2,068 research outputs found
Origin and thermal evolution of Mars
The thermal evolution of Mars is governed by subsolidus mantle convection beneath a thick lithosphere. Models of the interior evolution are developed by parameterizing mantle convective heat transport in terms of mantle viscosity, the superadiabatic temperature rise across the mantle, and mantle heat production. Geological, geophysical, and geochemical observations of the compositon and structure of the interior and of the timing of major events in Martian evolution are used to constrain the model computations. Such evolutionary events include global differentiation, atmospheric outgassing, and the formation of the hemispherical dichotomy and Tharsis. Numerical calculations of fully three-dimensional, spherical convection in a shell the size of the Martian mantle are performed to explore plausible patterns of Martian mantel convection and to relate convective features, such as plumes, to surface features, such as Tharsis. The results from the model calculations are presented
The temperature dependence of the isothermal bulk modulus at 1 bar pressure
It is well established that the product of the volume coefficient of thermal
expansion and the bulk modulus is nearly constant at temperatures higher than
the Debye temperature. Using this approximation allows predicting the values of
the bulk modulus. The derived analytical solution for the temperature
dependence of the isothermal bulk modulus has been applied to ten substances.
The good correlations to the experiments indicate that the expression may be
useful for substances for which bulk modulus data are lacking
Quantum spectrum as a time series : Fluctuation measures
The fluctuations in the quantum spectrum could be treated like a time series.
In this framework, we explore the statistical self-similarity in the quantum
spectrum using the detrended fluctuation analysis (DFA) and random matrix
theory (RMT). We calculate the Hausdorff measure for the spectra of atoms and
Gaussian ensembles and study their self-affine properties. We show that DFA is
equivalent to statistics of RMT, unifying two different
approaches.We exploit this connection to obtain theoretical estimates for the
Hausdorff measure.Comment: 4+ pages. 2 figure
Using the seismology of non-magnetic chemically peculiar stars as a probe of dynamical processes in stellar interiors
Chemical composition is a good tracer of hydrodynamical processes that occur
in stars as they often lead to mixing and particle transport. By comparing
abundances predicted by models and those observed in stars we can infer some
constraints on those mixing processes. As pulsations in stars are often very
sensitive to chemical composition, we can use asteroseismology to probe the
internal chemical composition of stars where no direct observations are
possible. In this paper I focus on main sequence stars Am, lambda bootis, and
HgMn stars and discuss what we can learn of mixing processes in those stars
from seismology.Comment: 10 pages,6 figures. accepted in Journal of astrophysics and
astronomy. proceedings of aries conferemce on asteroseismology. december 200
Relation Between First Arrival Time and Permeability in Self-Affine Fractures with Areas in Contact
We demonstrate that the first arrival time in dispersive processes in
self-affine fractures are governed by the same length scale characterizing the
fractures as that which controls their permeability. In one-dimensional channel
flow this length scale is the aperture of the bottle neck, i.e., the region
having the smallest aperture. In two dimensions, the concept of a bottle neck
is generalized to that of a minimal path normal to the flow. The length scale
is then the average aperture along this path. There is a linear relationship
between the first arrival time and this length scale, even when there is strong
overlap between the fracture surfaces creating areas with zero permeability. We
express the first arrival time directly in terms of the permeability.Comment: EPL (2012)
3-D multiobservable probabilistic inversion for the compositional and thermal structure of the lithosphere and upper mantle: III. Thermochemical tomography in the Western-Central U.S.
Acknowledgments We are indebted to F. Darbyshire and J. von Hunen for useful comments on earlier versions of this work. This manuscript benefited from thorough and constructive reviews by W. Levandowski and an anonymous reviewer. We also thank J. Connolly, M. Sambridge, B. Kennett, S. Lebedev, B. Shan, U. Faul, and M. Qashqai for insightful discussions about, and contributions to, some of the concepts presented in this paper. The work of J.C.A. has been supported by two Australian Research Council Discovery grants (DP120102372 and DP110104145). Seismic data are from the IRIS DMS. D.L.S. acknowledges support from NSF grant EAR-135866. This is contribution 848 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au) and 1106 in the GEMOC Key Centre (http://www.gemoc.mq.edu.au).Peer reviewedPublisher PD
A model for the distribution of aftershock waiting times
In this work the distribution of inter-occurrence times between earthquakes
in aftershock sequences is analyzed and a model based on a non-homogeneous
Poisson (NHP) process is proposed to quantify the observed scaling. In this
model the generalized Omori's law for the decay of aftershocks is used as a
time-dependent rate in the NHP process. The analytically derived distribution
of inter-occurrence times is applied to several major aftershock sequences in
California to confirm the validity of the proposed hypothesis.Comment: 4 pages, 3 figure
Kinetic description of hadron-hadron collisions
A transport model based on the mean free path approach to describe pp
collisions is proposed. We assume that hadrons can be treated as bags of
partons similarly to the MIT bag model. When the energy density in the
collision is higher than a critical value, the bags break and partons are
liberated. The partons expand and can make coalescence to form new hadrons. The
results obtained compare very well with available data and some prediction for
higher energies collisions are discussed. Based on the model we suggest that a
QGP could already be formed in the pp collisions at high energies
MR447: Seasonal Water Table and Temperature Relationships in Calcareous Till and Residual Soils of Central Maine
Water table depths and soil temperatures were monitored for four growing seasons in six calcareous till pedons developed on gently rolling to level till plains in Corinth and Exeter, Maine. These soils are part of a new catena that supports potato production in southeastern Penobscot County. Three of these coarse-loamy to fine-loamy pedons are moderately well drained Oxyaquic Eutrudepts taxadjuncts in potato fields, and three are somewhat poorly drained Aquic Dystric Eutrudepts in predominantly deciduous forest. Soil morphology, hydrologic data, and a,a dipyridyl applications support the described subgroup classification of each pedon, along with the udic moisture regime. Despite a smooth, glaciated landscape that would suggest the presence of extensive lodgment till, five observation sites lacked a densic contact and one contained residuum (saprolite) in the substratum. Apparent water tables in the SPD very deep soils, as well as oxyaquic hydrology in the deep soils on 0 to 3 percent slopes, suggest the more permeable subglacial melt-out till predominating, rather than lodgment till in all of these pedons. Growing season concepts were compared based on frost-free season at 0 and -2.2° C thresholds, soil temperatures in the plow layer, soil temperature at 50 cms and well-water temperature. The commencement of the growing season in the spring did not differ much across all five concepts. However, in the fall there was a 4- to 8-week lag between the air or shallower soil-temperature growing-season concepts and the deeper soil or well-water-temperature growing-season concepts. Daytime air temperature during the first 2 years of monitoring differed significantly between spring and fall seasons, but not between field and forest sites within each season.https://digitalcommons.library.umaine.edu/aes_miscreports/1027/thumbnail.jp
A search for solar-like oscillations in the Am star HD 209625
The goal is to test the structure of hot metallic stars, and in particular
the structure of a near-surface convection zone using asteroseismic
measurements. Indeed, stellar models including a detailed treatement of the
radiative diffusion predict the existence of a near-surface convection zone in
order to correctly reproduce the anomalies in surface abundances that are
observed in Am stars. The Am star HD 209625 was observed with the Harps
spectrograph mounted on the 3.6-m telescope at the ESO La Silla Observatory
(Chile) during 9 nights in August 2005. This observing run allowed us to
collect 1243 radial velocity (RV) measurements, with a standard deviation of
1.35 m/s. The power spectrum associated with these RV measurements does not
present any excess. Therefore, either the structure of the external layers of
this star does not allow excitation of solar-like oscillations, or the
amplitudes of the oscillations remain below 20-30 cm/s (depending on their
frequency range).Comment: 5 pages, 4 figures, A&A accepte
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