745 research outputs found
FARM LEVEL CONSEQUENCES OF CANADIAN AND U.S. DAIRY POLICIES
Agricultural and Food Policy, Livestock Production/Industries,
Hastings-Levitov aggregation in the small-particle limit
We establish some scaling limits for a model of planar aggregation. The model is described by the composition of a sequence of independent and identically distributed random conformal maps, each corresponding to the addition of one particle. We study the limit of small particle size and rapid aggregation. The process of growing clusters converges, in the sense of Caratheodory, to an inflating disc. A more refined analysis reveals, within the cluster, a tree structure of branching fingers, whose radial component increases deterministically with time. The arguments of any finite sample of fingers, tracked inwards, perform coalescing Brownian motions. The arguments of any finite sample of gaps between the fingers, tracked outwards, also perform coalescing Brownian motions. These properties are closely related to the evolution of harmonic measure on the boundary of the cluster, which is shown to converge to the Brownian web
Phosphatidylinositol 4,5-bisphosphate regulates SNARE-dependent membrane fusion
Phosphatidylinositol 4,5-bisphosphate (PI 4,5-P2) on the plasma membrane is essential for vesicle exocytosis but its role in membrane fusion has not been determined. Here, we quantify the concentration of PI 4,5-P2 as ∼6 mol% in the cytoplasmic leaflet of plasma membrane microdomains at sites of docked vesicles. At this concentration of PI 4,5-P2 soluble NSF attachment protein receptor (SNARE)–dependent liposome fusion is inhibited. Inhibition by PI 4,5-P2 likely results from its intrinsic positive curvature–promoting properties that inhibit formation of high negative curvature membrane fusion intermediates. Mutation of juxtamembrane basic residues in the plasma membrane SNARE syntaxin-1 increase inhibition by PI 4,5-P2, suggesting that syntaxin sequesters PI 4,5-P2 to alleviate inhibition. To define an essential rather than inhibitory role for PI 4,5-P2, we test a PI 4,5-P2–binding priming factor required for vesicle exocytosis. Ca2+-dependent activator protein for secretion promotes increased rates of SNARE-dependent fusion that are PI 4,5-P2 dependent. These results indicate that PI 4,5-P2 regulates fusion both as a fusion restraint that syntaxin-1 alleviates and as an essential cofactor that recruits protein priming factors to facilitate SNARE-dependent fusion
Interdisciplinary Research on Healthy Aging:Introduction
Background: This is an introduction to a Special Collection of Demographic Research on Interdisciplinary Research on Healthy Aging. The collection is an outcome of an international conference in China on biodemography and multistate modeling in healthy aging research. Causal analysis is the common theme of the papers. Healthy aging is an outcome of pathways of causally related distant and proximate determinants and intervening factors that mediate the effects of the determinants. Objective: The objective is to introduce the papers in this SC and to highlight the place of multistate modeling in causal analysis. Methods: We adopt the common distinction between structural causal modeling and dynamic causal modeling. The papers in the SC concentrate on structural causal modeling. Multistate models (and, more particularly, the continuous-time Markov process model) are oriented more toward dynamic causal modeling. In dynamic causal modeling the causal dependencies are defined in terms of events (outcomes), exposure time, and transition rates that relate exposures to events. Results: The contributions to the SC illustrate the progress made in structural causal modeling in the study of healthy aging. Dynamic causal analysis, however, has progressed comparatively slowly. Contribution: The papers in the SC and the brief introduction to multistate modeling in causal analysis pave the way to enhanced causal analysis in the study of healthy aging and in demography
A polarized atomic hydrogen beam
We describe the design and operating characteristics of a simple polarized atomic hydrogen beam particularly suitable for applications to crossed beams experiments. In addition to experimental measurements, we present the results of detailed computer models, using Monte-Carlo ray tracing techniques, optical analogs, and phase-space methods, that not only provide us with a confirmation of our measurement, but also allow us to characterize the density, polarization, and atomic fraction of the beam at all points along its path. As a subsidiary result, we also present measurements of the relative and absolute efficiencies of the V/G Supavac mass analyzer for masses 1 and 2
Interacting dark matter contribution to the Galactic 511 keV gamma ray emission: constraining the morphology with INTEGRAL/SPI observations
We compare the full-sky morphology of the 511 keV gamma ray excess measured
by the INTEGRAL/SPI experiment to predictions of models based on dark matter
(DM) scatterings that produce low-energy positrons: either MeV-scale DM that
annihilates directly into e+e- pairs, or heavy DM that inelastically scatters
into an excited state (XDM) followed by decay into e+e- and the ground state.By
direct comparison to the data, we find that such explanations are consistent
with dark matter halo profiles predicted by numerical many-body simulations for
a Milky Way-like galaxy. Our results favor an Einasto profile over the cuspier
NFW distribution and exclude decaying dark matter scenarios whose predicted
spatial distribution is too broad. We obtain a good fit to the shape of the
signal using six fewer degrees of freedom than previous empirical fits to the
511 keV data. We find that the ratio of flux at Earth from the galactic bulge
to that of the disk is between 1.9 and 2.4, taking into account that 73% of the
disk contribution may be attributed to the beta decay of radioactive 26Al.Comment: 7 pages, 4 figures. Includes minor corrections, and a discussion of
threshold energies in XDM models. Published in JCA
Edge effects and vertical stratification of aerial insectivorous bats across the interface of primary-secondary Amazonian rainforest
Research ArticleEdge effects, abiotic and biotic changes associated with habitat boundaries, are key drivers
of community change in fragmented landscapes. Their influence is heavily modulated by
matrix composition. With over half of the world’s tropical forests predicted to become forest
edge by the end of the century, it is paramount that conservationists gain a better understanding
of how tropical biota is impacted by edge gradients. Bats comprise a large fraction
of tropical mammalian fauna and are demonstrably sensitive to habitat modification. Yet,
knowledge about how bat assemblages are affected by edge effects remains scarce. Capitalizing
on a whole-ecosystem manipulation in the Central Amazon, the aims of this study
were to i) assess the consequences of edge effects for twelve aerial insectivorous bat species
across the interface of primary and secondary forest, and ii) investigate if the activity
levels of these species differed between the understory and canopy and if they were modulated
by distance from the edge. Acoustic surveys were conducted along four 2-km transects,
each traversing equal parts of primary and ca. 30-year-old secondary forest. Five
models were used to assess the changes in the relative activity of forest specialists (three
species), flexible forest foragers (three species), and edge foragers (six species). Modelling
results revealed limited evidence of edge effects, except for forest specialists in the understory.
No significant differences in activity were found between the secondary or primary forest
but almost all species exhibited pronounced vertical stratification. Previously defined bat
guilds appear to hold here as our study highlights that forest bats are more edge-sensitive
than edge foraging bats. The absence of pronounced edge effects and the comparable
activity levels between primary and old secondary forests indicates that old secondary forest can help ameliorate the consequences of fragmentation on tropical aerial insectivorous
batsinfo:eu-repo/semantics/publishedVersio
Tidal Venuses: Triggering a Climate Catastrophe via Tidal Heating
Traditionally stellar radiation has been the only heat source considered
capable of determining global climate on long timescales. Here we show that
terrestrial exoplanets orbiting low-mass stars may be tidally heated at high
enough levels to induce a runaway greenhouse for a long enough duration for all
the hydrogen to escape. Without hydrogen, the planet no longer has water and
cannot support life. We call these planets "Tidal Venuses," and the phenomenon
a "tidal greenhouse." Tidal effects also circularize the orbit, which decreases
tidal heating. Hence, some planets may form with large eccentricity, with its
accompanying large tidal heating, and lose their water, but eventually settle
into nearly circular orbits (i.e. with negligible tidal heating) in the
habitable zone (HZ). However, these planets are not habitable as past tidal
heating desiccated them, and hence should not be ranked highly for detailed
follow-up observations aimed at detecting biosignatures. Planets orbiting stars
with masses <0.3 solar masses may be in danger of desiccation via tidal
heating. We apply these concepts to Gl 667C c, a ~4.5 Earth-mass planet
orbiting a 0.3 solar mass star at 0.12 AU. We find that it probably did not
lose its water via tidal heating as orbital stability is unlikely for the high
eccentricities required for the tidal greenhouse. As the inner edge of the HZ
is defined by the onset of a runaway or moist greenhouse powered by radiation,
our results represent a fundamental revision to the HZ for non-circular orbits.
In the appendices we review a) the moist and runaway greenhouses, b) hydrogen
escape, c) stellar mass-radius and mass-luminosity relations, d) terrestrial
planet mass-radius relations, and e) linear tidal theories. [abridged]Comment: 59 pages, 11 figures, accepted to Astrobiology. New version includes
an appendix on the water loss timescal
Validity of diagnostic pure-tone audiometry without a sound-treated environment in older adults
Objective: To investigate the validity of diagnostic pure-tone audiometry in a natural
environment using a computer-operated audiometer with insert earphones covered by
circumaural earcups incorporating real-time monitoring of environmental noise. Design: A
within-subject repeated measures design was employed to compare air (250 to 8000 Hz) and
bone (250 to 4000 Hz) conduction pure-tone thresholds measured in retirement facilities with
thresholds measured in a sound-treated booth. Study sample: 147 adults (average age 76 ±
5.7 years) were evaluated. Pure-tone averages were normal in 59%, mildly (>40 dB)
elevated in 23% and moderately (>55 dB) elevated in 6% of ears. Results: Air-conduction thresholds (n=2259) corresponded within 0 to 5 dB in 95% of all comparisons between the
two test environments. Bone-conduction thresholds (n=1669) corresponded within 0 to 5 dB
in 86% of comparisons. Average threshold differences (-0.6 to 1.1) and standard deviations
(3.3 to 5.9) were within typical test-retest reliability limits. Thresholds recorded showed no
statistically significant differences (Paired Samples T-test:p˃0.01) except at 8000 Hz in the
left ear. Conclusion: Valid diagnostic pure-tone audiometry can be performed in a natural
environment with recently developed technology, offering the possibility of access to
diagnostic audiometry in communities where sound-treated booths are unavailable.http://www.tandf.co.uk/journals/titles/14992027.asphb201
Dual bio-responsive gene delivery via reducible poly(amido amine) and survivin-inducible plasmid DNA
A bioreducible poly(amido amine) (SS-PAA) gene carrier, known as poly (amido-butanol) (pABOL), was used to transfect a variety of cancer and non-cancer cell lines. To obtain cancer-specific transgene expression for therapeutic efficiency in cancer treatment, we constructed survivin-inducible plasmid DNA expressing the soluble VEGF receptor, sFlt-1, downstream of the survivin promoter (pSUR-sFlt-1). Cancer-specific expression of sFlt-1 was observed in the mouse renal carcinoma (RENCA) cell line. pABOL enhanced the efficiency of gene delivery compared to traditional carriers used in the past. Thus, a dual bio-responsive gene delivery system was developed by using bioreducible p(ABOL) for enhanced intracellular gene delivery and survivin-inducible gene expression system (pSUR-sFlt-1 or pSUR-Luc reporter gene) that demonstrates increased gene expression in cancer that has advantages over current gene delivery system
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