19,995 research outputs found
Asymptotic Derivation and Numerical Investigation of Time-Dependent Simplified Pn Equations
The steady-state simplified Pn (SPn) approximations to the linear Boltzmann
equation have been proven to be asymptotically higher-order corrections to the
diffusion equation in certain physical systems. In this paper, we present an
asymptotic analysis for the time-dependent simplified Pn equations up to n = 3.
Additionally, SPn equations of arbitrary order are derived in an ad hoc way.
The resulting SPn equations are hyperbolic and differ from those investigated
in a previous work by some of the authors. In two space dimensions, numerical
calculations for the Pn and SPn equations are performed. We simulate neutron
distributions of a moving rod and present results for a benchmark problem,
known as the checkerboard problem. The SPn equations are demonstrated to yield
significantly more accurate results than diffusion approximations. In addition,
for sufficiently low values of n, they are shown to be more efficient than Pn
models of comparable cost.Comment: 32 pages, 7 figure
Influence of correlations on molecular recognition
The influence of the patchiness and correlations in the distribution of
hydrophobic and polar residues at the interface between two rigid biomolecules
on their recognition ability is investigated in idealised coarse-grained
lattice models. A general two-stage approach is utilised where an ensemble of
probe molecules is designed first and the recognition ability of the probe
ensemble is related to the free energy of association with both the target
molecule and a different rival molecule in a second step. The influence of
correlation effects are investigated using numerical Monte Carlo techniques and
mean field methods. Correlations lead to different optimum characteristic
lengths of the hydrophobic and polar patches for the mutual design of the two
biomolecules on the one hand and their recognition ability in the presence of
other molecules on the other hand.Comment: 15 pages, 5 figure
Spectroscopic Constraints on the Form of the Stellar Cluster Mass Function
This contribution addresses the question of whether the initial cluster mass
function (ICMF) has a fundamental limit (or truncation) at high masses. The
shape of the ICMF at high masses can be studied using the most massive young
(<10 Myr) clusters, however this has proven difficult due to low-number
statistics. In this contribution we use an alternative method based on the
luminosities of the brightest clusters, combined with their ages. If a
truncation is present, a generic prediction (nearly independent of the cluster
disruption law adopted) is that the median age of bright clusters should be
younger than that of fainter clusters. In the case of an non-truncated ICMF,
the median age should be independent of cluster luminosity. Here, we present
optical spectroscopy of twelve young stellar clusters in the face-on spiral
galaxy NGC 2997. The spectra are used to estimate the age of each cluster, and
the brightness of the clusters is taken from the literature. The observations
are compared with the model expectations of Larsen (2009) for various ICMF
forms and both mass dependent and mass independent cluster disruption. While
there exists some degeneracy between the truncation mass and the amount of mass
independent disruption, the observations favour a truncated ICMF. For low or
modest amounts of mass independent disruption, a truncation mass of 5-6*10^5
Msun is estimated, consistent with previous determinations. Additionally, we
investigate possible truncations in the ICMF in the spiral galaxy M83, the
interacting Antennae galaxies, and the collection of spiral and dwarf galaxies
present in Larsen (2009) based on photometric catalogues taken from the
literature, and find that all catalogues are consistent with having a
(environmentally dependent) truncation in the cluster mass functions.Comment: 6 pages, 5 figures, in press, A&A Research Note
Separability of Black Holes in String Theory
We analyze the origin of separability for rotating black holes in string
theory, considering both massless and massive geodesic equations as well as the
corresponding wave equations. We construct a conformal Killing-Stackel tensor
for a general class of black holes with four independent charges, then identify
two-charge configurations where enhancement to an exact Killing-Stackel tensor
is possible. We show that further enhancement to a conserved Killing-Yano
tensor is possible only for the special case of Kerr-Newman black holes. We
construct natural null congruences for all these black holes and use the
results to show that only the Kerr-Newman black holes are algebraically special
in the sense of Petrov. Modifying the asymptotic behavior by the subtraction
procedure that induces an exact SL(2)^2 also preserves only the conformal
Killing-Stackel tensor. Similarly, we find that a rotating Kaluza-Klein black
hole possesses a conformal Killing-Stackel tensor but has no further
enhancements.Comment: 27 page
Singapore Convention Presents an Opportunity for Georgia in Mediation
On Dec. 20, 2018, the United Nations General Assembly adopted the Singapore Convention. The Singapore Convention ensures that a mediation settlement reached by parties will be binding and enforceable in accordance with a streamlined procedure. The convention will compel contracting states to recognize international mediation settlement agreements in commercial disputes. On Aug. 7, the opening day of the convention, a record 46 nations signed the Singapore Convention on Mediation, including the United States.
The Singapore Convention presents a unique opportunity for Georgia to become a forum for hospitable mediation. Much like it adopted an international arbitration code, the state could consider enacting an international mediation law tied to the provisions of the Singapore Convention. Such legislation could enhance Georgia’s appeal as a mediation forum and build upon its reputation as a jurisdiction hospitable to business, including the resolution of business disputes
Extraction efficiency of drifting electrons in a two-phase xenon time projection chamber
We present a measurement of the extraction efficiency of quasi-free electrons
from the liquid into the gas phase in a two-phase xenon time-projection
chamber. The measurements span a range of electric fields from 2.4 to 7.1 kV/cm
in the liquid xenon, corresponding to 4.5 to 13.1 kV/cm in the gaseous xenon.
Extraction efficiency continues to increase at the highest extraction fields,
implying that additional charge signal may be attained in two-phase xenon
detectors through careful high-voltage engineering of the gate-anode region
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