763 research outputs found
Diverse features of dust particles and their aggregates inferred from experimental nanoparticles
Nanometre- to micrometre-sized solid dust particles play a vital role in star
and planet formations. Despite of their importance, however, our understanding
of physical and chemical properties of dust particles is still provisional. We
have conducted a condensation experiment of the vapour generated from a solid
starting material having nearly cosmic proportions in elements. A laser flash
heating and subsequent cooling has produced a diverse type of nanoparticles
simultaneously. Here we introduce four types of nanoparticles as potential dust
particles in space: amorphous silicate nanoparticles (type S); core/mantle
nanoparticles with iron or hydrogenised-iron core and amorphous silicate mantle
(type IS); silicon oxycarbide nanoparticles and hydrogenised silicon oxycarbide
nanoparticles (type SiOC); and carbon nanoparticles (type C), all produced in a
single heating-cooling event. Type IS and SiOC nanoparticles are new for
potential astrophysical dust. The nanoparticles are aggregated to a wide
variety of structures, from compact, fluffy, and networked. A simultaneous
formation of nanoparticles, which are diverse in chemistry, shape, and
structure, prompts a re-evaluation of astrophysical dust particlesComment: 9 pages, 3 figure
Finite-temperature phase structures of hard-core bosons in an optical lattice with an effective magnetic field
We study finite-temperature phase structures of hard-core bosons in a
two-dimensional optical lattice subject to an effective magnetic field by
employing the gauged CP model. Based on the extensive Monte Carlo
simulations, we study their phase structures at finite temperatures for several
values of the magnetic flux per plaquette of the lattice and mean particle
density. Despite the presence of the particle number fluctuation, the
thermodynamic properties are qualitatively similar to those of the frustrated
XY model with only the phase as a dynamical variable. This suggests that cold
atom simulators of the frustrated XY model are available irrespective of the
particle filling at each site.Comment: 13 pages, 9 figure
Sulfuric acid as a cryofluid and oxygen isotope reservoir of planetesimals
The Sun exhibits a depletion in O relative to O by 6 %
compared to the Earth and Moon. The origin of such a non-mass-dependent
isotope fractionation has been extensively debated since the
three-isotope-analysis became available in 1970's. Self-shielding
of CO molecules against UV photons in the solar system's parent molecular cloud
has been suggested as a source of the non-mass-dependent effect, in which a
O-enriched oxygen was trapped by ice and selectively incorporated as
water into planet-forming materials. The truth is that the Earth-Moon and
other planetary objects deviate positively from the Sun by ~6 % in their
isotopic compositions. A stunning exception is the magnetite/sulfide
symplectite found in Acfer 094 meteorite, which shows 24 % enrichment in
O relative to the Sun. Water does not explain the enrichment
this high. Here we show that the SO and SO molecules in the molecular
cloud, ~106 % enriched in O relative to the Sun, evolved through the
protoplanetary disk and planetesimal stages to become a sulfuric acid, 24 %
enriched in O. The sulfuric acid provided a cryofluid environment in
the planetesimal and by itself reacted with ferric iron to form an amorphous
ferric-hydroxysulfate-hydrate, which eventually decomposed into the symplectite
by shock. We indicate that the Acfer-094 symplectite and its progenitor,
sulfuric acid, is strongly coupled with the material evolution in the solar
system since the days of our molecular cloud.Comment: 19 pages, 3 figure
Origin of long-range order in a two-dimensional nonequilibrium system under laminar flows
We study long-range order in two dimensions where an order parameter is
advected by linear laminar flows. The linear laminar flows include three
classes: rotational, shear, and elongational flows. Under these flows, we
analyze an ordered state of the scalar model in the large- limit. We
show that the stability of the ordered state depends on the flow pattern; the
shear and elongational flows stabilize but the rotational flow does not. We
discuss a physical interpretation of our results based on interaction
representation in quantum mechanics. The origin of the long-range order is
interpreted from the advection of wavenumbers along the streamlines and its
stretching effect stabilizes the order.Comment: 6+5pages, 3+1figure
- …