30,259 research outputs found
Analysis of Sparse MIMO Radar
We consider a multiple-input-multiple-output radar system and derive a
theoretical framework for the recoverability of targets in the azimuth-range
domain and the azimuth-range-Doppler domain via sparse approximation
algorithms. Using tools developed in the area of compressive sensing, we prove
bounds on the number of detectable targets and the achievable resolution in the
presence of additive noise. Our theoretical findings are validated by numerical
simulations
Gauge-invariant coherent states for Loop Quantum Gravity II: Non-abelian gauge groups
This is the second paper concerning gauge-invariant coherent states for Loop
Quantum Gravity. Here, we deal with the gauge group SU(2), this being a
significant complication compared to the abelian U(1) case encountered in the
previous article. We study gauge-invariant coherent states on certain special
graphs by analytical and numerical methods. We find that their overlap is
Gauss-peaked in gauge-invariant quantities, as long as states are not labeled
by degenerate gauge orbits, i.e. points where the gauge-invariant configuration
space has singularities. In these cases the overlaps are still concentrated
around these points, but the peak profile exhibits a plateau structure. This
shows how the semiclassical properties of the states are influenced by the
geometry of the gauge-invariant phase space.Comment: 60 pages, 8 figure
Gauge-invariant coherent states for Loop Quantum Gravity I: Abelian gauge groups
In this paper we investigate the properties of gauge-invariant coherent
states for Loop Quantum Gravity, for the gauge group U(1). This is done by
projecting the corresponding complexifier coherent states, which have been
applied in numerous occasions to investigate the semiclassical limit of the
kinematical sector, to the gauge-invariant Hilbert space. This being the first
step to construct physical coherent states, we arrive at a set of
gauge-invariant states that approximate well the gauge-invariant degrees of
freedom of abelian LQG. Furthermore, these states turn out to encode explicit
information about the graph topology, and show the same pleasant peakedness
properties known from the gauge-variant complexifier coherent states.Comment: 36 page
A Bipartite Kronig-Penney Model with Dirac Potential Scatterers
Here we present a simple extension to the age-old Kronig-Penney model, which
is made to be bipartite by varying either the scatterer separations or the
potential heights. In doing so, chiral (sublattice) symmetry can be introduced.
When such a symmetry is present, topologically protected edge states are seen
to exist. The solution proceeds through the conventional scattering formalism
used to study the Kronig-Penney model, which does not require further
tight-binding approximations or mapping into a Su-Schrieffer-Heeger model. The
topological invariant for this specific system is found to be the winding of
the reflection coefficient, ultimately linked to the system wavefunction. The
solution of such a simple and illustrative 1D problem, whose topological
content is extracted without requiring further tight-binding approximations,
represents the novel aspect of our paper. The cases in which chiral symmetry is
absent are then seen to not host topologically protected edge states, as
verified by the behaviour of the reflection coefficient and the absence of
winding.Comment: 15 pages, 16 figures. Noticed crucial typos in equations 8 and 9
leading to a change of figures 5 and 11. The analysis is unchanged however.
Change of abstract to better present novel aspects of pape
THE DISTRIBUTION OF FULL INCOME VERSUS MONEY INCOME IN THE UNITED STATES
This paper compares the distribution of money income and full income across households in the United States. The concept of full income was introduced in Becker's household model and provides a framework for estimating the economic value of productive non-market activities and leisure. If the allocation of time is voluntary, full income may be a better measure of economic welfare than money income. Non-parametric Lorenz curves and Gini coefficients are used to compare the two distributions. The data are from the Census Bureau's Survey of Income and Program Participation for 1984-86. Full income is more equally distributed than money income. However, the distribution remains very unequal. The income distributions are also compared for specific types of households.Consumer/Household Economics,
Minimality and mutation-equivalence of polygons
We introduce a concept of minimality for Fano polygons. We show that, up to
mutation, there are only finitely many Fano polygons with given singularity
content, and give an algorithm to determine the mutation-equivalence classes of
such polygons. This is a key step in a program to classify orbifold del Pezzo
surfaces using mirror symmetry. As an application, we classify all Fano
polygons such that the corresponding toric surface is qG-deformation-equivalent
to either (i) a smooth surface; or (ii) a surface with only singularities of
type 1/3(1,1).Comment: 29 page
Variable Selection and Model Choice in Structured Survival Models
In many situations, medical applications ask for flexible survival models that allow to extend the classical Cox-model via the
inclusion of time-varying and nonparametric effects. These structured survival models are very flexible but additional
difficulties arise when model choice and variable selection is desired. In particular, it has to be decided which covariates
should be assigned time-varying effects or whether parametric modeling is sufficient for a given covariate. Component-wise
boosting provides a means of likelihood-based model fitting that enables simultaneous variable selection and model choice. We
introduce a component-wise likelihood-based boosting algorithm for survival data that permits the inclusion of both parametric
and nonparametric time-varying effects as well as nonparametric effects of continuous covariates utilizing penalized splines as
the main modeling technique. Its properties
and performance are investigated in simulation studies.
The new modeling approach is used to build a flexible survival model for
intensive care patients suffering from severe sepsis.
A software implementation is available to the interested reader
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