Intrinsic Universality in Self-Assembly

We show that the Tile Assembly Model exhibits a strong notion of universality where the goal is to give a single tile assembly system that simulates the behavior of any other tile assembly system. We give a tile assembly system that is capable of simulating a very wide class of tile systems, including itself. Specifically, we give a tile set that simulates the assembly of any tile assembly system in a class of systems that we call \emph{locally consistent}: each tile binds with exactly the strength needed to stay attached, and that there are no glue mismatches between tiles in any produced assembly. Our construction is reminiscent of the studies of \emph{intrinsic universality} of cellular automata by Ollinger and others, in the sense that our simulation of a tile system $T$ by a tile system $U$ represents each tile in an assembly produced by $T$ by a $c \times c$ block of tiles in $U$, where $c$ is a constant depending on $T$ but not on the size of the assembly $T$ produces (which may in fact be infinite). Also, our construction improves on earlier simulations of tile assembly systems by other tile assembly systems (in particular, those of Soloveichik and Winfree, and of Demaine et al.) in that we simulate the actual process of self-assembly, not just the end result, as in Soloveichik and Winfree's construction, and we do not discriminate against infinite structures. Both previous results simulate only temperature 1 systems, whereas our construction simulates tile assembly systems operating at temperature 2

A Compact Starburst Core in the Dusty Lyman Break Galaxy Westphal-MD11

Using the IRAM Plateau de Bure Interferometer, we have searched for CO(3-2) emission from the dusty Lyman break galaxy Westphal-MD11 at z = 2.98. Our sensitive upper limit is surprisingly low relative to the system's 850 um flux density and implies a far-IR/CO luminosity ratio as elevated as those seen in local ultraluminous mergers. We conclude that the observed dust emission must originate in a compact structure radiating near its blackbody limit and that a relatively modest molecular gas reservoir must be fuelling an intense nuclear starburst (and/or deeply buried active nucleus) that may have been triggered by a major merger. In this regard, Westphal-MD11 contrasts strikingly with the lensed Lyman break galaxy MS1512-cB58, which is being observed apparently midway through an extended episode of more quiescent disk star formation.Comment: 5 pages, 1 figure (emulateapj), accepted by ApJ

Studying the Dynamics of Star Forming and IR Luminous Galaxies with Infrared Spectroscopy

With the advent of efficient near-IR spectrometers on 10m-class telescopes, exploiting the new generation of low readout noise, large format detectors, OH avoidance and sub-arcsecond seeing, 1-2.4 micron spectroscopy is becoming a key means of obtaining detailed galaxy dynamics and for studies of high-z galaxies. In the following we present the results of three recent IR spectroscopy studies on the dynamics of ULIRG mergers, super star clusters in the Antennae, and on the properties of the rotation curves of z~1 disk galaxies, carried out with ISAAC on the VLT and NIRSPEC on the Keck.Comment: To appear in the Proceedings of the ESO Workshop "The Mass of Galaxies at Low and High Redshift", R. Bender and A. Renzini Eds. (Springer-Verlag

Impact of Experimental Hookworm Infection on the Human Gut Microbiota

The interactions between gastrointestinal parasitic helminths and commensal bacteria are likely to play a pivotal role in the establishment of host-parasite cross-talk, ultimately shaping the development of the intestinal immune system. However, little information is available on the impact of infections by gastrointestinal helminths on the bacterial communities inhabiting the human gut. We used 16S rRNA gene amplification and pyrosequencing to characterize, for the first time to our knowledge, the differences in composition and relative abundance of fecal microbial communities in human subjects prior to and following experimental infection with the blood-feeding intestinal hookworm, Necator americanus. Our data show that, although hookworm infection leads to a minor increase in microbial species richness, no detectable effect is observed on community structure, diversity or relative abundance of individual bacterial species

A coupled terrestrial and aquatic biogeophysical model of the Upper Merrimack River watershed, New Hampshire, to inform ecosystem services evaluation and management under climate and land-cover change

Accurate quantification of ecosystem services (ES) at regional scales is increasingly important for making informed decisions in the face of environmental change. We linked terrestrial and aquatic ecosystem process models to simulate the spatial and temporal distribution of hydrological and water quality characteristics related to ecosystem services. The linked model integrates two existing models (a forest ecosystem model and a river network model) to establish consistent responses to changing drivers across climate, terrestrial, and aquatic domains. The linked model is spatially distributed, accounts for terrestrial–aquatic and upstream–downstream linkages, and operates on a daily time-step, all characteristics needed to understand regional responses. The model was applied to the diverse landscapes of the Upper Merrimack River watershed, New Hampshire, USA. Potential changes in future environmental functions were evaluated using statistically downscaled global climate model simulations (both a high and low emission scenario) coupled with scenarios of changing land cover (centralized vs. dispersed land development) for the time period of 1980–2099. Projections of climate, land cover, and water quality were translated into a suite of environmental indicators that represent conditions relevant to important ecosystem services and were designed to be readily understood by the public. Model projections show that climate will have a greater influence on future aquatic ecosystem services (flooding, drinking water, fish habitat, and nitrogen export) than plausible changes in land cover. Minimal changes in aquatic environmental indicators are predicted through 2050, after which the high emissions scenarios show intensifying impacts. The spatially distributed modeling approach indicates that heavily populated portions of the watershed will show the strongest responses. Management of land cover could attenuate some of the changes associated with climate change and should be considered in future planning for the region

Ultraviolet Fe II Emission in Fainter Quasars: Luminosity Dependences, and the Influence of Environments

We investigate the strength of ultraviolet Fe II emission in fainter quasars com- pared with brighter quasars for 1.0 :( z :( 1.8, using the SDSS (Sloan Digital Sky Survey) DR7QSO catalogue and spectra of Schneider et al., and the SFQS (SDSS Faint Quasar Survey) catalogue and spectra of Jiang et al. We quantify the strength of the UV Fe II emission using the W 2400 equivalent width of Weymann et al., which is defined between two rest-frame continuum windows at 2240–2255 and 2665–2695 ˚A. The main results are the following. (1) We find that for W 2400 2: 25 ˚A there is a universal (i.e. for quasars in general) strengthening of W 2400 with decreasing intrinsic luminosity, L3000. (2) In conjunction with previous work by Clowes et al., we find that there is a further, differential, strengthening of W 2400 with decreasing L3000 for those quasars that are members of Large Quasar Groups (LQGs). (3) We find that increasingly strong W 2400 tends to be associated with decreasing FWHM of the neighbouring Mg II λ2798 broad emission line. (4) We suggest that the dependence of W 2400 on L3000 arises from Lyα fluorescence. (5) We find that stronger W 2400 tends to be associated with smaller virial estimates from Shen et al. of the mass of the central black hole, by a factor ∼ 2 between the ultrastrong emitters and the weak. Stronger W 2400 emission would correspond to smaller black holes that are still growing. The differential effect for LQG members might then arise from preferentially younger quasars in the LQG environments

Molecular Gas in the Lensed Lyman Break Galaxy cB58

We have used the IRAM Plateau de Bure Interferometer to map CO(3-2) emission from the gravitationally lensed Lyman break galaxy MS1512-cB58. This is the first detection of a molecular emission line in any Lyman break system; its integrated intensity implies a total molecular gas mass of 6.6e9 Msun, while its width implies a dynamical mass of 1.0e10 csc^2i Msun (for a flat Lambda=0.7 cosmology). These estimates are in excellent concordance with nearly all parameters of the system measured at other wavelengths, and yield a consistent picture of past and future star formation with no obvious discrepancies requiring explanation by differential lensing. In particular, we find that the age and remaining lifetime of the current episode of star formation are likely to be similar; the surface densities of star formation and molecular gas mass are related by a Schmidt law; and the fraction of baryonic mass already converted into stars is sufficient to account for the observed enrichment of the interstellar medium to 0.4 Zsun. Barring substantial gas inflow or a major merger, the stars forming in the current episode will have mass and coevality at z=0 similar to those of a spiral bulge. Assuming cB58 is a typical Lyman break galaxy apart from its magnification, its global parameters suggest that the prescriptions for star formation used in some semi-analytic models of galaxy evolution require moderate revision, although the general prediction that gas mass fraction should increase with redshift is validated. [abridged]Comment: 41 pages, 6 figures, accepted by Ap

Genetic and Spatial Structuring of Populus tremuloides in a Mixed-Species Forest of Southwestern Utah, USA

Populus tremuloides Michx. (aspen) is an iconic species of the southwestern United States, where it is known for its extensive clonality. The size of clones and pattern of clonal distribution within and among stands can provide important clues to the species\u27 evolution and ecology, but there are very few studies that have conducted the type of sampling necessary to define these features. We examined the genetic composition and habitat associations of aspen in a mixed-species forest in Cedar Breaks National Monument on the Markagunt Plateau, southwestern Utah. Genetic analysis of 94 stems ≥1 cm diameter at breast height (dbh) selected from a population census of 2742 stems within a contiguous 13.64-ha plot revealed 2 spatially cohesive triploid genets and 2 diploid genets (all differing in 8 to 15 alleles). Aspen abundance within the 13.64 ha varied between 0 and 634 stems/ha across 8 distinct habitat types. Regenerating aspen stems (1 cm ≤ dbh \u3c 5 cm) varied between 0 and 112 stems/ha, with higher levels of regeneration in habitats with greater aspen dominance relative to other tree species. Recent regeneration may have been stimulated by a Dendroctonous rufipennis outbreak in the 1990s, which killed a high proportion of Picea engelmannii. Even though the visual impression is of a single aspen clone, the 4 identified genets suggest a higher-than-expected level of genetic diversity in this mixed-species stand which may confer resilience to increasing climate variability and drought. Furthermore, aspen regeneration in areas of both low and high adult aspen densities show that these mixed stands can support vigorous aspen populations

The fusion crust of the Winchcombe meteorite: A preserved record of atmospheric entry processes

Fusion crusts form during the atmospheric entry heating of meteorites and preserve a record of the conditions that occurred during deceleration in the atmosphere. The fusion crust of the Winchcombe meteorite closely resembles that of other stony meteorites, and in particular CM2 chondrites, since it is dominated by olivine phenocrysts set in a glassy mesostasis with magnetite, and is highly vesicular. Dehydration cracks are unusually abundant in Winchcombe. Failure of this weak layer is an additional ablation mechanism to produce large numbers of particles during deceleration, consistent with the observation of pulses of plasma in videos of the Winchcombe fireball. Calving events might provide an observable phenomenon related to meteorites that are particularly susceptible to dehydration. Oscillatory zoning is observed within olivine phenocrysts in the fusion crust, in contrast to other meteorites, perhaps owing to temperature fluctuations resulting from calving events. Magnetite monolayers are found in the crust, and have also not been previously reported, and form discontinuous strata. These features grade into magnetite rims formed on the external surface of the crust and suggest the trapping of surface magnetite by collapse of melt. Magnetite monolayers may be a feature of meteorites that undergo significant degassing. Silicate warts with dendritic textures were observed and are suggested to be droplets ablated from another stone in the shower. They, therefore, represent the first evidence for intershower transfer of ablation materials and are consistent with the other evidence in the Winchcombe meteorite for unusually intense gas loss and ablation, despite its low entry velocity