122 research outputs found
Iron and Nickel Isotopic Ratios in Presolar SiC Grains
We report the first Fe isotopic anomalies and the first Ni isotopic ratio measurements in presolar SiC grains of separate KJG from the Murchison meteorite. With NanoSIMS, we analyzed Fe and Ni in 37 X grains from Type II supernovae and 53 SiC grains of other types. The Ni/Fe and Co/Fe ratios in grains of all types are much higher than in the gas from which the grains are believed to have condensed. A majority of the X grains and a couple of mainstream grains contain Fe-rich subgrains. Most X grains have large excesses in 57Fe,61Ni, and 62Ni.60Ni excesses are small and the 54Fe/56Fe ratios of almost all X grains are normal. These isotopic compositions are best explained by mixing of material from the He/N zone of Type II supernovae with material from the He/C zone. The lack of any 54Fe excesses is puzzling in view of the fact that the Si/S zone, whose contribution resulted in the 28Si excesses in X grains, is very rich in 54Fe. It has yet to be seen whether elemental fractionation between Si and Fe is an explanation. The 57Fe deficits observed in a few X grains remain unexplained. In comparison to the X grains, fewer mainstream and AB grains have anomalies. Observed 62Ni excesses in some mainstream grains are larger than predicted for AGB stars of solar metallicity and are not accompanied by corresponding 61Ni excesses. A Y grain and a Z grain have excesses in 54Fe and 62Ni, but close to normal 57Fe/56Fe and 60,61Ni/58Ni ratios. These isotopic compositions are not expected for grains from low-metallicity AGB stars
The effect of aqueous alteration and metamorphism in the survival of presolar silicate grains in chondrites
Relatively small amounts (typically between 2-200 parts per million) of
presolar grains have been preserved in the matrices of chondritic meteorites.
The measured abundances of the different types of grains are highly variable
from one chondrite to another, but are higher in unequilibrated chondrites that
have experienced little or no aqueous alteration and/or metamorphic heating
than in processed meteorites. A general overview of the abundances measured in
presolar grains (particularly the recently identified presolar silicates)
contained in primitive chondrites is presented. Here we will focus on the most
primitive chondrite groups, as typically the highest measured abundances of
presolar grains occur in primitive chondrites that have experienced little
thermal metamorphism. Looking at the most aqueously altered chondrite groups,
we find a clear pattern of decreasing abundance of presolar silicate grains
with increasing level of aqueous alteration. We conclude that the measured
abundances of presolar grains in altered chondrites are strongly biased by
their peculiar histories. Scales quantifying the intensity of aqueous
alteration and shock metamorphism in chondrites could correlate with the
content in presolar silicates. To do this it would be required to infer the
degree of destruction or homogenization of presolar grains in the matrices of
primitive meteorites. To get an unbiased picture of the relative abundance of
presolar grains in the different regions of the protoplanetary disk where first
meteorites consolidated, future dedicated studies of primitive meteorites,
IDPs, and collected materials from sample-return missions (like e.g. the
planned Marco Polo) are urgently required.Comment: 15 pages, 3 figures, published in PASA as part of the Proceedings of
the 2008 Torino Conference "The Origin of the Elements Heavier than Iron
New stellar sources for high-density, presolar graphite grains
WepresentC,N,O,Si,Al-Mg,K,Ca,andTiisotopicanalyses ofsevenhigh-density(ORG1f, � � 2:02 2:04 gcm � 3 ) graphite grains from Orgueil with 12 C/ 13 C ratios smaller than 20. The presence of 44Ti in three of these grains indicates an origin in Type II supernovae (SNe). The 13 C excesses in these SNe grains, however, remain enigmatic. The remaining grains have extremely large Ca and Ti isotopic anomalies, some of which are much larger than those predicted for envelopes of asymptotic giant branch (AGB) stars. These anomalies in conjunction with low 12 C/ 13 C ratios can only be explained by pure nucleosynthetic He-shell components of AGB stars. Born-again AGB stars that experience a late He flash are able to explain the low 12 C/ 13 C ratios of some of the grains along with the presence of extreme enrichments in the Ca and Ti isotopes. This study indicates that high-density graphite grains havemultiple stellar sources: SNe and born-again AGB stars, in addition to the previously established low-metallicity AGB stars. Subject headingg dust, extinction — meteors, meteoroids — nuclear reactions, nucleosynthesis, abundances — stars: abundances — stars: AGB and post-AGB — supernovae: genera
APLIKASI PENJADWALAN RENTAL STUDIO MUSIK BERBASIS WEB STUDI KASUS STUDIO MUSIK MEGA TOP
Aplikasi Penjadwalan Rental Studio Musik Studi Kasus Studio Musik Mega Top pada era teknologi sekarang ini informasi merupaka hal yang sangat berharga dan penting bagi masyarakat. Secara umum masyarakat ingin mendapatkan informasi yang sesuai dengan kebutuhan. Kemudahan dalam mendapatkan informasi bisa di dapatkan melalui komputer yang sudah terintegrasi dengan sistem aplikasi maupun internet (Interconectivity Network). Sistem aplikasi dapat berupa program aplikasi yang di jalankan untuk mengolah data sesuai dengan kasus yang bersangkutan, pada tugas akhir ini akan di bahas tentang pembuatan program aplikasi untuk memudahkan pemesanan jadwal rental studio musik yang belum di pesan (booking) atau kosong. Pemesanan jadwal rental studio musik yang kosong di maksudkan untuk mempercepat proses usaha penyewaan studio musik. Kecepatan dan ketepatan sangat diperlukan karena tiga faktor yaitu: Studio musik tersebut mempunyai dua kamar studio. Studio musik tiap kamar menyediakan 7 shift per hari. Menyediakan penyewaan alat musik. Dari ketiga faktor tersebut maka di perlukan sebuah metode pemesanan jadwal secara optimal dengan mempertimbangkan waktu.
Kata kunci : Penjadwalan, Rental, Studio musik
SIMS Studies of Allende Projectiles Fired into Stardust-type Aluminum Foils at 6 km/s
We have explored the feasibility of C-, N-, and O-isotopic measurements by NanoSIMS and of elemental abundance determinations by TOF-SIMS on residues of Allende projectiles that impacted Stardust-type aluminum foils in the laboratory at 6 km/s. These investigations are part of a consortium study aimed at providing the foundation for the characterization of matter associated with micro-craters that were produced during the encounter of the Stardust space probe with comet 81P/Wild 2. Eleven experimental impact craters were studied by NanoSIMS and eighteen by TOF-SIMS. Crater sizes were between 3 and 190 microns. The NanoSIMS measurements have shown that the crater morphology has only a minor effect on spatial resolution and on instrumental mass fractionation. The achievable spatial resolution is always better than 200 nm, and C- and O-isotopic ratios can be measured with a precision of several percent at a scale of several 100 nm, the typical size of presolar grains. This clearly demonstrates that presolar matter, provided it survives the impact into the aluminum foil partly intact, is recognizable even if embedded in material of Solar System origin. TOF-SIMS studies are restricted to materials from the crater rim. The element ratios of the major rockforming elements in the Allende projectiles are well characterized by the TOF-SIMS measurements, indicating that fractionation of those elements during impact can be expected to be negligible. This permits information on the type of impactor material to be obtained. For any more detailed assignments to specific chondrite groups, however, information on the abundances of the light elements, especially C, is crucial
Solving the stellar 62Ni problem with AMS
An accurate knowledge of the neutron capture cross sections of 62,63Ni is
crucial since both isotopes take key positions which affect the whole reaction
flow in the weak s process up to A=90. No experimental value for the
63Ni(n,gamma) cross section exists so far, and until recently the experimental
values for 62Ni(n,gamma) at stellar temperatures (kT=30 keV) ranged between 12
and 37 mb. This latter discrepancy could now be solved by two activations with
following AMS using the GAMS setup at the Munich tandem accelerator which are
also in perfect agreement with a recent time-of-flight measurement. The
resulting (preliminary) Maxwellian cross section at kT=30 keV was determined to
be 30keV = 23.4 +/- 4.6 mb. Additionally, we have measured the
64Ni(gamma,n)63Ni cross section close to threshold. Photoactivations at 13.5
MeV, 11.4 MeV and 10.3 MeV were carried out with the ELBE accelerator at
Forschungszentrum Dresden-Rossendorf. A first AMS measurement of the sample
activated at 13.5 MeV revealed a cross section smaller by more than a factor of
2 compared to NON-SMOKER predictions.Comment: Proceedings of the 11th International Conference on Accelerator Mass
Spectrometry in Rome, Sept. 14-19, 2008; to be published in Nucl. Instr.
Meth.
Recommended from our members
SEM-EDS analyses of small craters in stardust aluminium foils: implications for the Wild-2 dust distribution
Implications for the Wild-2 dust distribution of the statistical results obtained by SEM-EDS from nearly 300 impact craters on aluminium foils of the Stardust sample tray assembly
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
New attempts to understand nanodiamond stardust
We report on a concerted effort aimed at understanding the origin and history
of the pre-solar nanodiamonds in meteorites including the astrophysical sources
of the observed isotopic abundance signatures. This includes measurement of
light elements by secondary ion mass spectrometry (SIMS), analysis of
additional heavy trace elements by accelerator mass spectrometry (AMS) and
dynamic calculations of r-process nucleosynthesis with updated nuclear
properties. Results obtained indicate: a) there is no evidence for the former
presence of now extinct 26Al and 44Ti in our diamond samples other than what
can be attributed to silicon carbide and other "impurities"; this does not
offer support for a supernova (SN) origin but neither does it negate it; b)
analysis by AMS of platinum in "bulk diamond" yields an overabundance of r-only
198Pt that at face value seems more consistent with the neutron burst than with
the separation model for the origin of heavy trace elements in the diamonds,
although this conclusion is not firm given analytical uncertainties; c) if the
Xe-H pattern was established by an unadulterated r-process, it must have been a
strong variant of the main r-process, which possibly could also account for the
new observations in platinum.Comment: Workshop on Astronomy with Radioactvities VII; Publications of the
Astronomical Society of Australia, accepte
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