Dense Particle Clouds in Laboratory Experiments in Context of Drafting and Streaming Instability

The streaming instability, as an example of instabilities driven by particle feedback on a gas flow, has been proven to have a major role in controlling the formation of planetesimals. Here, we present experiments to approach this situation in the laboratory for particles in the Knudsen flow regime. In these experiments, we observe a particle cloud trapped for about 30 s in a rotating system under Earth's gravity. For average dust-to-gas ratios up to 0.08, particles behave like individual test particles. Their sedimentation speed is identical to that of a single free-falling particle, even in locally denser regions. However, for higher dust-to-gas ratios, the motion of particles becomes sensitive to clumping. Particles in locally denser regions now sediment faster. Their sedimentation speed then depends linearly on the overall dust-to-gas ratio. This clearly shows a transition from tracerlike behavior to collective behavior. Beyond these findings, these types of experiments can now be used as a gauge to test the particle feedback models in astrophysical hydrocodes which are currently used for numerical simulations of streaming instabilities

Mutations in Drosophila Greatwall/Scant Reveal Its Roles in Mitosis and Meiosis and Interdependence with Polo Kinase

Polo is a conserved kinase that coordinates many events of mitosis and meiosis, but how it is regulated remains unclear. Drosophila females having only one wild-type allele of the polo kinase gene and the dominant Scant mutation produce embryos in which one of the centrosomes detaches from the nuclear envelope in late prophase. We show that Scant creates a hyperactive form of Greatwall (Gwl) with altered specificity in vitro, another protein kinase recently implicated in mitotic entry in Drosophila and Xenopus. Excess Gwl activity in embryos causes developmental failure that can be rescued by increasing maternal Polo dosage, indicating that coordination between the two mitotic kinases is crucial for mitotic progression. Revertant alleles of Scant that restore fertility to polo–Scant heterozygous females are recessive alleles or deficiencies of gwl; they show chromatin condensation defects and anaphase bridges in larval neuroblasts. One recessive mutant allele specifically disrupts a Gwl isoform strongly expressed during vitellogenesis. Females hemizygous for this allele are sterile, and their oocytes fail to arrest in metaphase I of meiosis; both homologues and sister chromatids separate on elongated meiotic spindles with little or no segregation. This allelic series of gwl mutants highlights the multiple roles of Gwl in both mitotic and meiotic progression. Our results indicate that Gwl activity antagonizes Polo and thus identify an important regulatory interaction of the cell cycle

Substellar Objects in Nearby Young Clusters (SONYC) III: Chamaeleon-I

SONYC - Substellar Objects in Nearby Young Clusters - is a survey program to investigate the frequency and properties of substellar objects with masses down to a few times that of Jupiter in nearby star-forming regions. In this third paper, we present our recent results in the Chamaeleon-I star forming region. We have carried out deep optical and near-infrared imaging in four bands (I, z, J, Ks) using VIMOS on the ESO Very Large Telescope and SOFI on the New Technology Telescope, and combined our data with mid-infrared data from the Spitzer Space Telescope. The survey covers ~0.25 sqdeg on the sky, and reaches completeness limits of 23.0 in the I-band, 18.3 in the J-band, and 16.7 in Ks-band. Follow-up spectroscopy of the candidates selected from the optical photometry (I <~ 21) was carried out using the multi-object spectrograph VIMOS on the VLT. We identify 13 objects consistent with M spectral types, 11 of which are previously known M-dwarfs with confirmed membership in the cluster. The 2 newly reported objects have effective temperatures above the substellar limit. We also present two new candidate members of Chamaeleon-I, selected from our JK photometry combined with the Spitzer data. Based on the results of our survey, we estimate that the number of missing very-low-mass members down to ~0.008 MSun and Av <= 5 is <= 7, i.e. <= 3% of the total cluster population according to the current census.Comment: Accepted by Astrophysical Journa

Microbial community composition of transiently wetted Antarctic Dry Valley soils

During the summer months, wet (hyporheic) soils associated with ephemeral streams and lake edges in the Antarctic Dry Valleys (DVs) become hotspots of biological activity and are hypothesized to be an important source of carbon and nitrogen for arid DV soils. Recent research in the DV has focused on the geochemistry and microbial ecology of lakes and arid soils, with substantially less information being available on hyporheic soils. Here, we determined the unique properties of hyporheic microbial communities, resolved their relationship to environmental parameters and compared them to archetypal arid DV soils. Generally, pH increased and chlorophyll a concentrations decreased along transects from wet to arid soils (9.0 to ~7.0 for pH and ~0.8 to ~5 μg/cm3 for chlorophyll a, respectively). Soil water content decreased to below ~3% in the arid soils. Community fingerprinting-based principle component analyses revealed that bacterial communities formed distinct clusters specific to arid and wet soils; however, eukaryotic communities that clustered together did not have similar soil moisture content nor did they group together based on sampling location. Collectively, rRNA pyrosequencing indicated a considerably higher abundance of Cyanobacteria in wet soils and a higher abundance of Acidobacterial, Actinobacterial, Deinococcus/Thermus, Bacteroidetes, Firmicutes, Gemmatimonadetes, Nitrospira, and Planctomycetes in arid soils. The two most significant differences at the genus level were Gillisia signatures present in arid soils and chloroplast signatures related to Streptophyta that were common in wet soils. Fungal dominance was observed in arid soils and Viridiplantae were more common in wet soils. This research represents an in-depth characterization of microbial communities inhabiting wet DV soils. Results indicate that the repeated wetting of hyporheic zones has a profound impact on the bacterial and eukaryotic communities inhabiting in these areas

Large-scale synthesis of high moment FeCo nanoparticles using modified polyol synthesis

Binary alloys of Fe and Co have among the highest magnetizations of any transition metal alloy systems, but their affinity to form oxides act to reduce the magnetization of nanoparticles as their size is reduced below ∼30 nm. Here, we demonstrate the synthesis of single phase, size-controlled FeCo nanoparticles having magnetization greater than 200 emu/g via a non-aqueous method in which ethylene glycol served as solvent and reducing agent as well as surfactant. Experiments indicated pure-phase FeCo nanoparticles, having saturationmagnetization up to 221 emu/g for sizes of 20–30 nm, in single batch processes resulting in \u3e 2 g/batch. Post-synthesis oxidation of nanoparticles was investigated until very stable nanoparticles were realized with constant magnetization over time

Multiple Imputation for Multilevel Data with Continuous and Binary Variables

We present and compare multiple imputation methods for multilevel continuous and binary data where variables are systematically and sporadically missing. The methods are compared from a theoretical point of view and through an extensive simulation study motivated by a real dataset comprising multiple studies. The comparisons show that these multiple imputation methods are the most appropriate to handle missing values in a multilevel setting and why their relative performances can vary according to the missing data pattern, the multilevel structure and the type of missing variables. This study shows that valid inferences can only be obtained if the dataset includes a large number of clusters. In addition, it highlights that heteroscedastic multiple imputation methods provide more accurate inferences than homoscedastic methods, which should be reserved for data with few individuals per cluster. Finally, guidelines are given to choose the most suitable multiple imputation method according to the structure of the data

Pleistocene/Holocene Cave Fossils From Grand Canyon National Park: Ice Age (Pleistocene) Flora, Fauna, Environments, and Climate of the Grand Canyon, Arizona

The Colorado Plateau is a distinct physiographic province in western North America covering an area of roughly 337,000 km2 (130,115 mi2) across parts of Arizona, Colorado, New Mexico, and Utah. Elevations range from about 360 m (1,180 ft) in the overall Grand Canyon (GC; which includes the Grand Canyon National Park, GRCA) river corridor to an average at the eastern South Rim of 2,072 m (6,800 ft) to 3,850 m (12,630 ft) on the nearby San Francisco Peaks at Flagstaff, Arizona, with an average elevation of 1,525 m (5,000 ft). The Colorado River of Grand Canyon is located along the southwestern portion of the Colorado Plateau in Arizona and is renowned for its dramatic display of geomorphic effects created by fluvial incision and its unique dry-preservation of fossils from the Ice Age (late Pleistocene and Holocene [Quaternary]; most recent 2.58 million years). Although there were at least 22 glacial-interglacial cycles during the Ice Age, this discussion is limited to the most recent episode (called the Wisconsinan Glaciation), which includes the transition to the modern climate (latest Pleistocene and Holocene; the most recent 50,000 years of geologic history)

Remnant gas in evolved circumstellar disks: Herschel PACS observations of 10-100 Myr old disk systems

We present Herschel PACS spectroscopy of the [OI] 63 micron gas-line for three circumstellar disk systems showing signs of significant disk evolution and/or planet formation: HR 8799, HD 377 and RX J1852.3-3700. [OI] is undetected toward HR 8799 and HD 377 with 3 sigma upper limits of 6.8 x 10^-18 W m^-2 and 9.9 x 10^-18 W m^-2 respectively. We find an [OI] detection for RX J1852.3-3700 at 12.3 +- 1.8 x 10^-18 W m^-2. We use thermo-chemical disk models to model the gas emission, using constraints on the [OI] 63 micron, and ancillary data to derive gas mass upper limits and constrain gas-to-dust ratios. For HD 377 and HR 8799, we find 3 sigma upper limits on the gas mass of 0.1-20 Mearth. For RX J1852.3-3700, we find two distinct disk scenarios that could explain the detection of [OI] 63 micron and CO(2-1) upper limits reported from the literature: (i) a large disk with gas co-located with the dust (16-500 AU), resulting in a large tenuous disk with ~16 Mearth of gas, or (ii) an optically thick gas disk, truncated at ~70 AU, with a gas mass of 150 Mearth. We discuss the implications of these results for the formation and evolution of planets in these three systems.Comment: Accepted for publication in ApJ, 8 pages ApJ style (incl. references), 2 figures, 4 table

High-Energy Permanent Magnets for Hybrid Vehicles and Alternative Energy Uses

The report summarizes research undertaken by a multidisciplinary team aimed at the development of the next generation high-energy permanent magnets. The principal approach was relied on bottom-up fabrication of anisotropic nanocomposite magnets. Our efforts resulted in further development of the theoretical concept and fabrication principles for the nanocomposites and in synthesis of a range of rare-earth-based hard magnetic nanoparticles. Even though we did not make a breakthrough in the assembly of these hard magnetic particles with separately prepared Fe(Co) nanoparticles and did not obtain a compact nanocomposite magnet, our performed research will help to direct the future efforts, in particular, towards nano-assembly via coating, when the two phases which made the nanocomposite are first organized in core-shell-structured particles. Two other approaches were to synthesize (discover) new materials for the traditional singe-material magnets and the nanocomposite magnets. Integrated theoretical and experimental efforts lead to a significant advance in nanocluster synthesis technique and yielded novel rare-earth-free nanostructured and nanocomposite materials. Examination of fifteen R-Fe-X alloy systems (R = rare earth), which have not been explored earlier due to various synthesis difficulties reveal several new ferromagnetic compounds. The research has made major progress in bottom-up manufacturing of rare-earth-containing nanocomposite magnets with superior energy density and open new directions in development of higher-energy-density magnets that do not contain rare earths. The advance in the scientific knowledge and technology made in the course of the project has been reported in 50 peer-reviewed journal articles and numerous presentations at scientific meetings