238 research outputs found
Evolution of oxygen isotopic composition in the inner solar nebula
Changes in the chemical and isotopic composition of the solar nebula with
time are reflected in the properties of different constituents that are
preserved in chondritic meteorites. CR carbonaceous chondrites are among the
most primitive of all chondrite types and must have preserved solar nebula
records largely unchanged. We have analyzed the oxygen and magnesium isotopes
in a range of the CR constituents of different formation temperatures and ages,
including refractory inclusions and chondrules of various types. The results
provide new constraints on the time variation of the oxygen isotopic
composition of the inner (<5 AU) solar nebula - the region where refractory
inclusions and chondrules most likely formed. A chronology based on the decay
of short-lived 26Al (t1/2 ~ 0.73 Ma) indicates that the inner solar nebula gas
was 16O-rich when refractory inclusions formed, but less than 0.8 Ma later, gas
in the inner solar nebula became 16O-poor and this state persisted at least
until CR chondrules formed ~1-2 Myr later. We suggest that the inner solar
nebula became 16O-poor because meter-size icy bodies, which were enriched in
17,18O due to isotopic self-shielding during the ultraviolet photo dissociation
of CO in the protosolar molecular cloud or protoplanetary disk, agglomerated
outside the snowline, drifted rapidly towards the Sun, and evaporated at the
snowline. This led to significant enrichment in 16O-depleted water, which then
spread through the inner solar system. Astronomical studies of the spatial
and/or temporal variations of water abundance in protoplanetary disks may
clarify these processes.Comment: 27 pages, 5 figure
Forsterite-Bearing Type B CAI with a Relict Eringaite-Bearing Ultra-Refractory CAI
Forsterite-bearing Type B (FoB) Ca,Al-rich
inclusions (CAIs) are a rare type of coarse-grained igneous CAIs
found almost exclusively in CV3 chondrites [1–5]. Here we
describe the mineralogy, petrography, and oxygen-isotope
compositions of a FoB CAI Al-2 from Allende containing a relict
eringaite-bearing ultra-refractory (UR) inclusion. Eringaite is a
Sc-rich garnet [Ca_3(Sc,Y,Ti)_2Si_3O_(12)] that has been recently
identified in a cluster of UR inclusion fragments within an
amoeboid olivine aggregate in Vigarano [6]
Intra-chondrite Elemental Variations of Fine-grained Matrices in Carbonaceous Chondrites.
第3回極域科学シンポジウム/第35回南極隕石シンポジウム 11月30日(金) 国立国語研究所 2階講
Variations of Chemical Composition of Matrices among Carbonaceous Chondrites.
第2回極域科学シンポジウム/第34回南極隕石シンポジウム 11月17日(木) 国立国語研究所 2階講
Two Generations of Hexagonal CaAl_2Si_2O_8 (Dmisteinbergite) in the Type B2 FUN CAI STP-1
Dmisteinbergite (dmist) is a metastable hexag-onal form of CaAl_2Si_2O_8, with space group of P6_3/mcm, a = 5.10Å and c = 14.72Å [1]. First occurrence of meteoritic dmist has been reported in the Allende Type B2 FUN CAI STP-1 [2], where it appears to have crystallized from a ^(16)O-rich (Δ^(17)O ~ −25‰) silicate melt via rapid cooling [3]. Here we report on an-other textural occurrence of dmist in STP-1 - ^(16)O-poor (Δ^(17)O ~ −2‰) fine-grained crystals in alteration zone of the inclusion
Why igneous wollastonite is so rare in CAIs
Primary wollastonite (wo) thought to have crystallized
from a liquid is quite rare in CAIs, having been reported in only two igneous
inclusions, White Angel and KT-1 [1, 2]. Both of these CAIs exhibit
significant mass fractionations in multiple elements and KT-1 is a FUN
inclusion, so it is highly desirable to place as many constraints as possible on
their formation. Since phase diagrams previously developed for CAIs do not
involve wo [3], we use literature data on wo-saturated and wo-free phase
diagrams in the system CaO-MgO-Al_2O_3-SiO_2 (CMAS) to establish a basic
framework for describing crystallization of wo-bearing CAIs
Budget impact of modern drugs for the treatment of schizophrenia: regional aspects
The article presents the results of comparative pharmacoeconomic analysis of treatment of schizophrenia with antipsychotics of the first and second generation in Khabarovsk territory. Regional «portrait» of the patient with schizophrenia is presented. Results of the analysis of experts’ preferences in prescription of psychotropic drugs in treatment of schizophrenia are given. Sociological, pharmacoeconomic and pharmacoepidemiologic methods of the analysis are chosen for carrying out present research. Analysis of «cost-effectiveness» and «budget impact» are used together for pharmacoeconomic method. The results of the conducted researches have allowed to develop the model of optimization of medicines’ provision for patients with schizophrenia taking into account the regional features
Thermal Processing of Silicate Dust in the Solar Nebula: Clues from Primitive Chondrite Matrices
The most abundant matrix minerals in chondritic meteorites, hydrated
phyllosilicates and ferrous olivine crystals, formed predominantly in asteroids
during fluid-assisted metamorphism. We infer that they formed from minerals
present in three less altered carbonaceous chondrites that have silicate
matrices composed largely of micrometer- and nanometer-sized grains of
crystalline forsterite, Mg2SiO4, and enstatite MgSiO3, and amorphous,
ferromagnesian silicate. Compositional and structural features of enstatite and
forsterite suggest that they formed as condensates that cooled below 1300 K at
\~1000 K/h. Most amorphous silicates are likely to be solar nebula condensates
also, as matrix, which is approximately solar in composition, is unlikely to be
a mixture of genetically unrelated materials with different compositions. Since
chondrules cooled at 10-1000 K/h, and matrix and chondrules are chemically
complementary, most matrix silicates probably formed close to chondrules in
transient heating events. Shock heating is favored as nebular shocks capable of
melting millimeter-sized aggregates vaporize dust. The crystalline and
amorphous silicates in the primitive chondrite matrices share many
characteristic features with silicates in chondritic interplanetary dust
particles suggesting that most of the crystalline silicates and possibly some
amorphous silicates in the interplanetary dust particles are also nebular
condensates. Except for small amounts of refractory oxides that formed with
Ca-Al-rich inclusions at the inner edge of the disk and presolar dust, most of
the crystalline silicate dust that accreted into chondritic asteroids and
long-period comets appears to have formed from shock heating at ~2-10 AU.
Forsterite crystals around young stars may have a similar origin.Comment: 16 page
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