5,977 research outputs found
Holocene-Neogene volcanism in northeastern Australia: chronology and eruption history
Quaternary and late Neogene volcanism is widespread in northeastern Australia, producing at least 397 eruptions covering more than 20,000 km2, including at least 20 flows over 50 km long. Despite this abundance of young volcanism, before this study numerous eruptions had tentative ages or were undated, and the area requires a comprehensive evaluation of eruption patterns through time. To help address these issues we applied multi-collector ARGUS-V 40Ar/39Ar geochronology to determine the age of four of the younger extensive flows: Undara (160 km long, 189 ± 4/4 ka; 2σ, with full analytical/external uncertainties), Murronga (40 km long, 153 ± 5/5 ka), Toomba (120 km long, 21 ± 3/3 ka), and Kinrara (55 km long, 7 ± 2/2 ka). Verbal traditions of the Gugu Badhun Aboriginal people contain features that may potentially describe the eruption of Kinrara. If the traditions do record this eruption, they would have been passed down for 230 ± 70 generations – a period of time exceeding the earliest written historical records. To further examine north Queensland volcanism through time we compiled a database of 337 ages, including 179 previously unpublished K-Ar and radiocarbon results. The compiled ages demonstrate that volcanic activity has occurred without major time breaks since at least 9 Ma. The greatest frequency of eruptions occurred in the last 2 Ma, with an average recurrence interval of <10–22 ka between eruptions. Activity was at times likely more frequent than these calculations indicate, as the geochronologic dataset is incomplete, with undated eruptions, and intraplate volcanism is often episodic. The duration, frequency, and youthfulness of activity indicate that north Queensland volcanism should be considered as potentially still active, and there are now two confirmed areas of Holocene volcanism in eastern Australia – one at each end of the continent. More broadly, our data provides another example of 40Ar/39Ar geochronology applied to Holocene and latest Pleistocene mafic eruptions, further demonstrating that this method has the ability to examine eruptions and hazards at the youngest volcanoes on Earth
Gas of self-avoiding loops on the brickwork lattice
An exact calculation of the phase diagram for a loop gas model on the
brickwork lattice is presented. The model includes a bending energy. In the
dense limit, where all the lattice sites are occupied, a phase transition
occuring at an asymmetric Lifshitz tricritical point is observed as the
temperature associated with the bending energy is varied. Various critical
exponents are calculated. At lower densities, two lines of transitions (in the
Ising universality class) are observed, terminated by a tricritical point,
where there is a change in the modulation of the correlation function. To each
tricritical point an associated disorder line is found.Comment: 19 pages, 6 figures. to appear in J. Phys. A : Math. & Ge
Data report for the Siple Coast (Antarctica) project
This report presents data collected during three field seasons of glaciological studies in the Antarctica and describes the methods employed. The region investigated covers the mouths of Ice Streams B and C (the Siple Coast) and Crary Ice Rise on the Ross Ice Shelf. Measurements included in the report are as follows: surface velocity and deformation from repeated satellite geoceiver positions; surface topography from optical levelling; radar sounding of ice thickness; accumulation rates; near-surface densities and temperature profiles; and mapping from aerial photography
Effect of antiferromagnetic exchange interactions on the Glauber dynamics of one-dimensional Ising models
We study the effect of antiferromagnetic interactions on the single spin-flip
Glauber dynamics of two different one-dimensional (1D) Ising models with spin
. The first model is an Ising chain with antiferromagnetic exchange
interaction limited to nearest neighbors and subject to an oscillating magnetic
field. The system of master equations describing the time evolution of
sublattice magnetizations can easily be solved within a linear field
approximation and a long time limit. Resonant behavior of the magnetization as
a function of temperature (stochastic resonance) is found, at low frequency,
only when spins on opposite sublattices are uncompensated owing to different
gyromagnetic factors (i.e., in the presence of a ferrimagnetic short range
order). The second model is the axial next-nearest neighbor Ising (ANNNI)
chain, where an antiferromagnetic exchange between next-nearest neighbors (nnn)
is assumed to compete with a nearest-neighbor (nn) exchange interaction of
either sign. The long time response of the model to a weak, oscillating
magnetic field is investigated in the framework of a decoupling approximation
for three-spin correlation functions, which is required to close the system of
master equations. The calculation, within such an approximate theoretical
scheme, of the dynamic critical exponent z, defined as (where \tau is the longest relaxation time and \xi is the
correlation length of the chain), suggests that the T=0 single spin-flip
Glauber dynamics of the ANNNI chain is in a different universality class than
that of the unfrustrated Ising chain.Comment: 5 figures. Phys. Rev. B (accepted July 12, 2007
Chaos in computer performance
Modern computer microprocessors are composed of hundreds of millions of
transistors that interact through intricate protocols. Their performance during
program execution may be highly variable and present aperiodic oscillations. In
this paper, we apply current nonlinear time series analysis techniques to the
performances of modern microprocessors during the execution of prototypical
programs. Our results present pieces of evidence strongly supporting that the
high variability of the performance dynamics during the execution of several
programs display low-dimensional deterministic chaos, with sensitivity to
initial conditions comparable to textbook models. Taken together, these results
show that the instantaneous performances of modern microprocessors constitute a
complex (or at least complicated) system and would benefit from analysis with
modern tools of nonlinear and complexity science
The Drell-Yan process and Deep Inelastic Scattering from the lattice
We report on measurements of the h_1 structure function, relevant to
calculating cross-sections for the Drell-Yan process. This is a quantity which
can not be measured in Deep Inelastic Scattering, it gives additional
information on the spin carried by the valence quarks, as well as insights on
how relativistic the quarks are.Comment: 3 pages, Latex, 3 figures, espcrc2.sty included, Talk presented at
LATTICE96(phenomenology
Perturbative renormalization of bilinear quark and gluon operators
The renormalisation constants for local bilinear quark operators are
calculated using the Sheikholeslami-Wohlert improved action. In addition we
compute the renormalisation constant of the leading gluon operator for
different group representations and discuss the mixing of the operators E^2 and
B^2.Comment: 3 pages, poster contributed at Lattice96, St. Loui
A Model for the Analysis of Caries Occurrence in Primary Molar Tooth Surfaces
Recently methods of caries quantification in the primary dentition have moved away from summary ‘whole mouth’ measures at the individual level to methods based on generalised linear modelling (GLM) approaches or survival analysis approaches. However, GLM approaches based on logistic transformation fail to take into account the time-dependent process of tooth/surface survival to caries. There may also be practical difficulties associated with casting parametric survival-based approaches in a complex multilevel hierarchy and the selection of an optimal survival distribution, while non-parametric survival methods are not generally suitable for the assessment of supplementary information recorded on study participants. In the current investigation, a hybrid semi-parametric approach comprising elements of survival-based and GLM methodologies suitable for modelling of caries occurrence within fixed time periods is assessed, using an illustrative multilevel data set of caries occurrence in primary molars from a cohort study, with clustering of data assumed to occur at surface and tooth levels. Inferences of parameter significance were found to be consistent with previous parametric survival-based analyses of the same data set, with gender, socio-economic status, fluoridation status, tooth location, surface type and fluoridation status-surface type interaction significantly associated with caries occurrence. The appropriateness of the hierarchical structure facilitated by the hybrid approach was also confirmed. Hence the hybrid approach is proposed as a more appropriate alternative to primary caries modelling than non-parametric survival methods or other GLM-based models, and as a practical alternative to more rigorous survival-based methods unlikely to be fully accessible to most researchers
Isospin Splitting in the Baryon Octet and Decuplet
Baryon mass splittings are analyzed in terms of a simple model with general
pairwise interactions. At present, the masses are poorly known from
experiments. Improvement of these data would provide an opportunity to make a
significant test of our understanding of electromagnetic and quark-mass
contributions to hadronic masses. The problem of determining resonance masses
from scattering and production data is discussed.Comment: 9 pages, LATEX inc. 2 LATEX "pictures", CMU-HEP91-24-R9
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