo simulation, and
check the quantitative validity of our theoretical prediction of the diffusion
constant and the potential form.Comment: 10 pages, 5 figure
ALMA observations of the molecular gas in the debris disk of the 30 Myr old star HD 21997
The 30 Myr old A3-type star HD 21997 is one of the two known debris dust
disks having a measurable amount of cold molecular gas. With the goal of
understanding the physical state, origin, and evolution of the gas in young
debris disks, we obtained CO line observations with the Atacama Large
Millimeter/submillimeter Array (ALMA). Here we report on the detection of 12CO
and 13CO in the J=2-1 and J=3-2 transitions and C18O in the J=2-1 line. The gas
exhibits a Keplerian velocity curve, one of the few direct measurements of
Keplerian rotation in young debris disks. The measured CO brightness
distribution could be reproduced by a simple star+disk system, whose parameters
are r_in < 26 AU, r_out = 138 +/- 20 AU, M_*=1.8 +0.5 -0.2 M_Sun, and i = 32.6
+/- 3.1 degrees. The total CO mass, as calculated from the optically thin C18O
line, is about (4-8) x 10^-2 M_Earth, while the CO line ratios suggest a
radiation temperature on the order of 6-9 K. Comparing our results with those
obtained for the dust component of the HD 21997 disk from the ALMA continuum
observations by Mo\'or et al., we conclude that comparable amounts of CO gas
and dust are present in the disk. Interestingly, the gas and dust in the HD
21997 system are not co-located, indicating a dust-free inner gas disk within
55 AU of the star. We explore two possible scenarios for the origin of the gas.
A secondary origin, which involves gas production from colliding or active
planetesimals, would require unreasonably high gas production rates and would
not explain why the gas and dust are not co-located. We propose that HD 21997
is a hybrid system where secondary debris dust and primordial gas coexist. HD
21997, whose age exceeds both the model predictions for disk clearing and the
ages of the oldest T Tauri-like or transitional gas disks in the literature,
may be a key object linking the primordial and the debris phases of disk
evolution.Comment: 8 pages, 4 figures, accepted for publication in Ap
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