316 research outputs found
THE NUMÉRAIRE PROPERTY AND LONG-TERM GROWTH OPTIMALITY FOR DRAWDOWN-CONSTRAINED INVESTMENTS
© 2014 Wiley Periodicals, Inc. We consider the portfolio choice problem for a long-run investor in a general continuous semimartingale model. We combine the decision criterion of pathwise growth optimality with a flexible specification of attitude toward risk, encoded by a linear drawdown constraint imposed on admissible wealth processes. We define the constrained numéraire property through the notion of expected relative return and prove that drawdown-constrained numéraire portfolio exists and is unique, but may depend on the investment horizon. However, when sampled at the times of its maximum and asymptotically as the time-horizon becomes distant, the drawdown-constrained numéraire portfolio is given explicitly through a model-independent transformation of the unconstrained numéraire portfolio. The asymptotically growth-optimal strategy is obtained as limit of numéraire strategies on finite horizons
On the existence of sure profits via flash strategies
© Applied Probability Trust 2019. We introduce and study the notion of sure profits via flash strategies, consisting of a high-frequency limit of buy-and-hold trading strategies. In a fully general setting, without imposing any semimartingale restriction, we prove that there are no sure profits via flash strategies if and only if asset prices do not exhibit predictable jumps. This result relies on the general theory of processes and provides the most general formulation of the well-known fact that, in an arbitrage-free financial market, asset prices (including dividends) should not exhibit jumps of a predictable direction or magnitude at predictable times. We furthermore show that any price process is always right-continuous in the absence of sure profits. Our results are robust under small transaction costs and imply that, under minimal assumptions, price changes occurring at scheduled dates should only be due to unanticipated information releases
A compact ultrahigh-vacuum system for the in situ investigation of III/V semiconductor surfaces
A compact ultrahigh vacuum (UHV) system has been built to study growth and properties of III/V semiconductor surfaces and nanostructures. The system allows one to grow III/V semiconductor surfaces by molecular beam epitaxy (MBE) and analyze their surface by a variety of surface analysis techniques. The geometric structure is examined by scanning tunneling microscopy (STM), low-energy electron diffraction and reflection high-energy electron diffraction. The electronic properties of the surfaces are studied by angular resolved photoemission either in the laboratory using a helium discharge lamp or at the Berlin Synchrotron Radiation Facility BESSY. In order to meet the space restriction at BESSY the system dimensions are kept very small. A detailed description of the apparatus and the sample handling system is given. For the UHV-STM (Park Scientific Instruments, VP2) a new, versatile tip handling mechanism has been developed. It allows the transfer of tips out of the chamber and furthermore, the in situ tip cleaning by electron annealing. In addition, another more reliable in situ tip-preparation technique operating the STM in the field emission regime is described. The ability of the system is shown by an atomically resolved STM image of the c(4×4) reconstructed GaAs(001) surface
Reduction and reconstruction of stochastic differential equations via symmetries
An algorithmic method to exploit a general class of infinitesimal symmetries
for reducing stochastic differential equations is presented and a natural
definition of reconstruction, inspired by the classical reconstruction by
quadratures, is proposed. As a side result the well-known solution formula for
linear one-dimensional stochastic differential equations is obtained within
this symmetry approach. The complete procedure is applied to several examples
with both theoretical and applied relevance
Origami constraints on the initial-conditions arrangement of dark-matter caustics and streams
In a cold-dark-matter universe, cosmological structure formation proceeds in
rough analogy to origami folding. Dark matter occupies a three-dimensional
'sheet' of free- fall observers, non-intersecting in six-dimensional
velocity-position phase space. At early times, the sheet was flat like an
origami sheet, i.e. velocities were essentially zero, but as time passes, the
sheet folds up to form cosmic structure. The present paper further illustrates
this analogy, and clarifies a Lagrangian definition of caustics and streams:
caustics are two-dimensional surfaces in this initial sheet along which it
folds, tessellating Lagrangian space into a set of three-dimensional regions,
i.e. streams. The main scientific result of the paper is that streams may be
colored by only two colors, with no two neighbouring streams (i.e. streams on
either side of a caustic surface) colored the same. The two colors correspond
to positive and negative parities of local Lagrangian volumes. This is a severe
restriction on the connectivity and therefore arrangement of streams in
Lagrangian space, since arbitrarily many colors can be necessary to color a
general arrangement of three-dimensional regions. This stream two-colorability
has consequences from graph theory, which we explain. Then, using N-body
simulations, we test how these caustics correspond in Lagrangian space to the
boundaries of haloes, filaments and walls. We also test how well outer caustics
correspond to a Zel'dovich-approximation prediction.Comment: Clarifications and slight changes to match version accepted to MNRAS.
9 pages, 5 figure
Quantifying distortions of the Lagrangian dark-matter mesh in cosmology
We examine the Lagrangian divergence of the displacement field, arguably a
more natural object than the density in a Lagrangian description of
cosmological large-scale structure. This quantity, which we denote \psi,
quantifies the stretching and distortion of the initially homogeneous lattice
of dark-matter particles in the universe. \psi\ encodes similar information as
the density, but the correspondence has subtleties. It corresponds better to
the log-density A than the overdensity \delta. A Gaussian distribution in \psi\
produces a distribution in A with slight skewness; in \delta, we find that in
many cases the skewness is further increased by 3.
A local spherical-collapse-based (SC) fit found by Bernardeau gives a formula
for \psi's particle-by-particle behavior that works quite well, better than
applying Lagrangian perturbation theory (LPT) at first or second (2LPT) order.
In 2LPT, there is a roughly parabolic relation between initial and final \psi\
that can give overdensities in deep voids, so low-redshift, high-resolution
2LPT realizations should be used with caution. The SC fit excels at predicting
\psi\ until streams cross; then, for particles forming haloes, \psi\ plummets
as in a waterfall to -3. This gives a new method for producing N-particle
realizations. Compared to LPT realizations, such SC realizations give reduced
stream-crossing, and better visual and 1-point-PDF correspondence to the
results of full gravity. LPT, on the other hand, predicts large-scale flows and
the large-scale power-spectrum amplitude better, unless an empirical correction
is added to the SC formula.Comment: Changes in presentation to match MNRAS-accepted version, 14 pages, 15
figure
Only the Lonely: H I Imaging of Void Galaxies
Void galaxies, residing within the deepest underdensities of the Cosmic Web,
present an ideal population for the study of galaxy formation and evolution in
an environment undisturbed by the complex processes modifying galaxies in
clusters and groups, as well as provide an observational test for theories of
cosmological structure formation. We have completed a pilot survey for the HI
imaging aspects of a new Void Galaxy Survey (VGS), imaging 15 void galaxies in
HI in local (d < 100 Mpc) voids. HI masses range from 3.5 x 10^8 to 3.8 x 10^9
M_sun, with one nondetection with an upper limit of 2.1 x 10^8 M_sun. Our
galaxies were selected using a structural and geometric technique to produce a
sample that is purely environmentally selected and uniformly represents the
void galaxy population. In addition, we use a powerful new backend of the
Westerbork Synthesis Radio Telescope that allows us to probe a large volume
around each targeted galaxy, simultaneously providing an environmentally
constrained sample of fore- and background control sample of galaxies while
still resolving individual galaxy kinematics and detecting faint companions in
HI. This small sample makes up a surprisingly interesting collection of
perturbed and interacting galaxies, all with small stellar disks. Four galaxies
have significantly perturbed HI disks, five have previously unidentified
companions at distances ranging from 50 to 200 kpc, two are in interacting
systems, and one was found to have a polar HI disk. Our initial findings
suggest void galaxies are a gas-rich, dynamic population which present evidence
of ongoing gas accretion, major and minor interactions, and filamentary
alignment despite the surrounding underdense environment.Comment: 53 pages, 18 figures, accepted for publication in AJ. High resolution
available at http://www.astro.columbia.edu/~keejo/kreckel2010.pd
The fully connected N-dimensional skeleton: probing the evolution of the cosmic web
A method to compute the full hierarchy of the critical subsets of a density
field is presented. It is based on a watershed technique and uses a probability
propagation scheme to improve the quality of the segmentation by circumventing
the discreteness of the sampling. It can be applied within spaces of arbitrary
dimensions and geometry. This recursive segmentation of space yields, for a
-dimensional space, a succession of -dimensional subspaces that
fully characterize the topology of the density field. The final 1D manifold of
the hierarchy is the fully connected network of the primary critical lines of
the field : the skeleton. It corresponds to the subset of lines linking maxima
to saddle points, and provides a definition of the filaments that compose the
cosmic web as a precise physical object, which makes it possible to compute any
of its properties such as its length, curvature, connectivity etc... When the
skeleton extraction is applied to initial conditions of cosmological N-body
simulations and their present day non linear counterparts, it is shown that the
time evolution of the cosmic web, as traced by the skeleton, is well accounted
for by the Zel'dovich approximation. Comparing this skeleton to the initial
skeleton undergoing the Zel'dovich mapping shows that two effects are competing
during the formation of the cosmic web: a general dilation of the larger
filaments that is captured by a simple deformation of the skeleton of the
initial conditions on the one hand, and the shrinking, fusion and disappearance
of the more numerous smaller filaments on the other hand. Other applications of
the N dimensional skeleton and its peak patch hierarchy are discussed.Comment: Accepted for publication in MNRA
Non-intersecting squared Bessel paths and multiple orthogonal polynomials for modified Bessel weights
We study a model of non-intersecting squared Bessel processes in the
confluent case: all paths start at time at the same positive value , remain positive, and are conditioned to end at time at . In
the limit , after appropriate rescaling, the paths fill out a
region in the -plane that we describe explicitly. In particular, the paths
initially stay away from the hard edge at , but at a certain critical
time the smallest paths hit the hard edge and from then on are stuck to
it. For we obtain the usual scaling limits from random matrix
theory, namely the sine, Airy, and Bessel kernels. A key fact is that the
positions of the paths at any time constitute a multiple orthogonal
polynomial ensemble, corresponding to a system of two modified Bessel-type
weights. As a consequence, there is a matrix valued
Riemann-Hilbert problem characterizing this model, that we analyze in the large
limit using the Deift-Zhou steepest descent method. There are some novel
ingredients in the Riemann-Hilbert analysis that are of independent interest.Comment: 59 pages, 11 figure
OpenDF - A Dataflow Toolset for Reconfigurable Hardware and Multicore Systems
This paper presents the OpenDF framework and recalls that dataflow programming was once invented to address the problem of parallel computing. We discuss the problems with an imperative style, von Neumann programs, and present what we believe are the advantages of using a dataflow programming model. The CAL actor language is briefly presented and its role in the ISO/MPEG standard is discussed. The Dataflow Interchange Format (DIF) and related tools can be used for analysis of actors and networks, demonstrating the advantages of a dataflow approach. Finally, an overview of a case study implementing an MPEG-4 decoder is given
- …