663 research outputs found
Optimal Investment Under Transaction Costs: A Threshold Rebalanced Portfolio Approach
We study optimal investment in a financial market having a finite number of
assets from a signal processing perspective. We investigate how an investor
should distribute capital over these assets and when he should reallocate the
distribution of the funds over these assets to maximize the cumulative wealth
over any investment period. In particular, we introduce a portfolio selection
algorithm that maximizes the expected cumulative wealth in i.i.d. two-asset
discrete-time markets where the market levies proportional transaction costs in
buying and selling stocks. We achieve this using "threshold rebalanced
portfolios", where trading occurs only if the portfolio breaches certain
thresholds. Under the assumption that the relative price sequences have
log-normal distribution from the Black-Scholes model, we evaluate the expected
wealth under proportional transaction costs and find the threshold rebalanced
portfolio that achieves the maximal expected cumulative wealth over any
investment period. Our derivations can be readily extended to markets having
more than two stocks, where these extensions are pointed out in the paper. As
predicted from our derivations, we significantly improve the achieved wealth
over portfolio selection algorithms from the literature on historical data
sets.Comment: Submitted to IEEE Transactions on Signal Processin
Influence of osmotic and metal stresses on nitrogenase activity of cyanobacteria ýsolated from paddy fields
Samples were collected from paddy fields in Corum-Turk.ye. Nitrogen-free BG-11 medium was used for isolation of nitrogen fixing cyanobacteria. Acetylene reduction technique was used to determine the effects of different chemical agents on the nitrogenase activities of the cyanobacteria, which were identified at the genus level. Nostoc showed the highest nitrogenase activity (0.09 ethylene ƒÊl/mg.h) at 50 mM salt concentration. At 60 mM sucrose concentration, Nostoc showed the highest nitrogenase activity (0.08 ethylene ƒÊl/mg.h). The highest tolerances for the metals were present in Anabaena (0.006 ethylene ƒÊl/mg.h) for iron (20 ppm), Nodularia 0.1 ethylene ƒÊl/mg.h (for manganese 20 ppm) and Nostoc 0.96 ethylene ƒÊl/mg.h (for zinc 5 ppm)
Quasi Periodic Oscillations (QPOs) and frequencies in an accretion disk and comparison with the numerical results from non-rotating black hole computed by the GRH code
The shocked wave created on the accretion disk after different physical
phenomena (accretion flows with pressure gradients, star-disk interaction etc.)
may be responsible observed Quasi Periodic Oscillations (QPOs) in ray
binaries. We present the set of characteristics frequencies associated with
accretion disk around the rotating and non-rotating black holes for one
particle case. These persistent frequencies are results of the rotating pattern
in an accretion disk. We compare the frequency's from two different numerical
results for fluid flow around the non-rotating black hole with one particle
case. The numerical results are taken from our papers Refs.\refcite{Donmez2}
and \refcite{Donmez3} using fully general relativistic hydrodynamical code with
non-selfgravitating disk. While the first numerical result has a relativistic
tori around the black hole, the second one includes one-armed spiral shock wave
produced from star-disk interaction. Some physical modes presented in the QPOs
can be excited in numerical simulation of relativistic tori and spiral waves on
the accretion disk. The results of these different dynamical structures on the
accretion disk responsible for QPOs are discussed in detail.Comment: 13 figures, added reference, accepted for publication in Modern
Physics Letters
Robust Least Squares Methods Under Bounded Data Uncertainties
Cataloged from PDF version of article.We study the problem of estimating an unknown deterministic signal that is observed through
an unknown deterministic data matrix under additive noise. In particular, we present a minimax
optimization framework to the least squares problems, where the estimator has imperfect data
matrix and output vector information. We define the performance of an estimator relative to the
performance of the optimal least squares (LS) estimator tuned to the underlying unknown data
matrix and output vector, which is defined as the regret of the estimator. We then introduce an
efficient robust LS estimation approach that minimizes this regret for the worst possible data matrix
and output vector, where we refrain from any structural assumptions on the data. We demonstrate
that minimizing this worst-case regret can be cast as a semi-definite programming (SDP) problem.
We then consider the regularized and structured LS problems and present novel robust estimation
methods by demonstrating that these problems can also be cast as SDP problems. We illustrate
the merits of the proposed algorithms with respect to the well-known alternatives in the literature
through our simulations
Robust estimation in flat fading channels under bounded channel uncertainties
Cataloged from PDF version of article.We investigate channel equalization problem for time-varying flat fading channels under bounded
channel uncertainties. We analyze three robust methods to estimate an unknown signal transmitted
through a time-varying flat fading channel. These methods are based on minimizing certain meansquare
error criteria that incorporate the channel uncertainties into their problem formulations instead of
directly using the inaccurate channel information that is available. We present closed-form solutions to
the channel equalization problems for each method and for both zero mean and nonzero mean signals.
We illustrate the performances of the equalization methods through simulations.
© 2013 Elsevier Inc. All rights reserved
A Deterministic Analysis of an Online Convex Mixture of Expert Algorithms
Cataloged from PDF version of article.We analyze an online learning algorithm that adaptively
combines outputs of two constituent algorithms (or the
experts) running in parallel to model an unknown desired signal.
This online learning algorithm is shown to achieve (and in some
cases outperform) the mean-square error (MSE) performance of
the best constituent algorithm in the mixture in the steady-state.
However, the MSE analysis of this algorithm in the literature
uses approximations and relies on statistical models on the
underlying signals and systems. Hence, such an analysis may not
be useful or valid for signals generated by various real life systems
that show high degrees of nonstationarity, limit cycles and, in
many cases, that are even chaotic. In this paper, we produce
results in an individual sequence manner. In particular, we relate
the time-accumulated squared estimation error of this online
algorithm at any time over any interval to the time-accumulated
squared estimation error of the optimal convex mixture of the
constituent algorithms directly tuned to the underlying signal
in a deterministic sense without any statistical assumptions. In
this sense, our analysis provides the transient, steady-state and
tracking behavior of this algorithm in a strong sense without any
approximations in the derivations or statistical assumptions on
the underlying signals such that our results are guaranteed to
hold. We illustrate the introduced results through examples. © 2012 IEEE
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