1,078 research outputs found
Fractionalization in an Easy-axis Kagome Antiferromagnet
We study an antiferromagnetic spin-1/2 model with up to third
nearest-neighbor couplings on the Kagome lattice in the easy-axis limit, and
show that its low-energy dynamics are governed by a four site XY ring exchange
Hamiltonian. Simple ``vortex pairing'' arguments suggest that the model
sustains a novel fractionalized phase, which we confirm by exactly solving a
modification of the Hamiltonian including a further four-site interaction. In
this limit, the system is a featureless ``spin liquid'', with gaps to all
excitations, in particular: deconfined S^z=1/2 bosonic ``spinons'' and Ising
vortices or ``visons''. We use an Ising duality transformation to express vison
correlators as non-local strings in terms of the spin operators, and calculate
the string correlators using the ground state wavefunction of the modified
Hamiltonian. Remarkably, this wavefunction is exactly given by a kind of
Gutzwiller projection of an XY ferromagnet. Finally, we show that the
deconfined spin liquid state persists over a finite range as the additional
four-spin interaction is reduced, and study the effect of this reduction on the
dynamics of spinons and visons.Comment: best in color but readable in B+
Distinctive diets of eutherian predators in Australia
Introduction of the domestic cat and red fox has devastated Australian native fauna. We synthesized Australian diet analyses to identify traits of prey species in cat, fox and dingo diets, which prey were more frequent or distinctive to the diet of each predator, and quantified dietary overlap. Nearly half (45%) of all Australian terrestrial mammal, bird and reptile species occurred in the diets of one or more predators. Cat and dingo diets overlapped least (0.64 ± 0.27, n = 24 location/time points) and cat diet changed little over 55 years of study. Cats were more likely to have eaten birds, reptiles and small mammals than foxes or dingoes. Dingo diet remained constant over 53 years and constituted the largest mammal, bird and reptile prey species, including more macropods/potoroids, wombats, monotremes and bandicoots/bilbies than cats or foxes. Fox diet had greater overlap with both cats (0.79 ± 0.20, n = 37) and dingoes (0.73 ± 0.21, n = 42), fewer distinctive items (plant material, possums/gliders) and significant spatial and temporal heterogeneity over 69 years, suggesting the opportunity for prey switching (especially of mammal prey) to mitigate competition. Our study reinforced concerns about mesopredator impacts upon scarce/threatened species and the need to control foxes and cats for fauna conservation. However, extensive dietary overlap and opportunism, as well as low incidence of mesopredators in dingo diets, precluded resolution of the debate about possible dingo suppression of foxes and cats
Mixing and oscillations of neutral particles in Quantum Field Theory
We study the mixing of neutral particles in Quantum Field Theory: neutral
boson field and Majorana field are treated in the case of mixing among two
generations. We derive the orthogonality of flavor and mass representations and
show how to consistently calculate oscillation formulas, which agree with
previous results for charged fields and exhibit corrections with respect to the
usual quantum mechanical expressions.Comment: 8 pages, revised versio
The orally administered P-glycoprotein inhibitor R101933 does not alter the plasma pharmacokinetics of docetaxel
This Phase I study was performed to assess the feasibility of combining
docetaxel with the new P-glycoprotein inhibitor R101933 and to determine
the dose limiting toxicity of this combination. Fifteen patients received
oral R101933 alone at a dose escalated from 200 to 300 mg twice daily
(b.i.d.; cycle 0), an escalating i.v. dose of docetaxel (60, 75, and 100
mg/m2) as a 1-h infusion (cycle 1), and the combination (cycle 2 and
further). Dose limiting toxicity consisting of mucositis and neutropenic
fever was reached at the combination of docetaxel, 100 mg/m2, and R101933,
300 mg b.i.d., and the maximum tolerated dose was established at
docetaxel, 100 mg/m2, and R101933, 200 mg b.i.d. Plasma concentrations of
R101933 achieved in patients were in the same range as required in
preclinical rodent models to overcome paclitaxel resistance. The plasma
pharmacokinetics of docetaxel were not influenced by the R101933 regimen
at any dose level tested, as indicated by plasma clearance values of 26.5
+/- 7.78 liters/h/m2 and 23.4 +/- 4.52 liters/h/m2 (P = 0.15) in cycles 1
and 2, respectively. These findings indicate that the contribution of a
P-glycoprotein inhibitor to the activity of anticancer chemotherapy can
now be assessed in patients for the first time independent of its effect
on drug pharmacokinetics
Magnetic Reconnection in Extreme Astrophysical Environments
Magnetic reconnection is a basic plasma process of dramatic rearrangement of
magnetic topology, often leading to a violent release of magnetic energy. It is
important in magnetic fusion and in space and solar physics --- areas that have
so far provided the context for most of reconnection research. Importantly,
these environments consist just of electrons and ions and the dissipated energy
always stays with the plasma. In contrast, in this paper I introduce a new
direction of research, motivated by several important problems in high-energy
astrophysics --- reconnection in high energy density (HED) radiative plasmas,
where radiation pressure and radiative cooling become dominant factors in the
pressure and energy balance. I identify the key processes distinguishing HED
reconnection: special-relativistic effects; radiative effects (radiative
cooling, radiation pressure, and Compton resistivity); and, at the most extreme
end, QED effects, including pair creation. I then discuss the main
astrophysical applications --- situations with magnetar-strength fields
(exceeding the quantum critical field of about 4 x 10^13 G): giant SGR flares
and magnetically-powered central engines and jets of GRBs. Here, magnetic
energy density is so high that its dissipation heats the plasma to MeV
temperatures. Electron-positron pairs are then copiously produced, making the
reconnection layer highly collisional and dressing it in a thick pair coat that
traps radiation. The pressure is dominated by radiation and pairs. Yet,
radiation diffusion across the layer may be faster than the global Alfv\'en
transit time; then, radiative cooling governs the thermodynamics and
reconnection becomes a radiative transfer problem, greatly affected by the
ultra-strong magnetic field. This overall picture is very different from our
traditional picture of reconnection and thus represents a new frontier in
reconnection research.Comment: Accepted to Space Science Reviews (special issue on magnetic
reconnection). Article is based on an invited review talk at the
Yosemite-2010 Workshop on Magnetic Reconnection (Yosemite NP, CA, USA;
February 8-12, 2010). 30 pages, no figure
Fredholm determinants and pole-free solutions to the noncommutative Painleve' II equation
We extend the formalism of integrable operators a' la
Its-Izergin-Korepin-Slavnov to matrix-valued convolution operators on a
semi-infinite interval and to matrix integral operators with a kernel of the
form E_1^T(x) E_2(y)/(x+y) thus proving that their resolvent operators can be
expressed in terms of solutions of some specific Riemann-Hilbert problems. We
also describe some applications, mainly to a noncommutative version of
Painleve' II (recently introduced by Retakh and Rubtsov), a related
noncommutative equation of Painleve' type. We construct a particular family of
solutions of the noncommutative Painleve' II that are pole-free (for real
values of the variables) and hence analogous to the Hastings-McLeod solution of
(commutative) Painleve' II. Such a solution plays the same role as its
commutative counterpart relative to the Tracy-Widom theorem, but for the
computation of the Fredholm determinant of a matrix version of the Airy kernel.Comment: 46 pages, no figures (oddly
Reptiles as food: Predation of Australian reptiles by introduced red foxes compounds and complements predation by cats
Context: Invasive species are a major cause of biodiversity loss across much of the world, and a key threat to Australia’s diverse reptile fauna. There has been no previous comprehensive analysis of the potential impact of the introduced European red fox, Vulpes vulpes, on Australian reptiles.
Aims: We seek to provide an inventory of all Australian reptile species known to be consumed by the fox, and identify characteristics of squamate species associated with such predation. We also compare these tallies and characteristics with reptile species known to be consumed by the domestic cat, Felis catus, to examine whether predation by these two introduced species is compounded (i.e. affecting much the same set of species) or complementary (affecting different groups of species).
Methods: We collated records of Australian reptiles consumed by foxes in Australia, with most records deriving from fox dietary studies (tallying >35 000 samples). We modelled presence or absence of fox predation records against a set of biological and other traits, and population trends, for squamate species.
Key results: In total, 108 reptile species (~11% of Australia’s terrestrial reptile fauna) have been recorded as consumed by foxes, fewer than that reported for cats (263 species). Eighty-six species have been reported to be eaten by both predators. More Australian turtle species have been reported as consumed by foxes than by cats, including many that suffer high levels of predation on egg clutches. Twenty threatened reptile species have been reported as consumed by foxes, and 15 by cats. Squamate species consumed by foxes are more likely to be undergoing population decline than those not known to be consumed by foxes. The likelihood of predation by foxes increased with squamate species’ adult body mass, in contrast to the relationship for predation by cats, which peaked at ~217 g. Foxes, but not cats, were also less likely to consume venomous snakes.
Conclusions: The two introduced, and now widespread, predators have both compounding and complementary impacts on the Australian reptile fauna.
Implications: Enhanced and integrated management of the two introduced predators is likely to provide substantial conservation benefits to much of the Australian reptile fauna
Carbon Recombination Lines from the Galactic Plane at 34.5 & 328 MHz
We present results of a search for carbon recombination lines in the Galaxy
at 34.5 MHz (C) made using the dipole array at Gauribidanur near
Bangalore. Observations made towards 32 directions, led to detections of lines
in absorption at nine positions. Followup observations at 328 MHz
(C) using the Ooty Radio Telescope detected these lines in emission.
A VLA D-array observation of one of the positions at 330 MHz yielded no
detection implying a lower limit of 10' for the angular size of the line
forming region.
The longitude-velocity distribution of the observed carbon lines indicate
that the line forming region are located mainly between 4 kpc and 7 kpc from
the Galactic centre. Combining our results with published carbon recombination
line data near 76 MHz (\nocite{erickson:95} Erickson \et 1995) we obtain
constraints on the physical parameters of the line forming regions. We find
that if the angular size of the line forming regions is , then
the range of parameters that fit the data are: \Te K, \ne \cm3 and pathlengths pc which may correspond to thin
photo-dissociated regions around molecular clouds. On the other hand, if the
line forming regions are in extent, then warmer gas (\Te K) with lower electron densities (\ne \cm3) extending
over several tens of parsecs along the line of sight and possibly associated
with atomic \HI gas can fit the data. Based on the range of derived parameters,
we suggest that the carbon line regions are most likely associated with
photo-dissociation regions.Comment: To appear in Journal of Astrophysics & Astronomy, March 200
Hypogene Calcitization: Evaporite Diagenesis in the Western Delaware Basin
Evaporite calcitization within the Castile Formation of the Delaware Basin is more widespread and diverse than originally recognized. Coupled field and GIS studies have identified more than 1000 individual occurrences of calcitization within the Castile Formation outcrop area, which includes both calcitized masses (limestone buttes) and laterally extensive calcitized horizons (limestone sheets). Both limestone buttes and sheets commonly contain a central brecciated zone that we attribute to hypogene dissolution. Lithologic fabric of calcitized zones ranges from little alteration of original varved laminae to fabrics showing extensive laminae distortion as well as extensive vuggy and open cavernous porosity. Calcitization is most abundant in the western portion of the Castile outcrop region where surface denudation has been greatest. Calcitization often forms linear trends, indicating fluid migration along fractures, but also occurs as dense clusters indicating focused, ascending, hydrocarbon-rich fluids. Native sulfur, secondary tabular gypsum (i.e. selenite) and hypogene caves are commonly associated with clusters of calcitization. This assemblage suggests that calcium sulfate diagenesis within the Castile Formation is dominated by hypogene speleogemesis
The position of graptolites within Lower Palaeozoic planktic ecosystems.
An integrated approach has been used to assess the palaeoecology of graptolites both as a discrete group and also as a part of the biota present within Ordovician and Silurian planktic realms. Study of the functional morphology of graptolites and comparisons with recent ecological analogues demonstrates that graptolites most probably filled a variety of niches as primary consumers, with modes of life related to the colony morphotype. Graptolite coloniality was extremely ordered, lacking any close morphological analogues in Recent faunas. To obtain maximum functional efficiency, graptolites would have needed varying degrees of coordinated automobility. A change in lifestyle related to ontogenetic changes was prevalent within many graptolite groups. Differing lifestyle was reflected by differing reproductive strategies, with synrhabdosomes most likely being a method for rapid asexual reproduction. Direct evidence in the form of graptolithophage 'coprolitic' bodies, as well as indirect evidence in the form of probable defensive adaptations, indicate that graptolites comprised a food item for a variety of predators. Graptolites were also hosts to a variety of parasitic organisms and provided an important nutrient source for scavenging organisms
- …