11,048 research outputs found
On the Ernst electro-vacuum equations and ergosurfaces
The question of smoothness at the ergosurface of the space-time metric
constructed out of solutions (E,phi) of the Ernst electro-vacuum equations is
considered. We prove smoothness of those ergosurfaces at which Re(E) provides
the dominant contribution to f=-(Re(E)+|phi|^2) at the zero-level-set of f.
Some partial results are obtained in the remaining cases: in particular we give
examples of leading-order solutions with singular isolated "ergocircles".Comment: 15 pages, no figures, minor change
Towards a classification of vacuum near-horizons geometries
We prove uniqueness of the near-horizon geometries arising from degenerate
Kerr black holes within the collection of nearby vacuum near-horizon
geometries.Comment: 16 pages, 3 figures; minor changes to match published versio
Space-time diagrammatics
We introduce a new class of two-dimensional diagrams, the \emph{projection
diagrams}, as a tool to visualize the global structure of space-times. We
construct the diagrams for several metrics of interest, including the
Kerr-Newman - (anti) de Sitter family, with or without cosmological constant,
and the Emparan-Reall black rings.Comment: 41 pages, minor changes and correction
Two Dimensional Ir-Cluster Lattices on Moir\'e of Graphene with Ir(111)
Lattices of Ir clusters have been grown by vapor phase deposition on graphene
moir\'{e}s on Ir(111). The clusters are highly ordered, spatially and thermally
stable below 500K. Their narrow size distribution is tunable from 4 to about
130 atoms. A model for cluster binding to the graphene is presented based on
scanning tunneling microscopy and density functional theory. The proposed
binding mechanism suggests that similar cluster lattices might be grown of
materials other than Ir.Comment: Submitted to PRL on 27Apr0
A user's guide for V174, a program using a finite difference method to analyze transonic flow over oscillating wings
The design and usage of a pilot program using a finite difference method for calculating the pressure distributions over harmonically oscillating wings in transonic flow are discussed. The procedure used is based on separating the velocity potential into steady and unsteady parts and linearizing the resulting unsteady differential equation for small disturbances. The steady velocity potential which must be obtained from some other program, is required for input. The unsteady differential equation is linear, complex in form with spatially varying coefficients. Because sinusoidal motion is assumed, time is not a variable. The numerical solution is obtained through a finite difference formulation and a line relaxation solution method
Sadder but fitter. The evolutionary function of depressive symptoms following fetal loss
A literature review about an evolutionary model of fetal loss depression
is presented. This model conceptualizes depression following miscarriage
or stillbirth as an evolutionary protective mechanism to avoid
further fetal loss. It postulates that depressive symptoms delay the next
reproduction and save maternal resources. These symptoms along
with hypochondric symptoms of depression which lead to a search for
causes and reappraisal of environmental factors, are probably
adaptations to causes of further fetal loss (e.g. epidemics, famines,
infections, environmental toxins)
Induction Mapping of the 3D-Modulated Spin Texture of Skyrmions in Thin Helimagnets
Envisaged applications of skyrmions in magnetic memory and logic devices
crucially depend on the stability and mobility of these topologically
non-trivial magnetic textures in thin films. We present for the first time
quantitative maps of the magnetic induction that provide evidence for a 3D
modulation of the skyrmionic spin texture. The projected in-plane magnetic
induction maps as determined from in-line and off-axis electron holography
carry the clear signature of Bloch skyrmions. However, the magnitude of this
induction is much smaller than the values expected for homogeneous Bloch
skyrmions that extend throughout the thickness of the film. This finding can
only be understood, if the underlying spin textures are modulated along the
out-of-plane z direction. The projection of (the in-plane magnetic induction
of) helices is further found to exhibit thickness-dependent lateral shifts,
which show that this z modulation is accompanied by an (in-plane) modulation
along the x and y directions
Analytic Continuation of Quantum Monte Carlo Data by Stochastic Analytical Inference
We present an algorithm for the analytic continuation of imaginary-time
quantum Monte Carlo data which is strictly based on principles of Bayesian
statistical inference. Within this framework we are able to obtain an explicit
expression for the calculation of a weighted average over possible energy
spectra, which can be evaluated by standard Monte Carlo simulations, yielding
as by-product also the distribution function as function of the regularization
parameter. Our algorithm thus avoids the usual ad-hoc assumptions introduced in
similar algortihms to fix the regularization parameter. We apply the algorithm
to imaginary-time quantum Monte Carlo data and compare the resulting energy
spectra with those from a standard maximum entropy calculation
- …