1,164 research outputs found
Photophoretic Strength on Chondrules. 2. Experiment
Photophoretic motion can transport illuminated particles in protoplanetary
disks. In a previous paper we focused on the modeling of steady state
photophoretic forces based on the compositions derived from tomography and heat
transfer. Here, we present microgravity experiments which deviate significantly
from the steady state calculations of the first paper. The experiments on
average show a significantly smaller force than predicted with a large
variation in absolute photophoretic force and in the direction of motion with
respect to the illumination. Time-dependent modeling of photophoretic forces
for heat-up and rotation show that the variations in strength and direction
observed can be well explained by the particle reorientation in the limited
experiment time of a drop tower experiment. In protoplanetary disks, random
rotation subsides due to gas friction on short timescales and the results of
our earlier paper hold. Rotation has a significant influence in short duration
laboratory studies. Observing particle motion and rotation under the influence
of photophoresis can be considered as a basic laboratory analog experiment to
Yarkovsky and YORP effects
Abundance, Major Element Composition and Size of Components and Matrix in CV, CO and Acfer 094 Chondrites
The relative abundances and chemical compositions of the macroscopic
components or "inclusions" (chondrules and refractory inclusions) and
fine-grained mineral matrix in chondritic meteorites provide constraints on
astrophysical theories of inclusion formation and chondrite accretion. We
present new techniques for analysis of low count per pixel Si, Mg, Ca, Al, Ti
and Fe x-ray intensity maps of rock sections, and apply them to large areas of
CO and CV chondrites, and the ungrouped Acfer 094 chondrite. For many thousands
of manually segmented and type-identified inclusions, we are able to assess,
pixel-by-pixel, the major element content of each inclusion. We quantify the
total fraction of those elements accounted for by various types of inclusion
and matrix. Among CO chondrites, both matrix and inclusion Mg to Si ratios
approach the solar (and bulk CO) ratio with increasing petrologic grade, but Si
remains enriched in inclusions relative to matrix. The oxidized CV chondrites
with higher matrix-inclusion ratios exhibit more severe aqueous alteration
(oxidation), and their excess matrix accounts for their higher porosity
relative to reduced CV chondrites. Porosity could accommodate an original ice
component of matrix as the direct cause of local alteration of oxidized CV
chondrites. We confirm that major element abundances among inclusions differ
greatly, across a wide range of CO and CV chondrites. These abundances in all
cases add up to near-chondritic (solar) bulk abundance ratios in these
chondrites, despite wide variations in matrix-inclusion ratios and inclusion
sizes: chondrite components are complementary. This "complementarity" provides
a robust meteoritic constraint for astrophysical disk models
Shock compaction heating and collisional processes in the production of type 3 ordinary chondrites: Lessons from the (nearly) unique L3 chondrite melt breccia Northwest Africa 8709*
Northwest Africa (NWA) 8709 is a rare example of a type 3 ordinary chondrite melt breccia and provides critical information for the shock compaction histories of chondrites. An L3 protolith for NWA 8709 is inferred on the basis of oxygen isotope composition, elemental composition, diverse mineral chemistry, and overall texture. NWA 8709 is among the most strongly shocked type 3 chondrites known, and experienced complete melting of the matrix and partial melting of chondrules. Unmelted phases underwent FeO reduction and partial homogenization, with reduction possibly occurring by reaction of olivine and low‐Ca pyroxene with an S‐bearing gas that was produced by vaporization. Chondrules and metal grains became foliated by uniaxial compaction, and during compression, chondrules and fragments became attached to form larger clumps. This process, and possibly also melt incorporation into chondrules to cause “inflation,” may have contributed to anomalously large chondrule sizes in NWA 8709. The melt breccia character is attributed to strong shock affecting a porous precursor. Data‐model comparisons suggest that a precursor with 23% porosity that was impacted by a 3 km/s projectile could have produced the meteorite. The rarity of other type 3 ordinary chondrite melt breccias implies that the immediate precursors to such chondrites were lower in porosity than the NWA 8709 precursor, or experienced weaker shocks. Altogether, the data imply a predominantly “quiet” dynamical environment to form most type 3 ordinary chondrites, with compaction occurring in a series of relatively weak shock events
An acidic microenvironment in Tuberculosis increases extracellular matrix degradation by regulating macrophage inflammatory responses
Mycobacterium tuberculosis (M.tb) infection causes marked tissue inflammation leading to lung destruction and morbidity. The inflammatory extracellular microenvironment is acidic, however the effect of this acidosis on the immune response to M.tb is unknown. Using RNA-seq we show that acidosis produces system level transcriptional change in M.tb infected human macrophages regulating almost 4000 genes. Acidosis specifically upregulated extracellular matrix (ECM) degradation pathways with increased expression of Matrix metalloproteinases (MMPs) which mediate lung destruction in Tuberculosis. Macrophage MMP-1 and -3 secretion was increased by acidosis in a cellular model. Acidosis markedly suppresses several cytokines central to control of M.tb infection including TNF-α and IFN-γ. Murine studies demonstrated expression of known acidosis signaling G-protein coupled receptors OGR-1 and TDAG-8 in Tuberculosis which are shown to mediate the immune effects of decreased pH. Receptors were then demonstrated to be expressed in patients with TB lymphadenitis. Collectively, our findings show that an acidic microenvironment modulates immune function to reduce protective inflammatory responses and increase extracellular matrix degradation in Tuberculosis. Acidosis receptors are therefore potential targets for host directed therapy in patients
Strain-dependent host transcriptional responses to toxoplasma infection are largely conserved in mammalian and avian hosts
Toxoplasma gondii has a remarkable ability to infect an enormous variety of mammalian and avian species. Given this, it is surprising that three strains (Types I/II/III) account for the majority of isolates from Europe/North America. The selective pressures that have driven the emergence of these particular strains, however, remain enigmatic. We hypothesized that strain selection might be partially driven by adaptation of strains for mammalian versus avian hosts. To test this, we examine in vitro, strain-dependent host responses in fibroblasts of a representative avian host, the chicken (Gallus gallus). Using gene expression profiling of infected chicken embryonic fibroblasts and pathway analysis to assess host response, we show here that chicken cells respond with distinct transcriptional profiles upon infection with Type II versus III strains that are reminiscent of profiles observed in mammalian cells. To identify the parasite drivers of these differences, chicken fibroblasts were infected with individual F1 progeny of a Type II x III cross and host gene expression was assessed for each by microarray. QTL mapping of transcriptional differences suggested, and deletion strains confirmed, that, as in mammalian cells, the polymorphic rhoptry kinase ROP16 is the major driver of strain-specific responses. We originally hypothesized that comparing avian versus mammalian host response might reveal an inversion in parasite strain-dependent phenotypes; specifically, for polymorphic effectors like ROP16, we hypothesized that the allele with most activity in mammalian cells might be less active in avian cells. Instead, we found that activity of ROP16 alleles appears to be conserved across host species; moreover, additional parasite loci that were previously mapped for strain-specific effects on mammalian response showed similar strain-specific effects in chicken cells. These results indicate that if different hosts select for different parasite genotypes, the selection operates downstream of the signaling occurring during the beginning of the host's immune response. © 2011 Ong et al
Tracing chemical evolution over the extent of the Milky Way's Disk with APOGEE Red Clump Stars
We employ the first two years of data from the near-infrared, high-resolution
SDSS-III/APOGEE spectroscopic survey to investigate the distribution of
metallicity and alpha-element abundances of stars over a large part of the
Milky Way disk. Using a sample of ~10,000 kinematically-unbiased red-clump
stars with ~5% distance accuracy as tracers, the [alpha/Fe] vs. [Fe/H]
distribution of this sample exhibits a bimodality in [alpha/Fe] at intermediate
metallicities, -0.9<[Fe/H]<-0.2, but at higher metallicities ([Fe/H]=+0.2) the
two sequences smoothly merge. We investigate the effects of the APOGEE
selection function and volume filling fraction and find that these have little
qualitative impact on the alpha-element abundance patterns. The described
abundance pattern is found throughout the range 5<R<11 kpc and 0<|Z|<2 kpc
across the Galaxy. The [alpha/Fe] trend of the high-alpha sequence is
surprisingly constant throughout the Galaxy, with little variation from region
to region (~10%). Using simple galactic chemical evolution models we derive an
average star formation efficiency (SFE) in the high-alpha sequence of ~4.5E-10
1/yr, which is quite close to the nearly-constant value found in
molecular-gas-dominated regions of nearby spirals. This result suggests that
the early evolution of the Milky Way disk was characterized by stars that
shared a similar star formation history and were formed in a well-mixed,
turbulent, and molecular-dominated ISM with a gas consumption timescale (1/SFE)
of ~2 Gyr. Finally, while the two alpha-element sequences in the inner Galaxy
can be explained by a single chemical evolutionary track this cannot hold in
the outer Galaxy, requiring instead a mix of two or more populations with
distinct enrichment histories.Comment: 18 pages, 17 figures. Accepted for publication in Ap
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