Seed particle formation for silicate dust condensation by SiO nucleation

Clustering of the abundant SiO molecules has been discussed as a possible mechanism of seed particle formation for silicate dust in stellar outflows with an oxygen rich element mixture. Previous results indicated that condensation temperatures based on this mechanism are significant lower than what is really observed. This negative result strongly rests on experimental data on vapour pressure of SiO. New determinations show the older data to be seriously in error. Here we aim to check with improved data the possibility that SiO nucleation triggers the cosmic silicate dust formation. First we present results of our measurements of vapour pressure of solid SiO. Second, we use the improved vapour pressure data to re-calibrate existing experimental data on SiO nucleation from the literature. Third, we use the re-calibrated data on SiO nucleation in a simple model for dust-driven winds to determine the condensation temperature of silicate in stellar outflows from AGB stars. We show that onset of nucleation under circumstellar conditions commences at higher temperature than was previously found. Calculated condensation temperatures are still by about 100 K lower than observed ones, but this may be due to the greenhouse effect of silicate dust temperatures. The assumption that the onset of silicate dust formation in late-type M stars is triggered by cluster formation of SiO is compatible with dust condensation temperatures derived from IR observations.Comment: 11 pages, 11 figure

Modeling the Impact of Baryons on Subhalo Populations with Machine Learning

We identify subhalos in dark matter-only (DMO) zoom-in simulations that are likely to be disrupted due to baryonic effects by using a random forest classifier trained on two hydrodynamic simulations of Milky Way (MW)-mass host halos from the Latte suite of the Feedback in Realistic Environments (FIRE) project. We train our classifier using five properties of each disrupted and surviving subhalo: pericentric distance and scale factor at first pericentric passage after accretion, and scale factor, virial mass, and maximum circular velocity at accretion. Our five-property classifier identifies disrupted subhalos in the FIRE simulations with an $85\%$ out-of-bag classification score. We predict surviving subhalo populations in DMO simulations of the FIRE host halos, finding excellent agreement with the hydrodynamic results; in particular, our classifier outperforms DMO zoom-in simulations that include the gravitational potential of the central galactic disk in each hydrodynamic simulation, indicating that it captures both the dynamical effects of a central disk and additional baryonic physics. We also predict surviving subhalo populations for a suite of DMO zoom-in simulations of MW-mass host halos, finding that baryons impact each system consistently and that the predicted amount of subhalo disruption is larger than the host-to-host scatter among the subhalo populations. Although the small size and specific baryonic physics prescription of our training set limits the generality of our results, our work suggests that machine-learning classification algorithms trained on hydrodynamic zoom-in simulations can efficiently predict realistic subhalo populations.Comment: 20 pages, 14 figures. Updated to published version. Code available at https://github.com/ollienad/subhalo_randomfores

Secoviridae: a proposed family of plant viruses within the order Picornavirales that combines the families Sequiviridae and Comoviridae, the unassigned genera Cheravirus and Sadwavirus, and the proposed genus Torradovirus

The order Picornavirales includes several plant viruses that are currently classified into the families Comoviridae (genera Comovirus, Fabavirus and Nepovirus) and Sequiviridae (genera Sequivirus and Waikavirus) and into the unassigned genera Cheravirus and Sadwavirus. These viruses share properties in common with other picornavirales (particle structure, positive-strand RNA genome with a polyprotein expression strategy, a common replication block including type III helicase, a 3C-like cysteine proteinase and type I RNA-dependent RNA polymerase). However, they also share unique properties that distinguish them from other picornavirales. They infect plants and use specialized proteins or protein domains to move through their host. In phylogenetic analysis based on their replication proteins, these viruses form a separate distinct lineage within the picornavirales branch. To recognize these common properties at the taxonomic level, we propose to create a new family termed “Secoviridae” to include the genera Comovirus, Fabavirus, Nepovirus, Cheravirus, Sadwavirus, Sequivirus and Waikavirus. Two newly discovered plant viruses share common properties with members of the proposed family Secoviridae but have distinct specific genomic organizations. In phylogenetic reconstructions, they form a separate sub-branch within the Secoviridae lineage. We propose to create a new genus termed Torradovirus (type species, Tomato torrado virus) and to assign this genus to the proposed family Secoviridae

Efficiency Effects of Quality of Service and Environmental Factors: Experience from Norwegian Electricity Distribution

Since the 1990s, efficiency and benchmarking analysis has increasingly been used in network utilities research and regulation. A recurrent concern is the effect of environmental factors that are beyond the influence of firms (observable heterogeneity) and factors that are not identifiable (unobserved heterogeneity) on measured cost and quality performance of firms. This paper analyses the effect of geographic and weather factors and unobserved heterogeneity on a set of 128 Norwegian electricity distribution utilities for the 2001-2004 period. We utilize data on almost 100 geographic and weather variables to identify real economic inefficiency while controlling for observable and unobserved heterogeneity. We use the factor analysis technique to reduce the number of environmental factors into few composite variables and to avoid the problem of multi-collinearity. We then estimate the established stochastic frontier models of Battese and Coelli (1992; 1995) and the recent true fixed effects models of Greene (2004; 2005) without and with environmental variables. In the former models some composite environmental variables have a significant effect on the performance of utilities. These effects vanish in the true fixed effects models. However, the latter models capture the entire unobserved heterogeneity and therefore show significantly higher average efficiency scores

Toughening and Mechanical Properties of Epoxy Modified with Block Co-polymers and MWCNTs

AbstractThe objective of this work was to systematically develop and understand novel polymeric hybrid nanocomposites that include block copolymers (BCP) with tailored morphologies in order to generate high toughness. Furthermore, rigid fillers in the form of multi-walled carbon nanotubes (MWCNT) were added systematically together with block copolymers to study the combined effect of rigid nanofillers and more ductile BCP particles. The resulting matrix was extensively and carefully characterized by standard methods. This included thorough characterization of mechanical, fracture mechanical and thermal properties. Results show that both fracture toughness, KIc, and critical energy release rate, GIc, were increased linearly to a maximum of 2.10 MPa.m1/2 and 1.46 kJ/m2 respectively by the addition of 12 wt. % BCP. Fractography studies reveal toughening mechanisms of the nanocomposites that were identified as both the cavitation of spherical micelles and enhanced plastic deformation and furthermore fiber pull-out in the case of hybrid nanocomposites

A Rapid Chromatographic Method For Recovery Of 15No2- And No3- Produced By Nitrification In Aqueous Samples

The sensitivity and comparative simplicity of N-15 stable isotopic tracer techniques has been used to quantify rates of nitrification in aquatic systems. However, the most commonly used method for recovery of inorganic oxidized nitrogen compounds from aqueous samples, which is based on liquid-liquid partitioning, is time consuming and contamination prone. We describe a solid-phase rapid chromatographic method for recovery of (NO2-)-N-15 and NO3- produced by nitrification in aqueous samples. Compared to liquid-liquid partitioning, the advantages are significantly reduced processing time and reduced potential for contamination. Typical results are presented for the tidal, freshwater reaches of the James River estuary

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The connection between the host halo and the satellite galaxies of the Milky Way

Many properties of the Milky Way's dark matter halo, including its mass assembly history, concentration, and subhalo population, remain poorly constrained. We explore the connection between these properties of the Milky Way and its satellite galaxy population, especially the implication of the presence of the Magellanic Clouds for the properties of the Milky Way halo. Using a suite of high-resolution $N$-body simulations of Milky Way-mass halos with a fixed final Mvir ~ 10^{12.1}Msun, we find that the presence of Magellanic Cloud-like satellites strongly correlates with the assembly history, concentration, and subhalo population of the host halo, such that Milky Way-mass systems with Magellanic Clouds have lower concentration, more rapid recent accretion, and more massive subhalos than typical halos of the same mass. Using a flexible semi-analytic galaxy formation model that is tuned to reproduce the stellar mass function of the classical dwarf galaxies of the Milky Way with Markov-Chain Monte-Carlo, we show that adopting host halos with different mass-assembly histories and concentrations can lead to different best-fit models for galaxy-formation physics, especially for the strength of feedback. These biases arise because the presence of the Magellanic Clouds boosts the overall population of high-mass subhalos, thus requiring a different stellar-mass-to-halo-mass ratio to match the data. These biases also lead to significant differences in the mass--metallicity relation, the kinematics of low-mass satellites, the number counts of small satellites associated with the Magellanic Clouds, and the stellar mass of Milky Way itself. Observations of these galaxy properties can thus provide useful constraints on the properties of the Milky Way halo.Comment: 20 pages, 12 figures, accepted for publication in ApJ. A new section on the effect of host halo mass-assembly history on the central galaxy stellar mass is adde