5,253 research outputs found
Mechanistic Links Between the Sedimentary Redox Cycle and Marine Acid-Base Chemistry
The redox state of Earth's surface is controlled on geological timescales by the flow of electrons through the sedimentary rock cycle, mediated largely by the weathering and burial of CâSâFe phases. These processes buffer atmospheric pOâ. At the same time, COâ influxes and carbonate burial control seawater acidâbase chemistry and climate over long timescales via the carbonateâsilicate cycle. However, these two systems are mechanistically linked and impact each other via charge balance in the hydrosphere. Here, we use a lowâorder Earth system model to interrogate a subset of these connections, with a focus on changes that occur during perturbations to electron flow through the sedimentary rock cycle. We show that the net oxidation or reduction of the Earth's surface can play an important role in controlling acidâbase processes in the oceans and thus climate, and suggest that these links should be more fully integrated into interpretive frameworks aimed at understanding Earth system evolution throughout Precambrian and Phanerozoic time
The two-proton shell gap in Sn isotopes
We present an analysis of two-proton shell gaps in Sn isotopes. As the
theoretical tool we use self-consistent mean-field models, namely the
relativistic mean-field model and the Skyrme-Hartree-Fock approach, both with
two different pairing forces, a delta interaction (DI) model and a
density-dependent delta interaction (DDDI). We investigate the influence of
nuclear deformation as well as collective correlations and find that both
effects contribute significantly. Moreover, we find a further significant
dependence on the pairing force used. The inclusion of deformation plus
correlation effects and the use of DDDI pairing provides agreement with the
data.Comment: gzipped tar archiv containing LaTeX source, bibliography file
(*.bbl), all figures as *.eps, and the style file
Static Electric Dipole Polarizabilities of Na Clusters
The static electric dipole polarizability of clusters with
even N has been calculated in a collective, axially averaged and a
three-dimensional, finite-field approach for , including the
ionic structure of the clusters. The validity of a collective model for the
static response of small systems is demonstrated. Our density functional
calculations verify the trends and fine structure seen in a recent experiment.
A pseudopotential that reproduces the experimental bulk bond length and atomic
energy levels leads to a substantial increase in the calculated
polarizabilities, in better agreement with experiment. We relate remaining
differences in the magnitude of the theoretical and experimental
polarizabilities to the finite temperature present in the experiments.Comment: 7 pages, 3 figures, accepted for publication in the European Physical
Journal
Two-Photon Excitation of Low-Lying Electronic Quadrupole States in Atomic Clusters
A simple scheme of population and detection of low-lying electronic
quadrupole modes in free small deformed metal clusters is proposed. The scheme
is analyzed in terms of the TDLDA (time-dependent local density approximation)
calculations. As test case, the deformed cluster is considered.
Long-living quadrupole oscillations are generated via resonant two-photon
(two-dipole) excitation and then detected through the appearance of satellites
in the photoelectron spectra generated by a probe pulse. Femtosecond pump and
probe pulses with intensities and
pulse duration fs are found to be optimal. The modes of
interest are dominated by a single electron-hole pair and so their energies,
being combined with the photoelectron data for hole states, allow to gather new
information about mean-field spectra of valence electrons in the HOMO-LUMO
region. Besides, the scheme allows to estimate the lifetime of electron-hole
pairs and hence the relaxation time of electronic energy into ionic heat.Comment: 4 pages, 4 figure
Addressing current challenges in cancer immunotherapy with mathematical and computational modeling
The goal of cancer immunotherapy is to boost a patient's immune response to a
tumor. Yet, the design of an effective immunotherapy is complicated by various
factors, including a potentially immunosuppressive tumor microenvironment,
immune-modulating effects of conventional treatments, and therapy-related
toxicities. These complexities can be incorporated into mathematical and
computational models of cancer immunotherapy that can then be used to aid in
rational therapy design. In this review, we survey modeling approaches under
the umbrella of the major challenges facing immunotherapy development, which
encompass tumor classification, optimal treatment scheduling, and combination
therapy design. Although overlapping, each challenge has presented unique
opportunities for modelers to make contributions using analytical and numerical
analysis of model outcomes, as well as optimization algorithms. We discuss
several examples of models that have grown in complexity as more biological
information has become available, showcasing how model development is a dynamic
process interlinked with the rapid advances in tumor-immune biology. We
conclude the review with recommendations for modelers both with respect to
methodology and biological direction that might help keep modelers at the
forefront of cancer immunotherapy development.Comment: Accepted for publication in the Journal of the Royal Society
Interfac
Criteria for nonlinear parameters of relativistic mean field models
Based on the properties of the critical and the actual effective masses of
sigma and omega mesons, criteria to estimate the values of the isoscalar
nonlinear terms of the standard relativistic mean field model that reproduce
stable equations of state in respect to particle hole excitation at high
densities are derived. The relation between nuclear matter stability and the
symmetric nuclear matter properties are shown. The criteria are used to analyze
in a more systematic way the high-density longitudinal and transverse
instabilities of some parameter sets of relativistic mean field models. The
critical role of the vector and vector-scalar nonlinear terms is also discussed
quantitatively.Comment: 21 pages, 10 figures, 4 tables. Accepted for Publication in Physical
review
New Coordinates for the Amplitude Parameter Space of Continuous Gravitational Waves
The parameter space for continuous gravitational waves (GWs) can be divided
into amplitude parameters (signal amplitude, inclination and polarization
angles describing the orientation of the source, and an initial phase) and
phase-evolution parameters. The division is useful in part because the
Jaranowski-Krolak-Schutz (JKS) coordinates on the four-dimensional amplitude
parameter space allow the GW signal to be written as a linear combination of
four template waveforms with the JKS coordinates as coefficients. We define a
new set of coordinates on the amplitude parameter space, with the same
properties, which is more closely connected to the physical amplitude
parameters. These naturally divide into two pairs of Cartesian-like coordinates
on two-dimensional subspaces, one corresponding to left- and the other to
right-circular polarization. We thus refer to these as CPF (circular
polarization factored) coordinates. The corresponding two sets of polar
coordinates (known as CPF-polar) can be related in a simple way to the physical
parameters. We illustrate some simplifying applications for these various
coordinate systems, such as: a calculation of Jacobians between various
coordinate systems; an illustration of the signal coordinate singularities
associated with left- and right-circular polarization, which correspond to the
origins of the two two-dimensional subspaces; and an elucidation of the form of
the log-likelihood ratio between hypotheses of Gaussian noise with and without
a continuous GW signal. These are used to illustrate some of the prospects for
approximate evaluation of a Bayesian detection statistic defined by
marginalization over the physical parameter space. Additionally, in the
presence of simplifying assumptions about the observing geometry, we are able
to explicitly evaluate the integral for the Bayesian detection statistic, and
compare it to the approximate results.Comment: REVTeX, 18 pages, 8 image files included in 7 figure
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